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Summary Organisms respond to changes in their environment notes

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Notes and answers based around key questions and mark points for the mark scheme Used these notes to receive an A* as they are tailored to the mark points

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  • September 4, 2022
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  • 2022/2023
  • Summary
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Sunday, 4 September y

ORGANISMS RESPOND TO CHANGES IN THEIR ENVI-
RONMENTS
Response to Stimuli
Plants

Tropism

- a movement in response to a directional stimulus
Shoots responding to light

- IAA produced in the meristem of the plant shoot
- IAA moves to shaded side of the shoot in response to light
- Promotes cell elongation
- Elongation is facilitated by allowing water into the cell by osmosis
- this is a positive phototropism

Starch grains in roots

- sink to the bottom due to gravity as they are heavy
Why would scientists spray solutions on the bottom of leaves

- thicker cuticle on the top and no stomata
- so there is a longer diffusion distance
Types of movement

Taxis = a directional response to a stimulus (away / towards)

Kinesis = a non-directional response (response depends on intensity of the stimulus)

Reflexes

Simple reflex

Advantages

- Rapid responce
- Allows us to escape from predators
- is an instinct (does not need to be learnt)
Resting potential

How is it maintained when no pressure is applied

1

, Sunday, 4 September y
- sodium potassium pump (3:2 - more sodium pumped out than potassium moves in)
- the cell membrane of the sensory neurone is more permeable to potassium ions than
sodium
- sodium ions are actively transported out while potassium ions are pumped in
Pacinian corpuscle

Structure

- found at the end of a sensory neurone
- Covered in layers of connective tissue
- Separated by viscous gel (contains sodium ions)
- the membrane layers contain stretch mediated sodium ion channels

How are they involved in establishing a generator potential

- when pressure is applied it deforms and the stretch mediated sodium ion channels are
stretched and open
- allows sodium ions to diffuse into the axon
- a greater pressure causes more channels to open
- Causes depolarisation of the
mem- brane - causing a gener-
ator po- tential

Eye




Rod cells - sensitive to light - rhodopsin



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