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Nutrition and digestion

Nutrition= Getting food

It is one of the 7 Life Processes (remember MRS GREN)

While plants make their own food through Photosynthesis, animals are consumers; they have to Eat other organisms to get nutrients.

Animals need these 7 Groups of nutrients:

  • Carbohydrates
  • Proteins
  • Fats
  • Vitamins
  • Fibre
  • Mineral elements
  • Water

We need Carbohydrates, proteins and fats in relatively large amounts- they are Macro nutrients, Vitamins and mineral elements are needed in small amounts, they are Micro nutrients but they are still important for health.

The table below summarises what we need each nutrient for and the foods that can supply us with it:

Nutrient Uses (What we need it for) Source foods
Carbohydrates (sweet sugars and starches) Energy source- used directly in respiration

Cakes, Jam, sweets etc for sweet sugars

Rice, pasta, chips, bread etc for starch

Proteins For growth and repair (making new cells and enzymes)

Meat (beef, chicken, fish, lamb etc), eggs

Milk products, beans, peas

Fats Energy store, insulation (to keep warm), prevent water loss and for making cell membranes Fried foods, meat, fish
Fibre To prevent consipation (For a good working digestive system) Vegetables and plant foods
Minerals For health (there are many of them but they contribute to a healthy life in many ways e.g. Calcium-for strong teeth and bones, Iron- to make red blood cells) Fruits and vegetables, milk (calcium), meat (iron)
Vitamins For health (Like minerals, there are many of them but they contribute to a healthy life in many ways e.g. Vit D- for strong bones and teeth, helps absorb calcium, Vit C- for healthy gums, teeth and skin, Vit B group-they help in respiration) Fruits and vegetables, fish, meat
Water For hydration, to dissolve other nutrients and carry them around in blood, for cooling. Any wet food, drinks


Food tests

You may be required to find out what nutrients particular foods contain. Here are the 4 main tests that are usually done in Junior school science:

1. Testing for starch


  • Add a few drops of Iodine solution (orange-brown) to a sample of the food


  • A blue-black colour shows that starch is present

2. Testing for sugar/glucose


  • Dissolve a sample of the food in water
  • Add a few drops of Benedict solution
  • Heat in a water bath


  • An orange red colour indicates that glucose is present (The colour will go througha whole range on the spectrum from green, yellow brown to red depending on how much glucose is there)

3. Testing for proteins- the Biuret test


  • Add a few drops of Sodium hydroxide to the solution
  • Follow with a few drops of Copper sulphate solution


  • A lilac/purple colour shows that proteins are present.

4. Testing for fats/oils- The Ethanol emulsion test

  • Shake the sample in a test tube with Ethanol.
  • Add a few drops of water


  • A cloudy precipitate shows that fats are present


Deficiency diseases

A deficiency is a shortage of something

People can have a deficiency disease if they are short of any of these food nutrients e.g.

  • Scurvy- cracking, bleeding lips and gums = shortage of Vitamin C
  • Rickets- bent legs = shortage of Vitamin D
  • Anaemia- Very few red blood cells = shortage of Iron.

*Luckily, you can cure a deficiency disease by giving the person the nutrient that they are short of.



When you take in more carbohydrates than you need for activity, the excess is stored as fat. You put on weight and become overweight. This may continue until you are obese. Being overweight and obese refer to your Body Mass Index (BMI).

Obesity puts you at risk of heart disease, arthritis and diabetes.

The key is to make sure you balance the energy intake and use.

Heart disease

Eating too much animal fat is risky to your life. These saturated fats can block blood vessels around your heart and you may suffer a Heart attack. This is when heart muscle is starved of oxygen and it cannot pump.



 Challenge yourself

What is a water bath? Why is the sample not heated directly over a Bunsen burner flame?


Find out about another test for fats.

How can we find out how much Vit. C a food has?