Seeds and More Seeds (Sessions I and II)

Transcription

1 activities 27&28 Seeds and More Seeds (Sessions I and II) BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade 4 Quarter 3 Activities 27 & 28 SC.H The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results. SC.H The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H The student knows that to compare and contrast observations and results is an essential skill in science. SC.H The student knows that data are collected and interpreted in order to explain an event or concept. These activities also help prepare students to meet the following benchmarks in the next quarter: SC.G The student knows that living things compete in a climatic region with other living things and that structural adaptations make them fit for an environment. SC.G The student knows that green plants use carbon dioxide, water, and sunlight energy to turn minerals and nutrients into food for growth, maintenance, and reproduction. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 40 hands-on activities at this grade level. 1. Session I Activity 27: Remind students that corn plants produce lots of seeds (offspring) so a few can survive and sprout. Farmers plant corn and harvest the seeds, which are used to make corn products. Ask, How would it affect humans if corn plants produced fewer seeds? (Answers will vary, but students might mention we would need to use more land and plant more corn fields for our needs.) Then ask, Farmers today try to get corn plants to grow with more seeds on each ear of corn. Why do they do that? (Farmers want more corn seeds per acre planted so they can grow and sell more corn.) broward county hands-on science Quarter 3 307

2 2. Session II Activity 28: Have students list some possible reasons why seeds might not sprout in the local area. (Answers might include low rainfall and high temperature, both of which cause seeds to dry out; birds or rodents eating seeds; type of soil; and so on.) Ask students to write out an experimental plan to see whether potting soil or clay soil will work best to help seeds develop. (The students experimental design should reflect some attempt to control variables, such as amount of water and sun exposure.) 3. Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. 308 activities 27 & 28 Seeds and More Seeds

3 activities 27&28 Seeds and More Seeds OBJECTIVES Students sprout corn seeds and use the data to determine the germination success rate of an average corn plant. The students calculate the number of seeds produced by an average corn plant sprout a set of those seeds and determine the number that germinate infer why a corn plant produces so many seeds SCHEDULE Session I Activity 27 About 20 minutes Session II Activity 28 About 30 minutes, 4 5 days after Session I VOCABULARY germinate seed MATERIALS For each student 1 Activity Sheet 27 1 magnifier For each team of four 1 bag, plastic, resealable 1 cup, plastic For the class 1 corn, ear 1 roll paper towels* 4 pkg seeds, corn water, tap* *provided by the teacher PREPARATION Session I Activity Make a copy of Activity Sheet 27 for each student. Soak all corn seeds in water overnight. Divide the corn seeds equally among the plastic cups so that each team receives at least 60 soaked seeds. BACKGROUND INFORMATION In order for a species to survive, individual organisms must produce offspring. But that isn t all. The offspring must grow up and reproduce new organisms themselves. In most plants, reproduction occurs with seeds, structures that contain a tiny new plant and its stored food supply. When seeds are dropped in the right environment, they germinate, or sprout. If they grow into adult plants, they can produce seeds of their own. But not all seeds produced by a plant germinate and grow to adulthood. Seeds may be eaten by animals or fall onto rocks or into a lake, where they cannot grow. They may rot or be attacked by disease. Producing many seeds is one way to increase the chances that a species will survive. The more seeds that a plant produces, the greater the chance that some of them will germinate, grow into adults, and produce more seeds. This is why many plants produce dozens, hundreds, or even thousands of seeds. broward county hands-on science Quarter 3 309

4 Activity Sheet 27 Seeds and More Seeds Session I Activity How many kernels, or seeds, are on the ear of corn? about How many seeds would a corn plant produce if it had three ears? about How many of the seeds on one corn plant do you predict might actually germinate? Answers will vary. Session II Activity 28 Number of Seeds At start That germinate That do not germinate A Sample from ear of corn B On 1 whole ear of corn (A 10) C On 1 corn plant with 3 ears (B 3) About 50 About 500 About 1500 About About About About About About Why do you think corn plants produce so many seeds? Answers will vary. Students may suggest that since not all seeds germinate, it s a good idea to produce a lot so the chances of some growing into plants are higher. Guiding the Activity Additional Information Session I Activity 27 1 Distribute a copy of Activity Sheet 27 to each student. Show the ear of corn to students. Explain that each kernel is a seed made by the corn plant. a 310 Write the word seed on the board. Explain that a seed is a structure that contains a baby plant and the food it needs to survive until it can grow and make its own food. Most plants use seeds to reproduce, or make more of their own kind. Invite a team of two volunteers to count the number of kernels on the ear of corn. Have them share the number with the rest of the class. Have students record the number on their activity sheets. activities 27 & 28 Seeds and More Seeds b Figure Counting kernels. Explain how to count the kernels: first count the number of seeds in one row, as shown by (a) in Figure Then, multiply (a) by the number of rows, as shown by (b) in the figure. An average ear of corn will contain around 500 seeds.

5 2 Guiding the Activity Tell students to suppose that an average corn plant has three ears of corn. Ask, How many seeds in total would that corn plant produce? Additional Information Students may suggest multiplying the number of kernels on the one cob by 3 to find out how many total seeds an average corn plant would produce. 3 Have students multiply the number of kernels on the one cob by 3 and record the total on their activity sheet. Write the word germinate on the board. Explain that germinate means to sprout and start to grow. Ask, How many of these seeds do you think will germinate? Tell students that they are going to put a certain fraction of the seeds into a moist bag to see how many sprout. That fraction will be 1/10. That means that they will try to sprout one out of every ten seeds on the cob. As a class, divide the number of seeds on the cob by ten. Have students record the number in Column A of the chart on the activity sheet. This number will be around Answers will vary. Encourage discussion. Then have students record their predictions on their activity sheet. This number should be around 50 seeds. 4 Distribute a cup of soaked seeds, a moist paper towel, and a plastic bag to each team. Tell students that you have soaked these seeds over night to get them ready for sprouting. Have students count out the correct number of seeds (around 50) and keep them in the cup. Tell them to return any extra seeds to you. Tell students to lay the moist paper towel flat inside the plastic bag, spread out the soaked seeds on the towel, and seal the bag (see Figure 27 2). Place the bags in a warm place out of direct light. Figure Spread the corn seeds in a single layer. Check the bags every day to be sure the paper towels are still damp. If they look dry, add a few drops of water and reseal the bag. broward county hands-on science Quarter 3 311

6 5 Guiding the Activity Session II Activity 28 Additional Information After about 4 days, have students take the seeds out of the bag and spread them out on a dry paper towel. Distribute a magnifier to each student. Ask, How can you tell that a seed has germinated? Students should see a tiny root and stem emerging from the seed. Ask, How many seeds (kernels) germinated? How many did not germinate? Have students record their data in Column A of the activity sheet chart. 6 Help students calculate the number of seeds that would have germinated on one whole ear of corn by multiplying by 10 the number of seeds that germinated. Calculate the number of seeds that would not have germinated on one whole ear of corn by multiplying by 10 the number of seeds that did not germinate. Both answers should be recorded in Column B of the chart. Ask, Based on your observations, how many seeds would germinate on a corn plant with three ears of corn? How many seeds would not germinate? To find out, have students multiply each number in Column B by 3. Tell students to record their answers in Column C of the chart. 7 Ask, Why do you think some of the corn seeds did not germinate? Answers will vary. Students may suggest that some of the seeds were dried out or old. Ask, In nature, what might be some other reasons why seeds would not germinate? Students may suggest that seeds could get swept into lakes or eaten by animals. Encourage discussion Remind students that corn plants use seeds to reproduce, or make more corn plants. Ask, Why do you think corn plants produce so many seeds? activities 27 & 28 Seeds and More Seeds Students may realize that not all seeds will sprout. The more seeds a plant produces, the greater the chance that some of the seeds will germinate and grow into new plants.

7 R EINFORCEMENT Have students count and germinate the seeds of other plants. If dandelions are blooming, they are a good choice. Have students compare the germination rate of these plants with that of corn. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. C LEANUP The plastic bags, paper towels, and germinated seeds can be discarded. broward county hands-on science Quarter

8 Connections 314 Science Challenge Different types of seeds may require different temperature conditions for germination to occur. Let teams investigate the effect of temperature on the germination of peas, castor beans, and corn, as follows: Label three clear containers Cold, Hot, and Room Temperature, and stuff each one with moist paper towels. In each container, place three seeds of each type in a different location along the side (so germination can be observed) and label each type. Cover the containers with plastic wrap secured with tape, and wrap black paper around each one. Put the Cold container in the refrigerator (or outdoors if the season is cold), the Hot container in direct sunlight or on a radiator or heat vent, and the Room Temperature container in any classroom location out of direct sunlight. Remove the black paper each day to examine the seeds. In which container do seeds germinate first? Which germinates last? Let the sprouts grow for several days, and watch for other differences among the containers and seed types, such as rate of root and stem growth. Tell students that many types of seeds need a cool period before they can germinate. To demonstrate this, have students compare the germination rates of three groups of pansy seeds kept under different temperature conditions in a freezer, in a refrigerator, and at room temperature for 3 5 days before planting. The seeds that were refrigerated before planting should germinate first. Science Extension Have students prepare germination bags with other types of seeds, such as pole beans, lima beans, radishes, corn, sunflowers, and zinnias. When the seeds activities 27 & 28 Seeds and More Seeds have germinated, have students compare the seedlings roots, stems, and leaves. Let teams do the following activity to observe seeds increase in volume as they absorb water during germination. Fill a 100-mL graduated cylinder to the 30-mL mark with dried peas or beans, then add water to the 90-mL mark. Cover the cylinder to prevent evaporation. Over the course of the day, observe the container at half-hour intervals, and read and record the volume of the seeds and of the water. What happens as the seeds absorb water? (The seeds volume increases, but the water level remains the same.) Let students leave the container undisturbed overnight and check the seeds volume again the next morning. (Also see the Science and Math connection.) Science and the Arts Recipes using dried peas or beans require that they be soaked overnight before cooking. Ask students to look through cookbooks or magazines to find simple but interesting recipes that use dried peas or beans. Let the class review all of the recipes and choose one or two to prepare in the classroom. (If you do not have access to an oven in the school, ask students to select recipes that involve boiling, which could be done with a hotplate, or baking in a crockpot.) Science and Math Have students construct a line graph showing the results of the second Science Extension above. Tell them to label the vertical axis Volume of Seeds and the horizontal axis Time, with half-hour intervals labeled. Ask students why a line graph, not a bar graph, is appropriate for these data. (The seeds continue to increase in volume between measurements.)