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Boundless Biology
The Animal Body: Basic Form and Function
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Animal Form and Function
Characteristics of the Animal Body
Every animal has a distinct body plan, adapted in response to environmental pressures, that limits its size
and shape.
Learning Objectives
Describe how form and function are related in an organism
Key Takeaways
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
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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.