zoology notes: 001 Title

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Unit 1

The first chapter of Unit 1, the introduction, discusses the definition of zoology. It explains the scientific method, a method

scientists use to get to the bottom of things. It shows a brief history of zoological life. It also discusses characteristics that living things

have in common. It then differentiates animals from other living things and compares animals to plants. Chapter 1 also includes

discussions on the importance of studying zoology, as well as some of the different branches that fall under this scope of studyFinally, it mentions important scientists whose contributions make up the basis of what we know about animals today.

Chapter 2 deals with the chemical make-up of organisms. It starts with subatomic particles then discusses different types o

atoms. It also includes discussion in bonds formed between atoms and molecules and compounds formed by these bonds. Finally, it

discusses the four major types of organic compounds: carbohydrates, proteins, fats, and nucleic acids.

Chapter 3 is concerned with the cell and structures that are commonly seen in them. It also discusses the ways the cell divides to

produce daughter cells with either a diploid or haploid number of chromosomes and their significance.

The last chapter of Unit 1, Chapter 4, deals with the major types of tissues formed by cells: epithelial, connective, muscular, and

nervous. It also discusses where some of these tissues may be found.

Chapter 1: An IntroductionZoology is the scientific study of animal life.

Animals differ from one another in size, structure, manner of life, and other features and over the years, man has accumulated

tremendous amounts of information about them. Yet, we have so much more to learn about them. Zoology will enrich your own life by

helping you understand the fascinating diversity of creatures that share this planet with us.

But, before we go into any actual study of any animal, it is first essential for us to understand this definition of zoology. What do

we mean by scientific? What are the characteristics of living things? What constitutes life? What are animals? What differentiates

them from other living things?

TABLE OF CONTENTS

UNIT 1 1

Chapter 1. An Introduction 2

Chapter 2. The Chemistry of Living Matter 11 Chapter 3. Cells 18

Chapter 4. Tissues 25

UNIT 2 29

Chapter 5. The Integumentary System 30

Chapter 6. The Skeletal System 35

Chapter 7. The Muscular System 39

Chapter 8. The Digestive System 44

Chapter 9. The Respiratory System 48

Chapter 10. The Circulatory System 53

Chapter 11. The Urinary System 57

Chapter 12. The Reproductive System 59

Chapter 13. The Nervous System 64 Chapter 14. The Endocrine System 68

UNIT 3 72

Taxonomy 73

References 74

Lecture Notes in

ZOOL101A- General Zoology

Prepared by:

Michael V. Lu, DVM


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Science

Science is a process for evaluating experimental and observed knowledge (the scientific method), a global community of

scholars, and the organized body of knowledge gained by this process and carried by this community (and others). Natural sciences

study nature; social sciences study human beings and society. The basic commitment of science is to collect objective data (facts tha

are observable and measurable) and then reach conclusions and formulate generalizations by analyzing such data.

Scientists collect data either by observation or by controlled experimentation. When collecting data by observation, scientist

must ensure that the data are as free as possible of subjective bias, recorded and analyzed instrumentally when possible, and extensive

enough so that such factors as range of variability can be defined, preferably statistically.

When collecting data by experimentation, scientists begin by asking questions, which they then try to answer. A testable questionis called a hypothesis. Hypotheses are often tested by means of a controlled experiment, in which one or more experimental groups are

compared with one or more control groups, under conditions that are held standard except for one factor, the variable. The number of

organisms used is important: an experiment based on only a few test organisms is apt to be non-predictive and unreliable.

Upon reaching a conclusion, the scientist tries to form a generalization and compares this generalization to others. A

generalization that represents a cohesive statement of principle is known as a theory. It should be pointed out that no matter how firm

the database upon which a scientific theory rests, the theory must always remain subject to revision in the light of additional data.

The Scientific Method

Scientific study involves a system that scientists use to get to the bottom of things. The observation of living things has

generated a lot of questions about them. How they came to be? How are plants constructed? How do animals move? Why are animals

and plants important? Scientists answer these and other questions by using an experiment-based process called the scientific method.

The scientific method is a systematic way to describe and explain phenomena based on observing, comparing, reasoningpredicting, testing concluding, and interpreting. This is what science is all about. Rather than just being a set of facts that describe and

explain the universe, science is a dynamic process wherein the excitement lies in the intriguing observations and carefully crafted

experiments devised to help us learn more about the world around us.

The scientific method begins with observations that prompt us to ask the cause of these observations. These causal questions lie

at the heart of the scientific method. Science is fundamentally about finding answers to these kinds of questions. To find answers tothese questions, scientists use past experiences, ideas, and observations to propose hypotheses that may produce predictions. To

determine if these predictions are accurate, scientists perform experiments. If the experimental results match the predictions of a

hypothesis, the hypothesis is accepted; if they dont, the hypothesis is rejected. The effect of this is to make scientific progress by

revealing answers piece by piece.

By testing a single hypothesis, a scientist has not ruled out other possible causes for an observation. To do so, he would have to

devise alternative hypotheses, make predictions for them, and obtain experimental results to compare with the predictions. By this

process, he may be able to reject all his hypotheses. Either way, he makes progress by testing several hypotheses, not just one.

Although the scientific method is a powerful tool for answering some kinds of question, it is not foolproof. Most experiments do

not distinguish other possible interpretations. Most of the time it is impossible to recreate conditions in the laboratory or consider all

factors that influence the occurrence of events.

Any conclusion marks an end to the scientific method for a particular experiment but it seldom ends the process of scientific

inquiry. To the curious scientific mind, a conclusion is never the final answer. There is always something more to study, somethingnew to learn.

A Short History of Animal Life

Although it is impossible to replicate conditions that happened billions of years ago, scientists through experimentation and

deductive reasoning have come up with theories regarding the origin of life.The most ancient rocks found to date occur in western Australia and are about 4.2 billion years old. The oldest well-preserved

fossils known to date are unicellular prokaryotes buried in silt that became the 3.4 billion-year-old sedimentary strata of the Fig Tree

Group formation in South Africa.

The earliest organic molecules probably formed abiotically, at a time when oxygen was lacking in the atmosphere. The heat of

thermal springs may well have provided the first bonding energy for generating organic molecules and the first molecular or cellular

unit that could be considered living in the sense of reproducing itself and taking up additional materials as nutrients from the

environment. The sun provided an enduring and reliable flow of free energy for early organisms to tap. The simplest modern

organisms that carry on photosynthesis are indeed prokaryotes, mostly known as cyanophytes (blue-green algae). When eukaryotic

cells evolved, some are thought to have acquired as internal symbionts cyanophytes that survived ingestion to become chloroplasts of

these new autotrophic organisms.


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The entire period from 3.5 to 1 billion years ago may be referred to as the age of blue-green algae because during their long

reign the blue-greens not only flourished but changed forever the composition of the earths atmosphere. They gave off great

quantities of oxygen gas as waste product of photosynthesis.

Cells with nuclei first appear in sedimentary strata about 1.5 billion years old. The 1 billion-year-old Bitter Springs Formation of

Australia contains beautifully preserved green algae (chlorophytes) showing nuclei and even nuclear division. To date, no evidence ofmulti-cellular life (other than algae) has been found in rocks other than about 700 million years. The best-preserved fossil assemblage

of this age comes from the Ediacara Hills of Australia and includes a variety of soft-bodied metazoans: jellyfish, corals, segmented

worms, together with a number of puzzling forms of unknown affinities. The scarcity of fossiliferous strata older than this seems to

have been caused by a series of Precambrian glaciations that deeply eroded most continental surfaces.

The Paleozoic Era.

The Paleozoic Era spans 370 million years, from the beginning of the Cambrian Period to the end of the Permian Period.

At the beginning of the Cambrian Period, a remarkable proliferation and diversification of invertebrate life took place within

what appears to have been only a few million years. As a result, all of todays major animal phyla, and several long extinct ones, are

present in rocks of that age. The cause of this proliferation and diversification remains obscure. For one thing, the build-up oatmospheric O2 may have reached the concentrations necessary for this gas to diffuse downward throughout water masses so that

bottom-dwelling creatures could begin to flourish. Then too, perhaps the extensive erosion caused by Precambrian glaciations raised

marine concentrations of dissolved minerals, especially calcium, to some critical threshold necessary for the optimal functioning of

nerves and muscles and the deposition of shells and skeletons.

Over the ensuing 75 million years of the Ordovician Period, invertebrates and multi-cellular plants colonized the land, and

vertebrate fishes appeared. During the Silurian Period, the first jawed fishes appeared and so flourished that the 50 million years of theensuing Devonian Period are known as the age of the fishes. Amphibian fossils first appeared in rocks of later Devonian age, as the

earliest land vertebrates. These animals characterized the 65 million-year Carboniferous Period (sometimes called the age ofamphibians) but declined during the 50 million years of cooling and drying climates that marked the Permian Period. Reptiles, which

diverged from early amphibian stock during the Carboniferous, were not so disadvantaged by these changes and began to proliferate

and spread.

Towards the end of the Paleozoic, drifting continents caused by expanding seafloors collided to form a supercontinent we call

Pangaea. The continental collisions that ended the Paleozoic obliterated intervening marine habitats, allowed the terrestrial biota of

previously isolated land masses to come into competition, and triggered a period of mountain building that affected climate anddrained continental seas. Nearly half the known families of animal life became extinct.

The Mesozoic Era.The Mesozoic is known as the age of reptiles for these became the dominant vertebrates and diversified into many forms,

including the largest creatures that have ever walked the earth, marine species as massive as whales, and the most spectacular animals

ever to soar the skies. The geographic spread of reptiles was facilitated by the fact that the land they so successfully invaded was the

one world ofPangaea.

The Jurassic Period saw the advent of birds and mammals and the start of the breakup ofPangaea, carrying terrestrial organisms

apart, to new climates and destinies. The drifting continents fragmented further during the Cretaceous Period, while reptiles continued

to dominate the earth. Then something catastrophic took place: almost suddenly some 25 percent of all existing animal familiesdisappeared, not only the dinosaurs and other still-successful reptilian groups, but a wide variety of marine invertebrates from gian

ammonites (a type of mollusk) down to microscopic zooplankton. So far as we can tell, no Mesozoic land animal with a body mass

over 25 kg survived into the Cenozoic.

In various parts of the world a thin layer of clay rich in iridium (an element common in meteorites) and soot separates a rich

fossil record from a very sparse fossil record marking the onset of the Cenozoic Era. This suggests that a large meteorite impacted theearth, ejecting into the stratosphere such an enormous amount of particulate matter that months of darkness ensued, with plummetingtemperatures and suppression of photosynthesis. Soot may have come from fire storms caused as continent-wide forests were ignited

by the passage through the atmosphere of such a massive extraterrestrial object. Smoke from such fire storms would have intensified

and prolonged the crisis of darkness and cold. Many animals would die of starvation or cold during the long darkness.

Surprisingly, it appears that such mass extinction events have occurred with a periodicity of about 26 million years for as far

back as such events can be traced. Scientists have come up with possible explanations why such events are so regular. If our sun, like

many stars, is one of a binary pair, it may have a small companion star (already named Nemesis) with an orbit so eccentric that it

passes through the solar system only once in 26 million years, towing a mass of comets collected from the dense Oortcomet cloud

that lies beyond Pluto. Alternatively, the unidentified celestial object may be a planet with a less far-flung orbit, which intersectsEarths orbit only every 26 million years with its gravitational train of comets. Either way, this unknown celestial object may not be

readily found, for it should now be at about its farthest point from the sun, not due to return for another 13 million years.


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TimeScale

Era Periods and Epochs

Cenozoic Tertiary

65

135

18

0

23

0

Mesozoic

Cretaceousprimitive mammals

crocodilesturtles snakes dinosaurs

Jurassic toothed birdsplesiosaurs winged reptiles ichthyosaurs insects

Triassic

ammonites

280

345

40

5

42

50

0

600

Paleozoic

Permian

primitive reptiles

C

arboniferous

blastoids amphibianscrinoids sharks

Devonian bony fishes scorpions

sea stars, etc lobefins arachnids

Silurian cystoids placoderms limulus

Ordovician ostracoderms

coelenteratesmollusks eurypterids

echinoderms

Cambrian

brachiopods trilobites

crustaceans annelids

Proterozic

Archeozoic protozoans sponges

Fig. 1.1. Distribution of major animal groups in the geologic record. Solid curving lines commence at

time when each group first appeared, with broken lines indicating presumed earlier origins. Lines

terminating with a indicate when certain groups became extinct.; those ending in an arrow indicate

that the group contains modern descendants. The time scale is in millions of years. (Modified from

Jessop, 1995)

The most profound effect of mass extinctions is that the survivors proliferate in a depopulated world providing opportunity for a

great variety of genetic variants. Under these circumstances, evolution of a new biota can take place quite rapidly until the

environment is again saturated with enough different life forms to maintain stable ecosystems over long periods of time. However, if

a mass extinction is excessively severe, little may remain from which new forms can evolve.

The Cenozoic Era.

The past 65 million years have witnessed the explosive proliferation of birds and mammals. Hominid (human-like) fossils

(mostly found in Africa) have been dated at an age of about 3 million years (Australopithecus afarensis), 1.7 million years (Homo

habilis), and 1.5 million years forHomo erectus, with skulls transitional toHomo sapiens dating from 250,000 to 350,000 years ago.


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Although we have named ourselves wise man, to most of the living world we are catastrophe personified, for countless anima

and plant species have diminished into endangerment or extinction as Homo sapiens has proliferated. Awareness and concern can stil

turn the tide, if we really are wise enough to conserve our biological heritage and guard ourselves, too, from extinction.

Characteristics of Living Things

Living things have common themes that separate them from non-living things. All living things have organization, undergometabolism, growth and reproduction, respond and adapt to changes in the environment.

Organization.All living things are made up of cells. Some organisms are

made up of only one cell (unicellular) while others are made upof more than one (multi-cellular). In multi-cellular organisms,

each cell has specific functions and specific roles in keeping the

organism alive. Even within cells, specific structures have their

own functions and roles. Even beyond the organism level, we

find that organisms often group themselves into populations.

Populations of different species make up a community which is

part of an ecosystem which makes up the biosphere.

Metabolism.

All living things undergo metabolism. Metabolism is the

collective term for all the essential biochemical processes that goon inside the body. Digestion, respiration, photosynthesis, and

the elimination of waste materials are only some of the processes

constantly in progress. There are two phases of metabolism.

Anabolism is the constructive or building up phase whilecatabolism is the destructive or breaking down phase.

Growth.

Living things grow and develop. Growth involves increase

in size (increase in the number of cells for multi-cellularanimals) and development involves change in shape and form.

Reproduction.Living things reproduce. Reproduction is necessary for the

perpetuation of the species. Reproduction can be asexual (singleparent) or sexual (recombination of genes from two interacting

parents).

Irritability / Responsiveness.

Irritability is defined as the ability of an organism to

respond to stimuli. The stimulus may be simple, such as in

bacteria moving away from or toward a heat source. It may becomplex i.e. a bird responding to a complicated series of signals

in a courtship ritual.

Adaptation.

Adaptation is the ability of an organism to change inresponse to the environment. The process of changing to

promote survival includes: adaptability of the individua

organism in direct response to some specific challenge and

mutability (alteration) of genes and chromosomes producing a

range of variability in offspring. Each species, whether plant or

animal, exhibits an adaptation to the environment distinct from

other animals.

AnimalsLiving things are classified on the basis of evolutionary relationships that exist among them. Modern scientists usually recognize

five major kingdoms that represent all known species of living things. The table below shows the five kingdoms and the major

differences that exist between them.

Kingdom Type of Cell Cell Organelles Cellular Organization Representative

Monera Prokaryotic No membrane around

organelles, no plastids,

no mitochondria

Unicellular and/or

colonial

Blue-green

algae, bacteria

Protista Eukaryotic All cell organelles Unicellular and/or

colonial

Protozoa

Plantae Eukaryotic

with walls

Present but cells

simpler

Multicellular with

tissues

Higher plants

Fungi Eukaryotic Lack plastids andphotosynthetic

pigments

Syncytial Mushrooms,molds

Animalia Eukaryotic

without walls

Lack plastids and

photosynthetic

pigments

Multicellular with

tissues

Any animal

Table 1.1. Characteristics of five kingdoms (Modified from Storer et al, 6th Ed., 1979)


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Plants vs. Animals.

Although the basic unit of structure and function of both plants and animals is the eukaryotic cell and plant and animal cells are

so much alike as to strongly suggest a common ancestor, there are two salient points of difference: (1) animal cells lack chloroplasts;

and (2) animal cells are not enclosed in cell walls.

Other differences are noted in the table below.

Animals Plants

Mode of

nutrition

Heterotrophic (do not photosynthesize,

lack chloroplasts)

Autotrophic (carry out photo synthesis,

contain chloroplasts)

Extent of

Growth

Determinate Indeterminate

Cell Wall Absent Made up of cellulose, rigid, inert

Nervous

System

Present in most Absent

Mobility Mostly mobile Mostly immobile

Primary Food

Reserve

Glycogen (multiply branched glucose

chain), saturated fats

Starch (unbranched glucose chain),

unsaturated oils

Waste

Products

CO2 and nitrogenous wastes, kidneys

needed in most animals

O2 from photosynthesis, CO2 from

metabolism, kidneys not needed since

nitrogenous wastes not generated

Table 1.2. Some major differences between animals and plants (Modified from Glinoga)

Importance of Zoology

Animals are very important to people. Understanding how they function enables one to make wise decisions about many things

that affect the individual, family, and the community. The use of organism to produce consumer needs is called biotechnology. Use of

bacteria to turn milk into cheese or the use of live yeast to make bread rise are techniques of biotechnology. Farming, pest control,

livestock management, nutrition, food processing, and food preservation also involve biotechnology. Animals provide us with food

non-edible economic products, biomedical products, research material. They also have ecological, aesthetic, and affectional value.

Food.

Livestock, game, fish, shellfish, honey, eggs, dairy

products, exotic fare such as insects, grubs, and highly relished

Palolo worms are just some examples of animals and animal

products that we eat to nourish our bodies.

Transport and Labor.

Horses, donkeys, llamas, camels, dogs, oxen, buffalos, andelephants are all still used in different parts of the world for

transport and labor.

Non-edible Economic Products.

Leather, down, fur, silk, wool, ivory, limestone, chalk have

various uses as clothing, shoes, accessories and ornaments.

Biomedical Products.

We use venom from snakes to make anti-venom. Pig heart

valves may be used to replace diseased human heart valves.

Insulin and antibodies for protective inoculation against various

diseases are of animal origin.

Research.

Laboratory animals are used to create animal models of

human diseases and their treatment.

Ecological Value.

Animals are essential parts of the food chain Plant eaters(herbivores) are a source of food for carnivores (meat eaters) and

omnivores (plant and meat eaters). They are also essential for the

pollination of most flowers and as agents of biocontrol.

Aesthetic Value.

Animals have been subjects and inspirations for works ofarts, from cave paintings to present day creations. Some cultures

revere totem animals and cultivate in themselves the positive

attributes they perceive in animals.

Affectional Value.

Pets and residents in wildlife parks fulfill various non-

economic human needs. They are even used by somepsychotherapists in their work with patients.

Branches of Zoology

Since zoology presents a wide range of topics, scientists often choose a specific category to study. Some zoologists, for example

devote their time to studying animals belonging to one particular taxonomic group. Others study one or more aspects of anima

structure, function, or behavior, often using a comparative approach. Here are only a few of the branches of science that fall under thescientific study of animal life.

Taxonomy classification and naming of plants and animalsBotany plant life

Zoology animal lifeProtozoology animals that are basically unicellular


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Helminthology worms (mainly parasitic)Entomology insectsParasitology organisms that live and subsist on or in other

organisms

Ichthyology fishesHerpetology amphibians and reptiles

Ornithology birdsBiochemistry chemical compounds and processes in living

organismsMolecular biology molecules and processes in cells

Cytology cell structures and functionHistology microscopic structure of tissuesGross anatomy non-microscopic structures of organismsEmbryology growth and development of the new individual

Physiology living processes or functions within organismsNutrition use and conversion of food substances

Genetics hereditary traits and their transmissionEcology relationships between biotic (living) and abiotic

(physicochemical) environments

Important Contributors to Zoology

Our present knowledge about this subject is based on previous works of past scientists. Zoology would not be as advanced as it is

today if not for the great pioneers of the science. Here are only some of the scientists who contributed greatly to the scientific study o

living things.

Aristotle, 350 B.C. description of plants and animals and

theories of hereditary production and evolution

Robert Hooke, 1665 coined the term cell describing the

texture of cork using magnifying lenses

Anton von Leeuwenhoek, 1667 microscopic discovery of

bacteria, protozoa and spermatozoa

Carolus Linnaeus, 1735 basis for modern classification of

living things; binomial nomenclature

Matthias Schleiden (a botanist) and Theodor Schwann (a

zoologist), 1839 put forth the thesis that cells were the units of

structure in plants and animals.

Rudolf Virchow, 1855 stressed the role of the cell in

pathology and stated that all cells came from pre-existing cells

Omni cellulae e cullula

Charles Darwin and Alfred Wallace, 1859 foundations omodern theory of evolution

Louis Pasteur, 1860 conclusive experimental refutation of thetheory of spontaneous generation

Gregor Mendel, 1865 foundations ofgenetics

James Watson and Francis Crick, 1953 discovered the

structure ofDNA

Chapter 2. The Chemistry of Living Matter

Matter is made up of elements, substances which cannot be broken down by ordinary chemical means into simpler particles.Each element is a collection of a particular kind of discrete particle matter called the atom. An atom is the smallest unit of an element

that retains the chemical properties of that element.

Subatomic Particles.

Atoms are made up of even smaller, subatomic particles: the proton, the neutron, and the electron. Protons have positive charges

electrons are negatively charged, and neutrons are neutral.

Each element has a different number of protons. The atomic number is a count of the number of protons in the elemental atom

Oxygen, for example, has 8 protons therefore its atomic number is 8. Carbon has 6. Hydrogen has 1. Nitrogen has 7.

Generally, atoms have approximately the same number of protons, neutrons, and electrons. Each proton or neutron has a mass o

about 1.7x10-24 gram. For convenience, this mass is defined as 1 atomic mass or 1 Dalton. The mass of an electron is about 1/2000 tha

Fig. 1.2. Carolus LinnaeusFig. 1.3. Gregor Mendel


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of a proton, so it is often disregarded when considering atomic mass. The protons and neutrons form the nucleus while electrons trave

at the speed of light orbiting the nucleus. The atomic mass of an element is the number of protons plus neutrons in each nucleus.

Isotopes.

Atoms with the same number of protons but different number of neutrons are called isotopes. Two isotopes of ordinary hydrogen

(1 proton, 0 neutrons) are deuterium (1 proton, 1 neutron) and tritium (1 proton, 2 neutrons). Isotopes share the same atomic number

but differ in atomic mass, the sum of the atoms protons and neutrons. Thus, all hydrogen isotopes have the atomic number 1, bu

atomic masses of 1, 2, and 3, respectively. Isotopes with extra neutrons are often unstable and undergo radioactive decay at typical and

predictable rates, giving off subatomic nuclear particles until they reach stability. Tritium, with a half-life of 12.5 years, is very usefu

in biological research as a radioactive tag that allows hydrogen-containing compounds to be traced through metabolic pathways.

Ions.

Atoms with the same number of protons but different number of electrons form ions. NaCl (sodium chloride, table salt) when in

water, dissolves and separates into its constituent ions, Na+ and Cl-. The Na ion is positively charged because one of its electrons has

been kidnapped by the Cl ion. Na+ then, has 11 protons, 11 neutrons, and only 10 electrons. Cl- on the other hand, has 17 protons, 17

neutrons, but 18 electrons, making it negatively charged. Positively charged ions are called cations and negatively charged ions are

called anions.

Chemical Bonds.

Following the octet rule, the innermos

shell, or the lowest quantum level, for any atom

never contains more than two electrons. Each

shell external to this innermost shell may contain

up to eight electrons. The number of electrons inthe outermost shell determines the combining

power (valence) of an atom. If the outermosshell contains eight electrons, (or in the case of

He, 2 electrons in the outermost shell) the atom

will be unable to bond with any other atom and

the element is said to be inert.

Atoms with less than eight electrons in the

outermost shell form bonds with other atoms tosaturate this shell. There are three major kinds of

chemical bonds: covalent bonds, ionic bonds

and hydrogen bonds. Covalent bonds involve the

sharing of electrons. The two atoms both lackelectrons in their outer shells. They fill up the

vacancies by sharing a pair of electrons. Ionic

bonds involve the transfer of electrons from one

atom to another so the atom either loses or gainselectrons. Hydrogen bonds form relatively weaker bonds between polar molecules or polarized side groups of non-polar molecules

They are important in maintaining the shape of macromolecules aiding in the performance of their biological functions.

A molecule consists of two or more atoms joined by bonds. The atoms composing a molecule may be the same (O 2, H2) o

different (H2O, CH4). A molecule composed of different atoms is called a compound.

Electrolytes.

The combination of water with a chemical compound dissolved in it is called a solution. A compound that dissociates into anions

and cations when dissolved in water forms a solution which will conduct an electric current. Hence, any chemical compound which

will dissociate into ions in water is called an electrolyte. Electrolytes are described as strong or weak, depending on how completelyionize. Strong electrolytes ionize completely; weak electrolytes ionize slightly.

Acids, Bases, and Salts.

The hydrogen ion H+ is one of the most important ions in living organisms. The hydrogen atom contains a single electron. When

this electron is completely transferred to another atom (not just shared with another as in covalent bonds), only the hydrogen nucleus

(essentially a single proton) remains. Any compound that releases H+ ions (protons) when dissolved in solution is called an acid. An

acid is classified as strong or weak depending on the extent to which the acid molecule is dissociated in solution. Examples of strong

acids that dissociate completely in water are hydrochloric acid (HCl) and nitric acid (HNO 3). Weak acids such as carbonic acid

(H2CO3) dissociate only slightly.

A base, or alkali, is a compound that releases OH- ions or accepts hydrogen ions in solution. Examples are caustic soda (NaOH)

and ammonia water (NH4OH) which are common household chemicals.


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Acids and bases, when concentrated, are severe irritants and will burn the skin and the delicate covering of the eyes and mouth.

A salt is a compound resulting from the chemical interaction of an acid and a base. For example, common salt, sodium chloride

(NaCl), is formed by the interaction of hydrochloric acid (HCl) and sodium hydroxide (NaOH). In water, the HCl dissociates into H

and Cl- ions, the hydroxide reacts with H+ to form water and Na+ and Cl- remain as a dissolved form of salt. This reaction is shown in

the following equation:

HCl + NaOH NaCl + H2O

acid base salt water

Hydrogen Concentration (pH).

pH means potential hydrogen where pH indicates neutrality. Pure water if fully ionized to H+ and OH- would potentially yield a

molar concentration of 107 H+ and 107 OH- (i.e. pH 7). A mildly acidic solution if fully ionized would yield 10 6 H+ and 108 OH- and

would be designated pH 6 and so forth.

With few exceptions, living systems do not tolerate strongly acidic or alkaline conditions, and their vital processes must take

place within a range from pH 6 to pH 8. Saliva has a pH of 6.8. Gastric juice is the most acid substance in the body (pH 1.6). The pH

of human blood must remain between 7.35 to 7.45. If human blood plasma merely becomes neutral, pH 7, this seemingly harmlessdeviation actually would represent a life threatening acidosis. This slightly basic range is zealously guarded by buffers that can

neutralize excess H+ and OH-.

description pH examples

14 NaOH, lye

very basic 13 oven cleaner

12 hair remover

11 ammonia

10 soap, milk of magnesia

weakly basic 9 chlorine bleach, phosphate detergent

8 seawater, egg white

neutral 7 pure water

6 urine, milk, saliva

weakly acidic 5 black coffee, rain water

4 tomatoes, grapes

3 vinegar, wine, soft drinks, beer, orange juice, pickles

2 lemon juice, lime juice

very acidic 1 stomach acid

0 HCl, battery acid

Table 2.1. The pH of some solutions.

Buffers.

The hydrogen ion concentration in the extra-cellular fluid (ECF) must be regulated so that the metabolic reactions within the

cells will not be adversely affected by a constantly changing hydrogen ion concentration (pH) to which they are extremely sensitive

To maintain pH within physiologic limits, there are certain substances that tend to compensate for any change in the pH when acids or

alkalis are produced in metabolic reactions or are added to the body fluids. These are called buffers. A buffer is a mixture of slightlyionized weak acid and its completely ionized salt. In such a system, added H+ combine with the anion of the salt to form

undisassociated acid, and added OH- combines with H+ to form water. The most important buffers in the blood and other body fluids

are bicarbonates and phosphates. For example, blood contains carbonate buffers made up of salts sodium and potassium bicarbonate(NaHCO3 and KHCO3) and of the weak carbonic acid (H2CO3). If a strong acid, such as HCl, enters the blood, the salts of the buffer

convert it to a weak acid which cannot lower the pH as much as HCl can:

NaHCO3 + HCl NaCl + H2CO3sodium

bicarbonat

e

hydrochlori

c acid

sodium

chloride

carbonic

acid

On the other hand, if a strong base, such as sodium hydroxide (NaOH) enters the blood, the carbonic acid will neutralize it:


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H2CO3 + NaOH NaHCO3 + H2O

carbonicacid

sodiumhydroxide

sodiumbicarbonate

water

Water.

Water is the predominanchemical component of living

organisms. It makes up from 60

90% of the protoplasm. Its unique physical properties, which includ

the ability to solvate a wide range

of organic and inorganic molecules

derive from waters dipola

structure and exceptional capacity for forming hydrogen bonds. An excellent nucleophile, water is a reactant or product in many

metabolic reactions. Water has a slight propensity to dissociate into hydroxide ions and protons.

A water molecule is an irregular, slightly skewed tetrahedron with oxygen at its center. The two hydrogen atoms and the

unshared electrons of the remaining orbitals occupy the corners of the tetrahedron. Water is a dipole, a molecule with electrical chargedistributed asymmetrically about its structure. The strongly electronegative oxygen atom pulls electrons away from the hydrogen

nuclei, leaving them with partial positive charge while its two unshared electron pairs constitute a region of local negative charge. This

enables water to dissolve large quantities of charged compounds such as salts.

Organic Compounds

Of the 92 naturally occurring elements, 16 can be found in living things, and only 4 make up 99% of living matter. These

elements are carbon, hydrogen, oxygen, and nitrogen. In the study of animals, we will mostly be concerned with organic compounds

that is, compounds that always contain carbon and hydrogen. Four of the most important organic matters are carbohydrates, proteins

lipids, and nucleic acids.

Carbohydrates.

Glucose and other simple sugars (monosaccharides), as well as their polymer(polysaccharides), are called carbohydrates. Carbohydrates generally contain one oxygen and

2 hydrogen atoms for every carbon. For example, glucose and fructose consist of six carbon

atoms, 12 hydrogen atoms, and 6 oxygen atoms, and have the formula C 6H12O6. Galactose

mannose, and many other monomers have this same formula, differing only in the

arrangement of the elements. Common carbohydrates having different chemical formulas

include ribose, xylose, arabinose, and ribose (C5H10O5); deoxyribose (C5H10O4); glucuronic

acid and galacturonic acid (C6H12O7); and rhamnose (C6H12O5).

Carbohydrates are synthesized from H2O and CO2 by plants through photosynthesis (a

process on which all life depends because it is the starting point in the formation of food).

They provide much of the immediate or ultimate food for animals and are much used by

humans (food, fabrics, wood, paper, etc.). The main role of carbohydrates in the protoplasm is

to serve as a source of chemical energy.

Monosaccharides are the end product in the digestion of carbohydrates. Over 200 are known but most important are glucose,

fructose, and galactose. Except immediately after a meal, glucose is the only monosaccharide present in significant quantities in the

blood and interstitial fluids of man and animals. There are two reasons for this:

1. Usually 80% to 100% of the monosaccharides absorbed from the gastrointestinal tract is glucose, and only rarely is more

than 20% of these fructose and galactose together.2. Within less than an hour after absorption from the gut, essentially all the fructose and galactose will have entered the cells

and been converted into glucose.

These 3 monosaccharides form disaccharides in the following manner:

- glucose and fructose form sucrose (cane sugar)

- glucose and galactose form lactose (milk sugar)

- glucose and glucose form maltose

The polysaccharide typical in animals is glycogen. It is commonly stored in vertebrate liver and can be reconverted into glucose

for transport by the blood.

Fig. 2.5. The molecular structure of

fructose (left) and glucose (right).


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Proteins.

A protein consists of one or more polypeptides and may also include sugars or other kinds of small molecules. A polypeptide is

a chain of amino acids linked together by carbon-nitrogen bonds called peptide bonds. They contain C, H, O, N, and usually S.

Most abundant of organic materials in animal protoplasm are the proteins. They function as enzymes, components of celmembranes, contractile elements of muscle, hormones, receptors on the cell surface and within the cell, antibodies, buffers, oxygen

carriers (hemoglobin) and oxygen storers (myoglobin), blood constituents (albumin most abundant), blood clotting factors, sources

of energy, and as important components of intracellular fabric of connective tissue.

There are basically 20 amino acids that form all kinds of proteins found in living things. Ten are classified as essential amino

acids, meaning those that cannot be synthesized in the body and must be supplied in the diet in adequate quantities. Deficiency will

result in a negative nitrogen balance with loss of weight and arrest of growth. The other ten are classified as non-essential amino acids

meaning they can be synthesized by the body.

Essential Amino Acids

Phenylalanine arginine isoleucine methioninevaline threonine leucine

tryptophan histidine lysine

Non-essential Amino Acids

alanine glutamine praline cysteine

asparagine glutamic acid serine

aspartic acid glycine tyrosine

Table 2.2. Essential and non-essential amino acids.

Pepsin II and gastricin (pepsin I) are the most important peptic enzymes of the stomach; they are most active at a pH of 2 to 3

and completely inactive at a pH of 5. Pepsin is capable of digesting collagen. They break down proteins into proteoses, peptones and

polypeptides. These are then hydrolyzed by pancreatic enzymes trypsin and chymotrypsin into dipeptides and smaller polypeptides.

Dipeptidases and aminopolypeptidases in the epithelial cells of the small intestine are responsible for the hydrolysis of peptides into

amino acids.

Lipids.Unlike other bio-logical polymers, lipids are not defined by specific, repeating, monomeric subunits. Rather, they are defined by

their water-repellant property. The only common structural theme shared by all lipids is a large proportion of non-polar hydrocarbon

groups. These hydrocarbon groups are often made from polymers of two-carbon compound called acetate.

Lipids are fats and other related substances. They are insoluble in H 2O but soluble in organic liquids like ether, chloroform, andacetone. Three types of lipids generally exist in animals: neutral fats, phospholipids, and sterols.

Neutral Fats.

Neutral fats (triglycerides) are composed of a glycerol and three

molecules of fatty acids. Neutral fats make up the major fuel of

animals.

Phospholipids.

Phospholipids (where one of the three fatty acids is replaced by

phosphoric acid and an organic base) is an important component

of the molecular organization of tissues especially membranes

(e.g. Lecithin is an important phospolipid of nerve membrane).

Sterols.

Sterols are complex alcohols which have fat-like properties

Cholesterol, the most common sterol in animal tissue, is a

component of cell membranes. Cholesterol can also undergorearrangement to form such substances as sex hormones and bile

acids.

Fats are emulsified in the small intestines by bile acids and broken down into glycerol and fatty acids by enteric and pancreatic

lipases.

Nucleic Acids.

The most complex biological polymers are nucleic acids The two most common nucleic acids are deoxyribonucleic acids andribonucleic acids. DNA and RNA are polymers made up of repeated units called nucleotides; nucleotides are composed of: a sugar, a

nitrogenous base, and a phosphate group.


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DNA RNA

Sugar deoxyribose ribose

Nitrogenous base

Purine Adenine (A) Adenine (A)

Guanine (G) Guanine (G)

Pyrimidine Cytosine (C) Cytosine (C)

Thymine (T) Uracil (U)

Table 2.3. Differences between molecules of DNA and RNA.

Nucleic acids are unique because they can replicate themselves. Furthermore, DNA can make RNA, which guides the assembly

of proteins. Nucleic acids form the molecular foundation for every living organism.

Chapter 3. Cells

After atoms and molecules, the next higher level of complexity in living organisms includes cells and their components. All

living things are made up of cells. Some cell components occur in all living cells, while others occur only in the cells of leaves, roots

or other parts of plants. Depending on their components, cells can divide, grow, transport substance, secrete substances, or harvestenergy from organic molecules. Most types of cells also contain genetic material that controls the activities of the cell. This genetic

material is inherited by new cells after cell division.

The Cell Theory

The modern version states that:- Cells are the morphological and physiological units of all living things.

- The properties of a given organism depend on those of its individual cells.

- Cells originate only from other cells, and continuity is maintained through the genetic material.

Prokaryotic and Eukaryotic Cells

All living species are composed of eukaryotic or prokaryotic cells. The differences between prokaryotic and eukaryotic cells are:

Prokaryotic Cell Eukaryotic Cell

nuclear membrane absent present

chromosomes usually singular, ring-shaped,

consisting only of DNA, without

associated proteins, and lack

centromeres

multiple, not ring-shaped,

consisting of DNA together with

attached proteins and have

centromeres

organelles membrane-bound organelles are

absent

membrane-bound organelles are

present in the cytoplasm

size diameter seldom exceeds 2 m diameter typically 20 m or more

capacity to

differentiate

lacks the capacity to differentiate

into specialized tissues in multi-

cellular organisms

great capacity to differentiate in

structure w/in multi-cellular

bodies

organisms occurs only as bacteria and

cyanophytes (blue-green algae)

makes up bodies of protists, fungi,

plants, and animals

Fig. 3.1. Differences between prokaryotic and eukaryotic cells.

Structures Found in the Cell

Looking through a light microscope, the only animal cell structures that can be seen are the nucleus, the cytoplasm, and the cellmembrane. In plants cells, these structures can also be seen in addition to the cell wall. Other organelles can only be seen through anelectron microscope. Organelles are usually membrane-bound structures inside the cytoplasm that have specific metabolic functions

These organelles float in the hyaloplasm. The hyaloplasm, or cytosol, is the clear, aqueous medium that bathes all cytoplasmic bodiesand serves as a reservoir of solutes and water.

Organelles that are common in plants and animals include the cell membrane, the nucleus, nucleoli, endoplasmic reticulum,

ribosomes, golgi apparatus, mitochondria, and microbodies. Organelles that can only be seen in plants include the cell wall, central

vacuole, and plastids.

Substances inside the cytoplasm that do not have metabolic roles are called inclusion bodies. Inclusion bodies are passive, often

very temporary materials such as pigments, secretory granules, and aggregates of stored proteins, lipids, or carbohydrates, which can

be utilized by the cell in its life processes.


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Cell Membrane.

The cell membrane may also be called the plasma membrane, plasmalemma, or cytolemma. It is selectively permeable

depending on the lipid content of the membrane, allowing entry of certain molecules into the cytoplasm while disallowing others. The

cell membrane also contains pumps which regulate the ion concentrations within the cell and its immediate vicinity. It contains a

variety of enzymes and has specific receptor sites which mediate important cell functions such as endocytosis, phagocytosis, antigenrecognition, and antibody production. Hormone-triggered cellular events also depend on specific surface receptors.

The cell membrane is composed of phospholipids and proteins

Phospholipids form the basic structure of the membrane referred to as bi

layer, two parallel layers with their hydrophilic heads facing the aquaeous

medium on the membrane surface and their hydrophobic tails facing the

interior of the membrane. Proteins partially or completely penetrate the

phospholipids bi-layer and are responsible for functional properties of the

membrane.

You may also find other structures on or near the cellular surface

Microvilli are finger-like projections of the plasma membrane tha

increase the surface area for absorption. Desmosomes are oval disks withanchoring fibrils that lie just within the plasma membranes of epithelia

cells subject to being stretched. Gap junctions are hollow pipes formed

by a ring of six dumbbell-shaped protein subunits that penetrate th

plasma membrane of certain tissues and allow free flow of materials from

cell to cell. Cilia and flagella are motile fibrils that protrude from the

surface of certain types of cells, being covered by an extension off theplasma membrane.

The Nucleus.

The nucleus is usually the most conspicuous organelle in a cell. It contains most of a cells DNA, which occurs with proteins in

thread-like chromosomes. The nucleus is surrounded by two membranes, together called the nuclear envelope. The outer membrane iscontinuous with the endoplasmic reticulum. The inner and outer nuclear membranes are separated by a space of 20-40 nm, except

where they fuse to form pores in the envelope. These nuclear pores are small circular openings, 30-100 nm in diameter, bordered byproteins that probably influence the passage of molecules between the nucleus and the rest of the cell. Inside the nucleus is a smaller

structure, the nucleolus, which serves as the site for the synthesis of ribosomal RNA (rRNA).

Fig. 3.1. The phospholipid bi-layer that makes up the

cell membrane.


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Microfilaments and Microtubules.

Microfilaments are thread-like aggregates of protein molecules that serve to maintain cell shape, bring about changes in cell

shape, and allow cells to contract. Microtubules are hollow tubules, much stouter than microfilaments, made of a unique protein

tubulin. They too, can maintain cell shape, and also serve as spindle fibers that separate the chromosomes during cell division.

Centrioles.

Centrioles occur as a single pair of tin can-shaped organelles in the cells of animals, fungi, and certain lower plants. During cel

division the pair separate, move to opposite ends of the cell, and produce spindle fibers that separate the chromosomes.

Ribosomes.

Ribosomes are organelles that serve as the site for the biosynthesis of large varieties of proteins destined either for extra- or

intra-cellular use. Ribosomes are either attached to membranes or move freely in the cytosol (the semi-fluid matrix between

organelles). The number of ribosomes varies among cell types and in different stages of cell development. They are especially

abundant in dividing cells because these cells make large amounts of protein.

Endoplasmic Reticulum.

The endoplasmic reticulum is a network of channels or tubules which constitutes the bulk of the endo-membrane system. It is

continuous with the nuclear membrane. Two regions of ER can be distinguished in electron micrographs. One region is called the

rough ER because the many ribosomes attached to it give it a rough appearance.

In contrast, the other region is called the smooth ER because it has no ribosomes attached to it. The smooth ER, in most cells,

makes up the terminal portions of rough ER. It gives rise to transfer vesicles that carry substances synthesized within the rough ER to

other location, especially the golgi complex. Functions of the smooth ER include:

- Steroid hormone synthesis in the testicular interstitial

cells, cells of the corpus luteum, and cells of the

adrenal cortex

- Synthesis of complex lipids and drug detoxification in

hepatocytes

- Lipid resynthesis in the intestinal absorptive cells

- Release and capture of Ca++ ions in striated muscle

cells

- Concentration of Cl- ions in gastric parietal cells

Golgi Complex.

Fig. 3.2. The different organellesfound in the cytoplasm

Fig. 3.3. The process of exocytosis.


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A Golgi complex (Golgi apparatus) is usually two-sided, with oneside facing the smooth ER and one side facing the plasma membrane

They receive material from the smooth ER, either through direc

connections or in vesicles released by the ER. These vesicles contain

proteins, lipids, and other substances, which are often chemicall

modified in the golgi bodies and then sorted into separate packets. These

packets eventually move to the edge of the golgi bodies near the outerface, where the golgi body membrane is pinched off into another vesicle

This vesicle moves to the plasma membrane or to other sites in the cell.

Vesicles that move to the plasma membrane are secretory vesicles

because they fuse with plasma membrane and secrete their contents to the

exterior of the cell. This type of secretion is called exocytosis

Endocytosis, the reverse process, involves taking substances into the cell

Pinocytosis is a type of endocytosis that involves taking up of liquids anddiluted substances. Phagocytosis, another type of endocytosis, involvestaking in of larger substances even bacteria.

Microbodies.

The smallest membrane bound organelles in a cell are called microbodies. These tiny organelles are often associated with

membranes of the ER, but they may also be closely associated with chloroplast and mitochondria. Different types of microbodies have

specific enzymes for certain metabolic pathways. Two of the most important kinds of microbodies are lysosomes and peroxisomes.

Lysosomes are involved in the hydrolysis of foreign (hetero-phagosomes) or intracellular sub-stances (autophagosomes) using

hydrolytic enzymes. These enzymes

also serve to digest aging organelles or sometimes liberate their enzymes en masse, causing cell suicide (autodigestion). They are

not present in plants.Peroxisomes are the major sites of oxygen utilization within the cell and are particularly rich in catalase which converts toxic

hydrogen peroxide (H2O2), formed during certain metabolic processes, into harmless water and oxygen.

Mitochondria.

Many of the reactions of aerobic respiration are catalyzed by enzymes bound to

mitochondrial membranes. The chief function of the mitochondria is to supply

energy to the cell through cellular respiration, thus earning the distinction of being

the powerhouse of the cell. A cell may contain several hundred mitochondria

usually depending on the energy requirement of a cell. Dividing cells and cells that

are metabolically active need large amounts of energy and usually have the larges

numbers of mitochondria.

Vacuoles.

Vacuoles are membranous sacs that enclose a variety of substances, often for only

temporary storage.

Cell Division

There are two types of cell division that occur in living things depending on the type of cell: mitosis and meiosis. Mitosis occurs

in body cells (soma cells) while meiosis occurs only in sex cells (egg cells and sperm cells).

Mitosis.

.5. The mitochondria.


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Mitosis is the type of cell division resulting in equal number of chromosomes. This ensures genetic equality of the daughter

cells. It occurs in embryonic development, growth, repair of injury, and in replacement of body covering at molting.

Four phases comprise the mitotic division: prophase, metaphase, anaphase, and telophase. In prophase, genetic material becomes

evident as distinct chromosomes that shorten, thicken, and stain deeply. Towards the end of prophase the nuclear membrane and the

nucleolus disappear. In metaphase, chromosomes lie radially in an equatorial plate and separate. In anaphase, halved chromosomes

move toward their respective poles. Telophase is marked by the end of polar movement, formation of nuclear membrane and the

formation of cell membrane across the former plane of the equatorial plate.

prophase metaphase anaphase telophase

chromosomes DNA complex coils

(chromatids attached to

one another by

centromeres) and

becomes easily stained

arranged in a line along

the median plane,

centromeres attached to

spindle fibers

centromeres divide,

chromatids move toward

opposite poles

chromosomes reach the

general location of the

centrioles

nucleolus disappears during late

prophase

absent absent reappears

nuclear

membrane

disappears during late

prophase

absent absent reforms around each group

of chromosomes

centrioles and

spindle fibers

migrates to opposite

poles, forms spindle fibers

spindle fibers attached

to centromeres of

chromatids

spindle fibers shorten

pulling chromatids

spindle fibers disappear

cellular

membrane

intact intact intact indents at the point of the

equatorial plane dividing the

cytolasm into two

Table 3.1. Comparison between stages of mitosis.

The period between cell divisions wherein the cell builds up genetic material to start another cycle is called interphase. It is

divided into three phases.

Phase

Gap1 (G1) usually lasts 8 hrs or longer depending on the type of cell and level of

nutrition; characterized by growth of daughter cells by undergoing internal

chemical changes in preparation for DNA replication

Synthesis (S) typically lasts about 8 hrs; period of DNA replication or synthesis

Gap2 (G2) usually lasts 5 hrs; beginning of active mitosis, replication of organelles

Table 3.2. Description of the phases of interphase.

Meiosis. In meiosis, cell division results in the reduction of chromosomal number to haploid (half the normal number of

chromosomes) set. Daughter cells (egg and sperm cells) unite during fertilization carrying genes from both parents to provide the

Fig. 3.6. The different stages of mitosis.


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correct number of chromosomes. Although both types of cell division involves the same phase (prophase, metaphase, anaphase, and

telophase), meiotic cell division consists of two successive cell division named meiosis I and meiosis II.

Meiosis I.

In prophase I, the members of each chromosome pair come together (synapsis). This is essential for the orderly separation o

the two members of each chromosome pair in the ensuing anaphase. Crossing-over may occur at this phase. Crossing over is

the exchange in position of one part of one strand of chromosomes with the equivalent part of the other strand. During the

metaphase I, the centromeres do not divide so during anaphase, the two members of each homologous chromosomes pair are

separated. Meiosis I is often called the reductional phase because at its end each daughter cell contains only one member of

each chromosome pair, although each chromosome still consists of two DNA molecules, or chromatids, held together by the

undivided centromere.

Meiosis II.

Depending on the species, meiosis II may begin at once or be delayed. In either case, DNA replication does not occur. When

meiosis II starts, the chromosomes move to the midline of the new spindle. The centromeres finally divideand one of the two

chromatids of each chromosome passes to each daughter cell. The result is four haploid cells with each chromosome now

consisting of only one DNA molecule.

Chapter 4. Tissues

Fig. 3.6. Gametogenesis (spermatogenesis and oogenesis) and Meiosis.


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The bodies of multi-cellular organisms, particularly animals, are organized on the basis of tissues, organs, and organ systems

Organ systems are composed of organs, which are in turn composed of tissues. Tissues are

aggregates of cells that are usually similar in both structure and function. The study of the

structures and functions of tissues is called histology.

Tissues are divided into four major categories: epithelial, connective, muscular, andnervous. During embryonic development, three germ layers differentiate into the four

major categories of tissues by a process called histogenesis. The three germ layers are the

ectoderm (outer), mesoderm (middle), and endoderm (innermost).

Epithelial tissues differentiate from all three germ layers. Connective and muscular

tissues differentiate from the mesoderm and nervous tissues differentiate from the

ectoderm.

Epithelial Tissue

Epithelial tissue forms the covering or lining of all free body surfaces, both external

and internal. The chief functions of epithelial tissues are: protection, absorption, secretion,

and excretion. Epithelial tissues are avascular (lack blood vessels). Nutrition and waste

removal are provided by the network of blood vessels in underlying connective tissues.

In general, epithelial cells are attached to a specialized structure called basement

membrane which serves as an anchor for the inner side of cells affording protection to the

underlying connective tissues.

Unique structures along the lateral surface of epithelial cells, called intercellular

junctions, play essential functional roles in various kinds of epithelial tissues. Threedistinct types of junctions have been identified. Tight junctions govern permeability. Gap

junctions make intercellular communication possible by exchange of chemical substances.Desmosomes or adhering junctions provide strong mechanical linkage between cells,

thereby preventing tissue disruption from stretching.

Cells composing epithelial tissues are classified according to their shape,

arrangement of cell layers, and function.

Classification as to shape:

1. Squamous flat and often serve as a protective layer.2. Cuboidal resembling small cubes. They are found in five

regions of the body as lining tissues for ducts, secretory

glands, renal tubules, germinal coveings of the ovaries, and

pigmented layer of the retina of the eye.

3. Columnar tall and often rectangular. They line ductssuch as the urethra and are found in mucus-secreting

tissues, mucosa of the stomach, bile ducts, villi of the

intestines, uterine tubes, and upper respiratory tract.

Classification as to arrangement of cell layers:

1. Simple arrangement has one layer.2. Stratified arrangement has multiple layers.3. Pseudo-stratified arrangement seems to consist of several

layers but is actually a single layer with all cells resting on the

basement membrane.

4. Transitional consists of several layers of closelypacked, soft, pliable, and easily stretched cells. When the

surface is stretched, the cells are flat but they appear saw-

toothed when relaxed. They line the renal pelvis of the

kidneys, the ureters, the urinary bladder, and the upper

part of the urethra.

Classification as to function:

1. Mucous membrane serve four general functions:protection, support for associated structures, absorptionof nutrients into the body, and secretion of mucus

enzymes, and salts. They line the digestive, respiratory,

urinary, and reproductive tracts.

2. Glandular epithelium arise as involutions ofepithelial cells, specializing in synthesizing and

secreting certain special compounds. They are found in

sweat glands, sebaceous glands, glands of the

alimentary tract, pancreas, mammary glands, and large

salivary glands.

3. Endothelium serve as lining epithelium of lymphaticvessels, blood vessels and the lining of the hear

(endocardium).

Connective Tissue

Fig. 4.1. Types of epithelial tissues.


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The second major division of tissues, connective tissues, which include the connective tissue proper and a number of specialized

connective tissues, perform many functions including support and nourishment for other tissues, packing material in spaces between

organs, and defense for the body by phagocytosis and antibody production.

Connective tissues have fewer cells that are set apart due to an abundance of intercellular substances or ground substances that

contain fibers except in blood. The ground substance may be fluid, gelatinous, or solid. Solid ground substances are often calledmatrix.

General functions of connective tissues include:

1. Binding tissues and organs

2. Mechanical support

3. Storage of fats (in adipose tissue) and

certain minerals (calcium in bones)

4. Exchange of metabolites between blood

and tissue (lymph)

5. Play a significant role in the repair or

healing of wounds, particularly the

loose connective tissues

6. Protection against infection

The Connective Tissue Proper

1. Loose connective tissue fibers are loosely arranged in a meshworka. Areolar tissue most widely distribute connective tissue which is pliable and crossed by many delicate threads. The

tissue resists tearing and is somewhat elastic.

b. Adipose tissue specialized connective tissue with fat-containing cells. Since fat is a poor conductor of heat, adiposetissue protects the body from excessive heat loss or excessive rise in temperature.

c.Reticular form the network of lymphoid tissue, the liver, and the bone marrow.

2. Dense connective tissue has compact or loosely packed fibers

a. Dense regular fibers are arranged in parallel bundles (tendons, white ligaments, fascia, aponeuroses).b. Dense irregular fibers are closely interwoven in a random way (dermis of the skin, capsules of organs, tendon

sheaths).

Specialized Connective Tissue

1. Cartilage tissue whose intercellular substances contain fibers, firm but pliable in consistency. Cells of cartilage, calledchondrocytes, are large and rounded with spherical nuclei and are clustered in small cavities called lacunae. Cartilages are

covered with a dense connective tissue called the perichondrium. Since cartilages are avascular, chondrocytes are nourished

by diffusion through the matrix of substances from perichondrial blood vessels.

a. Hyaline cartilage somewhat elastic, semi-transparent with an opalescent bluish-gray tint. They are found in the noselarynx, trachea, bronchi, ends of ribs, and surfaces of bones.

b. Elastic cartilage yellowish with greater opacity, flexibility, and elasticity. They are found in the external ear, walls ofexternal auditory and eustachian tubes, and epiglottis.

c. Fibro-cartilage most resistant type. They are found in the intervertebral disks, in the pubis synthesis, in themandibular joints and in sites of attachment of certain tendons to bones. This type of cartilage has no perichondrium.

2. Bone firm tissue formed by the impregnation of intercellular material with organic salts. It is a living tissue supplied byblood vessels and nerves and is constantly being remodeled. The two types of bones are compact, forming the dense outer

layer, and cancellous or spongy, forming the inner, lighter tissue.

3. Dentin closely related to bone. The crown of the tooth is covered by enamel, the hardest substance in the body. Enamel isecreted onto the dentin by epithelial cells of the enamel organ. Dentin resembles bone but is harder and denser.

4. Blood and Hematopoetic Tissue red bone marrow is the blood-forming (hematopoetic) tissue. Blood is a fluid tissuecirculating through the body, carrying nutrients to cells and removing waste products. Solid or formeed elements of theblood are: red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets (thrombocytes).

5. Lymphoid Tissue found in lymph nodes, thymus, spleen, and tonsils. Reticular tissue forms its framework, andlymphocytes lie within the reticular tissue. Lymphoid tissue plays a role in immunity.

Muscular Tissue

Muscular tissues are primary tissues of motion responsible for locomotion and movement of the different parts of the body. They

are composed of muscle fibers and intercellular substances (loose areolar connective tissue).

Three Types of Muscle Tissue

1. Skeletal muscle striated, voluntary muscle has cross-striations and can be controlled at will.


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2. Smooth muscle non-striated, involuntary without striations and is under the control of the autonomic nervous system.

3. Cardiac muscle striated, involuntary found exclusively in the heart.

Nervous Tissue

The fourth type of tissue, nervous tissue, is divided into two categories: nervous tissue proper (neurons) and accessory cells

(neuroglia). Nervous tissue is the most highly organized tissue in the body initiating, controlling, and coordinating the bodys ability toadapt to its environment. In nervous tissue proper, the specialized conducting cells are neurons, linked together to form nerve

pathways. A neuron is composed of dendrites, a cell body (soma), and an axon.

Fig. 4.2 Types of muscle tissue. From left: skeletal muscle, smooth muscle, and cardiac muscle.

Fig. 4.3. A typical neuron with dendrites, a body, and an axon.

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