Topic 6 Tropism Flashcards
Hi
What is tropism?
Growth response to directional stimulus
What is phototropism
In response to light
What is geotropism?
Gravity
Hydrotropism
In response to water
A plant growing towards the light is an example of…
Positive phototropism
Roots growing down is an example of
Positive geotropism
Negative phototropism
What does the tip of a coleoptile contain that causes elongation of cells + growth in the plant?
Auxin
Also detects stimulus of light
What happens when a tip is cut off/ covered?
Doesn’t grow towards light (grows straight up instead)
Light not detected by auxin
What happens when light is shone directly above coleoptile?
- auxins evenly distributed
- tip grows directly upwards cos growth is equal
What happens when there is unidirectional light (shone from one side) on the coleoptile?
- auxins diffuse to dark side
- causes cells on dark side to elongate + grow at faster rate
- unequal growth bends shoot towards the light
(Auxin makes cell walls weaker, water can enter via osmosis so cells swell up)
Why are roots positively geotropic?
- grow down into earth cos
- obtain water -> osmosis
- obtain mineral ions eg nitrates -> active transport
- anchor into ground
Will the shoot of a seedling grow down? Why?
No
It will grow up because it is negatively geotropic
Will the root of a seedling grow down? Why?
Yes
Positively geotropic
Does auxin accelerate/retard cell elongation in roots/shoots
Retards in roots
Accelerates in shoots
