Chapter 6 Nutrition

  • The type of feeding employed by plants is called autotrophic nutrition.
  • It involves the synthesis of organic compounds from inorganic raw materials.
  • The different types of autotrophic nutrition that involve the synthesizing of organic compounds from inorganic materials are photosynthesis and chemosynthesis.
  • Organisms that are unable to synthesize their own food substances from simple raw materials must obtain their food in organic form.
  • Such organisms include nearly all animals, all fungi, most bacteria and a few flowering plants. They are known as heterotrophs and their mode of nutrition is know as heterotrophic.
  • The three types of heterotrophic nutrition are holozoic nutrition, saprophytic nutrition and parasitic nutrition.
  • Food is essential for the following:
(a) Provides energy for all biochemical reactions needed for living. Mammals and birds need energy to maintain body temperature.
(b) Provides the materials needed to build cells and tissue for the growth process.
(c) To replace damaged and dead cells. For example the red blood cells need to be constantly replaced.

  • The seven classes of food includes carbohydrate, proteins, lipid, mineral salts, vitamins, roughage and water.
  • Carbohydrates
(a) Starch and sugars are important components of our diet. Starch is present in rice, flour, potatoes and cereals. The main source sugar is sugar cane. Sucrose is cane sugar
(b) Carbohydrates consist of the elements:
carbon hydrogen and oxygen in the
ratio 1 : 2 : 1.
The basic formula ofcarbohydrate is (CH20)n where n is 1. 3, ... For example the formula for glucose is
C6H1206 or (CH20)6.
(c) Glucose is oxidised to release energy, carbon dioxide and water.
(d) Excess glucose is converted into glycogen and fat in the liver. The glycogen is stored in the liver and muscle tissue while the fat is stored in the abdomen and below the skin.
(e) Carbohydrates can be classified into 3 groups.
(i) Monosaccharides include simple sugars like
glucose and fructose.
(ii) Disaccharide is a combination of two units of monosaccharide. Examples are: Maltose is made up of two molecules of glucose. Sucrose is made up of glucose and fructose and lactose is made up of glucose and galactose
(iii) Polysaccharide is a polymer monosaccharides that are comb:a to form a long chain. Example of polysaccharides are starch, chitin cellulose.
(a) Protein is made up a chain of amino acids. When hydrolysed, protein is broken down into amino acids, and absorbed into the blood stream to be used in the synthesis of other types of protein. These proteins are used to synthesise tissues.
(b) Besides the elements C, H and 0 protein also contains nitrogen, phosphorus and sulphur.
(c) Excess amino acids are processed in the liver to produce urea and glycogen. Glycogen is stored in the liver.
(d) Meat, fish, egg, milk and cereals are all sources of protein.

(a) Lipid is composed of the elements carbon, hydrogen and oxygen and exist in various forms such as oil, fat, wax, steroid and phospholipid.
(b) Lipid is an important source of energy. The lipid layer stored in the adipose tissue beneath the skin acts as a heat insulator. Lipid is also a solvent for the vitamins A, D, E and K.
(c) Lipid is divided into two types that is saturated fats and unsaturated fats. Animal fats, butter, margerine and egg yolk have high lipid contents.
Vitamin is an organic compound with the following characteristics:-
  • cannot be digested and does not release energy.
  • not a structural substances
  • needed by the body in very small quantity to
  • maintain health
  • vitamins is required for biochemical reactions and to function as co-enzymes.
Deficiency in specific vitamins can lead to specific deficiency diseases. Deficiency diseases like pellagra, beri-beri, scurvy and rickets can be prevented or overcome by including vitamins in the diet.
The two groups of vitamins are the water soluble, vitamins B and C and the fat soluble, vitamins A, D, E and K.

Mineral Salts
  • Mineral salts are required in small quantities in the ionic form by the body. This is to ensure good health and also to allow physiological processes to proceed efficiently.
  • Macrominerals like magnesium, potassium, calcium, phosphorus and sulphur are required in big amounts, while microminerals like ferum, boron, molybdenum, zinc, manganese and copper are required in smaller quantities.
  • (c) Babies require more calcium and phosphorus compared to adults for building strong bones and teeth. Adolescent girls require more iron than adolescent boys.
  • Consists of cellulose fibres needed for enhancing the peristaltic and defaecation processes. No enzymes for cellulose digestion are present in man.
  • Roughage in the diet prevents constipation

  • About 70 percent of the body is water. The role of water is as a structural molecule and the main participant in biochemical reactions.
  • Water is required for the digestive process and also to transport the products of digestion.
  • A balanced diet is of utmost importance to health.
  • Fats and carbohydrates are sources of energy while proteins are a source of amino acids needed as building units for the growth process, as well as to replace damaged dead cells and tissues.
  • Nutrients when taken in excess or the lack of it can have a negative effect on health.
(a) Excess intake of sugar can lead to tooth decay and obesity.
(b) Excess intake of fat can lead to artheriosclerosis where the fat is deposited on the inside of the artery walls narrowing it.
(c) Salt if taken in excess can lead to hypertension and damaged kidney.
(d) Excess fat soluble vitamins like vitamin A, D, E and K can lead to toxicity in the body, as the vitamins will be stored in the body.
(e) Roughage and water are important components of a balanced diet as they prevent constipation.
(f) Lack of protein in the body can lead to a disease known as kwashiorkor.
(g) Lack of calcium and phosphorus in the diet may lead to osteoporosis.

Digestion can be divided into
(a) Physical digestion.
  • The mechanical breakdown of large food substances into smaller ones. This involves the cutting, grinding and chewing action of the teeth and the movement of food substances through the intestines by peristalsis.
(b) Chemical digestion involves the breakdown of large insoluble, complex food substances in to smaller, soluble and simple substances. The hydrolytic enzymes play an important role in chemical digestion of food.
  • The food that is ingested goes through the following pathway while undergoing the digestive process.
  • Mouth —> oesophagus —> stomach —> small intestine —> big intestine—> anus
  • In the mouth the food is chewed to form the bolus (like a small ball) which is then swallowed and passes through the oesophagus.
  • Peristaltic action of the muscles of the oesophageal wall moves the food to the stomach.
  • The gastric juice secreted by the stomach wall contains hydrochloric acid, and the enzymes pepsin and renin. The partly digested food leaves the stomach as chyme.
  • Absorption of digested food particles takes place in the small intestine.
(a) Duodenum - receives the pancreatic juice from the pancreas and bile from the gallbladder,
(b) Ileum - secretes the intestinal juice to complete the digestive process.

  • The amino acids, glucose, mineral salts, vitamin B and vitamin C are absorbed into the capillary vessel via the villus by diffusion and active transport. They are then transported via the hepatic portal vein to the liver.
  • The fatty acids, glycerol together with the fat soluble vitamins A, D, E and K, are absorbed into the lacteal via the epithelial villi and transported by the lymph-vessel to the left subclavicle vein.
  • 22. The colon absorbs water and eliminates th non-digested food substances. These are acte«l| upon by microorganisms in the colon to release) vitamin B and K.
  • Defaecation is a process whereby the wall the rectum constricts (contracts) to force faeces out through the anus.
  • Plants require 2 groups of minerals for optimum growth.
  • (a) Macronutrients consists of carbon. hydrogen, oxygen, nitrogen, phosphorus-potassium, calcium, magnesium and sulfur These are required in large quantities.
  • (b) Micronutrients include boron, molibdenum. zinc, mangan, copper and ferum. These are required in small quantities.
  • Photosynthesis is a process carried out by green plants. Glucose is synthesised from' inorganic substances such as carbon dioxide and water with the aid of light energy from the sun which is absorbed by the chlorophyll in the green plants.
  • Photosynthesis occurs in two stages.
  • (i) Light reaction - Photolysis of water takes place. In the presence of light the water molecule is split into hydrogen and oxygen.
  • (i) Dark reaction - This stage does not require light. Carbon dioxide combines with hydrogen from the photolysis of water. Carbon dioxide fixation then produces simple carbohydrate like glucose which is then converted into starch for storage purpose.
  • The rate of photosynthesis is influenced by the light intensity, concentration of carbon dioxides, temperature and water supply.
Food quality as well as food quantity can be increased by the following methods and technology:
(i) The scattering method of pady planting
(ii) Hydrophonic and aerophonic methods of
planting vegetables.
(iii) Cross-breeding
(iv) Tissue culture
(v) Genetic engineering
(vi) Efficient utilisation of land.
(vii) The use of biological control to eliminate

Food processing is important
(i) in overcoming food spoilage by oxidation and microbial activities.
(ii) to lengthen the life span of food
(iii) to recduce food wastage
(iv) to widen the consumption of food.
(v) to provide sufficient food for all.
The methods of food processing include
(i) Dehydration
(ii) Freezing
(iii) Drying
(iv) Salting
(v) Preservation
(vi) Sterilizing


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