Autotrophic nutrition MCQs With Answer

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Autotrophic nutrition MCQs With Answer

Autotrophic nutrition is central to understanding photosynthesis, chemosynthesis, chloroplast biochemistry and carbon fixation pathways — essential topics for B. Pharm students studying plant-derived drugs and metabolic pathways. This concise, Student-friendly post covers key terms like chlorophyll, Calvin cycle, C3, C4, CAM pathways, photorespiration and ATP/NADPH balance. The questions that follow deepen comprehension of light and dark reactions, electron transport, pigments, enzymology (Rubisco, PEP carboxylase), and ecological significance of autotrophs in drug source plants and microbial chemosynthesis. Clear MCQs with answers help reinforce concepts relevant to pharmacognosy, biochemistry and pharmaceutical biotechnology. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is autotrophic nutrition?

  • Obtaining organic molecules by eating other organisms
  • Synthesizing organic molecules from inorganic substances
  • Absorbing ready-made food from environment
  • Deriving energy only from organic compounds

Correct Answer: Synthesizing organic molecules from inorganic substances

Q2. In higher plants, where does the majority of photosynthesis occur?

  • Roots
  • Stem cortex
  • Chloroplasts in mesophyll cells
  • Vacuoles

Correct Answer: Chloroplasts in mesophyll cells

Q3. Which pigment is the primary photoreceptor in oxygenic photosynthesis?

  • Carotene
  • Chlorophyll a
  • Xanthophyll
  • Phycoerythrin

Correct Answer: Chlorophyll a

Q4. What is the balanced overall chemical equation for photosynthesis?

  • CO2 + H2O → CH4 + O2
  • 6CO2 + 6H2O → C6H12O6 + 6O2
  • C6H12O6 + 6O2 → 6CO2 + 6H2O
  • 2CO2 + 2H2O → C2H4O2 + O2

Correct Answer: 6CO2 + 6H2O → C6H12O6 + 6O2

Q5. Where do light-dependent reactions take place within the chloroplast?

  • Stroma
  • Thylakoid membranes
  • Outer membrane
  • Intermembrane space

Correct Answer: Thylakoid membranes

Q6. Where does the Calvin cycle (light-independent reactions) occur?

  • Thylakoid lumen
  • Peroxisome
  • Stroma of chloroplast
  • Mitochondrial matrix

Correct Answer: Stroma of chloroplast

Q7. Which molecules are the main products of the light reactions used in carbon fixation?

  • ATP and NADPH
  • ADP and NADP+
  • Glucose and O2
  • Pyruvate and FADH2

Correct Answer: ATP and NADPH

Q8. What is the first stable product of CO2 fixation in C3 plants?

  • Oxaloacetate
  • 3-Phosphoglycerate (3-PGA)
  • Phosphoenolpyruvate (PEP)
  • Glyceraldehyde-3-phosphate (G3P)

Correct Answer: 3-Phosphoglycerate (3-PGA)

Q9. Which enzyme catalyzes the carboxylation of RuBP during the Calvin cycle?

  • PEP carboxylase
  • Rubisco
  • ATP synthase
  • Glyceraldehyde-3-phosphate dehydrogenase

Correct Answer: Rubisco

Q10. In C4 photosynthesis, the initial CO2 fixation product is:

  • 3-Phosphoglycerate
  • Oxaloacetate (a four-carbon compound)
  • Ribulose-1,5-bisphosphate
  • Glycerate

Correct Answer: Oxaloacetate (a four-carbon compound)

Q11. CAM plants fix CO2 predominantly at which time?

  • Daytime only
  • Nighttime
  • At dawn and dusk only
  • Randomly throughout 24 hours

Correct Answer: Nighttime

Q12. Photorespiration occurs when Rubisco reacts with which gas instead of CO2?

  • Nitrogen
  • Oxygen
  • Methane
  • Hydrogen

Correct Answer: Oxygen

Q13. Chemosynthetic autotrophs obtain energy from:

  • Sunlight
  • Chemical oxidation of inorganic substances
  • Decomposition of organic matter only
  • Fermentation

Correct Answer: Chemical oxidation of inorganic substances

Q14. Photosystems are complexes embedded in the chloroplast thylakoid; they contain reaction centers and:

  • Glycolytic enzymes
  • Antenna pigments
  • DNA polymerase
  • Pyruvate dehydrogenase

Correct Answer: Antenna pigments

Q15. Which reaction center pigment is associated with Photosystem II?

  • P700
  • P680
  • P450
  • P400

Correct Answer: P680

Q16. The oxygen released during photosynthesis originates from:

  • CO2
  • Water (H2O)
  • Glucose
  • Ozone

Correct Answer: Water (H2O)

Q17. Cyclic photophosphorylation produces which of the following?

  • ATP only
  • NADPH only
  • ATP and NADPH
  • Oxygen and NADPH

Correct Answer: ATP only

Q18. Non-cyclic electron flow in photosynthesis yields which combination?

  • ATP and NADPH and O2 evolution
  • Only ATP
  • Only NADH
  • Only O2 without ATP

Correct Answer: ATP and NADPH and O2 evolution

Q19. Chlorophyll absorbs light most effectively in which regions of the spectrum?

  • Green only
  • Blue and red regions
  • Infrared only
  • Ultraviolet only

Correct Answer: Blue and red regions

Q20. Carotenoids primarily function in photosynthesis by:

  • Fixing CO2
  • Acting as accessory pigments and providing photoprotection
  • Generating ATP directly
  • Transporting electrons to NADP+

Correct Answer: Acting as accessory pigments and providing photoprotection

Q21. The Hill reaction demonstrates which key concept?

  • Oxygen is produced from CO2 during the Calvin cycle
  • Light-dependent electron flow can reduce external acceptors and oxygen evolves from water
  • ATP is synthesized in mitochondria only
  • Rubisco activity is independent of light

Correct Answer: Light-dependent electron flow can reduce external acceptors and oxygen evolves from water

Q22. RuBP in the Calvin cycle refers to:

  • Ribulose-1,5-bisphosphate
  • Ribose-5-phosphate
  • Ribulose-5-phosphate
  • Ribitol-1-phosphate

Correct Answer: Ribulose-1,5-bisphosphate

Q23. Which enzyme is characteristic of C4 mesophyll cells for initial CO2 fixation?

  • Rubisco
  • PEP carboxylase
  • Citrate synthase
  • Malate dehydrogenase only

Correct Answer: PEP carboxylase

Q24. Liebig’s law of the minimum states that plant growth is controlled by:

  • The total number of nutrients present
  • The nutrient or factor in the shortest supply relative to need
  • Only light intensity
  • Genetic factors alone

Correct Answer: The nutrient or factor in the shortest supply relative to need

Q25. Cellular respiration that consumes sugars produced by photosynthesis occurs primarily in which organelle?

  • Chloroplast
  • Golgi apparatus
  • Mitochondrion
  • Ribosome

Correct Answer: Mitochondrion

Q26. The light saturation point refers to the light intensity at which:

  • Photosynthesis rate is maximal and further increases in light do not increase the rate
  • Photosynthesis ceases
  • Respiration exceeds photosynthesis
  • All chlorophyll is destroyed

Correct Answer: Photosynthesis rate is maximal and further increases in light do not increase the rate

Q27. Quantum yield in photosynthesis measures:

  • Number of photons emitted by chlorophyll
  • Amount of CO2 fixed or O2 evolved per photon absorbed
  • Light intensity per unit area
  • Proportion of green light absorbed

Correct Answer: Amount of CO2 fixed or O2 evolved per photon absorbed

Q28. Chloroplast DNA is located primarily in which compartment?

  • Thylakoid lumen
  • Stroma
  • Inner membrane
  • Intermembrane space

Correct Answer: Stroma

Q29. Xanthophyll pigments are important because they:

  • Directly fix CO2
  • Provide photoprotection by dissipating excess energy
  • Synthesize ATP in the dark
  • Transport electrons to PSII

Correct Answer: Provide photoprotection by dissipating excess energy

Q30. Ferredoxin functions in photosynthesis as a:

  • Carbon dioxide transporter
  • Protein scaffold for photosystems
  • Electron carrier that helps reduce NADP+
  • Starch-synthesizing enzyme

Correct Answer: Electron carrier that helps reduce NADP+

Q31. The immediate CO2 acceptor in the Calvin cycle of C3 plants is:

  • PEP
  • RuBP
  • Oxaloacetate
  • Malate

Correct Answer: RuBP

Q32. Conditions that favor increased photorespiration include:

  • Low temperature and high CO2
  • High temperature and high O2 relative to CO2
  • High humidity and low light
  • High CO2 and low O2

Correct Answer: High temperature and high O2 relative to CO2

Q33. In the Calvin cycle, NADPH is used primarily for:

  • Energy currency in ATP synthesis
  • Reducing 1,3-bisphosphoglycerate to G3P
  • Transporting CO2 into chloroplast
  • Starch degradation

Correct Answer: Reducing 1,3-bisphosphoglycerate to G3P

Q34. The oxygen-evolving complex of Photosystem II contains which essential metal?

  • Iron (Fe)
  • Manganese (Mn)
  • Magnesium (Mg)
  • Calcium only

Correct Answer: Manganese (Mn)

Q35. Which of the following is an example of a chemosynthetic organism?

  • Green algae
  • Nitrifying bacteria
  • Higher plants
  • Cyanobacteria using sunlight

Correct Answer: Nitrifying bacteria

Q36. Triose phosphate (G3P) exported from the chloroplast is used primarily for:

  • DNA synthesis
  • Sucrose synthesis in the cytosol
  • Electron transport in mitochondria
  • Fatty acid β-oxidation

Correct Answer: Sucrose synthesis in the cytosol

Q37. Kranz anatomy is characteristic of which photosynthetic strategy?

  • C3 plants
  • C4 plants
  • CAM plants
  • Chemosynthetic bacteria

Correct Answer: C4 plants

Q38. Which process increases ATP production without producing NADPH in the chloroplast?

  • Non-cyclic photophosphorylation
  • Cyclic photophosphorylation
  • Calvin cycle
  • Photorespiration

Correct Answer: Cyclic photophosphorylation

Q39. Stomatal opening is primarily controlled by changes in guard cell:

  • Cell wall composition
  • Turgor pressure due to ion (K+) uptake
  • Number of chloroplasts
  • Rate of mitosis

Correct Answer: Turgor pressure due to ion (K+) uptake

Q40. Which enzyme reduces 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate in the Calvin cycle?

  • Phosphoglycerate kinase
  • Glyceraldehyde-3-phosphate dehydrogenase
  • Fructose bisphosphatase
  • Rubisco

Correct Answer: Glyceraldehyde-3-phosphate dehydrogenase

Q41. How many ATP and NADPH molecules are consumed per CO2 fixed in the Calvin cycle?

  • 1 ATP and 1 NADPH
  • 3 ATP and 2 NADPH
  • 2 ATP and 3 NADPH
  • 4 ATP and 4 NADPH

Correct Answer: 3 ATP and 2 NADPH

Q42. The light compensation point is defined as the light intensity where:

  • Photosynthesis rate is zero
  • Photosynthesis equals respiration
  • Only photorespiration occurs
  • Light damage starts

Correct Answer: Photosynthesis equals respiration

Q43. Which of the following is a typical C4 crop plant?

  • Wheat
  • Maize (corn)
  • Barley
  • Potato

Correct Answer: Maize (corn)

Q44. In experimental assays of the Hill reaction, DCPIP is used as a substitute for:

  • Oxygen
  • NADP+
  • ATP
  • CO2

Correct Answer: NADP+

Q45. Which group contributes most to global primary production and O2 generation in oceans?

  • Deep-sea chemosynthetic bacteria
  • Marine phytoplankton
  • Terrestrial trees only
  • Zooplankton

Correct Answer: Marine phytoplankton

Q46. The antenna complex in photosystems functions to:

  • Fix CO2 into sugars
  • Capture light energy and funnel it to the reaction center
  • Synthesize chlorophyll
  • Generate oxygen directly

Correct Answer: Capture light energy and funnel it to the reaction center

Q47. Why do C4 plants have a lower rate of photorespiration compared to C3 plants?

  • They lack Rubisco
  • They concentrate CO2 around Rubisco using PEP carboxylation and bundle sheath compartmentalization
  • They perform photosynthesis at night only
  • They use CAM metabolism exclusively

Correct Answer: They concentrate CO2 around Rubisco using PEP carboxylation and bundle sheath compartmentalization

Q48. Regeneration of RuBP in the Calvin cycle requires which energy molecule?

  • FADH2
  • ATP
  • NADH
  • GTP only

Correct Answer: ATP

Q49. Which photosynthetic adaptation is common in water-stressed (arid) plants to reduce water loss?

  • C3 pathway enhancement
  • CAM pathway with nocturnal CO2 uptake
  • Complete loss of stomata
  • Increased photorespiration

Correct Answer: CAM pathway with nocturnal CO2 uptake

Q50. For B.Pharm students, why is understanding autotrophic nutrition important in pharmaceutical studies?

  • It explains animal drug metabolism only
  • It helps understand biosynthesis of plant secondary metabolites used as drugs
  • It is unrelated to pharmacognosy
  • It only concerns ecological fieldwork

Correct Answer: It helps understand biosynthesis of plant secondary metabolites used as drugs

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