What is the smallest and most numerous structural unit that possesses the characteristics of living matter?

The correct answer is cells, as they are the fundamental building blocks of all living organisms. Cells are the smallest units of life that can carry out all the necessary functions to maintain life, including metabolism, growth, and reproduction. Each cell can perform essential processes independently, which is a key characteristic of living matter.

Cells also can vary greatly in structure and function, allowing for the diversity of life we observe across different organisms. For example, in multicellular organisms, cells can specialize into different types, such as nerve cells, muscle cells, and blood cells, each with specific roles.

While tissues, organs, and organ systems are crucial for the complexity of living organisms, they are made up of cells. Tissues are groups of similar cells working together for a specific purpose, organs are structures composed of different tissues working together, and organ systems consist of groups of organs that perform an overall function in the organism. Therefore, while these larger units are composed of cells, they do not represent the smallest unit that exhibits the characteristics essential for life.