Video narration
Watch a human body shrink: organ, tissue, then one tiny cell. Every living organism is made of cells. Each cell is a structural building block and a functional unit that keeps life going. Think of the cell as a tiny school. The cell membrane is its boundary, deciding what enters and leaves. Inside, the cytoplasm is the working space where many life processes take place. The nucleus is the control centre, directing cell activities. And mitochondria release energy for those activities, like the school's energy supply. That tiny school works differently in plants. Plant cells have a cell wall, chloroplasts that use sunlight to help prepare food, and a large vacuole. Animal cells do not have a cell wall or chloroplasts. Remember: membrane controls movement, cytoplasm supports life processes, nucleus controls, and mitochondria release energy. Tiny, yet its working parts keep life going: that is life's basic unit.