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
Online
Highly Accurate Predicted Question Paper for ISC Class XII Biology Paper 1 (Theory) 2027 based on Engine analysis of specimen and past trends.
This predicted paper is generated using advanced analytics of the 2027 Specimen Question Paper, past year papers, and syllabus weightage. It mimics the exact structure of the ISC 2027 Board Examination and targets the most probable concepts for the actual exam.
Maximum Marks: 70
Time Allotted: Three Hours
Reading Time: Additional Fifteen Minutes
(Question 1, eighteen subparts, 1 mark each)
Answer the following questions briefly.
(i) A person is diagnosed with a sexually transmitted infection characterized by primary chancres and secondary skin rashes. Identify the causative agent of this disease. (Recall) [1] (a) Neisseria gonorrhoeae (b) Treponema pallidum (c) Trichomonas vaginalis (d) Human Papilloma Virus
(ii) Which of the following represents the correct sequence of steps in the Polymerase Chain Reaction (PCR)? (Recall) [1] (a) Extension → Denaturation → Annealing (b) Annealing → Extension → Denaturation (c) Denaturation → Annealing → Extension (d) Denaturation → Extension → Annealing
(iii) In an ecosystem, an orchid growing as an epiphyte on a mango branch is an example of which population interaction? (Understand) [1] (a) Mutualism (b) Commensalism (c) Parasitism (d) Amensalism
(iv) The distance between two consecutive base pairs in a DNA double helix is 0.34 nm. If the total number of base pairs in a mammalian cell's DNA is 6.6 × 10⁹, what is the approximate length of the DNA? (Apply) [1] (a) 2.2 meters (b) 2.2 millimeters (c) 1.2 meters (d) 3.4 meters
(v) Identify the class of drugs that interact with receptors principally present in the brain and are known for their effects on the cardiovascular system of the body. (Recall) [1] (a) Opioids (b) Cannabinoids (c) Coca alkaloids (d) Barbiturates
(vi) Assertion: Analogous structures are a result of convergent evolution. Reason: Different structures evolving for the same function and hence having similarity are called analogous structures. (Analyse) [1] (a) Both A and R true, R correct explanation of A (b) Both A and R true, R not correct explanation of A (c) A true, R false (d) Both A and R false
(vii) Assertion: Agrobacterium tumefaciens is a popular cloning vector for plants. Reason: It delivers a piece of T-DNA to transform normal plant cells into a tumor and directs these tumor cells to produce the chemicals required by the pathogen. (Analyse) [1] (a) Both A and R true, R correct explanation of A (b) Both A and R true, R not correct explanation of A (c) A true, R false (d) Both A and R false
(viii) A genetic disorder is caused by the presence of an additional copy of the X chromosome in a male, resulting in a karyotype of 47, XXY. Identify the disorder. (Recall) [1]
(ix) What term is used for the illegal exploitation of biological resources and traditional knowledge by multinational companies without proper authorization or compensation? (Understand) [1]
(x) During sewage treatment, what is the large mass of bacteria associated with fungal filaments to form mesh-like structures called? (Recall) [1]
(xi) The pie chart represents global biodiversity of vertebrate groups. If a sector represents the largest number of species among vertebrates, which class does it depict? (Analyse) [1]
(xii) Identify the start codon which also codes for the amino acid methionine. (Recall) [1]
(xiii) Baculovirus : Narrow spectrum biocontrol :: Trichoderma : ________. (Understand) [1]
(xiv) A DNA segment reads 5'-GAATTC-3'. Name the restriction endonuclease that recognizes and cuts this specific palindromic sequence. (Recall) [1]
(xv) If a population of 50 Paramecia in a pool increases to 150 after one hour, what is the birth rate of the population per hour? (Apply) [1]
(xvi)(a) Expand the abbreviation BOD. (Recall) [1]
(xvi)(b) The enzyme ADA is crucial for the immune system to function. Name the disease caused by its deficiency that is treated via gene therapy. (Recall) [1]
(xvii) State the underlying principle of DNA fingerprinting. (Recall) [1]
(xviii)(a) Give a reason: Cleistogamous flowers are invariably autogamous. (Understand) [1]
(xviii)(b) Give a reason: The pyramid of energy is always upright in any ecosystem. (Understand) [1]
(Seven questions × 2 marks each)
A couple seeks genetic counseling. The man is colorblind (X^c Y) and the woman has normal vision but her father was colorblind. (i) What is the genotype of the woman? (Understand) (ii) What is the probability that their son will be colorblind? (Apply)
An alien DNA is ligated at the BamH I site of a pBR322 vector. (i) Which antibiotic resistance gene is inactivated? (Recall) (ii) How will you differentiate the recombinants from the non-recombinants in a culture medium? (Analyse)
(i) Diagrammatically represent a typical nucleosome. (Recall) OR (ii) State two differences between euchromatin and heterochromatin. (Understand)
With reference to human diseases: (i) Name the widely used diagnostic test for Typhoid. (Recall) (ii) Which species of Plasmodium causes the most serious and potentially fatal (malignant) malaria? (Recall)
With reference to human reproduction: (i) What is the function of the acrosome of a human sperm? (Understand) (ii) Name the hormone that triggers ovulation and state its source. (Recall)
State two crucial differences between Active Immunity and Passive Immunity. Give one example of each. (Analyse)
(i) Identify the type of natural selection where more individuals acquire peripheral character values at both ends of the distribution curve. (Recall) (ii) What does the competitive exclusion principle state? (Understand)
(Seven questions × 3 marks each)
Draw a neat, well-labeled diagram of the T.S. of a mature human testis, showing the seminiferous tubules and interstitial cells. (Recall)
(i) Explain the blue-white screening (insertional inactivation of the lacZ gene) as a superior method for selecting recombinant bacteria. (Understand) OR (ii) Describe the structure and function of a stirred-tank bioreactor. (Understand)
Explain the medical applications of the bioactive molecules Cyclosporin A and Statins, and mention their respective microbial sources. (Understand)
Darwin's finches on the Galapagos Islands represent one of the best examples of a specific evolutionary process. (i) Name the evolutionary process. (Recall) (ii) Define the process named in (i). (Understand) (iii) Give another classic example of this process from Australian mammals. (Recall)
(i) Mention the names of any three outbreeding devices that flowering plants have developed to encourage cross-pollination. (Recall) (ii) Explain briefly how any one of them functions. (Understand)
Describe the structure of a transcription unit in DNA, clearly identifying the promoter, structural gene, and terminator with respect to the template and coding strands. (Understand)
A 35-year-old woman undergoes amniocentesis. (i) What is amniocentesis? (Recall) (ii) State one legitimate medical application of this technique. (Understand) (iii) Why has the government imposed a statutory ban on its use for certain purposes? (Analyse)
(Three questions × 5 marks each)
(i) (a) Trace the complete process of spermatogenesis in humans. (Understand) (b) How does it differ from oogenesis with respect to the growth phase and the number of functional gametes produced? (Analyse) OR (ii) (a) Explain the Assisted Reproductive Technologies (ART): IVF, ZIFT, and GIFT. (Understand) (b) Under what specific clinical conditions is GIFT recommended over IVF? (Evaluate)
(i) (a) Describe the Hershey-Chase experiment using bacteriophages. (Understand) (b) What definitive conclusion was drawn from this experiment regarding the nature of the genetic material? (Analyse) OR (ii) (a) Explain the regulation of gene expression using the lac operon as a model when lactose is absent and when it is present. (Understand) (b) Why is this type of regulation termed 'negative control'? (Evaluate)
(i) (a) Explain the 'Evil Quartet' responsible for the current crisis of biodiversity loss. (Understand) (b) Distinguish between in situ and ex situ approaches to conservation, giving one example of each. (Analyse) OR (ii) (a) Describe the various steps involved in the treatment of sewage (Primary and Secondary treatment) before it can be discharged into a river. (Understand) (b) What is the significance of "flocs" in this process? (Evaluate)
(i) (b) Treponema pallidum (ii) (c) Denaturation → Annealing → Extension (iii) (b) Commensalism (iv) (a) 2.2 meters (Calculation: 6.6 × 10⁹ × 0.34 × 10⁻⁹ m = 2.24 m) (v) (b) Cannabinoids (vi) (a) Both Assertion and Reason are true, and Reason is the correct explanation for Assertion. (They evolve due to similar environmental pressures, demonstrating convergent evolution). (vii) (a) Both Assertion and Reason are true, and Reason is the correct explanation for Assertion. (viii) Klinefelter's Syndrome (ix) Biopiracy (x) Flocs (xi) Fishes (xii) AUG (xiii) Free-living fungi (or effective against root pathogens) (xiv) EcoRI (xv) Birth rate = (150 - 50) / 50 = 2 Paramecia per original Paramecium per hour. (xvi)(a) Biochemical Oxygen Demand (xvi)(b) Severe Combined Immunodeficiency (SCID) (xvii) VNTR (Variable Number of Tandem Repeats) / Polymorphism in DNA sequences (xviii)(a) Because the flowers never open, ensuring that only pollen from the same flower can pollinate the stigma; there is no chance of cross-pollination. (xviii)(b) Because energy is always lost as heat at each step (10% law) when moving from a lower trophic level to a higher trophic level.
(i) Genotype of woman: X^c X (Carrier, since her father was colorblind). (ii) Cross: X^c Y (Man) × X^c X (Woman). Sons inherit Y from father and one X from mother. The mother produces X^c and X gametes. Thus, 50% of the sons will be X^c Y (colorblind) and 50% will be XY (normal). Probability = 50%.
(i) Tetracycline resistance gene (tet^R). (ii) By replica plating on ampicillin and tetracycline plates. Recombinants will grow on ampicillin but die on tetracycline, whereas non-recombinants will grow on both.
(i) Diagram should show a core of histone octamer surrounded by roughly 200 bp of DNA, with an H1 histone linking the DNA. (ii) Euchromatin is loosely packed, transcriptionally active, and stains lightly. Heterochromatin is densely packed, transcriptionally inactive, and stains darkly.
(i) Widal test. (ii) Plasmodium falciparum.
(i) Acrosome contains hydrolytic enzymes (sperm lysins, e.g., hyaluronidase) that help the sperm digest the ovum's protective layers (zona pellucida) for fertilization. (ii) Luteinizing Hormone (LH); secreted by the Anterior Pituitary gland.
Active Immunity: Develops when the host's own immune system produces antibodies against an antigen (slow response). Example: Immunity after natural infection or vaccination. Passive Immunity: Pre-formed antibodies are directly injected into the body (fast response). Example: Anti-tetanus serum or colostrum (IgA) given to infants.
(i) Disruptive Selection. (ii) Gause's competitive exclusion principle states that two closely related species competing for the exact same limited resource cannot co-exist indefinitely; the competitively inferior one will be eliminated.
Diagram of T.S. of testis. Labels must include: Seminiferous tubule, Spermatogonia, Primary spermatocytes, Spermatids, Spermatozoa, Sertoli cells, Interstitial spaces, Leydig cells.
(i) The lacZ gene codes for β-galactosidase, which turns the chromogenic substrate X-gal blue. When an alien DNA is inserted into the lacZ gene, it undergoes insertional inactivation. Thus, recombinant colonies cannot produce β-galactosidase and remain white, while non-recombinants turn blue. This single-step visual differentiation is superior to simultaneous antibiotic plating. (ii) A stirred-tank bioreactor is a cylindrical vessel with a curved base to facilitate mixing. It has an agitator system (impellers), an oxygen delivery system (sparger), and control systems for foam, temperature, and pH. Function: It provides optimal conditions for the large-scale culture of microbes, plant, or animal cells to produce desired biological products.
(i) Adaptive Radiation. (ii) The process of evolution of different species in a given geographical area starting from a point and radiating to other areas of geography (habitats). (iii) Australian marsupials (e.g., Kangaroo, Koala, Tasmanian wolf).
(i) Dichogamy, Heterostyly, Self-incompatibility. (ii) Self-incompatibility is a genetic mechanism that prevents self-pollen (from the same flower or other flowers of the same plant) from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
A transcription unit consists of:
(i) A prenatal diagnostic technique where amniotic fluid surrounding the fetus is extracted to analyze fetal cells and dissolved substances. (ii) To detect chromosomal abnormalities (e.g., Down syndrome) or metabolic disorders. (iii) To prevent its misuse for illegal sex determination, which leads to female foeticide and disrupts the natural sex ratio.
(i)(a) Spermatogenesis: Spermatogonia multiply by mitosis. Some grow into Primary Spermatocytes (2n). They undergo Meiosis I to form two Secondary Spermatocytes (n). These undergo Meiosis II to form four Spermatids (n), which differentiate into Spermatozoa (spermiogenesis). (i)(b) 1. Growth phase is much longer in oogenesis than in spermatogenesis. 2. Spermatogenesis produces four functional sperms from one primary spermatocyte, whereas oogenesis produces only one functional ovum (and polar bodies) from one primary oocyte. (ii)(a) IVF (In Vitro Fertilization): Fertilization occurs outside the body in simulated laboratory conditions, followed by embryo transfer. ZIFT (Zygote Intrafallopian Transfer): Zygote or early embryo (up to 8 blastomeres) is transferred into the Fallopian tube. GIFT (Gamete Intrafallopian Transfer): Transfer of an ovum collected from a donor into the Fallopian tube of another female. (ii)(b) GIFT is recommended for females who cannot produce viable ova but can provide a suitable environment for fertilization and embryonic development inside their fallopian tubes.
(i)(a) Hershey and Chase grew some bacteriophages on a medium with radioactive phosphorus (³²P) to label DNA, and others on radioactive sulfur (³⁵S) to label proteins. They allowed these phages to infect E. coli. The mixture was agitated in a blender to separate viral coats from bacteria, then centrifuged. (i)(b) Bacteria infected by ³²P-phages were radioactive, while those infected by ³⁵S-phages were not (radioactivity remained in the supernatant). This proved definitively that it is the DNA (not protein) that enters the host cell and acts as the genetic material. (ii)(a) In the absence of lactose, the repressor protein (synthesized by the i gene) binds to the operator region, preventing RNA polymerase from transcribing the structural genes (z, y, a). In the presence of lactose (inducer), it binds to the repressor, changing its shape so it cannot bind the operator. RNA polymerase then transcribes the operon. (ii)(b) It is termed 'negative control' because the operon is normally kept switched OFF by a repressor protein until an inducer removes the repression.
(i)(a) 'Evil Quartet' includes: 1. Habitat loss and fragmentation (most important cause). 2. Over-exploitation (e.g., Steller's sea cow, passenger pigeon). 3. Alien species invasions (e.g., Water hyacinth, Nile perch). 4. Co-extinctions (extinction of host leads to extinction of specific parasites). (i)(b) In situ conservation protects species in their natural habitats (e.g., National Parks, Biosphere Reserves). Ex situ conservation protects endangered species outside their natural habitats under human care (e.g., Zoological parks, Botanical gardens, Seed banks). (ii)(a) Primary treatment: Physical removal of large/small particles through sequential filtration and sedimentation to form primary sludge and effluent. Secondary treatment: Biological process where effluent is aerated. Aerobic microbes grow into flocs and consume organic matter, reducing BOD. The effluent is then passed to a settling tank where flocs sediment (activated sludge). (ii)(b) Flocs are masses of bacteria associated with fungal filaments. They are essential as they vigorously consume the major part of the organic matter in the effluent, significantly reducing the Biochemical Oxygen Demand (BOD) and purifying the water.