ISC Class 12 Biology Competency Focused Questions 2026, Download PDF for Board Exam Preparation

Particulars

Details

Conducting Board

Council for the Indian School Certificate Examinations (CISCE)

Exam Level

ISC Class 12

Subject

Biology

Paper

Paper 1 (Theory)

Exam Date 2026

Friday, March 6, 2026

Type of Questions

Competency-focused (concept-based and application-based)

Availability

PDF download

Official Website

cisce.org 

Question Numbers

Questions

1

A homozygous pea plant with axial flowers and inflated pods was crossed with another homozygous pea plant with terminal flowers and constricted pods. When the plant of F1-generation was self-pollinated, a total of 800 plants were produced in F2-generation. Among these plants, how many would have terminal flowers and inflated pods?

(a) 50

(b) 300

(c) 150

(d) 450

2

In a prescribed period, the same number of oogonia and spermatogonia produced by two humans could yield different number of gametes subsequently. This occurs because of

which of the following options?

(a)The difference in the number of primary oocytes and primary spermatocytes formed.

(b)The difference in the number of secondary oocytes and secondary spermatocytes

formed.

(c)The difference in the number of polar bodies formed.

(d)The difference in their mode of cell divisions.

3

When an infected female mosquito bites a human, it transmits a pathogen, causing swelling in the arms, legs and genitals.

Name the organism that causes the above-mentioned symptoms.

(a) Salmonella typhi

(b) Corynaebacterium diphtheriae

(c) Wuchereria bancrofti

(d) Ascaris lumbricoides

4

Why is the incubation period especially important in the epidemiology of HIV infection?

(a) The load of virus in the body is the heaviest.

(b) The individual is normally asymptomatic during this stage.

(c) Transmission of HIV is easiest during this stage.

(d) This is the only infective stage for HIV transmission.

5

In a laboratory, a Biochemical Oxygen Demand (BOD) test was conducted with three water samples. These were marked as follows:

A-River water

B-Untreated sewage water

C- Discharged water from a sewage treatment plant.

However, the attendant conducting the experiment forgot to note down names of the

samples with BOD values. The BOD values recorded are given below:

6mg/L, 300mg/L, 25mg/L

Identify the correct water sample with the BOD value from below:

(a) A-6mg/L, B-25mg/L, C-300mg/L

(b) A-25mg/L, B-300mg/L, C-6mg/L

(c) A-300mg/L, B-25mg/L, C-6mg/L

(d) A-300mg/L, B-6mg/L, C-25mg/L

6

An experiment conducted by the students of class XII found that secondary treatment of

municipal and residential waste in their locality could produce biogas. The presence of

which of the following in the given waste would account for it?

(a) Anaerobic bacteria

(b) Aerobic bacteria

(c) Yeast

(d) Algae

7

A doctor advised his patient who was suffering from indigestion to include curd in his diet for early recovery. Identify the medicinal role of curd and the organism involved in its production from the

options given below:

(a) Antacid-Clostridium sp.

(b) Antalkali-Lactobacillus acidophilus

(c) Antakali-Propionibacterium shermani

(d) Antacid - Lactobacillus acidophilus

8

Riya, Ali and John were asked to study the following cases and interpret them.

They interpreted these cases by suggesting a possible disease for each as tabulated below:

Whose interpretation(s) is/ are correct?

(a) Riya

(b) Ali

(c) John

(d) Both Riya and John

9

Given below is the graphical representation of Meselson and Stahl’s experiment wherein E. coli cultured in 15NH4Cl medium was transferred to a medium containing 14NH4Cl and allowed to multiply for some time. Study it carefully and answer the question that follows.

Identify the type of DNA indicated by curve ‘P’ and ‘Q’.

(a) P: 14N 14N and Q: 15N 15N

(b) P: 15N 15N and Q: 14N 14N

(c) P: 14N 15N and Q: 14N 14N

(d) P: 14N 14N and Q: 14N 15N

10

The given Venn diagram represents two processes (P and Q) of the central dogma with some missing components (R and S).

Identify P, Q, R and S.

11

What will happen if the ‘o’ gene of lac operon is mutated such that it loses affinity for the ‘i’ gene product?

(a) No transcription of structural genes will take place.

(b) Continuous transcription of structural genes will take place.

(c) β-galactosidase and permease will be synthesized, but transacetylase will not be synthesized.

(d) RNA polymerase will be unable to bind to the promoter.

12

Given below are four statements regarding the steps involved in Deoxyribonucleic acid (DNA) fingerprinting. Identify the INCORRECT statement.

1. Sample size of the DNA is increased by electrophoresis.

2. DNA fragments are denatured by restricting endonuclease.

3. Separated DNA fragments are fixed by Ultraviolet (UV) light.

4. Double-stranded DNA (dsDNA) is hybridised with radiolabelled variable number tandem repeats (VNTR) probe.

(a) 1 and 2

(b) 2 and 3

(c) 1, 3 and 4

(d) 1, 2 and 4

13

Golden Rice was made by adding two special genes to rice, one from daffodils and one from a soil bacterium. These genes help the rice produce more vitamin A. Which cloning vector from below was used for the process of transfer of gene?

(a) Agrobacterium

(b) pBR322

(c) Retrovirus

(d) BAC

14

During the synthesis of recombinant insulin, the gene for alpha and beta polypeptides are inserted into the plasmid by the side of which of the following gene?

(a) Antibiotic resistant gene

(b) Lac Z promoter gene

(c) Beta galactosidase gene

(d) Replication gene

15

The Atlantic cod (Gadus callarias) is a fish which lays about 5,000,000 eggs in its lifetime. On average, only two of these eggs survive to become an adult cod. How does this promote evolution?

(a) All offsprings are genetically identical, so become better adapted.

(b) Laying many eggs provides food for other species to survive and become better adapted.

(c) Some young cod change to become adapted to the environment and survive and pass

on their genes.

(d) Offsprings with favourable variation survive and pass on their genes.

ISC Class 12 Biology Competency Focused Questions 2026

Friday, March 6

Biology - Paper 1 (Theory)