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• Nutrition – Mode of taking food and its utilisation in the body is called nutrition
• Autotrophs – Organisms that make food for themselves. E.g. Plants
• Heterotrophs – Organisms that depend on other organisms for food. E.g. humans, animals, etc
• Photosynthesis – It is the process of synthesis of food by the green plants
  • Process takes place in green leaves and requires chlorophyll, sunlight, carbon dioxide and water.
  • Carbon dioxide is taken inside in the plant body through stomata
  • Water and minerals required in the process are transported from the roots
  • Sunlight is used by chlorophyll along with carbon dioxide and water to prepare food.
  • In this process oxygen is released
• Modes of nutrition – Autotrophic and heterotrophic
• Autotrophic nutrition – With the help of the process of photosynthesis green plants prepare their own food. That means green plants, blue-green algae have ability to prepare food for themselves. Such plants are called autotrophs and carry out autotrophic nutrition.
• Heterotrophic nutrition – When one organism depend on other organisms for food, such a nutrition are called heterotrophic nutrition. Heterotrophic mode of nutrition could be parasitic, saprophytic, symbiotic or Insectivorous.
• Parasitic nutrition – mode of nutrition in which organism obtain nutrient from other organisms body is called parasitic mode of nutrition. E.g. parasitic plants are Dodder, corpse flower, Rafflesia, Hydnoraceae, broomrape etc.
• Saprophytic Nutrition – Mode of nutrition in which organism obtain nutrients from dead and decaying organic substances is called saprophytic mode of nutrition, and the organism which have this mode of nutrition are called saprotrophs. E.g. rhizopus, mucor or pin mould, Yeast, and mushroom
• Symbiotic Nutrition: some organisms which live together like ‘friends’; they share shelter and food. In science we call such relationship as symbiotic relationship. E.g. rhizobium bacteria and leguminous plants such as peas, moong, beans etc.
• Insectivorous Nutrition: some plants like Venus flytrap, pitcher plant, sundews, butterworts can eat insects.
• Nitrogen Fixation: Atmospheric nitrogen is converted to nitrogen compounds by bacteria like blue green algae, rhizobium. The process is known as nitrogen fixation. Rhizobium lives in root nodules of leguminous plants. Lightning also fixes atmospheric nitrogen.
• Nitrogen Cycle: When atmospheric nitrogen is fixed, it s converted to compounds and are absorbed by plant roots. Plants uses these compound in synthesis of different nitrogen compounds. Animals use these compound from plants. Plants and animals die, bacteria and fungi present in soil convert & decompose them into nitrogenous compounds. These are absorbed by roots of plants. Excess of nitrogen is again passed back to atmosphere with help of certain bacteria.