Plant responses to the environment

HideShow resource information
  • Created by: Holly
  • Created on: 04-05-13 12:54
Preview of Plant responses to the environment

First 283 words of the document:

Responding to the environment: Plants
Plants respond to stimuli:
Respond to changes (biotic and abiotic conditions) to increases their chances of survival, by
avoiding stress and avoid being eaten.
Stimuli - Biotic:
Predators that can pose as a threat
Some plants produce toxic substances, e.g. White Clover produce toxic substance to avoid
being eaten by cattle
Stimuli - Abiotic:
Anything that's not living that can pose as a threat e.g drought
e.g Some plants respond to extreme cold by producing their own form of antifreeze.
Tropisms: is a directional growth response in which the direction of the response is
determined by the direction of the external stimuli.
Responses can either be tropic (directional) or nastic (non-directional)
Two forms of tropisms:
1. Positive tropisms- towards stimuli
2. Negative tropisms ­ away from stimulus
4 types of tropisms:
1. Phototropism: shoots grow towards light, enables photosynthesis
2. Geotropism: roots grow towards the pull of gravity (anchors roots in soil and helps
them take up water)
3. Chemotropism: Pollen tubes grow down the style, attracted by chemicals, towards
the ovary where fertilisation takes place
4. Thigmotropism: Shoots of climbing plants (e.g ivy) grow spirally around supports
(when they touch them). This allows them to reach above competitors and obtain
more light.
Nastic responses (non-directional responses to stimuli):
Nyctinastic: associated with diurnal (daily) light and temperature changes
An example of this is flowers opening and closing in response to day length and temperature
Thigmonastic: where the response is the same regardless of the direction of the stimulus

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

The movement is the same once triggered, e.g. closing petals, closing leaves.
An example of this type of response can be seen in the mimosa leaves which close when
touched, giving a sudden movement and giving the plant a wilted appearance
Plants growth regulators/hormones:
Hormones coordinate plant responses to the environment stimuli. They are chemical
messengers, transported away from site of manufacture to target cell/tissue. They bind
to specific receptors which are complementary to them.…read more

Page 3

Preview of page 3

Here's a taster:

Plant Growth:
Cell wall around plants cells limits the cell's ability to divide and expand, because of this
growth can only happen in parts of the plant where immature cells that are capable of
diving-meristem.…read more

Page 4

Preview of page 4

Here's a taster:

Results in root bending away from light into the soil where its dark
Leaf Abscission:
Abscission: The natural detachment of parts of a plant, typically dead leaves and ripe fruit
Usually triggered by the shortening of day length in autumn
Why is it useful?
Helps plants converse water
Avoid frost damage
Avoid fungal infection
Leaves cannot photosynthesise much in winter anyway due to low light levels (not needed).…read more

Page 5

Preview of page 5

Here's a taster:

Experiments of Apical dominance:
1. Hypothesis: a drop in auxin concentration causes the lateral buds to develop
Test 1: apical bud is removed and a paste containing auxins was applied to the cut end of
the shoot
Findings: Both found lateral buds remained dormant
Conclusion: A high concentration of auxin prevents lateral bud growth.
Not enough evidence to support finding, there may be another factor involved...
2.…read more

Page 6

Preview of page 6

Here's a taster:

Increase cell division by stimulating the production of the protein that controls
the cell cycle
3. The internodes of dwarf plants have fewer and shorter cells than tall plants
Mendel's peas and the Le allele:
If a low gibberellin conc was applied to dwarf peas, there was a rapid growth of internodes.
This is because dwarf plants lack the gene for gibberellin production.…read more

Page 7

Preview of page 7

Here's a taster:

Mass-production of plants
Delay leaf abscission…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »