Questions of Assertion Reason Chapter 5 Molecular Basis of Inheritance biology CBSE Class 12 are very simple to understand as this chapter deals with Molecular Basis of Inheritance. To solve assertion reason type questions of biology, deeper understanding of concept about Molecular Basis of Inheritance is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.
How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.
How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.
In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.
Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:
|Assertion (A)||Reason (R)||MCQ Options (Fixed for all questions)|
|If True||True||(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).|
|If True||True||(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).|
|If True||False||(c) Assertion (A) is true but reason (R) is false.|
|If False||True||(d) Assertion (A) is false but reason (R) is true.|
|If False||False||(e) Both Assertion and Reason are false.|
Now, lets practice some Assertion Reason Questions of Biology : Chapter 5 Molecular Basis of Inheritance.
Read instructions carefully before answering the questions.
For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.
Assertion: In a DNA molecule, A–T rich parts melt before G–C rich parts.
Reason: In between A and T there are three H–bond, whereas in between G and C there are two H-bonds.
Assertion: The two chains of DNA have anti-polarity.
Reason: In one chain of DNA, ribose sugar at 5′ end consists of a free phosphate moiety while at the other end the ribose has a free 3′ OH group.
Assertion: Adenine cannot pair with cytosine.
Reason: Adenine and cytosine do not have a perfect match between hydrogen donor and hydrogen acceptor sites. Hence, they cannot pair.
In DNA, the code letters are A, T, G, and C, which stand for the chemicals adenine, thymine, guanine, and cytosine, respectively. In base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine.
Assertion: The sugar phosphate backbone of two chains in DNA double helix show anti-parallel polarity.
Reason: The phosphodiester bonds in one strand go from a 3′ carbon of one nucleotide to a 5′ carbon of adjacent nucleotide, whereas those in complementary strand go vice versa.
Assertion: DNA is considered to be better genetic material than RNA for most organisms.
Reason: 2′-OH group present in DNA makes it labile and less reactive.
Assertion: Histones are basic proteins of major importance in packaging of eukaryotic DNA. DNA and histones comprise chromatin forming the bulk of eukaryotic chromosome.
Reason: Histones are of five major types H1, H2A, H2B, H3 and H4.
Assertion: DNA is associated with proteins.
Reason: DNA binds around histone proteins that form a pool and the entire structure is called a nucleosome.
Assertion: Histones are basic in nature.
Reason: Histones are rich in the amino acids lysine and arginine.
Histones contain a large proportion of the positively charged (basic) amino acids, lysine and arginine in their structure. DNA is negatively charged due to the phosphate groups on its backbone.
Assertion: DNA acts as a genetic material in all organisms.
Reason: It is a single-stranded biomolecule.
DNA is the hereditary material found in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells that determines the composition of the organism. There is another type of genetic material found in cells and viruses known as ribonucleic acid (RNA). DNA is double stranded as well as single stranded biomolecule.
Assertion: In Griffith’s experiment, a mixture of heat-killed virulent bacteria R and live non-virulent bacteria S, lead to the death of mice.
Reason: ‘Transforming principle’ got transferred from heat killed R strain to S strain and made it virulent.
When bacteria Streptococcus pneumoniae are grown on a culture plate, some produce smooth shiny colonies (S) while others produce rough colonies (R). This is because the S strain bacteria have a mucous (polysaccharide) coat, while R strain does not. Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia. In Griffith’s experiment, some ‘transforming principle’, transferred from the heat-killed S strain, had enabled the R strain to synthesize a smooth polysaccharide coat and become virulent which must be due to the transfer of the genetic material. This is known as transformation.
Assertion: Template or antisense strand, having 3′ → 5′ polarity takes part in transcription.
Reason: Non-template or sense strand, having 5′ → 3′ polarity, does not take part in
Assertion: The uptake of DNA during transformation is an active, energy requiring process.
Reason: Transformation occurs only in those bacteria, which possess the enzymatic machinery involved in the active uptake and recombination.
Transformation does not involve passive entry of DNA molecules through permeable cell walls and membranes. It does not occur ‘naturally’ in all species of bacteria, only in those species possessing the enzymatic machinery involved in the active uptake and recombination processes. Even in these species, all cells in a given population are not capable of active uptake of DNA. Only competent cells, which possess a so – called competence factor are capable of serving as recipients in transformation.
Assertion: Killer strain of Paramecium aurelia can kill sensitive strain.
Reason: If sensitive strain is provided kappa particle, it becomes killer.
Paramecium aurelia has two strains : killer and sensitive. The killer strain is able to kill the sensitive strain protist by means of chemical paramecin, secreted by minute cytoplasmic particles called kappa particle. The sensitive strain protists do not have kappa particles. The sensitive strain can also become killer if it receives sufficient kappa particles.
Assertion: Scaffold proteins are non histone chromosomal proteins.
Reason: They are rich in lysine and arginine.
Structural nonhistone chromosomal proteins are called scaffold proteins as they constitute the core axis of the chromosome. They contain very little lysine and arginine but instead possess abundant tyrosine and tryptophan types of amino acids.
Assertion: Viruses having RNA genome have shorter life span and mutate faster.
Reason: RNA is unstable and thus mutates faster.
Unlike DNA, RNA is usually single stranded. Additionally, RNA contains ribose sugars rather than deoxyribose sugars, which makes RNA more unstable and more prone to degradation. RNA is synthesized from DNA by an enzyme known as RNA polymerase during a process called transcription. Viruses having RNA have shorter life span and mutate at faster rate.