Chapter 1Chapter 11 Nature and Scope of Biological

Science1.1 The Science Biology

1.1.1 Definition of BiologyThe word biology comes from the Greek words bios, which means life, and logos, which means thought. Biology is the science of life. Biologists study the structure, function, growth, origin, evolution and distribution of living organisms. An organism is a living entity consisting of one cell e.g. bacteria, or several cells e.g. animals, plants and fungi. Aspects of biological science range from the study of molecular mechanisms in cells, to the classification and behaviour of organisms, how species evolve and interaction between ecosystems.

1.1.2 Main Fields of BiologyModern biology is vast science. Over 2,000,000 different kinds or species of organisms have been identified and new ones are still being discovered. They range in size and complexity from tiny bacteria to trees and humans. Because biology is such a large field, it is broken down into several subdivisions for easier study. These observations are formed according to the group of organisms being studied or the approach taken to the study of the organisms.

1.1.2.1 Group of Organisms Being StudiedExamples of some of the main fields of biology formed according to the group of organisms being studied:Botany The study of plants.Zoology The study of animals.Microbiology The study of microscopic organisms.Bacteriology The study of bacteria.Virology The study of viruses.Mycology The study of fungi.Entomology The study of insects.Ornithology The study of birds.

1.1.2.2 Approaches Taken to the Study of OrganismsExamples of some of the main fields of biology formed according to the approach taken to the study of the organisms:

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Taxonomy The classification of organisms.Morphology The study of the external form and structure of organisms.Anatomy The study of the internal structure of organisms.Physiology The study of the function of organisms.Cytology The study of cells.Ecology The study of the relationship of organisms to their environment.Genetics The study of inheritancePathology The study of diseases.

1.1.3 A New Definition of BiologyBiology was first defined as the science that deals with the study of life. However, as we learn more, we see that biology involves many other things. It is also a study of all those things that affect life. Thus the following is a more accurate definition of biology: Biology is the study of living things and the things that were once alive, together with the matter and energy that surround them.

1.2 Characteristics of Living Things1.2.1 What Is Life?

What is life? What is the difference between a living and a nonliving thing? You would have no trouble deciding that a dog running down the street was alive; nor would you have any trouble deciding that a stone was nonliving. However, if you ask yourself whether a bean seed, an apple, or a potato is living or nonliving, you may have problems deciding on the answer. All these appear just as nonliving as a stone. Yet we know that all three can produce a living plant. Since it seems unlikely that a nonliving thing can produce a living plant, we can assume that the bean seed, apple, and potato are living. What, then, are the characteristics of living things?

1.2.2 Characteristics of Living ThingsThere are nine characteristics of living things.1. The need for energy2. Movement3. Cellular structure and organization4. Growth and development5. Maintenance and repair6. Reproduction7. Response to stimuli8. Variation and adaptation

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9. Metabolism

1.2.2.1 The Need for EnergyAll living things require a continuous supply of energy to support their more obvious characteristics such as movement, growth, and reproduction. Almost all the energy used by living things comes originally from the sun (Figure 1.1). Green plants, through photosynthesis, store some of the sun’s energy in compounds such as glucose. These plants, through respiration, then ‘burn’ or breakdown the glucose, releasing the energy needed to support their life processes.

Animals get their supply of energy by eating the plants or by eating other animals that have eaten plants. By doing this, they obtain glucose and other compounds which they too, break down through respiration to release energy to support their life processes.

Figure 1.1: All living things have common characteristics. These characteristics are functions that require energy.

1.2.2.2 MovementOne of the most obvious characteristics of living things is movement. Most animals show obvious signs of movement when they are alive. Although movement in plants is not as obvious, it does occur. This movement can be very slow, such as (1) the opening of buds on a tree or (2) the turning of leaves of a plant toward the sun. In contrast, (3) the tiny sundew of northern bogs and (4) the Venus flytrap of Carolinian bogs show much more rapid motion. One of the most interesting examples of motion in plants is shown by (5) the Mimosa pudica, commonly called the sensitive plant. If this plant is touched, its leaves quickly fold up.

Many animals, plants, and microscopic organisms show few or no outward signs of movement. Yet under the microscope, you can see that the cell contents of these organisms

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are in continuous motion. This proves that in one way or another, all living things show movement.

Locomotion: Some organisms show a special type of movement called locomotion. Locomotion is the movement of an organism from one place to another. Most animals can carry out locomotion but very few plants can. Remember that both movement and locomotion, in a biological sense, must be initiated or caused by the organism itself. Locomotion does not occur when the wind blows a plant from one place to another, nor does movement occur when the wind moves the branches of a tree.

1.2.2.3 Cellular Structure and OrganizationCell: All living things are made up of cells. Some have only one cell; others have millions of cells. Some cells are very simple and others are very complex. However, from bacteria and amoebas to trees and humans, the cell is the basic unit in which substance are organized to produce a living thing.

Protoplasm: Living cells contain a complex mixture of substances that is called protoplasm. This mixture is found only in living cells. The protoplasm itself, however, is not alive. None of the materials of which protoplasm is made carbohydrates, fats, proteins, waters, and other compounds are alive. Yet, living cells have the ability to organize all these materials into what biologists call a living condition. Protoplasm differs from one kind of organism to another and even from one individual to another of the same kind. It even differs from one part of an individual to another part of the same individual. In fact, the composition, or makeup, of any particular sample of protoplasm is always changing.

Organism: Living things have the ability to organize materials into protoplasm and to organize protoplasm and other substances into cells. Living things are therefore called organisms because of this ability to organize substances.

1.2.2.4 Growth and DevelopmentGrowth of Living Things: All living things grow at some time during their lives. The total growth may be very small, as in the case of a bacterium or an amoeba. Total growth can be quite extensive, as in the case of a whale or a large tree. Yet, whether great or small, growth is a characteristic of all living things.

Growth of Non-living Things: However, many nonliving things can also grow. For example, crystals of sugar, salt, and bluestone can be made to grow larger. You probably

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have seen an icicle grow. How, then, can we say that growth is a characteristic of living thing? What kind of growth are we referring to?

The crystals and the icicle grow larger by adding more material of the same kind to their surfaces. The growth of living things is quite different from this. A dog does not grow by the collection of more dogs on its surface; nor does a mango plant grow by the collection of more mango plants on its surface. Yet, neither of these organisms grows simply by taking in food. They must organize the food, along with water, minerals, and other chemicals, into the complex materials that make up protoplasm and the other parts of living cells.

Living things grow, not by adding more of their own material to their surfaces, but by organizing materials that they take in to form their own special kind of protoplasm.

Development: If you plant a bean seed, it will become a bean plant. It never becomes a potato plant or a tree. It becomes a unique living thing with specialized parts that make it different from other living things. The series of changes that take place as an organism grows toward its final form is called development. All living things undergo development.

1.2.2.5 Maintenance and RepairMost living things live long after growth appears to have stopped. Yet, in one sense, they continue to grow as long as they are alive. They may not grow any larger but they must continually maintain and repair the materials of which they are made. For example: (1) Skin cells on your body wear away and must be replaced by new ones. A cut on your finger heals because new tissues are produced to cover the cut. (2) Some organisms, such as the salamander, house lizard and crayfish, can even grow new limbs or tail to replace lost ones by recognizing old, and adding new, material.

Living things use great deal of energy in the maintenance and repair of worn-out and damaged parts. This is a characteristic of all living things.1.2.2.6 ReproductionReproduction: Reproduction is the process whereby all living organisms produce offspring. Only living things can produce offspring similar to themselves. (1) Shrimps lay eggs that hatch and develop into shrimps. (2) Bluebirds lay eggs that eventually produce bluebirds. (3) Horses give birth to horses. (4) Apple seeds grow into apple plants. (5) Mango seeds become mango trees. It is a basic law of biology that only life can produce life and like produces like.

Organisms must be able to reproduce themselves because they have a limited life span. After most organisms are formed, they go through a period of rapid growth. They eventually reach a stage called maturity at which growth in size usually ceases but maintenance and

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repair may continue. They then enter a period of decline in which maintenance and repair of worn-out and damage materials are no longer fast enough to keep the organisms in a stable state. Finally death occurs.

Life Span: Life spans vary considerably from one type of organism to another. (1) Some insects live only a few weeks. (2) A person in Western world can expect to live, on the average, about seventy years. (3) A horse lives about thirty years. (4) Some trees live for a few decades and others for hundreds of years. (5) Some redwood trees in California have lived for several thousand years. (6) Some simple organisms such as bacteria and amoebas appear to have an indefinite life span. In a sense, they live forever, because they reproduce by splitting in two. The offspring repeat this process. Clearly such organisms never die of old age!

Organisms use a great deal of energy in the reproduction of offspring. This also is a characteristic of all living things.

1.2.2.7 Response to StimuliIrritability: All living things are able to respond to certain stimuli or change in their

environment (surroundings). (1) A dog comes when you whistle. (2) A fly moves when you try to swat it. (3) A Mimosa (sensitive) plant folds its leaves in response to darkness, touch, and heat. (4) A plant in a window turns its leaves toward the light. (5) Earthworms seek out moist soil containing decaying vegetation.

In all these examples a stimulus sound, touch, heat, light, moisture causes a response by a living thing. A living thing’s response to a stimulus is called irritability.

Irritability in Animals: Irritability is valuable to animals in many ways. It helps them obtain food and avoid predators. It is most highly developed in those animals that have nervous systems and keen sense organs such as eyes, nose, and ears.

Irritability in Plants: Plants usually respond slowly to stimuli because they lack sense organs, muscles, and other parts needed for a quick response. However, they usually respond to light by turning their leaves towards it. They also respond to gravity by sending roots downward into the soil.

Irritability in Microorganisms: Even single-celled organisms such as amoebas show irritability. Such organisms respond to touch, light, heat, and other environmental stimuli.

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Coordination: Response to stimuli must be coordinated if they are to be effective. Even simple organisms have many parts and each part must do the right thing at the right time if the proper response is to be carried out. For example, when you call a dog to supper, stimuli will be received by one or more of the eyes, ears, and nose. The responses to these stimuli must be coordinated within the dog before it can respond properly. Some muscles must contract; others must relax; digestive juices must be secreted. A system of nerves and a system of chemical regulators called hormones coordinates these responses in a dog and many other animals. In plants, only hormones are involved in the coordination of responses.

Behaviour: Organisms respond to stimuli by changing their relationship to it. For example, a dog usually comes when you whistle. It changes its location in response to the stimulus. Such responses, which often occur in definite pattern, are called behaviour. Remember that behaviour must begin with the organism. A ball rolling down a hill is not showing behaviour. It is simply being pulled along by the force of gravity. However, a dog that responds to a whistle creates a change in its relationship to its environment. Your whistle does not pull the dog to you. Organisms use a considerable amount of energy as they respond to stimuli within their environments.

1.2.2.8 Variation and AdaptationVariation: Change occurs as a result of a characteristic feature is called variation. Offspring always differ in some ways from one another and from their parents. These differences are called variations. Most variations do not affect an organism’s chances of survival. For example, the fact that your hair is a different colour from your parents will not likely affect your chances of survival.

Adaptation: The process by which a certain type of organisms becomes better suited to survive in its environment is called adaptation. Keep in mind that organisms do not change in order to survive in a changing environment. The deer in our example did not grow long legs because they needed them to survive in the deep snow.

Organisms do not change to survive; they survive because they change.

1.2.2.9 MetabolismWhat is Metabolism: Metabolism is the exchange of matter and energy between an organism and its environment, and the changes that occur in this matter and energy when they are within the organism.

In effect, metabolism is the sum of all the processes occurring in an organism.1. It includes taking in food, or ingestion, as well as taking in water and air.

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2. It also includes all the changes in food materials that occur within organisms during digestion.

3. It includes all changes that occur as the products of digestion are assimilated, or put together, during growth, maintenance, and repair.

4. It includes the release of energy through respiration.5. Finally, it includes the elimination of by-products through excretion.

Anabolism vs. Catabolism: Metabolism has two distinct phases, anabolism and catabolism.1. Anabolism: Anabolism is a constructive or building-up phase; it includes assimilation, or

building of protoplasm from simple compounds and elements that were obtained as a result of ingestion and digestion. It also includes the process of photosynthesis.

2. Catabolism: Catabolism is a destructive or breaking-down phase; it involves the release of energy by the breakdown of food materials through respiration.

1.3 Review Questions1-Nature and Scope of Biological Science

1. State the two main aspects of every science.2. Explain the origin of the word Biology.3. Give a simple definition of biology.4. State the modern definition of biology.5. Name, with definition and example, five subdivisions of biology formed according to the group of organisms being studied.6. Name, with definition and example, five subdivisions of biology formed according to the approach taken to the study of the organisms.

2-Characteristics of Living Things1. Why do all living things require energy? Show that energy of all living things originally come from the sun.2. What are the nine characteristics of living organisms?3. Describe with examples of movement in plants.4. What is locomotion?5. What is protoplasm?6. Why is a living thing called an organism?7. Describe the differences between the growth of a living and a nonliving thing.

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8. What is development?9. What is the difference between development and growth?10. How do maintenance and repair differ from growth?11. What is reproduction? Why is reproduction necessary?12. What is stimulus? What is irritability? Describe an example of the importance of irritability to an animal.

Describe an example of the importance of irritability to a plant.13. What is behaviour? Describe an example of behaviour.14. What are variations? What is adaptation?15. What is metabolism? Name and define the two phases of metabolism. Name and briefly describe five processes

that can occur during metabolism.

Chapter 2Chapter 22 Classification of Living Things2.1 The Needs for Classification2.1.1 Introduction

Biologists believe that there may be over two million (2,000,000) different kinds of organisms. Already over 1.5 million (1,500,000) different kinds have been identified and new ones are still being discovered. One biologist estimates that for each kind of organism now alive, another 400 kinds once lived but have since become extinct. Therefore, as many as one billion (1,000,000,000) different kinds of living things may have existed on the earth at one time or another.

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How can we keep track of such a bewildering number of organisms? How can we even name the organisms now alive when no known language has two million words in it? Biologists have answers to these questions.

2.1.2 What is Classification?Whenever we work with a large number and variety of things, we usually sort them into groups. Each group contains those things that are similar to one another. We may then separate each of those groups into smaller groups that are even more alike.

The grouping of similar things for a specific purpose is called classification. Although it may be instinctive for human to classify things, there are also practical reasons for doing this. For example:

1. A supermarket manager classifies the foods in his/her store by storing all the cereals together, all the meats together, all the cookies together, and so on.

2. Stamp collectors classify their stamps. They place all the Canadian stamps in one page and all the American stamps in another.

3. The words in a dictionary are classified by alphabetical listings.

Clearly, we classify things to make it easier to keep track of what we have, and to find particular items.

2.2 Classification Scheme2.2.1 Early Biological Classification

2.2.1.1 Prehistoric Concept of ClassificationBiologists have long recognized the need to classify living things. In fact, humans have been classifying living things for thousands of years. The earliest humans probably classified organisms as plants and animals. They may have further classified plants as edible or poisonous, and the animals as harmful or harmless. However, it was 300 BC before the first serious attempt was made to classify all the organisms known. This attempt was made by the Greek philosopher and scientist, Aristotle and his students.

2.2.1.2 Aristotle’s Classification System Since only about 1,000 kinds of organisms were known at that time, a very simple classification scheme could be used. Aristotle and his students first classified the organisms as (1) Plant or (2) Animal. They then classified the animals according to where they lived. This resulted in three groupings: (1) Air animals, (2) Water animals, and (3) Land animals. They classified the plants according to the structure of stems. (1) Those with soft stems

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were called herbs, (2) those with a single woody stem were called trees, and (3) those with many small woody stems were called shrubs (Figure 2.1).

Figure 2.1: Aristotle’s classification system.

Aristotle’s classification system survived for almost two thousand years. However, by the beginning of the 18th century, over 10,000 kinds of organisms were known and Aristotle’s system was unable to classify them all. Many of newly discovered organisms would not fit into any category of Aristotle’s simple system. A new system was obviously needed.

2.2.2 Modern Biological Classification2.2.2.1 TaxonomyTaxonomy (from Ancient Greek: taxis, "arrangement," and -nomia, "method") is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. Organisms are grouped together into taxa (singular: taxon) and given a taxonomic rank; groups of a given rank can be aggregated to form a super group of higher rank and thus create a taxonomic hierarchy. The Swedish botanist Carolus Linnaeus is regarded as the father of taxonomy, as he developed a system known as Linnaean classification for categorization of organisms and binomial nomenclature for naming organisms.

2.2.2.2 The Contribution of Carolus LinnaeusCarolus Linnaeus, a Swedish botanist, developed a simple classification system that forms the basis of our modern method of classification. At the start of the 18 th century about 10,000 kinds of organisms were known. By the end of that century over 70,000 kinds were known. Linnaeus tried to develop a classification system for this large number of organisms. By 1753 his system was well developed and modern taxonomy began.

2.2.2.3 The Basis for Linnaeus Classification

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Biologists use the word diversity to mean differences, or the number of kinds of living things. There seem to be so many kinds of living things and they seem to be so different from one another. Yet, if we study them closely, we can see many likenesses. For example, at first glance lions, horses, humans, and mice seem to have little in common. A closer look however, shows that all have hair, a distinct head, four limbs, two ears, and warm blood. That is, they have similar structural features.

Linnaeus decided to use structural features as the basis for his classification system. Therefore, he grouped organisms according to their structural similarities. These organisms with very similar structural features were considered to be the same species. Thus all modern-day humans belong to one species, all house cats belong to one species, and all sugar maple trees belong to one species.

2.2.2.4 Binomial NomenclatureOnce Linnaeus had decided on a basis for classifying organisms, he then developed a system for naming them. His system is quite simple. He gave each species a name that consists of two words. This system is called binomial nomenclature. He used Latin words for these names because all scientists wrote in Latin in time of Linnaeus. Thus, the human is Homo sapiens, and the domestic (house) cat is Felis domesticus. The first word of each name is called the genus and the second word is called the species. The genus begins with a capital letter and the species does not. The genus and species are either printed in italics or underlined.

2.2.2.5 Why Use Scientific Names?One reason for using Latin scientific name instead of common names is that common names can be confusing or misleading. For example Felis concolor is called a cougar, mountain lion, puma, panther, painter, and many names. The common name for a domestic cow is “la vache” in French, “die Kuh” in German, “la vaca” in Spanish, and “garoo” in Bengali. However, in all languages the scientific name is the same, and there is no confusion if we call the cow Bos taurus.

2.2.3 Modern Basis for Classification2.2.3.1 Homologous StructureCarolus Linnaeus used structural features as the basis for his classification system. He grouped organisms according to their structural similarities. Today, taxonomists still use structural similarities as a basis for classification. They look for homologous structures just as Linneaus did. Homologous structures are structures that show the same basic pattern, the same general relationship to other parts, and the same pattern of development.

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However, they need not have the same function. For example, the human arm, the whale flipper, and the bat’s wing, all these appendages are homologous structures that show the same basic pattern. Also, all three appendages are found in the same part of the body. Finally, the bones in all three appendages develop in similar ways. Although their functions are different, they are homologous structures.

2.2.3.2 Similar BiochemistryBiochemistry is the study of the chemical compounds formed by living things. Many biologists believe that closely related organisms form similar chemical compounds in their body. They use this belief to help classify organisms. For example, the horseshoe crab was, at one time, classified as a close relative of the true crab. However, chemical analysis showed that its blood was more like spider’s blood than crab’s blood. Thus, the horseshoe crab is now classified as a close relative of spiders.

2.2.3.3 Genetic SimilarityMost biologists agree that genetic similarity is the best evidence that organisms are closely related. Every organism makes a special compound called DNA that bears hereditary characters. Thus it seems reasonable to assume that the greater the similarity of DNA among organisms, the more closely they may be related.

2.3 The Genus and Species Concept2.3.1 The Genus ConceptA genus (plural genera) groups species that are similar. For example, maple trees belong to the genus Acer. Thus sugar maple (Acer saccharum), silver maple (Acer saccharinum), and red maple (Acer rubrum) belong to the same genus Acer. Their leaves are similar and other features are similar but not identical. Every genus has characteristics that make it stand out clearly from other living things.

2.3.2 The Species ConceptLinnaeus grouped as a species those organisms that he felt were very similar in structural features. In simple terms, a single species is a distinct kind of organism, with a characteristic shape, size, behaviour, and habitat that remains constant from year to year.

A species (plural also species) is defined as a group of individuals that are alike in many ways and interbreed under natural conditions to produce fertile offspring (children). Potato (Solanum tuberosum) and the eggplant or brinjal (Solanum melongena) belong to the same genus because they are similar in many ways. However, they belong to two different

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species because they are not identical and they have reproductive barrier, that is, they cannot mate (cross or breed) with one another to produce fertile offspring. The members within a species can mate or cross. Thus all varieties of potatoes are in the species because they can interbreed to produce fertile offspring.

2.4 The Main Classification Groups (Taxa)There are seven main taxa or classification groups (Table 2.1). This system of classification can be compared to a tree. Many leaves (Species) are on a tiny twig (Genus). Several tiny twigis (genera) are on a larger twig (Family). Several larger twigs (families) are on a little branch (Order). Some little branches (orders) are on a larger branch (Class). Some larger branches (classes) are on a main limb of the tree (Phylum). The few main limbs (phyla) make up the whole tree (Kingdom).

1. Species: Species (plural also species) is a group of individuals that are alike in many ways and interbreed under natural conditions to produce fertile offspring (children).

2. Genus: Genus (plural genera) is a group of species that are closely similar in structure and evolutionary origin.

3. Family: Family is a group of similar kinds of genera. That is, similar genera are grouped to form a taxon called Family.

4. Order: Similar families are grouped to form a taxon called order.5. Class: Similar orders are grouped to form a taxon called class.6. Phylum or Division: Similar classes are grouped to form a taxon called phylum or

division. Zoologists favour phylum and botanists favour division.7. Kingdom: All the phyla or divisions that contain animals are grouped in the kingdom

Animalia, and all the phyla or divisions that contain plants are grouped in the kingdom Plantae.

Table 2.1: Classification of some organisms

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2.5Review QuestionsClassification of Living Things

1. What is classification? Give two reasons why human classify things.2. Describe Aristotle’s classification system for living things.3. What is taxonomy?4. What did Linnaeus use as the basis for his classification system?5. What is binomial nomenclature? Give two examples.6. What is a genus?7. What is a species according to Linnaeus? What is the modern definition of species?8. Why is it important that biologists in all countries use scientific names (binomial nomenclature) for organisms?9. List, in order, the seven main taxa (classification groups) with example of each group, starting at kingdom.10. Name the three modern bases for classification.11. Describe, with an example, similar biochemistry in classification of organisms.

Chapter 3Chapter 33 Cells and Levels of Biological

Organization3.1 Cell Structure and Function: The Cell Theory3.1.1 What is a Cell?The cell (from Latin cella, meaning "small room") is the basic structural, functional, and biological unit of all known living organisms. Cells are the smallest unit of life that can replicate independently, and are often called the "building blocks of life"

All organisms, regardless of size, are made of cells. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). For example, an amoeba has only one cell. Humans have about 100 trillion cells (100,000,000,000,000 or 1014). Thus the cell is the basic structural unit of life.

3.1.2 The Cell TheoryIn biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. Cell Theory was eventually formulated in 1838. This is usually credited to Matthias Schleiden and Theodor Schwann. However, many other scientists like Rudolf Virchow contributed to the theory. Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells.

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The three tenets to the cell theory are as described below:1. All living organisms are composed of one or more cells.2. Cells are the structural and functional units of all living things.3. All cells arise from pre-existing, living cells.

3.1.3 Protoplasm and Its ActivityCells consist of a protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Protoplasm is a granular, jelly-like substance that makes up most of the cell. It varies in composition from organism to organism and even from cell to cell in the same organism. It is about 70% water. The remaining 30% is carbohydrates, lipids, and proteins, with lesser amounts of many elements and compounds. Protoplasm is often called the living material of a cell. Yet, biologist do not agrees as to whether or not it is actually alive. Certainly no one portion of a cell’s protoplasm is alive. None of its components water, carbohydrates, lipids, and proteins is alive. Yet, somehow the protoplasm can organize all these substances into a “living condition”.

3.1.4 How Does the Protoplasm Do All Biological Functions?The answer is that the protoplasm is organized. Certain parts carry out certain job. Many of these parts are called organelles (little organs). They are specialized parts that are found in the cytoplasm. Each organelle carries out certain functions. Yet it depends on the other organelles, too. The operation of the organelles in a cell can be compared to the operation of the organs in our body. Our stomach, lungs, brain, liver, and kidneys are organs. Each carries out certain functions. Yet they are all dependent on each other and must function together if body is to survive. The organization of different structures for specific jobs is called division of labour.

3.2 Cell AnatomyThere are two types of cells, eukaryotes, which contain a nucleus, and prokaryotes, which do not. Prokaryotic cells are usually single-celled (unicellular) organisms, while eukaryotic cells can be either single-celled or part of multicellular organisms.

3.2.1 Prokaryotic CellsProkaryotic cells were the first form of life on Earth, as they have signaling and self-sustaining processes. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus. Prokaryotes include two of the domains of life, Bacteria and Archaea. The DNA of a prokaryotic cell consists of a single chromosome

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that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid. Most of the prokaryotes are smallest of all organisms. Most prokaryotes range from 0.5 to 2.0 µm in diameter.

3.2.2 Eukaryotic CellsPlants, animals, fungi, slime moulds, protozoa, and algae are all eukaryotic. These cells are about fifteen times wider than a typical prokaryote and can be as much as a thousand times greater in volume. The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membrane-bound compartments in which specific metabolic activities take place. Most important among these is a cell nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. This nucleus gives the eukaryote its name, which means "true nucleus".

3.2.3 Subcellular ComponentsAll cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, regulates what moves in and out (selectively permeable), and maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells (except red blood cells which lack a cell nucleus and most organelles to accommodate maximum space for hemoglobin) possess DNA, the hereditary material of genes, and RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells (Figure 3.1).

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Figure 3.1: An animal cell and its components

3.2.3.1 Cell MembraneThe cell membrane, or plasma membrane, surrounds the cytoplasm of a cell. In animals, the plasma membrane is the outer boundary of the cell, while in plants and prokaryotes it is usually covered by a cell wall. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids, which are amphiphilic (partly hydrophobic and partly hydrophilic). Hence, the layer is called a phospholipid bilayer, or sometimes a fluid mosaic membrane. Embedded within this membrane is a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell. The membrane is said to be 'semi-permeable', in that it can either let a substance (molecule or ion) pass through freely, pass through to a limited extent or not pass through at all. Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones.

3.2.3.2 CytoskeletonThe cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell, and cytokinesis, the separation of daughter cells after cell division; and moves parts of the cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of microfilaments, intermediate filaments and microtubules.

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3.2.3.3 Genetic MaterialsTwo different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Cells use DNA for their long-term information storage. The biological information contained in an organism is encoded in its DNA sequence. RNA is used for information transport (e.g., mRNA) and enzymatic functions (e.g., ribosomal RNA). Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts.

3.2.3.4 OrganellesOrganelles (“little organs”) are parts of the cell which are adapted and/or specialized for carrying out one or more vital functions, analogous to the organs of the human body (such as the heart, lung, and kidney, with each organ performing a different function). Both eukaryotic and prokaryotic cells have organelles, but prokaryotic organelles are generally simpler and are not membrane-bound.

There are several types of organelles in a cell. Some (such as the nucleus and Golgi apparatus) are typically solitary, while others (such as mitochondria, chloroplasts, peroxisomes and lysosomes) can be numerous (hundreds to thousands). The cytosol is the gelatinous fluid that fills the cell and surrounds the organelles.

Cell Nucleus: A cell's information center, the cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes, and is the place where almost all DNA replication and RNA synthesis (transcription) occur. The nucleus is spherical and separated from the cytoplasm by a double membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called messenger RNA (mRNA). This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. The nucleolus is a specialized region within the nucleus where ribosome subunits are assembled. In prokaryotes, DNA processing takes place in the cytoplasm.

Mitochondria and Chloroplasts – The Power Generators: Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondria play a critical role in generating energy in the eukaryotic

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cell. Respiration occurs in the cell mitochondria, which generate the cell's energy by oxidative phosphorylation, using oxygen to release energy stored in cellular nutrients (typically pertaining to glucose) to generate ATP. Mitochondria multiply by binary fission, like prokaryotes. Chloroplasts can only be found in plants and algae, and they capture the sun's energy to make ATP through photosynthesis.

Endoplasmic Reticulum: The endoplasmic reticulum (ER) is a transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface that secrete proteins into the ER, and the smooth ER, which lacks ribosomes. The smooth ER plays a role in calcium sequestration and release.

Golgi Apparatus: The primary function of the Golgi apparatus is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell.

Lysosomes and Peroxisomes: Lysosomes contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. Peroxisomes have enzymes that rid the cell of toxic peroxides. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system.

Centrosome – The Cytoskeleton Organizer: The centrosome produces the microtubules of a cell – a key component of the cytoskeleton. It directs the transport through the ER and the Golgi apparatus. Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle. A single centrosome is present in the animal cells. They are also found in some fungi and algae cells.

Vacuoles: Vacuoles store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane. Some cells, most notably Amoeba, have contractile vacuoles, which can pump water out of the cell if there is too much water. The vacuoles of eukaryotic cells are usually larger in those of plants than animals.

Ribosomes: The ribosome is a large complex of RNA and protein molecules. They each consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids. Ribosomes can be found either floating freely or bound to a membrane (the rough endoplasmatic reticulum in eukaryotes, or the cell membrane in prokaryotes).

3.3 Biological Organization20

3.3.1 Levels of Biological OrganizationOrganization is the characteristic of living things. That is, all the structures in a living thing must be organized in a way that produces and maintains a “living condition”. Many levels of organization exit.

3.3.1.1 The Cellular LevelThe cell is the basic structural unit of all living things. Nothing smaller than a single cell can be called a living. Thus one can say that the cellular level is the simplest level at which structures can organized into a living condition.

3.3.1.2 The Tissue LevelA tissue is a group of cells that have the same structure and function. It is the second level at which structures can be organized in an organism. Most species of animals have many types of tissue, such as, muscle tissue, bone tissue, nerve tissue, and skin tissue. Most species of plants also have tissues, such as, conductive tissue, photosynthetic tissue, storage tissue, and epidermal tissue.

3.3.1.3 The Organ LevelAn organ consists of several tissues working together as a unit to perform a specific function. It is the third level of organization of biological structures. For example, heart is an organ. It consists of muscle tissue, nerve tissue, elastic connective tissue, fibrous tissue, and many other types. All these tissues work together to pump blood. If any one tissue failed to do job, the organ would stop operating. Our arm is also an organ. It is made of bone tissue, muscle tissue, skin tissue, nerve tissue, blood tissue, and several other types of tissues. Our stomach, brain, and kidney are also organs.

3.3.1.4 The Organ System LevelAn organ system is a group of organs that work together to perform a specific function. This fourth level of organization is found only in animals. A single organ may not be enough to permit a complex animal to carry out one of the major functions of its body. Two or more organs, working together, may be needed.

The human digestive system is an example of an organ system. In order to perform digestion properly in such a complex organism as the human, several organs are needed. Among these are the jaws, salivary glands, oesophagus, stomach, intestine, and liver. Other organ systems in the human body are the breathing system, the circulatory system, the nervous system, and the skeletal system.

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3.3.2 Levels Below the CellThere are many levels of organization smaller than the cell. While these are not biological in nature, it is still interesting to think about them.

3.3.2.1 Organelle LevelBelow the cellular level is the organelle level. The organelles function together to make the cell.

3.3.2.2 Macromolecular LevelBelow the organelles level is the macromolecular (giant molecule) level. The macromolecules such as lipids and proteins go together to make organelles.

3.3.2.3 Molecular LevelBelow the macromolecular level is a level made up of molecule. Molecules go together to make macromolecules.

3.3.2.4 Atomic LevelBelow the molecular level is the atomic level. Atoms join together to make a molecule.

3.3Review Questions1-Cell Structure and Function: Cell Theory1. State the cell theory.2. What is protoplasm? What is it made of? 3. How does the protoplasm do all these things?4. What are organelles?5. What is meant by division labour?6. What is the main function of nucleus? Name and describe the main parts of the nucleus.7. Make a table with the column heading “Organelle” and “Function”. Complete the table for all the organelles

present in the cell and summarize the function in just a few words.

2-Levels of Biological Organization1. Make a list of the levels of biological organization.2. Explain the terms cell, tissue, organ, and organ system. Give two examples of each.3. Describe the relationships among the following levels of biological organization: individual, community, biome,

and biosphere. Give one example of each.4. Describe the levels of organization below the cell?

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Chapter 4Chapter 44 Energy Acquisition in Living

Things: Photosynthesis and Respiration

4.1The Need for Energy4.1.1 Photosynthesis and Cellular RespirationAll living things need a continuous supply of energy. This energy is needed to support life profess such as movement, growth, and reproduction. Almost all energy used by living things originally comes from the sun. Green plants and many other organisms contain chlorophyll. These living things, through photosynthesis, store some of the sun’s energy in the bonds of glucose molecules. They do this by converting light energy into chemical potential energy. The glucose that is made during photosynthesis is the basic energy source for almost all organisms. Organisms break down glucose during the process of cellular respiration. This releases some of the energy that was stored in the bonds of the glucose molecules.

4.1.2 Autotrophs and HeterotrophsAutotrophs: Organisms that produce their own food are called autotrophs. Therefore, organisms that contain chlorophyll are autotrophs. They use the glucose that they produce during photosynthesis as an energy source during reparation.

Heterotrophs: Organisms that depend on other organisms for food are called heterotrophs. All heterotrophs depend directly or indirectly on autotrophs food. The dependence is direct in the case of plant eaters, or herbivores, such as rabbits, deer, and cow. They eat plants and convert stored carbohydrates in the plants into glucose. The glucose is then “burned”

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during respiration to release needed energy. The dependence is indirect in the case of flesh eaters, or carnivores, such as tiger, lion, and wolves. These animals feed on herbivores such as rabbits. The rabbits eat autotrophic organisms such as grass. The carnivores depend on autotrophs for glucose that is needed for energy.

4.2 Photosynthesis4.2.1 Definition of PhotosynthesisPhotosynthesis is the process by which light energy is changed to chemical potential energy and stored in the bonds of glucose molecules.

4.2.2 The Composition of GlucoseGlucose belongs to a family o organic compounds called carbohydrates. Its molecular formula is C6H12O6. If we write its formula as C6(H2O), we can see why it is called “carbo...hydrate”. It contains carbon. It also contains hydrogen and oxygen in the same proportion as water.

4.2.3 The Summation Equation for PhotosynthesisAs the name implies, light energy (photo) is used in building complex substance from simple substances (synthesis). Photosynthesis process occurs only in organisms that contain chlorophyll. The simple substances used in photosynthesis are water and carbon dioxide. During photosynthesis light energy is changed to and stored as chemical potential energy in the bonds of glucose molecules.

Photosynthesis is the process by which green plants and certain other organisms use the energy of light to convert carbon dioxide and water into the simple sugar glucose. In so doing, photosynthesis provides the basic energy source for virtually all organisms. An extremely important by-product of photosynthesis is oxygen, on which most organisms depend.

Theses equations are just summation equations. They simply “sum up” what happens during photosynthesis. They tell us what photosynthesis starts with and what it ends with (Figure

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4.1). They indicate that chlorophyll must be present. However, these equations do not tell us how the process occurs.

Figure 4.1: The diagram sums up what happens during photosynthesis. Water and carbon dioxide enter the leaf. Glucose and oxygen are produced.

4.2.4 The Role of Photosynthetic Pigments4.2.4.1 Main Photosynthetic Pigments: ChlorophyllsA green leaf appears green in white light. Therefore, it must contain pigments that absorb the red and blue wave lengths of the spectrum but reflect green wave length. Of course these pigments are chlorophyll. Nearly all the blue light is absorbed by the chlorophyll. Also, much of the orange and red light is absorbed. However, little green and yellow light is absorbed. Therefore, plants that contain chlorophyll as their main pigment appear green because chlorophyll reflects mainly green and yellow light.

Chlorophyll, the pigment found in plants, some algae, and some bacteria that gives them their green colour and that absorbs the light necessary for photosynthesis. Chlorophyll absorbs mainly violet-blue and orange-red light. There are at least five chlorophyll molecules. All are somewhat alike in structure and properties. The two most common types are chlorophyll a and chlorophyll b. Chlorophyll is found in cell organelles called chloroplasts. The chlorophyll functions as a catalyst in the process of photosynthesis. A catalyst is a substance that affects the rate of a chemical reaction without being permanently changed

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itself. Thus chlorophyll speeds up the process of photosynthesis, but is not used up in the process.

4.2.4.2 Accessory Photosynthetic PigmentsApparently other pigments, the carotenes and the xanthophylls, also assist in photosynthesis. It is believed that that they aid chlorophyll in absorbing the light energy needed for photosynthesis.

4.3 Cellular Respiration4.3.1 Cellular Respiration vs. BreathingRespiration is the process by which living cells break down glucose molecules and release stored chemical potential energy. It is also called cellular respiration. It occurs in the mitochondria. You must not confuse respiration with breathing.

Breathing is simply the exchange of gases between an organism and its environment. Cellular respiration is the “burning” of glucose in cells to release the energy required to support life process. The word “burning” is placed in quotation mark because the really does not burn. A better term to use is oxidation.

4.3.2 Cellular Respiration vs. OxidationOxidation is the loss or removal of electron(s) from a substance. In cellular respiration glucose is oxidized.

In some respects, oxidation in cell, or cellular respiration, is similar to oxidation, or burning, of fuels such as coal, wood, and oil. When a fuel is burned, chemical potential energy in the molecules of the fuel is released as heat and light energy. In a similar manner, when glucose is oxidized in cells, chemical potential energy in the glucose molecules is released partly as heat energy.

However, there is one important difference between the burning of fuel and the oxidation of glucose in living cells. The burning of fuel produces very high temperatures. Clearly, such high temperatures cannot occur in cells. The cells would be destroyed. Thus, during cellular respiration, the rate of oxidation must be controlled. As a result, it occurs in several small steps. Each step is assisted by an enzyme. The enzyme permits that step to take place at the normal temperature of the organisms. Enzymes are proteins that act as catalysts to

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regulate the speed of the many chemical reactions involved in the metabolism of living organisms.

4.3.3 The Summation Equation for Cellular RespirationCellular respiration begins with two substances, glucose and oxygen. The process produces energy. Oxidation of most organic compounds produces carbon dioxide and water. Therefore, we will assume that they are formed in cellular respiration. We breathe out carbon dioxide and water vapour produced in our body by cellular respiration. The following are the summation equations for cellular respiration:

4.4 Energy Transfer by ATP4.4.1 Adenosine Triphosphate (ATP)In most cellular processes, enzymes alone are not enough to start a reaction. The reaction needs an “energy boost” as well. For this purpose, cells have substances that can quickly store or release energy in any part of the cell. The substance is called adenosine triphosphate, or ATP. ATP is the molecule found in all living organisms that plays the key role in the storage, transfer, and release of energy in a cell. That is, it is the main immediate source of usable energy for the activities of the cells.

ATP has a complex structural formula. We will write it simply as A~~. The A stands for adenosine and each stands for one phosphate group. The wavy lines (~) represent high-energy phosphate bonds.

ATP is built up by the metabolism of foodstuffs in the cell in special compartments called mitochondria. It is then distributed to all parts of the cell. The two bonds between the three phosphate groups are high-energy bonds, that is, they are relatively weak and yield their energy readily when split by enzymes. These bonds play the key role in the storage, transfer, and release of energy in a cell. With the release of the end phosphate group, 7 kilocalories of energy become available for work, and the ATP molecule becomes ADP (adenosine diphosphate). Most of the energy-consuming reactions in cells are powered by the conversion of ATP to ADP; they include the transmission of nerve signals, the movement of muscles, the synthesis of protein, and cell division. Usually, ADP quickly regains the third

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phosphate unit by using food energy through the cellular respiration. The process can be summarized in this equation:

In words the equation says: ATP produces ADP, a phosphate group, and energy. Also, ADP combines with a phosphate group and energy to produce ATP.

The change from ATP to ADP and from ADP to ATP occurs over and over again throughout the cell. The energy is stored in ATP and transported to where it is needed. There the ATP converts to ADP, releasing the needed energy.

4.4.2 Role of ATP in Cellular Respiration – The ATP-ADP CycleThe energy stored in ATP molecules is the only energy that is directly usable by cells. As a result, the energy released by glucose during cellular respiration must be stored in the bonds of ATP. The Figure 4.2 shows how the ATP-ADP cycle connects with the process of cellular respiration.

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Figure 4.2: The ATP-ADP cycle.

Enzymes permit the energy of glucose to be released in a slow, controlled manner. As it is released, it combines with a phosphate group, , and ADP to form high-energy bonds in ATP. The ATP travels to places in the cell where energy is needed. It then loses a phosphate group and becomes ADP. The energy stored in the high-energy bond is released at this time. That energy powers all life processes.

Biologists have shown that, for every molecules of glucose that is oxidized, 38 molecules of ATP are formed. Therefore, the summation equation for cellular respiration showing the involvement of the ATP-ADP cycle could be written as shown in Figure 4.2.

4.4.3 Anaerobic RespirationThe process of cellular respiration requires free oxygen, oxygen gas. As a result, it is called aerobic respiration. However many microorganisms, such as, yeast and some bacteria can respire without free oxygen. This type of respiration is called anaerobic respiration. Anaerobic respiration is the process by which certain microorganisms break down glucose molecules in the absence of molecular oxygen and release stored chemical potential energy. During anaerobic respiration, glucose is broken down to release the chemical potential energy in its bonds. In this respect, anaerobic respiration is like aerobic respiration. However, in anaerobic respiration, oxygen is not involved. Enzymes do the job alone.

Anaerobic respiration may be two types: alcohol fermentation, and lactic acid fermentation.

4.4.3.1 Alcohol FermentationBacteria and yeast that live in area where there is no oxygen must respire anaerobically. Since one of the end products is alcohol, this process is often called alcohol fermentation.

The summation equation for this type of anaerobic respiration is:

4.4.3.2 Lactic Acid FermentationAnaerobic respiration does occur in some of our body cells from time to time. In fact, it often occurs in the muscle cells of many animals. During periods of heavy physical activity, your muscle cells may not be able to get oxygen fast enough to carry out the usual aerobic cellular respiration. When this occurs, muscle cells begin to respire anaerobically. Glycogen,

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or animal starch, is stored in muscles. During anaerobic respiration, this glycogen changed to glucose. The glucose is then broken down anaerobically. No free oxygen is involved. Since the end product is lactic acid, this process is often called lactic acid fermentation. Even without oxygen muscle cells can still break down glucose to get needed energy.

The summation equation for this type of anaerobic respiration is:

4.4.3.3 Energy Release During Anaerobic RespirationIt can be seen that the products of anaerobic respiration (alcohol and lactic acid) have more than one carbon atom in each molecule. Therefore, not all the bonds in the glucose were completely broken during anaerobic respiration. This is not true in aerobic respiration. Thus, the same amount of glucose will release more energy during aerobic respiration than during anaerobic respiration.

4.5Review Questions1-Photosynthesis

1. Define photosynthesis and respiration. In which cells do photosynthesis and respiration take place?2. Distinguish between an autotroph and a heterotroph. Give example.3. Write a summation equation for photosynthesis. Include both a word equation and a chemical equation.4. What is chlorophyll? What is the function of chlorophyll in photosynthesis? Name two other pigments that assist

in photosynthesis.

2-Cellular Respiration1. Distinguish between breathing and cellular respiration.2. What is an enzyme?3. In what way is cellular respiration similar to the oxidation (burning) of a fuel?4. In what major way is cellular respiration differing from the oxidation of a fuel? 5. Write a summation equation for cellular respiration in words and in symbols.6. Outline the role of the ATP-ADP cycle in cellular respiration.7. Write a summation equation for cellular respiration that shows the involvement of ATP and ADP.8. Distinguish between aerobic respiration and anaerobic respiration.9. Give a description of alcohol fermentation. Include the summation equation.10. Give a description of lactic acid fermentation. Include the summation equation.11. Why does anaerobic respiration produces less energy from glucose than aerobic respiration?

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Chapter 5Chapter 55 Cell Division, Reproduction and

Development5.1 Cell Division

Reproduction is important to the existence of species.  All organisms existing today are present because their ancestors reproduced.  These ancestors can be traced backwards in geological time to the origin of life about 3.8 billion years ago.  Some of the organisms that existed at that time reproduced, and their offspring reproduced, and so on through evolution to the present day. There are two types of nuclear division: mitosis and meiosis.

5.1.1 Somatic Cell Division – The Mitosis5.1.1.1 MitosisMitosis typically results in new somatic (body) cells. Formation of an adult organism from a fertilized egg, asexual reproduction, regeneration, and maintenance or repair of body parts is accomplished through mitotic cell division.

5.1.1.2 Importance of MitosisThe goal of mitosis is to produce two identical daughter cells from one cell.  In sexually reproducing multicellular organisms, mitosis is often concerned with increasing cell numbers (growth), for example:1. A unicellular zygote divides to produce the billions of cells necessary to form an adult

multicellular organism.2. Skin cells divide to replace tissue lost due to injury or wear (repair).

Mitosis ensures genetic continuity. That is, it ensures that the daughter cells carry the same genetic information as the mother cell.

It does this by making sure that each daughter cell has the same number and kind of chromosomes as the mother cell. Every cell in an organism has the same number of chromosomes. In fact, the body cells of all normal individuals of the same species have the same number of chromosomes. For example, all normal human cells have 46 chromosomes, and all onion plant cells have 16.

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5.1.1.3 Stages of MitosisTo complete cell division, there are 4 sequential steps:

1. Prophase2. Metaphase 3. Anaphase 4. Telophase

5.1.2 Gametic Cell Division – The Meiosis5.1.2.1 Meiosis

The process of meiosis takes place only in the cells, which will form either the sperm or egg. Meiosis results in the formation of either gametes (in animals) or spores (in plants). These cells have half the chromosome number of the parent cell.

5.1.2.2 Importance of MeiosisThe goal of meiosis is to produce four cells with half the original genetic information of the mother cell.  Each daughter cell must end up with a complete set of genes, but only half the number of copies found in the original cell.  Meiosis involves two divisions and only the first division results in a reduction (by 1/2) of the homologous chromosomes.  No two chromosomes of a homologous pair segregate together.

We began life when a sperm cell from our father united with an egg cell from our mother. A cell called a zygote was formed by this union. If the sperm and egg each had 46 chromosomes, the zygote would have 92. You developed from the zygote by mitosis. Therefore, every cell in your body would have 92 chromosomes. But this is not so. If it were, you would not be a human. Clearly something has happened along the way to reduce the number of chromosomes from possible 92 to 46.

A process called meiosis ensures that the chromosomes number stays constant from generation to generation. Also, meiosis contributes to genetic variation of the offspring.

5.1.2.3 Stages of MeiosisMeiosis comprises two successive nuclear divisions with only one round of DNA replication. That is, two cell divisions occur to produce four daughter cells. This results in each daughter cell, or gamete, receiving the haploid number of chromosomes (half the number of the mother cell). Four stages can be described for each nuclear division.

First Division of Meiosis (Chromosomal Reduction Division)1. Prophase 1

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2. Metaphase 13. Anaphase 14. Telophase 1

Second Division of Meiosis: Gamete Formation 1. Prophase 22. Metaphase 23. Anaphase 24. Telophase 2

One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.

5.1.2 Summary of Mitosis and MeiosisMeiosis ensures genetic continuity by reducing the chromosome number of male and female gametes to the haploid number (gamete formation). Then, when these gametes unite to form a zygote during fertilization, the diploid number is restored (Table 5.1). The zygote develops through mitosis and cell division into an organism with body cells that have the diploid number of chromosomes (development).

Table 5.1: Differences between mitosis and meiosisMitosis MeiosisTakes place in most cells Takes place only in sex cellOne cell ® two cells One cell ® four cellsOriginal diploid cell ® two new diploid cells Original diploid cell ® four new haploid cellsOriginal cell is same in genetic content as new cells

Original cell is not same in genetic content as new cells

5.2 ReproductionReproduction is the process whereby all living organisms produce offspring. There are basically two types of reproduction: sexual and asexual reproduction.

5.2.1 Sexual ReproductionIn sexual reproduction, two special sex cells unite. These reproductive cells are called gametes. In some species, the gametes are alike. However, in many species the two gametes are different. In this case, one is called a male gamete, or sperm. The other is called a female gamete, or egg. Usually a male parent reproduces the sperm and female

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parent produces the egg. However, some species can produce both sperm and egg in one individual. Such individuals are called hermaphrodites. The earthworm is a hermaphrodite as are many species of snails. Most flowering plants are also hermaphrodite. They produce male and female gametes in each flower.

When a male gamete unites with a female gamete, a cell results that is called a zygote. The process by which gametes unite is called fertilization.

5.2.2 Asexual ReproductionAsexual reproduction is the formation of a new individual from cells of the parent, without the union of gametes (sex cells, sperm and egg), meiosis, gamete formation, or fertilization. The offspring of organisms that reproduce asexually are genetically identical to their parents and to each other. Without sexual reproduction, the species cannot benefit from the variability introduced by mixing genes. Therefore, evolutionary adaptation to changing environmental conditions may proceed slowly. There are several types of asexual reproduction.

Types of Asexual ReproductionBinary Fission: Binary fission is the simplest form and involves the division of a single organism into two complete organisms, each identical to the other and to the parent. Fission is common among unicellular organisms such as bacteria, many protists, some algae such as Spirogyra and Euglena.

Regeneration: A similar form of asexual reproduction is regeneration, in which an entire organism may be generated from a part of its parent. The term regeneration normally refers to re-growth of missing, or damaged body parts in higher organisms, but whole body regeneration occurs in Hydra, starfish, and many plants.

Asexual Spore: Spores are another form of asexual reproduction and are common among bacteria, protists, and fungi. Spores are DNA-containing capsules capable of sprouting into new organisms; unlike most seeds, spores are produced without sexual union of gametes, that is, reproductive cells.

Budding: Budding is another method of asexual reproduction in which a group of self-supportive cells sprouts from and then detaches from the parent organism. Unlike eggs or spores, buds are multicellular and usually contain more than one cell layer. Hydra and sea squirts reproduce by budding.

Vegetative Reproduction: Vegetative reproduction is common among plants and consists of certain parts that grow out from a main parent plant and eventually root and sprout to

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form new, independent plants. Examples are the runners of strawberries, the tubers of potatoes, and the bulbs of onions.

Parthenogenesis: Parthenogenesis is an important means of asexual reproduction in which new individuals are formed from unfertilized eggs. It occurs in some insects, amphibians, reptiles, and birds and in some species of plants.

5.2.3 Chromosome Number and Structure5.2.3.1 ChromosomeChromosome, microscopic structure within cells that carries the molecule deoxyribonucleic acid (DNA), the hereditary material that influences the development and characteristics of each organism.

5.2.3.2 Chromosome Number and StructureFollowing facts about chromosomes need to know for better understanding of mitosis, and meiosis.1. Every body cell in an organism has the same number of chromosomes (chromosome

number).2. The body cells of all normal individuals of the same species have the same chromosome

number. A normal human cell has 46 chromosomes.3. The chromosomes in each body cell normally occur in pair, called homologous pair. The

chromosomes in a homologous pair are similar in structure and in the arrangement of genetic information they carry. Thus the 46 chromosomes in a human cell make up 23 homologous pairs.

4. The genetic information of the chromosomes is located at specific points or position called genes.

5. The number of chromosomes in a complete set of homologous chromosomes is called the diploid number. This number is represented by 2n. Thus the diploid number (2n) for human is 46. Every body cell that we have contains the diploid number of chromosomes. That is 2n = 46. This diploid number is arranged in 23 homologous pairs.

6. A gamete contains one homologue from each homologous pair of chromosomes. In other words, it has half the diploid number of chromosomes. The number is called the haploid number. It is represented by n. The haploid number for humans is 23. That is, n = 23. A human sperm (male gamete) contains 23 chromosomes (one of each homologous pair). A human egg (female gamete) also contains 23 chromosomes (one of each homologous pair).

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7. During fertilization, the sperm and egg unite to form zygote. The zygote will have 46 chromosomes, in 23 homologous pairs. Thus fertilization has restored the diploid number of chromosomes.

8. All our body cells came from that zygote by mitosis. Therefore, all our body cells also have diploid number of chromosomes, which is 46.

9. Some diploid (2n) body cells in our reproductive organs produce haploid (n) gametes by meiosis.

5.3 Development5.3.1 What is Development?Development generally means that the cell or organism will increase in size and mass as well as show new features and function during the whole life from start to end of life . After mitosis, the daughter cells must undergo development. Normally, it slows down when a certain mature size is reached. We have developed through many stages: fertilized egg to embryo to unborn baby to child to adolescent. Our development has not stopped yet. We will continue to develop physically. We will move through young adulthood to middle age to old age and finally, to death.

5.3.2 Development of OrganismsAfter mitosis, in many organisms the cells are not alike. Although mitosis ensures that the daughter cells will have the same genetic information as the mother cell, yet cells that come from the same mother cell can develop in different ways. We began our life as one cell (zygote) but now we contain many different kinds of cells. Clearly, more than cell growth has occurred. Cells have become specialized to perform different functions. Biologists say that cell differentiation has occurred.5.3.3 Growth vs. Developmental Growth5.3.3.1 GrowthGrowth is an increase in size and mass. Growth can be accomplished in two ways. First, a cell can grow simply by increase in size and mass. It takes in substances from environment and assimilates them, or puts them together, to form more cellular material. However, such growth seems to cease when a cell reaches a certain size. Then growth can only be accomplished by the second way, an increase in cell numbers by cell division.

5.3.3.2 Developmental Growth

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A human egg has a mass of about 1 g (10-6 g). A human sperm has a mass of about 1 ng (10-9 g). Two combine to start the development of a human. At birth, an average child has a mass of about 3 kg (3,000 g). This mass is about one billion times greater than the mass of the egg and sperm. Growth has certainly occurred. However, it is easy to see that such growth involves more than just an increase in size and mass. As an organism develops, it takes on form, or shape, and this type of growth is called developmental growth.

The shape changes constantly during development. Some parts grow faster or slower than others. Thus some features appear sooner than others. Compare the proportions of heat to body and head to legs (Figure 5.1). Clearly, some parts of the human body develop faster or slower than other parts. Some features appear sooner than other features.

Figure 5.1: A comparison of proportion in human body for a 2-month fetus and a 15-year-old adolescent

5.3.4 DifferentiationIn addition to growth, development also involves differentiation. Differentiation is the gaining of specific structural features and functions by a cell. After differentiation, cells become specialized to catty out certain activities in an organism. As we grow from one cell to our present sixty to hundred trillion, certain cells became specialized to perform certain functions. Some became cells of the nervous system. Other became cells of the skeletal system. Still others became cells of the excretory, breathing, circulatory, and digestive systems. All these diverse cells, with their various forms and functions, began with the same single cell.

It is clear that differentiation is very orderly process. Cells do not differentiate in a haphazard way. For example, in order for a “dog cell” to end up as a dog, the growth and differentiation of one cell must be coordinated with the growth and development of all other cells. Otherwise, one would have a strange looking dog. Such coordination requires some

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sort of communication between the different cells in the developing organism. Development, therefore, depends on coordinated growth and differentiation.

5.3.5 AgingDifferent species of organisms have different average life spans. The life span may vary from a few days for some insects to a few thousand years for redwood trees. However, sooner or later, an organism grows old and dies.

What causes age? Why does an organism grow old and die? Why does a person become less active, get grey hair, suffer hearing and eyesight loss, and get wrinkled, sagging skin? Why is death a normal part of development?

1. Many biologists suspect that environmental conditions around the cell cause aging. One environmental factor that may cause aging is the sun’s radiation.

2. Other biologists believe that changes occur during differentiation that upset some metabolic processes. This would lead to a gradual slowing down, or aging, of all cell.

5.3.6 Cell ReplacementWhen an organism dies, its cells die. However, cells within an organism can die without the organism dying. Some cells simply wear out. Fortunately, they are replaced for most of the life span of an organism. In one sense, we get a new body about every seven years. It takes about that long for all our worn-out cells to be replaced by new ones. However, not all cells can be replaced. For example, a nerve cell, if destroyed, cannot be replaced.

Some biologists believed that up to 2% of our cells die each day. If no cells died, our mass would double in about 100 days, provided that cell division continued normally and we maintained our proper diet. But cells do die, billions every day. Our mass stays fairly constant because the rate of cell replacement equals the rate of cell death.

5.4 Review Questions1-Cell Division

1. Define mitosis. What the stages of mitosis?2. Describe the importance of mitosis.3. Define meiosis. What the stages of mitosis?4. What are the importances of meiosis?5. Distinguish between mitosis and meiosis.

6. Summarize the process of mitosis and meiosis with a table and diagram.

2-Reproduction1. Distinguish between sexual reproduction and asexual reproduction.

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2. Define the following terms: (i) Gametes, (ii) Hermaphrodites, (iii) Zygote and (iv) Fertilization.3. With example, describe the following processes of asexual reproduction: (i) Binary fission, (ii) Regeneration, (iii)

Asexual spores, (iv) Budding, (v) Vegetative reproduction, and (vi) Parthenogenesis.4. What is a chromosome? What is meant by “chromosome number”?6. What are homologues? What is the origin of each homologue of a homologous pair?7. Distinguish between the diploid and the haploid number of chromosomes.8. Why must gametes contain only the haploid number of chromosomes?9. Describe the facts about chromosomes that are needed to know for better understanding of mitosis, and

meiosis.

3-Development1. What is meant by cell development?2. What is cell growth? How does it occur?3. What is developmental growth?4. What do you understand by cell differentiation?5. Mention two possible reasons aging.6. Describe, with example, the importance of cell replacement to organisms.

Chapter 5Chapter 56 Ecology and Ecosystem

6.1 Ecology6.1.1 What is ecology?Ecology is the study of the relationships among organisms and between organisms and their environment. That is, ecology is the study of the relationship of living organisms to their physical and biological environment. The physical environment (abiotic) includes light and heat or solar radiation, moisture, wind, oxygen, carbon dioxide, nutrients in soil, water, and atmosphere. The biological environment (biotic) includes organisms of the same kind as well as other plants and animals.

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The term ecology was introduced by the German biologist Ernst Heinrich Haeckel in 1866; it is derived from the Greek oikos (“household”), sharing the same root word as economics. Thus, the term implies the study of the economy of nature.

6.1.2 Levels of Biological OrganizationNo organism lives completely on its own. Each organism is dependent upon other organisms and upon the environment in which it lives. Therefore, it is important to study organisms at levels above the individual level. These levels are the population, community, biome, and biosphere levels. Ecology is the field of biology that deals with the study of organisms at these levels.

6.1.2.1 PopulationA population is a group of individuals of the same species, living together in the same area. Examples of populations are pine trees in a forest, hilsha fish in a river, the frog in a pond, and the geese on a lake.

6.1.2.2 CommunityA community is a naturally occurring group of organisms living together in the same area. A community consists of several populations. For example, a forest community might consists of the beech tree population, the maple tree population, the trillium population, the raccoon population, the great-horned owl population, the earthworm population,, the mosquito population,, and hundreds of other populations. The forest community includes the populations of all living things in the forest.

6.1.2.3 BiomeA biome is the biological life in any large geographical region with characteristic climate. A biome has a characteristic geography. That is, it has a characteristic climate (rainfall and temperature) and a characteristic topography (land shape). Therefore, it will be dominated by characteristic plant, animal, and microbial populations. These populations may occur in many communities throughout a biome.

For example, a desert is a biome. It may consist of a sand plain community, a sand dune community, an oasis community and others. Each community will have its own populations of desert organisms. The tundra of northern Canada is a biome. It consists of bog communities, coastal communities, lake communities, and others.

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6.1.2.4 BiosphereThe biosphere is the region on earth in which life exist. Organisms live in the lower regions of the atmosphere. That is biosphere is the earth's relatively thin zone of air, soil, and water that is capable of supporting life, ranging from about 10 km (about 6 miles) into the atmosphere to the deepest ocean floor. Life in this zone depends on the sun's energy and on the circulation of heat and essential nutrients. The biosphere is made up of many biomes. Among them are desert biomes, coniferous forest biomes, deciduous forest biomes, grassland biomes, marine biomes, and others.

6.2 Ecosystem6.2.1 What is an Ecosystem?

An ecosystem is an interacting system that consists of groups of organisms and their non-living or physical environment. An ecosystem consists of two main parts, a biotic community biological environment) and an abiotic (non-living or physical environment) environment.

6.2.2 Size of EcosystemThere are no fixed limits to the size of an ecosystem. Any community of organisms interacting with its environment forms an ecosystem. A forest is an ecosystem. It consists of a community of living things plus abiotic factors such as wind speed, light intensity, and temperature. A lake is also an ecosystem, as is a meadow, a city park, a house aquarium, and even our mouth.

6.2.3 Interrelationship Among the Factors of an EcosystemThe most important thing to remember about an ecosystem is that all its parts, biotic and abiotic, are highly interrelated. Each part is affected by all the other parts. Therefore, if one part is changed in any way, all the other parts will be changed also.

6.2.4 Structure of EcosystemAs ecosystems are defined by the network of interactions among organisms, and between organisms and their environment, they can be of any size but usually encompass specific, limited spaces. The study of ecosystems mainly consists of the study of certain processes that link the living, or biotic, components to the non-living, or abiotic, components.

The biotic community includes all the living organisms in the ecosystemanimals, plants, and microorganisms. The abiotic environment includes all the non-living aspects of the ecosystemwater, carbon dioxide, soil minerals, light, humidity, temperature, wind, and other physical factors.

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6.2.5 Abiotic Factors in Ecosystem6.2.5.1 Abiotic Factors of Terrestrial EcosystemFive main abiotic factors affect terrestrial ecosystems. They are (i) temperature, (ii) moisture, (iii) light, (iii) wind, and (v) soil characteristics. Each organism has a range of tolerance for each of these factors. This range depends on the factor and on the organisms. When the range is exceeded, in either direction, the organism suffers. Within each range of tolerance there is a point at which each organism lives best. This is called optimum. However, conditions are seldom at the optimum. Organisms with the broadest range of tolerance generally survive best.

6.2.5.2 Abiotic Factors of Aquatic EcosystemMany abiotic factors affect aquatic ecosystems. For example, a stream ecosystem may be affected by (i) temperature, (ii) speed of the water, (iii) nature of the stream bottom and banks, (iv) light, (v) the chemical properties of the water and many others.

A pond or lake ecosystem may also be affected by (i) temperature, (ii) light, (iii) depth, (iv) the nature of the bottom, (v) the transparency of the water, (vi) the chemical properties and other factors. The life in the pond or lake is determined, in part, by these factors. The life, in turn, influences these factors.

6.2.6 Biotic Factors in Ecosystem6.2.6.1 Habitat

The habitat of an organism is the place in which it lives. An ecosystem, such as a woodlot, has many habitats. For example, the habitat of an earthworm is the rich woodlot soil. The habitat of a land snail is the moist leaf litter. The habitat of a porcupine is the hollow tree. The habitat of a blue jay is the branches of the trees.

Habitats may overlap. For example, the porcupine may seek out a meal of bark in the branches that are also the habitat of the blue jay. However, since these animals do not eat the same food, no problems result from the overlap of their habitats.

6.2.6.2 NicheThe niche of an organism is its role in the community. For example, the niche of a deer is to feed on grass and other plants, to become food for wolves, to provide blood for black-knife and mosquitoes, to fertilize the soil with nutrients, and so on. The niche of a frog in a pond is to feed on insects, to become food for snakes and other animals, and many other things.

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Many people confuse habitat and niche. It may help you to remember the difference if you think of the habitat as the “address” of the organism and the niche as its “occupation”, or “job”.

If two species have the same habitat and similar niches, they will compete with one another. For example, mule deer and elk often live in the same mountain valley. That is, they have the same habitat. Both species eat grass and other plants. Both are prayed upon by wolves and are attacked by many of the same parasites. That is, they have similar niches. Clearly, they will compete for available space and food in the valley.

6.2.7 Trophic (Nutritional) LevelsAll the organisms in an ecosystem depend on one another and their physical environment. This interdependence shows up clearly when one studies the way in which various organisms in an ecosystem obtain their food.

6.2.7.1 Producer LevelAll living things need energy to support life process. Almost all this energy originally comes from the sun. Green plants and many microorganisms contain chlorophyll. These living things, through photosynthesis, store some of the sun’s energy in the bonds of glucose molecules. They make their own food, or store their own energy, by converting light energy into chemical potential energy. Organisms that produce their own food are called autotrophs (“self-feeders”), or producers. Biologists say that they occupy the trophic level (“feeding level”) of producer.

6.2.7.2 Consumer LevelOrganisms that depend on other organisms for food are called heterotrophs (“other feeders”). All ecosystems have heterotrophs. Most heterotrophs are animals that feed on plants or on other animals. These organisms are called consumers. They occupy the trophic level of consumer.

Herbivores: Those animals that feed directly on producers (plants) are called first-order consumers, or herbivores (“plant eaters”). Deer, rabbits, and cow are herbivores.

Carnivores: Animals that eat other animals are called carnivores (“flesh eaters”). Those carnivores that feed on herbivores are called first-order carnivores, or second-order consumers. The wolf and fox are first-order carnivore, since they eat deer and rabbits respectively. Animals that eat first-order carnivores are called second-order carnivores, or third-order consumer. For example, snakes are second-order carnivore Ecosystems also have what is called top carnivores, such as hawk, flacon and eagle.

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Omnivores: Animals that are both herbivores and carnivores are called omnivores (“all eaters”). For example, a fox eats berries as well as mice and rabbits. Humans are omnivores.

Predators: Animals that feed on live organisms are called predators. The organisms that are eaten are called prey. Tiger and lion are predators, while deer, cow, goat, etc. are their prey.

Scavengers: Animals that feed on dead organisms are called scavengers. Snails, crayfish, and some fish are scavengers of lake and ponds. Crow, magpies, and vultures are also scavengers. Some animals may be predators sometimes and scavengers at other times, depending on the food available.

6.2.7.3 Decomposer LevelThe trophic level of decomposer is a most important level in all ecosystems. All organisms eventually die, and all animals produce waste products. If decomposers were not present, non-living organic matter would soon smother all life on earth. The organisms that break down non-living organic matter and return valuable nutrients to the ecosystem are called decomposers. Most decomposers are bacteria and fungi. Decomposers are saprophytes. Organisms that feed on non-living organic matter are called saprophytes.

6.2.8 Food Chain and Food Webs6.2.8.1 What is Food Chain?

The organisms in an ecosystem are generally linked together through predator-prey relationships in what is called a food chain (Figure 6.1).

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Figure 6.1: The general pattern for a food chain, illustrated by one example.

A food chain represents the transfer of energy through a series of organisms in a community (a group of organisms living in the same environment). It usually starts with a producer (an organism that manufactures simple food by a process such as photosynthesis) and ends with a top consumer. Producers are eaten by herbivors or primary consumers. Carnivores may be secondary, tertiary or quaternary consumers. For example, clover is food for the rabbit. The rabbit, in turn, is food for the fox. This simple food chain may be summarized in the following way:

All food chains follow the general pattern shown in the figure above. Of course, some food chains are longer than others. Some may have more carnivore levels than others.

6.2.8.2 What is Food Web or Net?A food web consists of all the food chains in a single ecosystem. Each living thing in an ecosystem is part of multiple food chains.

Each food chain is one possible path that energy and nutrients may take as they move through the ecosystem. All of the interconnected and overlapping food chains in an ecosystem make up a food web.

6.3 Review Questions1-Ecology

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1. Define ecology. What do you understand by physical and biological environment?2. Describe, with example, the terms population, community, biome, and biosphere.3. What is an ecosystem? Give an example of an ecosystem.4. Distinguish between the biotic and the abiotic parts of an ecosystem.

2-Structure of Ecosystem1. State five main abiotic factors that affect the terrestrial ecosystem.2. State the abitic factors that affect (i) a stream ecosystem, and (ii) a pond or lake ecosystem.3. Distinguish between habitat and niche.4. Distinguish between an autotroph and a heterotroph.5. What do you understand by trophic level? Name and describe the three main trophic levels that occur in all

ecosystems.6. What is the difference between a food chain and a food web?7. Outline, with example, the general pattern for a food chain.8. Define, with example, the followings: (i) Saprophytes, (ii) Herbivores, (iii) Carnivores, (iv) Omnivores, (v)

Predators, and (vi) Scavengers.

Chapter 7Chapter 77 Nutritional Requirements7.1 The Nutrient and Nutrition

7.1.1 What is Food?Humans are heterotrophs, organisms that cannot produce their own food. Heterotrophs must ingest, or take in, food. At least 95% of the species of organisms on earth all animals, all fungi, and most protists and bacteria are heterotrophs.

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Food provides the heterotrophs or “other-feeders” with two things: (1) energy, and (2) the raw materials to build the substances they need. The energy in food is described in units called calories, or properly kilocalories (thousands of calories, or kcal). The raw materials are nutrients.

Nutrients are the raw materials, which provide the essential matter and energy for life. Nutrition refers to all the processes by which living organisms obtain and use these nutrients.

7.1.2 Classes of NutrientsThere are six classes of nutrients: (1) Carbohydrates, (2) Fats (Lipids), (3) Proteins, (4) Vitamins, (5) Minerals, and (6) Water. These are the substances, in fact, that make up most of our body. Assuming that you are a proper weight for your height, your body is made up of about 60% water, and about 20% fat. The other 20% is mostly protein, carbohydrate, combinations of these two substances, and two major minerals found in your bones: calcium and phosphorus. Other minerals and vitamins make up less than 1% of you.

7.2.2.1 Energy Nutrients: Carbohydrates, Lipids and ProteinsCarbohydrates, lipids, and proteins are organic (carbon-containing) compounds and are used by your body as a source of energy, or kilocalories. They are, therefore, often referred to as the energy nutrients. Proteins, however, are not a preferred energy source. In addition, these three organic compounds are used as building blocks for growth and repair, as well as to produce other substances your body may need. Your body does not obtain energy from vitamins, minerals, or water.

7.2.2.2 VitaminsVitamins are organic molecules required by the body in small amounts for metabolism, to protect health, and for proper growth in children. The 13 well-identified vitamins are classified according to their ability to be absorbed in fat or water (Table 7.1). The fat-soluble vitamins — A, D, E, and K — are generally consumed along with fat-containing foods, and because they can be stored in the body's fat, they do not have to be consumed every day. The water-soluble vitamins — the eight B vitamins and vitamin C — cannot be stored and must be consumed frequently, preferably every day (with the exception of some B vitamins).

Table 7.1: Functions and sources of some vitamins important to humans

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7.2.2.3 MineralsMinerals are inorganic substances and are transported aroud the body as ions dissolved in the blood and other body fluids. Your body uses a variety of minerals that perform a variety of functions (Table 7.2).

Table 13.2: Functions and sources of some minerals important to humans

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7.2.2.4 WaterA large portion of all living things is water. For example, about 70% of your body mass is water. Water has many functions in living organisms. The main ones are:1. Water provides the medium in which all the body’s reactions take place.2. It aids in the digestion and absorption of food.3. It is a medium of transport, through arteries and veins, with an organism.4. It even lubricates your joints and cushions organs such as the brain and spinal cord.5. It helps in the excretion of harmful by-products of metabolic processes.6. It aids in the regulation of heat loss.

7.2 Food as Fuel: Calories Count7.2.1 Sources of EnergyLike all animals cells, human cells require energy to carry out biochemical, mechanical, and transportation tasks. Cells derive energy from the chemical bonds in fats, carbohydrates, and proteins an animal eats, digests, and absorbs; any energy an animal does not

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immediately use can be stored as the carbohydrate glycogen in the liver or muscles or as fat in fat cells.

7.2.2 Calories Count1. Food energy is usually measured in kilocalories (kcal), also called Calories (Cal). 2. A large apple contains about 70 Cal worth of energy-producing compounds; and jogging

1.6 km (1 mile) burns about 100 Cal of stored energy. 3. The food energy in a slice of bread could bring a liter of water to a boil, and a pound of

body fat has enough energy to bring 52 liters (13 gal) to a boil!4. Each person has a minimum daily energy requirement that varies with age, sex, body

size, activity level, and other factors. In general, a normally active female college student needs around 1,800-2,000 Cal a day to fuel her total metabolic needs; a male college student needs about 2,200-2,500 Cal. Carbohydrate and protein each provide about 4 Cal/g, while fat provides more than twice as much, or 9 Cal/g.

5. A person would have to run for about 30 minutes, for example, to burn off the calories in a cheeseburger.

7.2.3 Body Fat and Weight ControlWhen an animal’s food intake exceeds its energy needs, the inevitable result is an increase in amount of leftover energy stored as body fat. This basic biological fact means that the secret of weight control lies in taking in only as many kilocalories as the body needs for fuel.

To stay trim and fit with a desirable percentage of body fat and healthy, efficient heart and lungs, a person should perform continuous, rhythmic, aerobic exercise (such as walking, jogging, swimming, or cycling) three to five times per week for 15-60 minutes, depending on the intensity of the exercise. Sound weight-loss diets combine calorie reductions, primarily through diminished intake of sugar and fat, with increased physical activity. Some dieters find it useful to focus on the biological function of eating: to take in the nutrients the body needs for energy, maintenance, and repair. As one wise saying goes, “Eat to live, don’t live to eat”. “Eat less to eat more”.

7.3 Review QuestionsNutritional Requirements

1. Define nutrient and nutrition.2. What are the six classes of nutrients?3. Which nutrients are called energy nutrients? Why?4. Describe the importance of vitamins, with example, in our diet.5. Describe the functions of calcium, potassium and magnesium.6. Why is water so important to animals?7. List five vitamins with their major function and their source. What are signs and symptoms of their deficiency?

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8. List five minerals with their major function and their source. What are the signs and symptoms of their deficiency?

Chapter 8Chapter 88 Human Digestive System8.1 The Anatomy of Digestive System8.1.1 Overview of Digestive System

Digestive system consists of a series of connected organs whose purpose is to break down, or digest, the food we eat. Food is made up of large, complex molecules, which the digestive

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system breaks down into smaller, simple molecules that can be absorbed into the bloodstream. The simple molecules travel through the bloodstream to all of the body's cells, which use them for growth, repair, and energy.

Digestion generally involves two phases: a mechanical phase and a chemical phase. In the mechanical phase, teeth or other structures physically break down large pieces of food into smaller pieces. In the chemical phase, digestive chemicals called enzymes break apart individual molecules of food to yield molecules that can be absorbed and distributed throughout the body.

8.1.2 Structural Regions of Digestive SystemThe digestive system of most animals consists mainly of a long, continuous tube called the alimentary canal, digestive tract, or gastrointestinal tract. If a human adult’s digestive tract were stretched out, it would be 6 to 9 m (20 to 30 ft) long. This digestive tract has a mouth at one end, through which food is taken in, and an anus at the other end, through which digestive wastes are excreted. The digestive tract of humans can be divided into six regions that are very different in structure (Figure 8.1). These six structural regions are (1) the mouth or the oral cavity, (2) the esophagus or food tube, (3) the stomach, (4) the small intestine, (5) the large intestine or colon, and (6) the anal region or anus.

The human digestive system also consists of accessory structures in addition to the gastrointestinal tract (Figure 8.1). Some of the accessory structures, such as (1) the salivary glands and (2) the pancreas, produce digestive enzymes. Two others, (3) the liver and (4) the gallbladder, produce and store bile, which assists in fat digestion. The teeth and tongue are also accessory organs.

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Figure 8.1: The human digestive system. Food breaks down as it moves through the chambers of digestive tract. Accessory organs aid in digestion.

8.1.2.1 The Mouth Region – Digestion BeginsMouth or Oral Cavity: In humans, digestion begins in the mouth, where both mechanical and chemical digestions occur. The mouth quickly converts food into a soft, moist mass. Three pairs of salivary glands empty saliva into the mouth through ducts to moisten the food. Saliva contains the enzyme amylase, which begins to hydrolyze (break down) starch—a carbohydrate manufactured by green plants.

Once food has been reduced to a soft mass, it is ready to be swallowed. The sense receptor in mouth region also helps monitor the characteristic of the food in terms of texture, temperature, and taste.

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Saliva: Dissolving, Digestion and Lubrication: Your mouth produces up to 1.5 liters of liquid every day in order to dissolve, digest, and lubricate your food. This liquid is called saliva. Saliva is produced when food being tasted or chewed. Saliva is a solution of three main substances: water, amylase, and mucin.

1. Water helps to moisten dry food and dissolves any soluble nutrients. Water is also essential for tasting food.

2. Amylase is an enzyme that helps break starch molecules apart into shorter molecules of maltose sugar.

3. The protein mucin is produced as a lubricating and protective coating throughout the mouth, nasal cavity, and trachea. Mucin serves a very important non-digestive function by keeping all internal surfaces lubricated and protected from drying out.

8.1.2.2 The Esophagus – Swallowed Food and Liquids Pass to the StomachThe esophagus (food tube) is a muscular tube about 25 cm (10 inches) and 2.5 cm (1 inch) long tube reaching the stomach. Food advances through the alimentary canal by means of rhythmic muscle contractions (tightening) known as peristalsis.

8.1.2.3 Stomach – Stores, Digests, and Pushes Food to the Small IntestineThe stomach, located in the upper abdomen, is a sac-like structure with strong, muscular walls. The stomach can expand significantly to store all the food from a meal for both mechanical and chemical processing. The stomach contracts about three times per minute, churning the food and mixing it with gastric juice. This fluid, secreted by thousands of gastric glands in the lining of the stomach, consists of water, hydrochloric acid, an enzyme called pepsin, and mucin (the main component of mucus). Up to 2 liters of gastric juice is added to your meals every day by your stomach.

1. Water keeps the food moistens and dissolves any soluble nutrients.2. Hydrochloric acid creates the acidic environment that pepsin needs to begin breaking

down proteins. It also kills microorganisms that may have been ingested in the food. 3. The protein-digesting enzyme, pepsins, breaks down proteins into small peptides.4. Mucin coats the stomach, protecting it from the effects of the acid and pepsin.

About four hours or less after a meal, food processed by the stomach, called chyme, begins passing a little at a time through the pyloric sphincter into the duodenum, the first portion of the small intestine.

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8.1.2.4 The Small Intestine – Digests and Absorbs NutrientsDigestion and Absorption of Food: Most digestion, as well as absorption of digested food, occurs in the small intestine. This narrow, twisting tube, about 2.5 cm (1 in) in diameter, fills most of the lower abdomen, extending about 6 meters (20 feet) in length. Over a period of three to six hours, peristalsis moves partially digested food (or chime) through the duodenum into the next portion of the small intestine, the jejunum, and finally into the ileum, the last section of the small intestine. Chemical digestion of food in the small intestine is takes place by aid of three kinds of digestive juices secreted by the liver, the pancreas, and the intestinal linings.

The Liver: The liver secretes bile into the small intestine through the bile duct. Bile breaks large fat globules into small droplets, which enzymes in the small intestine can act upon.

The Pancreas: Pancreatic juice, secreted by the pancreas, enters the small intestine through the pancreatic duct. Pancreatic juice contains enzymes that break down sugars and starches into simple sugars, fats into fatty acids and glycerol, and proteins into amino acids.

Intestinal Lining: Glands in the intestinal walls secrete additional enzymes called intestinal juice that breaks down starches and complex sugars into nutrients that the intestine absorbs.

The great length of the small intestine ensures that nutrients can be fully digested and have a good chance of being absorbed. The small intestine’s capacity for absorption is increased by millions of finger-like projections called villi, which line the inner walls of the small intestine. Each villus is covered with finger-like projections called microvilli cover the cell surfaces. This combination of villi and microvilli increases the surface area of the small intestine’s lining by about 150 times, multiplying its capacity for absorption. Beneath the villi’s single layer of cells are capillaries (tiny vessels) of the bloodstream and the lymphatic system. These capillaries allow nutrients produced by digestion to travel to the cells of the body.

8.1.2.5 The Large Intestine – Completes Nutrient and Water AbsorptionFunctions of Large Intestine: A watery residue of indigestible food and digestive juices remains unabsorbed. This residue leaves the ileum of the small intestine and moves by

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peristalsis into the large intestine, where it spends 12 to 24 hours. The large intestine is 1.5 to 1.8 meters (5 to 6 feet) long and about 6 cm (2.5 inch) in diameter.

The large intestine serves several important functions. (1) It absorbs water — about 6 liters (1.6 gallons) daily — as well as dissolved salts from the residue passed on by the small intestine. (2) In addition, bacteria in the large intestine promote the breakdown of undigested materials and make several vitamins, notably vitamin K, which the body needs for blood clotting.

The large intestine moves its remaining contents toward the rectum, which makes up the final 15 to 20 cm (6 to 8 in) of the alimentary canal. The rectum stores the feces—waste material that consists largely of undigested food, digestive juices, bacteria, and mucus—until elimination. Then, muscle contractions in the walls of the rectum push the feces toward the anus.

Water Reabsorption in the Large Intestine: The digestive glands secrete 5 to 6 liters of water on your food every day. This water comes from the sources shown in the Table 8.1. The water is added to dissolve the enzymes, and to lubricate or dissolve the nutrients. The large intestine reabsorbs the water into the bloodstream. Therefore, rather than drink 5.6 liters of replacement water every day, you automatically recycle all but 0.2 liter.

Table 8.1: Sources of water used in digestion

8.1.2.6 The Anal Region or AnusThe anus is the terminal portion of the alimentary tract which communicates with the external environment. Two sphincters control its aperture. It allows faeces and gas to leave the body. Defeacation is the process where faeces are expelled from the rectum through the anus. Anal sphincters give control over the regularity of defeaction, and this may be consciously controlled in some species. The anal canal lubricates the passage of faeces.

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8.2 Food Digestion8.2.1 Why is Chemical Digestion Needed?

Chemical digestion of carbohydrates, fats, and proteins is need for three main reasons.1. First, these molecules are too large to pass through a cell membrane.2. Second, fat and some carbohydrates are insoluble in water. Before nutrients can enter

the blood, they must be dissolved in water.3. Third, the carbohydrates, fats, and proteins that you eat are not usually the same

carbohydrates, fats, and proteins that your body uses. In fact, your body rearranges plant animal carbohydrates, fats, and proteins into “people” carbohydrates, “people” fats, and “people” proteins.

8.2.2 How Does Chemical Digestion Occur?Most chemical digestion in your body uses a water molecule to break the bonds between the parts of the large molecules. This process is called hydrolysis. Specific enzymes may speed up the hydrolysis of the large molecules by positioning the water molecule in just the right place for the chemical reaction to occur. For example, proteinases or proteases help hydrolyze proteins, lipases help hydrolyze lipids or fats, and carbohydrases help hydrolyze carbohydrates.

8.2.2.1 Chemical Digestion in the MouthOur saliva contains a digestive enzyme called amylase. The only carbohydrate that this enzyme helps to hydrolyze is starch. Many starch molecules are found in grains, potatoes, and many other foods. The starch molecules are very large (polymer of glucose units) and insoluble in water. Therefore, they must be broken apart before they can be absorbed into your body.

8.2.2.2 Chemical Digestion in the StomachGastric juice contains hydrochloric acid, water, mucin, and a protease called pepsin. The combined action of these substances furthers the chemical digestion of food.

Hydrochloric Acid: The hydrochloric acid in your stomach assists digestion in four ways.1. It helps dissolve insoluble minerals.2. It kills many bacteria taken in with the food.3. It aids in the digestion of starch.4. It provides the acidity needed to keep the pepsin enzyme working.

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Pepsin: Pepsin, a protease enzyme, also helps water molecules split proteins apart. Hydrolysis of a protein by pepsin produces several shorter chains of amino acids. These shorter chains are further split up into single amino acids in the small intestine.

Mucin: The hydrochloric acid is very strong, strong enough to dissolve metals. The stomach lining is prevented from being dissolved by the mucin it produces. The mucin itself is continually being digested by the acid and pepsin. Therefore, mucin must be continually produced. If not enough mucin is produced by the stomach, the acid does start dissolving the lining and the muscle layer of stomach. This painful event is known as an ulcer.

8.2.2.3 Chemical Digestion in the Small IntestineThere are three main sources of chemicals that assist digestion in the small intestine. These are the liver, the pancreas, and the intestinal lining.

Liver: The liver produces no digestive enzymes. Rather, it makes complex mineral salts in a solution called bile. Bile salts can be stored and concentrated unit needed in the gall gladder. Fats and oils do not dissolve in water. Bile salts break up large drops of fat into many smaller droplets. The fat is said to be emulsified. Bile salts also prevent the small droplets from going back together again. The liver has a further function. It stores glucose in the form of starch-like molecules called glycogen.

Pancreas: The pancreas produces three enzymes:1. Protease, which hydrolyze protein,2. Amylase, which hydrolyze starch, and3. Lipase, which hydrolyze fat or oil.

These enzymes and the bile from the liver enter into the duodenum (small intestine) through the same opening. 1. The breaking down of the fat droplets caused by the bile salts allows the lipase to

hydrolyze fat molecules much faster. Hydrolysis of fat molecules produces smaller molecules of glycerol and fatty acids.

2. The amylase that the pancreas makes is a different enzyme from the amylase in saliva. But it acts in the same way to produce maltose from starch.

3. The Protease, like pepsin, secreted by the pancreas, split proteins into shorter chains of amino acids.

Intestinal Lining: The lining of the small intestine contains many tiny intestinal glands.

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1. These glands produce enzymes that split the shorter chains of amino acids into individual amino acid molecules.

2. The glands also produce enzymes that help hydrolyze disaccharides like maltose, lactose, and sucrose into simple sugars like glucose and fructose.

Mucin is the other major substance produced by glands of the lining. Mucin helps lubricate and protect the intestinal lining.

8.3 Peptic Ulcer and Heartburn8.3.1 Peptic Ulcers 8.3.1.1 Gastric Ulcer and Duodenal UlcerPeptic ulcers are ulcers of the stomach (gastric ulcer) or small intestine (duodenal ulcer). In addition to the pain caused by the ulcer itself, peptic ulcers give rise to such complications as hemorrhage from the erosion of a major blood vessel; perforation of the wall of the stomach or intestine, with resultant peritonitis; or obstruction of the gastrointestinal tract because of spasm or swelling in the area of the ulcer.

Cause of Peptic Ulcers 1. The direct cause of peptic ulcers is the destruction of the gastric or intestinal mucosal

lining by hydrochloric acid, an acid normally present in the digestive juices of the stomach.

2. Infection with the bacterium Helicobacter pylori is thought to play an important role in causing both gastric and duodenal ulcers.

3. Injury of the gastric mucosal lining, and weakening of the mucous defenses, such as by non-steroidal anti-inflammatory drugs, are also responsible for gastric ulcer formation.

4. Excess secretion of hydrochloric acid, genetic predisposition, cigarette smoking, and psychological stress are important contributing factors in duodenal ulcer formation and exacerbation.

8.3.2 HeartburnHeartburn is another acid-related condition, which is characterized by a burning feeling in the chest and a sour or bitter taste in the mouth. Heartburn typically develops when the acidic contents of the stomach flow back into the esophagus and irritates the lower esophagus.

Taking an antacid tablet neutralizes the acid in the esophagus so that the acid-sensitive nerve endings there are no longer stimulated. Unfortunately, most antacid remedies end up neutralizing some of the acid in the stomach as well. This slows down normal protein

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digestion, and also stimulates the gastric glands to produce more replacement acid. Therefore, you could end up with an even more acidic stomach.

8.4 Review Questions1-Human Digestive System: Anatomy

1. What is the function of the digestive system?2. What are the major and accessory parts of the digestive system?3. What is the function of mouth region in digestion?4. What is saliva? What are its constituents? What are the functions of these constituents?5. How are different constituents of saliva useful in the digestion process?6. Describe the composition of gastric juice. What are the functions of these constituents?7. Describe the sources and functions of the three digestive fluids that help in chemical digestion in the small

intestine.8. What are the three major functions of the large intestine?9. How much water is supplied by your body to aid chemical digestion in the alimentary canal each day? How

much of this water is reabsorbed?

2-Human Digestive System: Digestion1. What is digestion? 2. How are digestion carried out chemically?3. What is the function of an enzyme in digestion? Describe the three major enzymes that help digest the energy

nutrients?4. Name the enzymes that are present in salivary gland, stomach, small intestine and pancreas.5. Why is chemical digestion of starch, proteins, and fats necessary?6. Why do most minerals not need chemical digestion?7. Why are fats emulsified before their digestion?8. How does chemical digestion occur in the stomach?9. Distinguish between ulcer and heartburn.10. Describe chemical digestion in the small intestine.

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Chapter 9Chapter 99 Human Respiratory System9.1 Gas Exchange and Breathing

9.1.1 Gaseous Nutrient and WasteMost animals are aerobic, that is, they need oxygen. Carbon dioxide also affects animals, since too much of it can be harmful. Oxygen is essential for cells, which use this vital substance to liberate the energy needed for cellular activities. This process is called cellular respiration. In addition to supplying oxygen, the respiratory system aids in removing of carbon dioxide, preventing the lethal build up of this waste product in body tissues.

9.1.2 Inhalation and ExhalationThe respiratory and circulatory systems work together to deliver oxygen to cells and remove carbon dioxide in a two-phase process called respiration.1. The first phase of respiration begins with breathing in, or inhalation. Inhalation brings air

from outside the body into the lungs. Oxygen in the air moves from the lungs through blood vessels to the heart, which pumps the oxygen-rich blood to all parts of the body. Oxygen then moves from the bloodstream into cells, which completes the first phase of respiration. In the cells, oxygen is used in a separate energy-producing process called cellular respiration, which produces carbon dioxide as a by-product.

2. The second phase of respiration begins with the movement of carbon dioxide from the cells to the bloodstream. The bloodstream carries carbon dioxide to the heart, which pumps the carbon dioxide-laden blood to the lungs. In the lungs, breathing out, or exhalation, removes carbon dioxide from the body, thus completing the respiration cycle.

9.1.3 Cellular Respiration vs. BreathingCellular respiration: Cellular respiration is the process by which living cells break down foods and release the stored chemical potential energy.

Breathing: Breathing is the means by which respiratory gases are exchanged between the entire organism and its environment. Breathing is simply a mechanical process. Breathing causes air containing a high concentration of oxygen to enter the lungs and cause air containing a high concentration of carbon dioxide to leave the lungs.

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9.2 The Human Respiratory System9.2.1 Anatomy of Respiratory SystemThe organs of the respiratory or gas exchange system extend from the nose to the lungs and are divided into the upper and lower respiratory tracts (Figure 9.1). The upper respiratory tract consists of (1) the nose or nasal passages and (2) the pharynx, or throat. The lower respiratory tract includes (3) the larynx, or voice box; (4) the trachea, or windpipe, which splits into two main branches called bronchi; tiny branches of the bronchi called bronchioles; and (5) the lungs, a pair of saclike, spongy organs. The nose, pharynx, larynx, trachea, bronchi, and bronchioles conduct air to and from the lungs. The lungs interact with the circulatory system to deliver oxygen and remove carbon dioxide.

Figure 9.1: The human respiratory system. The respiratory system can be explained as a group of organs that help us breathe. Breathing involves inhalation of oxygen and exhalation of carbon dioxide.

9.2.1.1 Upper Respiratory TractNasal Passage: The uppermost portion of the human respiratory system, the nose is a hollow air passage that functions in breathing and in the sense of smell. The nasal cavity moistens and warms incoming air, while small hairs and mucus filter out harmful particles and microorganisms.

Pharynx: Air leaves the nasal passages and flows to the pharynx, a short, funnel-shaped tube about 13 cm (5 inches) long that transports air to the larynx.

9.2.1.2 Lower Respiratory TractLarynx: Air moves from the pharynx to the larynx, a structure about 5 cm (2 inches) long located approximately in the middle of the neck.

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Trachea, Bronchi, and Bronchioles: Air passes from the larynx into the trachea, a tube about 12 to 15 cm (about 5 to 6 inches) long located just below the larynx. The trachea branches into two tubes, the left and right bronchi, which deliver air to the left and right lungs, respectively. Within the lungs, the bronchi branch into smaller tubes called bronchioles.

Lungs: The two branches of the trachea, called bronchi, subdivide within the lobes into smaller and smaller air vessels. They terminate in alveoli, tiny air sacs surrounded by capillaries. When the alveoli inflate with inhaled air, oxygen diffuses into the blood in the capillaries to be pumped by the heart to the tissues of the body, and carbon dioxide diffuses out of the blood into the lungs, where it is exhaled.

9.2.2 Gas Exchange in LungsThe function of the breathing system is to absorb oxygen into the body and the expel carbon dioxide from the body.

Dark red blood, poor in oxygen and rich in carbon dioxide is pumped by the heart into the pulmonary arteries (Figure 9.2). Eventually, this blood ends up in a capillary surrounding the airspace of an alveolus. Fresh inhaled air in the airspace is about 21% oxygen. This is a very high concentration compared to what is in the blood. Therefore, oxygen molecules diffuse from the airspace into the blood stream through the thin lining of the alveolus.

Figure 9.2: Gaseous exchange.

The now bright red, oxygen-rich blood moves through the capillary into the pulmonary vein and back to the heart. It is continually replaced by oxygen-poor blood. Thus, the diffusion of oxygen never stops so long as the flow of blood continues. At the same time that oxygen

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diffusion is occurring, carbon dioxide is diffusing from the blood into the air space of the alveolus.

Fresh air contains only 0.034% carbon dioxide, which is a lower concentration than that in the blood. Therefore, diffusion of carbon dioxide occurs from the blood into the airspace. If you hold your breath you can stop the diffusion; the amount of carbon dioxide in the air space will increase until it eventually equals the concentration of carbon dioxide in the blood. The effect of gas exchange on fresh air is summarized in Table 9.1.

Table 9.1: Effect of gas exchange on the air we breathe

9.3 Review QuestionsHuman Respiratory System

1. Explain the difference between respiration and breathing.2. What is the function of the breathing system?3. What happens during the processes of inhalation and exhalation?4. Describe the mechanism of gas exchange in lungs.5. In a tabular form show the effect of gas exchange on the air we breathe.

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Chapter 10Chapter 1010 Human Circulatory System10.1 Circulatory System

10.1.1 Closed Cardiovascular SystemCirculatory system, or cardiovascular system, in humans, the combined function of the heart, blood, and blood vessels (arteries, veins and capillaries) to transport oxygen and nutrients to organs and tissues throughout the body and carry away waste products.

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enter interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the lymphatic system, is not closed.

10.1.2 Functions the Circulatory System Among its vital functions the circulatory system:1. Increases the flow of blood to meet increased energy demands during exercise and

regulates body temperature. 2. In addition, when foreign substances or organisms invade the body, the circulatory

system swiftly conveys disease-fighting elements of the immune system, such as white blood cells and antibodies, to regions under attack.

3. Also, in the case of injury or bleeding, the circulatory system sends clotting cells and proteins to the affected site, which quickly stop bleeding and promote healing.

10.1.3 Components of the Circulatory SystemThe circularly system or transport system of the human has four basic structures:1. A fluid tissue (the blood and lymph).2. A network of tubing (the veins and arteries) to carry the blood.3. Specialized tubing (the capillaries) to allow diffusion of molecules to and from blood.4. A pump (the heart) to keep the blood moving through the arteries, veins, and capillaries.

These structures all serve the function of transporting, distributing, and collecting the gases, nutrients, wastes, and regulating chemicals of the body.

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10.1.4 The Pathway Taken by the Blood Through the BodyThe pathway taken by the blood through the body must let every cell in the body come in close contact with the blood. The path taken by a single blood cell is always through the heart to an artery, through a capillary network, and then through a vein back to the heart (Figure 10.1). This cycle is repeated again and again.

Figure 10.1: The path taken by blood for continuous circulation.

Blood returning to the heart from the arms, head, abdomen, and legs has little oxygen left in it. As a result, the pathway that the blood follows should put more oxygen into the blood and then direct the re-oxygenated blood back out to the body tissues.

Systemic Circulation: It is the movement of blood between the heart and the rest of the body that is, the pathway that circulates oxygenated blood from lungs through heart to the rest of the body systems is called the systemic circuit.

Pulmonary Circulation: It is the movement of blood between the heart and lungs. That is, the part of the circulatory pathway that re-oxygenates the blood is called the pulmonary circuit (lung circulation).

Each of these circuits requires its own pump. The pulmonary circuit uses the right half of the heart; the system circuit uses the left half.

10.2 The Heart10.2.1 The Anatomy of Human Heart The heart provides the pressure needed to keep the blood flowing through the network of tubing. The fact that we bleed outward from our body when cut — shows that our blood is always under pressure.

The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left

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ventricle, right atrium and right ventricle (Figure 10.2). The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

The heart is the engine of the circulatory system. The walls of these chambers are made of a special muscle called myocardium, which contracts continuously and rhythmically to pump blood.

Figure 10.2: The anatomy of human heart.

10.2.2 The Heartbeat — Diastole and SystoleA heartbeat is a two-part pumping action that takes about a second.

Diastole: As blood collects in the upper chambers (the right and left atria), the heart's natural pacemaker (the Sino-Atrial or SA node) sends out an electrical signal that causes the atria to contract. This contraction pushes blood into the resting lower chambers (the right and left ventricles). This part of the two-part pumping phase (the longer of the two) is called diastole.

Systole: The second part of the pumping phase begins when the ventricles are full of blood. The electrical signals from the SA node travel along a pathway of the Atrioventricular (AV) node to the ventricles, causing them to contract. This is called systole. While blood is pushed

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from the right ventricle into the lungs to pick up oxygen, oxygen-rich blood flows from the left ventricle to the heart and other parts of the body.

The heart normally beats about 60 to 80 times a minute when you are at rest, but this can vary. As you get older, your resting heart rate rises. Also, it is usually lower in people who are physically fit.

During each heartbeat, typically about 60 to 90 ml (about 2 to 3 oz) of blood are pumped out of the heart. If the heart stops pumping, death usually occurs within four to five minutes. By reducing your risk factors for cardiovascular disease, you may help your heart stay healthy longer.

10.2.3 PulseAn impulse can be felt over an artery that lies near the surface of the skin. The impulse results from alternate expansion and contraction of the arterial wall because of the beating of the heart. When the heart pushes blood into the aorta, the blood’s impact on the elastic walls creates a pressure wave that continues along the arteries. This impact is the pulse. All arteries have a pulse, but it is most easily felt at points where the vessel approaches the surface of the body. The radial artery is most commonly used to check the pulse. Several fingers are placed on the artery close to the wrist joint. More than one fingertip is preferable because of the large, sensitive surface available to feel the pulse wave. While the pulse is being checked, certain data are recorded, including the number and regularity of beats per minute, the force and strength of the beat, and the tension offered by the artery to the finger. Normally, the interval between beats is of equal length.

10.2.3 Blood PressureBlood pressure (BP), sometimes referred to as arterial blood pressure, is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation, usually measured at a person's upper arm. A person’s blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure and is measured in millimeters of mercury (mm Hg). Normal resting blood pressure for an adult is approximately 120/80 mm Hg.

Blood pressure varies depending on situation, activity, and disease states, and is regulated by the nervous and endocrine systems. Blood pressure that is pathologically low is called hypotension, and pressure that is pathologically high is hypertension. Both have many causes and can range from mild to severe, with both acute and chronic forms. Chronic

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hypertension is a risk factor for many complications, including peripheral vascular disease, heart attack (the coronary arteries that supplies blood to the heart develops a blockage), and stroke (the loss of brain function due to a disturbance in the blood supply to the brain). Hypertension is generally more common, also due to the demands of modern lifestyles. Hypertension and hypotension go often undetected because of infrequent monitoring.

10.3 Blood10.3.1 Functions of Blood

An adult human has about 5 to 6 litres (1 to 2 gal) of blood, which is roughly 7 to 8 percent of total body weight.

1. Blood carries oxygen from the lungs to all the other tissues in the body.2. Blood carries nutrients to all the cells of the body. 3. Blood also transports special chemicals, called hormones, which regulate certain body

functions. 4. Blood carries gaseous waste products, predominantly carbon dioxide, back to the lungs

where they are released into the air. When oxygen transport fails, a person dies within a few minutes.

5. Blood carries chemical waste products produced during metabolism, such as urea and uric acid, are carried by the blood to the kidneys, where they are transferred from the blood into urine and eliminated from the body.

6. The blood is also responsible for the activities of the immune system, helping fend off infection and fight disease.

7. The blood carries the means for stopping itself from leaking out of the body after an injury (blood clotting).

8. Blood is vital to maintaining a stable body temperature; in humans, body temperature normally fluctuates within a degree of 37.0°C (98.6°F).

10.3.2 Composition of BloodBlood is a fluid in two phases:1. Blood plasma: a liquid phase consisting of water and dissolved materials, and2. Blood cells: a solid phase consisting of living cells suspended in the liquid phase.

10.3.1 Blood PlasmaAbout 55 percent of the blood is composed of a clear, yellowish liquid known as plasma. The plasma is a slightly alkaline fluid, with a typical yellowish colour. It consists of 90 % water

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and 10% dry matter. Nine parts of it are made up by organic substances, whereas one part is made up by minerals.

10.3.2 Blood CellsIn an average healthy person, approximately 45 percent of the blood is made of three major types of cells:1. Red blood cells, or RBC (also known as erythrocytes),2. White blood cells, or WBC (leukocytes), and 3. Platelets (also known as thrombocytes).

Red Blood Cell (RBC): Red blood cells, or erythrocytes, make up almost 45 percent of the blood volume. The red blood cells have no nuclei. Yet each red blood cell functions well for almost four months. The erythrocytes are the most numerous blood cells, i.e., about 4-6 millions/mm3. Their primary function is to carry oxygen from the lungs to every cell in the body.

White Blood Cell (WBC): White blood cells (or lymphocytes) only make up about 1 percent of blood. They have nuclei. They are colourless. They can change shape, and can move in any direction, like amoebas. The density of the leukocytes in the blood is 5,000-7,000/mm3. WBCs play a vital role in the body’s immune system—the primary defense mechanism against invading bacteria, viruses, fungi, and parasites.

Platelet: Platelets (or thrombocytes) are not true cells. They have no nucleus. They are the smallest cellular component of blood. Even if platelets appear round in shape, they are not real cells. Their density in the blood is 200,000-300,000/mm3. They are designed for a single purpose — to begin the process of coagulation, or forming a clot, whenever a blood vessel is broken.

10.3.3 Blood TypingAntigen A and Antigen B: There are several types of red blood cells and each person has red blood cells of just one type. Blood type is determined by the occurrence or absence of substances, known as recognition markers or antigens, on the surface of the red blood cell. Type A blood has just marker A on its red blood cells while type B has only marker B. If neither A nor B markers are present, the blood is type O. If both the A and B markers are present, the blood is type AB.

Rh Factor: Another marker, the Rh antigen (also known as the Rh factor), is present or absent regardless of the presence of A and B markers. If the Rh marker is present, the blood is said to be Rh positive, and if it is absent, the blood is Rh negative. The most common

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blood type is A positive — that is, blood that has an A marker and also an Rh marker. More than 20 additional red blood cell types have been discovered.

Importance of Blood Typing: Blood typing is important for many medical reasons. If a person loses a lot of blood, that person may need a blood transfusion to replace some of the lost red blood cells. Since everyone makes antibodies against substances that are foreign, or not of their own body, transfused blood must be matched so as not to contain these substances.

For example, a person who is blood type A positive will not make antibodies against the A or Rh markers, but will make antibodies against the B marker, which is not on that person’s own red blood cells. If blood containing the B marker (from types B positive, B negative, AB positive, or AB negative) is transfused into this person, then the transfused red blood cells will be rapidly destroyed by the patient’s anti-B antibodies. In this case, the transfusion will do the patient no good and may even result in serious harm.

For a successful blood transfusion into an A positive blood type individual, blood that is type O negative, O positive, A negative, or A positive is needed because these blood types will not be attacked by the patient’s anti-B antibodies.

10.4 Review Questions1-Human Circulatory System

1. What is the function of circulatory system?2. What are the four basic structures involved in the closed transport system?3. Why is a powerful heart needed in a closes circulatory system?4. What are the differences in structure among arteries, capillaries, and veins? What are the differences in their

function?5. What are arterial vessels, arteries and arterioles?6. Describe the pulmonary circuit of blood flow.7. Describe the systemic circuit of blood flow.8. How does the heartbeat occur?9. What is the difference between systole and diastole?10. What do you understand by pulse? 11. Name the body locations where the pulse is readily distinguished. 12. What is blood pressure (BP) and how is it measured? 13. Distinguish between hypotension, and hypertension.14. What might be consequences of chronic hypertension?

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2-Blood1. Mention the functions of blood in our body.2. Describe the composition of blood.3. Describe the different types of blood cells in terms of their structure and function.4. What is blood typing? How blood type is determined? 5. What are Antigen A and Antigen B? What is Rh Factor?6. Why is the blood typing important?

Chapter 11Chapter 1111 The Human Excretory System

11.1 What is Excretory System?11.1.1 Importance of the Excretory System

Through metabolic activities, living organisms obtain nutrients, assimilate materials for growth, maintenance, and repair, and release energy to carry out life functions. However, these same metabolic activities also produce a number of by-products. For example cellular respiration produces two main by-products: carbon dioxide and water. The metabolism of proteins results in the formation of some nitrogen-containing by-products, called nitrogenous wastes. In addition, the ingestion of food substances often results in a build-up of mineral salts in an organism.

When allowed to build up in excess amounts, these by-products have a poisonous, or toxic, effect on an organism. Therefore, a living organism must be able to rid itself of such harmful by-products. Unless it is able to do so, death will eventually result.

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The process by which metabolic by-products are eliminated from an organism is called excretion. The organs in the body that have a role in removing metabolic wastes are called excretory organs.

11.1.2 The Components of the Excretory SystemOur body produces a large amount of metabolic waste every day. If this waste builds up in our body, it becomes poisonous. Our circulatory system acts a “waste collection service”. It carries wastes to “dump sites”. This process is called excretion and the structures involved are the excretory organs. The human excretory system consists of four organs (Figure 11.1):

1. The lungs,2. The sweat glands in the skin,3. The liver, and4. The kidneys

Figure 11.1: Excretory System — The systems of the body that are involved in excretion.

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11.2 Excretion through the Excretory Organs11.2.1 Excretion Through the Lungs

Cellular respiration occurs in every living cell in our body. It is the reaction that provides energy (in the form of ATP molecules) for cellular activities.  If respiration stops, the cell no longer has energy for cellular activities and the cell dies.  As respiration occurs carbon dioxide is produced as a waste product.  As the carbon dioxide accumulates in body cells, it eventually diffuses out of the cells and into the bloodstream, which eventually circulates to the lungs.  And here, in the alveoli of the lungs, carbon dioxide diffuses from the blood, into the lung tissue, and then leaves the body every time we exhale.  We should note that some water vapour also exits the body during exhalation.

11.2.2 Excretion Through the Sweat GlandsAs you already know, sweat comes out of pores in your skin.  As you may not know, sweat is a mixture of three metabolic wastes: water, salts, and urea.  So as we sweat, our body accomplishes two things:

1. Sweating has a cooling effect on the body, and2. Metabolic wastes are excreted.The salts and urea left behind by the evaporating water nourish the large number of bacteria already on the skin. Body odour is cause by the waste substances produced by these bacteria, not by sweat itself.

11.2.3 Excretion Through the LiverThe liver is a large, important organ.  In fact it is the largest internal organ in our bodies.  Its numerous functions make it "part" of the circulatory, digestive, and excretory systems. The space below would make a nice spot for a chart summarizing the jobs of the liver.

Some proteins and other nitrogenous compounds are broken down in the liver by a process called deamination. As a result of these reactions, a nitrogenous waste called urea is formed.

11.2.4 Excretion Through the KidneysThe kidneys are the main excretory organs of the body. All our blood is filtered through the kidneys once every 4 minutes. The kidneys remove excess minerals and urea from the blood. At the same time, they regulate the water content and the pH (acidity) of the blood. The kidney's ability to perform many of its functions depends on the three fundamental functions of filtration, reabsorption, and secretion, whose sum is renal excretion. That is:

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11.2.4.1 Nephrons — The Function Unit of KidneyA human kidney contains functioning units called nephrons. A human has about one million (1,250,000) of these. Each nephron consists of two main structures, (1) a blood capillary network, and (2) a renal tubule. Wastes are removed from the blood by each nephron in two steps: (1) filtration, and (2) concentration. The resulting waste fluid is called urine.

11.2.4.2 Mechanism of NephronsFiltration: The outermost layer of the kidneys, the cortex, is composed of approximately 1,250,000 structural units called nephrons. The materials such as urea, salts, water, glucose, and others filtered by the nephron.

Concentration: As the filtrate travels through the nephrons, useful substances are reabsorbed into the surrounding capillaries (which connect to veins that will transport the "clean" blood back to the heart via the renal vein). About 180 litres of filtrate is produced each day, but only 1.5 litres of urine.   So as we can see, most materials that initially enter the nephron are reabsorbed, leaving only the urea, salts, and some water in the tubule.  These metabolic wastes form urine, which is transported to the urinary bladder by the collecting tubule.

Urine: About 200 ml of the liquid waste, called urine, can be stored in the bladder. Urine is about 96% water, 2% urea, and 2% other wastes. The urea has been concentrated almost 100 times by the action of the kidneys. The other wastes in the urine consist mainly of sodium and chloride ions (salt solution).

11.3 Review QuestionsThe Human Excretory System1. What is excretion?2. What are the structural components of the human excretory system?3. How is lungs function in elimination of metabolic wastes?4. What are sweat glands, and what are their functions?5. Describe two ways that the liver functions as part of the excretory system. 6. What are the functions of kidneys?7. Describe briefly how urea from the bloodstream is concentrated into urine.

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