Class 12 Biology, Chapter 5 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.
How to teach this chapter · Common misconceptions & worked visual for this chapter
Which base-pairing rule is correct for double-stranded DNA?
(b) A pairs with T, and G pairs with C
Purine–pyrimidine pairing maintains helix width and complementarity.
One DNA strand contains three groups of ten adenines paired across the double helix. How many thymines are opposite those positions?
(a) 30
Each adenine pairs with one thymine.
Which chromatin state is generally more transcriptionally accessible?
(c) Euchromatin
Less condensed euchromatin permits greater regulatory access.
A chromosome region becomes highly condensed and stains densely. What functional tendency is expected?
(b) Lower transcriptional activity
Condensation commonly accompanies reduced transcription.
Which treatment stopped transformation in the Avery–MacLeod–McCarty experiment?
(c) DNase
DNase destroys DNA and abolished transforming activity. Protease and RNase did not abolish it.
In Hershey–Chase, which labelled material entered bacteria and supplied hereditary information for producing new phages?
(c) 32P-labelled DNA
32P-labelled DNA entered bacteria and supplied hereditary information. The 35S-labelled protein coats remained outside.
Fully 15N-labelled bacteria are shifted to 14N medium. After one generation, which DNA band pattern does semiconservative replication predict?
(a) One intermediate-density band
Each daughter DNA molecule contains one old heavy strand and one new light strand. All molecules therefore form one intermediate-density band.
Fully 15N-labelled bacteria grow in 14N medium. Which DNA bands are expected after one generation and then after two generations of semiconservative replication?
(b) Intermediate only; intermediate and light
The first generation contains only hybrid DNA. The second contains equal amounts of hybrid and light DNA, producing intermediate and light bands.
Which process removes introns from a primary transcript?
(a) Splicing
The spliceosome removes introns and joins exons.
Which combination describes eukaryotic mRNA processing?
(d) 5′ capping, addition of a poly-A tail at the 3′ end, and splicing
Processing stabilises and prepares the transcript for export and translation.
What does degeneracy of the genetic code mean?
(b) Several codons can specify the same amino acid
Redundancy occurs across codons while each codon remains unambiguous.
Which ribosomal component catalyses peptide-bond formation?
(a) rRNA
rRNA in the large ribosomal subunit catalyses peptide-bond formation. This catalytic RNA makes the ribosome a ribozyme.
What happens to the lac repressor when inducer binds?
(b) Its affinity for the operator decreases, permitting transcription
Allolactose changes repressor conformation so it no longer occupies operator effectively.
Which issue belongs to ethical, legal, and social analysis of genome data?
(b) Consent, privacy, and the risk of unfair treatment because of a person's genes
Sensitive inherited information can affect individuals and relatives.
What pattern is expected in a child's DNA profile?
(a) Each tested allele or band comes from one of the two biological parents
Biparental inheritance contributes one allele at each autosomal locus from each parent.
Wrong
A cell must copy its whole genome into RNA whenever it needs a protein.
Why it feels right. Transcription sounds like the genome copying that occurs before cell division.
Right
Transcription makes RNA from selected regions of DNA. DNA replication copies the genome.
Worked example
