activity 1 diversity in living things · structure that supports the organism’s body)? if it...

532Active Biology

A Vote for Ecology

What Do You Think?It is estimated that 4% of all living species are found in CostaRica, even though this country comprises only 0.01% of thearea of the Earth.

• How many species do you think are found in Costa Rica?How many species are found globally?

• Why do you think that Costa Rica has such a largenumber of species?

Write your answers to these questions in your Active Biologylog. Be prepared to discuss your ideas with your small groupand other members of your class.

For You To Do

This activity provides you with an opportunity to view severalvery different species of organisms. It should give you anappreciation of the huge diversity of life that fills your world.

Activity 1 Diversity in Living Things

GOALSIn this activity you will:

• Observe a group of diverseorganisms.

• Relate the structure of anorganism to its adaptation tothe environment.

• Describe the organization ofthe biosphere.

• Define biodiversity andexplain its importance.

• Explain the effects of humanactivity on biodiversity.

• Read about the effects ofextinction.

• Practice safe laboratorytechniques for handlingliving organisms.

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533Coordinated Science for the 21st Century


Part A: Observing Animal Diversity

1. With your teacher, review theguidelines concerning the properhandling of laboratory animals.Follow these guidelines carefully.

2. In your Active Biology log make anenlarged copy of the table shownbelow. The table should extend acrosstwo facing pages. Each of the 13spaces should allow for several linesof writing.

3. In the Characteristics column, copythe words in italics from each of thefollowing questions. The 13th space isfor any other observations you make.All the specimens of one animalspecies and the materials andequipment needed for observing themare arranged at the station. Each teamwill have a turn at each station.Record only your observations, notwhat you have read or heard aboutthe organism.

1 What is the habitat of the animal?Does it live in water, on land, orboth?

2 Is body symmetry radial (symmetryabout a center) or bilateral (the leftand the right sides of the body aremirror images)?

3 Does the animal have a skeleton (astructure that supports the organism’sbody)? If it does, is it anendoskeleton (on the inside) or anexoskeleton (on the outside)?

4 Is the animal’s body segmented(divided into sections) or is itunsegmented?

Characteristic Hydra Planarian Earthworm Hermit Crab Frog

1

2

3

13

Characteristics Hydra Planarian Earthworm Hermit Crab Frog

Comparing Animals

BODY SYMMETRY

radial symmetry bilateral symmetry

Several of theactivities thatfollow involve theuse of organisms inwater. The waterthat the organismsare in should beconsidered acontaminant.Tables, equipment,and hands shouldbe washedcarefully so thatgerms are notinadvertentlypassed to people.


534Active Biology

A Vote for Ecology

5 Which type of digestive cavity doesthe animal have, a sac (only oneopening) or a tube (open at bothends)?

6 Does it have paired appendages? Are the limbs (arms, legs, fins, wings)found in pairs?

7 How does the animal obtain oxygen?Through lungs, gills, skin, or acombination of these?

8 Are any sense organs visible? If so,what types and where?

9 How does the animal move from oneplace to another?

10 Does it make any types of movementwhile it remains more or less in onespot?

11 How does the animal capture andtake in food?

12 How does it react when touchedlightly with a small brush?

Station 1: Observing Hydras

1. Place a single hydra in a small watchglass with some of the same water in

which it has been living. Wait untilthe animal attaches itself to the dishand extends its tentacles. Then slowlyadd a few drops of a daphnia culturewith a dropping pipette.

2. Touch the hydra gently with a softbrush. Observe its reactions.

3. Examine a prepared slide of alengthwise (longitudinal) section of ahydra under a compound microscope.Try to determine the presence orabsence of a skeleton and of adigestive system.

Station 2: Observing Planarians

1. Place one or two planarians in awatch glass containing pond oraquarium water. Add a small piece offresh raw liver. Observe using astereomicroscope or hand lens.

2. Use a compound microscope toexamine cross sections of a planarian.Examine whole mounts with astereomicroscope. Determine thepresence or absence of a skeleton anda digestive system.

As you moveamong thestations, keepyour handsaway from yourmouth andeyes. Wash yourhands well afterthe activity.




Station 3: Observing Earthworms

1. Pick up a live earthworm and hold itgently between your thumb andforefinger. Observe its movements.Do any regions on the body surfacefeel rough? If so, examine them witha hand lens.

2. Place a worm on a damp papertowel. Watch it crawl until youdetermine its anterior (front) andposterior (back) ends. Use a handlens to see how the ends differ.Describe.

3. Place an earthworm on loose soil andobserve its movements as it burrows.

4. Examine a model or a diagram of across section and lengthwise sectionof the earthworm’s body.

Station 4: Observing Hermit Crabs

1. Observe the movements of theappendages and the pattern oflocomotion (movement from oneplace to another) of a living landhermit crab. Observe the antennae.Touch them gently with a soft brush.Note the animal’s reaction.

2. Place a small piece of food from thefood dish in with the hermit crab.Observe how the hermit crab eats.

Station 5: Observing Frogs

1. Observe the breathing movements ofa frog while it is not moving.

2. Observe the variety of movements ofa live frog.

3. If possible, observe a frog capturingits food and feeding.

Wash your hands thoroughly before leaving the laboratory.

If you areobserving a livecrab in yourclassroom, keepyour fingers awayfrom the crab’spincers.

If you are handlinga live frog in theclassroom, do notrub your eyes.Wash your handsimmediately afterhandling.


536Active Biology

A Vote for Ecology

BIODIVERSITY

Organization in the Biosphere

The biosphere is the area on Earth where living organisms can befound. Most are found in a narrow band where the atmosphere meetsthe surface of the land and water. Life forms are referred to as thebiotic, or living, component of the biosphere.The abiotic, ornonliving, component is made up of items like rocks, soil, minerals, andfactors like temperature and weather.

Part B: Animal Adaptations to theEnvironment

1. Review what you have learned abouteach of the organisms in Part A. Byreading across the table, you shouldbe able to compare and contrast thecharacteristics of the five animals youhave studied.

a) For each animal, select twofunctions it performs as part of itsway of life. Describe how itsstructure enables it to performthese functions.

organism population

ORGANIZATION IN THE BIOSPHERE

Bio Wordsbiosphere: the area onEarth where livingorganisms can be found

biotic: the livingcomponents of anecosystem

abiotic: the nonlivingcomponents of anecosystem

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Just as you did in this activity, ecologists begin their studies with theorganism.Their investigations are designed to explore how theindividual interacts with its biotic and abiotic environment. However,an organism does not live on its own. It tends to form a group withothers of the same species. (A species is a group of organisms thatcan reproduce successfully only with others of the same type.) Thesegroups of species are called populations.When more than onepopulation occupies an area, a community of organisms is created.The abiotic component as well as the community form a functionalunit known as an ecosystem.

The Importance of Biodiversity and the Human Threat

In this activity you looked at some very different species of organisms.Scientists have discovered and named close to two million species.Thatwould mean looking at a lot of different organisms.Yet, it may be lessthan 20 percent of the species that exist! There are thousands oforganisms in the world that scientists know very little about. Morethan 750,000 species of insects have been identified.Yet, it is thoughtthat at least twice that many exist. Biological diversity, or biodiversity,is the sum of all the different types of organisms living on Earth.

community ecosystem

Bio Wordsorganism: an individualliving thing

species: a group oforganisms that caninterbreed under naturalconditions and producefertile offspring

population: a group oforganisms of the samespecies occupying a givenarea

community: all thepopulations of organismsoccupying a given area

ecosystem: a communityand the physicalenvironment that itoccupies

biodiversity: the sum of allthe different types oforganisms living on Earth


538Active Biology

A Vote for Ecology

Unfortunately, many organisms are disappearing.This is partly due toalterations of habitats.The result is a decrease in biodiversity.Ecosystems with a large number of different types of organisms arequite stable. Ecosystems with a small number of different organismsare less stable. Humans are partly responsible for this change.As the

human population grows it occupies moreland.This infringes on or destroys the habitatsof many organisms.

The smog created by automobiles and industryis killing many types of trees over a wide areaof southern California.The needles ofponderosa pines, for example, gradually turnbrown.The tops of palm trees have only smalltufts.When this happens, photosynthesis isgreatly reduced.The plants die.The EvergladesNational Park in southern Florida depends ona slowly moving sheet of water.The waterflows from north to south. Drainage ditchesbuilt at the northern edge of the Evergladeshave decreased the flow of water over theentire area.As a result, many alligator holeshave dried up.These holes helped to containfires in the Everglades. Now, destructive firesare more frequent in this national park.

Tropical rainforests are the most diverseecosystems on Earth.They are home for manydifferent species.Two-thirds of the world’sspecies are located in the tropics and

subtropics.The cutting of trees in the rainforests today has grown at a rapid rate.The trees are cut for lumber, grazing land, and other uses.This loss of habitat is destroying many species every day. Nearly half ofthe Earth’s species of plants, animals, and microorganisms will becomeextinct, be gone forever, or be severely threatened, during the next 25 years.

To find a similar rate of extinction (loss of species), you need to goback 65 million years.That was the end of the Cretaceous period whendinosaurs and other organisms disappeared. Because there are more

Bio Wordsextinction: thepermanent disappearanceof a species from Earth

Smog is also hazardous topeople.This is especiallytrue of those withrespiratory problems, theelderly, and children. Peoplehave died from the effectsof smog.




species today than therewere then, the absolutenumber of species lost willbe greater now. Hundredsof species of plants andanimals are threatenedtoday.They include thewhooping crane and somerare pitcher plants.Extinction is a naturalprocess. However, theprocess has been speededup because humans havechanged wholeecosystems.

Why is biodiversityimportant? Why does it matter if whooping cranes and pitcher plantsbecome extinct? One argument comes from genetics. In a field of cropplants planted by humans, all the plants are genetically similar.Theyhave all inherited the same characteristics.

In tropical regions, humans are cutting down, burning, orotherwise damaging the rainforests. Extinction of manyspecies as well as change in global climate are some ofthe effects of this deforestation.

About 90% of the world’s food comes from 15 species of plants.Three of them are corn,wheat, and rice. However, there are over 10,000 known species of cereals.


540Active Biology

A Vote for Ecology

If one individual gets a disease, all the plants may die. In a wildpopulation a vast pool of genetic characteristics are available.Thismeans that some of the plants could resist the disease.Therefore, notall the plants would be destroyed.The extinction of each wildpopulation erases genetic material that could mean healthy crops andanimals. Once extinction occurs, the genetic material is gone forever.

A second argument is related to the fact that simple ecosystems areunstable.Think of a field of corn as a simplified ecosystem. Suppose allthe corn dies.This means that the whole ecosystem would collapse.The simpler the ecosystem, the easier it is to disrupt its balance.Thefewer the species, the easier it is to upset an ecosystem. New speciesare evolving all the time. However, the process is very slow comparedto the rate at which humans are able to cause species to becomeextinct. Each time a species becomes extinct, the biosphere issimplified a little more. It becomes more difficult to maintain thestable biosphere on which all life depends.

A third argument comes from research on plants.The island ofMadagascar, off the east coast of Africa, is the only known habitat ofthe Madagascar periwinkle.This plant produces two chemicals notproduced by other plants. Both of these chemicals are used to fightHodgkin’s disease, a leukemia-like disease.As the human population onMadagascar grew, the habitat for the periwinkle shrank.The periwinklealmost became extinct. Fortunately, botanists collected and grew someof these plants before they were gone forever.The medicines madefrom the Madagascar periwinkle are worth millions of dollars eachyear.They also help many people with Hodgkin’s disease to live longer.These medicines never would have been known if the plant hadbecome extinct.

Extinction Can Cause a “Domino Effect”

Every organism in an ecosystem is connected to all the otherorganisms.The reduction in biodiversity caused by the extinction of asingle species can cause a “domino effect.” The removal of one partfrom an ecosystem, like the removal of a moving part from a car, cancause the collapse of an entire food chain. If a species acts as apredator, it keeps the population of its prey in check. If a species isprey, it provides an important food source.




For example, sea otters were over-hunted along the Pacific coasts ofAsia and North America.This removed the main predator of the seaurchin. Predictably, the number of sea urchins grew rapidly. Sea urchinseat kelp, a form of seaweed.As the number of sea urchins grew, theamount of kelp declined.As a result, the fish that relied on the kelp forhabitat and food were reduced in number.

Sea otters very nearly became extinct due to hunting pressure. Forhumans, killing the sea otters for their fur resulted in a decline in avaluable fishery.Where the sea otter has been reintroduced, seaurchin populations have fallen, kelp beds are being re-established, andthe number of fish is increasing.

Restoring the Balance Is a Difficult Task

Introducing the sea otter to the Pacific northwest is an example of anattempt to restore a natural balance. It is not always easy to do.Conservationists have also tried to restore the whooping crane. Inspring, whooping cranes fly north to live in the marshes and swampsof the prairies and the Canadian north.There they eat crayfish, fish,small mammals,insects, roots, andberries. Efforts bythe United Statesand Canada havehelped increase thepopulation from alow of 14individuals in 1940to 183 in 1999.Thewhooping cranemay be a successstory, and it maynot. Chemicalpesticides were theoriginal humanthreat to the crane.However, it wasalready struggling.

During the fur trade southern sea otters were hunted to nearextinction.They are still a threatened species, and may verywell be endangered.


542Active Biology

A Vote for Ecology

Reflecting on the Activity and the Challenge

In this activity you observed severalvery different living organisms. Youthen discovered that there are millionsof other different organisms alive onEarth. There are reasons why it isimportant to make sure that theseorganisms do not disappear foreverfrom the Earth. For your ChapterChallenge you may choose to research

an issue that relates to the disappearanceof a given species. You can now explainwhy it is important to maintainbiological diversity. Whether or notyour issue deals with biodiversity, thepublic still needs to understand whybiological diversity should concernthem. You need to provide the meaningand importance of biodiversity.

Cranes must fly a long waybetween their summer homes inthe north and their winter homeson the Gulf of Mexico.Along theway they are vulnerable tohunting and accidents. In addition,the whooping crane reproducesvery slowly. Each year femalesproduce two eggs, however, onlyone will mature.The first fledglingto crawl from the egg kills itsbrother or sister.This ensuresthere will be enough food for thesurvivor. However, it is verydifficult for the species toincrease its numbers.

Scientists do not understand allthe relationships between speciesecosystems.They cannot predictwhat will happen if biodiversity isreduced, even by one species. Ifone species becomes extinct, itcould be disastrous.The extent ofthe disaster may not be knownuntil later. Sometimes the balancecannot be restored.

Once widespread throughout NorthAmerica, the whooping crane wildpopulation dipped to just 15 birds in 1937.Through conservation efforts the whoopingcrane has begun a slow recovery. However,coastal and marine pollution, illegal hunting,and the draining of wetlands continue tothreaten the species.




Inquiring Further

1. The passenger pigeon and thehuman influence

Just over a century ago, the passengerpigeon was the most numerous speciesof bird on Earth. In the Eastern UnitedStates they numbered in the billions,more than all other species of NorthAmerican birds combined. OnSeptember 1, 1914, at 1:00 PM the lastsurviving passenger pigeon died at theage of 29. Research and report on howhumans were involved in theextinction of the passenger pigeon.

2. Extinction is forever

Humans were directly responsible forthe extinction of passenger pigeons.However, this bird is not the onlyorganism that has been threatened byhumans. Research and report onanother organism whose existence hasbeen or is endangered by humans.

1. Choose and identify two very different ecosystems.

a) For each, name some of the populations that might be found in eachcommunity.

b) Describe some of the abiotic factors that could affect each population.

2. What is biodiversity?

3. Explain how humans can influence biodiversity by changing the environment.

4. Why is maintaining biodiversity important?

5. a) Give an example of an ecosystem that has a high biodiversity.

b) Give an example of an ecosystem that has a low biodiversity.

6. Choose an organism other than one that you studied in this activity. List at leastthree structures that have helped the organism adapt to its environment. Describehow each helps the organism live in its ecosystem.

White rhinos are so large and powerful that in naturethey must give way only to the elephant.Yet, humansare a major threat to their existence.


activity 1 diversity in living things · structure that supports the organism’s body)? if it...

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