Table of Contents

Plants and Gravity

Teacher's Notes

Experiencing the weak Martian gravity

Transparency Master

When the first explorers reach Mars they will find an environment which has about one-third the gravitational pull of the earth, virtually no water and, because of its distance, a dimmer Sun.

Eventually astronauts will have to try to grow food on Mars in small closed shelters. How do plants respond to gravity, light and water?

Things to Emphasize

1. Almost all rooting plants are able to distinguish between up and down by sensing weight (the force of gravity).

2. Plants grow their roots in a direction that is at least partially determined by their ability to respond to the force of gravity.

3. Geotropism is a highly evolved survival mechanism.

4. Science investigation involves a multi-step inquiry process: ask an initial question, plan the investigation, record observations and collect data, analyze data to draw a conclusion, and communicate the findings.

Experiment

Transparency Master

In this experiment you will build a "glass sandwich" with a radish seed and felt filling.

Procedure

1. Assemble the sandwich as shown to the left. Any size glass plate will work, but a 10-20 cm plate will work best.

2. Place a few radish seeds near the centre of the felt pad and hold them in place with the top glass plate. Use an elastic band to hold the assembly together.

3. Water the whole assembly occasionally, enough to keep it moist, by immersing the entire assembly in a basin of clean water.

4. Stand the assembly upright in a warm location in your classroom and mark the upper left corner as a reference point.

5. After a few days the seeds will begin to germinate. When the roots have grown about 2-3 cm rotate the assembly 90⁰. Keep the felt pad uniformly moist at all times. Add water along the edge with a dropper as required.

6. Repeat the process every time the root extends a few centimetres and continue until you have rotated the plates 360^o

Observations

In the first few days the seed will send out a root system. These roots grow downward. If the panel is rotated the plant responds by growing its roots in the "new" downward direction. As the panel is rotated every week or so, the roots continue to change their direction of growth in response to the newly defined downward direction. This response is known as a geotropic response. The effect is called geotropism.

Observation Blackline Master

Explanation

The roots of some plants, such as the radish, are very sensitive to the force of the Earth's gravity. These plants have evolved to develop roots which spontaneously grow downward in response to the force of gravity.

Activity

When Our Seeds Germinated, Student Activity Master

Topics for Class Discussion

1. What are the survival advantages for plants which have evolved to become geotropic?

2. What do you predict would happen to a growing tulip if you planted a tulip bulb upside down?

3. On a very long space trip, such as a trip to Mars, it has been suggested that growing vegetables might provide an excellent source of nutrition for the astronauts. What do you think might happen to plants (or geminating seeds) if one tries to grow plants in the weightless environment of space?