Learning outcomes:
2.23
understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre
2.24
identify sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, and the mineral ions calcium and iron, water and dietary fibre as components of the diet - b
2.25
understand that energy requirements vary with activity levels, age and pregnancy
2.26
describe the structures of the human alimentary canal and describe the functions of the mouth, oesophagus, stomach, small intestine, large intestine and pancreas
2.27
understand the processes of ingestion, digestion, absorption, assimilation and egestion
2.28
explain how and why food is moved through the gut by peristalsis
2.29
understand the role of digestive enzymes, to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases
2.30
understand that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids
2.31
describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine
2.32
describe an experiment to investigate the energy content in a food sample.
Humans need to eat a balanced diet. This really means some of every food group, but not too much or too little of a particular one.
The two groups that provide energy (through respiration) are lipids and carbohydrates. Per mass lipids have about 10x more energy in them than carbohydrates. The energy in food is measured in Calories (equivalent to 4.2 kJ). In order to keep our bodies functioning (i.e. heart beating, basic respiratory requirement)

- Males need to consume 2500 Calories a day
- Females need to consume 2000 Calories a day

However, this will change if;

- You exercise
- You are growing
- You are ill
- You are pregnant
- You are old

You need to know an experiment that can show how much energy there is in food. The easiest way of doing this is to burn a sample of food and use it to heat a fixed volume of water. If you record the change in temperature of the water you can use the equation below to find out the energy the food gave to the water;

Energy = change in temp. x volume of water x 4.2J/g/oC

A potential problem is that not all the food will burn. To control this, you measure the start and end mass of the food and calculate the mass that actually burned. To standardize this, you can divide your calculated energy value by the change in mass to give you the change in mass per gram of food (which will allow you to compare values fairly between different food samples)

You need to know the specific sources and functions of the following minerals and vitamins
Vitamin - Mineral Function
Vitamin A - Present in fish, cheese and eggs. It forms an essential part of the pigment in rods and cones that detects light. Lack of Vitamin A can lead to blindness.
Vitamin C - Present in citrus fruit. It forms an essential part of collagen protein, which makes up skin, hair, gums and bones. Lack of Vitamin C causes scurvy.
Vitamin D - Present in fish, but made naturally by our body when sunlight shines on the skin. It is essential for regulating the growth of bones. Lack of Vitamin D can cause rickets.
Calcium - Present in milk, cheese & dairy foods. It is essential for bone growth and muscles. Lack of calcium can lead to osteoporosis.
Iron - Present in red meat and some vegetables (e.g. spinach). Is part of haemoglobin. Lack of iron causes anaemia.

Digestive System:


dig sys.GIF
The purpose of digestion is to break food into molecules that are small enough to be absorbed into the bloodstream.
There are two types of digestion;

Mechanical Digestion: digestion by physically breaking food into smaller pieces (i.e. not using enzymes). Carried out by;

- mouth and teeth chewing food
- stomach churning food

Chemical Digestion: digestion using enzymes

You need to know the following enzymes;

enzyme table.GIF

Bile salts are not technically enzymes. They are made in the liver and stored in the gall bladder. They help by emulsifying lipid (i.e. turning large fat droplets into lots of tiny droplets). This increases the surface area, which helps lipase actually break the lipid down.

Bile also has a second job. Bile is alkali, which is important for neutralizing stomach acid as soon as it leaves the stomach. Stomach acid is important because it kills any bacteria that enter the stomach. Stomach acid does not play a significant role in digestion.

KEY IDEAS:
Ingestion - taking food into the digestive system
Digestion - breaking food down into molecules small enough to be absorbed into the bloodstream.
Absorption - taking molecules into the bloodstream. This happens almost entirely in the small intestine(ileum)
Assimilation - using food molecules to build new molecules in our bodies. i.e. the food molecule physically becomes part of our body.
Egestion - Removing unwanted food from the digestive system (having a poo!). This is not excretion, because the unwanted food has never, technically, been inside the body.
Peristalsis - the contraction of muscle in the intestine wall behind a bolus of food (ball of food). This pushes the bolus through the intestine.

Small intestine adaptations:

SI adapt.GIF

Adaptation - Explanation

Thin wall - The intestine wall in thin, which speeds the rate of diffusion of molecules into the blood
Rich blood supply - This helps carry absorbed molecules away from the intestine quickly. This means there is always a low concentration of food molecules in the blood, which maintains a high concentration gradient
Intestine length - Roughly 7m long, which increases the surface area
Surface Area - Villi and microvilli increase the surface area of the small intestine by 1000x.

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