Biology unit guide
Unity and diversity
Cell theory, water, biological molecules, membranes and cell division.
Unit 1 looks like vocabulary and is examined as explanation. The commonest way to lose marks here is answering a "why" question with a "what" - describing that water is polar when the question asked why that lets it act as a solvent. Structure-to-function is the whole logic of the unit, and answers that make the link explicit score where answers that assume it do not.
Topics in this unit
What gets examined
- Explaining properties of water - cohesion, solvent behaviour, thermal stability - from its polarity and hydrogen bonding.
- Relating the structure of carbohydrates, lipids and proteins to their function and to each other.
- Describing the fluid mosaic model and how membrane structure enables each type of transport.
- Distinguishing simple diffusion, facilitated diffusion, osmosis and active transport by what each requires.
- The stages of mitosis in order, and what happens to chromosomes in each.
- Evidence for cell theory, and the recognised exceptions to it.
How to revise it
Answer structure-then-function, always
Name the structural feature, then say what it allows. Two sentences, two marks. Describing the structure alone is the single most common way to score half.
Learn transport by what it needs
Does it need a protein? Does it need ATP? Which way does it go relative to the gradient? Three questions separate all four transport types cleanly.
Draw mitosis rather than listing it
Sketching the chromosomes at each stage makes the order stick in a way a list does not, and diagram questions appear regularly.
Tie every water property back to hydrogen bonding
Cohesion, high specific heat, solvent behaviour - all of it comes from polarity and hydrogen bonds. One cause, several effects.
Where marks get lost
- Saying water is polar without explaining that this lets it surround and separate ions.
- Confusing osmosis with diffusion, or describing osmosis as movement of solute.
- Calling facilitated diffusion active because it uses a protein - it needs no ATP.
- Listing mitosis stages out of order, or including cytokinesis as a stage of mitosis.
- Describing the membrane as a rigid structure rather than a fluid mosaic.
Practise this unit
Reading about a unit only goes so far. Work through real IB-style questions on it, with mark schemes.