The Sun is the principal source of energy input for the biological systems on Earth.
- Everything gets its energy from the Sun directly or indirectly.
Flow of energy in organisms:
- With the exception of atomic energy and tidal power, all the energy released on Earth is derived from sunlight.
- Nearly all living things depend on the Sun to get energy. This is harnessed by photosynthesising plants and the energy is then passed through food chains.
  - During photosynthesis, light energy from the Sun is trapped by plants and converted into chemical energy.
  - The chemical energy is stored in the plants, which are then eaten by herbivores.
  - The herbivores are in turn eaten by carnivores. In this way, energy flows to the animals indirectly from the Sun.

Flow of energy in the environment:
- Coal comes from tree-like plants, buried millions of years ago. They took in light energy from the Sun for photosynthesis while they were still alive.
- Over time, these dead plants were buried under water and dirt. Heat and pressure eventually turn these dead plants into coal.
- These coals are burnt to release energy. In this way, energy is being transferred into the environment.
- Other than coal, sugar from sugarcane can be fermented to alcohol which can be used as motor fuel.
- Energy is therefore transferred into the environment again through the method of fossilisation and fermentation.
- Energy is also transferred back to the environment in the form of heat produced from respiration.

19.01 - Energy Flow

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