Plant Responses

Question 1

Stimulus

Answer 1

Something that causes a reaction in an organism.

Question 2

Response

Answer 2

Activity of a cell/organism in reaction to a stimulus.

Question 3

Structures needed to response

Answer 3

Chemical/hormonal system
Sense organs/ nervous system/
Immune system.

Question 4

External factors

Answer 4

Light intensity/ day length/ gravity/ temperature.

Question 5

Internal factors

Answer 5

Plant growth regulators. Chemicals produced in meristems of roots and shoots.

Question 6

Tropism

Answer 6

The change in growth of a plant in response to an external stimulus.
Positive- plant grows towards stimulus.
Negative- plant grows away from stimulus.
Advantage- allow the plant to obtain better growing conditions.

Question 7

Phototropism

Answer 7

Change in growth of plant in response to light from given direction.
Shoots- positively phototropic- get more light for photosynthesis
Roots- negatively phototropic- allow growth in soil.

Question 8

Geotropism

Answer 8

Change in growth of a plant in response to gravity.
Shoots- negatively geotropic- allows grow towards light.
Roots- positively geotropic- improve anchorage/absorption.

Question 9

Thigmotropism

Answer 9

Change in growth of a plant in response to touch.

Question 10

Hydrotropism

Answer 10

Change in growth of a plant in response to water in the soil.
Roots- grow towards damp soil
Also away from waterlogged soil.

Question 11

Chemotropism

Answer 11

Change in growth of a plant in response to chemicals.

Question 12

Growth Regulators

Answer 12

Are chemical that control the growth of plants.
Produced in meristems carried by vascular system.
Active in tiny amounts.
Interact with each other.

Question 13

Growth inhibitors

Answer 13

Reduce the growth in plants. Abscisic acid ( ABA) inhibits growth in seeds and results dormancy. Ethene inhibits growth in petioles results in lead fall.

Question 14

Growth promoter

Answer 14

Increase the growth of plants. eg IAA growth promoter.

Question 15

Commercial Uses of plant growth regulators

Answer 15

Ethene to ripe bananas.
Rooting powder.
Weed killer.

Question 16

Auxins

Answer 16

Growth regulator family. Indoleacetic acid ( IAA). Produced mainly in shoot tip meristems can also in young leaves and developing seeds.
Functions: -Causes different tissues to form.
- Loosen cellulose fibres allowing cell to elongate.
- Inhibit side branching in stems.

Question 17

Auxin effects

Answer 17

Causes tropism
Fruit formation

Question 18

How IAA causes tropism

Answer 18

IAA produced in the meristem/ in normal light passes equally in stem causing the stem to elongate and grow straight. If light comes to one side the cells on shady sides elongate and causes them to grow towards light.

Question 19

Plant protective adaptations

Answer 19

Chemicals/ cuticle/ thorns/Bark.