🌿 Biology Answer Key
Complete solutions based on the question paper | NEET / Higher Secondary pattern
PART I
Answer any 3 from 1 to 5 · 1 score each
1.Genetic mechanism preventing inbreeding depression in angiosperms?
Ans: (d) Self-Incompatibility
2.Correct sequence for recombinant DNA steps.
Ans: (b) (i) Isolation → (iv) Amplification → (ii) Insertion → (iii) Gene product → (v) Downstream processing
3.Indian crop variety patented by US company in 1997.
Ans: Basmati rice
4.Status of human population reflected in age pyramid (declining/stable/expanding).
Ans: (a) Declining population
5.Energy available to tertiary consumer if producer has 10,000 J.
Ans: 10 Joules (10% law: 10,000 → 1,000 → 100 → 10 J)
PART II
Answer any 9 from 6 to 16 · 2 scores each
6.Why some flowers don't require emasculation but bagging is essential?
Ans: Unisexual flowers (e.g., maize, coconut) lack both sex organs in same flower, so self-pollination is impossible — emasculation not needed. Bagging prevents unwanted cross-pollination by insects/wind.
7.Organic materials of exine & intine; property of exine that protects pollen.
Ans: Exine → sporopollenin (resistant to high temp, acids, enzymes). Intine → cellulose & pectin. Sporopollenin protects pollen from harsh environments.
8.Match the following (DNA Ligase, Exonucleases, Taq Polymerase, Restriction Endonuclease).
DNA Ligase → D. Joins the DNA fragments
Exonucleases → A. Remove nucleotides from ends of DNA
Taq Polymerase → B. Extends Primer on a DNA template
Restriction Endonuclease → C. Cut DNA at Specific Position
9.Why was Drosophila melanogaster selected by Morgan? (two reasons)
Ans: (1) Short life cycle (~2 weeks) → quick generational study. (2) Large number of offspring. (3) Distinct heritable traits. (4) Simple chromosome number (4 pairs).
10.Hormonal control of spermatogenesis (complete chart) & part containing enzymes for fertilization.
Ans: Hypothalamus → GnRH → Anterior Pituitary → FSH & LH. FSH acts on Sertoli cells → ABP; LH acts on Leydig cells → androgens. Enzymes: Acrosome (head of sperm) contains hyaluronidase for fertilization.
11.Ecological pyramid equation: dN/dt = rN((K-N)/K). What does K stand for?
Ans: K = Carrying capacity (maximum population size environment can sustain).
12.Identify interactions: barnacles on whale, mycorrhiza, tortoise & goats, ticks & dogs.
Ans: (a) Commensalism (+/0) (b) Mutualism (+/+) (c) Competition (-/-) (d) Parasitism (+/-)
13.Two limitations of ecological pyramids.
Ans: 1. Do not account for same species occupying multiple trophic levels. 2. Do not consider the role of decomposers. 3. Assume simple food chains, ignore food webs. (any two)
14.Processes where earthworm & bacteria carry out decomposition.
Ans: Earthworm → fragmentation (breaks detritus into smaller pieces). Bacteria → decomposition / humification & mineralisation (convert organic matter into inorganic nutrients).
15.Transgenic animals: definition, largest number among existing, three purposes.
Ans: Animals with foreign gene inserted. Largest number: Mice. Purposes: (i) Study gene regulation/disease models, (ii) Produce pharmaceutical proteins, (iii) Vaccine safety testing.
16.Primary productivity definition, equation, and secondary productivity.
Ans: Rate of synthesis of organic matter by producers. Equation: GPP – R = NPP. Secondary productivity: Rate of new organic matter formation by consumers.
PART III
Answer any 3 from 17 to 20 · 3 scores each
17.Identify figure (anther/microsporangium), parts B,C,D,E, function of E.
Ans: Figure = T.S of anther. B: Pollen sac, C: Pollen grains, D: Tapetum, E: Connective tissue/vascular bundle. Function of E: Provides nourishment & structural support; vascular bundle supplies water & nutrients.
18.Stirred-tank bioreactor features + why product cannot be marketed directly after downstream processing?
Ans: Features: stirring system, foam breaker, sparger for aeration, pH & temperature control, ports for addition/removal. Reason: Product is impure & mixed with culture media/cell debris; requires purification, quality control & formulation before marketing.
19.(a) Transgenic animals definition (b) name largest existing transgenic animal (c) three purposes.
Ans: (a) Animals with foreign DNA introduced. (b) Mice (transgenic mice). (c) 1) Study disease models, 2) Produce therapeutic proteins, 3) Test vaccine safety, 4) Study gene regulation.
20.(a) Start codon & amino acid (b) two stop codons (c) Why genetic code is degenerated?
Ans: (a) AUG – Methionine. (b) UAA, UAG, UGA (any two). (c) Multiple codons specify the same amino acid → minimizes harmful effects of mutations.
PART IV (Second Section)
Answer any 3 from 1 to 5 · 1 score each
1.Odd one out: Bone marrow, Spleen, Lymph nodes, Tonsil. Reason?
Ans: Tonsil – it is a mucosa-associated lymphoid tissue (MALT), while others are typical secondary lymphoid organs. (Bone marrow is primary lymphoid organ).
2.LNG-20 : Hormone releasing IUD :: Multiload 375 : ______
Ans: Copper releasing IUD
3.Symbols in pedigree analysis: square with cross, circle with cross, diamond.
Ans: Affected male, Affected female, Sex unspecified / miscarriage.
4.Milk produced during initial few days of lactation is called?
Ans: Colostrum
5.Expand HGP.
Ans: Human Genome Project
PART V
Answer any 9 from 6 to 16 · 2 scores each
6.(a) All copulations do not lead to fertilization — why? (b) After ovulation, remaining part of Graafian follicle transforms into?
Ans: (a) Reasons: absence of ovulation, low sperm count, blocked tubes, wrong timing, hormonal issues. (b) Corpus luteum.
7.Amniocentesis & why banned in India.
Ans: Prenatal diagnostic technique to detect genetic disorders. Banned: To prevent misuse for sex determination and female feticide.
8.Beta-globin sequences: (i) Val-His-Leu-Thr-Pro-Glu-Glu (ii) Val-His-Leu-Thr-Pro-Val-Glu. Which belongs to sickle cell anemia? Reason.
Ans: Sequence (ii) with Val at 6th position. Reason: Sickle cell anemia results from substitution of glutamic acid by valine at 6th position of beta chain.
9.Morgan selected Drosophila — two reasons.
Ans: Short generation time, large number of progeny, easily observable variations, simple karyotype.
10.Hormonal control of spermatogenesis (chart completion) & part of sperm with enzymes.
Ans: Hypothalamus → GnRH → Pituitary → FSH & LH → Testis. Acrosome (head) contains hydrolytic enzymes (hyaluronidase, acrosin) for fertilization.
11.Stirred-tank bioreactor features (any four).
Ans: Agitator, foam breaker, sparger for oxygen, pH control, temperature regulation, sampling ports.
12.Name the experiment conducted by Urey & Miller; aim of experiment.
Ans: Miller-Urey experiment. Aim: to simulate early Earth conditions and demonstrate formation of organic compounds (amino acids) from inorganic precursors.
13.Birds beaks in Darwin's journey: identify birds & island, evolutionary phenomenon.
Ans: Darwin's finches, Galapagos Islands. Phenomenon: Adaptive radiation.
14.Identify diagram (antibody structure) & label parts X, Y.
Ans: Diagram = Antibody (Immunoglobulin). X: Antigen binding site (Fab), Y: Constant region / Fc region.
15.Karyotype disorders: 45A+XY/XX ; 44A+XO ; 44A+XXY. Name disorders & one symptom each.
Ans: Turner syndrome (45, XO) → short stature, webbed neck. Klinefelter syndrome (47, XXY) → sterility, gynecomastia. (45A+XY/XX is Turner mosaic)
16.STI meaning, two examples, two preventive measures.
Ans: Sexually Transmitted Infections. Examples: Gonorrhea, Syphilis, HIV. Prevention: Condom use, mutual monogamy, vaccination (HPV).
PART VI
Answer any 3 from 17 to 20 · 3 scores each
17.Complete table: Karyotype 45A+XY/XX → disorder? 44A+XO → disorder? 44A+XXY → disorder? Write one symptom for each.
Ans: 45A+XY/XX → Turner syndrome (mosaic) / 44A+XO → Turner syndrome (classical) / 44A+XXY → Klinefelter syndrome.
Symptoms: Turner — short stature, underdeveloped ovaries; Klinefelter — small testes, gynecomastia.
Symptoms: Turner — short stature, underdeveloped ovaries; Klinefelter — small testes, gynecomastia.
18.Incidents of STIs high in 15-24 age. (a) STI meaning (b) two STIs (c) two preventive measures.
Ans: (a) Infections spread through sexual contact. (b) Chlamydia, Genital herpes, Syphilis. (c) Consistent condom use, limiting number of sexual partners, regular screening.
19.Evil Quartet: write A and B; two methods of biodiversity conservation with examples.
Ans: A: Habitat loss, B: Over-exploitation. Methods: In-situ (National Park, Sanctuary) and Ex-situ (Zoo, Gene bank).
20.Genetic code: (a) start codon & amino acid (b) two stop codons (c) why degeneracy?
Ans: (a) AUG → Methionine. (b) UAA, UAG, UGA. (c) Multiple codons encode same amino acid, reducing mutation impact.