During the lag phase
Answer: A
Correct answer: Microorganisms increase in size of cell and metabolic rate
In the lag phase there is no increase in cell number: the organisms are adapting to the new medium, synthesising the enzymes and intermediates they need. The cells grow larger and their metabolic rate rises, and only then does division begin.
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Which component of the gram-negative cell wall is responsible for endotoxic activity ?
Answer: B
Correct answer: Lipid A of the lipopolysaccharide
Lipid A anchors the lipopolysaccharide in the outer membrane and is the portion that triggers fever, hypotension and shock when released. The O-antigen determines serological type, and lipoteichoic acid belongs to gram-positive walls.
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Patient serum contains
Answer: D
Correct answer: known antibody
In the usual serological test the patient’s serum is the source of antibody - and because the antigen used is known, an antibody detected by it is identified, that is, known. The unknown quantity is whether it is present and at what titre.
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What is Chemotaxis?
Answer: C
Correct answer: In the presence of a chemical compound, swimming towards or away of a bacteria
Chemotaxis is movement in response to a chemical gradient - towards an attractant such as a sugar or amino acid, and away from a repellent. The cell cannot sense a gradient across its own length, so it compares concentrations over time, lengthening its runs when conditions improve and tumbling when they worsen.
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Which of the following is true about fungi
Answer: A
Correct answer: Eukaryotes
Fungi are eukaryotes: true nucleus, mitochondria, 80S ribosomes and a wall of chitin. Most are free-living saprophytes and grow perfectly well on cell-free media - which is exactly what distinguishes them from the obligate intracellular parasites.
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Which of the following statements about the Fc fragment of an antibody is not true?
Answer: A
Correct answer: posses antigen combining activity
Antigen binding is the work of the Fab fragments, whose variable regions form the binding sites. The Fc fragment is the constant stem, and it carries the effector functions instead: complement fixation, placental transfer of IgG, and binding to cells - skin fixation by IgE, and opsonisation through Fc receptors on phagocytes.
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The attachment structures of bacteria are the
Answer: D
Correct answer: all of the above
All three are names for the structures by which bacteria stick to a surface. Fimbriae and pili are the short hair-like appendages themselves - the words are often used interchangeably, though pilus is also used for the longer sex pilus - and colonisation factors is the general term for the adhesins that let a pathogen attach to a particular host tissue. Attachment is the first step of almost every infection.
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How many systems does the complement fixation reaction include?
Answer: A
Correct answer: 2 systems
The test uses two systems. The first is antigen, antibody and complement; if they match, the complement is consumed. The second - the haemolytic indicator system of sheep red cells and haemolysin - is then added to reveal whether any complement is left.
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K antigen is a
Answer: B
Correct answer: capsular antigen
K is the capsular antigen - from the German Kapsel. The other two in the Kauffman-White scheme are O, the somatic antigen of the lipopolysaccharide, and H, the flagellar antigen. Together they define the serotype of an enterobacterium.
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For penetration, viruses use
Answer: C
Correct answer: The mechanism called viropexia
Viropexis is the engulfment of the attached virus particle by the cell membrane, which folds round it and takes it in as a vesicle - receptor-mediated endocytosis. Enveloped viruses have a second option, fusing their envelope directly with the plasma membrane.
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