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Food contains several components known as nutrients.
“Nutrients are chemicals- inorganic as well as organic that an organism needs to live and grow”.
They are obtained from an organism’s surroundings. There are six major classes of nutrients classified as -proteins, vitamins, water, carbohydrates, dietary fiber, fats and minerals .
(a) Macronutrients– needed in relatively large amounts- carbohydrates, proteins, fat and water .
(b) Micronutrients– needed in relatively smaller amounts- vitamins and minerals.
On the basis of their functions, nutrients are divided as-
(a) Energy giving– carbohydrates, fats.
(b) Body building – proteins.
(c) Protective and Regulating nutrients – vitamins and minerals.
On the basis of their chemical nature, nutrients can be classified as –
(a) Inorganic nutrients – Green plants take inorganic substance such as H2O, CO2, minerals etc from air and soil and convert them into starch (an inorganic substance) through photosynthesis.
(b) Organic nutrients- Such as carbohydrates, proteins, fats etc are obtained from plants (in the form of cereals, vegetables, fruits etc) and animals (in the form of milk, eggs, meat etc) .
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The process of intake of nutrients and break them down to simpler molecules
(carbohydrates, fats, proteins etc) for utilization by the body in various biological activities is called nutrition. The way by which organism obtain their food from the environment is called mode of nutrition.
On the basis of the method of food procurement, there are mainly two modes of nutrition-
(A) Autotrophic Nutrition
(B) Heterotrophic Nutrition – Further divided into –
(i) Saprophytic nutrition
(ii) Parasitic nutrition
(iii) Holozoic nutrition
(A) Autotrophic Nutrition (autos = self + trophien = to nourish) –
In this, organisms (or autotrops) prepare their own organic food by utilizing only simple inorganic raw substances such as H2O, CO2 and minerals and external energy source (i.e. sunlight) e.g. all green plants and some bacterias(nitrifying ,iron).
(B) Heterotrophic Nutrition (hetero = other + trophien = to nourish) –
In this, organism (or heterotrophs) depend on other organisms (plants or animals) for their food. They directly or indirectly depend on autotrophs e.g. animals, fungi.
Heterotrophic nutrition is further divided into following-
(i) Saprophytic nutrition– (sapro = rotten) Saprotrops are decomposers. In saprophytic nutrition, the organisms (or saprotrops) get their food by digesting dead and decaying organism by releasing extracellular enzymes on to the dead matter and then absorb the soluble products of enzymatic digestion e.g. fungi like yeast, mushrooms, bread moulds (fungus), bacteria etc.
(ii) Parasitic nutrition – In parasitic nutrition, organism (or parasites) live in close association (outside or inside) with host species (plant or animal) and derive their food from their host without killing them. But during the process they harm the host e.g. albugo, puccinia, cuscuta, ticks, lice, leeches, tapeworms etc.
(iii) Holozoic nutrition– In this, organisms take in whole food (ingestion), break it into simpler
substances inside their bodies (digestion), absorb them (absorption) into blood and transport into
tissues and cells and use it to produce energy (assimilation) and further defaecate the unused
components of the food (egestion) e.g. human beings, cats, cows etc.
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