5. Plant and Animal responses

Question 1

What are the two types of plant response?

Answer 1

Tropisms and Nastic responses

Question 2

What are the types of tropisms?

Answer 2

Phototropism, Geotropism, Chemotropism, Thigmotropism

Question 3

What are tropisms?

Answer 3

A directional growth response

The direction of the response is determined by the direction of the external stimulus.

Question 4

What are nastic responses?

Answer 4

Non-directional responses to external stimuli

Question 5

What is Phototropism?

Answer 5

Shoots grow towards light.

Question 6

What is Geotropism?

Answer 6

Roots grow towards the pull of gravity, helps them to take up water.

Question 7

What is Chemotropism?

Answer 7

Growth dictated by chemicals.

Question 8

What is Thigmotropism?

Answer 8

Using the support of another solid structure.

Question 9

What role do hormones play in plant responses?

Answer 9

They coordinate plant responses to environmental stimuli.
They are chemical messengers that are transported to act on target cells or tissue.
They bind to specific receptors on plasma membranes.

Question 10

What is the role of Cytokinins?

Answer 10

Promotes cell division and expansion
Delay leaf deterioration
Overcome apical dominance
Promote bud growth

Question 11

What is the role of Abscisic acid?

Answer 11

Inhibits seed germination and growth
Closes stomata when plant is under stress by low water availability.
Inhibits bud growth.

Question 12

What is the role of Gibberellins?

Answer 12

Promotes seed germination
Promotes growth of stems
Controls cell elongation
Promotes fruit development
Aids stomatal opening

Question 13

What is the role of Ethene?

Answer 13

Promotes fruit ripening

Question 14

What is the role of Auxins?

Answer 14

Regulate plant growth and control other plant hormones
Inhibits growth of side shoots (Apical dominance)
Inhibits leaf deterioration

Question 15

What is Apical dominance?

Answer 15

Controlled by auxin which is in the tip of the main shoot.

High concentrations of auxin prevent the development of lateral branches near the apex.

Question 16

What causes apical dominance?

Answer 16

High auxin levels- High abscisic acid levels- Low cytokinin in lateral buds- Inhibit lateral bud growth.

Question 17

How is apical dominance overcome?

Answer 17

The tip of the stem is cut off.

Low auxin levels- Low abscisic acid- Higher cytokinin levels in lateral buds- Lateral buds grow.

Question 18

How do seeds germinate?

Answer 18

When seeds absorb water, the embryo releases gibberellin.
This enables the production of amylase, which can break down starch into glucose
Provides the substrate for respiration, so it grows.

Question 19

Where in the plant does growth occur?

Answer 19

Growth can only occur in places containing immature cells that are still capable of dividing.
These are meristems.

Question 20

What are apical meristems?

Answer 20

They are at the tip of the apex of roots and shoots and are responsible for them getting longer.

Question 21

What are lateral meristems?

Answer 21

They are found in the buds and give rise to shoots.

They form a cylinder near the outside of roots and shoots and help them get wider.

Question 22

Why do shoots bend towards the light?

Answer 22

Phototropin receptors detect light from one side, causing auxin to be transported to the shaded side.
More auxin causes the cells to elongate more on the shaded side.

Question 23

How are plant hormones used commercially?

Answer 23

Seedless fruits, Weedkillers, Control fruit ripening, Controls fruit drop, Restrict hedge growth, Preserve cut flowers and vegetables.