UPSC Zoology 2025

The directive 'write short notes' demands concise, information-dense responses for each sub-part. Allocate approximately 30 words/2 minutes per sub-part (a)-(d), reserving 30 words/3 minutes for part (e) which requires a diagram. Structure each note as: definition → key features → significance/example. For (e), prioritize a neat, correctly proportioned diagram with 8-10 labels over extensive text description.

• (a) Metagenesis: Define as alternation of generations between sexual (medusa) and asexual (polyp) phases in Cnidaria; specify Obelia as classic example; note that metagenesis is distinct from true alternation of generations (no meiosis in spore formation).
• (b) Book lungs: Identify as respiratory organs in arachnids (spiders, scorpions); describe stacked leaf-like lamellae in hemolymph-filled chamber; contrast with book gills in Limulus; note limitation for active metabolism.
• (c) Paedomorphosis: Define as retention of juvenile traits in adult; distinguish neoteny (delayed somatic development) from progenesis (precocious sexual maturation); cite axolotl (Ambystoma mexicanum) and human 'fetalization' as examples.
• (d) Torsion and detorsion: Explain 180° counter-clockwise rotation of visceral mass in gastropod larvae; describe consequences (asymmetry, loss of gill/auricle, torsion of nerve cords); note detorsion in some opisthobranchs and its evolutionary reversal.
• (e) Human eye diagram: Include cornea, iris/pupil, lens, ciliary body, suspensory ligaments, retina (rods/cones), fovea, optic disc, sclera, choroid; briefly state photoreception and image formation functions.

The directive 'describe' demands systematic, detailed exposition with appropriate illustrations. Allocate approximately 40% of time/words to part (a) given its 20 marks, and 30% each to parts (b) and (c). Structure: brief comparative introduction, then detailed anatomical progression from cyclostomes to mammals for (a); illustrated life cycle with gemmule formation for (b); caste system and symbiotic digestion for (c). Conclude with evolutionary significance across all three parts.

• Part (a): Progressive complexity from agnathans (cyclostomes with intra-oral tongue and keratinized teeth) through gnathostomes—fish (J-shaped stomach), amphibians (short intestine, liver, pancreas), reptiles (complete septum, muscular stomach), birds (gizzard, crop, cloaca), to mammals (differentiated dentition, complex stomach in ruminants, elongated intestine with caecum and vermiform appendix); mention Indian species like Labeo rohita, Naja naja, Bos indicus
• Part (a): Accessory digestive glands—liver (hepatic portal system), pancreas (exocrine and endocrine functions), gall bladder; their comparative development across vertebrate classes
• Part (b): Asexual reproduction—budding (external/internal), fragmentation, gemmule formation (thesocytes, spicule coat, Indian freshwater sponges like Eunapius/Ephydatia); sexual reproduction—oviparous vs viviparous species, spermatozoa transfer via water currents, internal fertilization, amphiblastula and parenchymula larvae with fate of cell layers
• Part (c): General features—soft-bodied, polymorphic, hemimetabolous, cryptic habitat; distribution—tropical to temperate, Indian species (Coptotermes, Odontotermes) causing agricultural damage; social organization—reproductive caste (king, queen, neotenics), sterile castes (workers, soldiers with mandibulate/nasute types), pheromonal regulation, trophallaxis
• Part (c): Symbiotic digestion—flagellates (Trichonympha, Holomastigotoides) in hindgut for cellulose breakdown; mound architecture in Odontotermes; economic importance as pests and soil engineers

The directive 'describe' demands detailed, systematic exposition of mechanisms and life cycles with visual support where specified. Allocate approximately 40% of time and words to part (a) given its 20 marks, 30% each to parts (b) and (c). Structure: brief comparative introduction on reproductive strategies across animal groups; for (a) categorize amphibian parental care types with mechanisms and Indian examples; for (b) draw and label 6-8 stages of Pheretima life cycle with developmental details; for (c) classify protozoan nutrition modes with cellular mechanisms. Conclude with evolutionary significance of these adaptations.

• Part (a): Types of parental care in amphibians—egg attendance (Rhinoderma darwinii gastric brooding), transport (Phyllomedusa, Hyla), feeding (Neotropical poison frogs), and nest guarding (Indian bullfrog Hoplobatrachus tigerinus); hormonal and behavioural mechanisms
• Part (a): Mechanistic details—male pregnancy in Syngnathidae analogues, skin feeding in Caecilian amphibians (Ichthyophis glutinosus from Western Ghats), oophagy and trophic egg production
• Part (b): Complete life cycle stages of Pheretima posthuma—cocoon formation, embryonic development within cocoon, hatching as young worm, juvenile growth, sexual maturity; alternation of generations not applicable but direct development emphasized
• Part (b): Diagrammatic representation showing: cocoon structure, cleavage stages, gastrulation, organogenesis, young worm emergence; accurate labelling of clitellum role in cocoon production
• Part (c): Holozoic nutrition (ingestion, digestion, egestion—Amoeba, Paramecium), holophytic/autotrophic (Euglena with chloroplasts), saprozoic/saprophytic (absorption of dissolved organic matter—Trypanosoma), parasitic (Plasmodium, Entamoeba histolytica), mixotrophic and pinocytosis
• Part (c): Cellular mechanisms—phagocytosis, food vacuole formation, intracellular digestion, contractile vacuole role in osmoregulation during nutrition

The directive 'discuss' in part (a) demands critical elaboration with balanced coverage of structure and function, while 'illustrated account' in (b) and 'explain' in (c) require visual integration and causal reasoning respectively. Allocate approximately 40% of time/words to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure as: brief comparative introduction to vertebrate reproductive and structural diversity → systematic treatment of each sub-part with integrated diagrams → concluding synthesis on evolutionary trends in vertebrate adaptation.

• Part (a): Testis structure showing seminiferous tubules, Leydig cells, Sertoli cells; ovary showing follicular stages, corpus luteum, stromal tissue; hormones (testosterone, estrogen, progesterone, inhibin, relaxin) with target organs and feedback mechanisms
• Part (a): Hypothalamic-pituitary-gonadal axis integration and functional coordination between male and female hormonal systems
• Part (b): Anapsid (turtle), Synapsid (mammal-like reptiles), Diapsid (lepidosaurian and archosaurian variants) skull types with temporal fenestrae number and position
• Part (b): Evolutionary progression from anapsid to diapsid condition and secondary modifications in snakes and birds
• Part (c): Anadromous (salmon, Hilsa ilisha), catadromous (eel), potamodromous (Indian major carps), oceanodromous migrations with specific Indian examples
• Part (c): Physiological triggers (photoperiod, temperature, hormonal control via pituitary-thyroid axis), navigation mechanisms, and ecological/economic significance for fisheries management

The directive 'write short notes' demands concise, information-dense responses for each sub-part with equal weightage (10 marks each). Allocate approximately 150 words and 10-12 minutes per sub-part. Structure each note with a precise definition, 2-3 key features/mechanisms, and one relevant example. No elaborate introduction or conclusion is needed; prioritize factual accuracy and technical terminology over narrative flow. For (a) and (e), emphasize geographical distribution and conservation significance; for (b) and (d), focus on physiological mechanisms; for (c), integrate molecular genetics with disease ecology.

• (a) Biodiversity hotspots: Definition by Myers (1988), criteria (≥1,500 endemic vascular plants, ≥70% habitat loss), mention of Himalaya and Western Ghats as Indian hotspots, conservation significance
• (b) Navigation in birds: Sun compass, star compass, magnetic compass (magnetite-based), olfactory maps, integration of multiple cues with example of Arctic tern or Indian homing pigeon studies
• (c) Sickle cell anaemia: Molecular basis (Glu→Val substitution at β6 position), HbS polymerization under hypoxia, heterozygote advantage/malaria resistance, distribution in Indian tribal populations (Saurashtra, Nilgiris)
• (d) Circadian rhythms: Endogenous oscillators (suprachiasmatic nucleus), zeitgebers (light, temperature), molecular clock mechanism (Clock/Bmal1, Per/Cry feedback loops), chronobiology applications
• (e) Biome: Definition as major ecological unit, distinction from ecosystem, classification by Whittaker (temperature-precipitation matrix), Indian examples (tropical thorn forest, montane forests), climate-vegetation coupling

The directive 'explain' demands clear exposition with causal reasoning across all three parts. Allocate approximately 40% of time/words to part (a) given its 20 marks, and roughly 30% each to parts (b) and (c). Structure as: brief definitions for each sub-part, followed by systematic elaboration of requested components (types/sources/consequences/controls for air pollution; mechanism/examples for alarm pheromones; technique/applications for DNA fingerprinting), with a concluding synthesis on chemical communication and molecular techniques in zoology.

• Part (a): Definition of air pollution (WHO/EPA criteria); classification into primary vs secondary pollutants, particulate vs gaseous; major sources (natural: dust, volcanic; anthropogenic: vehicular, industrial, thermal power, agricultural burning); health and ecological consequences (respiratory diseases, acid rain, global warming, eutrophication); control measures (legislative: Air Act 1981, BS-VI norms; technological: scrubbers, electrostatic precipitators, catalytic converters; biological: urban greening)
• Part (b): Definition of pheromones (Karlson & Lüscher 1959); distinction from allomones and kairomones; alarm pheromone mechanism (release-detection-response cascade); specific examples: honeybee (Apis mellifera) isoamyl acetate, ant (Formica) formic acid, fish (Ostariophysi) alarm substance (Schreckstoff), aphids (E)-β-farnesene
• Part (c): Definition of DNA fingerprinting (Alec Jeffreys 1984); mechanism details: VNTR/minisatellite or STR analysis, PCR amplification, gel electrophoresis/Southern blotting, DNA profiling; forensic applications: criminal identification (Nirbhaya case), paternity disputes, wildlife forensics (tiger/poaching cases), disaster victim identification, exoneration of falsely accused

This question demands clear explanation across three distinct domains: statistical methodology, microscopy instrumentation, and aquaculture practice. Allocate approximately 40% of time/words to part (a) given its 20 marks, with ~30% each to parts (b) and (c). Structure with brief introductions for each part, detailed explanatory body covering all directive components, and conclude with significance/applications. For (a), include a worked numerical example; for (b), draw the optical path; for (c), emphasize Indian species like Penaeus monodon and Litopenaeus vannamei.

• Part (a): Definition of Student's t-test as a parametric test for comparing means; significance in biological research for small sample sizes and hypothesis testing; correct formula t = (x̄₁ - x̄₂) / √[s²(1/n₁ + 1/n₂)] or paired/unpaired variants; step-by-step calculation with hypothetical biological data (e.g., growth rates of two fish groups)
• Part (a): Assumptions of t-test (normal distribution, homogeneity of variance, independence); interpretation of t-table values; degrees of freedom calculation; Type I/II error relevance
• Part (b): Principle of fluorescence microscopy based on fluorophore excitation and emission at longer wavelengths; Stokes shift concept; distinction from bright-field and phase-contrast microscopy
• Part (b): Instrumentation components: UV/visible light source (mercury/xenon arc lamp or laser), excitation filter, dichroic mirror, emission filter, objective lens, and detector; schematic of epifluorescence configuration
• Part (b): Applications in biological research: immunofluorescence, FISH, GFP tagging, live-cell imaging, cancer detection, and neurobiology studies
• Part (c): Suitable prawn species for culture: Penaeus monodon (giant tiger prawn), Litopenaeus vannamei (Pacific white shrimp), Macrobrachium rosenbergii (giant freshwater prawn); their distribution and aquaculture suitability in Indian context
• Part (c): Culture methods: extensive (traditional tidal ponds), semi-intensive (fertilized ponds with supplementary feeding), intensive (high stocking density with aeration and formulated feed); hatchery/nursery rearing, water quality management, and disease prevention (WSSV, EMS)
• Part (c): Brackishwater versus freshwater culture systems; polyculture with finfish; MPEDA guidelines and coastal aquaculture authority regulations in India

The directive 'describe' demands comprehensive coverage with factual precision across all three parts. Allocate approximately 40% of time/words to part (a) given its 20 marks, 30% each to parts (b) and (c). Structure: brief definitional opening for (a), then systematic treatment of filariasis; illustrated carbon cycle with clear biotic-abiotic compartments; and behavioural examples with evolutionary interpretation for (c). No conclusion needed—end with preventive/applied notes.

• Part (a): Precise distinction between infectious (pathogen-caused) and communicable (transmissible between hosts) diseases; Wuchereria bancrofti, Brugia malayi, Brugia timori as causative agents with Culex/Anopheles/Mansonia vectors; clinical staging (asymptomatic microfilaraemia, acute lymphadenitis, chronic elephantiasis); diagnostic methods (night blood smear, ICT card test, USG for adult worms); DEC/albendazole/ivermectin treatment; MDA strategy under National Filaria Control Programme
• Part (b): Complete carbon cycle diagram showing atmospheric CO2, producers (photosynthesis), consumers (respiration), decomposers, fossil fuels, and oceanic carbonate reservoir; quantification of pools and fluxes; mention of biological pump and anthropogenic perturbation
• Part (c): Sexual conflict defined as antagonistic coevolution between sexes over optimal reproductive strategies; intralocus and interlocus conflict; selfish genetic elements (segregation distorters, meiotic drive); specific examples—Drosophila seminal fluid proteins, water strider (Gerris) coercive mating, bedbug traumatic insemination, stalk-eyed fly eye-span sexual selection
• Part (c) continued: Evolutionary arms race and chase-away sexual selection; cost-benefit analysis for each sex; resolution mechanisms (sensory exploitation, cryptic female choice)
• Integrated applied context: One Health approach for filaria; carbon sequestration relevance to climate policy; behavioural ecology implications for conservation breeding

Write short notes demands concise, information-dense coverage of all five sub-parts with equal marks weighting. Allocate approximately 30 words per sub-part (150 words total), spending roughly 3 minutes per part. Structure each sub-part as: definition → key features → significance/application. For (a) emphasize cis-Golgi network and mannose-6-phosphate tagging; for (b) highlight amphibian oocyte relevance; for (c) include Indian prevalence data; for (d) use clear parental vs. recombinant gamete ratios; for (e) cite Indian examples like Western Ghats salamanders or sympatric cichlids.

• (a) Protein sorting: Cis-, medial-, trans-Golgi compartments; mannose-6-phosphate receptor mechanism for lysosomal enzymes; clathrin-coated vesicles; constitutive vs. regulated secretion pathways
• (b) Lampbrush chromosomes: Extended diplotene bivalents in amphibian oocytes; lateral loops of active transcription; RNA polymerase activity; morphological marker for gene expression studies
• (c) Thalassemia: α and β chain mutations; microcytic hypochromic anemia; hemoglobin electrophoresis (HbA2 elevation in β-thalassemia trait); prenatal diagnosis; high prevalence in Indian subcontinent (Gujarat, Maharashtra, Punjab)
• (d) Linkage phases: Coupling (cis) configuration AB/ab vs. repulsion (trans) Ab/aB; parental vs. recombinant gamete frequencies; test cross ratios deviating from 1:1:1:1; recombination frequency calculation
• (e) Speciation modes: Allopatric by geographic isolation (vicariance/dispersal) with Indian examples like Nicobar megapode; sympatric by polyploidy, host-race formation, or disruptive selection; reinforcement and prezygotic isolation

The directive 'explain' demands clear causal reasoning and elaboration of mechanisms. Structure your answer with a brief integrated introduction, then allocate approximately 20% time/words to (a)(i) on membrane composition, 20% to (a)(ii) comparing diffusion types, 30% to (b) on mutations and natural selection, and 30% to (c) with two complete pedigrees. Conclude by linking molecular mechanisms to evolutionary outcomes.

• (a)(i) Fluid mosaic model: phospholipid bilayer structure, integral and peripheral proteins, cholesterol, carbohydrate chains (glycocalyx); mention Singer-Nicolson model
• (a)(ii) Distinction between simple diffusion (passive, no protein, down gradient, e.g., O2, CO2) and facilitated diffusion (protein-mediated, passive, specific, e.g., GLUT transporters, aquaporins); include channel vs carrier proteins
• (b) Types of mutations (gene, chromosomal, genome), sources (spontaneous, induced), role in generating genetic variation; Hardy-Weinberg equilibrium reference; natural selection acting on variation with examples (antibiotic resistance, industrial melanism in Biston betularia)
• (c) Autosomal recessive pedigree: consanguinity, equal sex ratio, skipped generations; example: sickle cell anemia, thalassemia (Indian context) or albinism
• (c) Sex-linked inheritance pedigree: X-linked recessive showing criss-cross inheritance, more males affected, no male-to-male transmission; example: hemophilia, color blindness, or Duchenne muscular dystrophy
• Pedigree symbols: squares (male), circles (female), shaded (affected), half-shaded (carrier), lines showing relationships and generations numbered with Roman numerals

The directive 'describe' demands systematic, detailed exposition of mechanisms and processes. Allocate approximately 20% (400-500 words) to part (a) covering synthetic theory and mimicry equally, 35% (700-800 words) to part (b) on chain elongation given its 15 marks, and 30% (600-700 words) to part (c) on ribozymes with emphasis on technological applications. Structure with brief introductions for each sub-part, detailed mechanistic bodies with diagrams, and concluding significance statements.

• For (a)(i): Neo-Darwinian synthesis integrating Mendelian genetics, population genetics (Hardy-Weinberg), and natural selection; contributions of Dobzhansky, Mayr, Simpson, and Indian scientist P. Maheshwari on speciation
• For (a)(ii): Batesian mimicry (palatable mimic resembles unpalatable model, e.g., Papilio polytes female mimicking Pachliopta aristolochiae in India), Müllerian mimicry (mutual unpalatability, e.g., Danaus and Euploea), aggressive mimicry (e.g., Photuris fireflies), and automimicry
• For (b): Initiation complex formation, 70S ribosome assembly, charged tRNA entry to A-site, peptidyl transferase activity (23S rRNA), translocation (EF-G/GTP), and termination; contrast with eukaryotic 80S ribosome
• For (c): RNA catalysis via acid-base mechanism, self-splicing introns (Group I and II), RNase P, hammerhead ribozyme structure; technological applications including RNAi therapeutics, synthetic biology, and COVID-19 mRNA vaccine stabilization
• Evolutionary significance: RNA world hypothesis bridging genotypes and phenotypes, molecular basis of evolutionary novelty through gene duplication and neo-functionalization

The directive 'describe' demands systematic, detailed exposition of processes and features. Allocate approximately 40% of time/words to part (a) on rDNA construction and cloning (20 marks), 30% each to part (b) on horse evolution (15 marks) and part (c) on nomenclature (15 marks). Structure: brief introduction linking biotechnology, evolution and taxonomy as pillars of modern zoology; body with three clearly demarcated sections; conclusion emphasizing how these domains interconnect in contemporary biological research.

• Part (a): Isolation of target DNA and vector DNA; restriction enzyme digestion; ligation using DNA ligase; transformation into host cells; selection and screening of recombinant clones
• Part (a): Detailed description of cloning vectors (plasmids, cosmids, BACs, YACs) and host systems (E. coli, yeast); mention of antibiotic resistance and blue-white screening
• Part (b): Sequential morphological changes from Eohippus to Equus: reduction of toes (polydactyly to monodactyly), elongation of limbs, hypsodonty in dentition, enamel complexity, cranial and facial elongation
• Part (b): Environmental drivers of horse evolution: forest to grassland transition, cursorial adaptation for speed, grazing diet specialization; mention of fossil evidence from North America and India (Siwalik deposits)
• Part (c): Binomial nomenclature principles; priority rule, type concept, synonymy; role of ICZN; mandatory Latinization; authorship and date citation; rules for naming new species and higher taxa

The directive 'write on' demands descriptive coverage with precise terminology across all five embryology, biochemistry and neurophysiology topics. Allocate approximately 30 words per sub-part (150 words total), spending roughly equal time on each since all carry equal marks. Structure each part as: definition → mechanism/structure → functional significance. For (a) and (e), emphasize sequential steps; for (b) and (d), prioritize accurate diagrams with labelling; for (c), focus on energy profile curves and transition state theory.

• (a) Block to polyspermy: Fast electrical block (depolarization of egg membrane) and slow permanent block (cortical granule exocytosis → zona pellucida modification/hardening); mention species-specific variations in amphibians vs mammals
• (b) Fate map of frog embryo: Presumptive germ layers on blastula surface (ectoderm—animal pole, mesoderm—marginal zone, endoderm—vegetal pole); reference Vogt's vital staining experiments; significance for developmental patterning
• (c) Activation energy mechanism: Enzyme lowers activation energy (Ea) by stabilizing transition state; Michaelis-Menten kinetics relevance; energy profile diagram showing uncatalyzed vs catalyzed reaction pathways
• (d) Dipeptide unit structure: Peptide bond formation (condensation/dehydration synthesis); planar trans configuration; phi and psi angles; Ramachandran plot constraints; partial double bond character restricting rotation
• (e) Synaptic transmission: Electrical vs chemical synapses; neurotransmitter release (Ca²⁺-dependent exocytosis), postsynaptic receptor binding, EPSP/IPSP generation; synaptic delay and one-way conduction

The directive 'describe' demands systematic, detailed exposition of structures, reactions and developmental sequences with visual support where specified. Allocate approximately 40% effort to part (a) covering Krebs cycle NADH reactions and chemiosmosis (20 marks), 30% to part (b) on leukocyte characteristics and functions (15 marks), and 30% to part (c) on cardiac embryogenesis with diagrams (15 marks). Structure with brief contextual introductions, detailed body addressing each sub-part sequentially, and concluding synthesis on physiological integration.

• Part (a)(i): Three specific NADH-producing reactions in Krebs cycle — isocitrate → α-ketoglutarate (catalyzed by isocitrate dehydrogenase), α-ketoglutarate → succinyl-CoA (α-ketoglutarate dehydrogenase complex), and malate → oxaloacetate (malate dehydrogenase) — with correct substrates, products and enzyme names
• Part (a)(ii): Proton gradient mechanism — ETC complexes I, III, IV pumping H+ to intermembrane space, creating electrochemical gradient; ATP synthase (F0F1) structure and rotational catalysis; P/O ratios and chemiosmotic theory (Mitchell)
• Part (b): Lymphocytes — T-cell subsets (helper, cytotoxic, regulatory), B-cell antibody production, NK cells; monocytes — differentiation to macrophages and dendritic cells, antigen presentation; neutrophils — granule types (azurophilic, specific), respiratory burst, NETosis; comparative morphology and lifespan
• Part (c): Mammalian heart development — cardiogenic mesoderm, primary and secondary heart fields, heart tube formation, looping (dextral), septation (atrial, ventricular, conotruncal), valve formation; critical stages with species reference (mouse/human day equivalents)
• Diagrammatic requirements for (c): Sequential illustrations showing sagittal sections of developing heart from cardiogenic plate to four-chambered structure, with labels for sinus venosus, truncus arteriosus, bulbus cordis, primitive ventricle, atrium, and septation structures

The directive 'explain' demands clear causal reasoning and mechanistic detail across all sub-parts. Allocate approximately 40% of time/words to part (a) [20 marks], 30% to part (b) [15 marks], and 30% to part (c) [15 marks]. Structure: brief introduction noting the interconnected themes of molecular function, immune defense, and developmental patterning; then address each sub-part sequentially with diagrams integrated; conclude with a synthesis on how molecular mechanisms scale from protein function to organismal biology.

• For (a)(i): Cooperative binding, Hill coefficient (n≈2.8-3.0), T-R state transition, and how sigmoidal curve enables efficient O₂ loading/unloading
• For (a)(ii): HbA (α₂β₂) vs HbF (α₂γ₂), γ-chain substitutions (Ser/Ala at position 136), higher O₂ affinity of HbF, and physiological significance for placental O₂ transfer
• For (b): TCR-MHC Class I recognition, perforin-granzyme pathway, Fas-FasL mediated apoptosis, and memory T-cell formation
• For (c): Definition of homeotic genes as selector genes, Hox gene clusters, colinearity principle, and specific role in chick anteroposterior axis formation (e.g., Hoxb-1, Hoxc-6 expression patterns)
• Cross-cutting: Mention of 2,3-BPG modulation in (a), clinical relevance of HbF in thalassemia/sickle cell, and evolutionary conservation of Hox genes from Drosophila to vertebrates

The directive 'describe' demands systematic, detailed exposition of biological processes and structures. Allocate approximately 40% of time/words to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure: brief comparative introduction noting avian vs mammalian differences → sequential treatment of (a) fertilization stages with diagram, (b) cholesterol structure drawing with health applications, (c) ovarian hormone cascade with feedback loops → concluding synthesis on reproductive biology integration.

• (a) Chick fertilization: sperm entry → germinal disc → pronuclear fusion → cleavage initiation; diagram showing infundibulum, magnum, isthmus, uterus sequence
• (a) Polyspermy prevention mechanisms in birds (fast vs slow block) and early blastoderm formation
• (b) Accurate steroid nucleus structure (four fused rings: three cyclohexane, one cyclopentane) with hydroxyl at C3 and alkyl side chain at C17
• (b) Cholesterol roles: membrane fluidity, steroid hormone precursor, bile acid synthesis; diseases: atherosclerosis, familial hypercholesterolemia, gallstones
• (c) Estrogen, progesterone, inhibin secretion patterns across follicular and luteal phases with hypothalamic-pituitary feedback
• (c) Ovarian hormones in implantation, pregnancy maintenance, and menstrual/estrous cycle regulation in comparative context