response to stimuli: plants Flashcards
2.83
why do plants need to be able to grow in response to light?
to ensure their leaves can absorb light for photosynthesis
why do plants need to be able to grow in response to gravity?
to ensure that shoots grow upwards and roots grow downwards
what are tropisms?
the directional growth responses made by plants in response to light and gravity
if the growth is towards the stimulus what is the tropism?
positive
if the growth is away from the stimulus what is the tropism?
negative
what is growth towards the light?
a positive phototropism
what are phototropisms?
growth responses to light from one direction
what hormone controls the positive phototropism?
auxin
where is auxin found?
in the tip of the shoots and the roots
what is a response to gravity?
geotropism
why do roots grow downwards into the soil?
- to anchor the plant
- absorb water and minerals from the soil
what does auxin do?
coordinates and controls directional growth responses such as phototropisms and geotropisms
what does auxin do in the shoots?
promotes cell elongation
what does auxin do in the roots?
inhibits cell elongation
what is the distribution of auxin in the shoots affected by?
light and gravity
what is the distribution of auxin in the roots affected by?
primarily affected by gravity alone
what does the unequal distributions of auxin cause?
unequal growth rates in plant roots and shoots
what side does auxin accumulate on?
the dark side
what happens if the shoot is growing in uniform light?
- auxin distributed evenly on each side of the shoot
- mitosis is even on each side- shoot grows upwards
what happens if the shoot is growing in unidirectional light?
- auxin diffuses and accumulates on the dark side
- faster elongation
- more mitosis- bends towards the sunlight
compare unidirectional and uniform light?
- unidirectional- stimulus is on one side
- uniform- light is evenly distributed
what is the radicle?
the root
what is the plumule?
the shoot
what happens to the plant if light shines all around the tip?
auxin is distributed evenly throughout and the cells in the shoot grow at the same rate
