past paper

Question 1

An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries.

Answer 1

-muscle contracts
-ateriole narrows and vessel constricts

Question 2

A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why.

Answer 2

short diffusion pathway

Question 3

Blood flow in capillaries is slow. Give the advantage of this.

Answer 3

more time for diffusion of substances

Question 4

Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a swollen abdomen due to a build up of tissue fluid. Explain why a lack of protein in the blood causes a build up of tissue fluid.

Answer 4

-water potential is higher in the capillary
-less/no water removed
-by osmosis

Question 5

In which part of the brain is the cardiovascular centre located?

Answer 5

the medulla

Question 6

What would be the effect on heart rate of stimulating neurone B?

Answer 6

increase

Question 7

Describe how neurone C is involved in slowing down the heart rate.

Answer 7

-the Cardioinhibitory centre sends more impulses (along parasympathetic neurone to the SAN);
-acetylcholine is released;
-inhibiting the SAN;

Question 8

Describe how an impulse reaches the base of the ventricles of the heart from the sinoatrial node.

Answer 8

-it spreads through the atria / right atrium / through cardiac muscle;
-to the atrioventricular node;
-then through conduction fibres / bundle of His/Purkyne fibres);

Question 9

Describe three features, visible in the diagram, which show that the myofibril is contracted.

Answer 9

-H band not visible
-I band not visible
-A band occupies nearly all sarcomere
-Large zone of thick-thin overlap;

Question 10

Explain the role of calcium ions and ATP in bringing about contraction of a muscle fibre.

Answer 10

Calcium ions Bind to tropomyosin and removes it from actin so it reveal myosin binding sites;

ATP provides energy for the formation and breakdown of cross bridges.

Question 11

An action potential is generated at the cell body of the motor neurone.
Explain how this action potential passes along the motor neurone to the neuromuscular junction.

Answer 11

-Depolarisation of the axon membrane establishes local currents
-which opens Na+ channels of adjoining region
-adjoining region depolarises
-this process is repeated along the axon and impulses move by saltatory conduction

Question 12

Part A contains a large number of mitochondria.
Suggest how a large number of mitochondria help the sperm cell to function?

Answer 12

-mitrochondria is where aerobic respiration occurs
-which produces ATP which releases small pockets of energy

Question 13

Part B is the acrosome.Describe the function of the acrosome in fertilisation.

Answer 13

-contains enzymes
-which allows the sperm to penetrate egg

Question 14

How does the use of this type of contraceptive pill prevent a woman becoming pregnant?

Answer 14

-starts LH production
-stimulating ovulation

Question 15

Explain the role of the loop of Henle in the absorption of water from the filtrate.

Answer 15

-in the asending limb sodium ions are actively removed
-ascending limb is impermeable to water
-in descending limb sodium ions diffuse in
-low water potential in the medulla/tissue fluid
-the deeper into the medulla, the lower the water potential in the medulla/tissue fluid
-water leaves collecting duct by osmosis

Question 16

Explain the role of ADH in the production of concentrated urine.

Answer 16

-when the water potential of the blood too low
-detected by receptors in the hypothalamus
-pituitary gland secretes more ADH
-ADH increases the permeability of aquaporins in the collecting duct
-more water is reabsorbed
-by osmosis down the water potential gradient

Question 17

Describe and explain what happens to the shape of the diaphragm between times A and B.

Answer 17

moves down as Diaphragm/muscle contracts;

Question 18

The person’s pulmonary ventilation changed between times C and D.
Describe how the graph shows that the pulmonary ventilation changed.

Answer 18

-Pulmonary ventilation = tidal volume × breathing rate;
-Breathing rate increases per min (between C and D) as peaks get closer
-Tidal volume/volume of air (inhaled) per breath increases between C and D

Question 19

The way in which the cone cells are connected to the brain allows high visual acuity. Explain how.

Answer 19

1. (Each receptor cell has) separate neurone to brain / separate bipolar neurone /separate ganglion cell;
2. Impulses from each receptor kept separate / no retinal convergence;

Question 20

The way in which the cells labelled Y are connected to the brain allows vision in low light intensities. Explain how.

Answer 20

1. Several Y connected to same neurone to brain / same bipolar cell / same ganglion cell;
2. Stimulation of each individual cell is sub-threshold / is insufficient / cells together cause above-threshold stimulation of neurone / of bipolar cell / of ganglion cell;
3. Summation / described;

Question 21

Describe the trichromatic theory of colour vision.

Answer 21

1. 3 types of cones / of iodopsin;
2. Each type of receptor sensitive to a different colour / wavelength / red or green or blue;
3. Stimulation of different combinations of cones gives range of colour perception;

Question 22

Give three functions of the stomach acid in digestion

Answer 22

-kills some of the bacteria present in the food;
-provides an optimum pH (1-2) (for the enzyme Pepsin);
-activates pepsin

Question 23

Describe the role of bile and pancreatic juice in the digestion of lipids.

Answer 23

-Bile contains bile salts and alkaline;
-Alkaline neutralizes acid (to provide optimum pH)
-Bile salts emulsify lipids;
-Increases SA for lipase;
-Lipase breaks down fats;
-To fatty acids and glycerol;

Question 24

The heart is described as myogenic. What does myogenic mean?

Answer 24

No impulse (from nervous system) required / beats on its own;

Question 25

describe what happens after the atria contract in the heart

Answer 25

-blood passes through atrioventricular valves into the ventricles -ventricles contract -blood passes through semi-lunar valve into the aorta and into the pulmonary artery -ventricles relax

Question 26

Suggest and explain one advantage to an unborn baby of having a hole allowing blood to flow from the right atrium into the left atrium of its heart.

Answer 26

1. Allows left ventricle to pump (oxygenated) blood (from placenta) round body; 2. Lungs not carrying out gas exchange; 3. Improves efficiency of oxygen supply to body (except lungs) / support respiration;

Question 27

To improve the baby’s condition, an operation is carried out to: -increase the size of the hole between the right atrium and the left atrium -widen the artery connecting the pulmonary artery to the aorta Suggest how this operation improves the baby’s condition.

Answer 27

1. Left ventricle too small to pump enough blood round body; 2. Aorta too narrow to allow enough blood round body; 3. (Widening narrow artery) increases blood flow to aorta; 4. (Increasing the hole) enables blood from left atrium to be pumped by right side of heart; 5. More oxygenated blood round body; 6. Maintains respiration for energy / growth;

Question 28

Explain how aerobic respiration in cells leads to a change in the pH of blood plasma.

Answer 28

CO2 is produced (in respiration); forms carbonic acid / hydrogen ions released;

Question 29

What is the advantage to tissue cells of a reduction in the affinity of haemoglobin for oxygen when the plasma pH decreases?

Answer 29

-low pH because high rate of respiration; -cells need more O2; -more O2 released / O2 released faster;

Question 30

Explain the advantage for deer mice living at high altitude in having a dissociation curve which is to the left of the curve for deer mice living at low altitude.

Answer 30

-high altitudes have a low partial pressure of O2; -high saturation/affinity of Hb with O2 (at low ppO2) -sufficient/enough O2 supplied to cells / tissues;

Question 31

Suggest why it would be a disadvantage for the curve to be much further to the left.

Answer 31

difficult to unload/dissociate O2 (at tissues);

Question 32

Part B contains areas involved in interpreting and speaking words. Describe how these areas are involved in speaking a written word.

Answer 32

impulses enter visual sensory cortex Visual association area which recognizes the word; Impulses to Wernicke’s; Associates with correct auditory pattern; Impulses to Broca’s; Impulses via motor neurone to mouth to form word;