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Microorganisms, immunity and biotechnology
7 MDCAT Biology questions with answers and explanations.
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Gram-positive bacteria appear which colour after Gram staining?
- 1 Pink or red
- 2 Purple or violet
- 3 Green
- 4 Colourless
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Correct answer: Purple or violet
Their thick peptidoglycan wall keeps the crystal violet stain, so they look purple. Gram-negative bacteria look pink.
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Restriction enzymes are used to:
- 1 Join DNA fragments
- 2 Copy RNA
- 3 Cut DNA at specific sequences
- 4 Make proteins
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Correct answer: Cut DNA at specific sequences
Each restriction enzyme recognises a short DNA sequence and cuts there. Ligase is the enzyme that joins fragments.
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The polymerase chain reaction (PCR) is used to:
- 1 Amplify a DNA sequence
- 2 Sequence proteins
- 3 Stain bacteria
- 4 Break down RNA
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Correct answer: Amplify a DNA sequence
PCR makes millions of copies of a chosen DNA segment by repeated heating and cooling cycles with a heat-stable polymerase.
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Penicillin was discovered by:
- 1 Louis Pasteur
- 2 Edward Jenner
- 3 Alexander Fleming
- 4 Robert Koch
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Correct answer: Alexander Fleming
Fleming noticed in 1928 that a Penicillium mould killed bacteria on his culture plate.
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A vaccine protects the body mainly by:
- 1 Killing bacteria directly
- 2 Stimulating immune memory
- 3 Supplying ready-made antibodies for life
- 4 Raising body temperature
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Correct answer: Stimulating immune memory
A vaccine shows the immune system a harmless form of the microbe, so memory cells form and respond fast to a real infection.
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HIV mainly attacks which cells?
- 1 Red blood cells
- 2 Helper T cells
- 3 Neurons
- 4 Platelets
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Correct answer: Helper T cells
HIV infects CD4 helper T cells, which coordinate the immune response, so immunity gradually fails.
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Agrobacterium tumefaciens is used in genetic engineering to:
- 1 Digest cellulose
- 2 Transfer genes into plants
- 3 Make insulin in animals
- 4 Kill plant viruses
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Correct answer: Transfer genes into plants
Its Ti plasmid can carry a chosen gene into plant cells, which is how many transgenic plants are made.