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Chapter: Nutrition


Nutrition is the taking in of nutrients which are organic substances and minerals, then absorbing and assimilating them.

Organic Molecules:

Biological molecules found in the living organisms are usually called organic molecules. Organic molecules provide energy to carry out life processes and raw materials for the growth and repair of tissues. Nutrition provides living organisms with the molecules that they need. There are four different groups of organic substances used by living organisms and they are as follows.

  1. Carbohydrates
  2. Lipids
  3. Proteins
  4. Nucleic acids

1. Carbohydrates:

Carbohydrates are a type of biomolecules. They are one of the most important nutrients. They provide energy to our body. Carbon, hydrogen and oxygen form carbohydrates. The ratio of hydrogen and oxygen in most of the carbohydrates is 2:1. The carbohydrates in biochemistry are called as saccharides. The term saccharide comes from Greek and the meaning of it is sugar.

Synthesis of carbohydrates:

Monosaccharides are the simplest form of carbohydrates that is they are made of a single sugar unit. A well known example of monosaccharides is the glucose. Glucose is the main source of energy for most of the cells. It is easily transported in blood and dissolves in cytoplasm because of its soluble nature. Polysaccahrides are the complex form of carbohydrates that are formed from monosaccharides. Starch and glycogen are the most important polysaccharides. They are formed from several thousand glucose units. Thousands of glucose units join together by condensation reaction resulting in polysaccharides like starch and glycogen.

2. Lipids:

Lipids are group of organic compounds having oily and greasy consistency. Lipids are a heterogeneous group of compounds like fats, oils, steroids, waxes etc. lipids are mainly composed of carbon, hydrogen and oxygen but the ratio of H: O is greater than carbohydrates, i.e. it is more than 2:1.

Synthesis of lipids:

Three molecules of fatty acids undergo condensation reaction with one molecule of glycerol to form lipids.

3. Proteins:

Proteins are the most abundant organic molecules found in living system. They constitute about 50% of dry weight of cells. Proteins are considered as the fundamental basis of structure and function of life. Proteins are mainly composed of five different elements and they are carbon, hydrogen, oxygen, nitrogen and sulphur.

Synthesis of proteins:

Amino acids are the building blocks of proteins. There about 20 different amino acids known to be existing in nature. These amino acids are joined together in a particular sequence forming a long chain of amino acids which is called as protein. The sequence in which the amino acids are arranged determines the shape of a protein molecule.

Biochemical tests:

A. Test for starch:

  1. Iodine solution is used to check the presence of starch.
  2. Take about 2cm3 amount of an unknown solution and few drops of iodine to it.
  3. Now, gently shake the mixture.
  4. Appearance of a deep blue-black solution is considered as a positive result indicating the presence of starch.

B. Test for Proteins:

  1. Biuret reagent is used to check the presence of proteins.
  2. Add few drops of Biuret reagent to about 2cm3 of the unknown solution.
  3. Now, gently shake the mixture.
  4. Appearance of a purple colour is considered as a positive result indicating the presence of protein.

C. Test for reducing sugars:

  1. Benedict’s reagent is used to detect the presence of reducing sugars like glucose.
  2. Add 2cm3 of Benedict’s reagent to 2cm3 of the unknown solution.
  3. Now heat the mixture in a boiling water bath for about 2-3 minutes
  4. Appearance of an orange/brick red colour indicates the presence of glucose.

D. Test for fats:

  1. Add 2cm3 of ethanol to an unknown solution and then gently shake the mixture.
  2. Now pour the mixture into a test tube containing an equal amount of distilled water.
  3. Appearance of a milky white emulsion indicates the presence of lipid.

Sources of organic compounds and their importance:

1. Carbohydrates:

Sources of carbohydrates:

Starch which is one of the most important carbohydrates is obtained from rice, potato, wheat and other type of cereals. Refined sugars like sucrose and glucose are obtained from food sweeteners like deserts, sweets and soft drinks.

Functions of carbohydrates:

Glucose which is one of the most important carbohydrates is a very important source of energy for all the living organisms. Glucose provides energy which is utilized for cell division, muscle contraction and for the manufacture of large biomolecules. Excess glucose is converted into glycogen (polysaccharide) through the process of glycogenisis. Whenever energy is required by the body, especially during fasting conditions the glycogen is broken down into glucose through the process of glycogenolysis.

2. Lipids:

Sources of lipids:

  1. Saturated fats and cholesterol are mostly available through meat and animal food like egg, milk, cheese.
  2. Unsaturated fats are obtained from plant sources such as sunflower seeds and peanuts.

Functions of lipids:

  1. Fats and oils are very important sources of energy. They serve as an energy reserve as they are insoluble in water.
  2. Fats provide us with insulations. They provide electrical insulation around nerve cells and thermal insulation beneath the skin.
  3. Lipids are the important constituents of the cell membrane.
  4. Steroid hormones like the sex hormones are synthesized from cholesterol.

3. Proteins:

Sources of proteins:

  1. Meat, egg and fish are the most important sources of proteins from animals.
  2. Legumes like peas and beans, pulses are sources of proteins from plants.
  3. Soya bean which contains a very little amount of fat is the best source of protein. It is suitable for people with health problems caused by fat.

Functions of proteins:

Proteins play a very important role in our body. Let us look at the most important functions of proteins.

  1. All the enzymes which catalyse very important functions in the body are made up of proteins.
  2. Haemoglobin which is a very important transport molecule is formed of proteins.
  3. Structural materials in the muscles are nothing but proteins.
  4. Most of the hormones which play a very important role in our body are made of proteins. For example: insulin.
  5. Antibodies which play a very important role in providing immunity to the body are made up of proteins.

Sources of vitamins and their importance

1. Vitamin C:

It is a water soluble vitamin and is also called as ascorbic acid.

Sources of vitamin C:

  1. Citrus fruits like lemon, orange, sweet lime and green leafy vegetables are the important sources of vitamin C.

Functions of vitamin C:

  1. Vitamin C is required for the growth and repair of tissues in all parts of the body.
  2. Scars on the skin can be healed by consuming good amounts of vitamin C.
  3. Vitamin C protects the cells from ageing.

Deficiency symptoms of vitamin C:

  1. Deficiency of vitamin C results in scurvy. Scurvy results in sore gums and loose teeth, anemia, fragile blood vessels, swollen joints, delayed wound healing etc.

Vitamin D:

It is a fat soluble vitamin and resembles the structure of a steroid.

Sources of vitamin D:

Dairy products, eggs, fish liver oil are the major sources of vitamin D.

Functions of vitamin D:

  1. The most important and vital function of vitamin D is regulating the absorption of calcium and phosphorus.
  2. Vitamin D maintains the normal functioning of immune system.
  3. Sufficient intake of vitamin D helps in proper bone and teeth development.

Deficiency symptoms:

  1. Deficiency of vitamin D results in a bone disease called rickets, a condition where bones become soft and bend resulting in bow shaped legs.

Sources of minerals, their importance and deficiency symptoms:

1. Calcium:

Source of calcium:

Milk, cheese and fish are the important source of calcium. To some extent even green leafy vegetables provide us with calcium.

Functions of calcium:

  1. Calcium is required for the development of bones and teeth.
  2. Calcium interacts with troponin C and thereby by triggers muscle contraction.
  3. Most of the reactions in blood clotting cascade are dependent on calcium
  4. Calcium is required for the transmission of nerve impulses.
  5. Cell membranes permeability is maintained by calcium.
  6. Calcium facilitates release of hormones like insulin and PTH from the endocrine gland.

Deficiency symptoms:

  1. Poor clotting of blood.
  2. Rickets, osteomalacia, osteoporosis
  3. Uncontrolled muscle contractions.

2. Iron:

Sources of iron:

Green leafy vegetables like spinach, fruits like apple, red meat, liver, whole grains, tofu, and dark chocolates are some of the important sources of iron.

Functions of iron:

  1. Haemoglobin and myoglobin which contain iron are required for the transport of O2 and CO2.
  2. Cytochromes which contain iron are necessary to carry out electron transport chain.
  3. Peroxidase which is a lysosomal enzyme contains iron and is mainly useful for phagocytosis and killing of bacteria by neutrophils.

Deficiency symptoms:

Anaemia is a disease which occurs due to shortage of haemoglobin in the body. Iron is needed to produce haemoglobin. So indirectly deficiency of iron leads to anaemia.

3. Water:

Nearly 70% of the human body is composed of water and about two-thirds of this water is present in cytoplasm and the remaining amount is present in tissue fluids and blood plasma. Humans lose about 1.5 liters of water every day through urine, faeces and sweat. The water that is lost from the body has to be replaced by water in the diet. Water can be taken in three main ways.

  1. In the form of drink
  2. In food, especially salads containing tomato and lettuce.
  3. Water is also obtained through metabolic reactions taking place in the body as water is one of the products of metabolic reactions like aerobic respiration.

Loss of 5% water from the body leads to unconsciousness and 10% loss can be fatal.

4. Fibres:

The indigestible part of the food is called as dietary fibre. Cellulose from plant cell walls forms the dietary fibre. Taking large amounts of fibres in the diet helps in easy digestion by stretching the muscles of the gut walls and thereby pushing food along by peristalsis. Shortage of fibre in the diet can lead to constipation which later may result in bowel cancer.

Plant Nutrition


It is defined as the physico-chemical process by which plants convert light energy, normally derived from the sun into chemical energy that can be later released to fuel the organisms’ activities.

Plants require sunlight, carbon dioxide and water to carry out photosynthesis. Oxygen is released as the waste product of photosynthesis which is utilized by all life forms on earth for respiration.

Plants and other organisms which carry out photosynthesis are called photo autotrophs. Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on earth.

Equation of Photosynthesis:




Requirements for photosynthesis:

The process of photosynthesis depends on the following:

  1. Availability of light
  2. The presence of pigments to absorb light
  3. A supply of carbon dioxide and water
  4. A temperature suitable for enzyme activity

Let us look into detail of the above mentioned factors:

1. Availability of light:

Light provides energy for the process of photosynthesis. The light energy absorbed by the plant depends on the intensity of light, the wavelength of light, the duration of light availability.

2. Pigments for the absorption of light:

Chlorophyll is the pigment which absorbs light. Magnesium ions are required for the synthesis of chlorophyll and these ions are supplied from the soil.

3. Carbon dioxide concentration and availability of water: 

The concentration of carbon dioxide has a major influence on the rate of photosynthesis since it is the substrate that is in shortest supply. Shortage of water closes stomata which limits the carbon dioxide uptake. There is always sufficient water for the process of photosynthesis

4. Temperature:

Temperature affects the rate of enzyme activity. The rate of enzyme activity can be doubled with a 10oC rise in temperature. The rise in temperature is effective in leaves and roots.

Site of Photosynthesis:

Photosynthesis takes place in chloroplast which is found in the mesophyll cells of green leaves. Let us take a look at the structure of chloroplast for a better understanding of photosynthesis.

Structure of chloroplast:




  1. Inside the chloroplast is a membranous system consisting of grana, the stroma lamella and the fluid stroma.
  2. The stacks of thylakoids contain pigments which trap light energy and synthesize ATP and NADPH(chemical energy), these reactions are called light reactions as they are directly driven by light
  3. In stroma, enzymatic reactions take place leading to the incorporation of CO2 into the plant leading to the synthesis of sugar. Sugar is later converted into starch. These reactions are called dark reactions as they are not directly driven by light.

Leaf Structure



In order to carry out photosynthesis efficiently a leaf cell needs to exchange gases with the surroundings. Let us look into detail of leaf structure

1. Waxy cuticle:

It plays an important role by reducing the loss of water. The waxy cuticle is thicker on the upper surface since the upper surface is exposed more to the warming rays of sun.

2. Upper epidermis:

Upper epidermis forms the complete covering and is usually one cell thick. It is transparent in nature allowing free passage of light. The main function of upper epidermis is preventing the entry of disease causing microorganisms such as bacteria and fungi.

3. Palisade mesophyll :

These mesophyll cells are tall and thin. They are arranged in columns separated by narrow spaces. Mesophyll cells contain chloroplasts and the dense packing of these cells the absorption of maximum amount of light energy.

4. Vein:

It serves as the transport system in and out of the leaf. The xylem vessels deliver water and mineral salts and the phloem carry away the organic products of photosynthesis.

5. Spongy mesophyll:

These cells are loosely packed and covered with a thin layer of water. The air spaces present between these loosely packed cells help in the diffusion of gases through the leaf. The air spaces are saturated with water vapour so water diffuses out of the leaf.

6. Stomata:

They are the minute openings present in the lower epidermis. These minute openings allow the entry of carbon dioxide and the exit of oxygen. The stomata can be closed when no carbon dioxide intake is needed. Guard cells control the opening and closing of stomata.

Mineral Requirements

Plants need minerals to make food molecules such as amino acids, proteins and nucleic acids from the carbohydrates produced during photosynthesis. Plants take up minerals from the soil in the form of ions. Let us see what the actual role of ions is.

Minerals in soil: The type of minerals present in the soil depends on the decomposition of plant and animal remains present in the soil and the type of rock that is present beneath the soil. Minerals are taken out from the soil by plants. In uncultivated soils there is always a balance between the formation and loss of minerals. In cultivated soils, the ground is prepared for harvesting the plants. Plants take up minerals from the soil and as a result the level of minerals like nitrate and phosphorus reduces. So farmers add minerals to the soil in the form of fertilizers. Fertilizers could be natural like the sewage sludge, animal manure or they could be artificial fertilizers. NPK fertilizer is the most common artificial fertilizer. It contains three main nutrients- nitrogen (N), phosphorus (P) and potassium (K).

Magnesium ions: Magnesium is taken up the plants from the soil in the form of magnesium ions. The main role of magnesium is that it forms a part of the chlorophyll molecule. Deficiency of magnesium can lead to chlorosis. Chlorosis is a condition where plant leaves turn yellow.

Nitrogen ions: Nitrogen is taken up from the soil in the form of nitrate ions or ammonium ions. Nitrogen is mainly required by the plants for the synthesis of proteins including enzymes. Deficiency of nitrogen leads to stunted growth, with weak stem and dead leaves.


In order to maintain or improve the fertility of the soil, chemical fertilizers are supplied in proper doses before and during the cultivation of each crop. These chemicals are soluble in water and are readily absorbed by the plants. A chemical fertilizer is compact and concentrated and it is easily to handle.

Continuous use of chemical fertilizers can turn the soil infertile by reducing the organic matter present in the soil and by killing the natural microbial flora present in the soil. Organic farming technique has been developed to overcome this problem.

Balanced diet

A balanced diet is something that supplies our body with nutrition required for the proper functioning of the body. A balanced diet is defined as the diet which contains different types of food, processing the carbohydrates, fats, proteins, vitamins and minerals in a proportion to meet the requirements of the body. A balanced diet supplies a little more of each nutrient than required in order to keep an individual in a healthy state. The basic composition of balanced diet varies from country to country depending on the availability of food. Economic status, age, sex and the physical activity of individual influence the intake of diet. The nutrition expert group, formed by the Indian Council of Agricultural Research has recommended a balanced diet for Indians. This was prepared based on the foods available in India.


Malnutrition means ‘bad feeding’. Bad feeding includes the following:

  1. Eating too much of food, i.e. eating much more than what is required.
  2. Having too less food.
  3. Eating food in wrong proportion, for example eating more amounts of fatty food and too less amount of carbohydrate containing food.

Unbalanced diet results in several health problems. Let us look into some of them.

1. Coronary heart disease:

It results due to excessive consumption of saturated fats and cholesterol. High amounts of saturated fats and cholesterol in the diet can block the blood vessels which supply oxygen to heart muscles.

2. Constipation:

Constipation occurs because of taking very less amounts of fibre in the diet. Faeces are not passed regularly as they should because of taking very little amounts of fibre in the diet.

3. Obesity:

It is a condition of overweight and it occurs due to excessive consumption of food than required for carrying out normal body activity and metabolism.

Food Supply

Different types of farming techniques have been developed to increase the food production to meet the demand of increasing population. Let us take a look at some of the modern techniques

Chemical fertilizers:

Fertilizers are commercially produced plant nutrients. A chemical fertilizer contains the primary plant nutrients namely nitrogen, potassium and phosphorus, which makes the soil more fertile and enhances the growth of plants. Fertilizers can be of three main types:


Serial no:

Fertilizer type




Ammonium Sulphate, Urea, Ammonium nitrate.



Superphosphate, Ammonium phosphate, Ammophos.



Potassium chloride, Potassium sulphate, Potassium nitrate


In order to maintain or improve the fertility of the soil, chemical fertilizers are supplied in proper doses before and during the cultivation of each crop. These chemicals are soluble in water and are readily absorbed by the plants. A chemical fertilizer is compact and concentrated and it is easily to handle.


The crops in the field are exposed to many factors. The crop plants may be destroyed by insects, rodents, birds, etc. Sometimes the crops get infested by pests, weeds and diseases. Pests are organisms that bring about moderate to heavy damage to the standing crops. The common pests are insects, mites, aphids, rats, birds etc. Chemicals used to protect the crops from these organisms are called Pesticides. There are mainly two methods adopted to control the pests.

  1. Chemical control: The control of pests using pesticides is called chemical control. Pesticides are sprayed by using a hand operated machine or by power operated sprayer. Fumigation and dusting are other methods of using pesticides.
  2. Biological control: It is the method of controlling the pests by deliberately leaving biological agents like insects or any other living organism into the field. These organisms will kill the pests and save the crops.  Biological control is a very slow process of controlling the pests but is a highly specific and eco- friendly process too.


They are a type of pesticides used to kill the unwanted plants which are called as weeds. Therefore, herbicides are also called as weedkillers.

Artificial selection:

It is the intentional breeding of plants and animals. It is something similar to selective breeding. Farmers have allowed the reproduction of plants and animals with desirable characters, causing evolution of livestock. This is called artificial selection.

Modern agricultural equipment:

The modern agricultural equipment used today has made farming easy. Tractor is one of the modern equipment used in today’s agriculture. Cultivators, chisel pow, harrow and plough are the equipment used for soil cultivation. Planting is done using broadcaster seeder, planter, plastic mulch layer etc. fertilizers are sprayed using manure spreader, slurry irrigator, sprayer etc. Harvesting is done using various types of modern equipment like rotavator, bean harvester, combine harvester, conveyer belt.

Human digestive system and the process of digestion




Let us look and understand few terms.

  1. Ingestion: It is defined as the process of taking in food through mouth
  2. Egestion: It is defined as the process of passing out of undigested food in the form of faeces through the anus.

Process of digestion:

The alimentary canal is basically a long tube extending from the mouth to the anus. The tube has different parts. Various regions are specialised to perform different functions. The process of digestion is accomplished by mechanical and chemical processes.

  1. The buccal cavity performs two major functions, mastication of food and facilitation of swallowing. The teeth and tongue with the help of saliva masticate and mix up the food thoroughly.
  2. The saliva secreted into the oral cavity contains electrolytes and enzymes like salivary amylase and lysozyme which help in the breakdown of food. Mucus in the saliva helps in lubricating and adhering the masticated food particles into a bolus. Which is then transported into pharynx and then into oesophagus by swallowing.
  3. The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis.
  4. The gastro-oesophagal sphincter controls the passage of food into the stomach.
  5. The food is stored in the stomach for about 4-5 hours. The food inside the stomach is mixed thoroughly with the gastric juices secreted by the stomach. The mixing of the food takes place with the help of churning movements of the muscular wall of the stomach and the mixed food is called as chyme.
  6. Pepsin converts proteins into proteases and peptones. The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated HCl.
  7. Lipases are the enzymes used for the digestion of lipids and small amounts of this enzyme are secreted by the gastric glands.
  8. Various types of movements generated by the muscularis layer of small intestine help in the thorough mixing of food with various types of secretions of the small intestine and thereby facilitate the digestion of food.
  9. The bile, pancreatic juice and the intestinal juice are the secretions released in small intestine.
  10.  The pancreatic juice contains inactive enzymes like trypsin, chymotripsinogen, procarboxypeptidase, amylases, lipases, and nucleases. Trypsinogen is activated into active trypsin by the enzyme enterokinase secreted by the intestinal mucosa. Active trypsin activates other enzymes in the pancreatic juice.
  11. Bile which is released into duodenum contains bile salts, cholesterol and phospholipids which help in emulsification of fats.
  12. The enzymes present in the intestinal juices secreted by small intestine convert the proteins to amino acids, carbohydrates to glucose and fats into fatty acids and glycerol.
  13. The walls of the small intestine absorb the digested food. The inner lining of small intestine which has a number of finger like projections called villi increases the surface area of absorption.
  14. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body, where it is utilized for obtaining energy, building up new tissues and repairing of the old tissues.
  15. The unabsorbed food is taken up by large intestine where more villi absorb water from this material. The remaining material is removed from the body through anus. The removal of waste material from anus is regulated by anal sphincter.