Question

According to statolith theory, a plant distinguishes up from down by means of
A) Phytochrome
B) Amyloplasts
C) Auxin distribution
D) Ascent of sap

Answer 1

Hint: Plants have gravity sensing ability. Statolith helps the plants to sense gravity. The roots move towards the gravity whereas the stem moves against the gravity.

Complete Answer:
A) Statoliths are involved in gravity sensing. According to the statolith theory, a plant is able to differentiate up and down by means of amyloplast.
- They respond according to the gravity. In the stem, amyloplast or statoliths are present in the sheath cells or endodermis containing starch. They are present in the root tips as well.
- They sediment, due to which signals for auxins(plant growth regulators) is generated, This reorientation and redistribution results in the upward growth of stem and downward growth of roots.
B) Phytochrome-These are photoreceptors that help to induce changes in plant development. It is a phototropic factor. These are present in chloroplast.
C) Auxin distribution- Auxin concentration causes increased growth on the lower side of shoot so that it orients in a direction opposite to gravity.
D) Ascent of Sap- It is the upward movement of water and minerals from root to stem. The ascent of sap is against the gravitational pull.

Thus the correct answer is (A) Amyloplast contains statolith which helps in gravity sensing.

Note: The response to gravity is shown by all the plants. Roots move towards the gravitational pull whereas stems move against the gravity. It is also called geotropism.