🧬 Class 12 Biology — Important Questions 2026

Genetics (18M) + Reproduction (14M) + Ecology (14M) + Biotechnology (14M) + Human Welfare (14M)

Complete Chapter-wise Guide with Answer Hints & Diagram Tips — Score 60+ out of 70!

📅 Board Exam 2026 — Starts 17 February!

Biology is the highest-scoring subject for medical stream students — it rewards conceptual understanding and diagram-based answers. The key to scoring 60+ out of 70 is mastering Genetics & Evolution (18 marks = 26% of paper) and drawing neat, labeled diagrams which carry 2-3 marks each.

This guide covers all 16 chapters with the most expected questions, each with detailed answer hints so you know exactly what to write and which diagrams to draw. Whether you're preparing for CBSE Board or NEET, these questions cover both exams perfectly since the syllabus overlaps significantly.

Also check our other Class 12 Important Questions: Physics · Chemistry · Maths

⚠️ RBSE Students Note: CBSE Biology = 70 marks Theory. RBSE Biology = 56 marks Theory + 14 marks Practical. Chapter weightage is similar. Focus on Genetics (18M) and Reproduction (14M) — these two units alone = 32/70 marks (46%)! NEET aspirants: every Board question is also a NEET question, so this preparation does double duty.

📊 Class 12 Biology — Marks Distribution 2026

🌸 Unit I — Reproduction (14 Marks)

Ch 1: Reproduction in Organisms · Ch 2: Sexual Reproduction in Flowering Plants · Ch 3: Human Reproduction · Ch 4: Reproductive Health

⭐ Ch 2: Sexual Reproduction in Flowering Plants (Most Important!)

1. 🟣 Describe the process of double fertilization in angiosperms. What is the significance of this process? (5M) ⭐⭐⭐ Most Expected — Appears Almost Every Year!
   💡 Answer Hint: (1) Pollen grain germinates on stigma → pollen tube grows through style → enters ovule through micropyle. (2) Pollen tube releases 2 male gametes into embryo sac. (3) Syngamy: One male gamete (n) fuses with egg cell (n) → Zygote (2n) → develops into embryo. (4) Triple Fusion: Other male gamete (n) fuses with 2 polar nuclei (n+n) → Primary Endosperm Nucleus (3n) → develops into endosperm (nutrition for embryo). Significance: Ensures embryo gets nutrition immediately without waiting, gives angiosperms competitive advantage. Draw: Labeled diagram of embryo sac showing both fusion events = 2 extra marks!
2. 🟣 Draw a labeled diagram of the mature embryo sac (female gametophyte) of an angiosperm. Describe the role of each cell. (5M) ⭐⭐⭐
   💡 Answer Hint: Structure (7 cells, 8 nuclei): At micropylar end — 1 Egg cell (female gamete) + 2 Synergids (secrete chemicals to guide pollen tube, have filiform apparatus). At center — 2 Polar nuclei in central cell (fuse with sperm → 3n endosperm). At chalazal end — 3 Antipodal cells (nutritive function, degenerate later). Diagram tip: Draw oval shape, label micropylar end at bottom, chalazal at top. Show egg apparatus (egg + 2 synergids), central cell with 2 polar nuclei, 3 antipodals. Label filiform apparatus on synergids — examiners specifically look for this!
3. 🟡 Explain the development of a dicot embryo from the zygote stage. (3M) ⭐⭐⭐
   💡 Answer Hint: Zygote divides → forms proembryo → globular embryo → heart-shaped embryo → mature embryo. Mature dicot embryo has: (1) Embryonal axis with plumule (future shoot) at one end and radicle (future root) at other end. (2) Two cotyledons (seed leaves, store food). (3) Epicotyl (above cotyledon attachment) and hypocotyl (below cotyledon attachment). Compare with monocot: monocot has 1 cotyledon called scutellum, coleoptile covers plumule, coleorhiza covers radicle.
4. 🟡 What is apomixis? How is it different from polyembryony? Give examples. (3M) ⭐⭐
   💡 Answer Hint: Apomixis: Seed formation without fertilization — produces genetically identical offspring (clones). Mechanism: either diploid egg cell without meiosis, or nucellar cells develop into embryo. Example: Asteraceae, grasses. Polyembryony: Occurrence of more than one embryo in a seed. Example: Citrus (orange) — nucellar cells form extra embryos alongside sexual embryo. Difference: Apomixis = asexual seed formation; Polyembryony = multiple embryos (some sexual, some asexual).

⭐ Ch 3: Human Reproduction

1. 🟣 Describe the process of spermatogenesis with a labeled diagram. How is it different from oogenesis? (5M) ⭐⭐⭐ CLASSIC 5-marker!
   💡 Answer Hint: Spermatogenesis: Spermatogonium (2n) → [mitosis] → Primary spermatocyte (2n) → [Meiosis I] → 2 Secondary spermatocytes (n) → [Meiosis II] → 4 Spermatids (n) → [Spermiogenesis] → 4 Spermatozoa (n). Occurs in seminiferous tubules. Sertoli cells provide nutrition. Key differences from oogenesis: (1) Spermatogenesis produces 4 functional gametes; oogenesis produces only 1 functional ovum + 3 polar bodies. (2) Spermatogenesis continuous from puberty; oogenesis starts in fetal life, arrested at prophase I, resumes at puberty. (3) Equal cytoplasmic division in spermatogenesis; unequal in oogenesis.
2. 🟡 Draw a labeled diagram of the L.S. of a seminiferous tubule and describe the role of Sertoli cells and Leydig cells. (3M) ⭐⭐⭐
   💡 Answer Hint: Sertoli cells: Located inside seminiferous tubules, provide nutrition to developing sperm, help in spermiation (release of sperm), secrete inhibin (negative feedback on FSH). Leydig cells (Interstitial cells): Located outside seminiferous tubules in interstitial spaces, secrete testosterone (male hormone) in response to LH. Diagram tip: Show cross-section of tubule with spermatogonia at periphery, spermatocytes and spermatids moving towards lumen, Sertoli cells between them, Leydig cells in spaces between tubules.
3. 🟡 Describe the events of the menstrual cycle and the hormones involved. (3M) ⭐⭐⭐
   💡 Answer Hint: 4 Phases: (1) Menstrual phase (Day 1-5): Endometrium sheds, bleeding occurs, low estrogen and progesterone. (2) Follicular/Proliferative phase (Day 6-13): FSH stimulates follicle growth → follicle secretes estrogen → endometrium regenerates. (3) Ovulatory phase (Day 14): LH surge → Graafian follicle ruptures → ovulation. (4) Luteal/Secretory phase (Day 15-28): Ruptured follicle → corpus luteum → secretes progesterone → endometrium thickens for implantation. If no fertilization → corpus luteum degenerates → progesterone drops → menstruation. Average cycle = 28 days.

⭐ Ch 4: Reproductive Health

1. 🟡 Describe the various methods of contraception and their modes of action. (3M) ⭐⭐⭐
   💡 Answer Hint: Natural: Periodic abstinence (safe period), coitus interruptus, lactational amenorrhea. Barrier: Condoms (prevent sperm entry), diaphragm, cervical caps. IUDs: CuT (copper ions are spermicidal), Hormone-releasing IUDs (make uterus unsuitable). Hormonal: Oral pills (inhibit ovulation via progesterone-estrogen), Saheli (non-steroidal, weekly pill). Surgical: Vasectomy (cut vas deferens in males), Tubectomy (cut fallopian tubes in females) — permanent methods. Write mode of action for each = full marks.
2. 🟡 What is amniocentesis? Why has the Government of India banned it? (2M) ⭐⭐
   💡 Answer Hint: Amniocentesis: Medical procedure — amniotic fluid withdrawn from uterus → fetal cells cultured → chromosomal analysis to detect genetic disorders (Down syndrome, etc.). Why banned: Misused for sex determination of fetus → led to female foeticide. Government banned it under PCPNDT Act (Pre-Conception and Pre-Natal Diagnostic Techniques Act, 1994) to prevent sex-selective abortions. Procedure is legal only for detecting genetic abnormalities, not for sex determination.

🌸 Unit VI — Reproduction (14 Marks)

Ch 1: Reproduction in Organisms + Ch 2: Sexual Reproduction in Flowering Plants + Ch 3: Human Reproduction

⭐ Ch 2: Sexual Reproduction in Flowering Plants (Most Important!)

1. 🟣 Describe double fertilization in angiosperms. What is its significance? (5M) ⭐⭐⭐ GUARANTEED!
   💡 Answer Hint: (1) Pollen lands on stigma, germinates, pollen tube grows to ovule. (2) Two male gametes released in embryo sac. (3) Syngamy: 1st sperm + egg = zygote (2n) → embryo. (4) Triple fusion: 2nd sperm + 2 polar nuclei = PEN (3n) → endosperm. (5) Significance: Endosperm provides nutrition to developing embryo; ensures food reserve only when fertilization succeeds (energy efficient). Ovule becomes seed, ovary becomes fruit. DRAW embryo sac diagram — it carries 2 marks!
2. 🟣 Draw a labelled diagram of L.S. of an anatropous ovule. Describe development of embryo sac. (5M) ⭐⭐⭐
   💡 Answer Hint: Diagram labels: Integuments (outer + inner), micropyle, chalaza, funicle, nucellus, embryo sac. Development: MMC (2n) → meiosis → 4 megaspores (n) → 3 degenerate, 1 functional → 3 mitotic divisions → 8 nuclei, 7 cells: egg (1) + synergids (2) at micropylar end, antipodals (3) at chalazal end, central cell with 2 polar nuclei. This = Polygonum type (monosporic). Label at least 8 parts for full marks.
3. 🟡 Explain outbreeding devices in plants that prevent self-pollination. (3M)
   💡 Answer Hint: Plants evolved several mechanisms: (1) Dicliny/Unisexuality: Male and female flowers on different plants (papaya, date palm). (2) Dichogamy: Pollen and stigma mature at different times — protandry (anthers mature first) or protogyny (stigma matures first). (3) Self-incompatibility: Genetic mechanism prevents pollen germination on same flower (prevents inbreeding). (4) Mechanical barriers: Anther and stigma placed so self-pollination is avoided. Purpose: promotes cross-pollination → genetic variation → healthier offspring.

⭐ Ch 3: Human Reproduction

1. 🟣 Describe structure of human sperm with labelled diagram. What is spermatogenesis? (5M)
   💡 Answer Hint: Sperm structure (4 parts): (1) Head — haploid nucleus + acrosome (enzymes for egg penetration). (2) Neck — centriole (proximal + distal). (3) Middle piece — mitochondria spirally wrapped (energy). (4) Tail — flagellum for motility. Spermatogenesis: Spermatogonia (2n) → Primary spermatocyte (2n) → [Meiosis I] → 2 Secondary spermatocytes (n) → [Meiosis II] → 4 Spermatids (n) → [Spermiogenesis] → 4 Spermatozoa. Takes ~74 days. FSH + testosterone control.
2. 🟡 Describe the phases of the menstrual cycle and hormonal regulation. (3M)
   💡 Answer Hint: 28-day cycle: (1) Menstrual (1-5 days): Endometrium sheds, low hormones. (2) Follicular (6-13): FSH → follicle growth → estrogen rises → endometrium rebuilds. (3) Ovulation (Day 14): LH surge → follicle ruptures → ovum released. (4) Luteal (15-28): Corpus luteum → progesterone maintains endometrium. No fertilization → corpus luteum degenerates → progesterone drops → menstruation. Key hormones: FSH + LH (pituitary); Estrogen + Progesterone (ovary).
3. 🟡 Classify and explain methods of birth control. (3M)
   💡 Answer Hint: (1) Natural: Rhythm method, coitus interruptus, lactational amenorrhea. (2) Barrier: Condoms, diaphragm, cervical caps. (3) Hormonal: Oral pills (Mala-D), implants (Norplant). (4) IUDs: Copper-T (releases Cu ions), LNG-20 (hormone-releasing). (5) Surgical: Vasectomy (male), Tubectomy (female). (6) Emergency: Morning-after pills. Mention at least one example per category.

🧬 Unit II — Genetics & Evolution (18 Marks) — Highest Weightage!

Ch 5: Principles of Inheritance · Ch 6: Molecular Basis of Inheritance · Ch 7: Evolution

⭐ Ch 5: Principles of Inheritance and Variation

1. 🟣 Explain the inheritance of ABO blood groups in humans. How does this illustrate the concept of co-dominance and multiple alleles? (5M) ⭐⭐⭐ Most Asked!
   💡 Answer Hint: ABO blood groups controlled by gene I with 3 alleles: Iᴬ, Iᴮ, and i. Iᴬ and Iᴮ are co-dominant (both express when together → AB blood group), both dominant over i. Genotype-Phenotype: Iᴬ Iᴬ or Iᴬi → Blood Group A | Iᴮ Iᴮ or Iᴮi → Blood Group B | Iᴬ Iᴮ → Blood Group AB (co-dominance — both antigens present) | ii → Blood Group O. Multiple alleles: Gene has 3 alleles in population, but any individual has only 2 (diploid). Co-dominance: In Iᴬ Iᴮ, both alleles express equally — neither is dominant — both A and B antigens present on RBCs. This is different from incomplete dominance where blending occurs.
2. 🟡 Explain sex-linked inheritance with reference to colour blindness. Why are more males affected than females? (3M) ⭐⭐⭐
   💡 Answer Hint: Colour blindness gene is recessive, located on X chromosome. Let Xᶜ = colour blind allele, X⁺ = normal. Males (XY): Only need ONE Xᶜ to be affected (Xᶜ Y = colour blind). No corresponding allele on Y to mask it. Females (XX): Need TWO Xᶜ alleles (Xᶜ Xᶜ) to be affected. X⁺ Xᶜ = carrier female (normal vision). This is why males are more affected — they're hemizygous for X-linked genes. Cross: Carrier mother (X⁺ Xᶜ) × Normal father (X⁺ Y) → Daughters: 50% carrier, 50% normal | Sons: 50% colour blind, 50% normal. This criss-cross pattern (mother passes to son) is characteristic of X-linked inheritance.
3. 🟡 A cross between a tall plant (TT) and a short plant (tt) resulted in all tall progeny in F₁. When F₁ plants were selfed, the F₂ showed 3:1 ratio. Explain with a cross. (3M) ⭐⭐⭐
   💡 Answer Hint: P: TT × tt → F₁: All Tt (tall, because T is dominant). F₁ × F₁: Tt × Tt → F₂ Punnett square: TT : Tt : Tt : tt = 1:2:1 genotypic ratio = 3 Tall : 1 Short phenotypic ratio. This demonstrates Law of Segregation — alleles separate during gamete formation, each gamete gets one allele. Always draw: Punnett square + Gamete formation arrows = full marks. Test cross to verify: Tt × tt → Tt : tt = 1:1.

⭐ Ch 6: Molecular Basis of Inheritance — DNA, RNA, Central Dogma

1. 🟣 Describe the process of transcription in prokaryotes. How is it different in eukaryotes? (5M) ⭐⭐⭐ GUARANTEED 5-marker!
   💡 Answer Hint: Prokaryotic transcription: (1) Initiation: RNA polymerase binds to promoter (σ factor helps recognition). Template strand read 3'→5'. mRNA synthesized 5'→3'. (2) Elongation: RNA polymerase moves along template, adds NTPs complementary to template (A→U, T→A, G→C, C→G). (3) Termination: Reaches terminator sequence → ρ (rho) factor-dependent or independent termination. Eukaryotic differences: (1) 3 RNA polymerases: Pol I (rRNA), Pol II (mRNA), Pol III (tRNA). (2) Pre-mRNA undergoes processing: 5' capping, 3' polyadenylation, splicing (removal of introns, joining of exons). (3) Transcription in nucleus, translation in cytoplasm (coupled in prokaryotes). Diagram: Show template strand, coding strand, mRNA with 5'→3' direction.
2. 🟡 Describe the structure of DNA as proposed by Watson and Crick. (3M) ⭐⭐⭐
   💡 Answer Hint: Key features: (1) Double helix — two polynucleotide chains coiled around each other. (2) Sugar-phosphate backbone on outside, nitrogenous bases on inside. (3) Antiparallel strands: one 5'→3', other 3'→5'. (4) Base pairing: A=T (2 H-bonds), G≡C (3 H-bonds) — Chargaff's rule. (5) One complete turn = 3.4 nm = 10 base pairs. Distance between two bases = 0.34 nm. (6) Right-handed helix (B-form). Draw: Double helix with labeled bases, H-bonds shown as dotted lines between AT and GC pairs, indicate major and minor grooves.
3. 🟡 Explain the Lac Operon model of gene regulation in E. coli. (3M) ⭐⭐⭐
   💡 Answer Hint: Components: Regulatory gene (i) → produces repressor protein. Promoter (p) → RNA polymerase binding site. Operator (o) → repressor binding site. Structural genes: z (β-galactosidase), y (permease), a (transacetylase). Without lactose (repressed): Repressor binds to operator → blocks RNA polymerase → no transcription of structural genes. With lactose (induced): Lactose (inducer) binds to repressor → repressor changes shape → cannot bind operator → RNA polymerase transcribes z, y, a genes → enzymes produced → lactose metabolized. Draw: Show both states (repressed and induced) with all components labeled.
4. 🟡 What is the Human Genome Project (HGP)? Mention its salient features and goals. (3M) ⭐⭐
   💡 Answer Hint: HGP (1990-2003): International effort to sequence entire human genome. Salient features: Total genes ≈ 20,000-25,000 (less than expected). Genome size = 3.3 billion base pairs. Less than 2% codes for proteins (rest = non-coding/repetitive DNA). Average gene size = 3000 bp. Chromosome 1 has most genes (2968), Y chromosome has fewest (231). Goals: Identify all genes, determine sequences of 3.3 billion bases, store information in databases, develop analysis tools, address ethical/legal/social issues (ELSI). Methods used: BAC (Bacterial Artificial Chromosome) cloning + shotgun sequencing.

⭐ Ch 7: Evolution

1. 🟡 Differentiate between homologous and analogous organs with examples. What do they tell us about evolution? (3M) ⭐⭐⭐
   💡 Answer Hint: Homologous organs: Same structural origin, different functions. Example: Forelimbs of whale (swimming), bat (flying), horse (running), human (grasping) — all have humerus, radius, ulna but modified for different functions. Indicate divergent evolution from common ancestor. Analogous organs: Different structural origin, same function. Example: Wings of butterfly (exoskeletal) and wings of bird (endoskeletal) — different origin but both for flying. Indicate convergent evolution — similar environment leads to similar adaptations. Draw: Comparative diagram of forelimbs showing same bones in different arrangements.
2. 🟡 Explain Hardy-Weinberg principle. What factors can disturb genetic equilibrium? (3M) ⭐⭐⭐
   💡 Answer Hint: Principle: In a large, randomly mating population with no selection, mutation, migration, or genetic drift — allele frequencies remain constant. Equation: p² + 2pq + q² = 1 (where p = frequency of dominant allele, q = frequency of recessive allele, p+q = 1). 5 factors disturbing equilibrium: (1) Gene migration/gene flow (2) Genetic drift (random changes in small populations — Founder effect, Bottleneck effect) (3) Mutation (4) Genetic recombination (5) Natural selection. Each factor leads to evolution by changing allele frequencies.

🏥 Unit III — Biology & Human Welfare (14 Marks)

Ch 8: Human Health & Disease · Ch 9: Strategies for Food Production · Ch 10: Microbes in Human Welfare

⭐ Ch 8: Human Health and Disease

1. 🟡 Describe the life cycle of Plasmodium (malarial parasite) in the human body. How can malaria be prevented? (3M) ⭐⭐⭐
   💡 Answer Hint: In humans (asexual cycle): Infected female Anopheles mosquito bites → injects sporozoites → reach liver → multiply (schizogony) → enter RBCs → multiply → RBCs burst → release haemozoin (causes fever with chills, recurring every 48-72 hours). In mosquito (sexual cycle): Mosquito takes infected blood → gametocytes form gametes in gut → fertilization → zygote → develops on gut wall → sporozoites migrate to salivary glands. Prevention: Mosquito nets, DDT spraying, draining stagnant water, anti-malarial drugs (chloroquine). Draw: Life cycle diagram showing both hosts.
2. 🟡 Differentiate between innate immunity and acquired immunity. What are the types of acquired immunity? (3M) ⭐⭐⭐
   💡 Answer Hint: Innate immunity: Non-specific, present from birth, no memory. 4 barriers: (1) Physical — skin, mucus (2) Physiological — acid in stomach, tears (lysozyme) (3) Cellular — phagocytes (neutrophils, macrophages), NK cells (4) Cytokine — interferons (protect non-infected cells from virus). Acquired immunity: Specific, develops after exposure, has memory. Two types: (1) Humoral (B-cell mediated): B-lymphocytes produce antibodies (IgG, IgM, IgA, IgE, IgD) → neutralize pathogens in blood/lymph. (2) Cell-mediated (T-cell mediated): T-lymphocytes (helper T, cytotoxic T) → destroy infected cells, transplant rejection. Active immunity: Body makes own antibodies (vaccination). Passive immunity: Ready-made antibodies given (mother's IgA in colostrum).
3. 🟡 What are the harmful effects of drug and alcohol abuse? How can addiction be prevented? (2M)
   💡 Answer Hint: Opioids (heroin): Depressant, slows brain function, respiratory depression, addiction. Cannabinoids (marijuana): Affects cardiovascular system, hallucinations. Cocaine: Stimulant, interferes with dopamine transport, causes euphoria then depression. Alcohol: Liver damage (cirrhosis), nervous system damage, social problems. Prevention: Education about effects, counseling, avoiding peer pressure, seeking professional help, support from family. Adolescence is most vulnerable period.

⭐ Ch 10: Microbes in Human Welfare

1. 🟡 How are microbes used in the production of (a) antibiotics, (b) biogas, and (c) sewage treatment? (3M) ⭐⭐⭐
   💡 Answer Hint: (a) Antibiotics: Penicillin from Penicillium notatum (Alexander Fleming, 1928). Used to kill/inhibit disease-causing bacteria. (b) Biogas: Methanobacterium (methanogen) breaks down cellulosic material in biogas plant → produces methane (CH₄), CO₂, H₂. Works in anaerobic conditions. Gobar gas plant design by IARI/KVIC. (c) Sewage treatment: Primary — physical removal (sedimentation, filtration). Secondary — biological treatment: aerobic microbes in aeration tanks reduce BOD (Biochemical Oxygen Demand) of effluent. Activated sludge pumped into anaerobic digesters → methane + other gases. Treated water safe to discharge into water bodies. Key term: BOD = measure of organic matter (higher BOD = more polluted).
2. 🟡 Name the microbes used in the following: (i) Curd from milk (ii) Bread making (iii) Ethanol production (iv) Swiss cheese holes (2M)
   💡 Answer Hint: (i) Lactobacillus — converts lactose to lactic acid, coagulates milk protein casein. (ii) Saccharomyces cerevisiae (Baker's yeast) — ferments sugar, produces CO₂ (makes bread rise). (iii) Saccharomyces cerevisiae (Brewer's yeast) — same species, produces ethanol from sugars (fermentation). (iv) Propionibacterium shermanii — produces CO₂ gas which creates large holes in Swiss cheese. Also remember: Roquefort cheese = Penicillium roqueforti. Idli/dosa = Leuconostoc mesenteroides.

🔬 Unit IV — Biotechnology & Its Applications (14 Marks)

Ch 11: Biotechnology Principles & Processes · Ch 12: Biotechnology & Its Applications

⭐ Ch 11: Biotechnology — Principles and Processes

1. 🟣 Describe the steps involved in recombinant DNA technology (Genetic Engineering). (5M) ⭐⭐⭐ GUARANTEED 5-marker!
   💡 Answer Hint: 6 Steps: (1) Isolation of DNA: From donor organism using enzymes (lysozyme for bacteria, cellulase for plant cells). Purify DNA using ethanol precipitation. (2) Cutting with Restriction Enzymes: EcoRI recognizes GAATTC sequence, cuts at specific sites → produces sticky ends (palindromic sequences). (3) Insertion into vector: Gene of interest joined with vector (plasmid like pBR322) using DNA ligase → recombinant DNA. (4) Transfer into host: Methods: Heat shock (CaCl₂ treatment at 42°C), electroporation, gene gun (biolistics), microinjection. (5) Selection of transformants: Using selectable markers (antibiotic resistance genes — ampᴿ, tetᴿ). Insertional inactivation: gene inserted in tetᴿ → tetracycline sensitive = recombinant. Blue-white screening using lacZ gene. (6) Multiplication in bioreactor: Large-scale culture → downstream processing → purification of product.
2. 🟡 What is a cloning vector? Name the features required for a cloning vector. Explain any two. (3M) ⭐⭐⭐
   💡 Answer Hint: Cloning vector = DNA molecule that carries foreign gene into host cell and replicates. Features: (1) Origin of replication (ori): Sequence where replication starts — controls copy number. (2) Selectable markers: Antibiotic resistance genes (ampᴿ, tetᴿ) to identify transformants from non-transformants. (3) Cloning sites (MCS): Recognition sites for restriction enzymes where foreign DNA is inserted — preferably within a marker gene for insertional inactivation. (4) Small size: Easy to manipulate and introduces into host. Examples: pBR322 (plasmid), λ phage, BAC, YAC.
3. 🟡 Explain Gel Electrophoresis and its use in DNA fingerprinting. (3M) ⭐⭐
   💡 Answer Hint: Gel Electrophoresis: DNA fragments separated by size on agarose gel. DNA is negatively charged → moves towards anode (+). Smaller fragments move faster → travel further. Stain with ethidium bromide → visualize under UV as bands. DNA Fingerprinting: Uses VNTR (Variable Number Tandem Repeats) or STR (Short Tandem Repeats) — regions with repetitive DNA that vary between individuals. Steps: Isolation → Restriction digestion → Electrophoresis → Southern blotting → Hybridization with probe → Autoradiography. Applications: Paternity disputes, criminal identification, immigration cases, study of population genetics.

⭐ Ch 12: Biotechnology and Its Applications

1. 🟡 What is Bt cotton? How has it been developed? What are the concerns related to GM crops? (3M) ⭐⭐⭐
   💡 Answer Hint: Bt cotton: Genetically modified cotton containing cry gene (cry1Ac, cry2Ab) from bacterium Bacillus thuringiensis. Gene produces Cry protein (crystal protein) → insecticidal → kills cotton bollworm larvae. Mechanism: Inactive protoxin in Bt → insect ingests → alkaline gut pH activates it → creates pores in gut lining → insect dies. GM crop concerns: (1) Allergic reactions in humans (2) Antibiotic resistance markers may transfer to gut bacteria (3) Genetic pollution — GM genes may spread to wild relatives (4) Monopoly of seed companies (5) Reduction in biodiversity. Also mention: Golden Rice (Vitamin A enriched, β-carotene gene from daffodil).
2. 🟡 How has biotechnology helped in producing genetically engineered insulin (humulin)? (3M) ⭐⭐⭐
   💡 Answer Hint: Problem: Earlier insulin from slaughtered cattle/pigs → caused allergies. Solution (Eli Lilly, 1983): Human insulin gene cloned in E. coli. Insulin has 2 chains: Chain A (21 amino acids) and Chain B (30 amino acids). Process: Prepared two DNA sequences for A and B chains → inserted separately into E. coli plasmids → bacteria produced chains → extracted and combined by disulphide bonds → functional human insulin (humulin). Key point: Proinsulin has extra C-peptide which is removed during maturation. rDNA technology produces mature insulin directly.

🌍 Unit V — Ecology (14 Marks)

Ch 13: Organisms & Populations · Ch 14: Ecosystem · Ch 15: Biodiversity · Ch 16: Environmental Issues

⭐ Ch 14: Ecosystem (Most Important in Ecology!)

1. 🟣 Describe the components of an ecosystem. Explain the process of decomposition and energy flow. (5M) ⭐⭐⭐ MOST Expected in Ecology!
   💡 Answer Hint: Components: (A) Abiotic — light, temperature, water, soil, minerals. (B) Biotic — Producers (autotrophs — plants, algae), Consumers (heterotrophs — herbivores, carnivores, omnivores), Decomposers (fungi, bacteria). Decomposition steps: (1) Fragmentation — detritivores (earthworm) break down detritus. (2) Leaching — water-soluble nutrients dissolve and move into soil. (3) Catabolism — enzymes degrade detritus. (4) Humification — accumulation of dark, resistant humus. (5) Mineralization — humus further degraded to release minerals. Energy flow: Unidirectional (Sun → Producers → Consumers). 10% Law (Lindeman): Only 10% energy transferred to next trophic level, 90% lost as heat. GPP − Respiration = NPP. Draw: Energy flow diagram with 10% transfer at each level.
2. 🟡 Describe the ecological pyramids. Why is the pyramid of energy always upright? (3M) ⭐⭐⭐
   💡 Answer Hint: 3 types: (1) Pyramid of Number: Usually upright (grassland: grass > insects > birds > hawks). Inverted in parasitic food chain and tree ecosystem. (2) Pyramid of Biomass: Usually upright on land (producers have most biomass). Inverted in aquatic ecosystem (phytoplankton biomass < zooplankton at any given time). (3) Pyramid of Energy: ALWAYS upright because energy decreases at each trophic level (10% law) — energy is lost as heat at each step and can never increase. This follows Second Law of Thermodynamics. Even in aquatic ecosystems where biomass pyramid is inverted, energy pyramid remains upright.
3. 🟡 What is ecological succession? Differentiate between primary and secondary succession. (3M) ⭐⭐
   💡 Answer Hint: Ecological succession: Sequential, gradual changes in species composition of an area over time, leading to climax community. Primary succession: On bare/lifeless area (newly cooled lava, bare rock). Pioneer species: lichens (on rock) or phytoplankton (in water). Very slow (hundreds of years). Stages on rock: Lichen → Moss → Herb → Shrub → Tree (climax). Secondary succession: On area where community has been destroyed but soil/sediment remain (after fire, flood, deforestation). Faster than primary. Pioneer species: grasses and herbs. Key terms: Sere = entire succession. Seral community = transitional stage. Climax community = stable, final stage.

⭐ Ch 15: Biodiversity and Conservation

1. 🟡 What are the causes of loss of biodiversity? Describe the strategies for conservation of biodiversity. (3M) ⭐⭐⭐
   💡 Answer Hint: Causes (The Evil Quartet): (1) Habitat loss and fragmentation (most important — deforestation, urbanization). (2) Over-exploitation (hunting, poaching, overfishing). (3) Alien species invasions (Nile perch in Lake Victoria, water hyacinth, Lantana). (4) Co-extinctions (when host species goes extinct, dependent parasites/mutualists also die). Conservation strategies: (A) In-situ (in natural habitat): National parks (e.g., Jim Corbett), wildlife sanctuaries, biosphere reserves, biodiversity hotspots (India has 4: Western Ghats, Himalayas, Indo-Burma, Sundaland). Sacred groves. (B) Ex-situ (outside natural habitat): Zoological parks, botanical gardens, seed banks, cryopreservation, tissue culture. India is one of 12 mega-biodiversity countries.

⭐ Ch 16: Environmental Issues

1. 🟡 Explain the greenhouse effect and its consequences. How is ozone depletion caused? (3M) ⭐⭐⭐
   💡 Answer Hint: Greenhouse effect: CO₂, CH₄, N₂O, CFCs trap infrared radiation → Earth's temperature increases. Natural greenhouse effect is necessary (without it, Earth would be −18°C). But enhanced greenhouse effect due to fossil fuels → global warming → polar ice melting → sea level rise → climate change → extreme weather events. Ozone depletion: CFCs (chlorofluorocarbons) in stratosphere → UV breaks CFC → releases Cl atoms → Cl acts as catalyst: Cl + O₃ → ClO + O₂ and ClO + O → Cl + O₂. One Cl atom destroys thousands of O₃ molecules. Result: Ozone hole (first detected over Antarctica in 1985). Montreal Protocol (1987) phased out CFCs. UV effects: Skin cancer, cataracts, immune suppression, damage to phytoplankton.
2. 🟡 What is eutrophication? How does it affect aquatic ecosystems? (2M) ⭐⭐
   💡 Answer Hint: Eutrophication: Excessive nutrients (nitrogen, phosphorus from fertilizers, sewage, detergents) enter water bodies → algal bloom (excessive algae growth) → algae die → decomposed by bacteria → massive oxygen consumption → dissolved oxygen drops → aquatic animals (fish) die → water becomes smelly, unusable. Natural eutrophication: Takes thousands of years (lake → pond → marsh → land). Cultural eutrophication: Human activities accelerate it drastically. Key term: BOD increases with eutrophication. Indicator organism: Eichhornia (water hyacinth) — grows rapidly in eutrophic water.

📈 Previous Year Analysis — Chapter-wise Frequency (2020-2025)

✏️ Diagram Strategy — Biology's Secret Weapon for Extra Marks!

In Biology, a well-drawn and properly labeled diagram can earn you 2-3 extra marks per question. CBSE examiners specifically look for diagrams even when not explicitly asked. Here are the must-draw diagrams for the 2026 Board Exam:

📌 Must-Draw Diagram: Structure of a Human Sperm

This diagram appears almost every year in Board & NEET. Label all 3 regions (Head, Mid piece, Tail) with at least 8 parts for full marks.

✅ High-Probability Diagram Checklist — Print & Tick Off!

Practice drawing each of these at least once before exam day. Tick off as you complete:

🎯 24 diagrams × practice 2 times each = Board Ready in 3 hours!

🔢 Biotech & Ecology — Key Equations (Numerical Questions!)

These equations appear in 1-2 mark questions. Memorize the formula + what each symbol means.

💡 Exam Tip: For exponential growth (J-curve), use dN/dt = rN (no K). The difference from logistic is the absence of carrying capacity.

🎯 Also Check — Board Exam 2026 Important Questions

Class 10: Science · Maths · SST · Hindi · English · Science One-Shot

📜 Scientists & Discoveries — Quick Revision Table (1-Mark Questions!)

Students often lose marks on "Match the Following" or 1-mark factual questions. Memorize this table — it covers all frequently asked scientist-discovery pairs.

❓ Frequently Asked Questions