Cells
All living organisms are made of cells. Animal and plant cells are eukaryotic: they have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall of cellulose, a permanent vacuole and often chloroplasts.
Bacterial cells are prokaryotic. They are smaller, with no nucleus. DNA is a single loop in the cytoplasm, and they may have plasmids, a cell wall and a flagellum.
Microscopy and size
- Light microscopes use light and lenses. They can view living cells but have lower resolution.
- Electron microscopes have much higher magnification and resolution, so organelles such as mitochondria and ribosomes can be seen.
- Image size = actual size × magnification. Rearrange to find the missing value and convert units carefully (1 mm = 1000 µm).
Cell division
Mitosis produces two identical diploid cells for growth and repair. The cell cycle includes growth, DNA replication and then mitosis. Stem cells can differentiate. Embryonic stem cells can become any cell type; adult stem cells are more limited. In plants, meristems provide stem cells throughout life.
Transport
- Diffusion is the net movement of particles from higher to lower concentration.
- Osmosis is the diffusion of water through a partially permeable membrane.
- Active transport moves substances against a concentration gradient and requires energy from respiration.
Download Topic 1 slides (PowerPoint)
Taught with support from Joseph Danso, Science Lecturer in London. Book a session.