3.2.1.2.1 Prokaryotic cells and viruses Quiz: AQA Biology, Unit 2

The 20 questions

1. How is the DNA of a prokaryotic cell arranged?

   • As many short linear molecules attached to the cell membrane only
   • As a double helix held within mitochondria
   • As linear chromosomes enclosed within a nucleus, bound to histone proteins
   • As a single circular DNA molecule free in the cytoplasm, not associated with proteins

2. What is the main chemical component of the cell wall of a bacterium?

   • Chitin, a polysaccharide
   • Phospholipid bilayer
   • Cellulose, a polysaccharide
   • Murein, a glycoprotein

3. What is a plasmid in a prokaryotic cell?

   • A membrane-bound organelle that makes ATP by aerobic respiration in the cytoplasm of the cell
   • A small, circular DNA molecule separate from the main circular chromosome
   • A linear chromosome containing histone proteins that is found within a nucleus in the cell
   • A flagellum used for movement through liquids by the rotation of a protein filament in the cell

4. What is the outer protein coat of a virus particle called?

   • Capsid
   • Murein
   • Cytoplasm
   • Flagellum

5. Why are viruses described as acellular?

   • They contain many organelles that are able to make proteins and lipids independently of host cells
   • They have no cell structure, such as a cell membrane, cytoplasm or ribosomes of their own
   • They are the smallest living cells, with a nucleus and a full set of membrane-bound organelles inside
   • They have a cell wall made of murein, which prevents them from dividing and makes them very rigid

6. What is the function of an attachment protein on a virus particle?

   • It produces ATP for the virus using host cell mitochondria
   • It digests the cell wall of the host cell using hydrolytic enzymes
   • It forms a flagellum that moves the virus through water
   • It binds to complementary receptors on the surface of a host cell

7. Prokaryotic ribosomes are smaller than eukaryotic ribosomes. Which statement is correct about this?

   • Prokaryotic ribosomes are membrane-bound, while eukaryotic ribosomes are free
   • Prokaryotic ribosomes are found only in the nucleus, while eukaryotic ribosomes are in the cytoplasm
   • Prokaryotic ribosomes are 80S, while eukaryotic ribosomes are 70S
   • Prokaryotic ribosomes are 70S, while eukaryotic ribosomes are 80S

8. A virus enters a host cell and injects its nucleic acid. What happens next?

   • The host cell's machinery replicates the viral nucleic acid and makes new virus particles
   • The host cell's nucleus is destroyed and the virus is released as a spore
   • The virus makes its own ribosomes and uses them to divide
   • The virus divides by binary fission inside the host cell

9. Antibiotics that inhibit murein synthesis are effective against bacteria. Why do they have no effect on viruses?

   • Viruses carry murein in their capsid, which protects the virus particle from the antibiotic completely
   • Viruses are eukaryotic cells, so they are unaffected by all antibiotics that act on any kind of cell
   • Viruses have no cell wall and no murein, so there is nothing for these antibiotics to act upon
   • Viruses have a cell wall that is far too thick for the antibiotic molecules to penetrate into the cell

10. Antibiotics that block 70S ribosomes do not usually harm human cells. Why?

    • Human cells contain no ribosomes in their cytoplasm, so the antibiotic has no target site to act on
    • Human cells have a nuclear envelope that stops the antibiotic from entering the cell's cytoplasm
    • Human cells have murein walls that resist the antibiotic and prevent it from entering the cell
    • Human cytoplasmic ribosomes are 80S, so they differ in structure from the bacterial 70S ribosomes

11. A bacterium is 2 micrometres long. What is its length in millimetres?

    • 0.02 mm
    • 0.2 mm
    • 0.002 mm
    • 2000 mm

12. Which structure is found in a prokaryotic cell but is absent from a virus particle?

    • Genetic material
    • An attachment protein
    • Ribosomes
    • A capsid

13. Viruses carry genetic material that may be DNA or RNA. What does this show about virus structure?

    • All viruses carry RNA as their genetic material, and DNA is found only inside a nucleus
    • All viruses carry DNA as their genetic material, and RNA is found only within the host cells
    • Viruses carry neither DNA nor RNA, but a protein that is able to replicate itself inside the cell
    • The type of nucleic acid varies between viruses, so the genetic material is not always DNA

14. Why are viruses not considered to undergo cell division by binary fission?

    • They are too small to contain any DNA or RNA, so they cannot divide into two new particles
    • They are non-living and cannot replicate themselves, so the host cell must make their components
    • They have a cell wall that prevents the division process from starting in the particle
    • They divide only once inside each host cell, using their own ribosomes to make the new particles

15. Explain how a bacterial plasmid can be passed between bacteria during binary fission, and why daughter cells may receive different numbers of copies.

    • Plasmids replicate only after division has finished, so the daughter cells receive none of them at first
    • Plasmids are passed between cells only when the chromosome is absent, so each daughter gets exactly one copy each time
    • Plasmids replicate with the chromosome, and during division the cytoplasm divides with a variable number of plasmid copies in each daughter
    • Plasmids are always divided equally between the daughter cells because they are physically linked to the chromosome

16. Explain why the specific shape of a virus attachment protein means a virus usually infects only certain types of cell.

    • The attachment protein fits complementary receptor molecules on particular host cell surfaces
    • The attachment protein digests every cell type it contacts, so it can only infect those cells that survive
    • The attachment protein is identical in all viruses, so it binds any cell
    • The attachment protein makes the host cell produce only one type of receptor

17. Explain how a prokaryotic cell can carry out aerobic respiration despite having no mitochondria.

    • Prokaryotes respire using their circular DNA, which is able to produce ATP directly without any enzymes
    • Enzymes for respiration are located in the cytoplasm and the cell-surface membrane, which carry out the reactions
    • Prokaryotes respire in their flagella, which contain all of the enzymes that are needed for the process
    • Prokaryotes use their murein walls as a source of energy, which is released by respiration in the wall

18. A student claims that viruses are living because they contain genetic material. Which evaluation is correct?

    • Incorrect, because having genetic material alone is not enough, as viruses cannot reproduce or metabolise without a host cell
    • Correct, because viruses carry out respiration within their capsid, which releases energy for replication
    • Incorrect, because viruses have ribosomes that make new virus particles from amino acids in the capsid
    • Correct, because all living organisms are defined only by the fact that they carry genetic material in cells

19. A researcher finds that a new bacterium has a flagellum and a capsule. Which feature is most likely to help the bacterium escape the immune system?

    • The circular DNA, which stores information that stops the immune system
    • The flagellum, which allows the bacterium to swim away from the immune cells
    • The cell wall of murein, which prevents phagocytes from engulfing the cell
    • The capsule, which surrounds the cell and can help it evade recognition

20. Explain why the presence of a single circular DNA molecule free in the cytoplasm is still sufficient for a prokaryote to function.

    • The circular DNA is held inside the nucleus, which controls all of the cell's functions in the cytoplasm
    • The circular DNA is replicated only once in each cell cycle, so the cell uses an incomplete set of genes
    • The circular chromosome carries the essential genes, and gene expression occurs in the cytoplasm without a nuclear membrane
    • The circular DNA is held in the cell wall, which releases the genes into the cytoplasm as they are needed

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