Which idea states that all living things are composed of cells and new cells arise from existing cells?

• A. Evolution
• B. Germ theory
• C. Cell theory
• D. Spontaneous generation

Answer: (C)

Cell theory states that every living organism is made up of cells, and that new cells come from existing cells by division. This idea explains why cells are the basic units of life across all organisms, from single-celled microbes to complex plants and animals. Growth and healing happen because cells divide to form new cells, increasing the number of cells in an organism and replacing damaged ones. This principle also helps explain why life doesn’t arise spontaneously from nonliving matter—life propagates through the transmission and division of existing cells. Historically, scientists observed that all tissues are cellular and that cells originate from preexisting cells, which solidified this foundational view of biology. The other concepts don’t fit because evolution describes changes in populations over time, germ theory explains disease-causing microbes, and spontaneous generation is the outdated idea that life can appear from nonliving material.