60 free MCQs on Photosynthesis in Higher Plants with worked answers and explanations. Light reactions, the Calvin cycle, C 3 /C 4 /CAM pathways, photorespiration, and factors affecting the rate of photosynthesis. One of the highest-yield NEET chapters.
Take the timed Photosynthesis in Higher Plants chapterwise test →Below are 60 practice questions on Photosynthesis in Higher Plants, sorted Easy → Hard. Tap “Show answer & explanation” under any question to check yourself. Want the full theory first? Read the Photosynthesis in Higher Plants notes.
Simplified photosynthesis diagram: light energy, CO2, and H2O enter the leaf and are converted in the chloroplast into glucose and O2.
Q1.
Photosynthesis takes place in the:
Answer: C. Chloroplast
Why: Photosynthesis occurs in chloroplasts, specifically in the thylakoid membranes (light reactions) and stroma (dark reactions).
Q2.
The overall equation for photosynthesis is:
Answer: B. 6CO<sub>2</sub> + 6H<sub>2</sub>O → C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub>
Why: 6CO<sub>2</sub> + 6H<sub>2</sub>O + light energy → C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub>. Carbon dioxide and water are converted to glucose and oxygen using light.
Q3.
Chlorophyll absorbs which colors of light most strongly?
Answer: B. Red and blue-violet
Why: Chlorophyll absorbs red and blue-violet light. Green light is reflected: this is why plants appear green.
Q4.
The dark reaction (Calvin cycle) occurs in the:
Answer: C. Stroma of chloroplast
Why: The Calvin cycle (dark reactions) occurs in the stroma of the chloroplast. It uses ATP and NADPH to fix CO<sub>2</sub> into sugars.
Q5.
Plants need which element for chlorophyll synthesis?
Answer: B. Magnesium
Why: Chlorophyll has magnesium (Mg) at its center. Magnesium deficiency causes yellowing (chlorosis) in plants.
Q6.
The Calvin cycle is also called:
Answer: B. C<sub>3</sub> cycle or dark reaction
Why: Calvin cycle = C<sub>3</sub> pathway = dark reaction (or light-independent reaction). First stable product is 3-carbon PGA (3-phosphoglycerate).
Q7.
Photorespiration is the process in which:
Answer: B. Rubisco fixes O<sub>2</sub> instead of CO<sub>2</sub>, reducing efficiency
Why: Photorespiration: at high O<sub>2</sub>/low CO<sub>2</sub>, Rubisco adds O<sub>2</sub> instead of CO<sub>2</sub> to RuBP. This wasteful process reduces photosynthesis efficiency in C<sub>3</sub> plants.
Q8.
In C<sub>4</sub> plants, CO<sub>2</sub> is initially fixed in mesophyll cells to form:
Answer: B. Oxaloacetate (4-carbon compound)
Why: C<sub>4</sub> plants first fix CO<sub>2</sub> into oxaloacetate (4-carbon) in mesophyll cells via PEP carboxylase, then transfer CO<sub>2</sub> to bundle sheath for Calvin cycle.
Q9.
The first product of the Calvin cycle (C<sub>3</sub> pathway) is:
Answer: C. PGA (3-phosphoglycerate)
Why: In the Calvin cycle, CO<sub>2</sub> + RuBP → 2 molecules of PGA (3-phosphoglycerate, a 3-carbon compound). Hence called C<sub>3</sub> pathway.
Q10.
The green pigment chlorophyll, essential for photosynthesis, is located within which cell organelle?
Answer: D. Chloroplast
Why: Chlorophyll is contained within the chloroplasts of plant cells, specifically embedded in the membranes of thylakoids, where it captures light energy for photosynthesis.
Q11.
Photosynthesis is the process by which green plants make their own:
Answer: A. food
Why: Plants synthesise glucose (food) from CO₂ and water using light.
Q12.
The green pigment that traps light energy in plants is:
Answer: A. chlorophyll
Why: Chlorophyll absorbs light for photosynthesis.
Q13.
Photosynthesis takes place chiefly in the:
Answer: A. leaves
Why: Leaves, rich in chloroplasts, are the main photosynthetic organs.
Q14.
The gas absorbed by plants during photosynthesis is:
Answer: A. carbon dioxide
Why: Plants take in carbon dioxide to build sugars.
Q15.
The gas released by plants during photosynthesis is:
Answer: A. oxygen
Why: Oxygen is released as a by-product of the splitting of water.
Q16.
The cell organelle in which photosynthesis occurs is the:
Answer: A. chloroplast
Why: Chloroplasts contain the chlorophyll and machinery for photosynthesis.
Q17.
The main source of energy for photosynthesis is:
Answer: A. sunlight
Why: Sunlight provides the energy that drives photosynthesis.
Q18.
The small pores on a leaf through which gases are exchanged are the:
Answer: A. stomata
Why: Stomata allow CO₂ in and O₂ out of the leaf.
Q19.
The chief food product formed in photosynthesis is:
Answer: A. glucose
Why: Photosynthesis produces glucose, a simple sugar.
Q20.
The water used in photosynthesis is absorbed by the:
Answer: A. roots
Why: Roots absorb water, which is carried up to the leaves.
Q21.
C<sub>4</sub> plants like maize have an advantage over C<sub>3</sub> plants because:
Answer: B. PEP carboxylase does not fix O<sub>2</sub>, reducing photorespiration in hot climates
Why: C<sub>4</sub> plants use PEP carboxylase (high affinity for CO<sub>2</sub>, no affinity for O<sub>2</sub>) in mesophyll, concentrating CO<sub>2</sub> for Rubisco in bundle sheath: minimizing photorespiration.
Q22.
The compensation point in photosynthesis is where:
Answer: B. Photosynthesis rate equals respiration rate (net gas exchange = 0)
Why: Compensation point: light intensity at which CO<sub>2</sub> fixed by photosynthesis = CO<sub>2</sub> released by respiration. Net gas exchange is zero.
Q23.
The ratio of cyclic to non-cyclic photophosphorylation differs in:
Answer: A. Amount of ATP and NADPH produced (cyclic makes only ATP; non-cyclic makes ATP + NADPH + O<sub>2</sub>)
Why: Cyclic photophosphorylation (PS I only): produces ATP only. Non-cyclic (PS II + PS I): produces ATP + NADPH, and water is oxidized releasing O<sub>2</sub>.
Q24.
In the dark, CAM plants open their stomata to:
Answer: B. Fix CO<sub>2</sub> at night as malate (stored in vacuole) to reduce water loss during day
Why: CAM plants (cacti, succulents): stomata open at night to fix CO<sub>2</sub> (as malate). Stomata closed during hot day to prevent water loss. CO<sub>2</sub> released from malate for Calvin cycle during day.
Q25.
ATP and NADPH from light reactions are used in the Calvin cycle to:
Answer: C. Reduce CO<sub>2</sub> to produce G3P (glyceraldehyde-3-phosphate)
Why: Calvin cycle: ATP and NADPH (from light reactions) provide energy and electrons to convert CO<sub>2</sub> into G3P, which is used to make sugars.
Q26.
Rubisco catalyzes in the Calvin cycle:
Answer: B. CO<sub>2</sub> fixation: CO<sub>2</sub> + RuBP → 2 PGA
Why: Rubisco (RuBisCO = ribulose bisphosphate carboxylase/oxygenase) catalyzes fixation of CO<sub>2</sub> onto RuBP to form 2 molecules of 3-PGA.
Q27.
The site of the light-dependent reactions of photosynthesis within the chloroplast is the:
Answer: C. Thylakoid membrane, within the grana
Why: Light reactions, including light absorption, water splitting and ATP/NADPH formation, occur on the thylakoid membranes, which contain the photosystems and electron transport chain.
Q28.
Photorespiration in C<sub>3</sub> plants occurs mainly because rubisco:
Answer: A. Can bind O<sub>2</sub> as well as CO<sub>2</sub> when CO<sub>2</sub> is low and O<sub>2</sub> is high
Why: Rubisco has both carboxylase and oxygenase activity; under high O<sub>2</sub>/low CO<sub>2</sub> conditions, it binds O<sub>2</sub> instead, initiating photorespiration, which consumes energy without fixing carbon or producing sugar.
Q29.
Splitting of the water molecule during photosynthesis (photolysis) takes place in association with:
Answer: C. Photosystem II, replacing electrons lost by chlorophyll
Why: Photolysis of water occurs near Photosystem II, supplying electrons to replace those lost by excited chlorophyll molecules, with O<sub>2</sub> released as a by-product.
Q30.
In C<sub>3</sub> plants, the first stable product formed after CO<sub>2</sub> fixation by rubisco is:
Answer: D. 3-phosphoglycerate (PGA), a 3-carbon compound
Why: In C<sub>3</sub> plants, rubisco fixes CO<sub>2</sub> onto RuBP to form an unstable 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglyceric acid (PGA), a 3-carbon compound.
Q31.
The light-dependent reactions of photosynthesis take place in the:
Answer: A. thylakoid membranes
Why: The light reactions occur on the thylakoid membranes of the chloroplast.
Q32.
The light-independent (Calvin cycle) reactions take place in the:
Answer: A. stroma
Why: The Calvin cycle occurs in the stroma of the chloroplast.
Q33.
The splitting of water molecules during photosynthesis is called:
Answer: A. photolysis
Why: Photolysis is the light-driven splitting of water, releasing oxygen.
Q34.
The two products of the light reaction that power the Calvin cycle are ATP and:
Answer: A. NADPH
Why: ATP and NADPH from the light reaction drive carbon fixation.
Q35.
The enzyme that fixes carbon dioxide in the Calvin cycle is:
Answer: A. RuBisCO
Why: RuBisCO catalyses the fixation of CO₂ onto RuBP.
Q36.
The first stable product of C<sub>3</sub> photosynthesis is a compound containing ___ carbon atoms:
Answer: A. three
Why: In C<sub>3</sub> plants the first product is 3-phosphoglycerate, a 3-carbon compound.
Q37.
Plants that first fix carbon dioxide into a 4-carbon compound are called:
Answer: A. C<sub>4</sub> plants
Why: C<sub>4</sub> plants (e.g. maize) first make a 4-carbon acid, reducing photorespiration.
Q38.
The colour of light least absorbed (and mostly reflected) by chlorophyll is:
Answer: A. green
Why: Chlorophyll reflects green light, which is why leaves look green.
Q39.
The oxygen released during photosynthesis comes from:
Answer: A. water
Why: The oxygen comes from the splitting of water, not from CO₂.
Q40.
Chlorophyll molecules are located within the ___ of the chloroplast:
Answer: A. thylakoids
Why: Chlorophyll is embedded in the thylakoid membranes.
Q41.
In the Q cycle of photosynthesis, the function is to:
Answer: B. Pump protons across thylakoid membrane via plastoquinone (PQ) oxidation/reduction, increasing H+ gradient for ATP synthesis
Why: Q cycle at the cytochrome b6f complex: transfers 2 electrons from plastoquinol (PQH2) to plastocyanin while pumping extra protons into the thylakoid lumen, boosting ATP synthesis.
Q42.
Ferredoxin-NADP+ reductase (FNR) in the light reactions:
Answer: B. Reduces NADP+ to NADPH using electrons from ferredoxin
Why: FNR: enzyme that accepts 2 electrons from 2 reduced ferredoxin molecules and transfers them to NADP+, reducing it to NADPH (final electron acceptor of the light reactions).
Q43.
The oxygen-evolving complex (OEC) in PS II contains:
Answer: B. A manganese cluster (Mn4CaO5) that oxidizes water to release O<sub>2</sub>
Why: OEC (oxygen-evolving complex) contains a Mn4CaO5 cluster. It cycles through 5 S-states (S0-S4). At S4, two water molecules are oxidized to release O<sub>2</sub>, 4H+ and 4e-.
Q44.
In the Calvin cycle, 3 turns are needed to produce one net G3P because:
Answer: B. Each turn fixes one CO<sub>2</sub> and regenerates RuBP; 3 CO<sub>2</sub> are needed to produce 1 net G3P (a 3-carbon molecule)
Why: Calvin cycle: 3 CO<sub>2</sub> + 3 RuBP → 6 PGA → 6 G3P. 5 G3P are used to regenerate 3 RuBP, leaving 1 net G3P. Full cycle uses 9 ATP and 6 NADPH for 3 CO<sub>2</sub>.
Q45.
Rubisco is a poor catalyst because:
Answer: B. It has low catalytic rate (kcat ~3/sec) and reacts with O<sub>2</sub> as well as CO<sub>2</sub> (oxygenase activity), causing photorespiration
Why: Rubisco: very slow turnover (~3 CO<sub>2</sub>/sec vs ~1000 for typical enzymes). Cannot fully discriminate between CO<sub>2</sub> and O<sub>2</sub>. At high O<sub>2</sub>/low CO<sub>2</sub>, adds O<sub>2</sub> (photorespiration), wasting energy.
Q46.
The 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway in plastids produces:
Answer: B. Terpenoids (isoprene, carotenoids, diterpenes) for photosynthesis and plant defense
Why: MEP pathway (methylerythritol phosphate/non-mevalonate pathway) in plastids produces IPP and DMAPP, precursors for carotenoids, chlorophylls, gibberellins, and isoprene.
Q47.
Crassulacean acid metabolism (CAM) evolved as:
Answer: B. Adaptation to arid conditions -- temporally separating CO<sub>2</sub> fixation (night) from Calvin cycle (day) to minimize water loss
Why: CAM: evolved in desert plants (cacti, agaves, succulents) for maximal water use efficiency. Night CO<sub>2</sub> fixation (PEP carboxylase) stores CO<sub>2</sub> as malate; day decarboxylation feeds Calvin cycle with stomata closed.
Q48.
State transition (dark-to-light adaptation) in chloroplasts involves:
Answer: B. Reversible phosphorylation of LHCII, which migrates between PS II and PS I to balance excitation
Why: State transitions: excess excitation of PS II activates STN7 kinase, which phosphorylates LHCII. Phospho-LHCII migrates to PS I (state 2). PPH1/TAP38 phosphatase reverses this, returning to state 1.
Q49.
The photorespiratory salvage pathway (C2 cycle) recycles:
Answer: B. Glycolate (toxic product of Rubisco oxygenase) back to PGA via chloroplast, peroxisome, and mitochondria
Why: C2 photorespiratory cycle: 2-phosphoglycolate from Rubisco oxygenase → glycolate (chloroplast) → glyoxylate (peroxisome) → glycine (mitochondria, releases CO<sub>2</sub> and NH<sub>3</sub>) → serine → PGA.
Q50.
The Hill reaction, a classic experiment demonstrating the light reaction of photosynthesis, established that:
Answer: B. Isolated chloroplasts can evolve oxygen from water in the presence of a suitable electron acceptor, even without CO<sub>2</sub> fixation
Why: Robert Hill demonstrated that isolated chloroplasts, supplied with an artificial electron acceptor, could evolve oxygen from water even in the absence of CO<sub>2</sub>, showing that O<sub>2</sub> evolution (water splitting) is independent of CO<sub>2</sub> fixation.
Q51.
In the Calvin cycle, carbon dioxide is first attached to the 5-carbon molecule:
Answer: A. RuBP
Why: CO₂ combines with ribulose-1,5-bisphosphate (RuBP) in carbon fixation.
Q52.
The two photosystems that take part in the light reactions are Photosystem I and:
Answer: A. Photosystem II
Why: Photosystems I and II work together in the light reactions.
Q53.
C<sub>4</sub> plants are efficient in hot, dry climates chiefly because they minimise:
Answer: A. photorespiration
Why: The C<sub>4</sub> pathway concentrates CO₂ around RuBisCO, suppressing wasteful photorespiration.
Q54.
The number of water molecules that must be split to release 6 molecules of O₂ in photosynthesis is:
Answer: A. 12
Why: Splitting 2 H₂O gives 1 O₂, so 6 O₂ requires 12 water molecules.
Q55.
The ATP and NADPH generated in the light reactions are used mainly to synthesise:
Answer: A. glucose
Why: These energy carriers power the Calvin cycle that builds glucose.
Q56.
CAM plants open their stomata at ___ to conserve water:
Answer: A. night
Why: CAM plants (e.g. cacti) take in CO₂ at night, keeping stomata shut in the hot day.
Q57.
Specialised bundle-sheath cells around the veins are a distinctive feature of ___ plants:
Answer: A. C<sub>4</sub>
Why: C<sub>4</sub> plants carry out the Calvin cycle in bundle-sheath cells.
Q58.
On a cloudy day, the factor most likely to limit photosynthesis is:
Answer: A. light intensity
Why: When light is scarce, light intensity becomes the limiting factor.
Q59.
Photorespiration begins when the enzyme RuBisCO binds ___ instead of carbon dioxide:
Answer: A. oxygen
Why: At high O₂/low CO₂, RuBisCO fixes oxygen, starting the wasteful photorespiration pathway.
Q60.
The stacked, coin-like piles of thylakoids in a chloroplast are called:
Answer: A. grana
Why: Thylakoids are stacked into grana within the chloroplast.