Plant growth factors

Question 1

How do organisms increase their chance of survival?

Answer 1

Organisms increase their chance of survival by responding to changes in their environment.

Question 2

what is tropisms?

Answer 2

Responses to directional stimuli that can maintain the roots and shoots of flowering plants in a favourable environment.

Question 3

tropisms can be either..?

Answer 3

positive or negative, growing away or from the stimulus.

Question 4

which three things to plants respond to?

Answer 4

1. light
2. gravity
3. water

Question 5

why do plants grow/respond towards light?

Answer 5

shoots grow towards light (positively phototropic) because light is needed for photosynthesis (LDR)

Question 6

why do plants respond to gravity?

Answer 6

plants need to be firmly anchored into the soil. roots are sensitive to gravity and grow in the direction of it’s pull (positively gravitropic)

Question 7

why do plants respond to water?

Answer 7

almost all plants grow towards water (positively hydrotropic) in order to absorb it for use in photosynthesis and other metabolic processes, as well as for support.

Question 8

why are plant growth factors used instead of plant hormones?

Answer 8

• they exert their influence by affecting growth, and they may be made by cells located throughout the plant rather than particular organs
• unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on a distant target organs

Question 9

what is an example of plant growth factors?

Answer 9

IAA - Indoleacetic acid

Question 10

What is IAA?

Answer 10

IAA is a type of auxin which controls cell elongation in shoots and inhibits growth of cells in the roots.

Question 11

where is IAA produced?

Answer 11

it is made in the tip of the shoots or the roots but can diffuse to other cells

Question 12

what is positive phototropism?

Answer 12

the growth of a plant in response to the direction of light

Question 13

Describe what causes a plant to bend towards the light?

Answer 13

• Cells in the tip of the shoot produce IAA, which diffuses down the shoot
• The IAA is initially transported evenly throughout all regions as it begins to move down the shoot
• light causes the movement of IAA from the light side to the shaded side of the root
• a greater concentration of IAA builds up on the shaded side of the shoot than the light side.
• as IAA causes cell elongation of the shoot cells and there is a greater concentration of IAA on the shaded side of the shoot, the cells on this side elongate more
• the shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light.

Question 14

why does IAA have opposite effects in the roots compared to the shoots?

Answer 14

IAA causes cell elongation in the shoots and a high concentration of IAA inhibits cell elongation in the roots

Question 15

What is negative phototropism?

Answer 15

growth of a plant away from the light

Question 16

describe negative phototropism in the roots?

Answer 16

• In the roots, There is a high concentration of IAA on the shaded side
• in roots, high concentration of IAA inhibits cell elongation, causing root cells to elongate more on the lighter side and so root bends away from the light

Question 17

What is Gravitropism?

Answer 17

a plants growth in response to gravity

Question 18

what is positive gravitropism?

Answer 18

a plants growth in response to the direction of gravity

Question 19

describe positive gravitropism in roots?

Answer 19

• cells in the root tip produce IAA, which is then transported along the root
• the IAA is initially transported to all sides of the root
• gravity then influences the movement of IAA from the upper side to the lower side of the root
• a greater concentration of IAA build up on the lower side of the root than the upper side of the root
• A IAA inhibits the elongation of root cells and there is a higher concentration on the lower side, the cells on this side elongate less than those on the upper side
• the relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity

Question 20

what is negative gravitropism?

Answer 20

shoots grow away from gravity

Question 21

describe negative gravitropism in the shoots?

Answer 21

• IAA will diffuse from the upper side to the lower side of the shoot
• if the plant is vertical, plant cells elongate
• if the plant is on it’s side, it will cause the shoot to bend upwards.

Question 22

what are the difficulties of studying different growth factors?

Answer 22

The effects of a plant growth factor can depend on:

what other growth factors are present. Another growth factor can increase the effect of the growth factor being studied (synergism) or reduce it (antagonism).

the species of plant

the developmental stage of the plant

the tissue being acted on, e.g. stems or roots

the concentration of the growth factor

Question 23

TAXES AND KINESES

Question 24

what is a stimulus?

Answer 24

a stimulus is a detectable change in the internal and external environment of an organism that leads to a response in the organism

Question 25

what increases a organisms chances of survival?

Answer 25

the ability to respond to stimuli, such as predators or extreme temperatures

Question 26

What is a taxis?

Answer 26

a simple response whose (motile organisms) direction is determined by the direction of the stimulus

Question 27

explain how an organism would achieve this?

Answer 27

as a result, a motile organism responds directly to the environmental changes by moving it’s whole body either towards a favourable stimulus or away from an unfavourable one.

Question 28

how are taxes classified?

Answer 28

they are classed according to whether the movement is towards the stimulus (positive taxis) or away from the stimulus (negative taxis) and also by the nature of the stimulus

Question 29

give some examples?

Answer 29

• single celled algae - will move towards light (positive phototaxis). this increases their chance of survival, since being photosynthetic, they require light to manufacture their food
• earthworms - will move away from light (negative phototaxis). this increases their chances of survival because it takes them into the soil, where they are better able to conserve water, find food and avoid predators
• some species of bacteria - will move towards a region where glucose is more highly concentrated (positive chemotaxis). this increases their chance of survival because they use glucose as a food source

Question 30

what is kinesis?

Answer 30

is a form of response in which the organism does not move towards or away from a stimulus. instead it changes the speed at which it moves and the rate at which it changes direction.

Question 31

what does kinesis mean?

Answer 31

movement in random directions

Question 32

why do they keep moving?

Answer 32

until they reach desirable conditions

Question 33

when does kinesis occur?

Answer 33

when an organism crosses a sharp dividing line between a favourable and unfavourable environment , it’s rate of turning increases. this raises it’s chances of a quick return to a favourable environment
- when negative stimulus is coming from all around (less directional) e.g light, temp, humidity

Question 34

the more unpleasant the stimulus the more..?

Answer 34

the more rapid the animal’s movement and the increase in rate of turns

Question 35

How does Kinesis help an organisms survival?

Answer 35

In unfavourable conditions animals can increase the probability of randomly finding more favourable conditions by increasing rate of movement and turns

Question 36

DONE!!