brodidit for students
Home / Practice / MDCAT / Biology / Microorganisms, immunity and biotechnology
Microorganisms, immunity and biotechnology
7 MDCAT Biology questions with answers and explanations.
Printable worksheet with answer key
-
Gram-positive bacteria appear which colour after Gram staining?
- 1 Colourless
- 2 Purple or violet
- 3 Pink or red
- 4 Green
Show answer
Correct answer: Purple or violet
Their thick peptidoglycan wall keeps the crystal violet stain, so they look purple. Gram-negative bacteria look pink.
-
Restriction enzymes are used to:
- 1 Make proteins
- 2 Join DNA fragments
- 3 Copy RNA
- 4 Cut DNA at specific sequences
Show answer
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.
-
The polymerase chain reaction (PCR) is used to:
- 1 Stain bacteria
- 2 Amplify a DNA sequence
- 3 Sequence proteins
- 4 Break down RNA
Show answer
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.
-
Penicillin was discovered by:
- 1 Robert Koch
- 2 Alexander Fleming
- 3 Edward Jenner
- 4 Louis Pasteur
Show answer
Correct answer: Alexander Fleming
Fleming noticed in 1928 that a Penicillium mould killed bacteria on his culture plate.
-
A vaccine protects the body mainly by:
- 1 Killing bacteria directly
- 2 Supplying ready-made antibodies for life
- 3 Stimulating immune memory
- 4 Raising body temperature
Show answer
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.
-
HIV mainly attacks which cells?
- 1 Red blood cells
- 2 Neurons
- 3 Platelets
- 4 Helper T cells
Show answer
Correct answer: Helper T cells
HIV infects CD4 helper T cells, which coordinate the immune response, so immunity gradually fails.
-
Agrobacterium tumefaciens is used in genetic engineering to:
- 1 Transfer genes into plants
- 2 Kill plant viruses
- 3 Digest cellulose
- 4 Make insulin in animals
Show answer
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.