IB Diploma Biology chapter 1: A Unity and diversity MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

62 exam-style questions on A Unity and diversity, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

62 questions · 6 topics · 10 per test

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What chapter 1 covers

Ten A Unity and diversity questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

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. 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.

3. 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.

4. Whole genome sequencing has become much faster and cheaper. Which is a potential use in medicine?

  1. A
    gene therapy that rewrites every mutation in all of the body cells of a patient in a single treatment
  2. B
    counting the chromosomes in a patient's cells to produce a karyogram under the light microscope
  3. C
    personalized medicine, in which treatments are chosen to suit an individual patient's genome
  4. D
    measuring the concentration of glucose in a patient's blood plasma after a meal
Show answer

Answer: C. Knowing a patient's genome could allow drugs and doses to be matched to that individual. Karyograms and blood glucose tests do not need a whole genome sequence.

5. A karyogram made from the cells of one person shows 47 chromosomes, with three copies of chromosome 21. How did the technician recognize the three copies?

  1. A
    by counting the genes on each chromosome and finding that one group of chromosomes carried the same genes three times
  2. B
    by reading the base sequence of each chromosome and finding that three of them were identical to each other
  3. C
    by arranging the chromosomes in the order in which they were photographed, so that copies appeared side by side
  4. D
    by pairing chromosomes by length, centromere position and banding pattern, so that one group had three members
Show answer

Answer: D. In a karyogram homologous chromosomes are paired by size, centromere position and banding pattern. Three chromosomes in the chromosome 21 group show trisomy (Down syndrome). Sequencing is not needed to make a karyogram.

6. A student's drawing of a cell is 24 mm wide at a magnification of × 600. A photograph of the same cell has a magnification of × 1500. How wide is the cell in the photograph?

  1. A
    6 mm
  2. B
    9.6 mm
  3. C
    60 mm
  4. D
    96 mm
Show answer

Answer: C. Actual width = 24 mm ÷ 600 = 0.04 mm (40 µm). At × 1500 the image is 0.04 × 1500 = 60 mm. 9.6 mm results from dividing by 1500 and multiplying by 600 (inverting the ratio).

7. Three oak-related species are named Quercus robur, Quercus petraea and Castanea sativa. Which conclusion is best supported by their names?

  1. A
    the first two are in the same genus and so are probably more closely related to each other than either is to the third
  2. B
    the first two are different varieties of one species, because they share a genus and differ only in their second names
  3. C
    the first two can interbreed to produce fertile offspring, because species in one genus always do so
  4. D
    the second and third belong to the same genus, because both have names ending in an ‘a’
Show answer

Answer: A. The first word is the genus. Species in the same genus share a recent common ancestor and similar traits, but sharing a genus does not mean they can interbreed. The second word is the species name.

8. Which pairing of microscopy technique and use is correct?

  1. A
    freeze fracture: showing where one particular protein is located in a living cell by using antibodies bound to fluorescent markers
  2. B
    cryogenic electron microscopy: determining the three-dimensional shape of a protein in a rapidly frozen sample
  3. C
    immunofluorescence: splitting a frozen membrane along the middle of the bilayer to reveal embedded proteins
  4. D
    fluorescent staining: producing images of individual ribosomes with a resolution of about 1 nm
Show answer

Answer: B. Cryo-EM freezes molecules very quickly so their structure is preserved and can be analysed; freeze fracture splits membranes; immunofluorescence uses fluorescent antibodies to locate a chosen protein. Light microscopy cannot resolve single ribosomes.

9. Which statement describes the meaning of ‘antiparallel’ in the DNA double helix?

  1. A
    the two sugar–phosphate backbones run in opposite directions, with complementary bases paired between them
  2. B
    the two sugar–phosphate backbones run in the same direction, with hydrogen bonds between complementary bases
  3. C
    the bases of one strand face outwards from the helix while the bases of the other strand face inwards
  4. D
    the two strands are identical in base sequence, but they twist around each other in opposite directions
Show answer

Answer: A. In a DNA molecule the two strands are complementary and run in opposite directions, with the bases inside the helix held together by hydrogen bonds.

10. A micrograph has a scale bar 18 mm long that represents 2 µm. A cell in the same micrograph measures 63 mm across. What is the actual width of the cell?

  1. A
    0.7 µm
  2. B
    3.5 µm
  3. C
    7 µm
  4. D
    14 µm
Show answer

Answer: C. One millimetre on the scale bar represents 2 ÷ 18 µm, so 63 mm is 63 × 2 ÷ 18 = 7 µm. 3.5 µm is 63 ÷ 18 with the 2 µm forgotten.

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A Unity and diversity: questions students ask

How many A Unity and diversity MCQs are there?

62, each with the answer and a short explanation, across 6 topics: A1.1 Water, A1.2 Nucleic acids, A2.2 Cell structure, A3.1 Diversity of organisms, A4.1 Evolution and speciation, A4.2 Conservation of biodiversity. Every chapter test draws ten of them, so you can take it many times.

Is the IB Diploma Biology chapter 1 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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