Cell Biology and Cell Physiology
What this domain tests
Cell biology in MSCE covers cell structure, the light microscope, movement across membranes and enzymes. Expect questions asking you to identify organelles from a description, compare plant and animal cells, calculate magnification, and explain osmosis in living tissue.
Core rules
- Magnification = image size ÷ actual size. Both measurements must be in the same unit.
- Resolution is the ability to distinguish two close points; it depends on wavelength and lens quality, not on how much you magnify.
- Plant cells have a cellulose wall, a large permanent vacuole and chloroplasts; animal cells do not.
- Diffusion is passive down a concentration gradient; osmosis is water movement through a partially permeable membrane; active transport moves substances against a gradient and needs ATP.
- Enzymes are proteins that lower activation energy; they are denatured by high temperature and by extremes of pH.
Worked example
A drawing of an onion epidermal cell is 60 mm long. The cell is actually 0.20 mm long. Magnification = 60 ÷ 0.20 = ×300. If the question gives the actual size in micrometres (200 µm), convert first: 200 µm = 0.20 mm, otherwise your answer is 1000 times too large.
Traps that cost marks
- Saying the cell wall controls entry - it is fully permeable; the cell membrane does.
- Writing “the cell shrinks” in plasmolysis without saying the vacuole pulls the cytoplasm away from the wall.
- Confusing turgid with flaccid, and using “crenation” for plant cells.
- Giving magnification without the × sign or without showing units in the working.