Chapter 12 (Chemical coordination in plants) Flashcards
Why are most plants’ responses to stimuli slow?
Because their response normally involves a change in their rate of growth.
How does a plant respond to stimuli?
By increasing growth near the tip of its shoot or roots.
What is tropism?
Growth response of a plant to a directional stimulus.
What is positive tropism and negative tropism?
- Positive tropism - Growth response of a plant is toward the direction of stimulus
- Negative tropism - Growth response of a plant is away from the direction of stimulus
What is phototropism and geotropism?
- Phototropism - growth responses to light from one direction.
- Geotropism - growth response to the direction of gravity.
Why does a shoot grows toward the light?
To ensure that the leaves, held out at and angle to the stem, will receive the maximum amount of sunlight for photosynthesis.
When does the shoot show negative geotropism?
In darkness or uniform light
What are benefits of positive geotropism of plant’s roots?
- It can reach to and absorb water and mineral ions
- It provide anchorage to plant
What are shoot and root response to the stimulus?
- Shoot - Positive phototropism, Negative geotropism
- Root - Negative phototropism, Positive geotropism
What is unidirectional light and uniform light?
- Unidirectional light - light from one direction
- Uniform light - light shown evenly from all directions
What is coleoptile?
Coleoptile is a protective sheath that covers the first leaves of a cereal seedling.
Why coleoptiles are often used to investigate tropisms?
They have simple structure and are easy to grow
Why the stimulus for growth pass through gelatin and not mica?
Since stimulus is a chemical that is soluble in water.
- It will pass through gelatin as it absorb water soluble chemicals
- It won’t pass through mica since it is impermeable to water
How does hormone cause bending?
By stimulating growth on the side of the coleoptile furthest from the light.
What happen to hormone, if the shoot is in the dark or in uniform light?
The hormone diffuses at equal rates on each side of the shoot.
