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Answering questions correctly makes all the difference. Here are some model questions and answers collected from previous papers and their mark schemes.

4.1 Sense Organs

The Eye

(Given with graph)

Describe and explain how the distribution of the rod cells and cone cells relates to variation in sensitivity and visual acuity in different parts of the retina

(BY04 June 96 Section B, 6 marks)

• Rods are more numerous than cones at the edges.
• Rods are very sensitive but with low acuity.
• The blind spot has no rods or cones.
• This is not sensitive and does not register acuity, as this is where the optic nerve leaves.
• The fovea is the peak of cone cells.
• This has very high acuity. 

Describe how a rod cell converts light energy into a nerve impulse

(BY04 June 96 Section B, 3 marks)

• Rod cells contain rhodopsin.
• When a photon of light falls on it, it is bleached/broken down.
• This generates an action potential (by depolarising the membrane) 

Describe how cone cells allow us to see colours

(BY04 June 96 Section B, 3 marks)

• There are three types of cells (trichromatic theory
• These detect different wavelengths of light,
• So different colours of light stimulate different cells.

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4.2 Synapses

Describe how information is transmitted across a neuromuscular junction between the neurone and the muscle

(Byo4 Feb 96 Section B, 5 marks)

• A nerve impulse reaches the motor neurone’s end plate, causing the membrane to become more permeable to Ca²⁺ ions
• Influx of Ca²⁺ ions causes synaptic vesicles to fuse with end plate
• Neurotransmitter (acetylcholine) is released
• This binds to receptor sites on sarcolemma, causing an influx of Ca+ ions
• Which switch on the calcium switch, causing muscle contraction

Explain one way in which drugs might affect this transmission of information

(Byo4 Feb 96 Section B, 2 marks)

• Block/mimic neurotransmitter
• By binding to receptor site         

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4.3 Muscle

What causes the banding pattern seen in a muscle fibril?

(Byo4 Feb 97 Section B, 3 marks)

• Myosin is a thick filament and forms the dark regions
• It is surrounded by thin actin filaments which form the lighter regions
• Partial overlapping results in a band pattern 

How and why will the banding pattern change when the muscle fibril contracts?

(Byo4 Feb 97 Section B, 4 marks)

• Myosin cross-bridges use ATP to move
• Causing actin filaments to slide over it
• So the light regions shorten
• And the dark regions stay the same length

Describe the mechanism which results in the muscle contracting.

(Byo4 Feb 96 Section B, 5 marks)

• Myosin (thick) filaments surrounded by actin (thin)
• Myosin cross-bridges use ATP to move
• Causing actin filaments to slide over it
• When the Ca²⁺ switches are activated by calcium

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4.5 & 4.6 Behaviour

In the examples given in (a), (b), and (c), identify the types of behaviour described in italics. Explain the reason for your answers.

(Byo4 Feb 96 Section B, 12 marks)

(a) Flies enter the base of traps and crawl up to the undyed area at the top where they may be killed by fast-acting insecticide. (3 marks)

• Taxis
• Moving directly towards a stimulus: light at top of trap (or away from gravity)
• Positive phototaxis (or negative geotaxis)

(b)Young toads come out of burrows when water is noisily sprinkled on soil, even if the soil is kept try by a plastic sheet (6 marks)

• Innate response
• Young all do same so can’t be learned
• Involuntary
• Sign stimulus:
• Sound of rain

(c) When aphids encounter a chemical produced naturally by aphids to insecticide sprays they disperse rapidly from the lettuce heart to its outer leaves (3 marks)

• Pheromone
• Chemical produced by one organism which influences behaviour of others
• Chemotaxis

Describe the main features of innate behaviour

(Byo4 Feb 97 Section B, 4 marks)

• Genetically inherited
• Does not make enormous demands on higher centres of nervous system
• Ensures ‘correct’ behaviour in young from birth
• Same in all members of a species

Describe the main features of imprinting

(Byo4 Feb 97 Section B, 4 marks)

• Simple and specialised form of learning
• Occurs during receptive period
• Resistant to change later
• Based in CNS
• Involves young identifying with another organism (normally first thing it sees moving)
• Enables skill acquisition from parent in a natural situation

Describe the main features of habituation

(BY04 June 96 Section B, 4 marks)

• Involves loss of response
• Caused by continuous repetition of stimulus
• No association with reward or punishment
• Important to young especially
• Based in CNS
• Fairly permanent

Explain how a rat learns to obtain a food pellet when placed in a Skinner box

(BY04 June 96 Section B, 4 marks)

• Initially rat presses lever accidentally
• Gets a reward (food)
• Associates action with reward
• So learns to pres lever

With the help of an example, describe what is meant by classical conditioning

(BY04 June 96 Section B, 4 marks)

• (Based on work of Pavlov and his dogs)
• Animal is presented with two stimuli at once
• Has an innate response to one stimulus
• Learns to associate the two stimulus
• Eventually the second stimulus alone brings the same response as the original