Cell Biology and Cell Division
Cell Biology and Cell Division
This domain tests cell ultrastructure, membrane transport, and the chromosome behaviour of mitosis and meiosis. Expect questions that ask you to identify an organelle from its function, compare plant and animal cells, or interpret a cell-division diagram.
Core rules
- Prokaryotic cells have no nucleus or membrane-bound organelles; their DNA is circular. Eukaryotic cells have a nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and-in plants-chloroplasts and a large permanent vacuole.
- Diffusion and osmosis are passive. Osmosis is water movement across a selectively permeable membrane from higher water potential to lower water potential. Active transport uses ATP and carrier proteins.
- Mitosis gives two genetically identical diploid cells. Meiosis gives four haploid cells and generates variation by crossing over in prophase I and independent assortment in metaphase I.
- Plant cytokinesis forms a cell plate; animal cytokinesis forms a cleavage furrow.
Worked example
A micrograph shows a cell 30 mm wide; the actual width is 0.03 mm. Magnification = image size ÷ actual size = 30 ÷ 0.03 = ×1000. Convert to the same unit first. Magnification changes apparent size; resolution is the ability to distinguish two nearby points.
Traps
Meiosis II has no DNA replication. After centromeres split, each chromatid is counted as a chromosome. Water moves toward the lower water potential, usually the more concentrated solution. A plant cell does not burst in pure water because the wall resists turgor pressure.