What are the basic units of life?

• A. Cells
• B. Tissues
• C. Organs
• D. Molecules

Answer: (A)

Life is organized at the cellular level; the smallest unit that can perform all the activities that define living things is a cell. Cells carry out metabolism, respond to the environment, grow, reproduce, and maintain homeostasis. In unicellular organisms, a single cell is the entire organism; in multicellular ones, countless cells specialize to form tissues and organs, yet the function of life still hinges on the activities inside cells. Tissues are groups of similar cells working together, organs are made of tissues, and molecules are the chemical building blocks that make up these structures. So the cell is the fundamental unit that carries out the processes that define life.