Human Nutrition


Biological Molecules


  • Carbohydrates are made up of Simple Sugars
  • Starch and glycogen are large, complex carbohydrates which are made up of many smaller units (e.g glucose and maltose) joined together in a long chain.


  • Proteins are made up of long chains of amino acids
  • They all contain carbon, nitrogen, hydrogen and oxygen atoms


  • Fats and oils are built from fatty acids and glycerol
  • Lipids contain carbon, hydrogen and oxygen atoms.
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Biological Molecules - Tests

Benedicts Reagent Test for Glucose

  • Add blue benedicts raegent to a sample and heat it
  • The colour changes from BLUE > BRICK RED

Iodine Test - Test for Starch

  • If starch is present, the sample changes from BROWNY/ORANGE > BLUE/BLACK
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Balanced Diet

- e.g pasta, rice, sugar
- They provide energy

- e.g butter, oily fish
- Provide energy, act as an energy store and provide insulation

- e.g meat, fish
- Needed for growth and repair of tissue and to provide energy insulation

- A > e.g liver, helps to improve vision and keep skin and hair healthy
- B > e.g oranges, needed to prevent scurvy
- C > e.g eggs, needed for calcium absorption

- calcium > e.g milk, cheese, needed to make bones and teeth
- iron > e.g red meat, needed to make haemoglobin for healthy blood

- e.g wholemeal bread, aids the movement of food through the gut

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Energy From Food


  • First get food that will burn easily, something dry e.g peanuts or pasta
  • Weigh a small amount of the food and skewer it on a mounted needle
  • Add 25cm3 of water to a boiling tube
  • Measure the temperature of the water, then set fire to the food using a bunsen burner. Make sure the flame is away from the water to avoid inaccurate results
  • Hold the burning food under the boiling tube till it goes out. Relight the food until it wont catch fire again
  • Measure the temperature of the water again


Energy in food (J) = Mass of water (g) x Temperature change (degrees c) x 4.2

Energy per gram of food (J/g) = Energy in food (J) / Mass of food (g)

The experment is not completely accurate because energy can be lost to the surroundings. Insulating the boiling tube e.g foil would make it more accurate.

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Enzymes and Digestion

  • Starch, proteins and fats are BIG molecules. They are too big to pass through the walls of the digestive system. They are also insoluble
  • Sugars, amino acids, glycerol and fatty acids are much smaller molecules, are soluble and can pass through the walls
  • The digestive enzymes break down the BIG molecules into smaller ones






  • Produced in the liver and stored in the gall bladder before its released into the small intestine
  • The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline and neutralises the acid and makes alkaline conditions. The enzymes work better in these conditions
  • Bile emulsifies fats and increases surface area to make digestion faster
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The Alimentary Canal

MOUTH - Salivary glands in the mouth produce amylase, teeth break down food mechanically

OESOPHAGUS - The muscular tube that connects the mouth and stomach

LIVER - Where bile is produced

STOMACH - Pummels food, produces protease enzyme (pepsin), produces hydrochloric acid to kill bacteria and provide the right pH for protease (pH 2)

GALL BLADDER - Where bile is stored 

PANCREAS - Produces protease, amylase and lipase enzymes. Releases these into the small intestine

LARGE INTESTINE - Where excess water is absorbed from the food

SMALL INTESTINE - Produces protease, amylase and lipase enzymes to complete digestion, also where the nutrients are absorbed out of the alimentary canal

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The Digestive Process

INGESTION - Putting food (or drink) into your mouth

DIGESTION - After ingestion, you need to digest food either mechanically or chemically

ABSORPTION - The process of moving the molecules through the walls of the intestines into the blood. Molecules are absorbed in the small intestine and water is absorbed in the large intestine

ASSIMILATION - When they move into body cells and become part of the cells

EGESTION - All of the undigested food, forming faeces via the anus


  • Large surface area because of micro villi, millions of folds
  • Good blood supply because of the capillary network, increasing the rate of diffusion
  • One cell thick to create a short diffusion pathway
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