HSC Biology (56) Important Question Paper 2026
Max. Marks: 70 | Time: 3 Hrs.
Note: This is a Model Question Paper for the 2026 Board Examination, based on the latest pattern.
General Instructions:
- The question paper is divided into four sections (A, B, C, D).
- Section A: Q.1 (10 MCQs) & Q.2 (8 VSA). Evaluation done for the first attempt only.
- Section B: Q.3 to Q.14 (Short Answer - 2 Marks). Attempt any 8.
- Section C: Q.15 to Q.26 (Short Answer - 3 Marks). Attempt any 8.
- Section D: Q.27 to Q.31 (Long Answer - 4 Marks). Attempt any 3.
- Draw neat and labeled diagrams wherever necessary.
SECTION – A (18 Marks)
Q. 1. Select and write the correct answer: (10 Marks)
(i) In monocot embryo the protective sheath of plumule is called:
- (a) perisperm
- (b) scutellum
- (c) coleorrhiza
- (d) coleoptile
Answer: (d) coleoptile
(ii) The synonymous term for centromere is:
- (a) primary constriction
- (b) telomere
- (c) secondary constriction
- (d) satellite
Answer: (a) primary constriction
(iii) Protein digesting enzyme is:
- (a) polymerase
- (b) protease
- (c) pectinase
- (d) RNA ase
Answer: (b) protease
(iv) Spermatids get transformed into a functional spermatozoa by the process of:
- (a) spermiogenesis
- (b) spermatogenesis
- (c) gametogenesis
- (d) oogenesis
Answer: (a) spermiogenesis
(v) Industrial melanism is one of the best example of:
- (a) geographical isolation
- (b) natural selection
- (c) reproductive isolation
- (d) adaptive radiation
Answer: (b) natural selection
(vi) Value of root pressure is +1 to +2 bars which is enough to pump water to a height of:
- (a) 50-60 meters
- (b) 10-20 meters
- (c) 30-40 meters
- (d) 20-30 meters
Answer: (b) 10-20 meters
(vii) ______ cellular fragments are formed from megakaryocytes.
- (a) Erythrocytes
- (b) Leucocytes
- (c) Thrombocytes
- (d) Monocytes
Answer: (c) Thrombocytes
(viii) Degeneration of dopamine producing neurons in the CNS causes:
- (a) Alzheimer's disease
- (b) Addison's disease
- (c) Grave's disease
- (d) Parkinson's disease
Answer: (d) Parkinson's disease
(ix) Choose the correct name of phases A, B and C in the given figure (Sigmoid Growth Curve):
- (a) Stationary, Log, Lag
- (b) Log, Lag, Stationary
- (c) Log, Stationary, Lag
- (d) Lag, Log, Stationary
Answer: (d) Lag, Log, Stationary
(x) Rivet Popper Hypothesis explains:
- (a) loss of biodiversity
- (b) biomagnification
- (c) species area relationship
- (d) significance of diversity
Answer: (d) significance of diversity (Ecosystem health)
Q. 2. Answer the following questions: (8 Marks)
(i) Write the ratio of methane, ammonia and hydrogen respectively in Urey and Miller's experiment.
Answer: The ratio is 1:2:2 (Methane : Ammonia : Hydrogen) or sometimes represented as 2:1:2 depending on the sequence in the textbook (CH4:NH3:H2). Standard MH Board answer: 2:1:2 (Methane:Ammonia:Hydrogen).
(ii) What are the cells of Rauber?
Answer: Cells of Rauber are the trophoblast cells that are in contact with the Embryonal knob (Inner Cell Mass) in the blastocyst.
(iii) Which gene is introduced in tobacco against pest like Zabrotes subfasciatus?
Answer: The Cowpea Trypsin Inhibitor (CpTI) gene.
(iv) How many haploid nuclei are present in mature female gametophyte of Angiosperms?
Answer: There are 8 haploid nuclei (but 7 cells) in a mature female gametophyte (Polygonum type).
(v) Name the connection between pulmonary trunk and aortic arch representing remnant of embryonic ductus arteriosus.
Answer: Ligamentum arteriosum.
(vi) Which endocrine gland plays an important role in the development of immune system?
Answer: Thymus gland (secretes Thymosin).
(vii) Mention the type of association between sea anemone and clown fish.
Answer: Commensalism (The fish gets protection, the anemone is neither harmed nor benefited).
(viii) Name the pioneer species in the aquatic habitat during primary succession.
Answer: Phytoplankton.
SECTION – B (16 Marks)
Attempt any EIGHT of the following questions:
Q. 3. (a) Why DNA replication is called semi-conservative replication? (b) Name the scientist who experimentally proved the same.
Answer:
(a) It is called semi-conservative because in the newly formed DNA molecule, one strand is old (conserved from the parent) and the other strand is newly synthesized.
(b) It was experimentally proved by Matthew Meselson and Franklin Stahl (1958).
(a) It is called semi-conservative because in the newly formed DNA molecule, one strand is old (conserved from the parent) and the other strand is newly synthesized.
(b) It was experimentally proved by Matthew Meselson and Franklin Stahl (1958).
Q. 4. Distinguish between Asexual and Sexual reproduction with reference to: (a) Cell division (b) Genetic makeup.
Answer:
| Feature | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| (a) Cell Division | Involves only Mitosis. | Involves both Meiosis (gamete formation) and Mitosis (growth). |
| (b) Genetic Makeup | Offspring are genetically identical (clones) to the parent. | Offspring show genetic variation due to recombination. |
Q. 5. Arrange the following stages of human evolution in the order of their increasing cranial capacity: (a) Homo Sapiens (b) Neanderthal man (c) Australopithecus (d) Homo-erectus.
Answer:
Correct Order: Australopithecus (450-600cc) → Homo-erectus (900cc) → Neanderthal man (1400cc) → Homo Sapiens (1450cc).
Q. 6. Identify chromosomal disorder caused due to non-disjunction of 21st chromosome and enlist its characteristics.
Answer:
Disorder: Down's Syndrome (Trisomy 21).
Characteristics:
Characteristics:
- Mild to moderate mental retardation.
- Flat face, rounded flat nose, mouth open with protruding tongue.
- Short stature and stubby fingers.
- Simian crease on palm.
Q. 7. What is radial and tangential translocation of food in plants?
Answer:
- Radial Translocation: Transport of food from phloem to the pith and cortex (from center to periphery or vice versa) via medullary rays.
- Tangential Translocation: Transport of food along the circumference of the stem to adjacent tissues.
Q. 8. Explain any two causes of genetic variation.
Answer:
- Gene Mutation: Sudden permanent change in the chemical structure of a gene that alters the phenotype.
- Recombination (Crossing Over): Exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase-I of meiosis.
- Gene Flow: Transfer of genes between populations via migration.
Q. 9. Identify A, B, C and D from the following table regarding respiratory system:
| Organism | Habitat | Respiratory organ |
|---|---|---|
| A | Terrestrial | Tracheal tubes and spiracles |
| Scorpions | Terrestrial | B |
| Sponges | C | Plasma membrane |
| Turtles | Underwater | D |
Answer:
- A: Insects (e.g., Cockroach)
- B: Book Lungs
- C: Aquatic
- D: Cloaca (Cloacal respiration)
Q. 10. Give the function of Nebenkern and Zona pellucida.
Answer:
- Nebenkern: It is the spirally arranged mitochondria in the middle piece of the sperm. It provides energy (ATP) for sperm motility.
- Zona Pellucida: It is a glycoprotein layer surrounding the ovum. It prevents polyspermy and ensures species-specific fertilization.
Q. 11. Give location of corpus callosum and arbor vitae of human brain.
Answer:
- Corpus Callosum: Located deep within the longitudinal fissure, connecting the two cerebral hemispheres.
- Arbor Vitae: Located in the Cerebellum (the white matter branching tree-like structure).
Q. 12. Match cells of immune system in column-I and their functions in column-II:
Answer:
- (i) Cytotoxic T cells → (c) Secretion of perforins
- (ii) Plasma cells → (d) Antibody production
- (iii) Antigen presenting cells → (a) Activation of helper T cells
- (iv) Red blood cells → (b) Blood group antigens (Surface antigens)
Q. 13. Give any two examples of commercially exploited products of transgenic plants.
Answer:
- Bt Cotton: Produces Cry protein to resist bollworms.
- Golden Rice: Enriched with Pro-vitamin A (Beta-carotene).
- Flavr Savr Tomato: Delayed ripening (polygalacturonase inhibition).
Q. 14. Write causative agent, two symptoms and mode of transmission of typhoid.
Answer:
- Causative Agent: Salmonella typhi.
- Symptoms: High fever, stomach pain, loss of appetite, constipation/diarrhea.
- Transmission: Fecal-oral route (Contaminated food and water).
SECTION – C (24 Marks)
Attempt any EIGHT of the following questions:
Q. 15. Suggest the specific term for the following:
Answer:
- (a) Both male and female reproductive organs in same organism: Hermaphrodite / Bisexual.
- (b) Y-linked gene: Holandric gene.
- (c) Unfertilised egg develops into haploid male bee: Arrhenotoky (Parthenogenesis).
Q. 16. Explain the role of diazotrophs in nitrification.
Answer:
Note: Diazotrophs usually refer to Nitrogen Fixers, not Nitrifiers. However, assuming the question asks about microbes in the Nitrogen cycle:
Nitrification is the oxidation of ammonia to nitrate.
Nitrification is the oxidation of ammonia to nitrate.
- Step 1: Ammonia ($NH_3$) is oxidized to Nitrite ($NO_2^-$) by bacteria like Nitrosomonas and Nitrococcus.
- Step 2: Nitrite is further oxidized to Nitrate ($NO_3^-$) by bacteria like Nitrobacter.
- Plants absorb nitrogen mainly in the form of Nitrate.
Q. 17. Explain the following events of cardiac cycle with respect to type of valves and duration:
Answer:
- (a) Atrial Systole (0.1 sec): Atria contract. AV valves (Tricuspid/Bicuspid) are open. Semilunar valves closed. Blood pumped into ventricles.
- (b) Ventricular Systole (0.3 sec): Ventricles contract. AV valves close (Lubb sound). Semilunar valves open. Blood pumped into Pulmonary trunk and Aorta.
- (c) Joint Diastole (0.4 sec): Both Atria and Ventricles relax. Semilunar valves close (Dubb sound). AV valves open. Filling of heart occurs.
Q. 18. What is reflex action? Explain with one example each of the types of reflex actions based on previous experiences.
Answer:
Reflex Action: A sudden, involuntary, and instantaneous response to a stimulus mediated by the spinal cord.
Types based on experience:
Types based on experience:
- Unconditioned Reflex (Inborn): Present from birth, no learning required.
Example: Salivation when tasting food, blinking when an object approaches eye. - Conditioned Reflex (Acquired): Learned through practice or experience.
Example: Salivation at the ringing of a dinner bell (Pavlov's dog), cycling, or swimming.
Q. 19. Select and fill in the boxes (i) to (vi) from given list of options.
Answer:
| (a) Incomplete dominance | (i) Flower colour of Mirabilis |
| (b) Pleiotropy | (ii) Sickle cell anaemia |
| (c) Codominance | (iii) Coat colour of cattle |
| (d) Multiple allelism | (iv) Human blood groups |
| (e) Sex chromosomal disorder | (v) Klinefelter's syndrome |
| (f) Autosomal disorder | (vi) Widow's peak |
Q. 20. Give the role of following mycoherbicides: (a) Phytophthora (b) Alternaria (c) Fusarium.
Answer:
Mycoherbicides are fungi used to control weeds.
- (a) Phytophthora palmivora: Controls milkweed vines in citrus orchards.
- (b) Alternaria crassa: Controls water hyacinth.
- (c) Fusarium sp.: Controls various weeds (generic example).
Q. 21. Explain the following terms with respect to survival of an organism in a changed environment: (a) Regulate (b) Conform (c) Migrate.
Answer:
- (a) Regulate: Organisms maintain a constant internal environment (homeostasis) despite external changes (e.g., Mammals regulate body temp).
- (b) Conform: Organisms cannot maintain constant internal environment; their body temperature or osmotic pressure changes with the ambient environment (e.g., Fish, Reptiles).
- (c) Migrate: Organisms move temporarily from a stressful habitat to a hospitable area and return when the stressful period is over (e.g., Siberian Cranes).
Q. 22. Describe any three causes for loss of biodiversity.
Answer:
- Habitat Loss and Fragmentation: Cutting forests causes loss of home for species. Large habitats broken into small patches affect migratory animals.
- Over-exploitation: Humans harvesting species faster than they can reproduce (e.g., Dodo, Passenger pigeon).
- Alien Species Invasions: Introduction of non-native species that turn invasive and decline local species (e.g., Water Hyacinth, African Catfish).
Q. 23. Give physiological effects and applications of cytokinin.
Answer:
- Promotes cell division (Cytokinesis).
- Delays senescence (aging) of leaves (Richmond-Lang effect).
- Promotes growth of lateral buds (counteracts apical dominance).
- Used in tissue culture to induce shoot formation.
Q. 24. What is mycorrhiza? Name its types and state any two benefits.
Answer:
Mycorrhiza: Symbiotic association between a fungus and roots of higher plants.
Types: (1) Ectomycorrhiza (2) Endomycorrhiza (VAM).
Benefits:
Types: (1) Ectomycorrhiza (2) Endomycorrhiza (VAM).
Benefits:
- Enhances absorption of water and minerals (especially Phosphorus).
- Protects roots from soil-borne pathogens.
SECTION – D (12 Marks)
Attempt any THREE of the following questions:
Q. 27. Describe mechanism of opening and closing of stomata with reference to: (a) Starch-sugar interconversion theory (b) Proton transport theory.
Answer:
(a) Starch-Sugar Interconversion Theory (Lloyd):
- Day (Opening): Photosynthesis lowers $CO_2$, pH rises. Starch phosphorylase converts Starch → Glucose-1-phosphate. DPD increases, water enters guard cells (Endosmosis), they become turgid, stomata open.
- Night (Closing): No photosynthesis, $CO_2$ rises, pH drops. Glucose converted back to Starch. DPD decreases, water leaves guard cells (Exosmosis), they become flaccid, stomata close.
(b) Proton Transport Theory (Levitt):
- Opening: In light, $H^+$ ions are pumped out of guard cells and $K^+$ ions enter (active transport). Accumulation of $K^+$ lowers water potential. Water enters, turgor pressure rises, stomata open.
- Closing: In dark or stress (ABA), $K^+$ ions move out. Water potential increases, water moves out, turgor falls, stomata close.
Q. 28. (a) Define Hormone. (b) Enlist properties. (c) Diagram of membrane bound receptor action.
Answer:
- (a) Hormone: A chemical messenger secreted by endocrine glands directly into the blood, acting on distant target organs.
- (b) Properties: Highly specific, required in very small quantities, low molecular weight, act as messengers, modified amino acids/steroids/proteins.
- (c) Diagram: .
Q. 29. With respect to diagram (Ovule), answer the following:
Answer:
- (a) Type of Ovule: Anatropous Ovule (Inverted).
- (b) First cell of embryo sac: Functional Megaspore.
- (c) Identify and Function:
- A (Micropyle): Small opening for entry of pollen tube.
- B (Secondary Nucleus / Definitive Nucleus): Formed by fusion of two polar nuclei. Fuses with second male gamete to form Endosperm (Triple Fusion).
Q. 30. How transgenic pigs and cattle are commercially beneficial?
Answer:
- Transgenic Pigs: Produced for organ xenotransplantation (sparingly used due to rejection issues), and to produce human hemoglobin. Also used as bioreactors for proteins.
- Transgenic Cattle: Produced to increase milk yield, improve milk quality (e.g., cows producing human protein alpha-lactalbumin), and produce meat with less fat. Can also produce pharmaceutical proteins in milk (Molecular Pharming).
Q. 31. With the help of a suitable diagram describe histology of testis.
Answer:
Histology of Testis (T.S.):
- Covered by Tunica Albuginea (fibrous connective tissue).
- Contains many circular Seminiferous Tubules.
- Germinal Epithelium: Cuboidal cells lining the tubule, undergoing spermatogenesis (Spermatogonia → Primary Spermatocyte → Spermatid → Sperm).
- Sertoli Cells (Nurse Cells): Pyramidal cells that provide nourishment to developing sperms and secrete Inhibin.
- Interstitial Cells (Leydig Cells): Present in connective tissue between tubules. They secrete male hormone Testosterone (Androgens).
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