2.10.3 Response to Stimuli: Plants Flashcards
Plants need to be able to grow in response to certain stimuli, for example. (give 2 examples)
1. plants need to be able to grow in response to light, to ensure their leaves can absorb light for photosynthesis
What is the directional growth responses made by plants in response to light and gravity known as?
tropisms
A response to light is what?
phototropism
A response to gravity is what?
geotropism (or gravitropism)
If the growth is towards the stimulus, the tropism is, what?
positive
If the growth is away from the stimulus the tropism is, what?
negative
As shoots grow upwards, away from gravity and towards the light (so that leaves are able to absorb sunlight), shoots show, what?
show a positive phototropic response and a negative geotropic response
As roots grow downwards into the soil, away from light and towards gravity (in order to anchor the plant and absorb water and minerals from the soil), roots show, what?
a negative phototropic response and a positive geotropic response
Plants produce plant growth regulators (similar to hormones in animals) called, what?
auxins
What do auxins do?
coordinate and control directional growth responses such as phototropisms and geotropisms
Where are auxins produced
in the tips of the shoots and the roots; they diffuse to the cells below the tips and have the following effects
In the shoots, auxins promote, what?
cell elongation (growth); more auxin = more cell elongation = more growth
In the roots, auxins inhibit, what?
cell elongation (growth); more auxin = less cell elongation = less growth
The distribution of auxin in the shoots is affected by, what?
by light and gravity
The distribution of auxin in the roots is primarily affected by, what?
by gravity alone
If a shoot or root is placed on its side, what will auxins do?
auxins will accumulate along the lower side as a result of gravity; so the uppermost side has a lower auxin concentration
In the shoots, what grows faster, the lower side or upper side
the lower side grows faster than upper side (more auxin = more cell elongation), so the shoot grows upwards
In the roots, what grows faster, the lower side or upper side
In the roots, the lower side grows slower than the upper side (as auxin inhibits cell elongation and growth in roots), so the root grows downwards
Unequal distributions of auxin causes what?
unequal growth rates in plant roots and shoots
