5. Plant and Animal responses Flashcards
What are the two types of plant response?
Tropisms and Nastic responses
What are the types of tropisms?
Phototropism, Geotropism, Chemotropism, Thigmotropism
What are tropisms?
A directional growth response
The direction of the response is determined by the direction of the external stimulus.
What are nastic responses?
Non-directional responses to external stimuli
What is Phototropism?
Shoots grow towards light.
What is Geotropism?
Roots grow towards the pull of gravity, helps them to take up water.
What is Chemotropism?
Growth dictated by chemicals.
What is Thigmotropism?
Using the support of another solid structure.
What role do hormones play in plant responses?
They coordinate plant responses to environmental stimuli.
They are chemical messengers that are transported to act on target cells or tissue.
They bind to specific receptors on plasma membranes.
What is the role of Cytokinins?
Promotes cell division and expansion
Delay leaf deterioration
Overcome apical dominance
Promote bud growth
What is the role of Abscisic acid?
Inhibits seed germination and growth
Closes stomata when plant is under stress by low water availability.
Inhibits bud growth.
What is the role of Gibberellins?
Promotes seed germination Promotes growth of stems Controls cell elongation Promotes fruit development Aids stomatal opening
What is the role of Ethene?
Promotes fruit ripening
What is the role of Auxins?
Regulate plant growth and control other plant hormones
Inhibits growth of side shoots (Apical dominance)
Inhibits leaf deterioration
What is Apical dominance?
Controlled by auxin which is in the tip of the main shoot.
High concentrations of auxin prevent the development of lateral branches near the apex.
What causes apical dominance?
High auxin levels- High abscisic acid levels- Low cytokinin in lateral buds- Inhibit lateral bud growth.
How is apical dominance overcome?
The tip of the stem is cut off.
Low auxin levels- Low abscisic acid- Higher cytokinin levels in lateral buds- Lateral buds grow.
How do seeds germinate?
When seeds absorb water, the embryo releases gibberellin.
This enables the production of amylase, which can break down starch into glucose
Provides the substrate for respiration, so it grows.
Where in the plant does growth occur?
Growth can only occur in places containing immature cells that are still capable of dividing.
These are meristems.
What are apical meristems?
They are at the tip of the apex of roots and shoots and are responsible for them getting longer.
What are lateral meristems?
They are found in the buds and give rise to shoots.
They form a cylinder near the outside of roots and shoots and help them get wider.
Why do shoots bend towards the light?
Phototropin receptors detect light from one side, causing auxin to be transported to the shaded side.
More auxin causes the cells to elongate more on the shaded side.
How are plant hormones used commercially?
Seedless fruits, Weedkillers, Control fruit ripening, Controls fruit drop, Restrict hedge growth, Preserve cut flowers and vegetables.
