Vitamins
B.5 Vitamins (1 hour)
Pause for thought
In the 1970s Frank Rowland and Mario Molina predicted that CFCs would interfere with the ozone layer. Their work was treated with scepticism, but in 1985 satellite evidence showed that the depletion of ozone above the Antarctic was in fact much greater than had been predicted. This coincided with a rise in the number of cases of skin cancer in countries like Australia and New Zealand due to the increasing amounts of ultraviolet radiation reaching the surface of the Earth. In order to protect their skin from exposure Australians stated to apply sunblock whenever they were out in the sun. However by trying to avoid one health problem they have inadvertently brought about a serious vitamin deficiency problem. Very few foods contain vitamin D and the body normally obtains its vitamin D through the action of the ultraviolet light from the sun with cholesterol in the skin. A lack of vitamin D leads to rickets and osteoporosis.
Even though it is now mandatory in Australia to fortify edible oils and spreads with vitamin D, it has been reported in 2014 that 25% of all Australians are suffering from vitamin D deficiency. In order to counterbalance this lack of vitamin D, many Australians have taken to buying vitamin D supplements (or multi-vitamin supplements which contain vitamin D) and it is reported that the sale of such supplements increased three-fold during the decade 2001 to 2010.
Trying to balance the negative effects of too much sunlight with the negative effects of too little sunlight is no easy task.
Nature of Science
The explanation of deficiency diseases (e.g. scurvy and beriberi) in terms of lack of specific vitamins (vital amines) was due to scientists seeking a cause for specific observations.
Learning outcomesAfter studying this topic students should be able to: Understand:
Apply their knowledge to:
| Clarification notesThe structures of vitamins A, C and D are given in Section 35 of the data booklet. Specific food sources of vitamins and the names of vitamin deficiency diseases are not required to be learned. International-mindednessThe sale of vitamin pills (and the food supplements industry in general) has become a very lucrative business in many countries. There is an increase in Vitamin D deficiency, partly because humans protect their skin more from sunlight. |
Teaching tipsMuch of this topic is simply factual information that students will need to learn. This is particularly true for the last part which looks at the causes and effects of nutrient deficiencies and possible ways of overcoming these problems. The syllabus states that specific food sources and the names of particular diseases caused by vitamin deficiency do not need to be learned but it is hard to see how the causes, effects and possible solutions can be discussed by students without mentioning some of the common names. The understanding really comes in when the structures are compared. Retinol (vitamin A) is essentially a long hydrocarbon chain and, although a molecule of retinol does contains a single polar -OH group, overall it is virtually non-polar so will be fat-soluble. It is probably also worth mentioning that it is coloured due to the large amount of conjugation of the double bonds, although this is really covered in B.9: Biological pigments.. Calciferol (vitamin D) also contains a single -OH group but again it is essentially a large hydrocarbon molecule with a structure that is almost (but not quite, as one of the rings is not closed) a steroid. Like retinol it is largely non-polar so the London dispersion forces of attraction between molecules of calciferol make it insoluble in water but soluble in fat. Ascorbic acid (vitamin C) is very different. Ascorbic acid is quite polar as it contains several -OH groups so can readily hydrogen bond to water molecules whereas it is insoluble in fat. Because it is soluble in water it is not retained by the body hence the need for fresh fruit etc. as a replacement source of vitamin C. Aspects of vitamin C obviously provide considerable scope for topics for the Individual Scientific Investigation. | Study guide
Page 131 QuestionsFor ten 'quiz' questions (for quick testing of knowledge and understanding with the answers explained) see MC test: Vitamins. For short-answer questions see Vitamins questions together with the worked answers on a separate page Vitamins answers. Vocabulary list:micronutrient Practical work
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Teaching slides
Teachers may wish to share these slides with students for learning or for reviewing key concepts.
Other resources
Unfortunately vitamins are big business so a search of 'vitamins' on the web and YouTube produces much that is useless from a scientific viewpoint.
1. A couple of reasonable sites for some information on vitamins are one from a sports coach and one from netdoctor.
2. The benefits of vitamin D and the problems of vitamin D deficiency.