HKDSE · DSE Biology
DSE Biology: Microorganisms and Humans (Elective) — Practice Questions & Answers
The biology of microorganisms, their uses in food production and industry, and their roles in disease and in stimulating immunity.
414 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
The importance of the bacterial host to a bacteriophage is that it:
- provides the machinery and materials for the virus to reproduce
- supplies oxygen for viral respiration
- protects the virus from antibiotics
- digests the virus for energy
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WhyThe host provides the machinery and materials for viral reproduction.
2
Multiple choice · Medium
Viruses are described as obligate intracellular parasites because they:
- cannot reproduce outside a living host cell
- make their own ATP
- reproduce by binary fission
- carry out independent metabolism
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WhyThey cannot reproduce outside a living host cell.
3
Multiple choice · Hard
Which statement about viruses is correct?
- they contain nucleic acid and protein but no cellular organelles
- they respire and grow like bacteria
- they contain both ribosomes and mitochondria
- they reproduce by mitosis
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WhyViruses contain nucleic acid and protein but no cellular organelles.
4
Fill in the blank · Easy
A virus must use the metabolic machinery of a living cell to reproduce.
Answer:
host
WhyHost cells supply what the virus lacks.
5
Fill in the blank · Medium
A virus that specifically infects bacteria is called a .
Answer:
bacteriophage / phage
WhyBacteriophages infect bacteria.
6
Fill in the blank · Hard
Because they can only reproduce inside cells, viruses are obligate intracellular .
Answer:
parasites
WhyThey depend on a host cell to replicate.
7
Multiple choice · Medium
In the life cycle of a bacteriophage, the population of free viruses rises sharply in a later phase because:
- newly assembled viruses are released when the host bacteria lyse
- the viruses begin to respire
- the bacteria reproduce faster
- the viruses fuse into larger particles
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WhyNewly assembled viruses are released when host bacteria lyse.
8
Multiple choice · Hard
Early in the infection there is little change in the number of free viruses because:
- the viral nucleic acid is being replicated and proteins synthesised inside the host before assembly
- all the viruses have died
- the host cells have become resistant
- the viruses are dividing outside the host
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WhyViral nucleic acid and proteins are being made inside the host before assembly.
9
Multiple choice · Easy
The drop in virus population at the end of the cycle occurs because:
- most susceptible host bacteria have been used up (lysed)
- the viruses have all reproduced sexually
- the temperature has fallen
- antibodies have destroyed the bacteria
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WhyMost susceptible host bacteria have been used up.
10
Fill in the blank · Easy
New bacteriophages are released when the host bacterium undergoes .
Answer:
lysis
WhyLysis bursts the host cell.
Key terms in Microorganisms and Humans (Elective)
Microorganism: A microscopic living organism such as a bacterium, virus or fungus.
Bacterium: A single-celled microorganism without a true nucleus.
Virus: A non-cellular infectious agent that can only reproduce inside a host cell.
Fungus: A microorganism such as yeast or mould that feeds by absorbing nutrients.
Yeast: A single-celled fungus used in baking and brewing that carries out fermentation.
Fermentation: The breakdown of sugar by microorganisms without oxygen to produce useful products.
Anaerobic respiration: The release of energy from glucose without oxygen, as carried out by yeast or bacteria.
Aseptic technique: A set of procedures used to prevent contamination by unwanted microorganisms.
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