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