What are groups of similar cells that act as a functional unit?

• A. Tissues
• B. Organ systems
• C. Cells
• D. Organs

Answer: (A)

Groups of similar cells that work together to perform a specific function form a tissue. This arrangement lets cells specialize and cooperate, making it easier to carry out tasks like movement, lining surfaces, or providing support. For example, muscle tissue is built from muscle cells that contract to produce force, epithelial tissue lines and protects surfaces, connective tissue provides structure and support, and nervous tissue transmits signals. Tissues then come together to form organs, where different tissues collaborate to carry out a particular task—organs themselves connect with other organs to form organ systems that support the whole organism. Cells are the individual units, organs are made of tissues, and organ systems are multiple organs working together, so the grouping described here is most accurately a tissue.