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Green plants absorb light in their leaves and convert it to energy by photosynthesis.

The Sun is the original source of energy for almost all organisms on the Earth. The way energy passes through an ecosystem is described as energy flow.

The distribution of organisms in a habitat may be affected by physical factors, such as temperature and light.

There is increasing evidence that the level of carbon dioxide in the Earth’s atmosphere is rising. There is also evidence that humans are responsible for this rise.