A vial holds 1 million cells and 20 per cent are lost on thawing. How many viable cells are recovered?
Answer: D
Losing a fifth leaves four fifths, which is 800,000. Some loss on thawing is normal, which is why vials are frozen at a higher density than the experiment strictly requires. Counting after thawing rather than before avoids an unpleasant surprise.
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Feeder cells are sometimes used in culture in order to
Answer: A
A layer of treated cells that cannot themselves divide supplies signals and matrix for the cells of interest. Defined media have replaced them in many applications but not all. Some stem cell work still depends on a feeder layer.
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Assertion (A): Feeder cells are treated so that they cannot divide.
Reason (R): Otherwise they would overgrow the cells of interest that they are meant to support.
Answer: B
Both are true and the reason gives the necessity: the layer must persist and secrete without competing, so irradiation or a drug is used to stop its division while leaving it metabolically active. The layer supports without competing, which is exactly what is wanted.
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Conditioned medium is medium that has
Answer: C
The factors secreted into it can support other cultures, which is a simple way to supply signals that are difficult to identify individually. It shares the drawback of serum in being undefined. Its usefulness lies in supplying factors nobody has yet identified.
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Consider the following statements about culture conditions.
1. Most mammalian cells are cultured at 37 degrees Celsius.
2. A carbon dioxide incubator maintains the pH of bicarbonate-buffered medium.
3. Cells grow equally well at room temperature.
Answer: D
The first two are correct. The third is wrong for mammalian cells, whose growth slows markedly below body temperature, though insect and fish lines are cultured cooler. The temperature follows the biology of the source organism.
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State whether the following is true or false.
All cultured cells are grown at 37 degrees Celsius.
Answer: A
Mammalian cells are, but insect cells are typically grown near 27 degrees and fish cells cooler still. The temperature chosen reflects the organism the cells came from rather than any universal rule. A line's optimum is inherited from the animal it was taken from.
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The single most important habit in avoiding contamination is
Answer: B
Contamination almost always enters through a lapse in handling rather than through the materials themselves. No additive compensates for careless work at the hood. Technique is learned by practice and is the real safeguard.
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State whether the following is true or false.
A contaminated culture can usually be rescued and should be treated rather than discarded.
Answer: C
Correct answer: False
A contaminated culture is discarded, and the incubator and hood are decontaminated. Antibiotics may suppress an infection without eliminating it, leaving a low-level contamination that alters the cells’ behaviour invisibly and seeds every other culture handled afterwards. Since a fresh vial can be thawed from the frozen stock, keeping a contaminated flask risks a great deal to save very little.
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