The five basic biological criterea for the presence of life and a brief explanation of each are as follows:
1: Organization. Living things are highly organized. All life on Earth is based on the cell as the base unit of organization. Some living organisms are composed of only one cell while others are composed of millions of cells all functioning as an organizational unit.
2: Energy. Living things have the ability to aquire raw materials and energy. These raw materials can include atmospheric gasses (oxygen, carbon dioxide), water, inorganic salts, and organic compounds (from food). Some living organisms can use these raw materials to produce their own food (plants convert the energy from the sun into food) while others take in external food for their energy.
3: Response to stimuli. Living things respond to stimuli in their environment. An example could be an animal withdrawing from a hot surface to a plant adjusting its position to increase its exposure to sunlight.
4: Reproduction. Living things can produce offspring to propagate and continue their species. This can be as simple as the division of a single cell to a highly complex series of events such as the combination of two gametes during sexual reproduction.
5: Adaptation. Living things have the ability to adapt to changes in their environments to continue surviving.