Introduction to metabolic pathways in higher plants is essential for B. Pharm students studying plant-derived drugs and phytochemistry. This concise overview covers primary metabolism — photosynthesis, glycolysis, the Calvin cycle, TCA cycle and respiration — and secondary metabolism that produces alkaloids, flavonoids, terpenoids and phenolics. Emphasis is on enzyme regulation, metabolic flux, compartmentalization in chloroplasts, mitochondria and cytosol, and biosynthesis of amino acids and fatty acids relevant to pharmacognosy and drug discovery. Understanding these biochemical routes helps predict metabolite profiles, extraction targets, and bioactivity. The focus is practical links to pharmaceutics, drug precursors and quality control. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which subcellular location is the primary site of the Calvin cycle in higher plants?
- Chloroplast stroma
- Mitochondrial matrix
- Cytosol
- Peroxisome
Correct Answer: Chloroplast stroma
Q2. What is the first stable product formed during CO2 fixation in the C3 Calvin cycle?
- 3-phosphoglycerate (3-PGA)
- Ribulose-1,5-bisphosphate (RuBP)
- Fructose-6-phosphate
- Glyceraldehyde-3-phosphate (G3P)
Correct Answer: 3-phosphoglycerate (3-PGA)
Q3. Rubisco exhibits which two enzymatic activities that influence carbon efficiency in plants?
- Carboxylation and oxygenation of RuBP
- Decarboxylation and transamination
- Hydroxylation and methylation
- Phosphorylation and dephosphorylation
Correct Answer: Carboxylation and oxygenation of RuBP
Q4. Which pathways are the major sources of NADPH for biosynthetic reactions in higher plants?
- Light reactions of photosynthesis and oxidative pentose phosphate pathway
- Glycolysis and TCA cycle
- Photorespiration and glyoxylate cycle
- Beta-oxidation and fermentation
Correct Answer: Light reactions of photosynthesis and oxidative pentose phosphate pathway
Q5. Where does glycolysis occur in plant cells and why is its location important for metabolite partitioning?
- Cytosol
- Chloroplast stroma
- Mitochondrial matrix
- Vacuole
Correct Answer: Cytosol
Q6. In higher plants, the tricarboxylic acid (TCA) cycle is localized primarily in which compartment?
- Mitochondrial matrix
- Chloroplast stroma
- Peroxisome
- Cytosol
Correct Answer: Mitochondrial matrix
Q7. The glyoxylate cycle, important for seedling conversion of lipids to carbohydrates, operates in which specialized organelle?
- Glyoxysome (specialized peroxisome)
- Chloroplast
- Mitochondrion
- Endoplasmic reticulum
Correct Answer: Glyoxysome (specialized peroxisome)
Q8. Which pathway in plants provides precursors for aromatic amino acids and many phenolic secondary metabolites?
- Shikimate pathway in plastids
- Methylerythritol phosphate (MEP) pathway
- Glycolysis
- Beta-oxidation pathway
Correct Answer: Shikimate pathway in plastids
Q9. The universal five-carbon building block for terpenoid biosynthesis is which compound?
- Isopentenyl diphosphate (IPP)
- Acetyl-CoA
- Phenylalanine
- Malonyl-CoA
Correct Answer: Isopentenyl diphosphate (IPP)
Q10. Which enzyme catalyzes the first committed step of the phenylpropanoid pathway, linking primary metabolism to many plant secondary metabolites?
- Phenylalanine ammonia-lyase (PAL)
- Chalcone synthase (CHS)
- Tyrosine decarboxylase
- Shikimate dehydrogenase
Correct Answer: Phenylalanine ammonia-lyase (PAL)
Q11. De novo fatty acid synthesis in plant cells occurs primarily in which compartment?
- Plastid (chloroplast) stroma
- Mitochondrial matrix
- Cytosol
- Peroxisome
Correct Answer: Plastid (chloroplast) stroma
Q12. Which regulatory mechanism commonly controls pathway flux by inhibiting the first committed enzyme when end-product concentration is high?
- Feedback (end-product) inhibition
- Allosteric activation by substrates
- Competitive inhibition by analogs
- Covalent modification by phosphorylation
Correct Answer: Feedback (end-product) inhibition
Q13. The primary molecular machine that synthesizes ATP using a proton motive force during oxidative phosphorylation is called what?
- ATP synthase (F-type ATPase)
- Cytochrome c oxidase
- NADH dehydrogenase
- Succinate dehydrogenase
Correct Answer: ATP synthase (F-type ATPase)
Q14. Photorespiration in C3 plants leads to which of the following outcomes affecting carbon economy?
- Consumes ATP and releases CO2 reducing photosynthetic efficiency
- Increases net carbon fixation per light photon
- Synthesizes additional amino acids without carbon loss
- Stimulates direct synthesis of isoprenoids
Correct Answer: Consumes ATP and releases CO2 reducing photosynthetic efficiency
Q15. The oxidative pentose phosphate pathway is especially important in plants because it provides which two key products?
- NADPH and ribose-5-phosphate
- ATP and pyruvate
- O2 and CO2
- Acetyl-CoA and malonyl-CoA
Correct Answer: NADPH and ribose-5-phosphate
Q16. Which cofactors commonly donate and accept hydride ions in plant dehydrogenase reactions for metabolism and biosynthesis?
- NAD+ and NADP+
- FAD and FMN
- Biotin and lipoic acid
- CoA and ATP
Correct Answer: NAD+ and NADP+
Q17. In C4 photosynthesis, which enzyme initially fixes bicarbonate into oxaloacetate in mesophyll cells?
- PEP carboxylase (PEPC)
- Rubisco
- Pyruvate kinase
- Rubisco activase
Correct Answer: PEP carboxylase (PEPC)
Q18. A defining feature of CAM (Crassulacean Acid Metabolism) plants that conserves water is:
- Fixing CO2 at night as malic acid stored in vacuoles
- Using Rubisco at night for carbon fixation
- Transporting malate to mitochondria for immediate respiration
- Opening stomata at midday to maximize light capture
Correct Answer: Fixing CO2 at night as malic acid stored in vacuoles
Q19. Which class of secondary metabolites is most commonly derived from amino acids and often has potent pharmacological activity?
- Alkaloids
- Terpenes
- Polyketides
- Carbohydrates
Correct Answer: Alkaloids
Q20. The initial substrates for the shikimate pathway are derived from which two metabolic intermediates?
- Phosphoenolpyruvate and erythrose-4-phosphate
- Acetyl-CoA and malonyl-CoA
- Pyruvate and glyceraldehyde-3-phosphate
- Oxaloacetate and alpha-ketoglutarate
Correct Answer: Phosphoenolpyruvate and erythrose-4-phosphate
Q21. Which enzyme complex irreversibly links glycolysis to the TCA cycle by converting pyruvate to acetyl-CoA?
- Pyruvate dehydrogenase complex (PDH)
- Pyruvate kinase
- Alcohol dehydrogenase
- Pyruvate carboxylase
Correct Answer: Pyruvate dehydrogenase complex (PDH)
Q22. During germination of oil-rich seeds, fatty acid beta-oxidation primarily occurs in which organelle type?
- Peroxisomes (glyoxysomes in oilseeds)
- Chloroplasts
- Mitochondria
- Endoplasmic reticulum
Correct Answer: Peroxisomes (glyoxysomes in oilseeds)
Q23. What is the major rate-limiting enzyme of glycolysis that is allosterically regulated by cellular energy charge?
- Phosphofructokinase (PFK)
- Hexokinase
- Glyceraldehyde-3-phosphate dehydrogenase
- Enolase
Correct Answer: Phosphofructokinase (PFK)
Q24. Which metabolic shuttle helps export reducing equivalents (NADPH/NADH) between chloroplast and cytosol in plants?
- Malate-oxaloacetate shuttle (malate valve)
- Glycerol-3-phosphate shuttle
- Urea cycle shuttle
- Acetyl-CoA shuttle
Correct Answer: Malate-oxaloacetate shuttle (malate valve)
Q25. The first committed enzyme of flavonoid biosynthesis that condenses malonyl-CoA with coumaroyl-CoA is:
- Chalcone synthase (CHS)
- Chalcone isomerase (CHI)
- Phenylalanine ammonia-lyase (PAL)
- Flavonol synthase (FLS)
Correct Answer: Chalcone synthase (CHS)
Q26. Plant cytochrome P450 monooxygenases involved in secondary metabolism typically require which electron donor/cofactor?
- NADPH and cytochrome P450 reductase
- FAD alone
- NADH and ferredoxin
- ATP and biotin
Correct Answer: NADPH and cytochrome P450 reductase
Q27. The plastid-localized non-mevalonate pathway for isoprenoid biosynthesis is known by which acronym?
- MEP pathway (methylerythritol phosphate)
- MVA pathway (mevalonate)
- PPP pathway (pentose phosphate)
- Glyoxylate pathway
Correct Answer: MEP pathway (methylerythritol phosphate)
Q28. Many plant alkaloids are biosynthesized from which types of primary metabolites?
- Amino acids such as tyrosine and tryptophan
- Fatty acids and glycerol
- Simple sugars only
- Inorganic nitrogen and sulfate
Correct Answer: Amino acids such as tyrosine and tryptophan
Q29. Which experimental approach is commonly used in plant metabolic flux analysis to trace carbon flow through pathways?
- 13C tracer studies analyzed by GC-MS or NMR
- Western blotting of enzymes
- RNA interference of pathway genes
- Light microscopy of plastids
Correct Answer: 13C tracer studies analyzed by GC-MS or NMR
Q30. Transcriptional regulation of phenylpropanoid and flavonoid biosynthesis in plants is often mediated by which family of transcription factors?
- MYB transcription factors
- p53 family proteins
- Heat-shock factors (HSFs)
- Sigma factors
Correct Answer: MYB transcription factors
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com