Effects of IAA

Question 1

Examples of plant’s responses to stimuli that maximise their chance of survival

Answer 1

-Plants growing towards light
-This maximises the rate of photosynthesis and glucose production
-Releasing harmful/foul-tasting chemicals in response to being eaten by a herbivore
-Roots growing towards water maximises the plant’s ability to gain water

Question 2

Stimuli that plants can respond to

Answer 2

-Water
-Light
-physical objects
-gravity
physical touch
herbivores

Question 3

Tropism

Answer 3

Directional growth response to the action of stimuli
-Phototropism is a growth response to light
-Geotropism (gravitropism) is a growth response to gravity
Tropism can be positive or negative, i.e, negative gravitropism is a growth away from gravity (upwards)

Question 4

Growth factors

Answer 4

Growth factors are produced in the growing regions of the plant before moving from the growing regions to other tissues
-Here they regulate cell growth in response to directional stimuli

Question 5

Examples of growth factors+ function

Answer 5

-Giberellins- flowering, seed germination, stem elongation
-Ethenes- fruit ripening and flowering
ABA- leaf loss + seed dormancy
Cytokinins- cell growth and division

Question 6

IAA and how does it work

Answer 6

-IAA is a type of auxin (plant growth factor)
-IAA produces plant responses such as phototropism by altering transcription of genes within a plant cell
Altering the expression of genes that code for proteins involved in cell growth can affect the growth of the plant

Question 7

IAA in plant shoots

Answer 7

-A higher rate of IAA in plant shoots INCREASES the rate of cell elongation

Question 8

what happens when light shines on one side of the shoot (phototropism)

Answer 8

-When light shines on one side of the shoot, IAA from the illuminated side is transported to the shaded side
-This means there is a higher concentration of IAA on the shaded side than the illuminated side
-This higher concentration of IAA on the shaded side causes an increased rate of cell elongation on the shaded side
-This causes the plant shoot to bend towards the light (positive phototropism)

Question 9

What happens when light is shone evenly onto the plant shoot

Answer 9

-IAA is evenly distributed across the plant shoot

Question 10

Difference between IAA in plant shoots and IAA in plant roots

Answer 10

-In roots, Increased concentrations of IAA lowers the rate of cell elongation

Question 11

What stimulus do plant roots respond to

Answer 11

-Gravity (geotropism)

Question 12

How does the plant root respond to gravity (bend downwards) in terms of IAA

Answer 12

-In roots, IAA is transported to the lower side of the root
-The higher concentration of IAA in the root inhibits cell elongation
-Therefore the upper side of the root has a much faster rate of cell elongation than the lower side of the root, causing the root to bend downwards