Cell Structure and Function
Cell Structure and Function covers cell organisation, biomolecules, enzymes, and the cell cycle. The exam checks whether you can relate a structure to its function and track chromosome or DNA content through division.
Core rules and concepts
- Prokaryotes lack a nucleus and membrane-bound organelles and have 70S ribosomes. Eukaryotes have a nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and other organelles. The plasma membrane follows the fluid mosaic model.
- Biomolecules: proteins are polymers of amino acids, carbohydrates include glucose and starch, lipids are hydrophobic, and nucleic acids store information. Enzymes lower activation energy and are affected by pH and temperature.
- Cell cycle: interphase includes G1, S, and G2. Mitosis produces genetically identical diploid cells. Meiosis has two divisions and produces four haploid cells; meiosis I is reductional and meiosis II is equational.
Worked example
A cell with 2n = 24 enters meiosis. After meiosis I, two cells form, each with n = 12 chromosomes, but each chromosome still has two chromatids. After meiosis II, four cells form, each with 12 chromosomes and one chromatid per chromosome. The reasoning tracks chromosome number separately from DNA amount.
Traps that cost marks
70S ribosomes occur in prokaryotes and also in mitochondria and chloroplasts. The middle lamella is made largely of calcium pectate. Meiosis II is equational, not reductional. Cytokinesis in plant cells uses a cell plate, not a cleavage furrow.