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Introduction : 

 Firstly, nutrition is the process of obtaining food necessary for every biological process. The food  which is in taken is called nutrients . This can be obtained  from others(heterotrophic) or by own self  (autotrophic).

Types of nutrition :

  • Autotrophic nutrition

The process where organism produces their food by themselves using simple inorganic materials and feed themselves and others too.

 They can be divided into following two subtypes

 a. Photo trophic nutrition : The process where organism produces their own nutrients  using light.

B. Chemotrophic   nutrition: The process where organism produces their own nutrients using chemicals. For instance, Sulphur bacteria oxidizes hydrogen sulphide to Sulphur producing nutrients in form of energy.

  •  Heterotrophic nutrition

The process where organism directly or indirectly obtain nutrients produced by autotrophs. There can be of following three subtypes:

  1. Holozoic nutrition : This process involves taking complex organic materials as a whole and breaking down to simple materials which are observed from digestive tract and utilized by different cells of the body .This type of Nutrition is characteristic to animals.

  2.  Parasitic nutrition:   This involves obtaining nutrients from off host which provides food or shelter to the parasite and obtained directly the nutrients from the host .They can be either ectoparasites   like leeches and  fleas or endoparasites like Plasmodium.

  3. Saprophytic nutrition:  In this nutrition saprophytes obtain nutrients from dead and decaying matters .For example Mucor, Rhizopus.

Macro nutrients

1. Carbohydrates

This is the main source  of energy for our body. On average, a gram of it provides 4 kcal of energy. Chemically their general formula is Cn (H2O) n .  

The general ratio of carbon, hydrogen and oxygen in carbohydrates is  1: 2: 1.

Chemically they are polyhydroxy derivatives of aldehyde and ketones or  also referred as hydrides of carbon.

They can be  classified on the basis of complexity :

1.      Monosaccharides : simplest monomeric form . eg: glucose, fructose

2.       Oligosaccharides : Polymer of at most 10 monomers. Eg : sucrose, raffinose, lactose

3.       Polysaccharides :  polymer of more than 10 monomers. For instance : cellulose, glycogen, starch .               Key Differences : 

MonosaccharidesOligo SaccharidesPoly saccharides
  • They  cannot be hydrolysed.
  • They  can be hydrolysed. 
  • They  can be also hydrolysed.
  • Water soluble, sweet in taste
  •  Water soluble , sweet in taste too.
  • Water insoluble  and tasteless.
  • They are all reducing sugars .
  • Except Sucrose all are reducing.
  • None of them are reducing.

Source  : mainly cereals like rice wheat and maize , potatoes, dried beans, sugar, milk, honey fruits, vegetables .

 Daily requirements : for normal healthy adult 45 to 65 % of total calories must be  taken per day .


·         Primary source of energy  ; vital for daily chores.

·         Structural formation also like cellulose in plants .

·         Genetic importance as deoxy ribose and  ribose sugar

·         Energy reserve for future like glycogen in animals.

·         Reduce absorption of  cholesterol so helpful to have  excess fats and prevent coronary diseases.

Deficiency :  leads to marasmus which is calorie intake less than protein intake in diet.


2. Proteins

They are complex nitrogenous compound which are polymerized form of amino acids via peptide  bond .

On the basis of complexity :

1.       Simple protein  : Only  primary bond which is peptide bond present .

2.       Conjugated  protein : bonded with other compounds like  carbohydrate called as glycoprotein.

3.       Derived protein : proteins derived after partial hydrolysis of original ones eg : peptones, proteoses

 Monomer amino acid  are of 20   different types which can be  classified  in  2 types :

Essential  amino acids Non essential amino acids 
  • They are not synthesized inside body so must be included in diet, 
  • They are made by body itself so their compulsion in diet is not necessary.
  • For instance : phenyl alanine, valine , tryptophan, threonine, isoleucine, methionine , histamine  arginine, leucine and lysine .
  • 10 out of 20 amino acids available  are essential .
  • For  instance : glycine, alanine, proline, serine, cystine, glutamine, aspargine, aspartate, glutamate , tyrosine 
  • The rest 10 are non essential


        Structure of amino acid where;                           R : Alkyl  or phenyl group 

Dietary source :

From animal : meat, milk, egg. They possess almost every amino acids .

From plants : pulses, cereals, beans, nuts .

 Daily  need :  for healthy adult about 70 gm per day .

Functions :

·         Main structure forming nutrient like collagen

·         Enzymes like trypsin are all made up of proteins .

·         Immunoglobulins for immunity are of proteins .

·         Myoglobin ,ferritin which are proteins  work for storage.

·         Actin, myosin, troponin complex are proteins in muscles for movement

·         They are secondary source of energy after carbs.

Deficiency : causes kwashiorkor i.e. protein  intake less than required  in diet.

3.     Lipids

They are esters of fatty acids and alcohols like glycerol . The ratio of carbon hydrogen and oxygen is 1: 2: less than 1 .This differs from carbohydrates  in proportion of oxygen which is 1 for carbohydrates.

Fatty acids : Carboxylic acid  with carbon number from 12 to 18 mainly. fatty  acids present  can be saturated or unsaturated.

 Classification : 

Simple lipids Compound lipids Derived lipids
  • Esters of fatty acid and glycerol.
  • Esters of fatty acid and alcohols along with additional groups bonded.
  • lipids after chemical modification of simpler ones or hydrolysed products of simple and complex lipids.
  • Eg : Oils fats
  • Eg : glycolipid (carbohydrate as prosthetic group)
  •  Eg: cholestrol, terpenes,  carotenoids 

 Sub types of simple lipids :

Oils FatsWax
  • liquid at room temperature.
  • solid or semisolid at room temperature .
  • Also solid at room temperature.
  • They are rich in unsaturated fatty acids.
  • They are rich in saturated fatty acids.
  • They  are  with  both types of fatty acids.
  • Alcoholic group is glycerol.
  • Alcoholic group is glycerol.
  • Alcoholic group other than glycerol.
  • Common in plants
  • Common in animals' adipose tissue.
  • Equally in both plants and animals
  • Eg: mustard oil, coconut oil.
  • Eg: margarine, Vanaspati ghee
  • Eg: bee hive wax, feather wax

Dietary sources :

Animal source :  dairy products like milk, ghee butter, cheese and many more , meats , fish.

Plant source : oil of coconut, mustard, sesame.


Daily  requirement :

For  healthy adult  50 gm fat per day. 

Roles :

·         Primary storage form of energy ; crucial  for hibernating organisms like frog.

·         Structural role as phospholipids in cell membrane .

·         Thermal insulation for homeostatic state.

·         Cholesterol; a derived lipid is must for steroid hormones like androgens ,for absorption of fat soluble vitamins  and precursor of vitamin D too.

·         Phosphoatidyl choline acts as respiratory surfactant in lungs to prevent its collapse.

 Deficiency : phrenoderma or toad skin characterized by dry scaly skin, hair loss and poor wound healing.

Excess of anything is  harmful while for  lipids, it could be fatal as it risks atherosclerosis and eventually cardiac arrest .