Prokaryotic cells and virusesAQA A-Level Biology: Flashcards
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How does the size of a prokaryotic cell compare with a eukaryotic cell?
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- How does the size of a prokaryotic cell compare with a eukaryotic cell?
- Prokaryotic cells are much smaller.
- Describe the DNA of a prokaryotic cell.
- A single circular molecule, free in the cytoplasm and not associated with protein.
- Describe eukaryotic DNA in the nucleus.
- Linear and bound to protein.
- Do prokaryotes have a nucleus?
- No; the DNA is free in the cytoplasm.
- What type of organelle is missing from prokaryotic cytoplasm?
- Membrane-bound organelles, such as mitochondria.
- How do prokaryotic ribosomes differ from eukaryotic ones?
- They are smaller.
- What is murein?
- A glycoprotein in the cell wall of prokaryotes.
- What is a plasmid?
- A small circular loop of DNA, separate from the main DNA, often carrying genes such as antibiotic resistance.
- What is the function of a capsule?
- A protective layer around the cell, e.g. against white blood cells.
- What is the function of a flagellum?
- Rotates to move the cell.
- Why does penicillin not harm human cells?
- It stops murein forming, and human cells do not have murein.
- Why are viruses described as acellular?
- They have no cell-surface membrane, cytoplasm or organelles.
- Why are viruses described as non-living?
- They cannot carry out metabolism or reproduce independently; they replicate only inside host cells.
- Name the three components of a virus particle.
- Genetic material (DNA or RNA), a protein capsid and attachment proteins.
- What do attachment proteins do?
- Bind to specific receptors on a host cell.
Exam questions on Prokaryotic cells and viruses
- A student compares the bacterium Escherichia coli, which is about 2 μm long, with a human liver cell, which is about 25 μm across.State two differences between the DNA of E. coli and the DNA of the human liver cell.2 marks
- Some antibiotics work by binding to bacterial ribosomes and stopping protein synthesis, but they do not affect protein synthesis in the cells of the person taking them. A scientist is investigating why.Suggest why an antibiotic that binds to bacterial ribosomes is unlikely to harm human cells, and why it stops the bacteria from growing.2 marks
- Pseudomonas aeruginosa is a bacterium that infects the lungs of patients with cystic fibrosis. Each cell has a capsule, flagella and several plasmids, and one plasmid carries a gene for antibiotic resistance. The bacteria live alongside human lung epithelial cells.Suggest how the capsule, the flagella and the plasmids help Pseudomonas aeruginosa to survive and spread in the lungs.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).