Plant growth factors

Question 1

Why is plants different to animals?

Answer 1

They have no nervous system

In order to survive plants ahev to change in both their internal and external envirnoment

Question 2

Example of factors plant respond to

Answer 2

• Light
• Gravity
• Water

Question 3

How do plants respond to light?

Answer 3

Shoots grow towards the light (e.g are positively phottropic) because light is needed for photosynthesis

Question 4

Why do plants respond to gravity?

Answer 4

Plants need to be firmly anchored in soil

Roots are sensitive to gravity and grow in the direction of its pull (e.g positively gravitropic)

Question 5

Why do plants respond to water?

Answer 5

Almost all plant roots grow towards water (i.e. positively hydrotropic)

In order to absorb it for use in photosynthesis and other metabolic processes, as well as for support

Question 6

Why is plant growth factors used for plant response than external stimuli hormone-like substances?

Answer 6

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

Question 7

What quantities are plant growth factors produced in?

Answer 7

Small quantities

Question 8

What is an example of a plant growth factor?

Answer 8

IAA

this belong to a group of substances called auxins

IAA controls plant cell elongation

Question 9

What is a tropism?

Answer 9

A directional growth of a plant in response to a directional stimuli

Question 10

What is unilateral light?

Answer 10

Light coming from the side

Question 11

Steps of phototropism in flowering plants

response to shots of flowering plants to unilateral light

First step

Answer 11

Cells in tip of the shoot produce IAA which is transported down the shoot

Question 12

Steps of phototropism in flowering plants

response to shots of flowering plants to unilateral light

Second step

Answer 12

The IAA is initally transported evenly throughout all regions as it begins to move down the shoot

Question 13

Steps of phototropism in flowering plants

response to shots of flowering plants to unilateral light

Third step

Answer 13

Light causes the movement of IAA from the light side to the shaded side of the shoot

Question 14

Steps of phototropism in flowering plants

response to shots of flowering plants to unilateral light

Fourth step

Answer 14

A greater concentration of IAA builds up on the shaded sife of the shoot than light side

Question 15

Steps of phototropism in flowering plants

response to shots of flowering plants to unilateral light

Fifth step

Answer 15

As IAA causes elongnation of shoot cells and there is a greater concentration of IAA on shaded side

The cells on this side elongate more

Question 16

Steps of phototropism in flowering plants

response to shots of flowering plants to unilateral light

Sixth step

Answer 16

The shaded side of the shoot elongates faster than light side

causing shoot tip to bend towards the light

Question 17

Explain this graph

Answer 17

IAA also controls the bending of roots in response to light

If there is a high concetration of IAA increases cell elongation in shoots - inhibits cel elongation in roots

e.g

IAA concentration of 10 parts per million increases shoot elongattion by 200% but decreases roots cell elongation by 100%

Roots the elongation of cells is greater on light side than on shaded side so roots bend away from light - negatively phototropic

Question 18

Steps

gravitropism in flowering plants

Response of horizontally-growing root to gravity

First step

Answer 18

Cells in the tip of the root produce IAA which is transported down the root

Question 19

Steps

gravitropism in flowering plants

Response of horizontally-growing root to gravity

Second step

Answer 19

The IAA is initally transported to all sides of the root

Question 20

Steps

gravitropism in flowering plants

Response of horizontally-growing root to gravity

Third step

Answer 20

Gravity influences the movement of IAA from the upper side o the lower side of the root

Question 21

Steps

gravitropism in flowering plants

Response of horizontally-growing root to gravity

Fourth step

Answer 21

A greater concentration of IAA builds on the lowr side of the root than upper side

Question 22

Steps

gravitropism in flowering plants

Response of horizontally-growing root to gravity

Fifth step

Answer 22

As IAA inhibits the cell elongation of root cells

there is a greater concentration on lower side then the cells on this side elongate less than the upper side

Question 23

Steps

gravitropism in flowering plants

Response of horizontally-growing root to gravity

Sixth step

Answer 23

The relatively greater elongation on the cells on upper side compared to lower side causes the root to bend downwards towards the force of gravity

Question 24

What happens to the shoots with gravitoprism in roots

Answer 24

There is greater concentration of IAA on lower side increasing cell elongation

Causing this side side elongate more than the upper side

Shoot grow upwards away from the force of gravity

Question 25

Diagram of phototropism

Answer 25

Question 26

Diagram of gravitropism

Answer 26

Question 27

Which direction does IAA go to?

Answer 27

Away from tip to shoots and roots where it is produced

Question 28

What number of effects does IAA have on a plant?

Answer 28

Increasing plasticity (ability to stretch) of their cell wall

(only occurs when young cell walls where the cells are able to elongate)

As the cells mature and develop greater rigidity - older shoots and plants won’t be able to respond

Question 29

What is acid growth hypothesis?

Answer 29

Proprosed explanation of how IAA increases the plasticity of cells

Question 30

What does acid growth hypothesis involve?

Answer 30

Active transport of hydrogen ions from cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cells to elongate by explansion

this can explain how elongation happens on only one side of stem/root causing them to bend as

plants respond relatively quickly to envirnoment stimuli like light or gravity

explained by uneven distribution of IAA, (moves away from tip of stem.root)