4.2 understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre

4.8 describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine

After food passes through the duodenum, it enters the small intestine where it is
absorbed into the blood stream. The small intestine is highly adapted to absorb the 
digested food in many ways. 

Villus
The surface of the small intestine is lined with millions of villi. 

Adaptations of the small intestine:
1. Very long: gives plenty of time for digestion and for food to be digested
2. Has a lot of villi: villi gives the small intestine a larger surface area, the larger the surface area, the faster food can be absorbed
3. Villi contain blood capillaries: digested food passes into the blood to be taken to the liver and the rest of the body, small diffusion distance
4. The walls of the villi are only one cell thick: allowing digested food to pass through the walls easily to enter the blood capillaries

4.3 understand that energy requirements vary with activity levels, age and pregnancy

Age/sex/occupation of person	Energy needed per day
Newborn baby	2000
Child aged 2	5000
Child aged 6	7500
Girl aged 12-14	9000
Boy aged 12-14	11000
Girl aged 15-17	9000
Boy aged 15-17	12000
Office worker	9500-10500
Heavy manual worker	15000
Pregnant woman	10000
Breast-feeding woman	11300

Energy is needed for all movement as wells as for keeping the body warm, for heartbeat, to allow messages to be sent through nerves and other body functions. However, the amount of energy needed also depends on the physical work, age, sex and condition.

Boys need more energy than girls in general and pregnant women need more energy due to the fetus. 

The amount of physical work done also varies energy requirements

Not only does the energy requirement vary, the content of the diet may vary too. For example, during pregnancy, a woman may need extra iron and calcium to aid the growth of the fetus. In younger women, the blood loss during menstruation can result in anemia (blood does not carry much oxygen) and hence need extra iron to compensate for blood loss. 

4.1 identify sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, the mineral ions calcium and iron and water and dietary fibre as components of the diet

Balanced diet

A balanced diet should include the seven components: 

• carbohydrates: provides quick energy
• lipids: provides slow energy
• proteins: growth and repair, emergency energy source if diet has insufficient carbohydrates and fats
• water: important as a solvent, for breaking up large molecules by hydrolysis and carrying substances around your body
• fiber: to give muslces of the gut something to work on. It abosrbs a lot of water
• minerals and vitamins: needed in tiny amounts. If you do not get enough of them, you will suffer deficiency diseases as shown below

VITAMIN/MINERAL	FUNCTION IN BODY	GOOD FOOD SOURCE	DEFICIENCY DISEASE
Iron	Part of hemoglobin in red blood cells, helps carry oxygen	Red meat, liver, eggs, vegetables (spinach)
Calcium	Making teeth and bones	Dairy products, fish, bread, vegetables
Vitamin C	Sticks together cells lining surfaces such as mouth	Fresh fruit and vegetable	Scurvy
Vitamin A	Making a chemical in the retina, protects surface of eye	Carrots, fish liver oils, liver, butter, margarine	Night blindness, damaged cornea of eye
Vitamin D	Helps bones absorb calcium and phosphate	Fish liver oils	Rickets, poor teeth

3.3 describe the tests for glucose and starch

Chemical test	Food	Procedure	Positive result
Iodine	Starch Found in: bread, pasta	Add a few drops of iodine to food This test works on solid food but for accuracy, crush solids in water.	Blue-black
Benedict’s	Glucose Found in naturally sweet foods Glucose is a reducing sugar; this food test involves reducing an alkaline solution of copper sulfate into copper oxide.	Add Benedict’s solution to food, put in water bath of around 70ºC. Solid foods should be crushed in water beforehand	Brick red
Biuret solution	Protein Found in: meat, fish, egg, milk Biuret solution potassium hydroxide + copper sulfate.	Add Biuret reagent to food Solid foods should be crushed in water beforehand	Light purple
Ethanol and water Emulsion	Lipids Found in oil, butter, margarine, avocado, salmon Fats are insoluble in water but dissolve in ethanol	Add ethanol to food, shake Then add water to food, shake For solid foods, filter after shaking.	Milky and cloudy

External links:

http://biology-igcse.weebly.com/-food-test-3---emulsion-ethanol-test-for-fats.html

3.2 describe the structure of carbohydrates, proteins and larger molecules made up from smaller basic units: starch and glycogen from simple sugars, proteins from amino acids, lipids from fatty acids and glycerol

~         Biological molecules: carbohydrates

-       Body’s main ‘fuel’ for supplying cells with energy

-       Starch is a large insoluble molecule. Starch is manufactured in the green leaves of plants from excess glucose produced during photosynthesis and serves the plant as a reserve food supply/ storage carbohydrate. Some plants that store glucose as starch: e.g. rice, barley, potato, wheat. Starch is made from a long chain of glucose molecules joined together. It is called a polymer of glucose. Monomer of starch: glucose. Starch is only found in plant tissues, but animal cells sometimes contain a very similar carbohydrate called glycogen, found in tissues where it acts as a store of energy.

-       Monosaccharaide: basic monomer units of carbohydrates. ‘Single’ sugars such as glucose and fructose are called monosaccharaides. 

-       Disaccharide: consist of 2 monosaccharaides joined by a glycosidic bond. Sucrose (table sugar) is made from 2 monosaccharaides (glucose and fructose) and is called a disaccharide. Lactose is also a disaccharide of glucose joined with a monosaccharaide galactose. Maltose is a disaccharide of glucose and glucose.

-       Polysaccharides: consist of thousands of monosaccharaides (monomers) linked by glycosidic bonds to form long chains. Polymers of monosaccharaides, e.g. starch and glycogen. 

~         Biological molecules: Lipids (fats and oils) 

-       Two types of molecule lipids are made of:glycerol and fatty acids

~         Biological molecules: proteins

-      









- The amino acids are linked together in long chains, usually folded up or twisted into spirals.

-       Monomers of proteins: Amino acids.

-       The shape of a protein is very important in allowing it to carry out its function. The order of amino acids and the number of amino acids in each protein decides the shape. As there are 20 different types of amino acids and the order and number of structures varies, there are thousands of different proteins in organisms.

-

3.1 identify the chemical elements present in carbohydrates, proteins and lipids

Carbohydrates contain 3 elements: carbon, hydrogen and oxygen (CHO). The ratio of hydrogen atoms to oxygen atoms is always 2:1. e.g. sucrose: C₁₂ H₂₂ O₁₁

Lipids contain the same 3 elements as carbohydrates: carbon hydrogen and oxygen (CHO). However, the proportion of oxygen in a lipid is much lower.

Proteins contain 4 elements: carbon, hydrogen, oxygen and nitrogen (CHON). Proteins are made of chains of amino acids. There are about 20 different amino acids, two of these also contain sulphur.

External links:
http://alevelnotes.com/Biological-Molecules/38
http://lesiuk-biology.wikispaces.com/Unit+C+-+Biological+Molecules
http://ibguides.com/biology/notes/digestion