Which one of the following is used for storing biological tissues?
- A.Liquid nitrogen
- B.Liquid helium
- C.Liquid argon
- D.Liquid bromine
Correct answer
Explanation
The correct answer is A, Liquid nitrogen. It is very cold, chemically inert and cheap, which makes it the standard coolant for preserving cells and tissues.
Liquid nitrogen boils at about −196 °C. At such low temperatures the chemical and enzyme activity inside cells almost stops, so tissues can be kept unchanged for years. This method, called cryopreservation, is used in blood banks, sperm and embryo banks for IVF and animal breeding, seed banks, and for storing stem cells, bone marrow and vaccines. Nitrogen makes up about 78% of air, so it is easy to obtain by liquefying air, and it does not react with the stored material.
Option B is wrong because liquid helium, at about −269 °C, is far costlier and is used mainly to cool superconducting magnets, such as those in MRI machines. Option C is wrong because liquid argon is also costlier and is used chiefly in industry and research, not routine tissue banks. Option D is wrong because bromine is a reddish-brown, toxic and corrosive liquid at room temperature that would destroy tissue.
Exam tip: cryopreservation = liquid nitrogen at −196 °C; MRI magnets = liquid helium.
Practice Questions
View allThe valency of phosphorus is
- A.2, 3
- B.3, 4
- C.4, 5
- D.3, 5
Show answer
Phosphorus has five electrons in its outer shell and shows two common valencies, 3 and 5. Phosphorus, atomic number 15, has the electronic configuration 2, 8, 5.
Read the full explanation →Which one of the following statements is NOT correct ?
- A.Single celled eukaryotes belong to Kingdom Protista
- B.Yeast, a fungus is multicellular
- C.The fungi constitute a unique kingdom of heterotrophs
- D.Ascomycetes, a saprophytic fungi is multicellular or rarely unicellular
Show answer
This statement is false, because yeast is one of the few fungi that are unicellular. In Whittaker's five-kingdom system, fungi form a separate kingdom.
Read the full explanation →Desalination of seawater is done by using reverse osmosis. The pressure applied to the solution is
- A.larger than osmotic pressure
- B.smaller than osmotic pressure
- C.equal to osmotic pressure
- D.equal to atmospheric pressure
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Only a pressure greater than the osmotic pressure of seawater can push pure water backwards through the membrane. In ordinary osmosis, water moves through a semipermeable membrane from the dilute side to the concentrated side.
Read the full explanation →Which one of the following does not form oxide on reaction with oxygen?
- A.Magnesium
- B.Lead
- C.Tin
- D.Silver
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Silver sits near the bottom of the reactivity series and does not combine with oxygen even when heated in air.
Read the full explanation →The foul smell of urine of a healthy man having healthy food, when spilled on floor, is mainly due to the bacterial decomposition of
- A.urea into sulphur dioxide
- B.sugar into carbon dioxide
- C.lipids into methane
- D.urea into ammonia
Show answer
Bacteria on the floor break down the urea in urine and release ammonia, which has a sharp, pungent smell. Urea, CO(NH2)2, is the main nitrogenous waste of humans.
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