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The processes that help carry out metabolic functions, such as respiration, digestion, excretion, circulation or transport, and reproduction, are collectively called life processes.

Life Processes

Nutrition is theprocess by which organisms can assimilate and utilise food for their basic needs.


Autotrophs are organisms such as plants and some bacteria that can synthesise their own food. This type of nutrition is known as autotrophic nutrition.

Autotrophs, Autotrophic Nutrition

Heterotrophs are organisms like animals and non-green plants that depend on other organisms for food, and utilise this food for their basic needs. This type of nutrition is known as heterotrophic nutrition

Heterotrophs , Heterotrophic Nutrition

Plants synthesise organic nutrients with the help of chlorophyll, atmospheric carbon dioxide, water and solar energy. This process is known as photosynthesis.

Photosynthesis Photosynthesis

Leaves have tiny pores on their surface, called stomata. The stomata contain guard cells that regulate the opening and closing of the stomata. They are opened only when the plant needs carbon dioxide for photosynthesis.

Stomata, Guard Cells

The chloroplasts in leaves contain closely packed flattened sacs, called thylakoids, arranged in piles, called granum.

Chloroplasts, Thylakoids, Granum Chloroplasts, Thylakoids, Granum Chloroplasts, Thylakoids, Granum

Granum lies in a colourless ground substance, called stroma.


Thylakoids contain green pigments, called chlorophyll, which trap solar energy.


Photosynthesis involves a series of photochemical reactions in two phases: Light reactions and dark reactions.

Light reaction occurs in the grana of the chloroplasts. Using light energy, water molecules split to release oxygen.

Light Reaction, Grana

The chlorophyll pigments trap light energy and excite an electron. This excited electron converts light energy into chemical energy. This chemical energy is stored as ATP (Adenosine Tri Phosphate) and NADPH (Nicotinamide Adenine Dinucleotide Phosphate).

Chlorophyll, Electron, ATP, NADPH Chlorophyll, Electron, ATP, NADPH

Dark reaction takes place in the stroma of the chloroplasts by reducing carbon dioxide to carbohydrates, utilising energy from ATP.

Dark Reaction, Stroma

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