Plant Responses

Question 1

Stimulus

Answer 1

Anything that causes a reaction in an organism

Question 2

Response

Answer 2

The activity of an organism as a result of a stimulus

Question 3

Tropism

Answer 3

A plants response to a stimulus

Question 4

Structures required for response

Answer 4

Chemical or hormonal system
Sense organs/ Nervous system (a)
Ability to move and grow
Immune system

Question 5

Phototropism

Answer 5

A plants response to light from a given direction

Question 6

Positive tropism

Answer 6

Occurs when the plant grows in the direction of the stimulus eg:light for photosynthesis

Question 7

Negative tropism

Answer 7

Occur when the plant grows away from the stimulus eg: chemotropism

Question 8

Advantage of tropisms

Answer 8

Allow plant to obtain better growing conditions

Question 9

Geotropism

Answer 9

Response to gravity

Question 10

Thigmotropism

Answer 10

Response to touch
Eg: Venus fly trap

Question 11

Hydrotropism

Answer 11

Response to water

Question 12

Chemotropism

Answer 12

Response to chemicals
Positive: rooting powder
Negative: herbicides

Question 13

Growth regulator

Answer 13

A chemical that controls the growth of a plant

Produced in the meristem and carried to their sites of action in vascular system

Question 14

Examples of growth regulators:
(Positive)

Answer 14

Growth promotors

Question 15

Examples of growth promotors

Answer 15

Auxin (IAA) - used for stem elongation, flower initiation and fruit growth
Gibberellin - used for stem cell elongation and seed germination
Cytokinin - used for cell division and differentiation

Question 16

Examples of growth regulators:
(Negative)

Answer 16

Growth inhibitors

Question 17

Growth inhibitors:

Answer 17

Reduce the growth of plants

Question 18

Examples of growth inhibitors

Answer 18

Abscissic acid - inhibits growth in seeds and results in dormancy
Ethylene (ethene) - inhibits growth in petioles and results in leaf fall in autumn
(Can ripen veg, not organic)

Question 19

Plant growth regulators (hormones) are…

Answer 19

Chemicals that interact with one another to control a particular development or response

Question 20

Commercial use of growth promotors:

Answer 20

1. Rooting powders (NAA, rapid root formation in stem cuttings)
2. Banana ripening (ethene)
3. Tissue culture (microprogation) (auxin promotes the formation of callus)
4. Produce seedless fruits eg: grapes

Question 21

Name a family of growth promoters

Answer 21

Auxins

Question 22

IAA

Answer 22

Indolacetic acid

Question 23

Production site for auxin

Answer 23

Mainly in shoot top meristem, young leaves and developing seeds

Question 24

Meristem is

Answer 24

Tissue capable of mitosis

Question 25

Effect of auxins

Answer 25

Cell enlargement and growth
Involved in phototropism and apical dominance

Question 26

The mechanism of phototropism

Answer 26

1. IAA is produced in the meristem and is passed down the stem
2. If the stem is exposed to light from one side IAA will diffuse down the shaded side
3. The cell on the shady side elongates, those on the bright side dont
4. The difference in elongation caused the stem to grow towards the light

Question 27

Apical dominance

Answer 27

Auxins are responsible for apical dominance, where the main Bud inhibits the growth of buds lower down the stem

Question 28

Plants adaptation for protection:
Anatomical/structural

Answer 28

Protective epidermis or bark
Thorns
Stinging hairs
Guard cells shrivel in drought and close stomata to prevent further water loss

Question 29

Plants adaptation for protection:
Chemical features:

Answer 29

Heat shock proteins (prevent denaturation)
Stress proteins (phytoalexins: attack cell walls of the infecting micro organisms)