All living things contain cells. Cells are the building blocks of life. A living thing can be made up of one cell or many cells, but it must have cells to be considered living. Cells provide the basic structure of organisms and provide the space for the organism to carry out functions to further its existence.
All living things can create energy and products such as complex carbohydrates, proteins and other building blocks to grow and pass on genetic material. Living things take raw materials from the environment to give themselves energy and help them to survive.
Living things are capable of reproduction and growth. This means that a cell can copy its genetic information and make a duplicate of itself. More complex organisms are able to reproduce in more complex ways by contributing part of their genetic material to an offspring organism. This part is combined with a part from another organism and a new organism is made.
Biologists believe that living things adapt to their environments and evolve in new ways to survive in certain conditions. This is based on the work of Charles Darwin. Genetic structures of living things evolve to survive in their environments, and the changes are expressed in the organisms' outward appearances.
Living things require energy from a source outside of itself. They gain this energy from the environment and convert it to usable fuel to survive. Plants use sunlight to grow and reproduce. Animals use food. Things that live require a food source to grow, reproduce and survive.
Living things respond to stimuli and to their environment. If the weather is cold, an animal seeks out shelter. If the sun is in a window, a plant bends to reach for it. Similarly, if bacteria is presented with a stimulus, it reacts to it in a controlled way if it is alive.