In the context of biology, tissues are formed by the association of cells that perform a common function. While tissues themselves do not have "functional groups" in the same sense as organic chemistry (where functional groups refer to specific groupings of atoms in molecules that confer specific properties), tissues can be categorized into four basic types based on their functions:
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Epithelial Tissue: Covers body surfaces, lines cavities and organs, and forms glands. It is involved in protection, absorption, secretion, and sensation.
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Connective Tissue: Supports, binds together, and protects tissues and organs of the body. Examples include bone, adipose (fat) tissue, and blood.
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Muscle Tissue: Responsible for the movement of the body and its parts. It is divided into three types: skeletal, cardiac, and smooth muscle.
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Nervous Tissue: Composed of neurons and glial cells, it is involved in receiving stimuli and transmitting electrical impulses throughout the body.
Each tissue type has specialized functions that enable the organism to maintain homeostasis and perform more complex activities. If you're referring to a specific type of association or interaction among tissues—like in organ formation or physiological processes—please provide additional context for a more precise answer.