Cell Structure and Function
Cell Structure and Function covers the cell cycle, biomolecules, organelles, transport, photosynthesis, and respiration. Questions test phase-specific events, organelle functions, and the inputs and outputs of energy pathways.
Core rules
- Cell cycle: G1, S, G2, M. DNA replicates in S phase; chromosome number remains constant. Mitosis produces two genetically identical diploid cells; meiosis produces four haploid cells.
- Biomolecules: carbohydrates, proteins, lipids, nucleic acids. Enzymes lower activation energy; competitive inhibitors compete for the active site.
- Transport: diffusion and osmosis are passive; facilitated diffusion uses proteins without ATP; active transport uses ATP.
- Organelles: mitochondria for aerobic respiration, chloroplast for photosynthesis, lysosomes for hydrolysis, ribosomes for protein synthesis.
- Photosynthesis: light reactions in thylakoids produce ATP and NADPH and split water, releasing O2; the Calvin cycle fixes CO2 in the stroma.
- Respiration: glycolysis in cytoplasm, Krebs cycle in mitochondrial matrix, oxidative phosphorylation on the inner membrane.
Worked example
A diploid cell has 2n = 8. At metaphase of mitosis, how many chromosomes and chromatids are present? After cytokinesis, what does each daughter cell contain? Reasoning: after S phase, each chromosome has two sister chromatids, so there are 8 chromosomes and 16 chromatids. At metaphase they align. Cytokinesis separates one chromatid from each pair into each daughter, giving 8 chromosomes per daughter cell.
Traps
DNA content doubles in S phase, but chromosome number does not. Oxygen released in photosynthesis comes from water, not CO2. ATP is not formed directly from glucose in one step. Facilitated diffusion uses proteins but no ATP. Chlorophyll absorbs mainly blue-violet and red light, not green.