Plant Responses Flashcards
What are the differences between plant and animal hormones?
Animal:
Hormones secreted by glands
Carried in the blood stream across the body
Target specific cells by binding to receptors
Plant:
Produced in unspecialised cells anywhere in a plant
Diffuse from cell to cell so a local effect
Enter cells and can have many different effects
A single plant hormone can have multiple effects what is it called when 2 different hormones work together or oppose each other?
- synergistic effect
- antagonistic effect
What is a positive growth response?
Growing towards the stimulus
What different kind of tropism can you get?
Phototropism
Gravitropism
Hydrotropism
What does tropism mean?
A directional growth response
Describe phototropism,include the hormone and response mechanism
- a shoot tip is illuminated asymmetrically
- this stimulus causes auxin to move into the darker side
- auxin activates H+ pumps when bound to surface proteins
- this lowers the pH in the cell wall activated an enzyme that breaks bonds between microfibrils
- enabling the cell wall to stretch under turgor pressure
General idea of phototropism:
Light causes auxin to distribute unevenly
Cells away from the light elongate more so the shoot bends towards the light
What does the plant hormone gibberellin do?
- stimulates growth in stems between nodes, acts in synergy with auxin
- stimulate fruit development
- break seed dormancy by activating amylase which mobilises food store
What are some commercial uses of gibberellin?
- useful for sugar cane as a longer steam means more sugar
- weed killer, as stem grows too long the weeds fall and die
What do cytokinins do?
- oppose the action of auxin in apical dominance
- promote lateral bud growth
- promote cell division in meristems (cytokinesis)
Cell differentiation in plants depends on the conc of plant hormones in the area; if the conc of auxin is higher than cytokinin what do the cells become?
Auxin promotes the production of roots so root cells
What do the plant cells differentiate into if the conc of cytokinin is higher or equal to auxin conc
Cytokinin promotes the production of shoot cells
If cytokinin is greater then shoot cells
If conc is equal then a undifferentiated mass (callus)
What is apical dominance?
The control of growth via apical and lateral buds
What relationship do auxin and cytokinin have with lateral bud growth?
Antagonistic
Auxin inhibits lateral bud growth and cytokinin stimulates it
Explain why trees have a Christmas tree shape
The apical bud produces auxin, which passes down the phloem and inhibits the growth of lateral buds
Further down the stem the auxin concentration is lower so there is more growth in lateral buds
