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Photosynthesis in Higher Plants — NEET Biology MCQs with Solutions
Free NEET Biology Photosynthesis in Higher Plants MCQs with step-by-step solutions covering Early Experiments, Site & Pigments, Light Reaction & Photophosphorylation, Chemiosmosis, C3 Pathway (Calvin Cycle), C4 Pathway & Photorespiration, Factors Affecting Photosynthesis. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Early Experiments, Site & Pigments · easy · theory
The most abundant photosynthetic pigment, absorbing chiefly blue and red light and reflecting green, is:
A. Chlorophyll b
B. Xanthophyll
C. Chlorophyll a ✓ Correct
D. Carotene
Solution: Chlorophyll a is the chief pigment (reaction centre); accessory pigments (chl b, carotenoids) widen the absorbed spectrum.
Q2 — Early Experiments, Site & Pigments · easy · theory
Photosynthesis in higher plants takes place in the:
A. Chloroplast (mesophyll) ✓ Correct
B. Cell wall
C. Mitochondrion
D. Nucleus
Solution: The chloroplast is the site: light reactions occur in the thylakoid (grana) and the Calvin cycle in the stroma.
Q3 — Light Reaction & Photophosphorylation · easy · theory
The splitting of water (photolysis) that releases O₂, protons and electrons is associated with:
A. Photosystem II ✓ Correct
B. The Calvin cycle
C. Photosystem I
D. Glycolysis
Solution: Water splitting occurs on the inner thylakoid side associated with PS II, replenishing its electrons.
Q4 — Light Reaction & Photophosphorylation · easy · theory
The products of the light reaction that are used in the dark reaction are:
A. ATP and NADH
B. Glucose and O₂
C. CO₂ and water
D. ATP and NADPH ✓ Correct
Solution: The light reaction produces assimilatory power (ATP + NADPH) used to fix CO₂ in the Calvin cycle.
Q5 — Chemiosmosis · easy · theory
ATP synthesis in the chloroplast is driven by a proton gradient across the ______ membrane:
A. Nuclear
B. Mitochondrial inner
C. Thylakoid ✓ Correct
D. Outer chloroplast
Solution: Protons accumulate in the thylakoid lumen; their flow back through ATP synthase makes ATP — chemiosmosis.
Q6 — Chemiosmosis · easy · theory
During the light reaction, protons accumulate in the ______ of the thylakoid:
A. Lumen (inner space) ✓ Correct
B. Cytosol
C. Intermembrane space of mitochondria
D. Stroma
Solution: Water splitting (in the lumen) and electron transport pump protons into the lumen, creating a gradient.
Q7 — C3 Pathway (Calvin Cycle) · easy · theory
The primary CO₂ acceptor in the Calvin (C3) cycle is:
A. RuBP (ribulose-1,5-bisphosphate) ✓ Correct
B. PEP
C. OAA
D. Pyruvate
Solution: RuBP (5-C) accepts CO₂; the first stable product is 3-PGA (a 3-carbon acid) — hence "C3".
Q8 — C3 Pathway (Calvin Cycle) · easy · theory
The first stable product of carbon fixation in the C3 pathway is:
A. Glucose
B. Oxaloacetic acid
C. Malic acid
D. 3-phosphoglyceric acid (3-PGA) ✓ Correct
Solution: CO₂ + RuBP → 2 molecules of 3-PGA (3-carbon), catalysed by RuBisCO.
Q9 — C4 Pathway & Photorespiration · easy · theory
The primary CO₂ acceptor in C4 plants (mesophyll cells) is ______, and the first product is ______:
A. PEP; oxaloacetic acid (OAA) ✓ Correct
B. PEP; malate only
C. RuBP; 3-PGA
D. RuBP; OAA
Solution: C4 plants fix CO₂ first via PEP carboxylase into OAA (4-carbon) in mesophyll cells.
Q10 — C4 Pathway & Photorespiration · easy · theory
C4 plants (e.g. maize, sugarcane) possess a special leaf anatomy called:
A. Isobilateral anatomy
B. Radial anatomy
C. Kranz anatomy ✓ Correct
D. Dorsiventral anatomy
Solution: Kranz ("wreath") anatomy features chloroplast-rich bundle sheath cells around the veins.
Q11 — Factors Affecting Photosynthesis · easy · theory
Blackman's law of limiting factors states that when several factors affect a process, its rate is limited by the factor that is:
A. At its maximum
B. Nearest to its minimum value ✓ Correct
C. Constant
D. Unrelated to the rate
Solution: The pace of the process is set by the most limiting (scarcest) factor at that time.
Q12 — Factors Affecting Photosynthesis · easy · theory
Which is NOT an external factor affecting photosynthesis?
A. Temperature
B. CO₂ concentration
C. Light
D. Number of chloroplasts (internal) ✓ Correct
Solution: External factors: light, CO₂, temperature, water. Internal factors include chlorophyll amount, leaf age, chloroplast number.
Q13 — Early Experiments, Site & Pigments · easy · numerical
Joseph Priestley's bell-jar experiments with a mint plant, a candle and a mouse led him to conclude that plants:
A. take up carbon dioxide only in darkness and release it in light
B. restore to the air whatever breathing animals and burning candles remove from it ✓ Correct
C. release a gas that is chemically identical to the one animals exhale
D. require sunlight in order to purify the surrounding air
Solution: Priestley showed a plant could "restore" air fouled by a candle or a mouse, revealing that plants release oxygen; he had not yet recognised the essential role of light (that was Ingenhousz).
Q14 — Early Experiments, Site & Pigments · easy · numerical
Ingenhousz, using an aquatic plant, added a crucial refinement to Priestley's conclusion by demonstrating that air purification by green plants occurs:
A. only at night, when stomata of the plant are fully open
B. only in sunlight and only from the green parts of the plant ✓ Correct
C. only in the roots, which absorb the impurities from water
D. equally well in light and darkness as long as CO₂ is present
Solution: Ingenhousz showed that bubbles of oxygen formed around the green parts only in sunlight, establishing that light is essential and that only green tissue does the purifying.
Q15 — Early Experiments, Site & Pigments · easy · numerical
A chloroplast is bounded by a double membrane; the flattened sacs stacked into grana and the fluid surrounding them are, respectively, the sites of:
A. thylakoids — carbon fixation; stroma — water splitting
B. thylakoids — light reaction; stroma — dark (biosynthetic) reaction ✓ Correct
C. stroma — light reaction; thylakoids — dark (biosynthetic) reaction
D. grana — sugar storage; stroma — pigment synthesis
Solution: The membrane-bound thylakoids house the light-harvesting machinery and light reactions, while the enzymatic (carbon-fixing) reactions of the Calvin cycle occur in the stroma.
Q16 — Early Experiments, Site & Pigments · easy · numerical
When chlorophyll a and chlorophyll b are separated by paper chromatography of a leaf extract, the two can be told apart because chlorophyll a and chlorophyll b differ mainly in that:
A. chlorophyll a is a carotenoid whereas chlorophyll b is a xanthophyll
B. chlorophyll a lacks magnesium whereas chlorophyll b contains it
C. chlorophyll a absorbs only green light while chlorophyll b absorbs only blue
D. chlorophyll a is blue-green and chlorophyll b is yellow-green ✓ Correct
Solution: Chlorophyll a appears bright/blue-green and chlorophyll b yellow-green; both are Mg-porphyrin pigments (neither is a carotenoid), differing by a side group.
Q17 — Light Reaction & Photophosphorylation · easy · numerical
The mobile electron carrier that shuttles electrons from the cytochrome b6f complex to photosystem I is:
A. plastoquinone
B. plastocyanin ✓ Correct
C. NADP reductase
D. ferredoxin
Solution: Plastocyanin, a copper-containing protein on the lumen side, transfers electrons from the cytochrome complex to P700 of PS I; plastoquinone works upstream (PS II to cytochrome).
Q18 — Light Reaction & Photophosphorylation · easy · numerical
The reaction-centre chlorophylls P700 and P680 are named after the wavelength each absorbs maximally; they belong, respectively, to:
A. photosystem II and photosystem I
B. the antenna complex and the oxygen-evolving complex
C. the stroma lamellae and the granal thylakoids only
D. photosystem I and photosystem II ✓ Correct
Solution: P700 (700 nm) is the PS I reaction centre and P680 (680 nm) is the PS II reaction centre — the numbers simply denote their absorption maxima.
Q19 — Light Reaction & Photophosphorylation · easy · numerical
The very last electron acceptor before NADP⁺ in the non-cyclic pathway, which passes electrons to NADP⁺ reductase, is:
A. plastocyanin
B. plastoquinone
C. cytochrome b6f
D. ferredoxin ✓ Correct
Solution: On the stroma side of PS I, ferredoxin receives the electron and, with NADP⁺ reductase, reduces NADP⁺ to NADPH; plastocyanin and plastoquinone act earlier in the chain.
Q20 — Light Reaction & Photophosphorylation · easy · numerical
In non-cyclic photophosphorylation the electrons that reduce NADP⁺ originate ultimately from:
A. ATP hydrolysis at the ATP synthase
B. the oxidation of NADPH in the stroma
C. the photolysis of water at photosystem II ✓ Correct
D. carbon dioxide fixed in the Calvin cycle
Solution: Splitting of water at PS II supplies the electrons that travel through the chain to replace those lost by PS I, ultimately reducing NADP⁺ and releasing O₂.
Q21 — Chemiosmosis · easy · numerical
The immediate energy currency that the CF1 head of ATP synthase produces as protons flow through it is:
A. NADPH from NADP⁺
B. oxygen from water
C. glucose from CO₂
D. ATP from ADP and inorganic phosphate ✓ Correct
Solution: ATP synthase (CF0–CF1) makes ATP by phosphorylating ADP; NADPH is made separately by ferredoxin/NADP reductase, and glucose is a Calvin-cycle product.
Q22 — Chemiosmosis · easy · numerical
For every ATP synthesised through the chloroplast ATP synthase, what physically moves through the enzyme?
A. Water molecules entering the lumen
B. Electrons transferred from ferredoxin
C. Carbon dioxide molecules bound to RuBP
D. Protons diffusing down their electrochemical gradient ✓ Correct
Solution: It is the transmembrane movement of protons (H⁺) down the gradient, not electrons or CO₂, that drives the conformational changes making ATP.
Q23 — Chemiosmosis · easy · numerical
Both the ATP and the NADPH generated by chemiosmosis and the electron transport chain are released on the side of the thylakoid membrane where they are used, namely the:
A. space between the two chloroplast envelope membranes
B. thylakoid lumen, where carbon fixation takes place
C. cytosol just outside the chloroplast
D. stroma, where the enzymes of the Calvin cycle operate ✓ Correct
Solution: The CF1 head and NADP reductase face the stroma, so ATP and NADPH are released there — exactly where the Calvin-cycle enzymes need them.
Q24 — C3 Pathway (Calvin Cycle) · easy · numerical
For each single CO₂ molecule fixed in the Calvin cycle, the number of RuBP molecules that must ultimately be regenerated to sustain the cycle is:
A. one ✓ Correct
B. two
C. three
D. six
Solution: The cycle is self-perpetuating: for every CO₂ fixed onto one RuBP, one RuBP must be regenerated so fixation can continue; six turns therefore regenerate six RuBP.
Q25 — C3 Pathway (Calvin Cycle) · easy · numerical
RuBisCO carries out the carboxylation step of the Calvin cycle by attaching CO₂ to:
A. ribulose-1,5-bisphosphate (a 5-carbon molecule) ✓ Correct
B. phosphoenolpyruvate (a 3-carbon molecule)
C. 3-phosphoglyceric acid (a 3-carbon molecule)
D. glucose (a 6-carbon molecule)
Solution: RuBisCO catalyses the addition of CO₂ to the 5-carbon RuBP; PEP is the acceptor only in the C4 pathway, and it is fixed by PEP carboxylase, not RuBisCO.
Q26 — C3 Pathway (Calvin Cycle) · easy · numerical
The Calvin cycle is often called the "dark reaction," yet it does not actually occur only in darkness. The reason it can proceed is that it:
A. depends on the ATP and NADPH supplied by the light reaction rather than on light directly ✓ Correct
B. occurs only at night when stomata close to conserve water
C. is driven by oxygen released during the splitting of water
D. uses light energy directly to fix carbon dioxide into sugars
Solution: The Calvin cycle needs no light itself but is fully dependent on the ATP and NADPH made in the light reaction, so it normally runs in the day; "dark" only means light-independent.
Q27 — C4 Pathway & Photorespiration · easy · numerical
When RuBisCO acts as an oxygenase on RuBP, the 2-carbon compound produced is:
A. oxaloacetate
B. malate
C. phosphoglycolate (glycolate) ✓ Correct
D. phosphoenolpyruvate
Solution: Oxygenation of RuBP yields one molecule of 3-C phosphoglycerate and one molecule of 2-C phosphoglycolate; the glycolate is then processed in the photorespiratory pathway.
Q28 — C4 Pathway & Photorespiration · easy · numerical
The cell organelle, besides the chloroplast, that is centrally involved in the photorespiratory (glycolate) pathway is the:
A. ribosome
B. Golgi apparatus
C. lysosome
D. peroxisome ✓ Correct
Solution: The photorespiratory pathway shuttles glycolate through the peroxisome (and mitochondrion); the chloroplast, peroxisome and mitochondrion cooperate in it.
Q29 — C4 Pathway & Photorespiration · easy · numerical
Between a C3 plant such as rice and a C4 plant such as maize, the C4 plant is generally the more efficient carbon fixer at high temperatures mainly because it:
A. possesses a form of RuBisCO that never binds carbon dioxide
B. does not need the Calvin cycle to make sugars
C. fixes carbon entirely without using any ATP or NADPH
D. avoids the loss of fixed carbon through photorespiration ✓ Correct
Solution: By concentrating CO₂ in the bundle sheath, C4 plants virtually eliminate photorespiration, which otherwise wastes fixed carbon in C3 plants — especially in hot, bright conditions; C4 plants still run the Calvin cycle.
Q30 — Factors Affecting Photosynthesis · easy · numerical
Which of the following is an INTERNAL (plant) factor, rather than an external factor, affecting the rate of photosynthesis?
A. the ambient temperature around the plant
B. the number and age of leaves and the amount of chlorophyll ✓ Correct
C. the concentration of carbon dioxide in the air
D. the intensity of the incident light
Solution: Leaf number, leaf age, chloroplast and chlorophyll content are internal (plant) factors; light, CO₂ and temperature are the external factors.