What makes an organism an animal?

All life on Earth can be divided into five different groups, called kingdoms. They are protists, bacteria, fungi, plants, and animals.

When you think of the word animal, many different ones come to mind, like tigers, dogs, fish, and monkeys, but organisms, like corals, sea anemones, snails and worms, are animals too.

All animals share several important traits. The list that follows describes the traits shared by all animals from snails to tigers to sea anemones to monkeys. These characteristics help scientists show that corals are animals, not plants. These traits also help scientists trace the evolution of animals and separate them into categories that are more familiar, like birds, reptiles, or mammals.

All animal bodies are made up of multiple cells. In most animals, those cells are organized into different tissues, like muscle or skin, that perform different functions. When an animal is developing the cells separate into these different tissues.

All animals eat other living things. All livings things need carbon to live. An organism can obtain carbon it needs by getting it from other living organisms. These kinds of organisms are called heterotrophs (het-er-oh-tro-f).

All animals can move from place to place. This is one thing that makes animals different than plants. Plants are fixed to the substrate in which they grow. Some animals cannot move throughout their entire life cycle, but can at the embryo stage.

Most animals reproduce sexually. This means that genetic information, or traits, that are crossed between individuals and offspring are similar, but not a copy of the parents. This allows for the diversity of animals that we see on Earth.

Animals are the most abundant living things on Earth. Scientists estimate that there are about nine million species. They exist in many forms and sizes, ranging from a few cells to organisms that weigh several tons. Animals can be found in every habitat on the planet.