2.23 understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre
A balanced diet gives you all the essential nutrients you need to carry out the life processes, in the right proportions. The essential nutrients you need are: carbohydrates, proteins, lipids, 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.
2.25 understand that energy requirements vary with activity levels, age and pregnancy
You have to eat the right foods in order to get the right amount of energy your body needs. However, this 'right amount' is not the same for everyone, and different people have different energy requirements. For example, the more active somebody is, the more energy they will need as opposed to somebody who is less active, so does not need as much energy. As children and teenagers are growing, they need more energy than older people, also because they are generally more active. Finally, pregnant women will need more energy than other women because as well as energy for their own bodies, they also need to provide energy that their babies need to develop.
The Mouth
- This is where mechanical digestion happens. (Breakdown of large, insoluble food molecules into small, soluble ones.) This is done through chewing the food with your teeth.
- Salivary glands in the mouth produce amylase enzyme in the saliva, A bolus (ball of food covered in saliva) is created. This makes it easier for the food to be swallowed and broken down.
The Oesophagus
- This is the muscular tube that connects the mouth and the stomach. It squeezes the boluses through your gut with a squeezing action (waves of circular muscle contractions) known as peristalsis.
The stomach
- The stomach produces hydrochloric acid so the protease enzyme has the right pH to work at its best ability. This enzyme helps to churn the food in the stomach and pass it through.
The Pancreas
- Here, protease, amylase and lipase enzymes are produced. They are then released into the small intestine.
Small Intestine
- The enzymes produced in pancreas help to complete digestion here. Nutrients are absorbed out of the alimentary canal into the body.
Large Intestine
- Here, excess water is absorbed from the food.
Diagram of the alimentary canal (gut).
2.27 understand the process of ingestion, digestion, absorption, assimilation and egestion.
- Ingestion - this is putting food or drink into your mouth.
- Digestion - break down of large, insoluble food molecules into smaller, soluble ones by mechanical digestion (teeth and stomach muscles used) or chemical digestion (enzymes and bile used.)
- Absorption - the process that moves molecules through the walls of the intestines (where digestion takes them), into the blood, with digested food molecules absorbed into the small intestine and water mainly absorbed in the large intestine.
- Assimilation - after digested food molecules have been absorbed (in small intestine), they are moved into body cells. They then become part of the cells.
- Egestion - removal of undigested food from the body as faeces, through the anus.
2.28 explain how and why food is moved through the gut by peristalsis
Muscular tissue lines the alimentary canal, and this muscular tissue performs a squeezing action, which is waves of circular muscle contractions, known as peristalsis. These contractions help squeeze boluses (balls of food) through your gut - preventing it from getting clogged up as it would do if the boluses did not pass through. That way, digestion would not properly occur so it would be very detrimental to the human body. It is therefore an important process.
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 by lipases
Digestive enzymes break down large insoluble food molecules, into soluble smaller ones. The molecules they break down are too large to pass through the walls of the digestive system, so they must be broken down in order for digestion to occur.
- The enzyme amylase converts starch into maltose. This maltose is then converted to glucose by maltose. So, amylase and maltose convert starch to glucose.
- Proteases convert proteins into amino acids.
- Lipases covert lipids into glycerol and fatty acids.
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 emulsifying lipids
Bile is produced in the liver and then stored in the gall bladder, before being released into the small intestine. In the small intestine, the enzymes work best in alkaline conditions, however the food that it must absorb is acidic after having been in the stomach. Bile is alkaline so it's presence will help the enzymes in the small intestine to work properly and do their job. Also, bile does emulsify fats. This means it breaks the fat into tiny droplets, giving a much bigger surface area of fat for the enzyme lipases to work on, making its digestion faster.
2.31 describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine
The small intestine is adapted for the absorption of food. One of the ways it is adapted is that it is very long, so there is time to break down and absorb all the food before it leaves the small intestine, helped because of the very large surface area the small intestine has.
The walls of the small intestine are covered in millions of tiny projections called villi. The cells on the surface area of these villi then each have their own microvilli, increasing the surface area even more.
They help the absorption of the products of digestion in this way, as well as their having a single permeable layer of surface cells, allowing molecules to pass through it easily.
It also has a good blood supply, so molecules can travel around at a faster pace.
2.32 describe an experiment to investigate the energy content in a food sample
To find out how much energy food contains, you can burn it. This is known as 'calorimetry' and can be done through the following experiment:
- The food you are burning should be able to burn easily - ie. a dry food, like peanuts or pasta.
- Weigh a small amount of food and then skewer it on mounted needle.
- Then, set up a boiling tube to be held with a clamp (securely, in place.) Add 25cm^3 of water to the tube. This will be used to measure the amount of heat energy that is released upon the food being burnt.
- Measure the initial temperature of the water, then use a Bunsen burner flame to set fire to the food.
- Immediately hold the now burning food under the boiling tube, until the flame goes out. Then relight the food and hold it under the tube, again until it goes out. Continue to do this until the food will not catch fire again.
- Lastly, measure the final temperature of the water (now that your food will no longer catch fire.)
- Then, the following equation must be used in order to calculate the amount of energy in the food.
- Energy in food (J) = Mass of water (g) x Temperature change of water (degrees celcius) x 4.2,
- Energy per gram of food (J/kg) = energy in food (J)/mass of food (g)
- The energy released from burning is lost in the surroundings during this experiment, so to make the experiment as accurate as possible, you can insulate the boiling tube with foil, which would minimise heat loss and keep more energy in the water.
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