responses in plants and animals Flashcards
how do plants increase their chances of survival by responding to their environemnt
They sense the direction of light and grow towards it to maximise light absorption for photosynthesis.
- They can sense gravity, so their roots and shoots grow in the right direction.
- Climbing plants have a sense of touch, so they can find things to climb up and reach the sunlight
what is tropism
A tropism is the response of a plant to a directional stimulus (a stimulus coming from a p articular direction).
how do plants respond to stimuli
Plants respond to stimuli by regulating their growth.
what is a positive tropism
growth towards the stimulus
what is a negative tropism
growth far away from the stimulus
what is phototropism
Phototropism is the growth of a plant in response to light.
Shoots are positively phototropic and grow towards light.
Roots are negatively phototropic and grow away from light.
what is gravitropism
Gravitropism is the growth of a plant in response to gravity.
Shoots are negatively gravitropic and grow upwards.
Roots are positively gravitropic and grow downwards.
what are responses brought about by
Responses are Brought About by Growth Factors
how do plants respond to directional stimulus
Plants respond to directional stimuli using specific growth factors
— these are hormone-like chemicals that speed up or slow down plant growth.
where are growth factors produced
Growth factors are produced in the growing regions of the plant (e.g. shoot tips, leaves)
and they move to where they’re needed in the other parts of the plant.
what are auxins
Growth factors called auxins stimulate the growth of shoots by cell elongation
— this is where cell walls become loose and stretchy, so the cells get longer.
High concentrations of auxins inhibit growth in roots though.
what is IAA
In d ole ace tic acid (IAA) is an important auxin that’s produced in the tips of shoots in flowering plants
what is IAA’s purpose
IA A is moved around the plant to control tropisms — it moves by diffusion and
active transport over short distances, and via the phloem over long distances
This results in different parts of the plant having different concentrations of IAA.
The uneven distribution of IA A means there’s uneven growth of the plant, e.g:
what does IAA do in phototropism
Phototropism — IA A moves
to the more shaded parts
of the shoots and roots,
so there’s uneven growth
what does IAA do in gravitropism
Gravitropism — IAA moves to
the underside of shoots and
roots, so there’s uneven growth.
