October 2014

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. (4.3)

• 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.

• Aim 8: There are numerous drugs that can enhance performance. Is the use of these drugs acceptable in terms of conducting a fair test as long as all athletes have equal access to them?

Nature of science:

Educating the public on scientific claims—scientific studies have shown that high-density lipoprotein could be considered “good” cholesterol. (5.2)

• 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.

• Excessive alcohol consumption may cause liver cirrhosis. Are attitudes to drugs and alcohol an example of something that is relative to culture? Is all knowledge dependent on culture?

Aims:

• Aim 6: Temporary mounts of hepatocytes can be prepared from fresh liver.
• Aim 8: Given the pressure on health resources, especially the availability of organs for transplant, should an alcoholic be allowed a liver transplant?

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. (1.9)

• 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.

• The Vitamin and Mineral Nutrition Information System (VMNIS), formerly known as the Micronutrient Deficiency Information System (MDIS), was established in 1991 following a request by the World Health Assembly to strengthen surveillance of micronutrient deficiencies at the global level.

Theory of knowledge:

• There are positive effects of exposure to sun such as the production of Vitamin D as well as health risks associated with exposure to UV rays. How can conflicting knowledge claims be balanced?

Utilization:

• Syllabus and cross-curricular links:
• Biology
• Topic 6.1
• Digestion and absorption Geography
• Part 2F The geography of food and health
• Chemistry
• Topic B5 Vitamins

Nature of science:

Avoiding bias—a random number generator helps to ensure population sampling is free from bias. (5.4)

• Sampling techniques are used to estimate population size.
• The exponential growth pattern occurs in an ideal, unlimited environment.
• Population growth slows as a population reaches the carrying capacity of the environment.
• The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration.
• Limiting factors can be top down or bottom up.

Applications and skills:

• Application: Evaluating the methods used to estimate the size of commercial stock of marine resources.
• Application: Use of the capture-mark-release-recapture method to estimate the population size of an animal species.
• Application: Discussion of the effect of natality, mortality, immigration and emigration on population size.
• Application: Analysis of the effect of population size, age and reproductive status on sustainable fishing practices.
• Application: Bottom-up control of algal blooms by shortage of nutrients and top-down control by herbivory.
• Skill: Modelling the growth curve using a simple organism such as yeast or species of Lemna.

• The issues around the growing global human population are of international concern regardless of different growth rates in different countries.

Utilization:

• Syllabus and cross-curricular links:
• Geography
• Part 1.1 Populations in transition
• Environmental systems and societies
• Topic 8.4 Human population carrying capacity