Cells are defined as what?

• A. The smallest chemical units
• B. The basic unit of all living things
• C. The collection of tissues
• D. The organ that regulates metabolism

Answer: (B)

Cells are the basic unit of all living things. They are the smallest unit that can carry out the essential life processes—metabolism, growth, response to the environment, and reproduction. In single-celled organisms, the entire organism is a cell, while in multicellular organisms many cells come together to form tissues and organs, but life begins at the cell level. The idea that cells are the smallest chemical units isn’t correct because atoms and molecules are smaller building blocks that make up cells. A collection of tissues isn’t a single life unit either—tissues combine to form organs, which are larger structures. And an organ that regulates metabolism isn’t what defines a cell; metabolism happens inside cells, not defined by a single organ.