*Topic 6: coordination and response Flashcards
What is a stimulus?
A detectable change in the environment
What is meant by the term tropism in plants?
When plants respond, via growth, to stimulus
What growth factor controls tropism?
Indoleacetic acid(IAA)
Where in the plant is Indoleacetic acid produced?
The tips of roots and shoots
How does Indoleacetic acid move to other parts of the plant?
By diffusion
What effect does indoleacetic acid have on shoots?
It causes cell elongation
What effect does indoleacetic acid have on roots?
It inhibits cell elongation
Explain why plants bend
towards the
light
Shoot tip cells produce indoleacetic acid (IAA) which causes cell elongation in shoots, and this IAA diffuses to other cells.
If there is unilateral light the IAA will diffuse towards the shaded side of the shoot resulting in a higher concentration of IAA there.
The IAA causes the cells on the shaded side to elongate more and this causes the plant to bend towards the light
How do positive phototropism’s in shoots increase plants chances of surviving?
shoots need light for the light dependant reaction in photosynthesis which is why plants grow and then bend towards the light
How do negative phototropism’s in roots increase the survival of plants?
roots don’t photosynthesise, they don’t require light and are more able to anchor the plant if they’re deep in the soil away from light
What are the 3 stimuli plants respond to?
light
gravity
water
describe positive gravitropism in plant roots
The indoleacetic acid (IAA) moves to the lower side of the roots in response to gravity so the upper side elongates and the roots bend down towards gravity and anchors the plant in. This is positive gravitropism
Describe negative gravitropism in plant shoots
The indoleacetic acid (IAA) will diffuse from the upper side to the lower side in response to gravity.
if a plant is vertical
