Plant Growth Factors Flashcards
What is tropism?
the response of a plant to a stimuli, involving growth
What are tropisms controlled by?
growth factors
What does IAA stand for and what is it an example of?
indoleacetic acid, a growth factor which is a type of auxin
What does IAA do?
control cell elongation. It stimulates it in the shoots and inhibits it in the roots
Where is IAA made?
in the roots and shoots, but it can diffuse to other cells
Why is it important that plants grow towards light?
as light is needed for the LDR for photosynthesis
What is it called when plants grow TOWARDS light?
positive phototropism
What direction does IAA diffuse in?
diffuses towards the shaded side
Describe how positive phototropism occur
- unilateral light causes IAA to diffuse towards the shaded side of the plant
- unequal concentrations of IAA
- causes cells on shaded side to elongate more than those in the light
- this causes the shoot to bend towards the light
Why does negative phototropism happen in the roots?
no need for light as roots do not photosynthesise, growing away from the light helps the roots anchor the plants and increases surface area for absorption of minerals and water
Describe how negative phototropism occurs
- IAA diffuse to the side of the roots that is furthest away from the light source
- uneven distribution and unequal; concentration of IAA
- this inhibits cell elongation in cells on shaded side
- so the roots bend downwards, away from the light
Describe how gravitropism will occur in the shoots
- IAA will diffuse downwards
- if vertical, this causes the cells to elongate so the plant grows upwards
- if the shoot is on its side, it will cause the shoot to bend upwards (due to uneven distribution of IAA)
What is negative gravitropism?
when plants grow against the force of gravity
what is positive gravitropism?
when plants grow towards the direction of gravity
Describe positive gravitropism
- in the roots
- IAA diffuses towards direction of gravity (downwards)
- unequal concentration of IAA, higher on the lower side
- this inhibits cell elongation on the lower side, whilst cells on the upper side still elongate faster
- causes the plant to bend downwards
What do plants respond to?
- light
- water
- gravity
Why is positive gravitropism beneficial to plants?
- roots grow into soil
- anchor the plant
- access water needed for photosynthesis
Explain how the movement of IAA in the shoots helps a plant to survive
- moves away from light/to shaded area
- cells on shaded side elongate faster
- shoot bends towards the light
- maximises light intensity for photosynthesis -> more organic molecules made so more likely to survive
How is the easy synthesis and absorption of IAA as well as its lethal properties for some plants important in agriculture?
- useful as a herbicide/selective weed killer
- affects broader-leaved plants (not narrow-leaved crops grown in agriculture)
What would happen if the tip was cut off of a shoot and there was unilateral light?
- no IAA produced
- no uneven cell elongation
- so no response to light
When investigating plant growth, what variables need to be controlled?
- size of shoot tip
- type of agar
- time period
- temperature
- age of shoots/stage in development
Why would a lid be kept on the petri dish when investigating the affect of IAA?
- prevents evaporation
- which affects IAA concentration
