Cells and Cell Processes
This domain tests how you link cell structure to function, explain movement across membranes, and interpret enzyme and energy-transfer experiments. Expect questions that ask you to identify an organelle from its role or predict the effect of changing one variable.
Cell structure
- Eukaryotic cells contain membrane-bound organelles; prokaryotic cells have no nucleus or mitochondria.
- Plant cells have a cellulose wall, chloroplasts and a permanent vacuole; animal cells do not.
- Mitochondria release energy by aerobic respiration, ribosomes build proteins, and chloroplasts carry out photosynthesis.
Transport and enzymes
Diffusion is passive movement from high to low concentration. Osmosis is water movement from higher water potential (more dilute) to lower water potential through a partially permeable membrane. Active transport moves substances against the gradient and needs ATP. Enzymes are protein catalysts with an active site; temperature and pH change rate. Above the optimum, the active site denatures.
Worked example
A cell measures 0.05 mm and its image is 50 mm. Magnification = image size ÷ actual size = 50 ÷ 0.05 = 1000×. Convert both measurements to the same unit first; magnification has no unit. To find actual size, rearrange: actual = image ÷ magnification.
Traps
- Root hair cells do not contain chloroplasts.
- Denaturation is a permanent shape change, not the enzyme being 'used up'.
- 'High concentration' is not the same as 'high water potential'.