14.2: Plant growth factors

Question 1

Plants respond to

3

Answer 1

light
gravity
water

Question 2

Why do plants respond to light

Answer 2

shoots grow towards light

Question 3

Why do plants respond to water

Answer 3

almost all plant roots grow towards water in order to absorb it for use in photosynthesis and other metabolic processes as well as its support

Question 4

Why do plants respond to gravity

Answer 4

plants need to be firmly anchored in the soil, roots are sensitive to gravity and grow in the direction of its pull

Question 5

Two aspects of plant growth factors

Answer 5

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

Question 6

IAA

stands for

Answer 6

indoleactic acid

Question 7

IAA

Answer 7

belongs the auxins group, plant elongation is one of the things it controls

Question 8

Unilateral light

Answer 8

Light from one side

Question 9

Shoots and roots response to light

Answer 9

shoots= positive phototropic response
roots= negative phototropic response

Question 10

What happens when unilateral light shines on a plant shoot?

Answer 10

IAA moves from the shoot tips to become concentrated on the shaded side in the plant shoot, this stimulates cell elongation causing a positive phototropic response where the shoot bends towards the light

Question 11

What happens when unilateral light shines on a plant root?

Answer 11

IAA moves from the root tips to become concentrated on the shaded side of the root, it inhibits elongation of cells and produces a negative phototropic response so the root bends away from the light

Question 12

Role of IAA in elongation growth

Answer 12

IAA increases plasticity of plant cell walls,

occurs only in young cells

Question 13

Acid growth hypothesis

Answer 13

proposed explanation of how IAA increases plasticity of plant cells,
involves active transport of H+ ions from the cytoplasm into spaces in the cell wall, causing the cell wall to become more plastic

Question 14

What do stimuli cause in relation to IAA

Answer 14

uneven distribution of IAA,
movement of IAA away from tip of stem/root
which causes elongation of one side of the shoot/root and therefore of bending away from or towards the stimuli