CBSE Class 12 Biology 2025 Sample Paper Solved Set 2

SECTION-A

Q. No. 1 to 12 are multiple choice questions. Only one of the choices is correct. Select and write the correct choice as well as the answer to these questions

1. Identify the statement that correctly differentiates between chasmogamous and cleistogamous flowers. 
a) Chasmogamous flowers are always self-pollinating, while cleistogamous flowers require crosspollination.
b) Chasmogamous flowers have their petals open and are adapted for cross-pollination, whereas cleistogamous flowers remain closed and are adapted for self-pollination.
c) Cleistogamous flowers are typically larger and more colorful to attract pollinators, while chasmogamous flowers are usually smaller and less conspicuous.
d) Both chasmogamous and cleistogamous flowers require external pollinators for reproduction.

Answer : b

2. Identify the methodology adopted to find out all the genes that produce proteins in Human Genome Project (HGP)?
a) Sequence Annotation
b) Expressed Sequence Tags
c) Karyotyping
d) DNA finger printing.

Answer : b

3. A researcher is investigating a new drug that is hypothesized to inhibit the function of DNA ligase, an enzyme crucial for DNA replication. Which of the following outcomes is most likely to occur in cells treated with this drug?
a) Increased synthesis of RNA primers on the leading strand
b) Formation of incomplete or fragmented DNA strands on the lagging strand
c) Enhanced speed of DNA replication overall
d) Inhibition of DNA unwinding at the replication fork

Answer : b

4. In a plant species, flower color is determined by a single gene with two alleles: R (red) and r (white). Incomplete dominance is observed, where heterozygous plants exhibit pink flowers. If a pink-flowered plant is crossed with a white-flowered plant, what is the expected phenotypic ratio of the offspring?
a) 1 red : 1 pink
b) 1 pink : 1 white
c) 1 red : 2 pink : 1 white
d) 3 pink : 1 white

Answer : b

5. Imagine an island ecosystem where a single species of bird, colonizes a previously uninhabited island. Over time, different populations of this bird evolve into distinct species with specialized beak shapes adapted to various available food sources on the island. If you were to analyze the evolutionary process of these bird species, which of the following scenarios would best illustrate adaptive radiation?
a) Bird populations develop different beak shapes to exploit various food sources on the island, depicting divergent evolution.
b) Bird populations evolve different beak shapes due to random genetic drift, with no relation to the availability of food sources depicting convergent evolution
c) Bird populations remain morphologically similar despite the different food sources available on the island showing no evolution.
d) Bird populations develop similar beak shapes regardless of the different food sources depicting random evolution.

Answer : a

6. A colour blind woman marries a normal man, what percentage of their children will be colour blind.
a) All their children will be colour blind.
b) All their sons will be colour blind.
c) All their daughters will be colour blind.
d) 50% sons and 50% daughters will be colour blind.

Answer : b

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