plant growth factors Flashcards
what can plants not do ?
- respond to environmental changes using muscles and glands
how do plants respond ?
- using tropisms
what is meant by the term tropism ?
- when plants respond via growth to stimuli
example of tropisms in plants
- positive phototropism
- negative gravitropism
- positive hydrotropism
- positive thigmatropism
what do plants respond to ?
- light
- gravity
- water
- touch
what are tropisms controlled by ?
- chemicals called auxins
what is an example of a type of auxin?
- IAA indoleacetic acid
how do plants increase their chance pf survival ?
- plants are sensitive
- they can detect environmental changes and respond to them
what are 3 responses to environmental changes ?
- the production of auxins
- movement
- directional growth
what is IAA ?
- a type of auxin that is produced in the tips of shoots of flowering plants
why is IAA transported around the plant ?
- to control tropisms
how does IAA move around the plant ?
- by diffusion and active transport over short distances
- in the phloem over long distances
what does IAA control ?
- can control cell elongation in shoots
- inhibit growth of cells in the roots
why do plants grow and bend towards the light ?
- because shoots need light for the LDR in photosynthesis so when they grow they bend towards the light
how does phototropism work ?
- shoot tip cells produce IAA
- causes cell elongation
- this IAA diffuses to other cells and is redistributed
- the IAA causes cells on the shaded side to elongate more and causes plant to bend towards the light
what happens to IAA in omni-directional light ?
- IAA is distributed evenly
what happens to IAA in uni-directional light ?
- IAA is redistributed
- transported in the opposite direction of the stimulus
what kind of phototropism do roots show ?
- negative phototropism
describe negative phototropism in roots ?
- a high conc of IAA inhibits cell elongation
- causes roots to elongate more on the lighter side
- so root bends away from light
describe gravitropism in roots ?
- positive gravitropism
- IAA causes directional growth in roots by inhibiting elongation
- IAA moves to the lower side of the roots so that the upper side elongates and the root bends down towards gravity and anchors the plant
describe gravitropism in shoots ?
- negative gravitropism
- IAA will diffuse from the upper side to the lower side of the shoot
- if a plant is vertical it will cause cell to elongate and the plant to grow upwards
- if a cell is on its side, it will cause the shoot to bend upwards
in which direction does IAA sediment in gravitropism ?
- IAA sediments in the direction of gravity
what did experimental evidence suggest about IAA ?
- light does not destroy IAA
- IAA is redistributed around the shoot
