Cell Biology Advanced
Organelles, membranes, and cell division in detail
A light microscope magnifies up to ×1500 with ~200 nm resolution. Can view living cells. An electron microscope reaches 0.1 nm resolution, revealing ultrastructure — but specimens must be dead.
Magnification = Image size ÷ Actual size. Resolution = ability to distinguish two close points.
The fluid mosaic model describes the cell membrane: a phospholipid bilayer with hydrophilic heads outward, hydrophobic tails inward. Proteins are scattered throughout. Cholesterol adds stability. The membrane is fluid — phospholipids move sideways.
Mitosis produces 2 genetically *identical* diploid cells (growth/repair). Meiosis produces 4 genetically *different* haploid gametes. Crossing over creates genetic variation.
Transport: **Diffusion** — high to low concentration (passive). **Osmosis** — water through a partially permeable membrane. **Active transport** — low to high using ATP energy.
Key Points to Remember
- 1Electron microscope vs light microscope
- 2Fluid mosaic model of cell membrane
- 3Mitosis and meiosis
- 4Transport across membranes
Pakistan Example
Osmosis in Lahore's Sugarcane Juice Stalls
When sugar is added to juice, the sugary solution has lower water potential, so water moves out of nearby cells by osmosis. Same process causes vegetables to wilt in Karachi's heat — water leaves cells, losing their rigidity.