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.