All living things are made of cells — the basic units of life. There are two main types: prokaryotic cells (no nucleus, like bacteria) and eukaryotic cells (with a nucleus, like plant and animal cells).

Every cell has essential components. The cell membrane controls what enters and leaves. The cytoplasm is the gel-like substance that fills the cell. The nucleus houses DNA, which contains genetic instructions. Mitochondria are the "powerhouses" that produce energy through cellular respiration.

Plant cells have additional structures: a rigid cell wall for support, chloroplasts for photosynthesis, and a large central vacuole for storage.

Cells reproduce through cell division. Mitosis produces two identical cells for growth and repair. Meiosis produces four genetically unique cells for sexual reproduction.