Creating Your Own Pond

Transcription

1 LESSON 4 Creating Your Own Pond INTRODUCTION An ecosystem is a community that includes living things and their environment, functioning together as a unit. There are many kinds of ecosystems. In this lesson, you will create your own pond ecosystem and begin observing the living and nonliving things found there. You will complete your observations in Lesson 12. Ponds are often the inspiration for great works of art, such as this painting by Claude Monet entitled The Japanese Footbridge NATIONAL GALLERY OF ART, WASHINGTON, D.C. 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 RGANISMS FROM M ACRO TO M ICRO

2 Getting Started Work with your group to develop a list of at least six organisms you might expect to find in and around a pond. Write this list in your science notebook. Share your list with the class. MATERIALS FOR LESSON 4 For your group 4 copies of Student Sheet 4.2: Sketches of Pond Macro and Micro 1 clear plastic cup with lid 2 compound light microscopes 2 depression slides 2 coverslips 2 hand lenses 1 plastic pipette 2 pairs of scissors 1 small cotton ball 1 metric ruler, 30 cm (12 in.) mL graduated cylinder 2 decaying leaves 2 pieces of hay 5 Lemna plants 5 grains of rice 1 black marker 1 box of colored pencils Gravel Soil Spring water STC/MS O RGANISMS FROM M ACRO TO M ICRO 39

3 Inquiry 4.1 Constructing Your Pond PROCEDURE 1. Use the scoop to measure 50 cubic centimeters (cm 3 ) of gravel into a graduated cylinder. (One cm 3 is equivalent in volume to 1 milliliter [ml].) 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 Place soil on the gravel until it reaches that mark. Use your scissors to cut the two leaves into smaller pieces and lay them flat on the surface of the soil and gravel. Cut the hay into pieces about 5 cm long and place them on the leaves, as shown in Figure 4.2. Gently pour into the cup approximately 350 ml of the water provided by your teacher. Use the tip of your pipette to transfer five Lemna plants from the culture container 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 science notebook. You will need the number for Lesson 12. Figure 4.1 The gravel, as well as the cup bottom, provides a base for your pond 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. Proceed to Inquiry 4.2 immediately after creating your pond. Figure 4.2 Lay the hay on top of the leaves. Then add water. Lemna Water Hay Leaves Soil Gravel 40 STC/MS O RGANISMS FROM M ACRO TO M ICRO

4 Inquiry 4.2 Observing Your Pond PROCEDURE Observe your pond at eye level. In the box provided on Student Sheet 4.2: Sketches of Pond Macro and Micro, sketch exactly what you see. Be very detailed about your observations. Label the layers you observe in the cup using the directions for scientific drawings that you were given in Lesson 2. Color your drawing as accurately as you can. Prepare and view a slide of water from your pond in the following manner: A. Add several strands of cotton to the depression in your slide. This helps slow the movement of any microorganisms that are present. B. Use a plastic pipette to obtain water from the bottom of your pond, just above the soil and gravel. Add one drop of pond water to the depression on the slide. C. Place a coverslip over the drop of water by placing one edge of the coverslip onto the slide and lowering the other edge slowly to avoid trapping air bubbles beneath, as illustrated in Figure 4.3. This type of slide is called a wet mount. D. Set the magnification to 100 ; then move the slide around while you look for microorganisms through the eyepiece of your microscope. Sketch in the circles on your student sheet any microorganisms that you may see Repeat Procedure Step 2 with a water sample from the top level of your pond. You will make further observations when you revisit your pond in a later lesson, so be as thorough as you can for comparison purposes. Use the marker to write your group members names near the top of your cup. Add five grains of rice to your pond; then place the lid loosely on top. This will slow down the evaporation of water as well as expose the water to oxygen. Figure 4.3 Place one edge of the coverslip down first. STC/MS O RGANISMS FROM M ACRO TO M ICRO 41

5 5. Follow your teacher s directions for storing the pond and cleaning up. REFLECTING ON WHAT YOU VE DONE Look back at the list you generated in your science notebook during Getting Started. On the basis of what you have observed, revise your list. Following your list of pond organisms in your science notebook, predict the ways in which you think your pond will change over the next 3 weeks. 42 STC/MS O RGANISMS FROM M ACRO TO M ICRO

6 EXCUSE ME, But Your Habitat Is in My Ecosystem! There are countless ecosystems in the world. An ecosystem can be as small as a puddle or as large as an ocean. An ecosystem can simply be a stretch of grassland or a rotten tree trunk. You ll find an ecosystem wherever groups of living and nonliving things interact. In the ocean, which is a saltwater environment, bottle-nosed dolphins interact with squid by eating them. Sea lions eat squid, too, so they compete with the dolphins. Since they all interact, bottle-nosed dolphins, squid, and sea lions all share the same ecosystem. Rainbow trout, which live in cool, freshwater streams, share their ecosystem with plants and other organisms, including those they prey on, such as snails and dragonflies. Both the freshwater stream and the saltwater ocean are known as aquatic or water-based ecosystems. Inside a Typical Ecosystem A Pond Plants, animals, and other organisms live within every ecosystem. The living component of an ecosystem is referred to as a community. A pond, for example, is an ecosystem in which a COURTESY OF HENRY MILNE/ NSRC This pond is home to a great diversity of organisms. STC/MS O RGANISMS FROM M ACRO TO M ICRO 43

7 community of organisms, including blackworms, dragonflies, and Lemna, all interact among themselves and with their nonliving environment. (The members of each species in a community are called a population. ) Within this pond ecosystem and others are many different habitats, or homes. Blackworms may live in the muddy fringes of the pond. This is where they find shelter. This is also where they find food. fish food first! This is their habitat the place where their needs are met. Dragonflies and damselflies live the first part of their lives in their pond water habitat as nymphs. They eventually climb up plant stems, where they change into their adult form. Then the area above and around the pond becomes their habitat. These damselfly nymphs eventually move out of the water, unless they become Other organisms that share this pond ecosystem may have different habitats. For example, Lemna, or duckweed, live on the water s surface, closer to the light from the sun. Crayfish, on the other hand, live at the bottom of the pond, scavenging for food that falls from upper layers. COURTESY OF CAROLINA BIOLOGICAL SUPPLY COMPANY ANIMALS ANIMALS MCDONALD WILDLIFE PHOTOGRAPHY 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 O RGANISMS FROM M ACRO TO M ICRO

8 NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA) PHOTO LIBRARY/NOAA CENTRAL LIBRARY The destruction of these trees greatly changes the nature of the ecosystems and habitats in this area. Finding an Organism s Niche Organisms 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 are their functions, their jobs their niches. Everything Changes Don 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 natural processes. However, change also occurs because of human intervention. A river gets dammed, creating a lake in the process. Grasslands get mowed and turned into soybean fields. Or trees get cut down and replaced by parking lots or housing developments. All over the world, animals, plants, and other species come and go and habitats and ecosystems shift and change over time. Change, in fact, is one thing we can always rely on. STC/MS O RGANISMS FROM M ACRO TO M ICRO 45