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Biology LibreTexts

33.1A: Characteristics of the Animal Body

  • Page ID
  • Every animal has a distinct body plan, adapted in response to environmental pressures, that limits its size and shape.


    Describe how form and function are related in an organism


    Key Points

    • A body plan encompasses symmetry, segmentation, and limb disposition.
    • Almost all animals have bodies made of differentiated tissues, which in turn form organs and organ systems.
    • Animal bodies have evolved to interact with their environments in ways that enhance survival and reproduction.

    Key Terms

    • physiology: a branch of biology that deals with the functions and activities of life or of living matter (as organs, tissues, or cells) and of the physical and chemical phenomena involved
    • body plan: an assemblage of morphological features shared among many members of a phylum-level group
    • anatomy: the art of studying the different parts of any organized body, to discover their situation, structure, and economy; dissection

    Animal Form and Function

    Animals vary in form and function. From a sponge to a worm to a goat, an organism has a distinct body plan that limits its size and shape. The term body plan is the “blueprint” encompassing aspects such as symmetry, segmentation, and limb disposition. Body plans have been considered to have evolved in a geologically-sudden flash during the Cambrian Explosion (roughly 542 million years ago). However, there is also evidence of a more gradual development of body plans. With a few exceptions, most notably the sponges and Placozoa, animals have bodies differentiated into separate tissues, which in turn make up more complex organs and organ systems. These include tissues such as muscles, which are able to contract and control locomotion, and nerves, which send and process signals. Typically, there is also an internal digestive chamber with one or two openings. Animals’ bodies are also designed to interact with their environments, whether in the deep sea, a rainforest canopy, or the desert. In addition, animal body plans have evolved in response to environmental pressures, as observed in fossil records, in order to enhance survival and reproductive success. Therefore, a large amount of information about the structure of an organism’s body (anatomy) and the function of its cells, tissues, and organs (physiology) can be learned by studying that organism’s environment. The arctic fox is an example of a complex animal that has adapted to its environment and illustrates the relationships between an animal’s form and function.


    Arctic fox: An arctic fox is a complex animal, well adapted to its environment. It changes coat color with the seasons and has longer fur in winter to trap heat.