Food Variety and Sources: Introduction, Plants as Source, Animals as Source, Food Chain, Food Chain in Ecology (For CBSE, ICSE, IAS, NET, NRA 2022)

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  • Food can be defined as a substance used in the body of an organism for sustaining growth and vital processes apart from furnishing energy.
  • It includes protein, carbohydrate, fats, and other nutrients.
  • The primary source of food is Plants. They convert solar energy to food by photosynthesis.
  • Food comes in a variety of form such as fruits that we eat directly and the other we need to prepare before consumption such as kheer, rice, dal, etc.
  • From plants we obtain Fruits, vegetables, pulses, grains, etc. Whereas Milk, eggs, meat, and other dairy products are obtained from animals.

Plants as Source

  • We cannot consume every part of the plant.
  • Root vegetables:
    • Spinach
    • Cabbage
    • Tomato
    • Brinjal
    • Lady՚s finger

Plants That Cause Allergies

Plants That Cause Allergies

Animals as Source

  • Food items that can be obtained includes milk, eggs, meat and many other products like cheese, ghee, honey, etc.
  • Also, animals depend on plants for their foods.
Animals Can be Classified into Three Groups

Herbivores (Primary Consumers)

  • These animals depend on plants directly.
  • They eat only plants.
  • Examples are Deer, rabbits, giraffe, etc.
  • Since herbivores consume plants to digest the carbohydrates photosynthetically, they are an important link in the food chain.

Carnivores (Secondary Consumers)

  • These are flesh eating animals.
  • These animals feed on herbivores animals.
  • Some of the examples are lion, tiger, etc.

Omnivores (Secondary Consumers)

  • Those animals which obtain their nutrients from both animals and plants products.
  • Some of the examples are bear, pig, crow, etc.

Food Chain

  • It can be defined as a linear network of links in a food web starting from producer organisms. This includes grass or trees which use radiation from the Sun to make their food.
  • It ends up at apex predator species like grizzly bears, detritivores like earthworms, or decomposer species such as bacteria.
  • Food chains are often used in ecological modeling.
  • As trophic level increases, the amount of energy transferred decreases.
    • Only ten percent of the total energy at one trophic level is passed to the next.
    • The remainder of the total energy is used in the metabolic process.
Food Chain, in Ecology
Terrestrial Food Chain

Three Groups Classification


  • Energy giving food
  • Body building food
  • Regulatory and protective foods


  • Carbohydrates and Fats.
  • Proteins.
  • Vitamins and Minerals.


  • Cereals, fats, sugar
  • Pulses, milk, meat
  • Fruits and vegetables

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