TN HSC Biology Model Paper 2027 — Full Paper With Solutions

This model paper follows the official TNDGE pattern for HSC Biology 2027. Theory: 70 marks in 3 hours. Practical: 30 marks separately.

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Paper Structure

Section	Type	Marks
Part 1	MCQ — 15 questions	15
Part 2	Very Short Answer — 6 of 9 (2 marks each)	12
Part 3	Short Answer — 9 of 14 (3 marks each)	27
Part 4	Long Answer — 3 of 5 (5 marks each)	15
Part 5	Higher Order Thinking — 1 question	...

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PART 1 — MCQ (1 Mark Each)

Q1. The fluid mosaic model of cell membrane was proposed by:

(a) Watson and Crick (b) Singer and Nicolson (c) Robert Brown (d) Hugo de Vries

Answer: (b) Singer and Nicolson (1972)

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Q2. Which of the following is a post-fertilisation structure?

(a) Ovule (b) Ovary (c) Seed (d) Style

Answer: (c) Seed
(After fertilisation: ovule → seed; ovary → fruit)

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Q3. The lac operon is an example of:

(a) Positive gene regulation (b) Negative gene regulation
(c) Post-translational modification (d) RNA splicing

Answer: (b) Negative gene regulation
(Repressor protein blocks transcription; inducer removes repressor)

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Q4. Bt cotton is resistant to:

(a) Fungal diseases (b) Viral diseases (c) Bollworm insects (d) Drought

Answer: (c) Bollworm insects
(Bt toxin from Bacillus thuringiensis kills Lepidopteran larvae)

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Q5. Which enzyme is called the molecular scissors?

(a) DNA ligase (b) DNA polymerase (c) Restriction endonuclease (d) RNA polymerase

Answer: (c) Restriction endonuclease

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Q6. The primary productivity of an ecosystem depends on:

(a) Number of consumers (b) Photosynthetic activity of producers
(c) Decomposition rate (d) Number of detritivores

Answer: (b) Photosynthetic activity of producers

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Q7. In a food chain, energy transfer from one trophic level to the next is approximately:

(a) 1% (b) 10% (c) 50% (d) 100%

Answer: (b) 10%
(Ten percent law — Lindemann, 1942)

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Q8. The hormone responsible for parturition (childbirth) is:

(a) Estrogen (b) Progesterone (c) Oxytocin (d) FSH

Answer: (c) Oxytocin
(Oxytocin stimulates uterine contractions during labour)

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Q9. Which of the following is NOT a method of contraception?

(a) Condom (b) IUD (c) Vasectomy (d) Amniocentesis

Answer: (d) Amniocentesis
(Amniocentesis is a prenatal diagnostic test, not contraception)

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Q10. Sickle cell anaemia is caused by:

(a) Addition of one base pair (b) Deletion of one base pair
(c) Substitution of one base pair (d) Translocation of chromosome

Answer: (c) Substitution — GAG changed to GTG in beta-globin gene

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Q11. The term 'Biodiversity' was coined by:

(a) E.O. Wilson (b) Robert May (c) Charles Darwin (d) Ernst Mayr

Answer: (a) E.O. Wilson (1986)

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Q12. Which of the following is an in-situ conservation method?

(a) Seed bank (b) Zoological park (c) National park (d) Botanical garden

Answer: (c) National park
(In-situ = conservation in natural habitat; ex-situ = outside natural habitat)

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Q13. The antibiotic penicillin was discovered by:

(a) Robert Koch (b) Alexander Fleming (c) Louis Pasteur (d) Edward Jenner

Answer: (b) Alexander Fleming (1928)

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Q14. Which type of RNA carries amino acids to the ribosome?

(a) mRNA (b) rRNA (c) tRNA (d) snRNA

Answer: (c) tRNA (transfer RNA)

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Q15. The founder effect is associated with:

(a) Large populations (b) Small isolated populations
(c) Sexually reproducing organisms only (d) Aquatic organisms only

Answer: (b) Small isolated populations

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PART 2 — Very Short Answer (2 Marks Each — Attempt 6 of 9)

Q16. What is the difference between autogamy and allogamy?

Answer:
Autogamy: Self-pollination — pollen transferred from anther to stigma of the same flower. Example: Wheat, Rice, Pea.
Allogamy: Cross-pollination — pollen transferred to the stigma of a different flower on same or different plant. Example: Maize, Papaya.

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Q17. Define totipotency. What is its significance in biotechnology?

Answer: The ability of a single plant cell to develop into a complete organism is called totipotency.

Significance: Forms the basis of plant tissue culture technology. A single explant cell can be grown in vitro into a complete plant. Used to produce disease-free plants, raise rare species, produce large numbers of identical plants (micropropagation), and create transgenic plants.

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Q18. What are interferons? Mention their function.

Answer: Interferons are glycoprotein molecules produced by virus-infected cells. They are a type of cytokine.

Function:

• Alert neighbouring uninfected cells to prepare antiviral defences
• Inhibit viral replication within infected cells
• Stimulate natural killer cells and macrophages
• Used therapeutically against viral infections and certain cancers

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Q19. Distinguish between innate and acquired immunity.

Answer:

Feature	Innate Immunity	Acquired Immunity
Nature	Non-specific	Specific
Present at birth	Yes	No — develops after exposure
Memory	Absent	Present
Examples	Skin, mucus, fever, phagocytes	Antibodies, T and B lymphocytes

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Q20. What is VNTR? Why is it important in DNA fingerprinting?

Answer: VNTR (Variable Number Tandem Repeats) are short DNA sequences repeated in tandem at specific loci. The number of repeats varies between individuals.

Importance in DNA fingerprinting: Since VNTR patterns are unique to each individual (except identical twins), they produce distinctive banding patterns when visualised on gel electrophoresis. Used in criminal investigation, paternity testing, and identifying disaster victims.

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PART 3 — Short Answer (3 Marks Each — Attempt 9 of 14)

Q21. Describe the structure of DNA double helix. Include key measurements.

Answer:
Watson and Crick (1953) proposed the double helix model based on X-ray data by Rosalind Franklin.

Structure:

• Two polynucleotide strands coiled around a central axis in antiparallel orientation (one 5'→3', other 3'→5')
• Sugar-phosphate backbone on the outside
• Nitrogenous bases face inward and pair through H-bonds
• Base pairing (Chargaff's rule):
  Adenine (A) pairs with Thymine (T) — 2 H-bonds
  Guanine (G) pairs with Cytosine (C) — 3 H-bonds

Key measurements:

• Pitch (one complete turn) = 3.4 nm
• Distance between base pairs = 0.34 nm
• Number of base pairs per turn = 10
• Diameter of helix = 2 nm

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Q22. Explain the process of translation (protein synthesis) briefly.

Answer: Translation is the process of synthesising a polypeptide chain from the mRNA sequence.

Three stages:

1. Initiation:

• mRNA binds to small ribosomal subunit
• Initiator tRNA (carrying Met) recognises start codon (AUG)
• Large ribosomal subunit joins — 70S complex (prokaryotes) or 80S (eukaryotes)

2. Elongation:

• Aminoacyl-tRNA enters A site
• Peptide bond forms between amino acids (peptidyl transferase)
• Ribosome translocates one codon (A→P→E site)
• Process repeats for each codon

3. Termination:

• Stop codon (UAA, UAG, or UGA) reached
• Release factors cause polypeptide chain to detach
• Ribosome dissociates

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Q23. What is ecological succession? Distinguish between primary and secondary succession.

Answer: The sequential and predictable change in species composition of an ecological community over time is called ecological succession.

Feature	Primary Succession	Secondary Succession
Starting point	Bare, lifeless area (no soil)	Previously inhabited area with soil
Duration	Thousands of years	Decades to centuries
Pioneer species	Lichens, mosses	Grasses, herbs
Examples	Bare rock, newly formed volcanic island	Abandoned farmland, burnt forest

Both end in a stable climax community suited to the local climate.

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Q24. Describe three methods of ex-situ conservation of biodiversity.

Answer: Ex-situ conservation means protecting species outside their natural habitats.

Three methods:

1. Zoological Parks (Zoos): Wild animals are maintained in captivity. Breeding programmes for endangered species (captive breeding). Example: Breeding of Indian rhino in Kaziranga.

2. Botanical Gardens: Living plant collections maintained for conservation, education and research. Royal Botanic Gardens, Kew (UK) and National Botanical Research Institute (Lucknow) are examples.

3. Seed Banks: Seeds of wild and cultivated plant varieties stored at very low temperatures (−20°C). National Bureau of Plant Genetic Resources (NBPGR), New Delhi maintains India's largest seed bank. Ensures genetic material is preserved even if species goes extinct in wild.

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PART 4 — Long Answer (5 Marks Each — Attempt 3 of 5)

Q25. Explain the Human Reproductive System in males. Include a labelled diagram.

Answer:

Male Reproductive System Components:

Testes (2):

• Located in scrotum outside the body cavity (temperature 2–3°C lower than body)
• Two functions: Spermatogenesis (sperm production) and testosterone secretion
• Seminiferous tubules lined with Sertoli cells and spermatogonia
• Leydig cells (interstitial cells) produce testosterone

Accessory Ducts:

• Epididymis: Comma-shaped structure on each testis; site of sperm maturation and storage
• Vas deferens: Carries sperm from epididymis to urethra
• Ejaculatory duct: Formed by union of vas deferens and seminal vesicle duct

Accessory Glands:

• Seminal vesicles (2): Secrete fructose-rich fluid — provides energy to sperm (60% of semen)
• Prostate gland: Secretes milky alkaline fluid — neutralises vaginal acidity (30% of semen)
• Bulbourethral glands (Cowper's glands): Secrete mucus for lubrication

Penis: Male copulatory organ; contains urethra for both urine and semen passage

Semen composition: Sperm + seminal vesicle secretion + prostatic fluid = ~2.5–5 mL per ejaculation containing 200–500 million sperm.

(Draw labelled diagram showing testes, epididymis, vas deferens, seminal vesicles, prostate, urethra and penis)

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Q26. Write an essay on Genetically Modified Organisms (GMOs). Include examples and benefits.

Answer:

Definition: Organisms whose genetic material has been altered using recombinant DNA technology by introducing genes from the same or different species.

Process of Creating GMOs:

1. Identify and isolate the gene of interest
2. Clone it into an appropriate vector (plasmid)
3. Transform it into host organism using Agrobacterium, biolistics, or microinjection
4. Screen and select successfully transformed organisms

Examples and Applications:

Bt Crops:

• Bt cotton, Bt brinjal — contain Cry gene from Bacillus thuringiensis
• Produces Bt toxin that kills bollworm larvae
• Reduces pesticide use by 50% in cotton cultivation

Golden Rice:

• Contains beta-carotene synthesis genes (from daffodil and bacteria)
• Addresses Vitamin A deficiency in developing countries
• Produces yellow/golden coloured rice

Flavr Savr Tomato:

• First GM food approved for human consumption (USA, 1994)
• Delayed ripening gene — longer shelf life

GM Insulin:

• Human insulin gene inserted into E. coli
• Produced in large quantities (Humulin)
• Replaced animal insulin, fewer allergic reactions

Benefits:

1. Increased crop yield and drought resistance
2. Reduced pesticide and herbicide use
3. Enhanced nutritional content
4. Disease-resistant varieties
5. Production of pharmaceutical proteins

Concerns:

• Potential allergenicity
• Environmental impact on non-target organisms
• Gene flow to wild relatives
• Ethical issues regarding corporate control of food supply

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Chapter-Wise Weightage

Chapter	Marks
Reproduction in Plants	8
Human Reproduction	8
Reproductive Health	5
Genetics — Mendel and Beyond	10
Molecular Biology (DNA, RNA, Gene Expression)	10
Evolution	6
Human Health and Disease	8
Biotechnology	8
Ecology and Environment	7

Tip: TN HSC Biology Part 4 long answers each carry 5 marks. Always include a labelled diagram wherever relevant — TN Board awards 1–2 marks specifically for diagrams. A well-labelled diagram of DNA structure, human reproductive system, or lac operon can add easy marks to your answer.