Cell Biology and Cell Processes
What this domain tests
Cell Biology and Cell Processes examines the building blocks of life: cell structure, specialised cells, microscopy, movement of substances and enzyme-controlled reactions. You must recognise organelles, explain their functions and apply transport ideas to unfamiliar situations.
Core rules
- Plant cells have a cellulose cell wall, a large permanent vacuole and chloroplasts; animal cells lack these but may have glycogen granules.
- The nucleus contains chromosomes; mitochondria release energy by respiration; ribosomes make proteins; chloroplasts carry out photosynthesis.
- Magnification = image size ÷ actual size. Use the same units before dividing.
- Diffusion is net movement of particles from high to low concentration; osmosis is water movement across a partially permeable membrane from high to low water potential; active transport uses energy to move substances against a gradient.
- Enzymes are proteins that catalyse reactions; they are specific and denature at high temperature or extreme pH.
Worked example
A cell is drawn 40 mm long. Its actual length is 0.05 mm. Magnification = 40 ÷ 0.05 = ×800. If the drawing is 8 mm and actual 0.02 mm, magnification = ×400. Always convert to the same unit; a common error is using mm for one value and µm for the other.
Traps
Do not say chloroplasts are in all plant cells-root cells usually lack them. Osmosis is about water, not any solute. Active transport is not diffusion with a carrier; it requires energy. Enzyme activity falls at high temperature because the active site changes shape, not because the enzyme is used up.