All organisms carry out life processes:
- Reproduction : living things can produce offspring (copies of the same type).
- Growth and movement : living things grow and move. For example, plants move in the sense that they grow towards the sun.
- Reaction to external stimuli: all living things can react to external stimuli. For example, many flowers close at night.
- Need for food : all living things require nutrition; plants create the food from sun light, while animals need to eat plants or other animals.
- Respiration for energy: all living things use food to obtain energy. For example, the energy for moving muscles comes from the energy gained by converting sugars to water and carbon dioxide.
- Excretion of waste: all living things excrete waste products. For example, animals excrete the carbon dioxide obtained when getting energy from sugar via the lungs.
Individual cells in an organism also carry out the life processes. This is why cells are called the basic unit of life. Cells in an organism are also living things.
Cells in a tree may reproduce leading to the growth of the tree. The tree itself may reproduce leading to the appearance of new trees.