Predicted ISC Biology Paper 2026

This predicted paper is based on the 2026 specimen paper blueprint and a thorough analysis of past trends. It is intended for practice and to highlight potentially important topics.

Maximum Marks: 70
Time Allotted: Three Hours

SECTION A - 20 MARKS

Question 1

(i) A patient is diagnosed with a disease where the filarial worm blocks the lymphatic vessels of the lower limbs. What is this condition called? [1]

(ii) A pea plant with genotype RrYy is crossed with a plant having genotype rryy. What is the probability of obtaining offspring with the genotype RrYy? [1]

(iii) How many base pairs would a DNA segment of 13.6 nm length have? [1]

(iv) At what stage is the embryo transferred into the uterus in the IUT technique? [1]

(v) Name the type of immunity provided by the administration of antivenom. [1]

(vi) A scientist wants to cut a DNA molecule at the specific sequence 5'-GAATTC-3'. Which restriction enzyme should be used? [1]

(vii) Construct a pyramid of biomass for a pond ecosystem. [1]

(viii) Observe the relation: Penicillium : Antibiotic :: Trichoderma : ________. [1]

(ix) A man with blood group A marries a woman with blood group B. Their child has blood group O. What is the genotype of the parents? [1]

(a) I^AI^A and I^BI^B
(b) I^Ai and I^Bi
(c) I^AI^A and I^Bi
(d) I^Ai and I^BI^B

(x) Which of the following is an example of an alien species invasion in India? [1]

(a) Nile Perch
(b) Dodo
(c) Parthenium
(d) Steller's Sea Cow

(xi) Assertion: The Lac operon is an inducible operon. Reason: The presence of lactose inactivates the repressor, allowing transcription to occur. [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) Assertion: In a test cross, the F1 hybrid is crossed with the dominant parent. Reason: It is used to determine the genotype of the F1 individual. [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 false and Reason is true.
(d) Both Assertion and Reason are false.

(xiii) Why is the pyramid of energy always upright? [1]

(xiv) A farmer notices that continuous inbreeding in his cattle population has led to reduced fertility. What is this phenomenon called? [1]

(xv) Answer the following: [2]

(a) Expand the abbreviation GEAC.
(b) Name the scientist who proposed the 'Rivet Popper Hypothesis'.

(xvi) A diploid organism has 10 chromosomes in its somatic cells. How many chromosomes will be present in its gametes? [1]

(xvii) The diagram shows a stage of oogenesis. Identify the structure labeled 'A'. [1] (Diagram shows a secondary oocyte with a polar body)

(xviii) Give a reason for each: [2]

(a) The Western Ghats are considered a biodiversity hotspot.
(b) An antibody molecule is represented as H2L2.

Question 2 (i) Draw an ideal pyramid of numbers for a forest ecosystem where a few large trees support a large number of herbivores, which in turn support a smaller number of carnivores. [2]

(ii) Explain the concept of 'Competitive Release' with a suitable example. [2]

Question 3 Describe the hormonal control of the menstrual cycle, mentioning the roles of FSH and LH. [2]

Question 4 What are the two key methods of contraception for females that involve surgical intervention? State the principle of each. [2]

Question 5 Explain the blue-white screening method for identifying recombinant colonies. [2]

Question 6 What is decomposition? Name any two factors that affect the rate of decomposition. [2]

Question 7 What is the significance of the Human Genome Project? Mention any two key findings. [2]

Question 8 In a population of 1000 individuals, 360 belong to genotype AA, 480 to Aa, and 160 to aa. Calculate the frequency of allele 'a' in this population. [2]

SECTION C - 21 MARKS

Question 9 A pedigree chart shows the inheritance of haemophilia. A carrier female marries a normal male. What is the probability of their son being haemophilic? Show the cross. [3]

Question 10 (i) Explain the contribution of Ahmed Khan in solving the problem of plastic waste. [3]

(ii) What are methanogens? Describe their role in a biogas plant. [3]

Question 11 Describe the structure of a mature anther with a well-labeled diagram. [3]

Question 12 Explain the Oparin-Haldane theory of the origin of life. [3]

Question 13 What is meant by 'in-situ' conservation? Name and briefly describe two methods of in-situ conservation. [3]

Question 14 Describe the process of spermatogenesis with a schematic representation. [3]

Question 15 Draw a labeled diagram of a typical antibody molecule. [3]

SECTION D - 15 MARKS

Question 16 (i) Describe the process of double fertilization in angiosperms. What is its significance? [5]

(ii) Explain the different methods of Assisted Reproductive Technology (ART) like IVF, ZIFT, and GIFT. [5]

Question 17 (i) Describe the steps involved in Recombinant DNA technology. [5]

(ii) What is PCR? Explain the different steps involved in this process. [5]

Question 18 (i) Describe the life cycle of Plasmodium in humans. [5]

(ii) What are the 'Evil Quartet' that cause biodiversity loss? Explain any two. [5]

Brief Answer Key

Section A

(i) Elephantiasis (ii) 1/4 or 25% (iii) 40 bp (iv) Embryo with more than 8 blastomeres (v) Artificial passive immunity (vi) EcoRI (vii) Inverted pyramid of biomass (viii) Biocontrol agent (ix) (b) I^Ai and I^Bi (x) (c) Parthenium (xi) (a) (xii) (c) (xiii) Due to the 10% law of energy transfer, energy is lost as heat at each successive trophic level. (xiv) Inbreeding depression (xv) (a) Genetic Engineering Appraisal Committee. (b) Paul Ehrlich. (xvi) 5 chromosomes (xvii) First polar body (xviii) (a) High species richness and high degree of endemism. (b) It is made of two heavy (H) and two light (L) polypeptide chains.

Section B

(i) Spindle-shaped pyramid. (ii) Expansion of a species' niche when a competitor is removed. E.g., Barnacles on the coast of Scotland.
FSH stimulates follicular growth and estrogen secretion. LH surge triggers ovulation and maintains the corpus luteum.
Tubectomy (cutting/tying fallopian tubes) and Vasectomy (cutting/tying vas deferens).
Insertional inactivation of lacZ gene in pUC8 vector. Recombinants are white, non-recombinants are blue on X-gal medium.
Breakdown of complex organic matter. Factors: Temperature, moisture, oxygen, chemical composition of detritus.
Mapped the entire human genome. Findings: 20,000-25,000 genes, less than 2% of the genome codes for proteins.
Frequency of 'a' (q) = 0.4

Section C

50% probability. (Cross: X^hX x XY)
(i) Developed Polyblend, a fine powder of recycled plastic, mixed with bitumen to lay roads. (ii) Anaerobic bacteria producing methane. They digest organic matter in the biogas plant.
Diagram of T.S. of anther showing epidermis, endothecium, middle layers, tapetum, and microspore mother cells.
Life originated from non-living organic molecules under primitive earth conditions (reducing atmosphere, high energy).
Conservation in natural habitats. E.g., National Parks (strict protection) and Biosphere Reserves (zoned areas for conservation and sustainable use).
Spermatogonia -> Primary spermatocyte -> Secondary spermatocyte -> Spermatid -> Spermatozoa.
Diagram of antibody showing 2 heavy chains, 2 light chains, antigen-binding sites, and disulfide bonds.

Section D

(i) Syngamy (sperm + egg -> zygote) and Triple Fusion (sperm + polar nuclei -> PEN). Significance: Forms embryo and nutritive endosperm. (ii) IVF: Fertilization outside the body. ZIFT: Zygote/early embryo transfer to fallopian tube. GIFT: Gamete transfer to fallopian tube.
(i) Isolation of DNA, cutting with restriction enzymes, ligation into a vector, transformation, selection, and obtaining the gene product. (ii) Polymerase Chain Reaction. Steps: Denaturation, Annealing, Extension.
(i) Sporozoites infect liver cells, multiply, release merozoites which infect RBCs, reproduce asexually causing RBC rupture (fever cycle), some form gametocytes. (ii) Habitat loss, Over-exploitation, Alien species invasion, Co-extinctions. Explanation of any two.