Cell Biology and Cellular Physiology
Core concepts
A candidate must be able to describe the plasma membrane as a fluid mosaic (phospholipid bilayer, integral and peripheral proteins, cholesterol, glycoproteins) and explain each transport mode: simple diffusion, facilitated diffusion, osmosis, primary active transport (Na⁺/K⁺ ATPase), and vesicular transport (endocytosis, exocytosis). Know the organelles and their functions - nucleus, mitochondria, rough and smooth ER, Golgi apparatus, lysosomes, ribosomes, cytoskeleton - and the difference between prokaryotic and eukaryotic organization. Be fluent in the ATP economy of the cell: glycolysis in the cytosol, Krebs cycle and oxidative phosphorylation in the mitochondrion.
Traps in questions
- Osmosis moves water, not solute; describe net water movement toward the more concentrated (hypertonic) compartment.
- The Na⁺/K⁺ pump exports 3 Na⁺ and imports 2 K⁺ per ATP - a net electrogenic effect, not a 1:1 exchange.
- Facilitated diffusion uses proteins but consumes no ATP; do not call it active transport.
- Mitochondria and chloroplasts have their own DNA - do not claim all DNA is nuclear.
- Distinguish tonicity (effect on cell volume) from osmolarity (total solute concentration).
Worked example / rule of thumb
A red blood cell placed in 0.9% NaCl stays stable; in distilled water it swells and lyses; in 3% NaCl it shrinks (crenation). Rule of thumb: water follows solute - predict the direction of water flow first, then the volume change of the cell. Always state the membrane permeability assumption: if the solute can cross the membrane, the outcome differs.
For physiology questions, trace a single ion or molecule through the membrane step by step and name the driving force (concentration gradient vs. electrochemical gradient vs. ATP).