Model Papers
MODEL PAPERS — new questions, not real past papers. Each paper follows the Dec 2025 pattern exactly: Section A 10 MCQs x 1 = 10 (all compulsory), Section B attempt any 4 of 6 short questions x 5 = 20, Section C attempt any 3 of 5 long questions x 10 = 30. Total 60 marks, 3 hours. No model-paper question is copied from the Dec 2025 paper.
Contents: Paper 1 · Paper 2 · Paper 3 · Paper 4 · Paper 5
Model Paper 1 — 60 marks, 3 hours
Section A — 10 x 1 = 10 (all compulsory)
A1. Water moves into a root cell when the cell's water potential is:
Answer: (b) Lower than the soil solution. Water flows from higher to lower water potential.
A2. Which process is responsible for the upward pull of water in tall trees?
Answer: (b) Transpiration pull. Transpiration pull, transmitted by cohesion, is the main force in tall trees.
A3. Sieve tube sap is rich in:
Answer: (b) Sucrose. Sucrose is the main transported sugar.
A4. The girdling experiment shows that organic food moves through:
Answer: (b) Phloem. Removing bark interrupts phloem and food accumulates above the girdle.
A5. P700 is the reaction centre of:
Answer: (b) Photosystem I. PSI reaction centre is P700; PSII is P680.
A6. The net ATP gain from glycolysis per glucose is:
Answer: (a) 2. Gross 4 ATP minus 2 invested = net 2 ATP.
A7. A competitive inhibitor increases the apparent:
Answer: (b) Km. More substrate overcomes competition; apparent Km rises, Vmax unchanged.
A8. Nitrite is reduced to ammonia in the:
Answer: (b) Chloroplast/plastid. Nitrate reduction is cytosolic; nitrite reduction is plastidic.
A9. The hormone that promotes seed dormancy is:
Answer: (c) Abscisic acid. ABA maintains dormancy and closes stomata in stress.
A10. Phytochrome Pfr is formed when Pr absorbs:
Answer: (b) Red light. Red light converts Pr to active Pfr; far-red reverses it.
Section B — Attempt any 4, 4 x 5 = 20
- Define water potential and explain solute and pressure potentials. Marking points: Definition; Ψ=Ψs+Ψp; pure water reference; examples of flaccid/turgid cells.
- Give the roles of nitrogen, phosphorus and potassium in plants. Marking points: N in proteins/chlorophyll; P in ATP/nucleic acids; K in stomata/enzyme activation.
- Distinguish apoplastic and symplastic phloem loading. Marking points: Routes, membranes crossed, transporters, plasmodesmata, examples.
- Write a short note on photorespiration. Marking points: RuBisCO oxygenase, phosphoglycolate, three organelles, CO2 loss, C4 avoidance.
- Write a short note on enzyme inhibition. Marking points: Competitive, non-competitive, uncompetitive; Km/Vmax effects; feedback inhibition.
- What is vernalization? Give one example. Marking points: Cold requirement, winter cereals, devernalization, difference from photoperiodism.
Section C — Attempt any 3, 3 x 10 = 30
- Describe the cohesion-tension theory of ascent of sap and compare root pressure. Marking points: Transpiration pull, cohesion/adhesion, evidence, limits of root pressure, guttation contrast.
- Discuss the pressure flow model of phloem translocation with experimental evidence. Marking points: Münch model, source-sink gradient, aphid stylets, tracers, girdling, objections.
- Describe the Calvin cycle and explain how C4 plants reduce photorespiration. Marking points: Three phases, RuBisCO, Kranz anatomy, PEP carboxylase, bundle-sheath CO2 concentration.
- Describe biological nitrogen fixation, including nitrogenase and its energy cost. Marking points: Rhizobium nodules, leghaemoglobin, MoFe/Fe proteins, 16 ATP, O2 sensitivity, GS-GOGAT link.
- Explain photoperiodism and the role of phytochrome in flowering. Marking points: SDP/LDP/day-neutral, critical night, Pr/Pfr interconversion, night-break experiments, florigen concept.
Model Paper 2 — 60 marks, 3 hours
Section A — 10 x 1 = 10 (all compulsory)
A1. A cell placed in a hypertonic solution will:
Answer: (b) Lose water and plasmolyse. Water leaves toward the lower water potential outside.
A2. Which element is needed for chlorophyll synthesis and is a micronutrient?
Answer: (b) Iron. Fe is a micronutrient cofactor for chlorophyll synthesis.
A3. Phloem loading is an example of:
Answer: (b) Active transport. Sucrose is actively loaded against its gradient.
A4. Companion cells are found beside:
Answer: (b) Sieve tube elements. They support sieve elements, which lack nuclei at maturity.
A5. Cyclic photophosphorylation occurs around:
Answer: (b) PSI only. Cyclic flow returns electrons to PSI, making ATP only.
A6. The TCA cycle begins when acetyl-CoA joins:
Answer: (b) Oxaloacetate. Acetyl-CoA + oxaloacetate gives citrate.
A7. An enzyme's active site is shaped by:
Answer: (b) Its amino-acid sequence and folding. Structure determines binding and catalysis; induced fit refines the fit.
A8. Free-living nitrogen fixation is carried out by:
Answer: (b) Azotobacter in soil. Azotobacter is a classic free-living fixer; Rhizobium is symbiotic.
A9. Gibberellins are best known for:
Answer: (b) Breaking seed dormancy and stem elongation. GA promotes germination, bolting and internode elongation.
A10. A day-neutral plant flowers:
Answer: (c) Regardless of day length. Day-neutral plants are not controlled by photoperiod.
Section B — Attempt any 4, 4 x 5 = 20
- Explain root pressure and guttation, and how they differ from transpiration. Marking points: Definitions, hydathodes, conditions, limits, table of differences.
- Write short notes on: (a) aquaporins (b) ionophores. Marking points: Water channels, homotetramer idea; valinomycin, gramicidin, mobile vs channel types.
- Compare C3, C4 and CAM plants. Marking points: First product, anatomy, water use, examples, photorespiration.
- Explain the GS-GOGAT pathway. Marking points: Glutamine synthetase, glutamate synthase, ammonia assimilation, comparison with GDH.
- Mention the physiological roles of cytokinins. Marking points: Cell division, senescence delay, shoot/root balance, apical dominance interaction.
- What are Pr and Pfr? How do they interconvert? Marking points: Absorption maxima, red/far-red cycle, active form, photomorphogenesis examples.
Section C — Attempt any 3, 3 x 10 = 30
- Explain water potential and its components, with examples of cell states. Marking points: Ψ, Ψs, Ψp, Ψm note; flaccid, turgid, plasmolysed; water movement rule.
- Describe glycolysis and anaerobic respiration, including energy yields. Marking points: Steps in outline, net 2 ATP, fermentation types, NAD+ regeneration.
- Discuss enzyme catalysis: activation energy, induced fit, and factors affecting activity. Marking points: Transition state, Km idea, temperature, pH, substrate concentration, inhibitors link.
- Describe nitrate and ammonia assimilation in plants. Marking points: Uptake, cytosolic nitrate reductase, plastid nitrite reductase, GS-GOGAT, amino acids.
- Describe the Z-scheme and the generation of ATP and NADPH. Marking points: PSII to PSI carriers, photolysis, chemiosmosis, cyclic vs non-cyclic.
Model Paper 3 — 60 marks, 3 hours
Section A — 10 x 1 = 10 (all compulsory)
A1. Diffusion pressure deficit is an older term related to:
Answer: (a) Water potential. DPD reflects the suction pressure of a cell; modern usage prefers water potential.
A2. Boron deficiency in plants affects mainly:
Answer: (b) Growing tips and reproductive development. B is needed for cell-wall and reproductive growth; tips die back.
A3. Phloem sap pH is typically:
Answer: (b) Alkaline (around pH 8). Phloem sap is alkaline, unlike acidic xylem sap.
A4. Source-to-sink flow in phloem is driven by:
Answer: (b) A turgor-pressure gradient. Pressure at the source exceeds pressure at the sink.
A5. Carotenoids in photosynthesis act as:
Answer: (b) Accessory pigments and photoprotection. They harvest light and protect chlorophyll from excess energy.
A6. In CAM plants, malic acid accumulates:
Answer: (b) At night. Night fixation stores CO2 as malate; it is released by day for the Calvin cycle.
A7. Non-competitive inhibition lowers:
Answer: (b) Vmax. Vmax falls; the inhibitor does not compete for the active site.
A8. Leghaemoglobin is found in:
Answer: (b) Root nodules. It protects nitrogenase from free oxygen in nodules.
A9. Auxin is transported in plants mainly:
Answer: (b) Polarly, from shoot tip downward. Polar auxin transport is basipetal in shoots and distinctive among hormones.
A10. Vernalization in winter wheat ensures flowering after:
Answer: (b) A cold winter period. Cold makes the plant competent to flower when days lengthen.
Section B — Attempt any 4, 4 x 5 = 20
- Explain the significance of transpiration. Marking points: Ascent, cooling, mineral uptake, limits and costs, antitranspirants note.
- Write a short note on the composition of phloem sap. Marking points: Sucrose, amino acids, hormones, minerals, pH, sampling evidence.
- Distinguish photophosphorylation: cyclic vs non-cyclic. Marking points: Products, oxygen, carriers, ATP/NADPH balance.
- Explain the role of nitrogenase and why it needs protection from oxygen. Marking points: MoFe and Fe proteins, ATP cost, leghaemoglobin, anaerobic strategies.
- Give the roles of ethylene in plants. Marking points: Triple response, ripening, senescence, abscission, Ethephon.
- Differentiate SDP, LDP and day-neutral plants with examples. Marking points: Critical night, examples, night-break test.
Section C — Attempt any 3, 3 x 10 = 30
- Describe transpiration pull and root pressure, and assess their roles in ascent of sap. Marking points: Cohesion-tension, evidence, root pressure limits, tall-tree argument.
- Explain oxidative phosphorylation and chemiosmotic theory. Marking points: ETC, proton gradient, ATP synthase, inhibitors/uncouplers briefly, ATP yield.
- Discuss the pressure flow model: mechanism, evidence and objections. Marking points: Münch, source-sink, aphid stylets, tracers, bidirectional flow problem.
- Describe the mechanism of enzyme catalysis and the main types of inhibition. Marking points: Active site, transition state, competitive/non-competitive/uncompetitive, Km/Vmax.
- Explain phytochrome, Pr/Pfr interconversion and photomorphogenesis. Marking points: Discovery outline, structure, red/far-red cycle, germination, de-etiolation, flowering.
Model Paper 4 — 60 marks, 3 hours
Section A — 10 x 1 = 10 (all compulsory)
A1. Stomatal opening is promoted by:
Answer: (b) Potassium uptake into guard cells. K+ uptake lowers guard-cell water potential, water enters, and stomata open.
A2. Which is a micronutrient?
Answer: (c) Molybdenum. Mo is needed in tiny amounts, e.g. for nitrate reductase.
A3. Unloading at a sink requires:
Answer: (b) Energy for metabolism and growth. Sinks use imported sucrose for growth, respiration or storage.
A4. The pressure flow model predicts sap moves:
Answer: (b) From high to low turgor pressure. Bulk flow follows the pressure gradient from source to sink.
A5. The oxygen released in photosynthesis comes from:
Answer: (b) Water. Photolysis of water at PSII releases O2.
A6. The oxidative pentose phosphate pathway produces:
Answer: (b) NADPH and ribose-5-phosphate. It supports biosynthesis and nucleotide synthesis.
A7. An apoenzyme plus its cofactor forms a:
Answer: (b) Holoenzyme. Holoenzyme is the catalytically active complete enzyme.
A8. Ammonia assimilation by GS-GOGAT produces:
Answer: (b) Glutamate/glutamine amino acids. Ammonia enters organic form as glutamine, then glutamate.
A9. Cytokinins delay:
Answer: (b) Leaf senescence. Cytokinins keep leaves green longer and promote division.
A10. Red light converts phytochrome:
Answer: (b) Pr to Pfr. Red (660 nm) drives Pr → Pfr; far-red reverses it.
Section B — Attempt any 4, 4 x 5 = 20
- List the factors affecting transpiration and explain two in detail. Marking points: Light, temperature, humidity, wind, leaf area, stomatal state, water availability.
- Write a short note on the girdling experiment. Marking points: Method, result, conclusion, limitation (xylem intact).
- Explain the glyoxylate cycle and its importance. Marking points: Glyoxysomes, bypass steps, fat to carbohydrate in oil seeds.
- Compare competitive and non-competitive inhibition. Marking points: Binding site, Km, Vmax, reversibility by substrate, examples.
- Mention the roles of gibberellins. Marking points: Elongation, germination, malting, bolting, sex expression note.
- Explain photoperiodism with SDP and LDP examples. Marking points: Critical night, night-break, examples, phytochrome link.
Section C — Attempt any 3, 3 x 10 = 30
- Explain the concept of water potential, its components, and water movement between cells. Marking points: Definitions, Ψs/Ψp, examples, plasmolysis, turgor.
- Describe photosynthesis: Z-scheme, ATP synthesis and Calvin cycle in outline. Marking points: Carriers, chemiosmosis, three Calvin phases, ATP/NADPH use.
- Describe the TCA cycle and oxidative phosphorylation. Marking points: Matrix reactions, carriers, ETC, ATP synthase, yields.
- Discuss biological nitrogen fixation and ammonia assimilation. Marking points: Nodules, nitrogenase, energy, leghaemoglobin, nitrate/nitrite steps, GS-GOGAT.
- Explain plant growth regulators: auxins and ethylene in detail. Marking points: Discovery, transport/biosynthesis, roles, applications, triple response, ripening.
Model Paper 5 — 60 marks, 3 hours
Section A — 10 x 1 = 10 (all compulsory)
A1. Water potential becomes more negative when:
Answer: (b) Solutes are added. Solutes lower Ψs and therefore Ψ.
A2. Chloride is classified as a:
Answer: (b) Micronutrient. Cl is needed in small amounts, e.g. in photolysis and stomatal function.
A3. Aphid stylet exudation supports the idea that phloem sap is:
Answer: (b) Under positive pressure. Sap exudes from cut stylets, showing positive turgor pressure.
A4. Phloem loading through plasmodesmata is called:
Answer: (b) Symplastic. Symplastic route avoids membrane crossing until the sieve element.
A5. Chlorophyll b differs from chlorophyll a mainly in:
Answer: (b) Absorbing a different light range as an accessory pigment. Chl b broadens absorption and passes energy to Chl a.
A6. Fermentation of glucose to ethanol yields a net of:
Answer: (a) 2 ATP. Only glycolytic ATP is gained; NAD+ is regenerated without oxygen.
A7. Feedback inhibition helps a cell to:
Answer: (b) Avoid overproduction of an end product. End products inhibit early enzymes in their own pathway.
A8. Nitrogen fixation converts N2 mainly to:
Answer: (b) Ammonia. Nitrogenase reduces N2 to ammonia, later assimilated into amino acids.
A9. ABA promotes:
Answer: (b) Stomatal closure. ABA is the key water-stress signal for stomatal closure.
A10. A light break during a long night will:
Answer: (b) Prevent SDP flowering. Breaking the long night with light prevents short-day induction.
Section B — Attempt any 4, 4 x 5 = 20
- Explain the importance of water in plants. Marking points: Solvent, transport, turgor, temperature buffer, reactions, photosynthesis reactant.
- Write short notes on: (a) sieve tube elements (b) companion cells. Marking points: Structure, nucleus loss, plasmodesmata, loading role.
- Differentiate C4 and CAM pathways. Marking points: Anatomy, timing, first product, water use, examples.
- Write a short note on factors affecting enzyme activity. Marking points: Temperature, pH, substrate, inhibitors, cofactors.
- Mention the roles of auxins in plant growth. Marking points: Apical dominance, rooting, parthenocarpy, phototropism, weed killers.
- Explain vernalization and devernalization. Marking points: Cold duration, examples, reversal by heat, flowering competence.
Section C — Attempt any 3, 3 x 10 = 30
- Describe the ascent of sap: transpiration pull, cohesion-tension and root pressure compared. Marking points: Mechanism, evidence, limits, environmental effects.
- Discuss the pressure flow model of phloem translocation, with evidence. Marking points: Source-sink, gradient, aphid/tracer evidence, objections and refinements.
- Describe respiration: glycolysis, TCA cycle and oxidative phosphorylation. Marking points: Sites, products, carriers, ATP yields, chemiosmosis.
- Describe enzyme structure, catalysis and inhibition. Marking points: Active site, induced fit, activation energy, inhibition types and graphs in words.
- Explain photoperiodism, phytochrome and vernalization in flowering control. Marking points: SDP/LDP, Pr/Pfr, night-break, cold requirement, interaction of cues.