Survival

Question 1

Which stimuli are plant shoots sensitive to and how do they respond?

Answer 1

Plants shoots are sensitive to:

Gravity - negative geotropism or gravitropism

Light - positive phototropism.

Question 2

Name the plant growth regulator released by the tip of a plant shoot.

Answer 2

IAA or indoleacetic acid

Question 3

Identify the two tropisms shown by plant roots.

Answer 3

Positive geotropism or gravitropism.

Positive hydrotropism.

(Negative phototropism).

Question 4

What effect does IAA have on the shoots of plants.

Answer 4

IAA causes cells to elongate in the stem.

Question 5

What effect does IAA have on cells in the root?

Answer 5

IAA inhibits cell elongation.

Question 6

What causes the IAA in a shoot to become unevenly distributed.

Answer 6

Light causes IAA to be transported to the shaded side of the shoot.

Question 7

Why might IAA in roots become unevenly distributed?

Answer 7

Gravity causes IAA to move to the lower surface of the root.

Question 8

Give 2 differences between taxis and phototropism.

Answer 8

Taxis - whole organism moves
Only happens in animals.

Tropism - growth response.
Only happens in plants.

Question 9

What is taxis behaviour?

Answer 9

Directional response to a directional stimulus.
Whole organism moves towards or away from the stimulus

Question 10

What is a kinesis?

Answer 10

Non-directional movement of an animal in response to a non-directional stimulus.
May lead to an increase/decrease in speed or turning frequency

Question 11

Why do animals show taxis or kinesis behaviour patterns?

Answer 11

They give a survival advantage.

Question 12

Why is it beneficial for a plant to show positive phototropism.

Answer 12

Allows shoot to grow towards light.
Increases light absorption for photosynthesis.
Greater GPP/biomass/organic material produced.

Question 13

Maggots often show negative phototaxis. What does this mean ?

Answer 13

Maggots move away from light.

Question 14

Why is it beneficial for maggots to show negative phototaxis?

Answer 14

Less visible to predators.
Less likely to dehydrate.

Question 15

What is the movement of a whole organism towards light called?

Answer 15

Positive phototaxis

Question 16

Define tropism

Answer 16

Growth response of a plant to a directional stimulus

Question 17

Why do woodlice increase their rate of turning if they exit favourable conditions

Answer 17

To increase probability that they re-enter the favourable conditions

Question 18

Why do woodlice decrease their rate of turning and move rapidly after detecting unfavourable conditions?

Answer 18

To increase chance that they will pass through the unfavourable conditions and enter a more favourable environment

Question 19

Give the term used to describe roots growing towards water

Answer 19

Positive hydrotropism

Question 20

Describe the process of negative phototropism in plant roots.

Answer 20

Cells in the root tip produce IAA
IAA is usually evenly transported down the root
Unidirectional light causes IAA to move to the shaded side
More IAA on shaded side than light side
IAA inhibits cell elongation in roots
Unequal growth causes root to bend away from light

Question 21

What effect does gravity have on IAA carrier proteins in plant cells.

Answer 21

More IAA protein carriers on the lower side of the cell.
More IAA on lower side
Roots elongation inhibited - root grows downwards
Encourages shoot elongation - shoot grows upwards

Question 22

Describe the role of H⁺ ions in cell elongation.

Answer 22

H+ ions are actively transported from cytoplasm into the spaces of the cell wall
Increase in H⁺ makes conditions more acidic
Increase the plasticity of the cell walls allowing for elongation.

Question 23

How could a student recognise kinesis in an organisms movement?

Answer 23

1. Turning increases as organism crosses form favourable to unfavourable conditions (return to original favourable environment)
2. If organism moves considerable distance into unfavourable conditions - turning slowly decreases begins to move in long straight lines, sharper turn (lead organism to new environment)