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IB Diploma Biology MCQs with answers

Practise IB Diploma Biology (SL / HL) with 373 exam-style MCQs, each with the answer and a short explanation. Every test is marked the moment you finish and shows your score chapter by chapter, so you know what to revise next. It is free and needs no sign-up.

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IB Diploma Biology MCQs with answers

Practise IB Diploma Biology (SL / HL) with 373 exam-style MCQs, each with the answer and a short explanation. Every test is marked the moment you finish and shows your score chapter by chapter, so you know what to revise next. It is free and needs no sign-up.

373 questions · 4 chapters

What each chapter covers 4 chapters

The questions follow the syllabus chapter by chapter. You can test the whole subject or one chapter at a time.

  1. A Unity and diversity 62 questionsA1.1 Water, A1.2 Nucleic acids, A2.2 Cell structure, A3.1 Diversity of organisms, A4.1 Evolution and speciation, A4.2 Conservation of biodiversity
  2. B Form and function 90 questionsB1.1 Carbohydrates and lipids, B1.2 Proteins, B2.1 Membranes and membrane transport, B2.2 Organelles and compartmentalization, B2.3 Cell specialization, B3.1 Gas exchange, B3.2 Transport, B4.1 Adaptation to environment, B4.2 Ecological niches
  3. C Interaction and interdependence 96 questionsC1.1 Enzymes and metabolism, C1.2 Cell respiration, C1.3 Photosynthesis, C2.2 Neural signalling, C3.1 Integration of body systems, C3.2 Defence against disease, C4.1 Populations and communities, C4.2 Transfers of energy and matter
  4. D Continuity and change 125 questionsD1.1 DNA replication, D1.2 Protein synthesis, D1.3 Mutations and gene editing, D2.1 Cell and nuclear division, D2.3 Water potential, D3.1 Reproduction, D3.2 Inheritance, D3.3 Homeostasis, D4.1 Natural selection, D4.2 Stability and change, D4.3 Climate change
Sample IB Diploma Biology MCQs with answers 12 questions

12 questions from the test, one or two from each chapter. Try each one, then open the answer.

1. A double-stranded DNA fragment contains 1 000 nucleotides in total, and 22% of them are adenine. How many guanine nucleotides does the fragment contain?

  1. A
    220
  2. B
    280
  3. C
    440
  4. D
    560
Show answer

Answer: B. A pairs with T, so thymine is also 22%. That leaves 100 − 44 = 56% for G and C together, and as G pairs with C, guanine is 28% of 1 000 = 280. 220 is the number of adenines and 560 is the number of G and C together.

2. Red blood cells from a person with a mutation that removes aquaporins are placed in distilled water. Compared with normal red blood cells, what is most likely?

  1. A
    they do not swell at all, because aquaporins are the only route by which water can cross the membrane
  2. B
    they burst more quickly, because the cell cannot pump water out without aquaporins
  3. C
    they shrink, because water leaves the cell when it cannot move through channels
  4. D
    they swell and burst more slowly, because water enters by osmosis at a lower rate
Show answer

Answer: D. Aquaporins increase the permeability of the membrane to water, so osmosis is faster. Some water still crosses the bilayer, so cells without aquaporins still swell, but more slowly.

3. Which group of organisms contains no species known to cause disease in humans?

  1. A
    protists, mostly unicellular eukaryotes with a nucleus
  2. B
    bacteria, prokaryotes whose cell walls contain peptidoglycan
  3. C
    archaea, prokaryotes whose cell walls contain no peptidoglycan
  4. D
    fungi, eukaryotes whose cell walls contain chitin
Show answer

Answer: C. Pathogens include viruses, bacteria, fungi and protists. No archaeon is known to cause any disease in humans.

4. A fish stock of 80 000 tonnes gains 12% of its mass each year through reproduction and growth. Fishing removes 9000 tonnes per year. Ignoring other losses, what happens to the stock in one year, and is the harvesting sustainable?

  1. A
    it rises by 600 tonnes, but the harvesting is not sustainable because fish are being removed
  2. B
    it rises by 600 tonnes, so the harvesting is sustainable
  3. C
    it rises by 9600 tonnes, so the harvesting is sustainable
  4. D
    it falls by 600 tonnes, so the harvesting is not sustainable
Show answer

Answer: B. Gain = 12% of 80 000 = 9600 tonnes. Net change = 9600 − 9000 = +600 tonnes. Harvesting is sustainable when the rate of removal does not exceed the rate of replacement, even though fish are being caught.

5. An electron micrograph shows a chloroplast that measures 52 mm in the image. Its actual length is 4 µm. What is the magnification?

  1. A
    × 13
  2. B
    × 1300
  3. C
    × 13 000
  4. D
    × 130 000
Show answer

Answer: C. Convert to the same units: 52 mm = 52 000 µm. Magnification = image size ÷ actual size = 52 000 ÷ 4 = × 13 000.

6. Why are the digestive enzymes of lysosomes kept inside a membrane?

  1. A
    so that they can be transported to chloroplasts and used in photosynthesis
  2. B
    so that they can be exported from the cell to digest food outside it
  3. C
    so that they cannot digest the cell's own components in the cytoplasm
  4. D
    because they are too large to exist freely in the cytoplasm of the cell
Show answer

Answer: C. Compartmentalization separates incompatible processes: the hydrolytic enzymes act only inside the lysosome or phagocytic vacuole.

7. An impulse travels 0.60 m along an axon in 20 ms. What is the speed of conduction?

  1. A
    300 m s−1
  2. B
    30 m s−1
  3. C
    0.03 m s−1
  4. D
    12 m s−1
Show answer

Answer: B. Speed = distance ÷ time = 0.60 m ÷ 0.020 s = 30 m s−1. Using 20 without converting milliseconds to seconds gives the wrong 0.03.

8. Over 50 years the mean temperature in a mountain region rises by 1.3 °C. Temperature falls by about 6.5 °C for every 1000 m increase in altitude. By about how far upslope would the zone with the original temperature have moved?

  1. A
    20 m
  2. B
    8450 m
  3. C
    5 m
  4. D
    200 m
Show answer

Answer: D. The zone with the original temperature has shifted to where it is 1.3 °C cooler: 1.3 ÷ 6.5 × 1000 = 200 m higher. This helps to explain why montane species now live at greater altitudes.

9. How many different base sequences are possible for a single strand of DNA that is 6 nucleotides long?

  1. A
    24
  2. B
    1296
  3. C
    4096
  4. D
    46 656
Show answer

Answer: C. There are 4 possible bases at each of 6 positions, so 46 = 4096. 64 = 1296 swaps the base and the power, and 4 × 6 = 24 adds instead of multiplying.

10. Xylem vessels are dead, hollow and have walls thickened with lignin. What is the function of the lignin?

  1. A
    it makes the walls impermeable, so that no water can leave the vessel at any point on its way up the stem
  2. B
    it makes the walls rigid, so they can resist the tension of water being pulled up without collapsing inwards
  3. C
    it keeps the cells alive, so that the cells can pump water actively up the stem against a gradient
  4. D
    it makes the lumen narrower, so that the pressure of the water rises as it moves up the stem
Show answer

Answer: B. Water in xylem is under tension, which would pull the walls inwards; lignin makes them rigid. Pits allow water in and out.

11. The action spectrum of a plant has peaks at about 430 nm and 660 nm and a trough at about 550 nm. What is the best explanation of the trough?

  1. A
    green light is fully absorbed by carotene, which cannot pass the energy on to the photosystems in the chloroplast
  2. B
    green light has too little energy to raise electrons in any pigment, so it can never be absorbed by chloroplasts
  3. C
    the stomata of a leaf close in green light, so almost no carbon dioxide can enter for the light-independent reactions
  4. D
    the pigments absorb little green light, which is mostly reflected or transmitted, so little energy drives photosynthesis
Show answer

Answer: D. Chlorophylls absorb mainly blue and red light. Green light is mostly reflected or transmitted, so the rate of photosynthesis is lower there, which is why leaves look green.

12. Which statement about evolution by natural selection is correct?

  1. A
    it makes the population evolve towards a goal that the environment requires, by producing the alleles that are needed
  2. B
    it changes the frequency of alleles over generations, because individuals with advantageous heritable traits leave more offspring
  3. C
    it occurs only when new mutations arise in response to a change in the environment, and not otherwise
  4. D
    it changes individuals during their lifetimes when they use a trait more, and the changed trait is then inherited by their offspring
Show answer

Answer: B. Natural selection acts on existing heritable variation: the individuals best suited to their environment survive and reproduce more, so their alleles become more common. Acquired characteristics are not inherited.

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Ways to practise 5 ways

When you get a question wrong, a short note called "The idea behind this" explains the topic it belongs to, with the rules to remember and a worked example.

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Is this IB Diploma Biology test free?

Yes. Every test and every explanation is free, and you do not need an account. If you sign in, your results are kept across your devices.

Are these past paper questions?

The 373 MCQs are our own, written to the syllabus in the style of the exam.

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Instantly. You get your score, the right answer and an explanation for every question, and a list of the topics to work on.

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