Nutrition is the process by which organisms obtain and use food for energy, growth, and repair. There are two main modes of nutrition: autotrophic nutrition, in which organisms prepare their own food using simple inorganic substances, and heterotrophic nutrition, in which organisms obtain food by feeding on other organisms. Plants are autotrophs; animals are heterotrophs.
Autotrophic: self-feeding — synthesise food from CO₂, water, minerals.
Heterotrophic: other-feeding — depend on other organisms for food.
Photoautotrophs use sunlight (photosynthesis); chemoautotrophs use chemical energy.
Heterotrophic types: holozoic (solid food), saprotrophic (dead matter), parasitic, symbiotic.
Autotrophs are producers; heterotrophs are consumers or decomposers in food chains.
Examples: Autotrophs — grass, algae; Heterotrophs — humans, fungi, bacteria.
Chlorophyll present in photoautotrophs; absent in heterotrophs.
Definition: Autotrophic nutrition is the mode of nutrition in which organisms synthesise their own food from simple inorganic substances (CO₂, water, minerals) using an external energy source.
Types:
Photosynthesis (Photoautotrophs): • Use sunlight as energy source • 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of sunlight and chlorophyll) • Examples: Green plants, algae, cyanobacteria
Chemosynthesis (Chemoautotrophs): • Use energy from chemical reactions (oxidation of inorganic substances) • No sunlight required • Examples: Sulphur bacteria (Thiobacillus), nitrifying bacteria (Nitrosomonas, Nitrobacter)
Organisms: • Green plants, algae, phytoplankton, cyanobacteria (blue-green algae) • These are also called producers in the food chain
Key features: • Can synthesise all needed organic molecules from inorganic sources • Independent of other organisms for food • Store energy as food (starch in plants) • Contain chlorophyll (in photoautotrophs)
Definition: Heterotrophic nutrition is the mode of nutrition in which organisms cannot synthesise their own food and must depend on other organisms (autotrophs or other heterotrophs) for their food.
Types of heterotrophic nutrition:
Holozoic nutrition: • Taking in solid food, digesting it internally • Examples: Humans, animals (Amoeba — engulfs food particles)
Saprotrophic (Saprophytic) nutrition: • Feeding on dead and decaying organic matter • Secrete digestive enzymes externally, absorb digested products • Examples: Fungi (mushrooms, yeast), bacteria of decay
Parasitic nutrition: • Obtaining food from a living host organism, causing harm to the host • Examples: Tapeworm, Cuscuta (dodder plant), lice, ticks, Plasmodium (malaria parasite)
Symbiotic nutrition: • Two organisms live together and both benefit • Examples: Lichens (algae + fungi), Rhizobium bacteria in legume roots
Organisms: • Animals, fungi, most bacteria, non-green plants (Cuscuta), parasites
Comparison Table:
Property | Autotrophic | Heterotrophic Food source | Self-synthesised (inorganic → organic) | Other organisms (organic compounds) Energy source | Sunlight (photo) / Chemical (chemo) | Already-made organic food Dependency | Independent | Dependent on other organisms Chlorophyll | Present (in photoautotrophs) | Absent (generally) Organisms | Green plants, algae, cyanobacteria | Animals, fungi, most bacteria Food chain role | Producers | Consumers/Decomposers Examples | Grass, mango tree, algae | Cow, humans, fungi, tapeworm Organic → inorganic | Converts CO₂+H₂O → food | Uses food, releases CO₂
Ecological significance: • Autotrophs: Form the base of every food chain; primary producers • Heterotrophs: Form higher levels of the food chain (consumers, decomposers)
Memory tip: • AUTO = self (autotrophs feed themselves) • HETERO = different/other (heterotrophs feed on others)
Autotrophic nutrition: organisms synthesise their own food from simple inorganic substances using sunlight or chemical energy (examples: green plants, algae). Heterotrophic nutrition: organisms cannot make their own food and depend on other organisms (examples: animals, fungi, bacteria). Autotrophs are producers; heterotrophs are consumers/decomposers.
Autotrophic nutrition is the mode where organisms synthesise their own food from inorganic substances. Types: (1) Photosynthesis — using sunlight (green plants, algae, cyanobacteria); (2) Chemosynthesis — using chemical energy (sulphur bacteria, nitrifying bacteria). Plants produce food: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Types of heterotrophic nutrition: (1) Holozoic — ingesting solid food (humans, Amoeba); (2) Saprotrophic — feeding on dead/decaying matter (fungi, bacteria); (3) Parasitic — feeding on a living host and harming it (tapeworm, Cuscuta, lice); (4) Symbiotic — mutual benefit (lichens = algae + fungi).
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