Previous Year Questions/ISC/Prediction
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
BioNotesBioNotesCreated by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Prediction of ISC Biology Question Paper for 2026 Based on the Trends
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
(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]
Answer: Elephantiasis
(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]
Answer: 1/4 or 25%
(iii) How many base pairs would a DNA segment of 13.6 nm length have? [1]
Answer: 40 bp (base pairs)
(iv) At what stage is the embryo transferred into the uterus in the IUT technique? [1]
Answer: Embryo with more than 8 blastomeres
(v) Name the type of immunity provided by the administration of antivenom. [1]
Answer: Artificial passive immunity
(vi) A scientist wants to cut a DNA molecule at the specific sequence 5'-GAATTC-3'. Which restriction enzyme should be used? [1]
Answer: EcoRI
(vii) Construct a pyramid of biomass for a pond ecosystem. [1]
Answer: Inverted pyramid of biomass
(viii) Observe the relation: Penicillium : Antibiotic :: Trichoderma : ________. [1]
Answer: Biocontrol agent
(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]
(x) Which of the following is an example of an alien species invasion in India? [1]
(xi) Assertion: The Lac operon is an inducible operon. Reason: The presence of lactose inactivates the repressor, allowing transcription to occur. [1]
(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]
(xiii) Why is the pyramid of energy always upright? [1]
Answer: Due to the 10% law of energy transfer, energy is always lost as heat at each successive trophic level.
(xiv) A farmer notices that continuous inbreeding in his cattle population has led to reduced fertility. What is this phenomenon called? [1]
Answer: Inbreeding depression
(xv) Answer the following: [2]
(xvi) A diploid organism has 10 chromosomes in its somatic cells. How many chromosomes will be present in its gametes? [1]
Answer: 5 chromosomes
(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]
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]
Answer: Spindle-shaped pyramid. (Self-Study Note: Draw a narrow base for trees, wide middle for herbivores, and narrow top for carnivores).
OR
(ii) Explain the concept of 'Competitive Release' with a suitable example. [2]
Answer: Expansion of a species' niche when a competitor is removed. E.g., The larger and competitively superior barnacle Balanus dominates the intertidal area, but when removed, the smaller Chthamalus barnacle population spreads out (coast of Scotland).
Question 3 Describe the hormonal control of the menstrual cycle, mentioning the roles of FSH and LH. [2]
Answer: FSH stimulates follicular growth and estrogen secretion. A surge in LH mid-cycle triggers ovulation and maintains the corpus luteum.
Question 4 What are the two key methods of contraception for females that involve surgical intervention? State the principle of each. [2]
Answer:
Question 5 Explain the blue-white screening method for identifying recombinant colonies. [2]
Answer: It involves insertional inactivation of the lacZ gene in a vector (like pUC8). Recombinants do not produce beta-galactosidase and appear white, while non-recombinants produce it and turn blue on X-gal medium.
Question 6 What is decomposition? Name any two factors that affect the rate of decomposition. [2]
Answer: Decomposition is the physical and chemical breakdown of complex organic matter. Factors: Temperature, moisture, oxygen availability, and chemical composition of detritus.
Question 7 What is the significance of the Human Genome Project? Mention any two key findings. [2]
Answer: It successfully mapped the entire human genome. Findings: Humans have about 20,000-25,000 genes, and surprisingly, less than 2% of the genome codes for proteins.
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]
Answer: Frequency of allele 'a' (q) = 0.4. (Calculation: q² = 160/1000 = 0.16, therefore q = v0.16 = 0.4)
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]
Answer: 50% probability. (Cross: Carrier female X?X? x Normal male X?Y -> Sons will inherit either X? or X? from the mother. Half the sons [X?Y] will be haemophilic).
Question 10 (i) Explain the contribution of Ahmed Khan in solving the problem of plastic waste. [3]
Answer: He developed 'Polyblend', a fine powder of recycled modified plastic, which is mixed with bitumen to lay roads, increasing water repelling properties and road life.
OR
(ii) What are methanogens? Describe their role in a biogas plant. [3]
Answer: Methanogens are anaerobic bacteria that produce methane gas. They digest organic matter (cellulose) in the biogas plant to produce the highly flammable biogas.
Question 11 Describe the structure of a mature anther with a well-labeled diagram. [3]
Answer: (Self-Study Note: Draw a T.S. of anther showing the four wall layers: epidermis, endothecium, middle layers, tapetum, enclosing the microspore mother cells).
Question 12 Explain the Oparin-Haldane theory of the origin of life. [3]
Answer: They proposed that life originated from pre-existing non-living organic molecules (e.g., RNA, protein) under primitive earth conditions (reducing atmosphere, high temperature, volcanic storms, lightning).
Question 13 What is meant by 'in-situ' conservation? Name and briefly describe two methods of in-situ conservation. [3]
Answer: In-situ means conservation of species in their natural habitats.
Question 14 Describe the process of spermatogenesis with a schematic representation. [3]
Answer: The process of sperm formation in testes. Schematic: Spermatogonia (2n) -> Primary spermatocyte (2n) -> Meiosis I -> Secondary spermatocyte (n) -> Meiosis II -> Spermatid (n) -> Spermiogenesis -> Spermatozoa (n).
Question 15 Draw a labeled diagram of a typical antibody molecule. [3]
Answer: (Self-Study Note: Draw a Y-shaped structure showing 2 heavy chains, 2 light chains, antigen-binding sites at the tips, and disulfide bonds linking the chains together).
Question 16 (i) Describe the process of double fertilization in angiosperms. What is its significance? [5]
Answer: Double fertilization involves two fusions in the embryo sac: Syngamy (sperm + egg -> diploid zygote) and Triple Fusion (sperm + 2 polar nuclei -> triploid Primary Endosperm Nucleus / PEN). Significance: Ensures the nutritive endosperm only forms if the egg is successfully fertilized, providing food for the developing embryo.
OR
(ii) Explain the different methods of Assisted Reproductive Technology (ART) like IVF, ZIFT, and GIFT. [5]
Answer:
Question 17 (i) Describe the steps involved in Recombinant DNA technology. [5]
Answer:
OR
(ii) What is PCR? Explain the different steps involved in this process. [5]
Answer: PCR (Polymerase Chain Reaction) is used to amplify multiple copies of a gene of interest. Steps:
Question 18 (i) Describe the life cycle of Plasmodium in humans. [5]
Answer:
(ii) What are the 'Evil Quartet' that cause biodiversity loss? Explain any two. [5]
Answer: The 'Evil Quartet' are the four major causes of biodiversity loss: Habitat loss, Over-exploitation, Alien species invasion, and Co-extinctions.