Food
Food is material rich in protein, carbohydrate and lipid and is needed by living organisms for energy, growth, repair, defence and reproduction. Food also contains vitamins and minerals
Protein
Amino acids are the subunits of proteins which are linked by peptide bonds in chains. There are twenty different amino acids . Proteins are made by ribosomes in cells. There are ten essential amino acids, i.e., need to be obtained in the diet which can be found in meat, fish, cheese, pulses.
The human body is not able to store excess protein so excess amino acids are converted to other useful materials in the liver. During this conversion a toxic waste known as urea is formed. Urea is passed from the liver into the blood and excreted by the kidneys.
Basic functions of proteins:
Proteins are needed for growth and repair of body tissue. Proteins can have structural functions in the body such as keratin in hair and skin, collagen in tendons, ligaments, connective tissue and bone, Some proteins are more active such as hormones, antibodies and enzymes.
Carbohydrate
Provide a source of energy. Carbohydrates can be stored as starch in plants or glycogen in animals. Carbohydrates also play a structural role eg cellulose walls of plant cells and chitin in the cell walls of fungi and the exoskeleton of arthropods. Chemically carbohydrates contain the elements C, H and O with the general Formula Cx(H2O)y . Monosaccharides are single sugars such as Glucose (in fruit, honey), Fructose and Galactose. Disaccharides are double sugars consisting of 2 monosaccharides combined. Maltose = glucose + glucose, Sucrose = glucose + fructose, Lactose (milk sugar) = glucose + galactose. Polysaccharides are chains of sugar units such as starch and glycogen
Composed of glycerol with three fatty acids linked to the glycerol.
Lipids have more than twice the energy of carbohydrate or protein. Functions: respiration, energy storage, heat insulation. Adipose tissue is a fat storage tissue in animals. Good Sources: butter, cheese, plant oils,
Vitamins
Vitamins are organic compounds not normally made by the organism but are required in small quantities in the diet for health.
Vitamin C (ascorbic acid) is found in fresh fruit and vegetables
and is soluble in water. It is needed to make and maintain connective tissue. Long term deficiency of vitamin C causes a disease called scurvy. The major symptoms of scurvy include internal bleeding, bruising, bleeding gums.
Vitamin D (calciferol) is obtained from milk, eggs, liver, and fish liver oils. Vitamin is also produced in skin exposed to UV light. Vitamin D is a fat-soluble vitamin. It is needed for bone and tooth formation, bone maintenance and the absorption of calcium from the gut. Long-term deficiencies cause diseases known as rickets and osteomalacia. The major symptoms of vitamin D deficiency include late teething, deformed legs and arms, weak bones.
Minerals
Sodium (Na) maintenance of the blood at the correct concentration. It is in salt and meat. Calcium (Ca): needed for teeth, bones and blood clotting. Found in milk and cheese
Phosphorus (P): needed for ATP, DNA, RNA, bone formation. Present in cheese and milk.
Iron (Fe): needed for the formation of haemoglobin. Found in meat and green vegetables.
Fluorine (F): needed to protect teeth form decay. In drinking water and toothpaste.
Iodine (I): needed by thyroid gland to make thyroxin hormone. Available in sea food
Water: H2O
Water expands when it freezes becoming less dense so ice floats in water. Prevents the complete freezing of ponds and lakes as the layer of floating ice insulates the warmer water below keeping it above 0°C and in a liquid state. The aquatic organisms survive the cold conditions of winter. Water is an ideal medium to transport suspended solids and solutes in the blood and through vascular tissues in plants. Water is an excellent solvent and an ideal medium for chemical reactions as it can contain a rich variety of solutes. The surface tension allows small animals to ‘walk on’ or ‘hang from’ the surface. Water ensures a temperature stable environment suitable for efficient constant enzyme action. Evaporation of sweat using body heat is an excellent cooling mechanism. Transpiration prevents leaves overheating in direct sunlight. Water is a raw material for photosynthesis.
Food Tests
Starch: iodine solution is used, a blue-black colour indicates that starch is present.
Reducing sugar: e.g. glucose, fructose, maltose, and lactose. (Sucrose is a non-reducing sugar).
Add an equal volume of Benedict’s Reagent to the food solution, heat but do not boil, a brick-red colour indicates that reducing sugar is present.
Lipid: rub the food onto brown paper; a translucent stain indicates fat is present.
Protein: Biuret test Add sodium hydroxide solution to the food solution. Then add a few drops of blue copper sulphate solution. Shake the contents vigorously. A purple violet colour indicates protein is present.
