The movement of plants due to gravity is called ‘gravitropism’. ‘Tropism’ means to move.

Plants are remarkable organisms that have the ability to grow towards or away from different stimuli, such as light, touch, and gravity. One way in which plants use this ability is through a process called gravitropism, which helps them to find “up.”

Gravitropism is the response of plants to the force of gravity. When a seed is planted, the plant’s roots grow downwards, while the stem grows upwards. This is because the roots are positively gravitropic, meaning they grow towards the force of gravity, while the stem is negatively gravitropic, meaning it grows away from gravity.

Plants use specialized cells called statocytes to sense the force of gravity. These cells are located in the root cap and contain tiny starch granules that move in response to changes in the plant’s orientation. When the plant is upright, the starch granules settle at the bottom of the cell, providing a signal to the plant to grow downwards. When the plant is tilted, the starch granules move to the side of the cell, indicating that the plant is no longer upright and needs to adjust its growth accordingly.

Experiments by NASA have shown that plants in space grow in weird spirals. One idea is that gravity makes heavy starch granules inside plant cells fall to the bottom of cells. This may trigger the plant’s ability to find ‘up.

Make a clinostat

One way to observe the effects of gravitropism is by using a clinostat, which is a device that rotates plants slowly, simulating a microgravity environment. A clinostat can be easily made in the classroom using Lego or Meccano.

To make a clinostat, you will need a rotating platform, a motor, and a power source. You can use Lego or Meccano to build the platform, attaching the motor to the bottom of the platform to provide the rotation. Place a small plant or seedling in a pot on top of the platform, and turn on the motor. The plant will slowly rotate, and you can observe the effects of microgravity on the plant’s growth and orientation.

Variables to test

• Try making your own clinostat and vary the speed that the plants rotate at. Does this make a difference?