The principles of biology are also governed by the laws of chemistry and physicsPrinciple 1: Cells are the simplest units of lifeoAn organism is a living thing. They maintain an internal order that is separate from the environmentoThe simplest unit of an organism is a celloThe cell theory states that (1) all organisms are composed of cells, (2) cells are the smallest units of life, and (3) new cells come from pre-existing cells via cell divisionPrinciple 2: Living organisms use energyoThe maintenance of organization requires energyoAll living organisms acquire energy from the environment and use that energy to maintain their internal orderoCells carry out a variety of chemical reactions that are responsible for the breakdownof nutrients. These reactions often release energy through a process called respiration. The energy can be used to synthesize the components that make up individual cells and living organisms. Chemical reactions involved with the breakdown and synthesis of cellular molecules are known as metabolism. Plants, algae, and certain bacteria can directly harness light energy to produce their own nutrients through photosynthesis. They are the primary producers of food on Earth. However, some organisms, such as animals and fungi, are consumers, meaning they must use other organisms as food to obtain energy.