Photosynthesis as the mode of nutrition in plants, algae and several groups of photosynthetic prokaryotes

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Where an organism gets its **energy** and where it gets its **carbon**.

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An organism that **makes its own organic carbon** from an inorganic source (**CO₂**). 'Auto' = self-feeding.

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An organism that obtains organic carbon by **taking in organic molecules** made by other organisms. 'Hetero' = feeding on others.

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An organism that can use **both modes** — making its own food like an autotroph AND taking organic food like a heterotroph (e.g. Euglena).

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**Carbon dioxide (CO₂)** — an inorganic carbon source.

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Both fix CO₂, but a **photoautotroph** uses **light** for energy, while a **chemoautotroph** oxidises **inorganic chemicals** (e.g. H₂S).

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Heterotrophic feeding in which food is **ingested and digested INTERNALLY** inside the body (most animals).

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A heterotroph that feeds on **dead** organic matter, digesting it **EXTERNALLY** with secreted enzymes and absorbing the products (decomposers).

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A heterotroph that feeds on a **living host** and **harms** it (e.g. a tapeworm, a head louse).

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Saprotroph digests **externally** and feeds on **dead** matter; a holozoic feeder ingests food and digests it **internally**.

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Some bacteria around **deep-sea vents** that oxidise chemicals such as hydrogen sulfide for energy.

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It is part of the niche: an **obligate aerobe** needs O₂, an **obligate anaerobe** is poisoned by it, a **facultative anaerobe** can use it or do without.

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Read the **energy source AND carbon source together** — e.g. light + CO₂ = photoautotroph; oxidising chemicals + CO₂ = chemoautotroph.