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IB Biology — Practice Questions flashcards

6 of 60 questions free to study here · 4 topics · the whole deck is built into Willys

Multiple-choice practice on the syllabus, one best answer each, on molecules, cells, evolution, transport, enzymes, neurons, immunity, ecology, inheritance and HL extensions.

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Practice deck · part of IB Biology · written against: IB Diploma Programme IB Biology subject guide for first assessment 2025 (themes A–D); SL and HL in one deck, HL-only cards under subtopic tags starting HL. Updated 2026-10-10.

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  1. In a sample of double-stranded DNA, 22 % of the bases are thymine. What percentage of the bases are guanine?

    A) 56 %
    B) 44 %
    C) 22 %
    D) 28 %
    D) 28 %

    Complementary base pairing makes A = T = 22 %, so A + T = 44 % and G + C = 56 %, shared equally: G = 28 %. 56 % is G and C together, not guanine alone.
    Unity and Diversity
  2. A thin column of water rises up the inside of a narrow glass tube to above the water level in the beaker around it. Which property of water mainly explains this?

    A) The high thermal conductivity of liquid water in the tube
    B) Hydrophobic attraction between water and the glass surface
    C) The buoyancy that water gives to objects immersed in it
    D) Adhesion of water molecules to the polar glass surface
    D) Adhesion of water molecules to the polar glass surface

    Water is polar, so it is attracted to other polar or charged surfaces such as glass or cellulose; this adhesion drives capillary action in narrow spaces. Glass is hydrophilic, not hydrophobic, which is why water wets it.
    Unity and Diversity
  3. A polypeptide of 150 amino acids is built by condensation reactions on a ribosome. How many water molecules are released?

    A) 149
    B) 300
    C) 151
    D) 150
    A) 149

    Each peptide bond releases one water molecule, and a chain of n amino acids has n − 1 peptide bonds, so 150 amino acids give 149.
    Form and Function
  4. Why do cellulose molecules form strong microfibrils, whereas amylose forms coiled chains?

    A) β-glucose units give highly branched chains that are held together by ionic bonds
    B) α-glucose units give straight chains that link side by side by disulfide bonds
    C) Alternating β-glucose units give straight chains that hydrogen-bond side by side
    D) Alternating α- and β-glucose units give helices that pack tightly into fibres
    C) Alternating β-glucose units give straight chains that hydrogen-bond side by side

    In cellulose, each β-glucose is inverted relative to the next, so chains are straight and lie parallel, joined by many hydrogen bonds. Amylose is made of α-glucose, which makes the chain coil.
    Form and Function
  5. The rate at which amylase digests starch rises steadily from 20 °C to 40 °C but falls sharply by 60 °C. What explains the fall above the optimum?

    A) Starch denatures and no longer fits into the active site
    B) Molecules have less kinetic energy, so collisions are rarer
    C) The enzyme's active site changes shape as it denatures
    D) The activation energy of the reaction rises with temperature
    C) The enzyme's active site changes shape as it denatures

    High temperature breaks the bonds holding the enzyme's three-dimensional shape, so the active site no longer fits the substrate (denaturation). Molecules actually move faster when warmer, and the fall is caused by the change in the enzyme, not in the starch.
    Interaction and Interdependence
  6. Codons: AUG = Met, GGA = Gly, UAC = Tyr, CCU = Pro. The template strand of a DNA section reads TAC CCT (written 3′ to 5′). Which amino acids does it code for?

    A) Met–Pro
    B) Met–Gly
    C) Tyr–Pro
    D) Tyr–Gly
    B) Met–Gly

    mRNA is complementary to the template strand, so TAC CCT is transcribed as AUG GGA, which codes for Met–Gly. Tyr–Pro comes from reading the template itself as if it were mRNA.
    Continuity and Change

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About these cards

Review status: Second-reader reviewed, with corrections applied.

Checked against:

  • IB Diploma Programme subject guide (topic outline only; no text copied).
  • Tag order follows the IB Diploma Programme Biology guide for first assessment 2025 (themes A–D across four levels of organisation).
  • OpenStax Biology 2e, consulted as a reference; no text copied.

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