Nutrients (cont'd)
Monacia Williams, Contributor

Welcome again to our series of lessons. I hope they have been useful so far and are helping you in your progress towards getting the coveted Grade One in the examination.

Today, we will be looking at the last macronutrient - lipids. These comprise fats and oils. Fats are solids at room temperature, while oils are liquids. Remember now that these molecules are not called macronutrients, because they are big molecules, but because they are required in large amounts in the diet. Do you remember that these macronutrients are called macromolecules and that polysaccharides and proteins are also polymers, but lipids are not polymers? Lipids are not polymers because they do not comprise repeating chains of the same units. Polysaccharides are polymers of monosaccharide units, while proteins are polymers of amino acids.

Composition of lipids

Lipids are composed of four molecules - three fatty acid molecules and one glycerol molecule. They contain the elements carbon, hydrogen and oxygen. Note that these are the same elements present in carbohydrates, but here the ratio of hydrogen to oxygen is 2:1, while in lipids there are very few oxygen molecules and many, many hydrogen molecules. This fact gives lipids many of its properties.

Characteristics and properties of lipids

• They are insoluble in water.
• They are an important source of energy, but are only used after carbohydrates have been used up by the body.
• They are important storage compounds for many plant seeds. Can you think of any? Did Soya bean, sunflower, coconut or corn come to mind? If they did, congratulations, you are correct!
• They are poor conductors of heat so they act as insulation. Most animals have a layer of fat under their skin. This layer is thicker in animals that live in countries with cold temperatures. In diving animals, the layer is called blubber and is an important insulator as well as an aid in maintaining buoyancy.
• They give waterproofing and water-repellant properties to plant leaves, insect cuticles, skin and fur.
• Fats also protect organs like the kidneys from mechanical damage.

Test for lipids

There are two tests that can be used to show the presence of fats in foods. You are required to know both. One is very easy to remember, but the other is a bit more difficult. The easy one is called the grease spot test; the more difficult is the emulsion or ethanol test.

Grease spot test

Place a drop of the unknown sample on to a piece of paper. Allow to dry. If a permanent, translucent spot results, the unknown either contained a lipid or was a lipid.

Emulsion or ethanol test

Add 3cm3 of liquid sample to a test tube then add the same quantity of ethanol. Shake the mixture vigorously and add 3cm3 of water. If a cloudy, white suspension results when the water is added, then the unknown either contained a lipid or was a lipid.

Micronutrients

These are the vitamins and minerals. Vitamins are organic molecules and minerals are inorganic molecules. They are required by the body in small amounts, hence they are called micronutrients.

Vitamins

Unlike the macronutrients, they have no common structure or function, but are essential for good health even though they are only needed in small amounts. You are required to know the source of each vitamin as well as its function in the body and the deficiency disease that the lack of it causes.

Vitamins can be placed in two groups:

• Fat soluble, for example vitamins A, D and E.
• Water soluble, for example B group vitamins and Vitamin C

Fat-soluble vitamins are taken in with fatty foods and water-soluble ones in fruits and vegetables.

This will help you to remember the sources or the foods from which the body can obtain these nutrients. Example: Vitamin A is fat-soluble and found in cod liver oil, egg yolk and dairy products. These are all fat-enriched foods. Vitamin C, which is water soluble, is found in citrus fruits and green vegetables.

You need to note also that questions are frequently set on the sources of the vitamins as well as the reactions of the body to their deficiencies, so make an effort to learn these before you move on to another topic.

Minerals

These differ from all the other nutrients in that they are inorganic molecules. This means that they do not contain carbon and are not formed in living organisms. The main minerals required are:

• Calcium
• Iron
• Iodine
• Phosphorus

For these you are also required to know their sources, their functions and the deficiency diseases that their lack will cause.

We have now completed our study of nutrients. I hope this study has helped to make the things you have learnt in class a bit clearer in your minds. Have fun studying!

Monacia Williams teaches at Glenmuir High School.