Life Processes

03 Nutrition Mode In Plants, Animals and Amoeba



In photosynthesis, green plants make their own food (like glucose) from carbon dioxide and water with sunlight energy in the presence of chlorophyll.

Photosynthesis takes place in the following three steps:

  • Absorption of sunlight energy by chlorophyll.
  • Conversion of light energy into chemical energy. Further, water splits into hydrogen and oxygen by light energy.
  • Reduction of carbon dioxide by hydrogen to form carbohydrate like glucose. Chemical energy obtained by the transformation of light energy helps in reduction.



Conditions Necessary for Photosynthesis:

  • Sunlight,
  • Chlorophyll,
  • Carbon dioxide, and
  • Water



How plants obtains carbon dioxide

  • The green plants take carbon dioxide from the air for photosynthesis.
  • The carbon dioxide gas enters the leaves of the plants through the stomata present on their surface.
  • A pair of guard cells surrounds the stomatal pore or stoma.
  • Guard cells control the opening and closing of stomatal pores.
  • The guard cells swell and become curved when water flows into them causing the stomatal pore to open.
  • On the other hand, when the guard cells lose water, they shrink, become straight and close the stomatal pore.
  • The aquatic plants (or water plants) use the carbon dioxide gas dissolved in water for carrying out photosynthesis.



How plants obtain water for photosynthesis

  • Plants absorb water for photosynthesis by the roots of the plants from the soil. This process is osmosis.
  • The plants also need raw materials such as nitrogen, phosphorus, iron and magnesium etc., for building their body. The plants take them from the soil.



Site of photosynthesis: Chloroplasts

  • Chloroplasts are the organelles in the cells of green plants which contain chlorophyll.
  • Photosynthesis takes place within chloroplasts.
  • In a cross section of a leaf, chloroplasts can be seen as numerous dis-like organelles in the photosynthetic cells (or mesophyll cells) of the palisade tissue just below the upper epidermis.



Animals obtain their Food from Plants or Other Animals

All the animals can be divided into three group on the basis of their food habits (or eating habits) These are:



  • Those animals which eat only plants are called herbivores.
  • Goat, Cow, Buffalo, Sheep, Horse, Deer, Camel, Ass, Ox, Elephant, Monkey, Squirrel, Rabbit, Grasshopper and Hippopotamus.




  • Those animals which eat only other animals as food are called carnivores.
  • Lion, Tiger, Frog, Vulture, Kingfisher, Lizard.




  • Those animals which eat both, plants and animals are called omnivores.
  • Man (Human beings), Dog, Crow, Sparrow, Bear, Mynah and Ant.



There are five steps in the process of nutrition in animals. These are


  • The process of taking food into the body is ingestion.




  • The process in which the food containing large, insoluble molecules breaks down into small, water-soluble molecules (which can be absorbed by the body) is digestion.




  • The process in which the digested food passes through the intestinal wall into the bloodstream is absorption.




  • Assimilation is the process in which the absorbed food is taken in by body cells and used for energy, growth and repair.




  • The process of removal of undigested food from the body is egestion.



  • Ingestion

Amoeba ingests food by using its pseudopodia. Pseudopodia are temporary finger-like projection formed around amoeba. Amoeba ingests food with pseudopodia. Amoeba engulfs the food with a little surrounding water to form a food vacuole.



  • Digestion

Amoeba digests food in the food vacuole by digestive enzymes. The enzymes from surrounding cytoplasm enter into the food vacuole. Inside the food vacuole, complex substances of the food are broken down into simpler ones.



  • Absorption

Absorption is the process, where the digested food present in the food vacuole of Amoeba is absorbs directly into the cytoplasm of Amoeba cell by diffusion.



  • Assimilation

Amoeba cell uses a part of the food absorbed to obtain energy through respiration.



  • Egestion

In egestion, a considerable amount of undigested food collects inside Amoeba, then its cell membrane suddenly ruptures at any place. Then, the undigested food expels out of the body of Amoeba.

Paramecium uses its hair like structures called cilia to sweep the food particles from water and put them into its mouth.

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