ISC Board Class 12 Biology Sample Paper 2025: Download Free PDF With Answers For Exam Tomorrow!

Question 1

Answer the following questions briefly.

(i)

Sapna has been diagnosed with an infection of the reproductive tract caused by bacteria. She experiences a burning sensation during urination, and pain around her genitalia and observes pus-containing discharge. Her doctor tells her that this infection has an incubation period of two to five days but can be cured.

What is the biological name of the causative agent of the disease Sapna is suffering from? (Recall)

[1]

(ii)

The number of chromosomes in the leaf cells of a male plant is 40 and in the stem cells of a female plant is 60. If they are artificially hybridised, what will be the number of chromosomes in the endosperm? (Application)

[1]

(iii)

How many cycles of PCR are required to produce 250 molecules of DNA, starting with a single parental strand? (Application)

[1]

(iv)

Which is the most commonly prescribed non-steroidal oral contraceptive pill in India? (Recall)

[1]

(v)

Tall pea plants having green pods were crossed with dwarf pea plants having yellow pods. Out of 80 plants, how many are likely to be tall plants in the F2 generation? (Application)

[1]

(vi)

Write a 6-nucleotide long palindromic sequence on a double-stranded DNA, which was reverse transcribed by the following nucleotide sequence on a retroviral RNA. (Create)

3’-GUA- - - 5’

[1]

(vii)

In the given figure of mammalian spermatozoon, “X” is an organelle. Identify the organelle. (Recall)

[1]

(viii)

Observe the relation between the first two words and then fill in the fourth word.

Histamine: Mast cells:: Antibody: (Analysis)

[1]

(ix)

Which of the following sequences of mRNA will NOT translate completely?

(Recall)

[1]

(a)

5' - AUG UUC AGC UCG UGA - 3'

(b)

5'- AUG AAC UAA CCA CUC - 3'

(c)

5' - AUG UUA CUC GCG UAA - 3'

(d)

5' - AUG CCA UAC GAC UAG - 3'

(x)

Which one of the following choices reflects the correct number of chromosomes in the zygote and the second polar body of Drosophila melanogaster?

[1]

(a)

I

(b)

II

(c)

III

(d)

IV

(xi)

Given below are two statements marked Assertion and Reason. Read both the statements carefully and choose the correct option. (Analysis)

Assertion: Earthworm is called a detritivore.

Reason: It breaks down the water-soluble inorganic nutrients, which percolate down into the soil.

[1]

(a)

Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

(b)

Both Assertion and Reason are true but Reason is not the correct explanation for Assertion.

(c)

Assertion is true and Reason is false.

(d)

Both Assertion and Reason are false.

(xii)

Given below are two statements marked Assertion and Reason. Read both the statements carefully and choose the correct option. (Analysis)

Assertion: E. coli was transformed by inserting the foreign DNA by using PvuI in pBR322.

Reason: It was done to make the transformed cells survive in the culture medium containing ampicillin.

[1]

(a)

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion.

(b)

Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.

(c)

Assertion is true and Reason is false.

(d)

Both Assertion and Reason are false.

(xiii)

What is the advantage of growing apomictic seeds in crop improvement?

(Understanding)

[1]

(xiv)

A farmer has two fields in which he wants to grow a cereal crop and a legume. He cannot afford to spend a lot of money on chemical fertilisers to increase the fertility of the soil.

Suggest a way to help him resolve the issue. (Application)

[1]

(xv)

Answer the following questions.

[2]

(a)

Expand the abbreviation MALT. (Recall)

(b)

David is a molecular biologist. He uses a technique to know the amino acids occupying the first and the last positions in the Chain – A and Chain – B of insulin. Name the scientist whose contribution made it possible for David to use this technique. (Recall)

(xvi)

In a flower, the megaspore mother cell forms four megaspores without undergoing meiosis. One of the four megaspores developed into the embryo sac. What would be the ploidy level of the antipodal cells in this embryo sac?

(Understanding)

[1]

(xvii)

The diagram given below represents a specific stage of human embryonic development. Identify the stage. (Recall)

[1]

(xviii)

Give a reason for each of the following. (Analysis)

[2]

(a)

The diagram given below represents vector pBr322 which was modified by a research scholar Dr. Rayon, but the vector was rejected by his guide.

(b)

The continuous inbreeding of crops may lead to reduced fertility and productivity. However, the self-pollinated crops do not show the ill effects of inbreeding.

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