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Mrs W A level Biology > Survival > Flashcards

Flashcards in Survival Deck (23)
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Which stimuli are plant shoots sensitive to and how do they respond?

Plants shoots are sensitive to:

Gravity - negative geotropism or gravitropism

Light - positive phototropism.


Name the plant growth regulator released by the tip of a plant shoot.

IAA or indoleacetic acid


Identify the two tropisms shown by plant roots.

Positive geotropism or gravitropism.

Positive hydrotropism.

(Negative phototropism).


What effect does IAA have on the shoots of plants.

IAA causes cells to elongate in the stem.


What effect does IAA have on cells in the root?

IAA inhibits cell elongation.


What causes the IAA in a shoot to become unevenly distributed.

Light causes IAA to be transported to the shaded side of the shoot.


Why might IAA in roots become unevenly distributed?

Gravity causes IAA to move to the lower surface of the root.


Give 2 differences between taxis and phototropism.

Taxis - whole organism moves
Only happens in animals.

Tropism - growth response.
Only happens in plants.


What is taxis behaviour?

Directional response to a directional stimulus.
Whole organism moves towards or away from the stimulus


What is a kinesis?

Non-directional movement of an animal in response to a non-directional stimulus.
May lead to an increase/decrease in speed or turning frequency


Why do animals show taxis or kinesis behaviour patterns?

They give a survival advantage.


Why is it beneficial for a plant to show positive phototropism.

Allows shoot to grow towards light.
Increases light absorption for photosynthesis.
Greater GPP/biomass/organic material produced.


Maggots often show negative phototaxis. What does this mean ?

Maggots move away from light.


Why is it beneficial for maggots to show negative phototaxis?

Less visible to predators.
Less likely to dehydrate.


What is the movement of a whole organism towards light called?

Positive phototaxis


Define tropism

Growth response of a plant to a directional stimulus


Why do woodlice increase their rate of turning if they exit favourable conditions

To increase probability that they re-enter the favourable conditions


Why do woodlice decrease their rate of turning and move rapidly after detecting unfavourable conditions?

To increase chance that they will pass through the unfavourable conditions and enter a more favourable environment


Give the term used to describe roots growing towards water

Positive hydrotropism


Describe the process of negative phototropism in plant roots.

Cells in the root tip produce IAA
IAA is usually evenly transported down the root
Unidirectional light causes IAA to move to the shaded side
More IAA on shaded side than light side
IAA inhibits cell elongation in roots
Unequal growth causes root to bend away from light


What effect does gravity have on IAA carrier proteins in plant cells.

More IAA protein carriers on the lower side of the cell.
More IAA on lower side
Roots elongation inhibited - root grows downwards
Encourages shoot elongation - shoot grows upwards


Describe the role of H+ ions in cell elongation.

H+ ions are actively transported from cytoplasm into the spaces of the cell wall
Increase in H+ makes conditions more acidic
Increase the plasticity of the cell walls allowing for elongation.


How could a student recognise kinesis in an organisms movement?

1. Turning increases as organism crosses form favourable to unfavourable conditions (return to original favourable environment)
2. If organism moves considerable distance into unfavourable conditions - turning slowly decreases begins to move in long straight lines, sharper turn (lead organism to new environment)