Plant hormones play a key role in promoting growth within plants. They are distributed unevenly throughout the stems and roots, causing parts of the plant to grow in specific directions. Germination marks the beginning of plant growth, which will continue given the right conditions.
Aim: To investigate the effect of gravity on the growth direction of newly germinated seedlings.
Setup: Two Petri dishes, each to contain 3 seedlings.
1. Evenly add damp cotton wool into two Petri dishes. Make sure the wool is sufficiently damp but not overly saturated to provide the right balance of moisture for seedling growth.
2. Carefully place 3 seedlings onto the cotton wool in each Petri dish.
3. Cover each dish with a lid to protect the developing seedlings.
4. Secure one Petri dish to a support stand, positioning it on its side.
5. Mount the second Petri dish onto a clinostat, a device used to negate the effect of gravity.
6. Place both Petri dishes in a light-proof box to remove the influence of light, leave for two days, and then prepare to observe the growth patterns of the seedlings.
In the first Petri dish, all roots (known as radicles) displayed a downward growth pattern. This is a positive gravitropic response.
This occurred regardless of their initial orientation, whether they faced upwards, downwards, or sideways. At the same time, all shoots (plumules) grew upwards, demonstrating a negative gravitropic response.
In the second Petri dish, all radicles and plumules extended directly outward, following the direction in which they were initially positioned. This is because the clinostat neutralised the effect of gravity, resulting in no gravitropic response at all.