Controlling plant growth

Question 1

What is phototropism and geotropism?

Answer 1

• Phototropism is a plant’s growth response to light.
• Geotropism is a plant’s growth response to gravity.

Question 2

Parts of a plant respond in different ways:

Answer 2

• Shoots are positively phototropic and negatively geotropic.
• Roots are negatively phototropic and positively geotropic.

Question 3

What are auxins?

Answer 3

Auxins are a group of plant hormones. They move through the plant in solution.

Question 4

Where are auxins made?

Answer 4

Auxins are made in the root and shoot tip.

Question 5

Why do plant shoots curve towards the Sun?

Answer 5

Different amounts of auxin are found in different parts of the shoot when the tip is exposed to light. More auxin is found in the shady part of shoots. A higher amount of auxin will increase the length of cells. Therefore the increase in cell length on the shady side of the shoot causes curvature of the shoot towards the light.

Question 6

Plant hormones have many commercial uses. They are used:

Answer 6

• As selective weedkillers, which kill specific weeds and increase crop yield.
• As rooting powder to increase root growth of cuttings.
• To delay or accelerate fruit ripening to meet market demands.
• To control dormacy in seeds.