Plant Responses

Question 1

Name a plant growth regulator that promotes growth and give a precise location for a site of action.

Answer 1

IAA
Causes root and shoot growth.
acts just behind the growing tip of the root or shoot.

Question 2

Through which part of a stem are growth promoters transported?

Answer 2

Mostly transported in vascular bundles, in either the xylen or phloem

Question 3

Outline two uses of growth promoters in horticulture.

Answer 3

1) Rooting powders are used to encourage stem cuttings to produce roots
2) ethene to ripen bananas

Question 4

Give an example of growth regulator that inhibits growth.

Answer 4

Abscisic acid causes stomata to close and the production of bud scales in reaction to stress.

Question 5

What do you understand by the term adverse external environment?

Answer 5

Means the area where the organism lives is not well-suited to it or harsh on it.

Question 6

Give two ways in which plants protect themselves from adverse external environments.

Answer 6

1) By closing stomata to prevent water loss during periods of water shortage
2) By developing a thick outer coat or bark to protect themselves
3) plants produce heat shock proteins that bind to proteins and help prevent them from denaturing if the temperature rises too much.

Question 7

Name the group of substances in plants which control responses to external stimuli.

Answer 7

Growth regulators

Question 8

What name is given to the regions in plants in which growth regulators are produced?

Answer 8

Meristematic regions

Question 9

Give locations for two of meristematic regions.

Answer 9

Root and shoot tip

Question 10

Most plant shoots are positively phototropic. Explain the term PHOTOTROPIC.

Answer 10

Plant shoots grow towards the light. Phototropic is the growth response of a plant to light, when it’s positive, it means the plant grows towards it.

Question 11

How do plants benefit from being positively phototropic?

Answer 11

The plant gets more light which speeds up photosynthesis.

Question 12

Explain the mechanism of response by a plant to named external stimulus.

Answer 12

External stimulus:
Light auxins are growth regulators, which work by loosening cell walls and allowing cells to expand.
Auxins are produced by the shoot tips of plants.
If a plant stem is exposed to light from one side, the auxin IAA will diffuse down the other side and cause the cells to elongate on the shady side. As a result the stem will bend over towards the light.

Question 13

What is a tropism?

Answer 13

A tropism is the growth response of a plant to a stimulus.

Question 14

What is a plant growth regulator?

Answer 14

Is a chemical produced in small amounts that controls (stimulates or inhibits) the growth of a plant.

Question 15

Give an example of a regulator in plants that inhibits growth.

Answer 15

IAA / ethene

Question 16

Give two uses of plant growth regulators in horticulture.

Answer 16

1) ethene ripens bananas

2) tissue culturing

Question 17

Distinguish between thigmotropism and chemotropism.

Answer 17

Thigmotropism is the plant’s response to touch, while chemotropism is the plant’s response to chemicals.

Question 18

What is an auxin?

Answer 18

plant growth regulator

Question 19

Give two examples of uses of synthetic (man-made) auxins.

Answer 19

1) Can be used to encourage cuttings

2) to develop roots, i.e. rooting powder

Question 20

State two ways in which growth regulators in plants are similar to hormones in animals.

Answer 20

1) produced in small amounts, can have positive or negative effect
2) travel from where they are produced to area where they cause effect