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Chapter 1Characteristics of Living Things

ALABAMA 7TH GRADE SCIENCE STANDARDS COVERED IN THIS CHAPTER INCLUDE:

1 Describe characteristics common to living things, including growth anddevelopment, reproduction, cellular organization, use of energy, exchange ofgases, and response to the environment.

CHARACTERISTICS OF LIFEAll living things, also called organisms, share the following seven characteristics:

1. Cells: Cells make up all living things.Cells can sometimes organize into complex structures. Multicellular organismshave many cells, and unicellular organ-isms have only one cell. Organisms canbe unicellular or multicellular.

2. Sensitivity: Organisms respond tofigure 1.1 Cell

change in the environment. Responsesare reactions to changes in the environment. Plants can respond to theenvironment by growing toward light sources or shedding leaves in winter.Animals can respond to environmental change by hibernating or by fleeingfrom predators. Responses occur many times in the life of one organism.

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Characteristics of Living Things

3. Growth: Organisms change over their lifetime.Organisms get bigger in size as they grow from infancyto adulthood. Highly intelligent animals, like humans,learn many life skills during the growth of childhood.Organisms may develop new structures or behaviors asthey age. Think of all the ways you have grown over theyears. You have gotten taller and increased body size.You have gained experiences, knowledge and maturity.All organisms show an increase in physical and mentalmaturity the closer they come to reaching adulthood.

4. Homeostasis: Organisms must maintain an internalenvironment that is suitable for life. Homeostasis is theability of an organism to keep a steady internal state.Living things need the correct amount of fluids, salts,hormones and food sources in order to survive. Also,more importantly, animals must maintain a suitableinternal temperature. Muscles that are too cold will notbody parts, like nerves, can easily be damaged by prolonged hot or coldtemperatures. This is one reason fevers can cause deafness, blindness andparalysis.

5. Reproduction: All living things must beable to reproduce. Organisms can reproducesexually or asexually. Sexual reproductionoccurs when two organisms create offspring,and asexual reproduction occurs when oneorganism is capable of creating offspring byitself.

6. Metabolism: Organisms must get energy Figure 1.3 Baby Snakes Hatchingfrom the environment and use the energythey obtain to live. Metabolism is the sum of all chemical reactions within anorganism. Metabolism is how organisms are able to get and use energy. Whenyou eat food, metabolism is how your body is able to break down the food andprovide energy for your cells. All the cells in your body need energy to keepyour body alive and functioning. Exchanging gases, like when you breathe, isalso considered part of metabolism.

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Figure 1.2 Growing Up

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Chapter 1

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7. Adaptation: Over time, organisms can

become specially suited to a particular

environment. Sea turtles have long,

flipper-like legs and cannot easily walkon land. They are adapted to living in theocean. Adaptations occur slowly, over the

course of many generations. Remember:adaptations occur to populations oforganisms, not to the individualorganisms themselves.

VIRUSES ARE DIFFERENT FROM LIVING THINGS

Figure 1.4 Sea Turtle

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You’ve heard ofthe flu, haven’t you? The flu is an illness causedby the influenza virus. It passes easily from person to person.

You may think a virus is a living thing because it can betransmitted by living things. But in fact, a virus is not a living

thing. A virus particle cannot eat, and it can only reproduce

inside a cell. Outside a cell, a virus does nothing and remains

inactive. So what is it? A virus is a small particle that contains proteins and hereditary

material (DNA or RNA), but it is not alive. The virus is surrounded by a protein coat.

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Figure 1.5 Virus Particle

Tail Fiber

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Characteristics of Living Things

ORGANISMS MODIFY THEIR ENVIRONMENTHumans change their environment. You can probably name many ways humans changetheir environment. Try to think ofsome now. Did you think ofthings like building roadsand neighborhoods, damming rivers or creating pollution? These are just a few waysthat humans change their surroundings. Did you know almost all other organisms alsochange their environment?

Think about it. Fungi and bacteria break down dead plants and animals into basicchemical components. Without these important recyclers, the Earth would becomeburied under mountains of waste. Here is another example: plants provide shade foranimals and other plants. Shade lessens the amount ofsunlight available to other plants.This changes the pattern of growth in the shaded area.

Some plants also change the air. These plants (with the help of bacteria) take nitrogenfrom the air and put it in the soil so other plants can use it. Can you think of another wayplants can alter the chemicals found in the air? Here’s a hint: think photosynthesis!

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Many animals also modify environments. Beavers build dams (Figure 1 .6). These damscreate ponds or swamps where meadows once stood. The creation of a pond is helpfulto beavers and fish. However, to mice and grass that once lived in the meadow, thecreation of a new pond is harmful. It all depends on your perspective. Without a doubt,all plants and animals change their environment in some way.

Figure 1.6 Organism Modifies Its Environment

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Chapter 1

Activity

Examine the description ofeach organism below. Then in the space provided, predict theimpact of that organism on the environment.

Organism Description EnvironmentalImpact

Earthworm Invertebrate worm that moves through the soileatingorganic matter and leaving behind waste high innitrogen.

Termite Invertebrate insect that consumes dead wood.

Clostridium Bacteria that live in the soil and water, breaks downanimal wastes.

Lichen Symbiotic fungi and algae that live on the surface ofrocks. Usually first organism to inhabit an areafollowing glacial retreat or volcanic eruption.

Herring Vertebrate animal that lives in large schools andconsumes vast quantities of plankton.

Kudzu A non-native species of plant introduced in 1876 toreduce soil erosion. Now named a pest weed, kudzuis actively destroyed by farmers and governmentagencies.

Rabbit Vertebrate mammal that lives in deciduous forestsand grasslands. Consumes grasses and small shrubsand other vegetation.

Grasses Vascular plant that requires high amounts of sunlight.Grows quickly and reproduces several times in asingle season, producing many seeds.

Black racer A fast moving vertebrate reptile found in grasslandssnake and forests alike. Its keen eyesight allows it to eat

rodents, frogs and small lizards.

BONUS: Broadleafdeciduous tree found in a hardwood forest.Sugar Maple Utilizes photosynthesis to convert solar energy to

cellular energy. Sugars found in fall leaves preventgermination of similar seeds. This helps keep maple

trees from growing too close to each other

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Characteristics of Living Things

CHAPTER 1 REVIEW

1. What statement does NOT correctly describe living things?

A They must grow.B They use sexual reproduction.C They use metabolism.B They are made of cells.

2. Which statement below correctly describes an organism’s response toenvironmental stimuli?

A Water in a rain cloud freezes into snow.B Solar radiation heats the soil to create wind.C Flowers bloom in springtime.B In a desert, evaporating water leaves behind salts.

3.Which statement correctly describes a metabolic process?

A Animals take in oxygen for cellular respiration.B Sea turtles come ashore only to lay eggs.C Baby orangutans learn from their mothers to build tree nests.B Adult male lions roar to protect their home territory.

4. Which characteristic listed below is common to all living organisms?

A is able to moveB uses sunlight to trap energyC reproduces using eggsD maintains homeostasis

5. Learning to dance is an example of what characteristic of living things?

A response to environmental stimuliB growth and developmentC metabolismB cellular organization

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