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  • Falsification of theories with one theory being superseded by another - scurvy was thought to be specific to humans, because attempts to induce the symptoms in laboratory rats and mice were entirely unsuccessful.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

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