What do you mean by animals?

Animals are a big category in the biological world. Generally, inorganic substances cannot synthesize organic substances, and only organic substances (plants, animals or microorganisms) can be used as food, so it has different morphological structure and physiological functions from plants to carry out life activities such as feeding, digestion, absorption, breathing, circulation, excretion, feeling, exercise and reproduction. Zoology classifies animals with the same or similar characteristics into the same category according to their shapes, internal body structures, characteristics of embryonic development, physiological habits and geographical environment, and becomes chordates and invertebrates.

Animals can be divided into aquatic animals and terrestrial animals according to whether they are aquatic or terrestrial; According to whether there are feathers, they can be divided into feathered animals and featherless animals. In addition to the above two features, we can also use other features to classify.

Animals also have a variety of classification methods. By dissecting different animals, we can find that some animals have thorns, while others have no thorns. We can divide all animals into vertebrates and invertebrates according to whether they have backbones or not.