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Biology · Class 9 · Chapter 8: Nutrition

8 min

Key points

Nutrition is the process by which organisms obtain and utilize food materials for their growth, maintenance and energy requirements
Autotrophic nutrition — organisms synthesize their own food from simple inorganic substances (e.g., green plants)
Heterotrophic nutrition — organisms depend on other organisms for their food (e.g., animals, fungi)
Photosynthesis occurs in chloroplasts and requires sunlight, CO₂, water and chlorophyll to produce glucose and oxygen
Dark reaction (Calvin cycle) occurs in stroma while light reaction occurs in thylakoids of chloroplasts
Limiting factors of photosynthesis include light intensity, CO₂ concentration and temperature
Parasitic nutrition involves obtaining food from living host organisms (e.g., tapeworm, Plasmodium)
Saprophytic nutrition involves obtaining food from dead organic matter (e.g., mushrooms, bacteria)
Symbiotic nutrition involves mutual benefit between two organisms (e.g., lichens, nitrogen-fixing bacteria in legumes)

Definitions

Nutrition: The process by which organisms obtain and utilize food materials for their growth, maintenance and energy requirements
Autotrophic Nutrition: The mode of nutrition in which organisms synthesize their own food from simple inorganic substances
Photosynthesis: The process by which green plants synthesize glucose from carbon dioxide and water in the presence of sunlight and chlorophyll
Parasitic Nutrition: The mode of nutrition in which organisms obtain their food from living host organisms
Saprophytic Nutrition: The mode of nutrition in which organisms obtain their food from dead and decaying organic matter

Worked example

Define nutrition. Differentiate between autotrophic and heterotrophic nutrition with two examples each. (6 marks)

Nutrition is the process by which organisms obtain and utilize food substances for their growth, development and maintenance of life. Autotrophic nutrition is the mode of nutrition in which organisms prepare their own food from simple inorganic substances like carbon dioxide and water using sunlight. Examples: Green plants, blue-green algae. Heterotrophic nutrition is the mode of nutrition in which organisms cannot prepare their own food and depend on other organisms for food. Examples: Animals, fungi.

Common mistakes

Students confuse raw materials (CO₂, H₂O) with products (glucose, O₂) in photosynthesis equation
Writing light reaction in stroma instead of thylakoids
Confusing parasitic and saprophytic nutrition examples
Not mentioning chlorophyll as essential requirement for photosynthesis
Forgetting to balance the photosynthesis equation properly

Quick recap

Nutrition is obtaining and utilizing food for life processes. Autotrophic organisms make their own food (plants), heterotrophic depend on others (animals). Balanced diet contains carbohydrates, proteins, fats, vitamins, minerals and water in proper proportions. Deficiency of nutrients causes specific diseases like scurvy (Vitamin C), rickets (Vitamin D), anemia (Iron).

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