Class 12 Biology MCQ – The Search for Genetic Material


This set of Class 12 Biology Chapter 6 Multiple Choice Questions & Answers (MCQs) focuses on “The Search for Genetic Material”.

1. Which of the following bacterium is responsible for causing pneumonia?
a) Staphylococcus saprophyticus
b) Streptococcus pyogenes
c) Staphylococcus aureus
d) Streptococcus pneumoniae
View Answer

Answer : d
Explanation: Streptococcus pyogenes causes tonsillitis and rheumatic fever. Staphylococcus aureus causes abscesses. Streptococcus pneumoniae causes pneumonia. Staphylococcus saprophyticus causes urinary tract infections.

2. When Streptococcus pneumoniae were cultured in a culture plate by Frederick Griffith, which among the following were produced?
a) Smooth colonies(S) and Rough colonies (R)
b) Shiny colonies (S) and Rough colonies (R)
c) Smooth colonies (S) and Rigorous colonies (R)
d) Silky colonies (S) and Rigorous colonies (R)
View Answer

Answer: b
Explanation: In 1928, Frederick Griffith cultured the pneumococcus bacterium. He observed that those bacteria were producing different colonies. These colonies were named as the S and R colonies. The S colonies are the Shiny colonies because they had the mucous(polysaccharide) coat. The R colonies are the Rough colonies because they did not possess the mucous coat.

3. The mice infected with the R strain of the bacterium dies, but when infected with the S strain, they do not die.
a) False
b) True
View Answer

Answer: a
Explanation: The S strain produced by the bacterium is said to be the virulent strain. The mice infected with the S strain will die due to its virulent nature. Whereas, the one infected with the R strain doesn’t die due to its avirulent.
Mice -> S strain -> Death
Mice -> R strain -> Alive

4. Which of the following is the wrong sequential order, when the S or the R strain of the bacterium is injected into the mice?
a) Mice -> S strain -> Dead
b) Mice -> R strain -> Alive
c) Mice -> Heat killed S strain -> Alive
d) Mice -> Heat killed S strain + live R strain -> Alive
View Answer

Answer: d
Explanation: When the heat killed S-strain of the bacterium is given along with the R strain to the mice, a process of transformation occurs. The heat killed S strain (avirulent) was able to transform the R strain (avirulent) to become a virulent strain. During this process of transformation, the heat killed S strained bacterium, transforms the R strain to produce the mucous(polysaccharide) and become virulent.

5. Which of the following is responsible for transforming the R strain into the S strain?
a) Purified bio-chemicals from S-strain
b) Purified bio-chemicals from R-strain
c) Purified bio-chemicals from heat killed S-strain
d) Purified bio-chemicals from heat killed R-strain
View Answer

Answer: c
Explanation: S-strains are the virulent ones which have the ability to kill a mouse when injected into it. But, when the heat killed S-strain is injected into the mouse along with the R-strain, the mouse happens to die due to transformation. The purified bio-chemicals (protein, DNA and RNA) from the heat killed S-strain, transforms the R-strain into the S-strain (virulent).

6. Which of the following is responsible for the inhibition of transformation in organisms?
a) DNase
b) RNase
c) Protease
d) Nuclease
View Answer

Answer: a
Explanation: The presence of protease (protein digesting enzymes) and RNase (RNA digesting enzymes) in the presence of the virulent or avirulent strains will not affect the process of transformation. But on the contrary, when the DNase is present, the process of transformation will not occur. This proves that the transformation process cannot occur as long as the DNase enzyme is present. The role of nuclease is to cleave the phosphodiester bonds between the nucleotides of nucleic acids.

7. What happens when S-strain and the biomolecule (Lipid) are together, when testing the transformation with regards to the R-strain?
Find what happens when S-strain & biomolecule are together testing transformation
a) R-strain
b) S-strain
c) R-strain and S-strain
d) Dead R-strain
View Answer

Answer: a
Explanation: Only DNase has the ability to inhibit transformation. The other enzymes like RNase and lipase do not possess that ability. The process of transformation is not seen when the biochemical DNase is with S-strain. Lipase is an enzyme that catalyzes the hydrolysis (H2O addition) of lipids and fats. The process of transformation will occur in lipids. As a result, R-strains will be produced in lipids.

8. Which of the following is considered to be as an incorrect difference between DNA and DNase?
DNA contains information for heredity & DNAse cleave phosphodiester bonds
a) Only I
b) Both II and III
c) Both III and IV
d) Only IV
View Answer

Answer: d
Explanation: DNA is the genetic material of an organism. It contains all the required information for heredity. DNase will not promote the DNA. It is used to cleave the phosphodiester bonds by hydrolysis. As a result of this, the DNA biomolecule is degraded.

9. What will be the state of the mouse that has been injected with the heat killed S-strain from the Staphylococcus pneumoniae?
a) Alive
b) Dead
c) On the verge of dying
d) Lives with pneumonia
View Answer

Answer: a
Explanation: The mouse fed with the S-strain from the Staphylococcus pneumoniae, happens to naturally die. This is on an account that the S-strains are virulent. Under such conditions, the mouse will not be able to survive. But, when the heat killed S-strains from Staphylococcus pneumoniae are injected into the mouse, it will live.

11. What will be the outcome when R-strain is injected into the mice?
Find the outcome when R-strain is injected into the mice
a) Mice dies as soon as it is injected
b) Mice lives with the bacteria and dies suddenly
c) Mice dies after ejecting out the bacteria
d) Mice lives even after injecting the R-strain of the bacterium
View Answer

Answer: d
Explanation: R-strains are the non-virulent strains. So, when they are injected into the mice, they won’t cause any damage to it. As a result, the mice will be able to live without complications. The bacteria contain both the S and R strains, but, only the R-strain is being injected in this scenario.

12. Which was considered to be as the genetic material prior to the works done by Oswald Avery, Colin MacLeod and Maclyn McCarty?
a) Nucleoids
b) Nucleons
c) Protein
d) Chromosome
View Answer

Answer: c
Explanation: Prior to the works done by Oswald Avery, Colin MacLeod and Maclyn McCarty, the genetic material was thought to be as the protein. Nucleoids are the irregular shaped structures in the prokaryotic cell. They contain nearly all of the genetic material of the prokaryotes. Nucleons are present inside the nucleus of an atom, alongside with the protons. Chromosome carries the genetic information of the genes.

Sanfoundry Global Education & Learning Series – Biology – Class 12.

To practice all chapters and topics of class 12 Biology, here is complete set of 1000+ Multiple Choice Questions and Answers.

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