B1g Flashcards
What as well as animals responds to changes in the environment?
Plants.
what is plant growth controlled by?
Chemicals called plant hormones.
What does growth towards light increase?
The plant’s chance of survival.
Why do roots grow downwards?
They grow towards gravity.
What are shoots?
Positively phototropic but negatively geotropic.
What are roots?
Negatively phototropic but positively geotropic.
What do auxins, plant hormones, do?
Move through the plant in solution, are involved in the response to light, phototropism, and are involved in the response to gravity (geotropism).
Why do shoots grow towards light?
When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shade than the side that’s in the light. This makes the cell grow (elongate) faster on the shaded side, so the shoot bends towards the light.
Why are shoots negatively geotropic?
When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side. This causes the lower side to grow faster, bending the shoot upwards.
Why are roots positively geotropic?
A root growing sideways will also have more auxin on its lower side. But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards.
Why are roots negatively phototropic?
If a root starts being exposed to some light, more auxin accumulates on the more shaded side. The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground.
Describe an experiment that shows auxins are produced in the tip of the plant.
Bending is only prevented when the tip is covered, so the auxin must be produced in the tip.
What can plant hormones be used in?
Agriculture to speed up or slow down plant growth.
What is the action of plant hormones in selective weed killers?
Developed from plant growth hormones which only affect the broad leaved plants, like weeds. They disrupt their normal growth patterns, which soon kills them, whilst leaving the grass and crops untouched as they are narrow leaved.
What is the action of plant hormones in rooting powder?
A cutting is part of a plant that has been cut off it, like the end of a branch with a few leaves on it. Normally, if you stick cuttings in the soil they won’t grow, but if you add rooting powder, which contains a plant growth hormone, they will produce roots rapidly and start growing as new plants. This enables growers to produce lots of clones of a really good plant very quickly.
