TOPIC 6 EXAM QUESTIONS 6.1-6.3 Flashcards
Give two safety precautions that should be followed when dissecting a
heart. (1)
Use a sharp scalpel/scissors
Wash hands/wear gloves
Disinfect bench/equipment
Cover any cuts
Cut away from self/others/on a hard surface
Safe disposal
Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process. (4)
- Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall
in pH
OR
Baro / pressure receptors detect rise in blood pressure; - Send impulses to cardiac centre / medulla;
- More impulses to SAN;
- By sympathetic (nervous system for chemoreceptors / CO2)
OR
By parasympathetic (nervous system for baro / pressure
receptors / blood pressure);
When the heart beats, both ventricles contract at the same time.
Explain how this is coordinated in the heart after initiation of the heartbeat
by the SAN. (2)
- Electrical activity only through Bundle of His / AVN;
- Wave of electrical activity passes over / through both ventricles at the
same time;
The fovea of the eye of an eagle has a high density of cones. An eagle
focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer. (3)
- High (visual) acuity;
- (Each) cone is connected to a single neurone;
Accept no retinal convergence.
Accept ‘bipolar/nerve cell’ for neurone. - (Cones send) separate (sets of) impulses to brain;
The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night.
Do not refer to rhodopsin in your answer (3)
- High (visual) sensitivity;
Accept retinal convergence. - Several rods connected to a single neurone;
Accept ‘bipolar/nerve cell’ for neurone - Enough (neuro)transmitter to reach/overcome threshold
Explain how a resting potential is maintained across the axon membrane in
a neurone. (3)
Higher concentration of potassium ions inside and higher
concentration of sodium ions outside (the neurone)
OR
potassium ions diffuse out
OR
sodium ions diffuse in;
Accept ‘more’ for ‘higher concentration’.
Accept ‘sodium ions can’t diffuse in (due to
alternative explanation).
2. (Membrane) more permeable to potassium ions (leaving
than sodium ions entering)
OR
(Membrane) less permeable to sodium ions (entering
than potassium ions leaving);
Accept for ‘less permeable to sodium ions’ is
‘impermeable to sodium ions’ or ‘sodium
gates/channels are closed’ (alternative
explanation).
3. Sodium ions (actively) transported out and potassium ions in;
Explain why the speed of transmission of impulses is faster along a
myelinated axon than along a non-myelinated axon.
(3)
- Myelination provides (electrical) insulation;
Reject thermal insulation.
Accept description of (electrical) insulation. - (In myelinated) saltatory (conduction)
OR
(In myelinated) depolarisation at nodes (of Ranvier); - In non-myelinated depolarisation occurs along whole/length (of axon);
Accept action potentials for depolarisation
A scientist investigated the effect of inhibitors on neurones. She added a
respiratory inhibitor to a neurone. The resting potential of the neurone
changed from –70 mV to 0 mV.
Explain why.
(3)
- No/less ATP produced;
- No/less active transport
OR
Sodium/potassium pump inhibited;
Accept Na+ not/fewer moved out and K+ not/fewer
moved in. - Electrochemical gradient not maintained
OR
(Facilitated) diffusion of ions causes change to 0 mV
OR
(Results in) same concentration of (sodium and
potassium) ions (either side of membrane)
OR
No net movement of (sodium and potassium) ions;
Describe the sequence of events involved in transmission across a cholinergic
synapse.
Do not include details on the breakdown of acetylcholine in your answer. (5)
- Depolarisation of presynaptic membrane;
Accept action potential for depolarisation. - Calcium channels open and calcium ions enter (synaptic knob);
Accept Ca2+. - (Calcium ions cause) synaptic vesicles move to/fuse with
presynaptic membrane and release
acetylcholine/neurotransmitter;
Accept abbreviations for acetylcholine as term is in
the question. - Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
Accept abbreviations for acetylcholine as term is in
the question. - (Acetylcholine attaches) to receptors on the postsynaptic membrane;
- Sodium ions enter (postsynaptic neurone) leading to depolarisation;
GABA is a neurotransmitter released in some inhibitory synapses in the
brain. GABA causes negatively charged chloride ions to enter postsynaptic
neurones.
Explain how this inhibits postsynaptic neurones. (3)
- (Inside of postsynaptic) neurone becomes more
negative/hyperpolarisation/inhibitory postsynaptic potential;
Ignore K+
Accept -75mV or any value below this as equivalent
to more negative
Accept ‘decrease in charge’ - More sodium ions required (to reach threshold)
OR
Not enough sodium ions enter (to reach threshold);
Accept Na+ for sodium ions - For depolarisation/action potential;
When a nerve impulse arrives at a synapse, it causes the release of
neurotransmitter from vesicles in the presynaptic knob.
Describe how (3)
) 1. (Nerve impulse / depolarisation of membrane) causes Ca 2+ channel
(proteins) to open;
2. Ca 2+ enter by (facilitated) diffusion;
3. Causes (synaptic) vesicles to fuse with (presynaptic)
membrane;
Explain how a decrease in the concentration of calcium ions within muscle
tissues could cause a decrease in the force of muscle contraction. (3)
- (Less/No) tropomyosin moved from binding site
OR
Shape of tropomyosin not changed so binding site not
exposed/available;
Ignore troponin.
Reject active site only once. - (Fewer/No) actinomyosin bridges formed;
Accept actin and myosin do not bind.
Reject active site only once. - Myosin head does not move
OR
Myosin does not pull actin (filaments)
OR
(Less/No) ATP (hydrol)ase (activation);
Reject ATP synthase.
In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production
of ATP by anaerobic respiration. (2)
- Regenerates/produces NAD
OR
oxidises reduced NAD;
Reject NADP and any reference to FAD.
Accept descriptions of oxidation e.g. loss of hydrogen. - (So) glycolysis continues;
The image shows glycogen granules present in skeletal muscle.
Explain their role in skeletal muscle.
(2)
- As a store of glucose
Ignore provide energy
OR
To be hydrolysed to glucose; - For respiration / to provide ATP;
During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in
pH leads to a reduction in the ability of calcium ions to stimulate muscle
contraction.
Suggest how. (3)
- Low pH changes shape of calcium ion receptors
Do not accept tropomyosin does not move - Fewer calcium ions bind to tropomyosin;
Accept troponin - Fewer tropomyosin molecules move away;
- Fewer binding sites on actin revealed;
- Fewer cross-bridges can form
OR
Fewer myosin heads can bind
Describe the roles of calcium ions and ATP in the contraction of a
myofibril. (5)
- Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
- (Calcium ions) cause movement of tropomyosin (on actin);
- (This movement causes) exposure of the binding sites on the
actin; - Myosin heads attach to binding sites on actin;
- Hydrolysis of ATP (on myosin heads) causes myosin heads to
bend; - (Bending) pulling actin molecules;
- Attachment of a new ATP molecule to each myosin head
causes myosin heads to detach (from actin sites).
What is the role of ATP in myofibril contraction? (2)
- (Reaction with ATP) breaks/allows binding of myosin to actin/
actinomyosin bridge; - Provides energy to move myosin head;
- Credit ‘breaks’ or ‘allows’ binding to actin
(because cyclical) - Allow in context of ‘power stroke’ or ‘re-cocking’
(because cyclical) - Ignore contraction on its own
