CUET UG Booster a biologyUnit 5 Test (E2) -

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CUET Booster Biology Unit 5 Test (M2)

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET Booster Biology Unit 5 Test (M2)

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QUESTION 1 OF 20

Which of the following is NOT true regarding the Griffith experiment findings?

Answer Review

1 Which of the following is NOT true regarding the Griffith experiment findings?

A The R strain produced rough colonies on a culture plate.

B Mice infected with the S strain died from pneumonia.

C The R strain naturally had a polysaccharide mucous coat.

D Heat-killed S strain bacteria injected alone did not kill mice.

💡 Short Explanation

S strain = Smooth, virulent, has a mucous coat. R strain = Rough, non-virulent, lacks a mucous coat. The statement in option C is biologically false.

✅ Correct Answer Explanation

The distinguishing feature of the R (Rough) strain in Griffith\'s experiment is the absence of the polysaccharide mucous coat, which is why it is non-virulent. Option C is the correct answer because it states the opposite of the known scientific fact. Options A, B, and D accurately describe Griffith\'s observations.

❓ Why Other Options Are Incorrect

Option A → True; R strain colonies are rough.
Option B → True; S strain is virulent and causes pneumonia.
Option D → True; heat-killing the S strain renders it non-infectious.

🎯 Strategy

Used

Extreme Word Filter: Identifying the statement that contradicts established experimental facts.

Final Logic: R strains are \"Rough\" specifically because they lack the \"Smooth\" (polysaccharide) coat.

🧠 Memory Trick

\"R = Rough = Really unprotected.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: The Transforming Principle – .

2 Match the bacterial injection (Column I) with its specific effect on mice (Column II) in Griffith\'s experiment:

Column I	Column II
1. Live S strain	R. Dies
2. Live R strain	P. Survives
3. Heat-killed S strain	Q. Survives
4. Heat-killed S strain + Live R strain	S. Transformation / Dies

A 1-R, 2-P, 3-Q, 4-S

B 1-S, 2-Q, 3-P, 4-R

C 1-R, 2-Q, 3-P, 4-S

D 1-P, 2-R, 3-S, 4-Q

💡 Short Explanation

1 (S) -> Dies (R). 2 (R) -> Survives (P). 3 (Heat S) -> Survives (Q). 4 (Mix) -> Transformation/Dies (S).

✅ Correct Answer Explanation

Live S-strain kills the mouse (R). Live R-strain is harmless, so the mouse survives (P). Heat-killed S-strain loses virulence, so the mouse survives (Q). The mixture of heat-killed S and live R causes transformation, killing the mouse (S).

❓ Why Other Options Are Incorrect

Options B, C, and D assign incorrect outcomes to the injections.

🎯 Strategy

Used

Option Grouping: Mapping outcomes to specific experimental conditions.

Final Logic: Matching 1-R, 2-P, 3-Q, 4-S correctly aligns the bacterial state with the mouse survival rate.

🧠 Memory Trick

\"S dies, R lives, Heat kills virulence, Mix kills.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: The Transforming Principle – .

3 Prior to the biochemical characterization by Avery, MacLeod, and McCarty (1933-44), what was the prevailing scientific belief regarding the biochemical nature of the genetic material?

A It was thought to be RNA.

B It was thought to be a protein.

C It was thought to be a polysaccharide.

D It was definitively known to be DNA.

💡 Short Explanation

Proteins were complex and diverse. DNA was thought to be a simple, repetitive polymer.

✅ Correct Answer Explanation

Before 1944, the majority of the scientific community favored proteins as the genetic material due to their greater structural diversity and complexity compared to the perceived \"simple\" structure of DNA.

❓ Why Other Options Are Incorrect

Option A → RNA was not considered the primary genetic candidate at that time.
Option C → Polysaccharides were not primary candidates.
Option D → This was the point being contested, not the consensus.

🎯 Strategy

Used

Contextual/Tonal Matching: Historical context of biological thought in the early 20th century.

Final Logic: Proteins were favored because they were seen as \"complex enough\" to carry information.

🧠 Memory Trick

\"Pre-Avery = Protein craze.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Biochemical Nature of Transforming Principle – .

4 Arrange the experimental deduction steps by Avery, MacLeod, and McCarty in the correct logical order:
I. Discover that DNA alone from S bacteria caused R bacteria to transform.
II. Purify biochemicals (proteins, DNA, RN

A II, IV, I, III

B I, II, IV, III

C II, I, III, IV

D IV, II, I, III

💡 Short Explanation

Purification (II) -> Negative tests (IV) -> Positive test/DNA (I) -> Conclusion (III).

✅ Correct Answer Explanation

First, they purified substances from S cells (II). Then, they treated samples with proteases/RNases and observed no change in transformation (IV). Next, they found that only DNA caused transformation (I). Finally, they concluded DNA is the genetic material (III).

❓ Why Other Options Are Incorrect

Other sequences misrepresent the logical progression of deduction.

🎯 Strategy

Used

Option Grouping: Logical flow of scientific experimentation.

Final Logic: Purify -> Rule out others -> Isolate the cause -> Conclude.

🧠 Memory Trick

\"Purify, Eliminate, Isolate, Conclude.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Biochemical Nature – .

5 Consider the following statements about DNase in the Avery, MacLeod, and McCarty experiment:
I. DNase digests DNA.
II. Digestion with DNase inhibited transformation.
III. Digestion with DNase accelerated the transformation of R cells to S cells. Which of the statements are correct?

A I and II only

B II and III only

C I and III only

D I, II, and III

💡 Short Explanation

DNase digests DNA (I). It inhibits transformation (II). It does not accelerate it (III).

✅ Correct Answer Explanation

DNase is an enzyme that breaks down DNA. By destroying the DNA in the extract, the \"transforming principle\" is eliminated, thereby inhibiting the transformation of R strain into S strain. Statement III is false because it stops, not accelerates, the process.

❓ Why Other Options Are Incorrect

Options B, C, and D contain Statement III, which is false.

🎯 Strategy

Used

Elimination: Identifying the false claim (III) and excluding options containing it.

Final Logic: If DNA is the transforming agent, destroying it (DNase) inhibits the effect.

🧠 Memory Trick

\"DNase = Destruction = Stop.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Biochemical Nature – .

6 Why did Avery, MacLeod, and McCarty\'s conclusion that DNA is the hereditary material face skepticism?

A Because they failed to isolate the transforming principle

B Because not all biologists were convinced by their experimental proof

C Because their experiment showed that RNA could also cause transformation

D Because they did not use the S and R strains correctly

💡 Short Explanation

Scientific consensus was slow to change. The \"protein-as-genetic-material\" belief was deep-seated.

✅ Correct Answer Explanation

Scientific revolutions often face resistance. Despite the clear experimental results, many biologists at the time were so entrenched in the belief that proteins were the genetic material that they were not convinced by the work of Avery, MacLeod, and McCarty.

❓ Why Other Options Are Incorrect

Option A → They successfully isolated the principle.
Option C → They showed RNA did not cause transformation.
Option D → They used the standard Griffith system correctly.

🎯 Strategy

Used

Contextual/Tonal Matching: Understanding the history of scientific discovery and paradigm shifts.

Final Logic: Scientific bias meant the discovery wasn\'t immediately accepted by everyone.

🧠 Memory Trick

\"New ideas often face resistance.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Biochemical Nature – .

📄 Passage

\"The unequivocal proof that DNA is the genetic material came from the experiments of Alfred Hershey and Martha Chase (1952). They worked with viruses that infect bacteria called bacteriophages. The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell. The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles.\"

According to the passage, what is the fundamental interaction between the bacteriophage T2 and the bacterial cell during infection?

A The bacteriophage swallows the bacterial cell whole.

B The bacterial cell destroys the viral genetic material upon entry.

C The bacteriophage\'s genetic material enters the bacteria, hijacking its machinery to make more viruses.

D The bacteria transfers its own DNA into the bacteriophage viral coat.

💡 Short Explanation

Phage attaches -> Injects material -> Hijacks cell -> Makes more virus.

✅ Correct Answer Explanation

The passage states: \"The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell... manufactures more virus particles.\" This describes the process of hijacking the host\'s cellular machinery.

❓ Why Other Options Are Incorrect

Option A → Phages inject genetic material, they don\'t swallow cells.
Option B → The bacteria is hijacked, not the one destroying the virus.
Option D → The process is the other way around.

🎯 Strategy

Used

Contextual/Tonal Matching: Analyzing the provided passage text.

Final Logic: The passage explicitly defines the viral infection mechanism as hijacking.

🧠 Memory Trick

\"Phage = Hijacker.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: The Genetic Material is DNA – .

📄 Passage

Based on the Hershey-Chase methodology described, why did viruses grown in a radioactive phosphorus medium contain radioactive DNA but not radioactive protein?

A Because phosphorus is actively expelled by viral proteins

B Because DNA contains phosphorus, whereas viral proteins do not

C Because sulfur replaces phosphorus in viral proteins

D Because the radioactive medium destroyed all viral proteins

💡 Short Explanation

DNA has phosphate backbone. Proteins have sulfur (in some amino acids), not phosphorus.

✅ Correct Answer Explanation

The chemical composition of DNA includes a sugar-phosphate backbone, making it a source of phosphorus. Proteins are composed of amino acids, which contain carbon, hydrogen, nitrogen, and oxygen, and often sulfur, but they lack phosphorus.

❓ Why Other Options Are Incorrect

Option A → Incorrect biological claim.
Option C → Sulfur is in proteins, but it does not replace phosphorus in the DNA labeling sense.
Option D → The medium does not destroy the virus.

🎯 Strategy

Used

Substitution: Using knowledge of biomolecule composition.

Final Logic: Phosphorus is a marker for DNA because it\'s a structural component of the nucleotide.

🧠 Memory Trick

\"DNA = Phosphate Backbone.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: The Genetic Material is DNA – .

9 Which of the following was NOT an outcome of the centrifugation step in the Hershey-Chase experiment?

A The virus particles were separated from the bacteria.

B The viral coats were removed from the bacteria.

C The bacteria formed a pellet at the bottom of the centrifuge tube.

D The lighter viral coats remained in the supernatant.

💡 Short Explanation

Blending removes the coats. Centrifugation separates the already-removed coats from the cells.

✅ Correct Answer Explanation

The physical act of removing (stripping) the viral coats from the bacterial surface is performed by the blender. Centrifugation simply separates the heavier, infected bacterial cells (which form a pellet) from the lighter, empty viral protein coats (which remain in the supernatant).

❓ Why Other Options Are Incorrect

Option A → Centrifugation separates components by weight.
Option C → Bacteria are denser and pelletize.
Option D → Viral coats are lighter and float in the liquid.

🎯 Strategy

Used

Elimination: Differentiating between the \"blender\" (removal) and \"centrifuge\" (separation) steps.

Final Logic: Blending removes; Centrifugation separates.

🧠 Memory Trick

\"Blend to strip, Spin to separate.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: The Genetic Material is DNA – .

10 In the Hershey-Chase experiment, the presence of radioactive P-32 exclusively inside the infected bacterial cells proved that:

A Proteins were responsible for viral replication. B) Both DNA and proteins entered the bacterial cell.

B (option not parsed — please edit)

C DNA was the genetic material passed from virus to bacteria.

D Radioactive sulfur was lethal to bacteria.

💡 Short Explanation

P-32 labeled DNA. P-32 was found inside the cell. Therefore, DNA entered the cell.

✅ Correct Answer Explanation

Since P-32 specifically labels DNA, its detection inside the host bacteria confirmed that the phage\'s DNA had successfully entered the cell. Because this DNA carried the instructions for viral replication, it proved that DNA—not protein—is the genetic material.

❓ Why Other Options Are Incorrect

Option A → Protein labeling (S-35) was found outside, not responsible for internal replication.
Option B → Only DNA entered, proteins stayed outside.
Option D → Irrelevant to the proof of genetic material.

🎯 Strategy

Used

Contextual/Tonal Matching: Interpreting the results of the Hershey-Chase proof.

Final Logic: P-32 inside = DNA inside = DNA is the genetic material.

🧠 Memory Trick

\"P-32 internal = DNA is the eternal (hereditary) material.\"

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: The Genetic Material is DNA

11 Which of the following molecules fundamentally fails to fulfill the first requirement of a genetic material (the ability to generate a replica)?

A Through their ability to mutate rapidly

B Through the rule of base pairing and complementarity

C By relying solely on protein enzymes to form templates

D By containing highly reactive 2\'-OH groups

💡 Short Explanation

Genetic material must replicate via templating. DNA and RNA use base pairing (A-T/U, G-C) for exact replication. This mechanism is the basis for hereditary transmission.

✅ Correct Answer Explanation

The fundamental requirement of any genetic material is the ability to generate a replica of itself. Both DNA and RNA achieve this through the principle of base-pairing and complementarity, where each strand acts as a template for synthesizing a new complementary strand. Options A and D relate to mutation and stability, not the mechanism of replication. Option C is incorrect because replication is primarily directed by the template, not just the enzymes.

❓ Why Other Options Are Incorrect

Option A → Rapid mutation is a property of some RNA viruses, not a mechanism of replication.
Option C → Enzymes facilitate the process, but the \"rule of base pairing\" is the fundamental requirement for the template mechanism.
Option D → The 2\'-OH group is a structural feature that decreases stability, not a replication mechanism.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Matching the \"requirement of replication\" to the well-known mechanism of base pairing.

Final Logic: Complementarity is the core biological rule that allows for accurate DNA and RNA replication.

🧠 Memory Trick

Complementary = Copying.

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Properties of Genetic Material –

12 Match the structural feature (Column I) to its specific contribution to nucleic acid stability (Column II):

Column I	Column II
1. 2′-OH group in RNA	P. Confers additional stability compared to uracil
2. Thymine in DNA	Q. Makes the molecule labile and easily degradable
3. Hydrogen bonding between strands	R. Allows strands separated by heat to come back together under appropriate conditions
4. Complementarity of strands	S. Contributes to the structural stability of the double helix

A 1-Q, 2-P, 3-S, 4-R

B 1-P, 2-Q, 3-R, 4-S

C 1-Q, 2-P, 3-R, 4-S

D 1-S, 2-R, 3-P, 4-Q

💡 Short Explanation

2\'-OH causes RNA instability (1-Q). Thymine is more stable than Uracil (2-P). H-bonding stabilizes the helix (3-S). Complementarity allows renaturation (4-R).

✅ Correct Answer Explanation

This question maps structural features to their functional outcomes. The 2\'-OH makes RNA reactive/labile (Q). Thymine provides stability compared to uracil (P). Hydrogen bonding is the force holding the double helix together (S). Complementarity is the principle that allows separated strands to re-anneal (renature) after heating (R). Option A is the only choice that matches these correctly.

❓ Why Other Options Are Incorrect

Option B → Incorrectly maps 2\'-OH to P.
Option C → Incorrectly maps 3-R and 4-S.
Option D → Incorrectly maps 1-S and 2-R.

🎯 Strategy

Used: Option Grouping

Application: Identify the most certain pairs (e.g., 2-P: Thymine stability) and narrow the options.

Final Logic: Thymine\'s stability (P) and RNA\'s 2\'-OH lability (Q) are definitive NCERT facts.

🧠 Memory Trick

2\'-OH = Quick to degrade (Labile).

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Properties of Genetic Material –

13 Which of the following statements is NOT true regarding the mutation of genetic materials?

A Both DNA and RNA are able to mutate.

B RNA mutates at a faster rate because it is unstable.

C Viruses having an RNA genome mutate and evolve faster.

D DNA mutates faster than RNA due to its double-stranded structure.

💡 Short Explanation

RNA is chemically unstable, leading to higher mutation rates. DNA is stable and double-stranded, leading to lower mutation rates. Statement D contradicts biological reality.

✅ Correct Answer Explanation

DNA is a very stable molecule and, compared to RNA, exhibits a much lower mutation rate. Its double-stranded structure and proofreading mechanisms during replication ensure high fidelity. RNA, being single-stranded and chemically reactive, mutates and evolves much faster. Therefore, the statement that DNA mutates faster is false.

❓ Why Other Options Are Incorrect

Option A → Both molecules undergo mutations.
Option B → RNA instability is linked to its higher mutation rate.
Option C → RNA viruses (like TMV or Influenza) are known for rapid evolution.

🎯 Strategy

Used: Elimination

Application: Identifying the statement that contradicts the known stability profile of DNA vs RNA.

Final Logic: DNA is the stable \"storage\" medium, meaning it is resistant to rapid change, not prone to it.

🧠 Memory Trick

DNA = Durable/Stable; RNA = Rapid evolution.

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: Properties of Genetic Material –

14 Though DNA is the preferred genetic material for storage, how does it fulfill the requirement of expressing Mendelian characters?

A It synthesizes proteins directly without any intermediates.

B It converts into RNA which directly acts as a protein.

C It is dependent on RNA for the synthesis of proteins.

D It relies on its 2\'-OH group to catalyze peptide bonds.

💡 Short Explanation

DNA carries information but cannot act directly as a template for translation. DNA must be transcribed into mRNA. The protein-synthesizing machinery (ribosomes) requires RNA.

✅ Correct Answer Explanation

DNA acts as the template for transcription, producing mRNA. This mRNA then serves as the template for protein synthesis in the ribosome. Because the cellular machinery for translation relies on RNA (rRNA/tRNA), DNA depends on these RNA intermediates to express the genetic traits (Mendelian characters) encoded in its sequence.

❓ Why Other Options Are Incorrect

Option A → DNA never synthesizes proteins directly; transcription is an obligate step.
Option B → RNA does not \"act as a protein\"; it codes for them.
Option D → DNA does not have a 2\'-OH group (it has a 2\'-H).

🎯 Strategy

Used: Elimination

Application: Eliminate incorrect biological pathways (direct synthesis, DNA having 2\'-OH).

Final Logic: Information storage (DNA) must be converted to an active form (RNA) to build phenotypic traits (proteins).

🧠 Memory Trick

DNA (Code) → RNA (Expression) → Protein (Trait).

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

15 Arrange the evolutionary sequence of genetic materials and processes in the correct logical order:
I. Evolution of protein synthesizing machinery around RNA
II. Chemical modification of RNA to form more stable DNA III. RNA acts as the first genetic material and catalyst

A III, I, II

B I, III, II

C III, II, I

D II, I, III

💡 Short Explanation

RNA was the first material/catalyst (III). Protein synthesis evolved using this RNA (I). DNA later evolved to stabilize the information (II).

✅ Correct Answer Explanation

The RNA World Hypothesis suggests the sequence: first, RNA acted as both the genetic material and the catalyst (III). Then, essential processes like translation evolved, relying on RNA-based machinery (I). Finally, to overcome the instability of RNA, chemical modifications led to the evolution of DNA (II), which took over the role of stable genetic storage.

❓ Why Other Options Are Incorrect

Option B, C, D → These suggest sequences that contradict the evolutionary logic of RNA being the precursor to the DNA-protein system.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Arrange based on the evolutionary progression from simple/reactive to complex/stable.

Final Logic: RNA (primitive/active) → DNA (advanced/stable).

🧠 Memory Trick

RNA First, DNA Second.

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

16 What dual role did RNA play in early evolutionary stages that made it essential but inherently unstable?

A It acted as both a lipid membrane and a genetic material.

B It acted as a genetic material as well as a catalyst.

C It acted as a repressor and an operator.

D It acted as a double-stranded storage and a repair mechanism.

💡 Short Explanation

RNA stores genetic info. RNA (ribozymes) catalyzes reactions. This versatility defines the \"RNA World.\"

✅ Correct Answer Explanation

The RNA World hypothesis highlights that RNA was the primary molecule for both information storage (genetics) and biochemical catalysis (ribozymes). This dual nature was essential for the origin of life but also made RNA problematic as a long-term storage medium due to its reactivity (instability).

❓ Why Other Options Are Incorrect

Option A → Lipids are not RNA.
Option C → These are regulatory genetic elements, not the primary \"dual roles\" of early RNA.
Option D → RNA is primarily single-stranded; double-stranded storage is a feature of evolved DNA.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Identifying the definition of the \"RNA World\" concept.

Final Logic: \"Dual role\" in biology and evolution refers to the genetic/catalytic functions of RNA.

🧠 Memory Trick

RNA = Replicator + Reactor.

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

17 Which of the following is NOT a consequence of having thymine in DNA instead of uracil?

A It confers additional stability to DNA.

B It makes DNA chemically less reactive than RNA.

C It makes the DNA molecule highly catalytic and labile.

D It makes DNA a better genetic material for long-term storage.

💡 Short Explanation

Thymine is stable (unlike Uracil in some contexts). DNA is the stable storage molecule, not the reactive catalyst. Option C is factually the opposite of the truth.

✅ Correct Answer Explanation

The replacement of uracil with thymine (5-methyl uracil) in DNA enhances the stability of the double helix and protects the genome. This modification makes DNA less reactive, not more catalytic or labile. Labile and catalytic characteristics are specific to RNA, not DNA.

❓ Why Other Options Are Incorrect

Option A, B, and D → These correctly describe the benefits of Thymine for DNA.

🎯 Strategy

Used: Elimination

Application: Exclude the options describing advantages of DNA, keeping the one describing a disadvantage (which is what the question asks for).

Final Logic: Thymine makes DNA stable; saying it makes it \"highly catalytic and labile\" is logically false.

🧠 Memory Trick

Thymine = Tough, not Trigger-happy (catalytic).

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

18 Consider the following statements regarding the reactivity of RNA:
I. The 2\'-OH group is present at every nucleotide in RNA.
II. RNA is known to be catalytic, which makes it reactive.
III. The reactivity of RNA makes it the preferred molecule for the storage of genetic information. Which of the statements are correct?

A I and II only

B II and III only

C I and III only

D I, II, and III

💡 Short Explanation

RNA has 2\'-OH (I is correct). Catalytic RNA is reactive (II is correct). Reactivity makes RNA unsuitable for storage (III is incorrect).

✅ Correct Answer Explanation

Statement I is correct: ribose sugar in RNA has an -OH at the 2\' position. Statement II is correct: being a catalyst (ribozyme) requires high chemical reactivity. Statement III is incorrect: because RNA is highly reactive, it is unstable and therefore not preferred for the long-term storage of genetic information (DNA is preferred for this).

❓ Why Other Options Are Incorrect

Options containing III are incorrect because they promote RNA as the preferred storage molecule, which contradicts evolutionary biology.

🎯 Strategy

Used: Elimination

Application: Recognize that statement III is factually incorrect based on the core theme of the chapter.

Final Logic: Reactivity = Instability = Bad for storage.

🧠 Memory Trick

Reactive RNA = Really Avoid for storage.

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

19 The assertion that DNA derived from RNA precursors is supported by the fact that:

A DNA requires RNA for the synthesis of proteins.

B Essential life processes such as metabolism and translation evolved around RNA.

C RNA directly codes for protein synthesis.

D All of the above are correct.

💡 Short Explanation

DNA is \"built\" on an RNA-evolved world. Translation and metabolism are RNA-centric. DNA is only the stable library, while the \"work\" is still done by RNA.

✅ Correct Answer Explanation

The evidence for DNA evolving from RNA precursors includes the fact that all basic cellular mechanisms (metabolism and protein translation) are built around RNA (ribozymes/ribosomes). Furthermore, the fact that DNA needs RNA to express itself (via mRNA) suggests that the RNA-based system existed first and DNA was a later, more stable \"add-on.\"

❓ Why Other Options Are Incorrect

A, B, and C are all individually correct observations cited by evolutionary biologists as evidence.

🎯 Strategy

Used: Option Grouping

Application: If multiple options seem logically correct and support the main thesis, \"All of the above\" is the most comprehensive choice.

Final Logic: These are all distinct pillars of the \"RNA World\" evidence.

🧠 Memory Trick

All Are Accepted.

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

20 How does the double-stranded nature of DNA allow it to resist evolutionary changes better than RNA?

A By allowing DNA to act as a reactive catalyst

B By giving it the ability to evolve a process of repair due to complementary strands

C By eliminating the need for mutation entirely

D By allowing it to replicate without any enzymes

💡 Short Explanation

Double-stranded DNA provides a template for repair. If one strand is damaged, the other holds the correct code. This increases stability over generations.

✅ Correct Answer Explanation

The double-stranded nature of DNA provides a massive evolutionary advantage: the \"backup\" copy. Because the two strands are complementary, if one strand is damaged (e.g., via deamination), the repair machinery can use the information on the undamaged strand to accurately fix the error. This is a critical feature that makes DNA a stable and reliable medium for long-term genetic storage.

❓ Why Other Options Are Incorrect

Option A → DNA is not a catalyst.
Option C → Mutation is essential for evolution; it is not eliminated.
Option D → DNA replication requires enzymes (e.g., DNA polymerase).

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Identify the primary benefit of \"double-strandedness\" in a storage molecule.

Final Logic: Double strand = Redundancy = Repair = Stability.

🧠 Memory Trick

Double = Duplicate (Backup/Repair).

📚 Class XII – Biology – Chapter: Molecular Basis of Inheritance – Topic: RNA World –

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