Recommended Prior Knowledge
Students need to know of the existence of chemical elements, particularly of carbon, oxygen, hydrogen and nitrogen, also that chemical energy is contained within the larger organic molecules. A knowledge of enzymes and enzyme action is necessary (Unit 1) as well as a very simple understanding of the circulatory system.
Otherwise, this Unit could be used as a starting point for the course with the above requirements being dealt with as they arise in the learning outcomes.
Context
This Unit provides the underlying biochemical knowledge essential for studying almost all of the other Units in the course.
Outline
The Unit begins with a study of the three major classes of organic nutrients and their food tests. Diet and its importance are considered, as well as the processing of dietary intake within the body. The action of specific enzymes is considered and the Unit ends with a link to Unit 5 with a consideration of the role of the liver.
Learning
5 a, b) List the chemical elements that make up carbohydrates, fats and proteins.
Describe tests for Starch (I
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solution), reducing sugars (Benedict’s solution), protein (Biuret test) and fats (ethanol emulsion test).
Suggested Teaching Activities
That carbohydrates and fats contain carbon, hydrogen and oxygen only (but in different proportions) and that proteins contain the same three elements plus nitrogen can be illustrated using a collection of four different shapes cut from paper or thin card and moved around on an OHP. Explain that ‘hydrate’ relates to water and carbohydrates always contain H and O in the same ratio as in water.
It is often preferable to ask students first to perform the tests on prepared solutions of starch, glucose and egg albumen, also on e.g. cooking oil. They should also carry out a test in each case on pure water and results should be recorded in a table as visible results in each case (e.g. Benedict’s turns red with reducing sugar; stays blue in its absence). Never allow students to say that a test ‘proves positive’ or
‘negative’.
Carry out tests first on prepared samples of each chemical, then either on mixtures or on
Online Resources http://www.bbc.co.uk/schoo ls/gcsebitesize/biology/hum ansasorganisms/0nutritiond igestionrev8.shtml
(food tests)
Other resources
‘GCE O Level Examination
Past Papers with Answers
Guides (Biology)’ is produced by CIE
(Foundation Books). CIE also produces the same material on CD.
Ian J. Burton – Topic 5
Nutrition
M. & G. Jones – 4 How
Animals Feed
Mary Jones – Unit 5 Animal
Nutrition – Diet
1 www.xtremepapers.net

Learning
5 c-h) List the principle sources of, and describe the dietary importance of carbohydrates, fats, proteins, vitamins
(C and D only), mineral salts (calcium and iron only), fibre (roughage) and water.
Understand the concept of a balanced diet.
Describe the deficiency symptoms of vitamins C and D and mineral salts calcium and iron.
Explain why diet, especially energy intake, should be related to age, sex and activity of an individual.
State the effects of malnutrition in relation to starvation, heart disease, constipation and obesity.
Discuss the problems that contribute to famine (unequal distribution of food, drought and flooding, increasing population).
Suggested Teaching Activities supplied foodstuffs. Record results and conclusions in tabular form. Table lines should be ruled and all columns have suitable headings.
It might be helpful here to consider the importance of the different chemical constituents of a diet before considering their sources. Principle sources will differ in different areas of the world.
Stress the importance of a diet containing sufficient of each constituent to satisfy the body’s needs. Both too little and too much of any one or more constituents can be harmful
[see e ), f) and g)]. A balanced diet is therefore one that contains correct proportions of all requirements.
Descriptions of the deficiency diseases resulting from a lack of vitamins C and D should be supported if possible with pictures.
The need for calcium in the development of strong bones and teeth should be mentioned and for iron in the manufacture of haemoglobin for oxygen transport.
The energy requirements for sedentary and physical life styles should be considered, including the likelihood that young people are generally more active than older ones.
Additional energy is also needed for growth in young people. A simple consideration and comparison of the metabolic rates of males and females should provoke discussion!
Online Resources http://www.usaid.gov/hum_r esponse/crg/fssfcornmeal.h
tm
(nutritional contents of a variety of foods) http://www.sambal.co.uk/di et.html
(informative explanation of balanced diet) http://www.purchon.com/bio logy/vitamins.htm
(list including vitamins C and D) http://www.nationalacademi
es.org/webextra/crops
(consideration of world food)
Other resources www.xtremepapers.net
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Learning
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5 i-k) Identify the main regions of the alimentary canal and the associated organs: mouth, salivary glands, oesophagus, stomach, duodenum, gall bladder, liver, ileum, colon, rectum and anus.
The alimentary canal may be drawn with these regions labelled (beware, drawings can be unacceptably inaccurate) or a good quality unlabelled diagram can be provided which the students label from a projected master.
Describe the main functions of these parts in relation to ingestion, digestion, absorption, assimilation and egestion of food as appropriate.
Identify the different types of human teeth and describe their structure and functions.
Suggested Teaching Activities
This objective illustrates well that eating too much as well as too little is a form of malnutrition.
Students in groups may be invited to list all the factors they can think of that contribute to famine. These can then be collected and discussed. Several not in the syllabus may be identified which might make for lively discussion.
‘Brainstorming’ in groups on causes of famine.
Students may enjoy a description of a trip through the alimentary canal as ‘seen’ by a well-protected bacterium attached to a plant cell wall. Such an imaginative scenario must them be supported with a more mundane demonstration diagram with parts labelled.
Avoid providing more labels than the syllabus requires.
The terms ingestion and absorption should not pose any great problems of understanding. It will need to be stressed that only certain large molecules are digested (in order to be absorbed). Assimilation as the incorporation of absorbed chemicals into the structure of an organism will need careful explanation. Many students confuse egestion and excretion, so the differences should be carefully explained.
Remember to include a reference to milk teeth and to wisdom teeth. ‘Cutting’ and ‘grinding’
(as appropriate) are more accurate descriptions of tooth function then ‘chewing’. A model of a tooth to show internal structure is
Online Resources http://www.bbc.co.uk/schoo ls/gcsebitesize/biology/hum ansasorganisms/0nutritiond igestionrev4.shtml
(the alimentary canal)
Other resources
Mary Jones – Unit 6 Animal
Nutrition – Digestion
Ian J. Burton - Topic 7
Animal Nutrition www.xtremepapers.net
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5 l-o)
Learning
State the causes of dental decay and describe the proper care of teeth.
Describe peristalsis.
Explain why most foods must be digested.
Describe digestion in the alimentary canal and the functions of a typical amylase, protease and lipase, listing the substrates and end-products.
Suggested Teaching Activities helpful and students should be supplied with good diagrams of a tooth in longitudinal section and of a dental arcade.
Students should label the structures shown on an LS of a tooth and name and label the functions of the different teeth in a lower or upper jaw.
Stress that sugar left on teeth, particularly whilst asleep, attracts bacteria and that it is the acid excreted by these bacteria as they feed on the sugar that dissolves the enamel
(toothpastes are therefore alkaline).
A bead in a length of rubber tubing illustrates the action. Reference should be made to food being pushed along the entire length of the gut by waves of contraction of circular muscles and of the antagonistic effect of the longitudinal muscles. The speed of a wave may be illustrated by the time taken for a mouthful of hot food to pass along the oesophagus (or drink swallowed when lying in a semi-recumbent position – it can be heard as it enters the stomach).
This has already been mentioned in j) above.
Only small molecules can pass through the membranes of the cells lining the gut to be absorbed into the body (until then, even when in the gut, they are still outside the body).
Starch, proteins and facts are too large to be absorbed and must be broken down into the smallest constituent parts. Shapes cut from thin card and projected with an OHP can illustrate effectively how starch is constructed
Online Resources http://health.howstuffworks.
com/adam-200088.htm
(including good animation) http://www.bbc.co.uk/schoo ls/gcsebitesize/biology/hum ansasorganisms/0nutritiond igestionrev6.shtml
(explanation of digestion) http://faculty.uca.edu/~jmurr ay/BIOL2407/lec/villi.mov
(villus absorption movie – involving download)
Other resources www.xtremepapers.net
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Learning
5 p-r) Describe the structure of a villus, including the roles of capillaries and lacteals.
Describe the significance of villi in increasing the internal surface area.
State the function of the hepatic portal vein as the route taken by most of the food absorbed from the small intestine to the liver.
Suggested Teaching Activities form a string of monosaccharide units, proteins from amino acids and fats from fatty acids and glycerol.
Where each molecule is dismantled can be related to a specific region of the alimentary canal and to a specific enzyme (and to pH). By the time food arrives in the ileum, only the end products of digestion are present (together with those chemicals that are not broken down, either because they are already small enough for absorption or because no enzymes are present for their breakdown).
Enzyme experiments involving protease and or lipase may be used to consolidate this section.
Villi are the means by which all food substances that are absorbed enter the body.
Refer to large surface area – of each villus and of villi collectively. Display a large annotated diagram to show villus structure in LS and that all absorbed substances pass into the blood capillaries except the digested fats (into the lacteals). It will need to be explained that lacteals unite to join the lymph system that feeds into the circulatory system (by-passing the liver), whilst the blood capillaries link directly with the liver via the HPV.
Made large labelled and annotated drawing of a villus.
Online Resources http://www.bbc.co.uk/schoo ls/gcsebitesize/biology/hum ansasorganisms/0nutritiond igestionrev4.shtml
(absorption)
Other resources
Bioscope CD ileum www.xtremepapers.net
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Learning
5 s) s) State that large molecules are synthesised from smaller basic units – glycogen from glucose, proteins from amino acids, lipids from glycerol and fatty acids. State the role of the liver in metabolism of glucose and amino acids, the role of fat as a storage substance and that the formation of urea and the breakdown of alcohol occur in the liver.
Suggested Teaching Activities
The breakdown of large molecules into small ones has already been considered. The reverse of this is a logical consequence and part of the process of assimilation, but stress that glucose is built up in animals not into starch, but into glycogen.
The liver – the ‘chemical factory’ of the body deals with the conversion of glucose into glycogen (and its storage) [See unit 5, 11 j) and k)]. A brief mention should be made at this point of the importance of insulin for this process, and that the hormone adrenaline promotes the conversion of glycogen into glucose which is released into the blood as part of blood glucose control. The breakdown of amino acids in excess into a carbohydrate
(also to be stored as glycogen) and the excretory product, urea, should be mentioned.
As a part of its role in removing poisons, the liver also breaks down alcohol [see also Unit 5,
11 i)].
Fat is a high-energy insulating storage substance. It is stored in the dermis and round kidneys. It is not considered to be ‘stored’ round the heart.
Poster making exercise to build understanding of these areas and to reinforce the learning of the rest of the Unit. Small groups of students cooperate to produce posters using illustrations and words to summarize key knowledge and understanding.
Online Resources www.xtremepapers.net
Other resources
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