Slides in this set

Slide 1

Preview of page 1

Plant responses
By Daniella Di-Fonzo…read more

Slide 2

Preview of page 2

· (a); explain why plants need to respond to their environment in terms of
the need to avoid predation and abiotic stress
· (b) define the term tropism;
· (c) explain how plant responses to environmental changes are co-
ordinated by hormones, with reference to responding to changes in light
· (d) evaluate the experimental evidence for the role of auxins in the
control of apical dominance and gibberellin in the control of stem
· (e) outline the role of hormones in leaf loss in deciduous plants;
· (f) describe how plant hormones are used commercially (HSW6a).…read more

Slide 3

Preview of page 3

plants need to respond to their environment
· Plants can increase their chances of survival by responding to the environment e.
· They grow towards light to maximise 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, and climb towards
· Plants are more likely to survive if they can respond to the presence of animals
that might eat them e.g.,
· Whit clover produces toxins so cattle cant eat them. Cattle eat lots of white clover when fields
are overgrazed
· Plants are more likely to survive if they can respond to abiotic factors like
drought or frost e.g.,
· Carrots produce their own antifreeze at low temperatures- the proteins lower the melting
point of water, by binding to ice crystals, preventing more ice crystals growing…read more

Slide 4

Preview of page 4

define the term tropism;
· Tropism is the response of a plant to a stimulus coming from a
particular direction (directional)
· Plants respond to directional stimuli by regulating their growth
· Positive tropism means growing towards the stimulus
· negative tropism means growing away from the stimulus
· An example of tropism is phototropism- 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…read more

Slide 5

Preview of page 5

how plants respond to changes in light direction
· Proteins called phototropins act
as receptors for light
· When they are hit by blue light,
they become phosphorylated (so
the side the light is coming from
becomes phosphorylated
· This brings about the active
transport, by transporter
proteins, of auxin (IAA) to the
shady side of the plant
· The presence of auxin stimulates
cell growth, so where there is
more auxin, there is more growth
· This is a permanent effect…read more

Slide 6

Preview of page 6

Auxins and apical dominance
· The top (terminal/ apical) bud on a plant contains apical meristem, which
contains undifferentiated cells that are constantly dividing. Some of the new
cells grow longer and cause stem elongation
· Auxins stimulate the growth of the apical bud and inhibit the growth of side
shoots- this is apical dominance
· This saves energy and prevents side shoots from the same plant competing
with the shoot tip for light
· Because energy isn't being used to grow side shoots, apical dominance allows
the plant to grow taller, faster, and out compete smaller plants for sunlight
· If you remove the apical bud, then the plants wont produce auxins and side
shoots will start growing by cell division and cell elongation
· Auxins become less concentrated as they move away from the apical bud, so
the bottom of a tall plant has low auxin concentration and side shoots will
start to grow near the bottom of it.…read more

Slide 7

Preview of page 7
Preview of page 7

Slide 8

Preview of page 8
Preview of page 8

Slide 9

Preview of page 9
Preview of page 9

Slide 10

Preview of page 10
Preview of page 10


No comments have yet been made

Similar Biology resources:

See all Biology resources »