Option D: Human physiology

Option D: Human physiology

Core

D.1 Human nutrition

Nature of science:

• Falsification of theories with one theory being superseded by another - scurvy was thought to be specific to humans, because attempts to induce the symptoms in laboratory rats and mice were entirely unsuccessful.

Understandings:

• Essential nutrients cannot be synthesized by the body, therefore they have to be included in the diet.

• Dietary minerals are essential chemical elements.

• Vitamins are chemically diverse carbon compounds that cannot be synthesized by the body.

• Some fatty acids and some amino acids are essential.

• Lack of essential amino acids affects the production of proteins.

• Malnutrition may be caused by a deficiency, imbalance or excess of nutrients in the diet.

• Appetite is controlled by a centre in the hypothalamus.

• Overweight individuals are more likely to suffer hypertension and type II diabetes.

• Starvation can lead to breakdown of body tissue.

Applications and skills:

• Application: Production of ascorbic acid by some mammals, but not others that need a dietary supply.

• Application: Cause and treatment of phenylketonuria (PKU).

• Application: Lack of Vitamin D or calcium can affect bone mineralization and cause rickets or osteomalacia.

• Application: Breakdown of heart muscle due to anorexia.

• Application: Cholesterol in blood as an indicator of the risk of coronary heart disease.

• Skill: Determination of the energy content of food by combustion.

• Skill: Use of databases of nutritional content of foods and software to calculate intakes of essential nutrients from a daily diet.

D.2 Digestion

Nature of science:

• Serendipity and scientific discoveries - the role of gastric acid in digestion was established by William Beaumont while observing the process of digestion in an open wound caused by gunshot.

Understandings:

• Nervous and hormonal mechanisms control the secretion of digestive juices.

• Exocrine glands secrete to the surface of the body or the lumen of the gut.

• The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms.

• Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food.

• The structure of cells of the epithelium of the villi is adapted to the absorption of food.

• The rate of transit of materials through the large intestine is positively correlated with their fibre content.

• Materials not absorbed are egested.

Applications and skills:

• Application: The reduction of stomach acid secretion by proton pump inhibitor drugs.

• Application: Dehydration due to cholera toxin.

• Application: Helicobacter pylori infection as a cause of stomach ulcers.

• Skill: Identification of exocrine gland cells that secrete digestive juices and villus epithelium cells that absorb digested foods from electron micrographs.

D.3 Functions of the liver

Nature of science:

• Educating the public on scientific claims - scientific studies have shown that high-density lipoprotein could be considered “good” cholesterol.

Understandings:

• The liver removes toxins from the blood and detoxifies them.

• Components of red blood cells are recycled by the liver.

• The breakdown of erythrocytes starts with phagocytosis of red blood cells by Kupffer cells.

• Iron is carried to the bone marrow to produce hemoglobin in new red blood cells.

• Surplus cholesterol is converted to bile salts.

• Endoplasmic reticulum and Golgi apparatus in hepatocytes produce plasma proteins.

• The liver intercepts blood from the gut to regulate nutrient levels.

• Some nutrients in excess can be stored in the liver.

Applications and skills:

• Application: Causes and consequences of jaundice.

• Application: Dual blood supply to the liver and differences between sinusoids and capillaries.

D.4 The heart

Nature of science:

• Developments in scientific research followed improvements in apparatus or instrumentation - the invention of the stethoscope led to improved knowledge of the workings of the heart.

Understandings:

• Structure of cardiac muscle cells allows propagation of stimuli through the heart wall.

• Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles.

• There is a delay between the arrival and passing on of a stimulus at the atrioventricular node.

• This delay allows time for atrial systole before the atrioventricular valves close.

• Conducting fibres ensure coordinated contraction of the entire ventricle wall.

• Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flow.

Applications and skills:

• Application: Use of artificial pacemakers to regulate the heart rate.

• Application: Use of defibrillation to treat life-threatening cardiac conditions.

• Application: Causes and consequences of hypertension and thrombosis.

• Skill: Measurement and interpretation of the heart rate under different conditions.

• Skill: Interpretation of systolic and diastolic blood pressure measurements.

• Skill: Mapping of the cardiac cycle to a normal ECG trace.

• Skill: Analysis of epidemiological data relating to the incidence of coronary heart disease.

Additional higher level

D.5 Hormones and metabolism

Nature of science:

• Cooperation and collaboration between groups of scientists - the International Council for the Control of Iodine Deficiency Disorders includes a number of scientists who work to eliminate the harm done by iodine deficiency.

Understandings:

• Endocrine glands secrete hormones directly into the bloodstream.

• Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a receptor–hormone complex.

• The receptor–hormone complex promotes the transcription of specific genes.

• Peptide hormones bind to receptors in the plasma membrane of the target cell.

• Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside the cell.

• The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland.

• Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis.

Applications and skills:

• Application: Some athletes take growth hormones to build muscles.

• Application: Control of milk secretion by oxytocin and prolactin.

D.6 Transport of respiratory gases

Nature of science:

• Scientists have a role in informing the public - scientific research has led to a change in public perception of smoking.

Understandings:

• Oxygen dissociation curves show the affinity of hemoglobin for oxygen.

• Carbon dioxide is carried in solution and bound to hemoglobin in the blood.

• Carbon dioxide is transformed in red blood cells into hydrogencarbonate ions.

• The Bohr shift explains the increased release of oxygen by hemoglobin in respiring tissues.

• Chemoreceptors are sensitive to changes in blood pH.

• The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata.

• During exercise the rate of ventilation changes in response to the amount of CO2 in the blood.

• Fetal hemoglobin is different from adult hemoglobin allowing the transfer of oxygen in the placenta onto the fetal hemoglobin.

Applications and skills:

• Application: Consequences of high altitude for gas exchange.

• Application: pH of blood is regulated to stay within the narrow range of 7.35 to 7.45.

• Application: Causes and treatments of emphysema.

• Skill: Analysis of dissociation curves for hemoglobin and myoglobin.

• Skill: Identification of pneumocytes, capillary endothelium cells and blood cells in light micrographs and electron micrographs of lung tissue.