According to the cell theory, new cells arise from:

• A. Existing cells
• B. Spontaneous generation
• C. Energy alone
• D. Mitosis in tissues

Answer: (A)

New cells come from existing cells, because cell theory holds that every cell is produced by the division of a pre-existing cell. The process behind this is cell division: a parent cell duplicates its contents and splits into two daughter cells, enabling growth, tissue repair, and reproduction. Spontaneous generation is not supported by evidence; life does not simply appear from nonliving matter. Energy is necessary to drive cellular processes, but it doesn’t by itself create new cells without a template. Mitosis in tissues describes how a cell divides to form new cells, but the fundamental source of those new cells is the pre-existing cell that divides.