Applications of radioisotopes in phytochemistry empower B. Pharm students to explore plant metabolism, biosynthetic pathways, and phytochemical localization with exceptional sensitivity. Radiotracers and radiolabelled compounds (14C, 3H, 35S, 32P, 11C, 125I) enable tracking of uptake, translocation, turnover rates, and secondary metabolite biosynthesis using autoradiography, liquid scintillation counting, gamma counters, and PET. Understanding specific activity, radiochemical purity, pulse‑chase experiments, and safety/regulatory practices is essential for accurate metabolic flux analysis, drug‑plant interaction studies, and pharmacognosy research. This topic links radiotracing techniques to practical phytochemical analysis, experimental design, and data interpretation for pharmaceutical applications. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary application of radioisotopes in phytochemistry?
- Quantitative formulation of herbal extracts
- Tracing biosynthetic pathways in plants
- Genetic modification of plant DNA
- Enhancing photosynthesis rates
Correct Answer: Tracing biosynthetic pathways in plants
Q2. Which radioisotope is most commonly used for tracing carbon incorporation into plant metabolites?
- 14C
- 32P
- 125I
- 60Co
Correct Answer: 14C
Q3. Which isotope is preferred for labeling sulfur-containing phytochemicals?
- 35S
- 14C
- 3H
- 32P
Correct Answer: 35S
Q4. For highest spatial resolution in tissue autoradiography which isotope is often chosen?
- 3H
- 14C
- 32P
- 125I
Correct Answer: 3H
Q5. Which detector is specifically designed for measuring gamma-emitting radioisotopes?
- Gamma counter
- Liquid scintillation counter
- Autoradiography film
- Mass spectrometer
Correct Answer: Gamma counter
Q6. What is the SI unit of radioactivity?
- Becquerel (Bq)
- Gray (Gy)
- Sievert (Sv)
- Roentgen (R)
Correct Answer: Becquerel (Bq)
Q7. Which technique is most suitable to quantify beta-emitting radiolabels in liquid plant extracts?
- Liquid scintillation counting
- Gamma counting
- Autoradiography
- High-resolution mass spectrometry
Correct Answer: Liquid scintillation counting
Q8. What is the main purpose of a pulse‑chase experiment using radiolabelled precursors in plants?
- To sterilize plant tissues before analysis
- To determine metabolic turnover and flux of labeled compounds
- To increase isotope half-life
- To label DNA permanently
Correct Answer: To determine metabolic turnover and flux of labeled compounds
Q9. Which is a major advantage of using radioisotopes in phytochemical studies?
- High sensitivity and ability to detect trace metabolites
- No regulatory requirements
- Unlimited safe disposal options
- Zero background noise in all samples
Correct Answer: High sensitivity and ability to detect trace metabolites
Q10. What is a significant limitation when using radioisotopes in plant research?
- Regulatory handling requirements and radiation hazards
- Inability to detect metabolic intermediates
- Radioisotopes always increase plant growth
- They eliminate the need for controls
Correct Answer: Regulatory handling requirements and radiation hazards
Q11. Which short-lived radioisotope is commonly used for in vivo PET imaging of plant metabolism?
- 11C
- 14C
- 35S
- 125I
Correct Answer: 11C
Q12. Which radioisotope has an approximate half-life of 5,730 years and is widely used in long-term carbon tracing?
- 14C
- 3H
- 32P
- 131I
Correct Answer: 14C
Q13. What does ‘specific activity’ refer to in radiolabelled compounds?
- Radioactivity per unit mass or mole of compound
- Total activity in a lab room
- Physical half-life of the isotope
- Number of labeled atoms only
Correct Answer: Radioactivity per unit mass or mole of compound
Q14. Autoradiography in phytochemistry is primarily used to:
- Localize radiolabelled molecules within plant tissues
- Increase the specific activity of labels
- Measure environmental radiation levels
- Sterilize plant sections for analysis
Correct Answer: Localize radiolabelled molecules within plant tissues
Q15. Which instrument is typically used to detect beta emissions from 14C-labeled extracts?
- Liquid scintillation counter
- Geiger-Müller counter
- Gamma camera
- Ultraviolet spectrophotometer
Correct Answer: Liquid scintillation counter
Q16. Radiochemical purity is defined as:
- The fraction of total radioactivity present in the desired chemical form
- The biological activity of the labeled compound
- The specific activity per mol
- The half-life of the isotope
Correct Answer: The fraction of total radioactivity present in the desired chemical form
Q17. To remove unbound radiolabel from plant tissue before analysis, you should:
- Perform thorough washing and appropriate solvent extraction
- Heat the tissue briefly and analyze directly
- Freeze-dry without washing
- Expose samples to direct sunlight
Correct Answer: Perform thorough washing and appropriate solvent extraction
Q18. The isotope dilution method in phytochemistry is used to:
- Quantify metabolite concentration using a labeled internal standard
- Increase radioactive decay rate
- Label proteins irreversibly
- Determine plant DNA sequence
Correct Answer: Quantify metabolite concentration using a labeled internal standard
Q19. Which radioisotope is commonly used to label nucleic acids for detection and tracing studies?
- 32P
- 14C
- 35S
- 3H
Correct Answer: 32P
Q20. Which technique integrates chromatography with radiometric detection to separate and identify radiolabelled phytochemicals?
- Radio‑HPLC (HPLC with radiometric detector)
- Gas chromatography without detector
- Plain TLC without detection
- UV spectrophotometry only
Correct Answer: Radio‑HPLC (HPLC with radiometric detector)
Q21. Proper disposal of radioactive plant waste typically requires:
- Decay-in-storage according to institutional and regulatory guidelines
- Throwing waste in ordinary trash
- Open-air burning
- Dumping in chemical drains
Correct Answer: Decay-in-storage according to institutional and regulatory guidelines
Q22. The half-life of a radioisotope is defined as:
- The time required for half the radioactive atoms to decay
- The time for radioactivity to double
- The time needed for sample preparation
- The time until all radioactivity is gone
Correct Answer: The time required for half the radioactive atoms to decay
Q23. For non-invasive, real-time imaging of whole-plant metabolite flow, which modality is most suitable?
- PET (Positron Emission Tomography)
- Autoradiography
- Liquid scintillation counting
- Gamma counting of homogenates
Correct Answer: PET (Positron Emission Tomography)
Q24. Which personal safety practice is essential when working with radioisotopes?
- Wearing and monitoring a personal dosimeter
- Using only paper gloves
- Working near open food
- No training is needed
Correct Answer: Wearing and monitoring a personal dosimeter
Q25. Which radioisotope commonly emits gamma photons suitable for external detection and immunoassays?
- 125I
- 14C
- 3H
- 35S
Correct Answer: 125I
Q26. Metabolic labeling of plants by feeding radiolabelled precursors is primarily used to:
- Trace incorporation into secondary metabolites
- Eliminate secondary metabolism
- Make plants radioactive for disposal
- Measure soil nutrient levels only
Correct Answer: Trace incorporation into secondary metabolites
Q27. Before radiometric detection, the best method to separate complex radiolabelled phytochemicals is:
- Chromatography (HPLC or TLC)
- Direct counting without separation
- Simple filtration only
- Heating to remove impurities
Correct Answer: Chromatography (HPLC or TLC)
Q28. Which factor most directly improves the detection sensitivity of a radiolabelled tracer experiment?
- Higher specific activity of the radiolabel
- Longer exposure to sunlight
- Using non-radioactive tracers only
- Decreasing solvent polarity
Correct Answer: Higher specific activity of the radiolabel
Q29. Which radioisotope is typically used to study phosphate uptake and metabolism in plants?
- 32P
- 14C
- 35S
- 3H
Correct Answer: 32P
Q30. ‘Counts per minute’ (CPM) in radiometric assays refers to:
- The number of detected radioactive events per minute by the counter
- The molar concentration of a metabolite
- The half-life of the isotope in minutes
- The temperature of the scintillation cocktail
Correct Answer: The number of detected radioactive events per minute by the counter
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.
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