The four basic needs of all living things are sunlight, air, water and food. The survival of living organisms also depends on limiting factors such as soils, temperature and physical barriers. These factors, which are specific to their environments, often limit where certain species can live.
Sunlight is considered the most important need since it provides all living things with heat and energy. Energy also comes from food in the form of nutrients. Water serves as a medium for cells and tissues and as a living environment for certain plants and animals. Air supplies essential gases, such as oxygen and carbon dioxide.