Lesson 3.8.4.1.2

3.8.4.1.2 Amplifying DNA: PCR and in vivo cloning Quiz: AQA Biology, Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

In partnership with Revision Ninja

Lesson 3.8.4.1.2, Amplifying DNA: PCR and in vivo cloning: 20 multiple choice questions for the AQA Biology (7402), Unit 8: The control of gene expression, written with Revision Ninja.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. The polymerase chain reaction (PCR) is best described as:

    • An in vivo method that uses living bacteria to copy DNA
    • An in vitro method to amplify DNA fragments
    • A technique that cuts DNA at specific sites
    • A method that separates DNA fragments by size only

  2. Which PCR step separates the two strands of DNA?

    • Ligation by DNA ligase
    • Denaturation at high temperature
    • Extension by DNA polymerase at about 72 degrees Celsius
    • Annealing of primers at a lower temperature

  3. Why is a heat-stable DNA polymerase used in PCR?

    • It cuts DNA at specific sequences
    • It works only in the cytoplasm of host bacteria
    • It is not denatured by the high temperature used in each cycle
    • It converts RNA into DNA

  4. In vivo cloning of a DNA fragment involves:

    • Culturing transformed host cells that replicate the vector and fragment
    • Cutting the fragment with restriction enzymes in a test tube
    • Heating DNA to separate its strands
    • Synthesising the fragment in a gene machine

  5. What are primers in PCR?

    • Short DNA sequences that bind to the ends of the target fragment and start copying
    • Long molecules of mRNA that code for protein, which are copied from the target fragment and then translated into an amino acid chain
    • Enzymes that cut DNA into fragments at specific base sequences, so that the target fragment can be separated from the rest of the DNA
    • Proteins that separate DNA strands by unwinding the double helix, so that each strand can be copied separately during the reaction

  6. After n cycles of PCR starting from one molecule of DNA, how many copies are made?

    • n copies
    • 2^n copies
    • n^2 copies
    • 2n copies

  7. Which of these is an in vivo method of amplifying a DNA fragment?

    • Separating DNA fragments by size using gel electrophoresis, which is a method used after the fragment has been copied
    • Heating DNA in a thermal cycler with primers and polymerase, which is a laboratory method that amplifies the fragment in a test tube
    • Hybridising a labelled probe to a membrane carrying the DNA, which detects the fragment but does not amplify it at all
    • Culturing bacteria transformed with a plasmid carrying the fragment

  8. How many copies of a DNA molecule are made after 10 cycles of PCR starting from one molecule?

    • 100
    • 1024
    • 512
    • 20

  9. Why is the temperature lowered during the annealing step of PCR?

    • To destroy any contaminating bacteria that might have entered the reaction tube, so that the PCR product is not mixed with other DNA
    • To stop DNA polymerase from working until the reaction has cooled to room temperature, so that no new strands form in the cycle
    • To make the DNA strands separate completely into single strands that can then be cut by restriction enzymes in the reaction tube
    • To allow the primers to bind to complementary sequences on the single strands

  10. What happens during the extension step of PCR?

    • Primers are removed from the DNA
    • The two strands of DNA are separated by heat
    • Restriction enzymes cut the DNA into fragments
    • DNA polymerase builds new complementary strands from the primers

  11. Five molecules of DNA undergo four cycles of PCR. How many molecules are produced?

    • 80
    • 20
    • 160
    • 40

  12. What is the main advantage of in vivo cloning over PCR?

    • It produces a stable, repeatable clone of the gene in host cells
    • It is faster and needs no living cells, because the gene is copied in a test tube within minutes of the sample being collected
    • It requires no primers or enzymes, since the host cells copy the vector without any help from DNA polymerase or other proteins
    • It produces many copies without any vector, because the host cell copies the fragment directly from the chromosome of the organism

  13. Why are bacteria often used as host cells for in vivo cloning?

    • They cannot divide and so keep the DNA stable
    • They do not contain any DNA of their own
    • They always produce the desired gene without a vector
    • They divide rapidly and can take up plasmid vectors

  14. A plasmid carries an antibiotic resistance marker. Why is this used in cloning?

    • The antibiotic stops PCR from working
    • Antibiotic resistance kills all bacteria that take up the plasmid
    • The antibiotic speeds up the replication of the fragment
    • Only bacteria that took up the plasmid survive on antibiotic medium

  15. Which statement best compares PCR with in vivo cloning?

    • PCR needs living cells to replicate the DNA, while in vivo cloning needs no living cells because the reaction is run in a test tube
    • PCR gives a stable clone of the gene that can be kept indefinitely, while in vivo cloning gives only a single copy that must be made again
    • PCR is faster and needs no living cells, while in vivo cloning gives a stable clone but takes longer
    • Both methods are identical in speed and require the same equipment, so the choice between them depends only on the cost of the primers

  16. What is the minimum number of PCR cycles needed to produce at least 1000 copies starting from one molecule?

    • 5
    • 100
    • 8
    • 10

  17. Which sequence is correct within one cycle of PCR?

    • Extension, then denaturation, then annealing of primers
    • Ligation, then denaturation, then extension
    • Annealing, then denaturation, then extension by DNA polymerase
    • Denaturation, then annealing of primers, then extension by DNA polymerase

  18. Why are primers needed in PCR in addition to DNA polymerase?

    • Primers are the enzymes that separate the two DNA strands during the denaturation step, so they must be added before each heating stage
    • Primers make the polymerase heat-resistant by binding to it, so the enzyme survives the high temperature of each PCR cycle
    • Primers cut the DNA into smaller fragments at specific sites, so the target region can be separated from the rest of the molecule
    • DNA polymerase can only add nucleotides to an existing 3 prime end, so primers provide that starting point

  19. Why might a PCR product be wrong if the annealing temperature is too high?

    • High temperature creates extra copies of the primer and the DNA in every cycle, so the reaction produces too much product to analyse
    • Primers become more specific at high temperatures, so the product is always the wrong fragment and no correct copies are ever made
    • The DNA is copied more accurately at high temperatures, because the polymerase proofreads each base more carefully when the reaction is hot
    • Primers may fail to bind specifically, so the wrong fragment or no fragment is amplified

  20. Why is in vivo cloning useful when a large, stable supply of a gene is required for research?

    • It is the only method that produces DNA without any primers, so it can copy a fragment without knowing any of its sequence in advance
    • It destroys the gene so that a new one must be made from scratch each time, which gives a fresh copy for every experiment run
    • It removes the need for any vector or host cell, because the fragment is copied directly in a test tube without any living organisms
    • Transformed host cells can be cultured to give a repeatable, growing supply of the cloned fragment

All AQA Biology quizzes