Principle

The main shoot of a plant generally follows a perpendicular direction away from the centre of gravity of the earth (negative geotropism), whereas the main root grows towards the centre of gravity (positive geotropism). If however the plant is placed on a rotating horizontal disk, this will alter the direction of growth of the shoot and of the root.

Benefits

• Quantitative determination of gravity effects on plant growth

Tasks

1. Measure the alignment of shoots and roots under the effect of centrifugal forces which are less than, equal to or greater than gravity
2. Raise sunflower seedlings in small beakers in a rotating drum
3. Set different centrifugal forces by changing the speed of rotation of the drum motor.

Learning objectives

• Positive geotropism of roots
• Negative geotropism of shoots
• Centrifugal force and rotational speed
• Statoliths
• Geotropism