Zoology 2021 Paper II 50 marks Discuss

Q2

(a) What is cell cycle ? Draw an overview of molecular events during cell cycle. Discuss the role of protein kinases in the regulation of meiotic cell cycle. 20 (b) Lysosomes are polymorphic, justify. Draw a diagram representing the dynamic aspect of lysosome system. Write down the functions of lysosomes. 15 (c) Glycoproteins are asymmetrically distributed in a plasma membrane, explain. Give an overview of membrane function. 15

हिंदी में प्रश्न पढ़ें

(a) कोशिका चक्र क्या है ? कोशिका चक्र के दौरान आणविक घटनाओं का सिंहावलोकन कीजिए । अर्धसूत्री कोशिका चक्र के नियमन में प्रोटीन काइनेजेस की भूमिका का वर्णन कीजिए । 20 (b) लयनकाय (लाइसोसोम्स) बहुरूपी होते हैं, सिद्ध कीजिए । लाइसोसोम प्रणाली के गतिशील पहलू को दर्शाते हुए आरेखित कीजिए । लाइसोसोम्स के कार्यों को कलमबद्ध कीजिए । 15 (c) प्रद्रव्य (प्लाज्मा) झिल्ली में ग्लाइकोप्रोटीन असममित रूप से वितरित होते हैं, स्पष्ट कीजिए । झिल्ली के कार्यों का एक सिंहावलोकन प्रस्तुत कीजिए । 15

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Directive word: Discuss

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How this answer will be evaluated

Approach

Begin with a concise definition of cell cycle for part (a), then allocate approximately 40% of effort to the 20-mark section covering molecular events and MPF/maturation-promoting factor kinase regulation in meiosis. Devote ~30% each to parts (b) and (c), ensuring polymorphism justification with dynamic lysosomal diagrams and glycoprotein asymmetry with membrane function overview. Structure as integrated responses per sub-part without separate introductions, using diagrams as demanded.

Key points expected

  • Part (a): Definition of cell cycle phases (G1, S, G2, M) with molecular checkpoints; cyclin-CDK complexes and their oscillation; specific role of MPF (Cdc2/cyclin B) in meiosis I and II entry, including inhibitory phosphorylation and activation loops
  • Part (a): Distinction between mitotic and meiotic kinase regulation—Wee1, Cdc25 phosphatase, and anaphase-promoting complex/cyclosome (APC/C) in meiotic arrest and progression
  • Part (b): Justification of polymorphism—primary, secondary, residual bodies; autophagic, heterophagic, and crinophagic pathways; dynamic diagram showing endosome-lysosome fusion and membrane recycling
  • Part (b): Lysosomal functions—intracellular digestion, autophagy, apoptosis initiation, bone remodeling (osteoclasts), and storage diseases (Tay-Sachs, Gaucher) as applied examples
  • Part (c): Glycoprotein asymmetry—sugar moieties exclusively on extracellular face; flippase activity and membrane fluidity constraints; glycocalyx structure and cell recognition
  • Part (c): Membrane function overview—selective permeability, signal transduction, cell-cell adhesion, transport mechanisms (facilitated diffusion, active transport), and membrane potential maintenance

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Accurately distinguishes cyclin-dependent kinase regulation in meiosis versus mitosis; correctly identifies Wee1/Cdc25 control of MPF activity and the unique metaphase I arrest mechanism; precise on lysosomal polymorphism types and glycoprotein topological asymmetry with flippase mechanismBasic cell cycle phases correct but conflates mitotic and meiotic kinase regulation; lysosomal types listed without functional linkage; mentions glycoprotein asymmetry without explaining maintenance mechanismConfuses meiosis and mitosis controls; describes lysosomes as static organelles only; states glycoproteins are present but misses asymmetry entirely or reverses orientation
Diagram / labelling20%10Two clear diagrams: (a) molecular event timeline showing cyclin oscillations and kinase activation thresholds across meiotic divisions; (b) dynamic lysosomal system with labelled primary/secondary lysosomes, phagosome fusion, and membrane retrieval arrows; proper orientation and scaleOne adequate diagram with minor labelling errors; second diagram attempted but incomplete or static representation only; missing key structural details like mannose-6-phosphate receptor recyclingDiagrams absent or unlabelled; confusing scribbles without structural accuracy; fails to show dynamic/process aspects as specifically demanded
Examples & nomenclature15%7.5Precise nomenclature: MPF, APC/C, securin/separase for (a); mannose-6-phosphate receptor, proton pump V-ATPase, cathepsins for (b); flippases, scramblases, glycocalyx components (selectins, integrins) for (c); cites Indian-relevant lysosomal storage disorders if applicableGeneric terms like 'enzymes' or 'proteins' instead of specific kinases; lysosomal enzymes unnamed; glycoprotein examples limited to vague 'cell surface markers'Incorrect terminology (e.g., 'mitosis-promoting factor' for MPF); invents non-existent structures; confuses lysosomes with peroxisomes or glycocalyx with basement membrane
Process explanation25%12.5Stepwise mechanistic explanation: for (a) phosphorylation cascade leading to nuclear envelope breakdown and sister chromatid cohesion release in meiosis; for (b) endocytic pathway maturation and substrate degradation sequence; for (c) co-translational glycosylation and vesicular trafficking maintaining asymmetryLists events sequentially without causal linkages; describes outcomes (DNA replication, digestion) without underlying molecular mechanisms; membrane transport mentioned without directionalityIsolated facts without process logic; confuses cause and effect; describes structures without explaining how they achieve functional outcomes
Evolutionary / applied context15%7.5Connects meiotic kinase conservation to yeast (Schizosaccharomyces pombe) studies and clinical relevance of aneuploidy; lysosomal diseases (Tay-Sachs prevalence in Ashkenazi Jewish/Indian Parsi populations) and autophagy in neurodegeneration; membrane asymmetry in immune recognition and viral entry (HIV gp120 binding)Brief mention of cancer for cell cycle or lysosomal storage diseases by name without population context; generic statement about membrane importance in cell signalingNo applied or evolutionary context; misses biomedical significance entirely; irrelevant digressions into cell theory history

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