LESSON4Creating Your Own Pond

Ponds are often the inspiration for great

works of art, such as this painting by Claude

Monet entitled The Japanese Footbridge.

INTRODUCTION

An ecosystem is a community that includes liv-ing things and their environment, functioningtogether as a unit. There are many kinds ofecosystems. In this lesson, you will create yourown pond ecosystem and begin observing theliving and nonliving things found there. You willcomplete your observations in Lesson 12.

OBJECTIVES FOR THIS LESSON

Construct a pond and observe, sketch,

and label its layers.

Observe and document the living things

in the pond, directly, and with

magnification.

Explain the types of changes that may

occur in your pond over a 3-week period.

38 STC/MS™ O R G A N I S M S — P R O M M A C R O TO M I C R O

Getting Started

•1 Work with your group to develop a list ofat least six organisms you might expect to

find in and around a pond. Write this listin your science notebook.

O Share your list with the class.

MATERIALS FOR

LESSON 4

For your group4 copies of Student

Sheet 4.2:Sketches ofPond—Macro andMicro

1 clear plastic cupwith lid

2 compound lightmicroscopes

2 depression slides2 coverslips2 hand lenses1 plastic pipette2 pairs of scissors1 small cotton ball1 metric ruler,

30 cm (12")1 250-mL graduated

cylinder2 decaying leaves2 pieces of hay5 Lemna plants5 grains of rice1 black marker1 box of colored

pencilsGravelSoilSpring water

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LESSON 4 C K E A T I N C ; YOUR OWN POND

Inquiry 4.1Constructing Your Pond

PROCEDURE

1 Use the scoop to measure 50 cubic

centimeters (cm3) of gravel into a

graduated eylinder. (One cm3 is

equivalent in volume to 1 milliliter

[niL].) Pour the gravel into the

plastic cup to form a layer on the

bottom, as shown in Figure 4,1.

Then, use the metric ruler and

your marker to put a mark about

1.5 cm from the bottom of the cup.

2 Place soil on the gravel until itreaches that mark.

O Use your scissors to cut the two

leaves into smaller pieces and lay

them Hat on the surface of the soiland gravel.

A Gut the hay into pieces about5 cm long mid place them on the

leaves, as shown in

Figure 4.2.

C Gently pour into the cup

approximately 350 mL ofthe water provided by your

teacher.

C Use the tip of your pipette

to transfer five Lemna

plants from the culturecontainer to your pond.

Using your hand lens,

count the number of leaves,called "fronds," on the five

plants. Record the number

of fronds in your sciencenotebook. You will need thenumber for Lesson 12.

Figure 4,1 The gravel, as well as the cup bottom,

provides a base for your pond.

7 Your final product should look like the

cup in Figure 4.2. Do not move the pond

for several minutes. This will allow the

soil to begin settling to the bottom.

8 Proceed to Inquiry 4.2 immediately after•

creating your pond.

Lemna

Figure 4.2 Lay the hay on top of the leaves. Then add water.

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LESSON 4 CREATING Y O U R OWN P O N D

Inquiry 4.2Observing Your Pond

PROCEDURE

•I Observe your pond at eye level. In thebox provided on Student Sheet 4.2:Sketches of Pond—Macro and Micro,sketch exactly what you see. Be verydetailed about your observations. Labelthe layers you observe in the cup usingthe directions for scientific drawings thatyou were given in Lesson 2. Color yourdrawing as accurately as you can.

^ Prepare and view a slide of water fromyour pond in the following manner:

A. Add several strands of cotton to thedepression in your slide. This helps slowthe movement of any microorganismsthat are present.

B. Use a plastic pipette to obtain water fromthe bottom of your pond, just above thesoil and gravel. Add one drop of pondwater to the depression on the slide.

C. Place a coverslip over the drop of waterby placing one edge of the coverslip ontothe slide and lowering the other edgeslowly to avoid trapping air bubblesbeneath, as illustrated in Figure 4.3.This type of slide is called a wet mount.

D. Set the magnification to IGOx; then movethe slide around while you look formicroorganisms through the eyepiece ofyour microscope. Sketch in the circles onyour student sheet any microorganismsthat you may see.

O Repeat Procedure Step 2 with a watersample from the top level of your pond.You will make further observations whenyou revisit your pond in a later lesson, sobe as thorough as you can for comparisonpurposes,

Use the marker to write your groupmembers' names near the top of yourcup. Add five grains of rice to yourpond; then place the lid loosely on top.This will slow down the evaporation ofwater as well as expose the water tooxygen.

Figure 4.3 Place one of the coverslip down first.

BTC/MS™ O R G A N I S M S — F R O M M A C R O TO M I C R O 41

LESSON 4 C R E A T I N G Y O U R OWN P O N D

C Follow your teacher's directions for stor-ing the pond and cleaning up.

REFLECTING ON WHAT YOU'VE DONE

1 Look hack at the list you generated inyour science notebook during "GettingStarted." On the basis of what you haveobserved, revise your list.

O Following your list of pond organisms inyour science notebook, predict the waysin which you think your pond will changeover the next 3 weeks.

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LESSON 4 C R E A T I N G Y O U R OWN P O N D

EXCUSE ME,But Your Habitat Is in My Ecosystem!There arc countless ecosystems in the world.An ecosystem can be as small as a puddle or aslarge as an ocean. An ecosystem can simply hea stretch of grassland or a rotten tree trunk.You'll find an ecosystem wherever groups of liv-ing and nonliving things interact.

In the ocean, which is a saltwater environ-ment, bottle-nosed dolphins interact withsquid—by eating them. Sea lions eat squid, too,so they compete with the dolphins. Since theyall interact, bottle-nosed dolphins, squid, andsea lions all share the same eeosvstem.

Rainbow trout, which live in cool, freshwaterstreams, share their ecosystem with plants andother organisms, including those they prey on,such as snails and tlragonflies. Both the fresh-water stream and the saltwater ocean are knownas aquatic—or water-based—ecosystems.

Inside a Typical Ecosystem—A PondPlants, animals, and other organisms live withinevery ecosystem. The living component of anecosystem is referred to as a "community." Apond, for example, is an ecosystem in which a

);̂ p'̂ sfesfe:.:'

This pond is home to a great diversity of organisms.

STG/MS™ ORGANISMS—FROM M A C R O TO M I C R O 43

LESSON 4 C R E A T I N G Y O U R OWN P O N D

community of organisms,including blackworms,dragonflies, andLemna, allinteract among themselvesand with their nonlivingenvironment. (The mem-bers of each species in acommunity are called a"population.")

Within this pond ecosys-tem—and others—aremany different habitats, orhomes. Blackworms maylive in the muddy fringesof the pond. This is wherethey find shelter. This isalso where they find food.This is their habitat—theplace where their needsare met.

Dragonflies and damselflies live the first partof their lives in their pond water habitat asnymphs. They eventually climb up plant stems,where they change into their adult form. Thenthe area above and around the pond becomestheir habitat.

These damselfly nymphs eventually move out of the water, unless they become

fish food first!

Other organisms that share this pond ecosys-tem may have different habitats. For example,Lemna, or duckweed, live on the water's sur-face, closer to the light from the sun. Crayfish,on the other hand, live at the bottom of thepond, scavenging for food that falls from upperlayers.

This ball of dung, which is waste matter from another organism, provides a food supply for

this beetle, appropriately named the "dung beetle."

44 STC/MS''

LESSON4 CREATING YOUR OWN POND

The destruction of these trees greatly changes the nature of the ecosystems and habitats

in this area.

Finding an Organism's NicheOrganisms within an ecosystem perform certain

jobs that keep the ecosystem functioning. In a

pond, for example, birds and frogs keep the

number of insects in check by eating them. In a

grassy pasture habitat, dung beetles may eat the

waste matter from cows and other animals,

which helps to recycle nutrients. These aretheir functions, their jobs—their niches.

Everything ChangesDon't think for a minute that ecosystems,

habitats, communities, and populations don't

change. They do. Ponds dry up. Forests are

ravaged by fires. Hurricanes blow down trees.

Organisms become extinct. These are all nat-

ural processes. However, change also occursbecause of human intervention. A river gets

dammed, creating a lake in the process.

Grasslands get mowed and turned into soy-bean fields. Or trees get cut down and replaced

by parking lots or housing developments.

All over the world, animals, plants, and otherspecies come and go—and habitats and ecosys-tems shift and change over time. Change, in

fact, is one thing we can always rely on. D

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