Coordination and Response (In Plants). Flashcards
Growth responses in plants are called tropisms. What are the growth responses?
Growth towards a stimulus is said to be a positive response and growth away from a stimulus is a negative response.
What are the two important stimuli for plants?
Two important stimuli for plants are light (phototropism) and gravity (gravitropism).
Define phototropism.
A response in which part of a plant grows towards or away from the direction from which light is coming.
Define gravitropism.
A response in which part of a plant grows towards or away from gravity.
What parts of a plant are positively phototropic and what parts are negatively phototropic?
Shoots normally grow towards light so they are positively phototropic and roots grow away from light so they are negatively phototropic.
What parts of a plant are positively gravitropic and what parts are negatively gravitropic?
Shoots generally grow away from the pull of gravity, so they are negatively gravitropic and roots generally grow towards the pull of gravity, so they are positively gravitropic.
Why must shoots grow upwards?
Shoots must grow upwards, away from gravity and towards the light so that the leaves absorb more sunlight for better photosynthesis.
Why must flowers grow upwards?
Flowers need to be held in the air, where insects, birds, or the wind can pollinate them.
Why must roots grow downwards?
Roots need to grow downwards, into the soil in order to anchor the plant in the soil and absorb water and minerals from between the soil particles.
What is auxin?
A plant hormone in the tips of shoots, which cause cells to elongate.
Explain the role of auxin in controlling the shoot growth:
- Auxin is made in the shoot tip.
- Auxin diffuses through the plant from the shoot tip.
- Auxin is unequally distributed in response to light and gravity.
- Auxin stimulates cell elongation.
How does an auxin control positive phototropism in a shoot?
Auxin concentrates on the shady side, this causes the cells on he shady side to elongate faster than cells on the light side, so the shoot grows towards the light.
