IB Biology: Water & Biological Molecules Revision

Water & Biological Molecules is a core part of IB Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.

Key concepts

Semi-conservativeEach new DNA has one parental strand

HelicaseUnwinds DNA double helix

DNA polymeraseAdds nucleotides 5' to 3'

mRNAMessenger RNA carrying codons

CodonTriplet of bases coding one amino acid

RibosomerRNA + protein; site of translation

PrimaryAmino acid sequence from N to C terminus

Secondaryα-helix and β-pleated sheet (H-bonds)

Tertiary3D fold from R-group interactions

QuaternaryMultiple polypeptide subunits

DenaturationLoss of 3D shape from heat or pH

Peptide bondCovalent C-N bond between amino acids

PolarityUneven charge — O δ⁻, H δ⁺ in water

Hydrogen bondWeak attraction between δ+ H and δ- atom

Common mistakes to avoid

Questions where students often pick the tempting wrong answer — make sure you know the right one:

What happens to an enzyme after it catalyses a reaction?✗ It is used up and must be replaced each time. ✓ Nothing — it is unchanged and can be reused many times.

What does heating an enzyme to a high temperature do?✗ It makes the enzyme work faster and faster with no limit. ✓ It denatures the enzyme, changing the active site so it stops working.

Practise Water & Biological Molecules — free games

Test yourself with these quick revision games for this topic:

▶ Two Truths, One Lie ▶ Reveal Race ▶ Connections Grid ▶ Falling Words ▶ Word Web

See all 17 games in the Subjects Arcade →

Water & Biological Molecules

Key concepts

Common mistakes to avoid

Practise Water & Biological Molecules — free games

More IB Biology topics