BioEd Online

Teacher Background

Scientists use clinostats to simulate the growth of plants in microgravity. A clinostat continually rotates plants through 360 degrees to eliminate a set direction for gravity, which also prevents the hormone, auxin, from accumulating on one side of the stems or roots. As a result, the clinostat may cause stems and roots to demonstrate unusual growth behaviors. Roots may grow toward stems, and stems may grow horizontally, rather than upwards.

Clinostats are gravity compensation devices that subject plants to conditions that mimic microgravity. They have been used since 1879, when German botanist, Julius von Sachs, invented the clinostat to measure the effects of light and gravity on the movement of growing plants. Sachs was a contemporary of Charles Darwin and corresponded extensively with him on these issues. Darwin and his son, Francis, also used clinostats to investigate plant growth.

Clinostats are moving platforms that rotate plants to prevent their growth mechanisms from sensing the direction of gravity. The rotational speed is kept low—usually from one to four revolutions per minute (rpm)—to avoid any significant centrifugal acceleration effects on the subjects. Some clinostats are tilted; others are able to move three axes of rotation to provide complete randomization of gravity effects. Adjusting rotation speed and inclination of the rotation plane can subject plants to conditions that simulate a wide range of reduced gravity levels.

Clinostats trigger the same changes that occur when plants are in the microgravity of Earth orbit, and would occur during transit to the Moon and Mars. Microgravity impacts cellular operations, causing cellular components to move randomly within the plant cell and become more mixed within the cytoplasm. Many scientists are interested in this research topic because it opens new doors in understanding how plants will grow, develop, and behave when under different gravitational conditions.

In this activity, students will construct a clinostat to investigate the effects of near micro-gravity on growing plants.

Note: For in-depth information regarding the role auxins play in plant growth and development, and about Brassica rapa, please download the Plants in Space Teacher's Guide.

Objectives and Standards

Inquiry

• Ask a question about objects, organisms and events in the environment.

• Plan and conduct a simple investigation.

• Use appropriate tools and techniques to gather data and extend the senses, and analyze and interpret data.

• Use data to construct a reasonable explanation.

• Think critically and logically to make the relationships between evidence and explanations.

• Use mathematics in all aspects of scientific inquiry.

• Communicate investigations and explanations.

Life Science

• Reproduction is a characteristic of all living systems; because no individual organism lives forever, reproduction is essential to the continuation of every species.

• All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.

• Behavior is one kind of response an organism can make to an internal or external stimulus.

• An organism’s behavior evolves through adaptation to its environment. How a species moves, obtains food, reproduces, and responds to danger are based in the species’ evolutionary history.

Earth and Space Science

• Gravity is the force that keeps planets in orbit around the sun and governs motion in the solar system. Gravity alone holds us to Earth’s surface and explains the phenomenon of the tides.

Materials and Setup

For complete list of materials, material options, safety issues and setup information, please download the PDF.

Materials per Student Group or Student

• Clinostat: Programmable robotic set, such as Lego® Mindstorms^® NXT, shown upper left; or VEX^® Robotics Design Systems.

• Wisconsin Fast Plants^® Brassica rapa seeds, one seed per bottle/flask (available from Carolina Biological Supply Company, Nasco Science or other biological supply company)

• Prepared germination bottles/flasks (See “Preparing the Plant Growth Media and Flasks,” page 7, and “Inserting Seeds into Media-Prepared Flasks,” page 8, for details.)

• Safety goggles

Setup

1. Classroom robot construction systems are common in many schools. If your school does not have access to such systems, clinostats can be constructed from other materials. A 110 VAC motor with a rotation rate of one to four RPM can be used (check with an electronics store for suitable motors). The plant is grown in the bottom half of a plastic pill bottle. The support stand is made from plastic, but can also be made from wood.

2. Depending upon the robotic system’s programming capabilities, it may be necessary to use intermittent rotation. Lego^® Mindstorms^® NXT robot motors rotate too quickly for effective clinostat operations. However, they can be programmed to rotate through one-half turn every 30 or 60 seconds. This effectively masks the direction of gravity (see http://mindstorms.lego.com; or www.ortop.org/NXT_Tutorial/index.html for an online tutorial).

3. Be sure to determine battery life. If a charge lasts for 12 hours, set up a system to switch out batteries before they are completely drained of energy.

4. Depending upon the robotic system’s programming capabilities, it may be necessary to use intermittent rotation. Lego® Mindstorms® NXT robot motors rotate too quickly for effective clinostat operations. However, they can be programmed to rotate through one-half turn every 30 or 60 seconds. This effectively masks the direction of gravity (see http://mindstorms.lego.com; or www.ortop.org/NXT_Tutorial/index.html for an online tutorial).

5. Be sure to determine battery life. If a charge lasts for 12 hours, set up a system to switch out batteries before they are completely drained of energy.

Procedure and Extensions

1. Explain the purpose of a clinostat.

2. Challenge students to design their own clinostat using a classroom robotic system. The clinostat must be able to support one or more plants and rotate them automatically through 360 degrees. (See “Robotic System Computers,” page 13.)

3. Use tape to mount the prepared flasks to the clinostat.

4. Start the clinostat rotating and begin plant observations. If using Brassica rapa, the seeds should germinate within 24 hours.

5. Have students record observations and compare their results to those of Mission STS-134, available at BioEd Online.

Handouts and Downloads

Download color images from the Plants in Space Teacher's Guide.