TOPIC 6 - 3.6.1

Question 1

Describe how a Pacinian corpuscle produces a generator potential when stimulated (3marks)

Answer 1

1.(Increased pressure) deforms / changes stretch-mediated sodium (ion) channel;
2.(Sodium channels open and) sodium ions flow in;
Accept Na+
3.Depolarisation (leading to generator potential)

Question 2

When a image is focused on the fovea, the person sees the object in colour. Explain why. (3)

Answer 2

Colour detected by cone cells;Fovea contains (only / mainly) cone cells;Three types of cone / cells described / each sensitive to differentwavelength / to red or green or blue;

Question 3

Explain the importance of reflex actions. (4)

Answer 3

1. automatic (adjustments to changes in environment) / involuntary;
2. reducing / avoiding damage to tissues / prevents injury / named injury e.g. burning;
3. role in homeostasis / example;
4. posture / balance;
5. finding / obtaining food / mate / suitable conditions;
6. escape from predators;

Question 4

Some people are completely colour blind. This is because they have no cone cells. People with complete colour blindness have difficulty in seeing detail in bright daylight. Suggest why. (5)

Answer 4

Only rods functional;
Rhodopsin bleached/broken down by bright light;
Slow/little resynthesis of rhodopsin/pigment;
No (light sensitive) cells in fovea where detailed vision occurs;
No detail/acuity as several rods connected to one (bipolar) neurone / each
cone cell connected to one (bipolar) neurone;

Question 5

Explain how a rise in blood pressure results in a decrease in the rate of heartbeat. (5)

Answer 5

1. pressure receptors / baroreceptors / stretch receptors in aorta / carotid arteries / carotid sinus; (reject carotid body)
2. send impulses to cardiovascular centre / medulla / cardio-inhibitory centre;
   (reject signals / messages / electronic)
3. impulses via parasympathetic nerves / vagus nerve
4. to SAN;
5. release of ACh / inhibits SAN / decreases impulses from SAN;
6. decreases impulses to AVN / decreased stimulation of AVN / decreases impulses from AVN;

Question 6

A woman takes moderate exercise. Explain what causes her heart rate to increase while she exercises (5)

Answer 6

1. rate of respiration increases (in muscle cells);
2. carbon dioxide concentration increases / pH falls / H+ increases / acidity increases;
   3.chemoreceptors in aortic / carotid bodies / medulla (accept reference to aorta / carotid arteries not sinus);
3. (more impulses to) medulla
4. increased frequency of impulses
5. along sympathetic pathway to sinoatrial node / SAN (not pacemaker);

Question 7

The heart controls and coordinates the regular contraction of the atria and ventricles.
Describe how. (5)

Answer 7

1. SAN → AVN → bundle of His / Purkyne fibres;
2. Impulses / electrical activity (over atria);
3. Atria contract;
4. Non-conducting tissue (between atria and ventricles);
5. Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract;
   6.Ventricles contract from apex upwards;