342 questions on Plant Physiology for NEET 2027, 5 of them from previous NEET papers. Below are 15 to try; tap a question to see its answer and explanation.
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Answer: (C) Auxin
Auxin from shoot apex suppresses lateral bud growth.
Quick tip: Auxin=apical dominance. Cytokinin=lateral growth (opposes auxin). Gibberellin=stem elongation.
NCERT Class 11, Chapter 15, page 255
Answer: (B) CO₂ concentrated around rubisco
Kranz anatomy: CO₂ concentrated in bundle sheath → rubisco works efficiently.
Quick tip: C4=Corn/Sugarcane/Sorghum. Kranz anatomy+CO₂ pump=no photorespiration.
NCERT Class 11, Chapter 13, page 223
Answer: (B) Thylakoid membrane
Light reactions: thylakoid membranes. Calvin cycle (dark): stroma.
Quick tip: Light=Thylakoid. Dark (Calvin)=Stroma. Remember L-T, D-S.
NCERT Class 11, Chapter 13, page 212
Answer: (B) Cytoplasm
Glycolysis in cytoplasm. No O₂ needed. 1 glucose → 2 pyruvate + 2 ATP (net).
Quick tip: Glycolysis=Cytoplasm. Krebs=Mitochondrial matrix. ETC=Inner mitochondrial membrane.
NCERT Class 11, Chapter 14, page 234
Answer: (B) Joseph Priestley
In 1770, Joseph Priestley performed a series of experiments with a bell jar, candle, and mouse, which demonstrated that a mint plant restored the air that had been fouled by a burning candle and a breathing mouse. Jan Ingenhousz later showed that sunlight was essential for this process.
Answer: (C) NAD+ and coenzyme A
Pyruvic acid + CoA + NAD+ gives acetyl CoA + CO2 + NADH + H+, in the mitochondrial matrix.
Answer: (D) 24
Sucrose is a disaccharide (C₁₂H₂₂O₁₁) composed of two hexose units, requiring the fixation of 12 CO₂ molecules. Each CO₂ molecule fixed in the Calvin cycle requires 2 molecules of NADPH during the reduction phase. Therefore, 12 × 2 = 24 NADPH molecules are required.
Answer: (C) Mitochondrial matrix
The tricarboxylic acid (TCA) cycle, elucidated by Hans Krebs, takes place in the mitochondrial matrix. The electron transport system is located on the inner mitochondrial membrane.
NCERT Class 11
Answer: (A) Zeatin
Zeatin was naturally isolated from corn kernels (maize grains) and coconut milk by Letham. Kinetin is a modified adenine base isolated from autoclaved herring sperm DNA and does not occur naturally in plants.
Answer: (A) The rate of glucose consumption decreases significantly
This phenomenon is known as the Pasteur effect. Aerobic respiration produces vastly more ATP per glucose molecule (up to 38 ATP) than fermentation (2 ATP), thereby inhibiting phosphofructokinase via allosteric control by high ATP/citrate and dramatically reducing the rate of glucose consumption.
Answer: (B) Pyruvic dehydrogenase, forming acetyl CoA
Pyruvic dehydrogenase converts pyruvic acid to acetyl CoA in the matrix, also producing NADH and CO2.
Answer: (D) 12
One glucose needs 6 CO₂, 18 ATP and 12 NADPH (6 turns of the cycle). For 2 glucose: 6 × 2 = 12.
Answer: (A) Lag, log (exponential), stationary
In a sigmoid curve, slow initial growth (lag phase) is followed by rapid exponential growth (log phase), which then slows into a stationary phase as nutrients become limiting.
NCERT Class 11
Answer: (C) 12
One sucrose molecule yields 2 hexoses (glucose + fructose), which form 4 molecules of pyruvate. In the link reaction, 4 pyruvates produce 4 CO₂ molecules (4 decarboxylations). Each turn of the Krebs cycle involves 2 decarboxylations (isocitrate → α-ketoglutarate and α-ketoglutarate → succinyl-CoA), so 4 turns produce 8 CO₂ molecules. Total decarboxylation events = 4 + 8 = 12.
Answer: (A) Phosphoenol pyruvate (PEP), a 3-carbon molecule
PEP carboxylase (PEPcase) fixes CO2 to PEP in mesophyll cells, forming OAA; the mesophyll cells lack RuBisCO.