All bacteria that inhabit the human body are
Answer: A
Correct answer: heterotrophs
Every bacterium living in or on the human body takes its carbon from organic compounds supplied by the host, so all of them are heterotrophs. Autotrophs and chemolithotrophs fix CO2 and oxidise inorganic compounds, which is a way of life for soil and water organisms, not for inhabitants of a body.
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Which of the following plant propagation method uses girdling?
Answer: C
Correct answer: layering
Layering roots a stem while it is still attached to the parent plant, and girdling - removing a ring of bark - is used to interrupt the downward flow of sugars so that they accumulate at that point and encourage roots to form. Air layering is the familiar example. Cuttings are detached before rooting, and grafting joins two plants.
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Trypsin is used for dissociating the tissue into single cells.
Answer: A
Trypsin is a proteolytic enzyme and is used for dissociating the tissue into single cells. During the primary culture, tissue samples are taken generally from the embryos rather than the adult organism because of easy dissociation.
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In which organism was the first cell line established?
Answer: C
Correct answer: Mouse
The first continuous cell line was established from the mouse - the L cell line, derived from mouse connective tissue in 1943. HeLa, from a human tumour, followed in 1951.
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Which of the following is NOT a major function of serum?
Answer: A
Correct answer: Promotion of tuber and bulb formation
Tubers and bulbs are plant structures, so that is nothing to do with serum. Serum’s real functions are to stimulate growth with hormones and growth factors, to promote attachment through fibronectin and similar proteins, and to supply transport proteins such as albumin and transferrin that carry hormones, lipids and iron.
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How does CO2 help in the cell metabolism during cell culture?
Answer: A
Correct answer: It participates in the de novo synthesis of purines and pyrimidines
CO2 is not merely a waste gas: as bicarbonate it is a substrate for carboxylation reactions, including the de novo synthesis of purines and pyrimidines and of fatty acids. That is why cultures are kept in a CO2 atmosphere - though it also maintains the bicarbonate buffer and hence the pH.
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Which of the following are the metabolic products of glucose and glutamine?
Answer: C
Correct answer: Lactate and ammonium
The two main substrates give the two main waste products: glucose fermented to lactate, and glutamine deaminated to ammonium. Both are toxic as they accumulate - lactate through the acid it produces, ammonium directly - and controlling them is the central problem in high-density culture.
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Which of the following techniques can be performed quantitatively to count bacteria of a particular type?
Answer: C
Correct answer: Both (a) and (b)
Pour plate and spread plate are both quantitative: a measured volume of a known dilution is plated, the colonies are counted, and multiplying back gives the count in the original sample. The streak plate is qualitative - it separates organisms to obtain pure colonies, but nothing about it measures how many there were.
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In the pour plate method, the mixed culture is diluted directly in tubes of
Answer: A
Correct answer: liquid agar medium
In the pour plate method the sample is mixed into molten agar cooled to about 45°C, and the mixture is poured into the dish. Colonies therefore develop within the agar as well as on it, which suits microaerophiles and gives good separation - at the cost of subjecting the cells to that brief warmth.
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During the growth of animal cells in culture, it is noticed that the cells do not look very healthy. After an investigation, this is found that there is a lot of lactic acid in the culture fluid. What is probably wrong with this culture?
Answer: D
Correct answer: The cells do not have enough oxygen
Lactate accumulates when cells fall back on anaerobic glycolysis, and that happens when the oxygen supply is inadequate for oxidative phosphorylation. The lactate then acidifies the medium, which damages the cells further. The remedy is better aeration or a lower cell density.
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