Biologists have come up with a list of characteristics that apply to all living things, from bacteria to blue whales. These characteristics are:
1. Living things are made of cells. All living things whether they consist of a single cell, like a bacterium, or many cells like humans are composed of cells.
2. Living things reproduce. All living things make more of themselves. In asexual reproduction, as seen in bacteria and some other organisms, a single parent passes on its genetic information to its offspring. In sexual reproduction, which occurs in plants and animals, two parents contribute genetic information to their offspring.
3. Living things are based on a universal genetic code. All living things use DNA (deoxyribonucleic acid) as their genetic code. DNA is a molecule that stores and transmits genetic information. It contains the instructions that the cell needs to make proteins, the molecules that carry out the cell's activities.
4. Living things grow and develop. As they grow, living things increase in size. During development, they change form and structure. A butterfly, for example, starts out as a caterpillar, then forms a pupa, and finally emerges as a butterfly.
5. Living things respond to their environment. Living things are able to sense and respond to their environment. For example, plants grow toward light and animals run away from danger.
6. Living things maintain homeostasis. Homeostasis is the ability of an organism to maintain internal balance. For example, humans maintain a constant body temperature despite changes in the external environment.
7. Living things take in and use energy. All living things need energy to carry out their activities. Plants get their energy from the sun through photosynthesis. Animals get their energy by eating plants or other animals.
8. Living things produce waste products. The products of metabolism, or the chemical reactions that occur inside cells, are waste products. Living things must remove these waste products in order to stay alive.
9. Living things reproduce. All living things reproduce to create offspring and ensure the survival of their species.
10. Living things evolve over time. Due to genetic variation and natural selection, populations of organisms change over time in a process called evolution. Natural selection is the process whereby certain heritable traits improve an organism's chance to survive and reproduce in its environment.
All living things share these characteristics. They are what make living things unique and different from non-living things.