DNA Smoothie Lab

Name ______________________________________ Period ________ Date ______________ Forces in Living Things Purpose: In this lesson, students will demonstrate and illustrate forces that affect motion in everyday life such as emergence of seedlings, turgor pressure, and geotropism (TEK 7.7C) Background: Unbalanced forces cause motion. These forces are observable in the everyday life of organisms. In plants the emergence of seedlings relies on unbalanced forces to allow the seedling to push its way to through the soil. Force in the form of pressure allows herbaceous stemmed plants to stand erect. This turgor pressure also keeps vegetables crisp. Plants also respond to forces in the way they grow. Geotropism is the growth of a plant in response to gravity. Materials: • • • • • • • Part 1 4 soaked corn seeds Tape Paper towel Petri dish Cotton balls Water (tap) Removable marker • • • • • • • Part 2 4 soaked pinto bean seeds 3 oz. paper cup 4 tablespoons of plaster of Paris Paper towel Craft stick Water Removable marker Procedures, Part1: 1. Take four soaked corn seeds, and place them in the bottom of a Petri dish with the seed ends facing toward the center. A corn seed should be placed on the 12, 3, 6, and 9 o’clock positions of the Petri dish. 2. Cut paper towel to fit the inside of the Petri dish. 3. Carefully cover corn seeds with the paper towel as to not disturb the positions of the corn seeds. 4. Pour a small amount of tap water into the Petri dish/corn system. 12 milliliters should be about enough. 5. Use 4 cotton balls to pack the Petri dish to secure the seeds. 6. Close the Petri dish by placing the top of the Petri dish on and taping it in place. 7. Using a grease pencil or other removable marker, write the names of each group member very small and neat on the top of the Petri dish. 8. Tape the Petri dish/corn system vertically in an area that receives no light. Make sure the corn seeds are facing outward so that easy observations can be made. Suggested areas: closet, cabinet, or any closed space will work. Procedures, Part 2: 1. Using a grease pencil or other removable marker, write the names of each group member very small and neat on the outside of the cup. 2. In the 3 oz. paper cup, use the craft stick to mix 4 tablespoons of plaster of Paris with enough water to make a mixture with the consistency of pancake batter. 3. After mixing the plaster, push the 4 soaked beans into the surface of the plaster so that over half the bean is in the plaster. 4. Soak a paper towel with water and place over the top of the beans in the cup. 5. Keep the paper towel wet throughout the investigation. Pre-lab: 1. Illustrate the set-up for both investigations. Part 1 - Geotropism Part 2- Emergence of Seedlings 2. Create a hypothesis for each investigation. Part 1: If ___________________________________________________________, then ______________________________________________. Part 2: If ___________________________________________________________, then ______________________________________________. 3. Create a data table to record the results of both investigations. Pre-lab Question: 1. How will the investigations in this lab demonstrate that force causes change? Post-Lab Questions: Part 1- Corn Seeds: 1. Describe the direction in which the roots of the seeds grew. 2. Identify the forces to which the roots are responding. 3. Why did the roots grow that direction? Part 2 – Plaster Seeds: 4. What affect did the seeds have on the plaster? 5. Why do you think this occurred? 6. What was going on in the seed? Potato Strips Demo Lab Questions: 7. Describe the differences in the two potato strips. 8. What force caused these changes? Post-Lab Answers: Part 1- Corn Seeds: 1. Describe the direction in which the roots of the seeds grew. The roots grew downward. 2. Identify the forces to which the roots are responding. The roots are responding to gravity. 3. Why did the roots grow that direction? The roots grew downward in a response called geotropism. Since gravity tends to pull things toward the center of the Earth, water is found underground. The primary function of the root is to absorb water for the plant. The downward growth of roots helps the roots find water. Part 2 – Plaster Seeds: 4. What affect did the seeds have on the plaster? Over time the plaster cracked. 5. Why do you think this occurred? The seeds broke the plaster. 6. What was going on in the seed? The seeds soaked up water which caused the cells of the seed to swell. This swelling created pressure inside the seed, which broke the plaster surrounding the seed. As the seedling grows, the number of cells increases. This growth continued to increase the pressure cracking the plaster. This forces continues as the seedling emerges. Potato Strips Demo Lab Questions: 7. Describe the differences in the two potato strips. The strip soaked in salt water was limp and bent rather than broke when force was applied. The potato soaked in water was crisp and snapped when force was applied. 8. What force caused these changes? The salt in the water surrounding the potato pulled the water inside the cells of the potato to move out of the cell. This caused the potato to become limp. When the potato was soaked in fresh water, water entered the cells of the potato causing the cells to swell. The swelling of cells due to water is called turgor pressure. This pressure inside the cells of the potato caused the potato to be crisp and break easily.