Animals are multicellular eukaryotes whose cells are bound together by collagen . Animals dominate human conceptions of life on Earth because of their size, diversity, abundance, and mobility. The presence of muscles and mobility is one of the primary characteristics of the animal kingdom.

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Q: What are the two major groups of animals?

The two major groups of animals are vertebrates and invertebrates . Vertebrates have backbones, and invertebrates do not.

Q: When did animals first appear?

Animals first appeared in the Ediacaran Period , about 635 million to 541 million years ago, as soft-bodied forms that left traces of their bodies in shallow-water sediments.

Q: What are the basic functional systems of animals?

Animals' basic functional systems include a musculoskeletal system, for supporting and moving the body; a nervous system , for receiving and processing sensory information and for carrying signals to control muscle and hormone activity; an endocrine system , for secreting hormones to chemically control bodily functions; a digestive system, for receiving and processing food; a circulatory system , for carrying nutrients and oxygen to cells and carrying away their wastes; and a reproductive system , for producing offspring to ensure species survival.

Q: How are animals different from plants and fungi?

Animals differ from plants and fungi in fundamental variations in morphology and physiology, notably in regard to animals’ development of muscles and mobility.

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Also known as: Animalia

Written by Virginia C. Maiorana, Leigh M. Van ValenSee All

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Feb 29, 2024 • Article History

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Category: Science & Tech

Key People:: Charles Elton; Carl E. Akeley; Spencer Fullerton Baird; Karl P. Schmidt; Ross Granville Harrison

Related Topics:: animal social behaviour; reptile; fish; animal behaviour; insect

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What is an animal?

What are the two major groups of animals?

When did animals first appear?

What are the basic functional systems of animals?

How are animals different from plants and fungi?

animal, (kingdom Animalia), any of a group of multicellular eukaryotic organisms (i.e., as distinct from bacteria, their deoxyribonucleic acid, or DNA, is contained in a membrane-bound nucleus). They are thought to have evolved independently from the unicellular eukaryotes. Animals differ from members of the two other kingdoms of multicellular eukaryotes, the plants (Plantae) and the fungi (Mycota), in fundamental variations in morphology and physiology. This is largely because animals have developed muscles and hence mobility, a characteristic that has stimulated the further development of tissues and organ systems. Animals dominate human conceptions of life on Earth not simply by their ...(100 of 14970 words)

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