Plant growth factors Flashcards
Why is plants different to animals?
They have no nervous system
In order to survive plants ahev to change in both their internal and external envirnoment
Example of factors plant respond to
- Light
- Gravity
- Water
How do plants respond to light?
Shoots grow towards the light (e.g are positively phottropic) because light is needed for photosynthesis
Why do plants respond to gravity?
Plants need to be firmly anchored in soil
Roots are sensitive to gravity and grow in the direction of its pull (e.g positively gravitropic)
Why do plants respond to water?
Almost all plant roots grow towards water (i.e. positively hydrotropic)
In order to absorb it for use in photosynthesis and other metabolic processes, as well as for support
Why is plant growth factors used for plant response than external stimuli hormone-like substances?
- They exert their influence by affecting growth, and they may be made by cells located throughout the plant rather than in a particular organ
- Unlike animal hormones, some plant growth factors affect the tissue that release them rather than acting on a distant target organ
What quantities are plant growth factors produced in?
Small quantities
What is an example of a plant growth factor?
IAA
this belong to a group of substances called auxins
IAA controls plant cell elongation
What is a tropism?
A directional growth of a plant in response to a directional stimuli
What is unilateral light?
Light coming from the side
Steps of phototropism in flowering plants
response to shots of flowering plants to unilateral light
First step
Cells in tip of the shoot produce IAA which is transported down the shoot
Steps of phototropism in flowering plants
response to shots of flowering plants to unilateral light
Second step
The IAA is initally transported evenly throughout all regions as it begins to move down the shoot
Steps of phototropism in flowering plants
response to shots of flowering plants to unilateral light
Third step
Light causes the movement of IAA from the light side to the shaded side of the shoot
Steps of phototropism in flowering plants
response to shots of flowering plants to unilateral light
Fourth step
A greater concentration of IAA builds up on the shaded sife of the shoot than light side
Steps of phototropism in flowering plants
response to shots of flowering plants to unilateral light
Fifth step
As IAA causes elongnation of shoot cells and there is a greater concentration of IAA on shaded side
The cells on this side elongate more
Steps of phototropism in flowering plants
response to shots of flowering plants to unilateral light
Sixth step
The shaded side of the shoot elongates faster than light side
causing shoot tip to bend towards the light
Explain this graph
IAA also controls the bending of roots in response to light
If there is a high concetration of IAA increases cell elongation in shoots - inhibits cel elongation in roots
e.g
IAA concentration of 10 parts per million increases shoot elongattion by 200% but decreases roots cell elongation by 100%
Roots the elongation of cells is greater on light side than on shaded side so roots bend away from light - negatively phototropic
Steps
gravitropism in flowering plants
Response of horizontally-growing root to gravity
First step
Cells in the tip of the root produce IAA which is transported down the root
Steps
gravitropism in flowering plants
Response of horizontally-growing root to gravity
Second step
The IAA is initally transported to all sides of the root
Steps
gravitropism in flowering plants
Response of horizontally-growing root to gravity
Third step
Gravity influences the movement of IAA from the upper side o the lower side of the root
Steps
gravitropism in flowering plants
Response of horizontally-growing root to gravity
Fourth step
A greater concentration of IAA builds on the lowr side of the root than upper side
Steps
gravitropism in flowering plants
Response of horizontally-growing root to gravity
Fifth step
As IAA inhibits the cell elongation of root cells
there is a greater concentration on lower side then the cells on this side elongate less than the upper side
Steps
gravitropism in flowering plants
Response of horizontally-growing root to gravity
Sixth step
The relatively greater elongation on the cells on upper side compared to lower side causes the root to bend downwards towards the force of gravity
What happens to the shoots with gravitoprism in roots
There is greater concentration of IAA on lower side increasing cell elongation
Causing this side side elongate more than the upper side
Shoot grow upwards away from the force of gravity
