Survival and Responses in Plants
- Created by: Sophie
- Created on: 05-04-15 16:19
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- Survival and Responses in plants
- Plants increase their chances of survival by responding to stimulus
- Grow towards direction of light for maximum light absorption for photosynthesis
- Sensing gravity, so roots and shoots grow in the right direction
- Climbing plants have a sense of touch so they can find things to climb and reach sunlight
- A tropism is a plant's growth response to an external stimulus
- The response of a plant to a directional stimulus
- Plants respond to stimulus by directing their growth
- Positive tropism= growth towards the stimulus
- Negative tropism= growth away from the stimulus
- Phototropism is the growth of the plant in response to light
- Shoots are positively phototropic
- Roots are negatively phototropic
- Geotropism is the growth of a plant in response to gravity
- Shoots are negatively geotropic
- Roots are positively geoptropic
- Responses are brought about by growth factors
- Growth factors are chemicals that speed up or slow down plant growth
- Produced in the growing regions of the plant and move to where they are needed in the plant
- A growth factor called Gillerellin stimulates flowering and seed germination
- Auxins stimulate growth by cell elongation- cell walls become lose and stretchy so the cells get longer
- High concentrations of auxins inhibit growth in roots though
- IAA is an important auxin
- Produced in tips and shoots of flowering plants
- Moves by diffusion and active transport over short distances, via the phloem to control tropisms
- Different parts of the plant have different amounts of IAA, uneven distribution leads to uneven growth of the plant
- Phototropism: IAA moves to shaded parts of shoots and roots so there's uneven growth
- Cells elongate on side of higher concentration so shoot bends towards light
- Geotropism: IAA moves to underside of shoots and roots
- Cells elongate so shoot grows upwards
- Root grows downwards
- Growth factors are chemicals that speed up or slow down plant growth
- Plants increase their chances of survival by responding to stimulus
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