Option D - Human Physiology

Question 1

Suggest a reason for high total serum cholesterol not always being an indicator of CHD risk. [1]

Answer 1

Total cholesterol is made up of both LDL and HDL. High total cholesterol could reflect high HDL levels, which are protective against CHD. Without knowing the proportion of LDL to HDL, total cholesterol alone is not a reliable measure of CHD risk.

Question 2

Describe the reactions that occur in the liver, leading to the production of bile. [3]

Answer 2

Surplus cholesterol is converted into bile salts.

Kupffer cells break down hemoglobin into globin and iron-containing heme groups. Globin is digested by peptidases to produce amino acids. Heme groups are broken down into iron and bilirubin (bile pigment).

Bilirubin and bile salts combine to produce bile.

Question 3

State one long-term consequence of jaundice in newborn babies if this condition is not treated. [1]

Answer 3

Neurological damage.

Question 4

State where in the digestive system Vibrio cholerae acts, leading to dehydration. [1]

Answer 4

Intestine

Question 5

Explain how cholera toxin causes dehydration. [3]

Answer 5

1. V. cholerae releases a toxin that binds to receptors on the surface of intestinal epithelium cells.
2. Open channels cause the loss of Cl- ions from cells.
3. The build-up of ions outside the cell causes water to be drawn out by osmosis.
4. This causes diarrhea/excessive water loss from the body.

Question 6

Describe how an electrocardiogram (ECG) can be used to show that the heart is beating normally. [3]

Answer 6

ECG measures the electrical activity of the heart. The pattern on the ECG should be regular.

Regular P wave shows normal sinoatrial node. QRS wave is triggered by signals from the AV node.

1. Atrial Systole - P wave
2. Ventricular Systole - QRS complex
3. Ventricular Diastole - T wave

Question 7

Describe the state of the heart valves at ventricular systole. [2]

Answer 7

When ventricular pressure exceeds atrial pressure, the AV valves are closed.

When ventricular pressure exceeds blood pressure in aorta, the semi-lunar valves open.

Question 8

Explain how cardiac muscle is adapted to its function. [3]

Answer 8

1. Cardiac muscle cells have many mitochondria for aerobic respiration.
2. Cardiac muscle cells are branched, allowing for faster signal propagation.
3. Cardiac muscle is myogenic so does not require the CNS to initiate contraction.
4. Cardiac muscles cells are not fused together but are connected by gap junctions at intercalated discs, which allows easier transmission between cells.

Question 9

Outline the reason that the curve for fetal hemoglobin is to the left of normal adult
hemoglobin. [1]

Answer 9

Fetal hemoglobin has a higher affinity for oxygen then normal adult hemoglobin.

Question 10

State where the curve for myoglobin would be drawn on the diagram. [1]

Answer 10

To left of the curve of fetal hemoglobin.

Question 11

Explain how emphysema is treated. [3]

Answer 11

1. Help smokers to quit smoking as smoking worsens emphysema.
2. Use bronchodilator to open the air passages in the lungs.
3. Corticosteroids can help relieve symptoms of emphysema.

Question 12

Explain the action of peptide hormones, using growth hormone as an example. [6]

Answer 12

Growth hormone is produced by the pituitary gland, and travels in blood plasma to the target organ/muscle.

Peptide hormone binds to receptor on the surface of the cell. The receptor triggers a series of reactions inside cell, the reactions are mediated by secondary messengers.

Secondary messengers allow amplification of the signal from the hormone.

Series of reactions can involve activating/inhibiting synthesis of enzymes.

Growth hormone stimulates protein synthesis.

Question 13

Predict with a reason the risk that a child have scurvy and anemia. [2]

Answer 13

1. Vitamin C below RDA leads to scurvy.
2. Low intake of iron leads to anemia.

Question 14

State one effect of a low intake of fiber, calcium, and fat. [3]

Answer 14

Low intake of fiber - Constipation

Low intake of calcium - Bone mineralization

Low intake of fat - Not enough energy

Question 15

Describe the production of acid in the digestive system. [6]

Answer 15

The gastric glands that line the stomach wall secrete an acidic solution that creates a low pH environment within the stomach. The secretion of digestive juices is controlled by both nervous and hormonal mechanisms.

Gastrin is secreted into the bloodstream from the gastric pits of the stomach and stimulates the release of stomach acids.

If stomach pH drops too low (becomes too acidic), gastrin secretion is inhibited by gut hormones.

The low pH environment of the stomach is maintained by proton pumps in the parietal cells of the gastric pits.

The proton pumps secrete H+ ions which combine with Cl– ions to form hydrochloric acid.

Question 16

Outline the use of drugs to reduce the production of stomach acid. [2]

Answer 16

Proton pump inhibitors are drugs which irreversibly bind to the proton pumps and prevent H+ ion secretion, which makes the stomach less acidic.

Question 17

Describe how two named risk factors can lead to coronary heart disease. [2]

Answer 17

1. Nicotine in smoking tobacco causes vasoconstriction.
2. Raised blood pressure damages arteries.

Question 18

Explain the production of prolactin in reference to its function in milk secretion. [2]

Answer 18

Suckling stimulates prolactin production. Prolactin is secreted by the anterior pituitary in response to the release of PRH (prolactin releasing hormone) from the hypothalamus.

Prolactin is responsible for the development of the mammary glands and the production of milk.

Question 19

Outline how red blood cells transport respiratory gases. [3]

Answer 19

1. Oxygen is bound to heme.
2. Carbon dioxide is carried in solution and bound to hemoglobin in the blood.
3. Carbon dioxide is transformed in red blood cells into hydrogen carbonate ions.

Question 20

Outline the recycling of red blood cell components in the liver. [3]

Answer 20

The breakdown of erythrocytes starts with phagocytosis of red blood cells by Kupffer cells. Kupffer cells break down hemoglobin into globin and iron-containing heme groups.

Globin is digested by peptidases to produce amino acids, which are recycled.

Heme groups are broken down into iron and bilirubin

Question 21

Explain how the epithelium cells of intestinal villi are adapted for absorption and what happens to absorbed material when it reaches the liver. [6]

Answer 21

Adaptations for absorption:
- Epithelial cells are one cell layer thick which facilitates transport.
- Epithelial cells joined by tight junctions which prevents leakage.
- Each cell has microvilli to increase absorption surface.
- Membranes contain protein channels used for co-transport/facilitated diffusion
of substances.

Storage in liver:
- Glucose is stored as glycogen.
- Fatty acids/fats stored in hepatocytes.

Question 22

Outline causes of hypertension. [2]

Answer 22

1. Excessive salt in diet.
2. Sedentary lifestyle.

Question 23

Suggest one reason that it is difficult to detect illegal use of human growth hormone to enhance athletic performance. [1]

Answer 23

Occurs naturally so hard to tell whether it has been injected.

Question 24

State one chronic liver disease. [1]

Answer 24

Cancer.

Question 25

State the reason that the posterior pituitary is considered an endocrine gland. [1]

Answer 25

It secretes hormones directly into the blood.

Question 26

State the effect of altitude on the partial pressure of oxygen in air. [1]

Answer 26

The higher the altitude, the lower the partial pressure.

Question 27

Explain the consequence of high altitude for gas exchange in humans. [3]

Answer 27

At high altitudes, air pressure is lower and hence there is a lower partial pressure of oxygen. Lower oxygen partial pressure reduces oxygen availability, as less oxygen is exchanged in the blood.

Breathing rate is increased. More carbon dioxide remains in the blood.

Less saturation of hemoglobin with oxygen. Red blood cell production will increase in order to maximize oxygen uptake and transport

Question 28

State one condition which would require the use of an artificial pacemaker. [1]

Answer 28

Heartbeat too slow/fast.

Question 29

Describe briefly how an artificial pacemaker works. [2]

Answer 29

Artificial pacemaker contains a battery and pulse generator.

It detects that the heart’s natural rhythm is incorrect. So it sends electrical impulses to correct the heartbeat and provide a regular rhythm.

Question 30

Explain how the structure of cardiac muscle cells allows propagation of stimuli
through the heart wall. [2]

Answer 30

1. Branching provides larger surface area of contact between cells, allowing for faster signal propagation.
2. Intercalated discs allows easier signal transmission between cells.

Question 31

State one health benefit of a diet high in fiber. [1]

Answer 31

Helps in movement of food along alimentary canal.

Question 32

Distinguish between essential and non-essential amino acids. [1]

Answer 32

Essential amino acids must be included in the diet and the body cannot make them, whereas the body can synthesize non-essential amino acids.

Question 33

Distinguish between essential and non-essential nutrients. [1]

Answer 33

Essential nutrients must be included in the diet and the body cannot make them, whereas the body can synthesize non-essential nutrients.

Question 34

Outline the possible consequences of a Helicobacter pylori infection of the stomach wall. [1]

Answer 34

Causes inflammation (stomach ulcer).

Question 35

The bacterium secretes an enzyme that breaks down urea, resulting in an increase
in pH. Outline how this would help the bacterium survive in the stomach. [1]

Answer 35

Neutralizes the acid the stomach secretes, that kills bacteria.

Question 36

Explain hormonal control of gastric secretion. [3]

Answer 36

Release of gastric juices is stimulated by gastrin. Gastrin stimulates secretion of gastric hydrochloric acid from the parietal cells.

Gastrin release is stimulated by presence of polypeptides in stomach.

Question 37

How physical exercise affects the affinity
of hemoglobin for oxygen.

Answer 37

During exercise, where tissues are respiring there is higher conc. of CO2 in the blood.

An increase in CO2 lowers the pH of the blood. A lower pH causes hemoglobin to release oxygen, as it decreases hemoglobin affinity for O2.

Oxygen is released in tissue where it is required for respiration.

Question 38

State the name of the blood vessel through which lactate from muscles reaches the liver. [1]

Answer 38

Hepatic artery

Question 39

Compare and contrast the possible metabolic pathways for lactate in hepatocytes and in mitochondria-rich tissue. [2]

Answer 39

1. Both produce pyruvate.
2. Hepatocytes produce glucose from lactate but mitochondria-rich cells cannot.

Question 40

List two functions of hepatocytes other than regulating lactate levels in the blood. [2]

Answer 40

1. Detoxification.
2. Secretion of bile.

Question 41

Outline the role of nerves in the secretion of gastric juices. [3]

Answer 41

1. Impulse from brain causes parietal cells to secrete HCl.
2. Sight and smell of food stimulates brain.
3. Food entering stomach stimulates chemoreceptors to send impulses to brain.