Nutrition may be defined  as the science  of food and its relationship  to health.  It is concerned primarily with  the part played by nutrients in  body  growth, development  and maintenance. The  word nutrient or " food factor" is used for specific  dietary  constituents such as  proteins,  vitamins and minerals. Dietetics is the practical  application of the  principles of nutrition; it includes the planning  of meals for the  well and the sick. Good nutrition means " maintaining  a nutritional  status that enables us to grow well and enjoy good health".

Changing concepts:

  Through centuries, food has been recognized as important for human  beings in health and disease. The history  of man, to a large extent, has been a struggle  to obtain food. Until the turn of the 19th century , the science  of nutrition had  a limited  range. Protein, carbohydrates  and fat had been recognized  early in the 19th  century  as energy_ yielding  foods and much attention was paid to their  metabolism  and contribution to  energy  requirements. The discovery of vitamins at the turn of the 20th century  " rediscovered " the science  of  nutrition.Between the two World Wars, research on protein gained  momentum .By about 1950, all the  vitamins  and essential amino acids had been  discovered.Nutrition gained recognition as a  scientific  discipline, with roots  in physiology and biochemistry. In fact nutrition was regarded  as a branch of physiology. 

  Great advances have been made  during the past 50 years in knowledge  of nutrition and in the practical  application  of that knowledge. Specific nutritional  diseases were identified and technologies   developed  to  control them, as for example, protein energy malnutrition,  endemic  goitre, nutritional anaemia, nutritional  blindness and diarrhoeal diseases.

Relation Of Nutrition To  Health 

 Good  nutrition  is  a basic  component of health. The relation of nutrition to health may be seen  from  the following  view  points. 

1) Growh   and   development  :

Good nutrition  is essential  for the attainment of normal growth  and development .Not only  physical growth  and development , but also  the intellectual  development , learning  and  behaviour are affected  by malnutrition. Malnutrition  during pregnancy  may affect the  foetus resulting  in still_ birth, premature birth, and " small_ for dates" babies. Malnutrition during early childhood  delays physical  and mental  growth; such  children  are slow in  passing their  " milestones ", and are slow learners in school. Good nutrition is also  essential  in adult life for the maintenance of  optimum  health and efficiency .In short, nutrition affects  human health from birth till death. 

2) Specific   deficiency  :

Malnutrition  is directly  responsible  for certain  specific  nutritional deficiency diseases. The commonly  reported ones in India are kwashiorkor, marasmus,  blindness due  to vitamin  A deficiency , anaemia, beriberi ,  goitre, etc. Good  nutrition  therefore  is essential  for the prevention  of specific  nutritional  for  the prevention  of specific  nutritional deficiency diseases  and promotion of health. 

3) Resistance to infection  : 

 Malnutrition  predisposes  to infection  like  tuberculosis .It also influence the course and out_ come  of many a clinical  disorder. Infection, in turn, may  aggravate malnutrition by  affecting  the food intake, absorption  and  metabolism. 

4) Mortality  and  morbidity :

The  indirect effects of malnutrition  on the community are even  more striking  _ a  high  general  death rate, high infant mortality  rate, high sickness rate, and a lower expectation  of life. Over_nutrition, which  is   another  form of malnutrition is responsible for obesity,  diabetes,  hypertension,  cardiovascular  and  renal diseases, disorders  of the  liver and  gall bladder. More recent reports suggest that diet perhaps  plays an important role  in  certain types of gastro_intestinal  cancers . It is now  quite  well accepted  that diet  and  certain  diseases are inter _ related.

Functions of Food 

The main functions of  food are: _

1) Provision of energy 

2) Body  building  and repair  

3) Maintenance  and regulation  of  tissue functions. 

 On the  basis  of the above functions  foods have been classified  in three categories as :

(1)  Energy _ yielding  foods:  These are foods rich in carbohydrates , and fat, e.g., rice, wheat, potatoes,  sugar, fats and oils.

2) Body building  foods : These are foods rich in protein, e.g., milk, eggs, meat, liver, fish, pulses, oilseed cakes. 

3) Protective  foods : These are foods rich in  vitamins,  minerals  and proteins, e.g., milk, green leafy vegetables. Protective foods  are so called  because  they protect the body against  infection,  disease,  and ill_ health. It  may be  mentioned  that diets in India are generally  poor in protective  foods.  

  A balanced  diet  must  contain  foods  from the above three groups. 

Constituents  of food 

 The dietary  constituents  of food are 

Proteins , fats and carbohydrates are  called " proximate principles " or energy yielding  foods. Together with water, they  form  the bulk  of food. The human body has the following  approximate composition :

Classification  of foods

 There are many ways of classifying  foods : 

1. Classification  by origin 

      1) Foods  of animal origin 

      2) Foods of vegetable origin 

2. Classification  by chemical  Composition 

      1) Proteins  

       2) Fats 

       3)  Carbohydrates  

       4)  Vitamins  

        5) Minerals 

3.  Classification  by predominant function 

1) Body_ building  foods, e.g., milk, meat, poultry,  fish, eggs, pulses, groundnuts, etc. 

 2)  Energy _ giving  foods, e.g., cereals, sugars, roots and tubers, fats and  oils.

  3)  Protective foods, e.g., vegetables, fruits, milk.

4. Classification  by nutritive  value 

   1)  Cereal  and millets 

    2)  Pulses ( legumes)
   3) Vegetables 

   4)  Nute  and oilseeds 

    5)  Fruits 

     6) Animal foods 

    7)  Fats  and oils 

     8) Sugar and jaggery  

    9) Condiments  and  spices 

     10)  Miscellaneous  foods 

Types of Nutrition 

   There are two types of nutrition , autotrophic and heterotrophic.A mixtue of both these types is found in carnivorous plants which are mainly autotrophic but obtain organic nutrients for supplementing their  nitrogen supply.

1. Autotrophic Nutrition : The organism build up their own organic substances from inorganic raw materials. Most of the autotrophs use solar radiations and are hence  called photoautotrophs. 
 Photosynthetic nutrition is also termed as holophytic nutrition. A few autotrophic bacteria obtain chemical energy by performing expergonic reactions. They are known as chemoautotrophs. The nutrition under _ taken by them is known as chemo chemosynthesis. 

2. Heterotrophic Nutrition : They cannot manufacture all the required organic substances by themselves  and obtain part or whole of organic nutrients from outside. It is of two types, parasitism and saprophytism.

Parasitism : The parasite,  obtains its nutrients from another living  organism,  called host. Only a few plants are parasites. Parasites differ in their host specificity. There are some parasites which can attack a number of hosts e.g., Botrytis cinerea. Such parasite  are called omnivores. Others are  specialists and attack only particular host. Parasite  which are nongreen  and obtain all the nutrients from the host  are called total or holoparasites, e.g., Cuscuta, Orobanche, Rafflesia. Some plant parasites are green . They are able to manufacture organic substances. They depends upon their host for water, minerals and some other chemicals. They are called partial or semi semiparasites, e.g., Viacum. Plant parasites obtain nourishment  from the host body and make connections with the supple channels for absorbing  nutrients. Depending upon the part penetrated by haustoria, plant parasites are of two types, stem  parasites and root parasites. 

  Cuscuta (Dodder, vern. Amarbel, Akashbel) is a total stem parasite  that grows on a number of plants like Zizyphus, Citrus, etc. It sends a number of haustoria into the host. Xylem and phloem of the haustorium make connections with sap and food channels  of host. Cassytha  is  another  total stem parasite that grows on Melia and other plants. Because  of presence of some  chlorophyll,  some consider it to be a partial parasite.

  Arceuthobium is a partial stem parasite. It does not possess stem and leaves.The plant body  consists of thread_like strands ( considered roots) which remain inside the host ( Pinus).Only small flowers come out of the bark of host.

Viscum (Mistletoe) is  a partial stem parasite that grows on Silver fir, Poplar, Apple, Walnut, Oak, etc.It has dichotomously branched green stems with leaves. It sends a primary haustorium or sucker into the host. It grows longitudinally  sending secondary  haustoria at intervals into Xylem of the host for obtaining water and minerals. Loranthus is similar to Viscum growing on Acacia, Mango, Dalbergia etc.

Orobanche (Broom rape) is a total root parasite found on Mustard, Cabbage, Potato, etc.Aerial shoots are brown with   scale  leaves and pinkish_ bluish flowers. An underground  tuberous  base sends root parasites are Balanophora and Cystanche ( on Calotropis).

Rafflesia  is a total root parasite  on Fig, Cissus and other forest trees. Like Archeuthobium, it does not possess stems and leaves. Vegetative parts are thread_ like strands( considered roots). Onlytheflowers come out of the host body. They  are the  largest in  the plant Kingdom with a diameter of 1m and weight  of 11 kg. Striga is a total root parasite on sugarcane and Sorghum.

Santalum album ( Sandalwood  Tree) is partial root parasite that forms connections with the roots of trees like Dalbergia, Albizzia, Morinda, etc.


It is the phenomenon  of obtaining  organic nutrients from organic matter or remains of both plant and animal origin present in the surrounding  substratum. The  plants performing saprophytism  are called saprophytes or saprotrophs. Saprophytes remove dead remains  of organisms  and are called nature's  scavengers. They also help in recycling of minerals. Some saprophytes cause spoilage  of food stuffs and other articles. Some of them are used industrially in preparation of products like vinegar, alcohol, curing of tea, tobacco and  coffee etc. Saprophytes belonging  to angiosperms are also known as humus plants, since they obtain nourishment from humus. Humus plants are usually  nongreen and possess only scale leaves. Only one humus plant is known to absorb nourishment  directly  from organic matter.It  is the orchid Wullschleigelia aphylla. All others utilize fungi for this purpose. They are really mycotrophic, e.g., Neottia ( Bird's  Nest  Orchid), Corallorhiza, Monotropa ( Indian pipe).

Carnivorous  or Insectivorous Plants. 

They are green and autotrophic  plants which behave like heterotrophic organisms  for supplementing  nitrogen supply through digesting  small animals e.g., Nepenthes, Sarracenia, Drosera, Dionaea, Utricularia. They usually   live in water logged habitats  which are deficient in nitrates.

Drosera  (Sundew). It is  a herbaceous  plant with 6_ 12 radical or cauline leaves.  The upper surface of leaf blade bears a number of hair or tentacles. Their tips are swollen and glandular. The glandular heads of the tentacles secrete a thick sticky juice which shines in the  sun like dew drops. Hence is the name sundew.

  Insects are attracted towards the leaves by since and odour of the glands. An insect which touches the head of the tentacle is stuck by its juice. The sensitised  tentacle bends. It gets covered  over by nearby tentacles so that the insect is trapped  completely. The tentacles secrete a digestive fluid over the insect. The digested components of insect body are absorbed. Soon after, the tentacles straighten and the undigested part of the insect falls off. 

Dionaea ( Venus Fly  Trap). It possesses a rosette of long _ petooled leaves. The lamina  has two lobes. The upper surface of each  lamina lobe contains 3 sensitive spines and many digestive glands. The leaf  margin bears curved spiny teeth. If an insect touches a sensitive spine twice in quick succession, the two lobes of the lamina  fold rapidly. The marginal teeth get interlocked , so the prey cannot escape.It is digested by the secretion of glands.

Aldrovanda (Water Flea Trap). It is a rootless, free_ floating aquatic plant having whorls of leaves with broad_ winged petioles and  two lobed winged lamina. The lamina have marginal teeth sensitive  hai and digestive glands ( like Dionaea). The leaves trap water  fleas and larvae  of animals. 

Utricularia (Bladderwort) : It is a rootless free floating  aquatic plant with highly  dissected  leaves. Some of the leaf segments are modified  into small bladders. Each bladder has an inwardly  opening  valve that rests on a collar, 

 branched trigger hair,unbranched sensitive  hair, external glands and internal glands. Secretion of external glands attract small aquatic animals like cyclops and Daphnia. When an animal  touches sensitive  hair,  the valve sinks inwardly. It draws the animal inside the bladder. Here it decays. The products of decay are  absorbed  by the internal glands. Afterwards, the bladder contracts to throw the undigested  contents. 

Neprnthes (Pitcher Pkant). It is a climber having large pitchers. In India, only one species, Nepenthes Khasiana, grows in north_ eastern parts. It is an endangered  species. Leaves  are modified  with a foliaceous leaf base, tendrillar petiole, lamino modified  into pitcher and leaf apex forming its lid. Both the pitcher  and lid have red or purplish colouration. The rim of  the pitcher bears nectatiferous glands. The inside of the pitcher is slippery.

It bears downwardly  directed hair and loosely arranged  scales. The lower half of the  pitcher possesses  glands and a digestive fluid having  micro_ organisms.  

Insects are attracted by the colour of lip and pitcher as well as the nectar of nectariferous glands. An insect which enters the pitcher  in search of nectar, slips downwardly  into the digestive fluid.  It cannot come out due to presence of downwardly  directed hair and loose scales. The breakdown  products of insects are absorbed  by the glandular  surface of the pitcher. 

Sarracenia :It is an insectivorous pitcher plant. The pitchers are sessile but are otherwise similar to those of Nepenthes. 

Pinguicula (Butterwort) : It has a rosette of sessile radical leaves. The upper surface of leaves possesses  glands that produce sticky substance and sessile glandular hair that secrete digestive enzymes. An insect crawling  over the upper surface  of the leaf gets stuck up. The leaf rolls upwardly  and inwardly to trap and  digest the insect. 

Inorganic Nutrition in Plants:

 Liebig  gave the law of minimum  which states that productivity of a soil depends upon the proportionate amount of deficient mineral. 30_ 40  elements  are often found  to be present in plant. All of them are not essential  for plants. Similarly, all elements essential  for animal growth are not required by plants. The most important  of them are iodine and sodium. Arnon and Stout proposed the criteria for knowing the essentiality of an element. They are: 

(1) It is indispensable for the growth of plants. 

(2) The element is directly  involved  in the nutrition of plants. It becomes a component of either a structural or functional  molecule. The element may additionally have a  corrective effect on mineral balance  and other  soil conditions. 

(3) A plant is unable to compete its vegetative  or reproductive phase in the absence  of the element. 

(4) The element cannot be replaced   by any other element. 

(5) The deficiency of the element produces disorders. 

(6) The element alone can correct the disorders produced by its deficiency. 

16 elements  have been found to be essential. They are C, H, O, N, P, K, S, Mg, Ca, Fe, B, Mn,Cu, Zn, Mo, Cl. Recently  four more elements  have been added to the list. These are silicon, cobalt, vanadium and nickel*. So now the total number  of essential  elements is considered  to be 20 instead  of 16. Others are called nonessential  elements.  However, some of the nonessential  elements have  been found to be required  in metabolic activities  of certain plants. They include sodium, aluminum, etc.Sodium is involved  in membrane permeability  through its essentially has not been proved. These elements are called functional  elements  or nonessential  functional elements.  Silicon is required  by most  grasses and cereals.Its deficiency produces leaf necrosis and stunted growth in rice.


Nutrients are organic and inorganic  complexes  contained in food. There are about 50 different  nutrients which are normally  supplied through the foods we eat. Each nutrient  has  specific  functions  in the body. Most natural  foods contain more th an one  nutrient. These may be divided into:  

(i) Macronutrients : These are proteins, fats and carbohydrates which are often called  " proximate principles " because they form the main bulk of food. In the Infian dietary, they contribute  to the total energy intake in the following  properties: 

    Proteins     ....     7  to 15 per  cent 

   Fats             ....      10 to 30 per cent 
 Carbohydrates  ....  65 to 80 per cent 

(ii) Micronutrients: These are vitamins  and minerals. They are called micronutrients  because  they are required in small amounts  which may vary from a fraction  of a milligram  to several grams. 


Nutrients Cycling :

More than 30 chemical elements  are cycled  through the  environment  by biogeochemical cycles. There are six important biogeochemical  cycles   that transport carbon,  hydrogen,  oxygen, nitrogen, sulphur and phosphorus. These six elements comprise the bulk of atoms in living things. Carbon, the most abundant  element in the human body, is not the most common  element  in the crust. 

■ Carbon cycle:  There is a relationship  between  photosynthesis  and cellular respiration . The latter releases carbon dioxide,  which is used in photosynthesis, which in turn releases  oxygen, and it is used in respiration. When organisms respire, some of this carbon is returned to the atmosphere  in the molecules of carbon dioxide. In aquatic ecosystems, carbon dioxide  from air combines with water to give carbonic acid, which breaks down to bicarbonate ions. 

■ Phosphorus  cycle : Weathering of rocks makes phosphate ions ( PO4‐ and HPO4‐) available  to plants throug  uptake from the soil. The mineral apatite contains  a small  amount  of phosphorus,  sufficient for all living things to utilize. Runoff returns phosphates to aquatic systems as sediments. Organisms use phosphate in phospholipids, ATP, teeth, bones  and shells. Phosphate is a limiting  nutrient because  most of it is being currently  used in organisms. Humans mine  phosphate ores for use in fertilizers, as an animal feed supplement, and for detergents. 

■ Hydrologic ( water) cycle:  Saltwater evaporates due to the sun's  energy, producing  fresh water in clouds and leaving  salts in the ocean.  Water vapour cools and condenses  to precipitation over oceans  and land. Run_ off forms freshwater  lakes, streams,  ponds, groundwater  and is held in plants and transpired. Some water infiltrates  the ground, becoming part of the groundwater, returning very slowly to the oceans. Although the water cycle shows water to be a renewable  resource,  only about 3 per cent of that water is fresh and suitable  for human use. 

■ Nitrogen  cycle : Atmospheric nitrogen gas ( N2) is unavailable  to plants. Plants, therefore,  depend on various types of nitrogen _ fixing bacteria to take up nitrogen gas and make it available to them as some form of organic nitrogen. Nitrogen fixation  occurs when nitrogen gas  is chemically  reduced  and nitrogen is added to organic compounds. Atmospheric  nitrogen is converted to ammonium  ( NH4+) by some cyanobacteria in aquatic  ecosystems and by nitrogen_ fixing bacteria  in the nodules  on roots of legume  ( beans, peas, clover, etc.)plants  in terrestrial  ecosystems. 


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