Introduction: You have learned how the Sun affects the growth of plants. This experiment will demonstrate how plants react to the presence of light and how the plant hormone auxin works in plants.

Vocabulary: auxin, tropism, phototropism, gravity, chlorophyll

Materials:

• Shoebox with a lid or cardboard box with dividers
• Paper cup
• 3 bean seeds
• Cardboard cut to width of shoebox
• Potting soil
• Scissors
• Tape or glue

Procedure:

1. Fill the paper cup with potting soil.
2. Plant the beans in the soil. Plant about 1/2" deep.
3. Water the soil and allow the beans to sprout.
4. Stand the shoebox on its narrow end.
5. Cut two cardboard pieces that fit inside the shoebox, these will be the maze walls so put alternating holes in them big enough for the plant to get through (approx. 2").
6. If using a cardboard box cut alternating holes in the divider. Holes should be about 2 inches across.
7. Make sure the walls will stay in place with tape or glue.
8. Cut a hole in the top that is big enough for the plant to get through.
9. As soon as the plant sprouts put it inside the shoebox at the opposite end from the hold you have cut.
10. Put the lid on the shoebox and make sure it will remain in place.
11. Place the box near a sunny window.
12. Open the lid daily to make note of plant growth.
13. Water the soil when needed.
14. Continue to observe until the plant grows out the hole in the lid.

Discussion:

1. Do you think the plants will wind their way through the holes to the outside of the box?
2. What does this experiment tell us about how plants respond to light from the Sun?
3. Are the plants sensitive to gravity?
4. How can you tell they are sensitive to gravity?
5. Which way do the stems always grow?
6. Which way do the roots always grow?
7. Do you think that turning the seed upside down would affect the way the plant grows?
8. List three things that are necessary for plant survival.

The plant winds around all obstacles and out the hole in the lid just to get to the light. The plant is growing toward the light because of phototropism. A buildup of a plant growth chemical called auxin happens on the dark side of plant stems. Auxin causes cells to grow longer on the other side of the stem which forces the stem to bend toward the light.

If the seed were planted upside down, the roots would start growing from the top of the seed and the stem would come out from the bottom. Then the would both turn around and grow the correct way. The roots would grow down because of gravity (geotropism) and the stem will always grow toward the Sun (phototropism). Phototropism is the result of the presence auxin.

Plants need gravity, light, and water for survival. Plants will also grown toward favorable conditions and away from unfavorable conditions.

The light energy from the Sun causes the plants to produce food in their leaves by photosynthesis. This enables them to grow.

     

              
             

©Copyright 1998 Elizabeth Beckett, Holly Bernitt, and Vishwa Chandra.