Part B

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Seedling Development

7. Set five corn kernels on a folded paper towel. Roll up the paper towel, and put a rubber band around the roll. Stand the roll in a beaker with 1 cm of water in the bottom. The paper towel will soak up water and moisten the corn. Keep water at the bottom of the beaker, but do not allow the corn kernels to be covered by the water.

8. Repeat step 7 with five bean seeds.

9. After three days, unroll the paper towels and examine the corn and bean seedlings. Use a glass-marking pen to mark the roots and shoots of the developing seedlings. Starting at the seed of the corn and at the cotyledon node of the bean, make a mark every 0.5 cm along the root of each seedling. And again starting at the seed of the corn and at the cotyledon node of the bean, make a mark every 0.5 cm along the stem of each seedling. Measure the distance from the last mark on the root to the root tip of each seedling. Also measure the distance from the last mark on the stem to the shoot tip of each seedling. Record these data in your lab report.

10. Draw a corn seedling and a bean seedling in your lab report. Using a fresh paper towel, roll up the seeds, place the rolls in the beakers, and add fresh water to the beakers.

11. Make a data table similar to the one shown below in your lab notebook. Expand your table by adding columns under each "Roots" and "Stems" head to account for every section of the roots and stems of your seedlings.

12. After two days, reexamine the seedlings. Measure the distance between the marks, and record the data in your data table.

13. CAUTION Use the scalpel carefully to avoid injury. Using the scalpel, make a cut about 2 cm from the tip of the root of a bean seedling. Place the root tip on a microscope slide and add a drop of water. Place a cover slip over the root tip. Using a compound light microscope on low power, observe the root tip. In your lab report, draw the root tip.

14. Clean up your materials and wash your

^^ hands before leaving the lab.

Analysis and Conclusions

1. What protects the tips of corn shoots as they push through the soil? What protects the bean shoots?

2. What types of leaves first appear on the bean seedling?

3. What substance does the black color in the corn kernel indicate? Why might you expect to find this substance in the seed?

4. Examine the data you recorded for steps 9 and 12. Has the distance between the marks changed? If so, where has it changed?

5. What parts of the embryo were observed in all seeds on the third day?

6. How does the structure and development of the corn kernel differ from the structure and development of the pea and bean seeds?

7. What was the source of nutrients for each seed embryo? What is your evidence?

8. Describe the growth in the seedlings you observed.

9. Corn and beans are often cited as representative examples of monocots and dicots, respectively. Relate the seed structure of each to the terms monocotyledon and dicotyledon.

Further Inquiry

Design an experiment to find out how monocots and dicots compare in general plant growth and in the structure of their leaves and flowers.

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