GCSE Plant Hormones

Question 1

What is phototropism?

Answer 1

A plant growth response towards or against light.

Question 2

What are auxins?

Answer 2

Plant growth hormones released by shoot tips. They do not like light and move by diffusion.

Question 3

Why is phototropism advantageous for plants?

Answer 3

Growing toward the sun means the plant gets more sunlight, which is needed for photosynthesis for energy

Question 4

What is geotropism?

Answer 4

A plant growth response for roots to grow into the earth.

Question 5

Why is geotropism advantageous?

Answer 5

Minerals and water need to be absorbed from soil for growth & repair / to anchor plants in soil.

Question 6

Describe how geotropism happens

Answer 6

Auxin inhibits cell growth in roots. Gravity causes auxin to collect at the underside of the root, causing the upper side of the root to grow at a faster rate than the underside, resulting in the root growing downwards.

Question 7

How might you carry out an investigation on tropisms?

Answer 7

1. Cut a 5cm hole in the lid of each cardboard box to ensure light direction is the same. Leave one cardboard box without a hole as a control.
2. Cut the cotton wool with maize seedlings into five equally sized pieces with 10 seedlings to ensure each seed can absorb the same amount of water and place them in petri dishes.
3. Measure the initial height of the seedlings.
4. Place one Petri dish in each box with forceps to avoid contamination. Use LED bulbs of intensities increasing in increments of 10 lux to ensure the temperature is constant.
5. Label each LED and place them over the hole in the cardboard box. Ensure the LEDs are all placed at the same distance from the seeds with a ruler.
6. Leave the maize shoots for 12 hours and measure the avg length of each maize shoot with a ruler. Calculate the difference between the initial measurement and this one to find how much the maize has grown
7. Repeat to find an avg and eliminate anomalies.

Question 8

Give uses of auxins

Answer 8

Weed killers, rooting powders, tissue culture (cloning)

Question 9

Give uses of ethene

Answer 9

Promotes fruit ripening, promotes leaf fall

Question 10

Give uses of gibberellins

Answer 10

Promotes germination, flowering and increases fruit size

Question 11

Explain phototropism

Answer 11

Shoot tip detects light and releases auxins.

Auxins diffuse down shaded side of shoot.

Unequal distribution of auxins causes cell elongation on only the shaded side.

This is called phototropism.