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UNIT 5 TOPIC 8: Grey Matter
Nerve Impulses and Neurones
Suggest one neurotransmitter substance that might bind to receptors of cardiac muscle cells in
the SAN (1) noradrenaline, acetylcholine, norepinephrine.

Describe the events that begin the depolarisation of the membrane of a neurone. (2)
First there is *depolarisation of the…

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action potential is less likely to occur. *Pain is not sensed as the impulse stopped before entering the
CNS/ leaving the sensory neurone.

Explain how the structure of the axon cell membrane is related to the conduction of nerve
impulses. (3)
*The phospholipid membrane restricts ion movement so that they…

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to help enable *faster conduction. There is no myelin sheath at the nodes of Ranvier so that
*depolarisation can occur there. At the nodes the impulse will jump from node to node (salutatory
conduction).

Part A is a: SENSORY NEURONE
Part B is a: RELAY NEURONE
Part C is a:…

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The Eye
Suggest why the pupil appears black (1)
*Pigment at back of eye absorbs light/no light is reflected out (from the choroid)

There are two sets of iris muscles, the radial muscles and the circular muscles. They work
antagonistically to alter the size of the pupil. Explain why these…

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Because *lack of visual stimulation during the *critical period limits brain development *due to a lack
of connections *within the visual cortex. *This means that the brain cannot interpret this visual
information correctly. *Mice are also different from humans.
Suggest why this type of treatment for blindness in humans could…

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Suggest why the environment should be kept constant in this investigation. (2)
To * reduce the number of variables/to keep all variables constant and to ensure that *only the
effect of the treatment is measured.

When light reaches a rod cell the voltage across the cell surface membrane can change.…

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Plants




How can the active form of phytochrome (Pfr) be converted back to the inactive form (Pr), other
than by exposing it to far red light? Darkness
Compare plant coordination with hormonal coordination in animals. (4)
*Both involve chemicals that are *transported away from the production site, however the
mechanism…

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*Acts as a control and can be used in *comparison e.g. to show that flowering would not happen
without the cover.
Using your own knowledge of photoreceptors, explain the results of these investigations.
What do they suggest about the control of flowering in cocklebur plants? (4)
*Six hours too short…

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the start of depolarisation, the ions that move into the axon causing the action potential are sodium
ions; when an impulse arrives at a synapse, the ions that enter the pre-synaptic membrane are
calcium ions. Acetylcholine is a chemical which acts as a neurotransmitter. The drug MDMA (ecstasy)
changes behaviour…

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Computed tomography (CT) and functional magnetic resonance imaging (fMRI) are used to
investigate brain structure and function. The CT scans below show two different human brains
with abnormal areas. These areas are indicated by arrows.




Describe how these images could help a doctor to determine appropriate treatment of the
abnormalities.…

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