Auxins, gibberellins and ethene, phototropism and gravitropism, and the commercial uses of plant hormones. Biology only content.
You can study this deck without signing up — your progress is kept in this browser. An account saves it properly, syncs it across devices, and lets you edit the cards.
1.What is a tropism?
A growth response of a plant towards or away from a stimulus.
2.What is phototropism?
The growth response of a plant to light.
3.What is gravitropism?
The growth response of a plant to gravity. It is also called geotropism.
4.Which hormone controls phototropism and gravitropism?
Auxin.
5.Where is auxin produced?
At the tips of shoots and roots.
6.What does auxin do in a shoot?
It causes the cells to elongate, so a higher concentration makes that side of the shoot grow faster.
7.Explain how a shoot grows towards light.
Auxin accumulates on the shaded side. Those cells elongate more than the cells on the lit side, so the shoot bends towards the light.
8.Why is growing towards light useful for a plant?
More light reaches the leaves, so the plant can photosynthesise faster.
9.What does auxin do in a root?
It inhibits cell elongation, so a higher concentration makes that side grow more slowly.
10.Explain how a root grows downwards.
Auxin gathers on the lower side of the root. It inhibits growth there, so the upper side grows faster and the root bends downwards.
11.Why is growing downwards useful for a root?
It anchors the plant and reaches water and mineral ions deeper in the soil.
12.Why do a shoot and a root bend in opposite directions to the same hormone?
Auxin promotes elongation in shoot cells but inhibits it in root cells.
13.Give three commercial uses of auxins.
As weed killers, as rooting powders, and for promoting growth in tissue culture.
14.How do auxins work as weed killers?
They cause broad leaved weeds to grow uncontrollably fast so they die, while narrow leaved crops such as grasses are unaffected.
15.What are gibberellins used for?
Ending seed dormancy, promoting flowering, and increasing fruit size.
16.What is ethene used for, and what does it do?
It is a gas that controls cell division and the ripening of fruit. It is used to ripen fruit during transport and storage.
17.Why is ethene useful commercially?
Fruit can be picked and transported unripe, so it is not damaged, then ripened with ethene just before it goes on sale.
18.How would you investigate phototropism?
Grow seedlings in identical conditions but give one group light from one side only, and compare the direction of growth after a few days.
19.Why should seedlings be grown in the dark first for a tropism experiment?
So they have not already responded to light, and any bending must be caused by the light in the experiment.
20.What happens if the tip of a shoot is cut off before an experiment?
No auxin is produced, so the shoot does not bend towards the light and growth is much reduced.
You remember far more by trying to recall an answer than by reading it. Run these as flashcards and the ones you keep getting wrong will come back more often.
Start studying