Summary
The cell is the smallest unit that is alive: every living thing is made of cells, from a single-celled bacterium to a human being, which has trillions. Each cell comes from another cell, feeds, grows and reproduces.
There are two main types. Prokaryotic cells, like those of bacteria, have no nucleus and are very simple. Eukaryotic cells, like those of plants and animals, keep their DNA inside a nucleus and have organelles: small structures each with a job. Mitochondria release energy, chloroplasts (only in plants) carry out photosynthesis, and the membrane controls what goes in and out.
Key points
- The cell is the basic unit of life: every living thing is made of cells.
- Prokaryotes (no nucleus, bacteria) versus eukaryotes (with a nucleus, plants and animals).
- The nucleus stores the DNA, which holds the cell's instructions.
- Mitochondria produce energy; chloroplasts carry out photosynthesis in plants.
- The membrane surrounds the cell and decides which substances enter and leave.
- The plant cell has a cell wall and a large vacuole; the animal cell does not.
- Cells multiply by dividing in two (mitosis).