Responses in Plants Flashcards
How do plants respond to stimuli?
Tropisms
What is a tropism?
The response of a plant to a directional stimulus (a stimulus coming from a particular direction).
How do plants respond to stimuli using tropisms?
By regulating their growth
What can tropisms be?
- Positive
* Negative
What is a positive tropism?
A growth towards the stimulus.
What is a negative tropism?
A growth away from the stimulus.
What are the types of tropism?
- Phototropism
* Gravitropism
What is a phototropism?
A growth in response to light.
How do plants do phototropisms?
- Shoots are positively phototropic (and grow towards light).
- Roots are negatively phototropic (and grow away from light).
What is a gravitropism?
A growth in response to gravity.
How do plants do gravitropisms?
- Shoots are negatively phototropic (and grow upwards, against gravity).
- Roots are positively phototropic (and grow downwards, with gravity).
How do plants do these tropisms?
Using specific growth factors.
What are growth factors?
Hormone-like chemicals that speed up or slow down plant growth.
Where are growth factors produced?
In the growing regions of the plants (e.g. shoots and roots).
What do growth factors do in response to stimuli?
They move to where they are needed in the plant.
What is an example of a growth factor used in plants?
Auxins
Where are auxins produced?
In the tips of shoots.
What do auxins do?
They diffuse backwards from the tips of shoots to stimulate the cell just behind the tips to elongate.
How do cells elongate because of auxin?
The cell walls become loose and stretchy, so the cell gets longer.
What happens if the tip of a shoot is removed?
No auxin will be available so the shoot stops growing.
What does auxin do (not just in shoots)?
It stimulates the growth in shoots, but high concentrations inhibit the growth in roots.
What is an example of an auxin?
Indoleacetic acid (IAA)
Where is IAA produced?
In the tips of shoots and roots in flowering plants.
What does IAA do?
It moves around the plant to control tropisms.
How does IAA move over short distances?
Via diffusion and active transport over short distances.
How does IAA move over long distances?
Via the phloem over long distances.
What does IAA moving over short and long distances via different methods mean?
That different parts of the plant have different concentrations of IAA, this uneven distribution causes uneven growth of the plant.
How does IAA aid phototropisms?
- IAA concentration increases on the shaded side of the shoot, so cells elongate and bend towards the other side (towards the light).
- IAA concentration increases on the shaded side of the root, growth is inhibited so the roots bend away from the light.
How does IAA aid gravitropisms?
- IAA concentration increases on the lower side of the shoot, so cells elongate upwards (away from gravity).
- IAA concentration increases on the lower side of the root, growth is inhibited so the roots grow downwards (with gravity).
How does IAA cause uneven growth?
- IAA moves to the more shaded side of the shoots and roots.
* IAA moves to the lower side of the shoots and roots.
If IAA (or any auxin) is on the right hand side of the tip of the shoot in the dark, what happens?
Cells elongate on that side causing the shoot to grow towards the left.
If IAA (or any auxin) is on the right hand side of the tip of the shoot in the light, what happens?
IAA will accumulate on the shaded side no matter where the IAA is placed initially, so cells will elongate on the shaded side, causing the shoot to grow towards the light.
