Cells and cell structure · Year 8
Every living thing is made of cells: some of just one, and you of about 30 trillion. A cell is the smallest unit of life. Animal and plant cells share the same basic parts, plant cells have a few extra ones, and bacteria are much smaller and simpler. Many cells are specialised: their shape and parts suit one job.
Key facts
- Animal cells have a nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes.
- Plant cells have all of these, plus a cell wall made of cellulose, chloroplasts and a permanent vacuole filled with cell sap.
- Nucleus: controls the cell and holds the genetic material (DNA). Cell membrane: controls what goes in and out. Cytoplasm: where most chemical reactions happen. Mitochondria: where aerobic respiration releases energy. Ribosomes: where proteins are made.
- Chloroplasts absorb light for photosynthesis. The cell wall strengthens and supports the cell. The vacuole keeps the cell firm.
- Plant and animal cells are eukaryotic (their DNA is inside a nucleus). Bacteria are prokaryotic: no nucleus, just one loop of DNA and small rings called plasmids.
- Specialised cells have features that suit their job: a sperm cell has a tail, a red blood cell has no nucleus, a root hair cell has a large surface area.
- Cells → tissues → organs → organ systems → organism. A tissue is a group of similar cells doing the same job.