Nutrition is one of the essential life processes studied in CBSE Class 10 Biology. All living organisms need energy obtained from food. Organisms are classified based on how they obtain nutrition: autotrophs make their own food through photosynthesis, while heterotrophs depend on other organisms for their nutritional needs.
Autotrophic nutrition is the process by which organisms synthesise their own food from simple inorganic substances. Green plants, algae, and some bacteria are autotrophs. They use carbon dioxide and water in the presence of sunlight and chlorophyll to produce glucose (food) and oxygen. The overall equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Photosynthesis occurs mainly in leaves. (1) Absorption of light energy by chlorophyll. (2) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen (light reactions). (3) Reduction of carbon dioxide to carbohydrates using hydrogen from water splitting (dark reactions / Calvin cycle). Stomata on the leaf surface allow CO₂ to enter and O₂ to exit.
Heterotrophs cannot synthesise their own food and depend on other organisms. Three main modes: (1) Holozoic — the organism ingests solid food, digests it internally, and absorbs nutrients (e.g., humans, Amoeba). (2) Saprophytic — the organism feeds on dead and decaying organic matter by secreting enzymes externally (e.g., fungi, some bacteria). (3) Parasitic — the organism lives on or inside a host and derives nutrition from it, often harming the host (e.g., tapeworm, Cuscuta, lice).
Amoeba captures food using temporary pseudopodia (false feet) through the process of phagocytosis. The food is enclosed in a food vacuole where digestion occurs. Paramecium uses hair-like cilia to sweep food into the oral groove. These are classic examples of holozoic nutrition in unicellular organisms.
Autotrophic organisms (like plants) make their own food from CO₂ and water using sunlight. Heterotrophic organisms (like animals and fungi) depend on other organisms for food.
Photosynthesis produces oxygen necessary for respiration in all aerobic organisms and is the primary source of food energy (glucose) for most ecosystems on Earth.
Some plants are partially or fully heterotrophic. Insectivorous plants (Venus flytrap, sundew) supplement nutrition by trapping insects. Parasitic plants (Cuscuta) derive nutrition from host plants.
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