Question
Explain how neurons develop in embryonic tissue to allow communication.
Answer/Explanation
Answer:
a. axon develops from (immature) neuron;
b. chemical stimuli cause (direction of) growth;
c. some neurons/axons migrate/extend to other areas;
d. dendrites develop;
e. (multiple) synapses form between neurons;
f. synapses are strengthened with use;
g. neural pruning causes unused synapses to be eliminated;
h. neural plasticity allows new connections/synapses;
Question
The graph shows the change in the membrane potential of an axon during an action potential.
(a) State the approximate value of the membrane potential at X.
(b) Y is the threshold potential. State what happens when the threshold potential is reached.
(c) Describe the movements in ions that occur during time t.
(d) Explain how a nerve impulse is passed on to other neurons.
Answer/Explanation
Ans:
(a) 0 mV; (accept answers in the range of –10 mV to +10 mV) (Units required)
(b)
sodium channels (start to) open
OR
depolarization/axon begins to depolarize
OR
action potential occurs;
(c) Na+/sodium ions diffuse into the axon (in the first part/half of t);
K+ /potassium ions diffuse out of the axon (in the second half/part of t)
(d)
a. impulses pass to another neuron at a synapse/across synaptic gap/cleft;
b. (depolarization causes) Ca2+/calcium ions to diffuse into the (presynaptic) neuron/axon;
c. depolarization (of presynaptic neuron) causes release of a neurotransmitter
OR
neurotransmitters diffuse across the synapse;
d. (neurotransmitters) bind to receptors on postsynaptic neuron/membrane;
e. (if the threshold potential is reached) an action potential occurs/sodium gates open (in the
postsynaptic neuron);
Question
Draw a labelled diagram of the human heart showing the attached blood vessels.
Describe the action of the heart in pumping blood.
Nerves connecting the brain and heart contain neurons that control heart rate. Explain how a nerve message passes from one neuron to another neuron.
Answer/Explanation
Markscheme
Remember, up to TWO “quality of construction” marks per essay.
NB: Drawings must be correctly proportioned and clearly drawn showing connections between structures. The drawing may show the heart without contraction or in any stage of contraction. Award [1] for any correctly labelled part that has been drawn to the stated standards.
a. atria/right atrium/left atrium – shown above the ventricles and must not be bigger than ventricles;
b. ventricle/left ventricle/right ventricle – shown below the atria, must have thicker walls than atria;
c. vena cava/superior vena cave/inferior vena cava – connected to right atrium;
d. pulmonary artery – shown from right ventricle (to lungs);
e. pulmonary vein(s) – shown (from lungs) to left atrium;
f. aorta – shown as large artery from left ventricle out of heart;
g. AV valves/atrioventricular valves / mitral/bicuspid and tricuspid – named correctly and shown between both atria and ventricles and labelled at least on one side;
h. semilunar valves – shown in aorta/pulmonary artery;
Valves need to open in correct direction.
Remember, up to TWO “quality of construction” marks per essay.
a. (both) atria collect blood (from veins);
b. sinoatrial/SA node sends impulses to muscle/fibres initiating contraction;
c. blood is pushed to ventricles by contraction of atria/atrial systole;
d. AV (atrioventricular) valves are open (as atria contract);
e. semilunar valves are closed so that ventricles fill with blood;
f. ventricles contract / ventricular systole;
g. AV (atrioventricular) valves close (and preventing backflow);
h. blood is pushed out through the semilunar valves/into pulmonary artery and aorta;
i. when ventricles relax/diastole, semilunar valves close preventing backflow of blood;
Do not accept the description of blood flow without a clear action.
Do not accept general statements such as systole = heart contraction and diastole = heart relaxation.
[4 max] if suggests that left and right sides are contracting at different times or simultaneous contraction not indicated.
Remember, up to TWO “quality of construction” marks per essay.
a. nerve impulse reaches the end of the presynaptic neuron;
b. (depolarization causes) calcium channels in membrane (to) open;
c. calcium diffuses into the presynaptic neuron;
d. vesicles of/containing neurotransmitter move to and fuse with presynaptic membrane;
e. (neurotransmitter) released (by exocytosis) into synaptic space/cleft;
f. (neurotransmitter) diffuses across the space/synapse;
g. (neurotransmitter) attaches to receptors on postsynaptic neuron;
h. receptors cause ion channels to open and sodium diffuses into the postsynaptic neuron;
i. the postsynaptic neuron membrane is depolarized;
j. (depolarization) causes a new action potential;
k. (neurotransmitter) on postsynaptic membrane is broken down;
l. (neurotransmitter) is reabsorbed into the presynaptic neuron;