Agar — chemistry, sources, preparation, evaluation, preservation, storage, therapeutic uses and commercial utility is a vital topic for B.Pharm students. Agar is a natural polysaccharide composed mainly of agarose and agaropectin, extracted from red algae such as Gelidium and Gracilaria. Understanding its chemistry (monomer units, sulfate content), preparation (alkali treatment, purification), analytical evaluation (gel strength, clarity, ash, moisture), and proper preservation/storage is essential for pharmaceutical applications. Agar’s roles include microbiological media, excipient in drug delivery, food stabilizer, and therapeutic dietary fiber. This keyword-rich overview links fundamental principles to commercial utility and lab practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What are the two main components of agar?
- Agarose and agaropectin
- Cellulose and hemicellulose
- Pectin and starch
- Chitosan and alginate
Correct Answer: Agarose and agaropectin
Q2. Which organisms are the primary commercial sources of agar?
- Gelidium and Gracilaria
- Ulva and Sargassum
- Porphyra and Laminaria
- Chlorella and Spirulina
Correct Answer: Gelidium and Gracilaria
Q3. Complete hydrolysis of agar yields which monosaccharides?
- D-galactose and 3,6-anhydro-L-galactose
- D-glucose and D-mannose
- Glucuronic acid and mannuronic acid
- L-rhamnose and D-fructose
Correct Answer: D-galactose and 3,6-anhydro-L-galactose
Q4. Which component primarily determines the gel strength of agar?
- Agarose and its linear chain structure
- Agaropectin sulfate groups
- Protein impurities
- Residual salts only
Correct Answer: Agarose and its linear chain structure
Q5. Typical gelling and melting temperature ranges for agar gels are:
- Gelling ~32–40°C; melting ~85–95°C
- Gelling ~0–5°C; melting ~20–30°C
- Gelling ~60–70°C; melting ~90–100°C
- Gelling ~45–55°C; melting ~65–75°C
Correct Answer: Gelling ~32–40°C; melting ~85–95°C
Q6. A common step in commercial agar preparation to improve gel strength is:
- Alkali treatment (NaOH) followed by washing and drying
- Acid hydrolysis without washing
- Direct sun-drying of seaweed without chemical treatment
- Fermentation with yeast
Correct Answer: Alkali treatment (NaOH) followed by washing and drying
Q7. Which parameter is most widely used to evaluate the quality of agar for microbiological use?
- Gel strength (measured at a defined concentration and temperature)
- Protein nitrogen content
- Viscosity at 100°C
- pH of a 0.1% solution only
Correct Answer: Gel strength (measured at a defined concentration and temperature)
Q8. What unit is commonly used to express agar gel strength in many pharmacopeial methods?
- g/cm² (grams per square centimeter)
- mPa·s (millipascal-second)
- °Brix
- ppm (parts per million)
Correct Answer: g/cm² (grams per square centimeter)
Q9. High sulfate content in agar typically affects gel properties by:
- Reducing gel strength and producing a weaker gel
- Increasing gel melting temperature dramatically
- Converting agarose to protein
- Eliminating gelling properties entirely
Correct Answer: Reducing gel strength and producing a weaker gel
Q10. Recommended storage conditions for powdered agar to preserve quality are:
- Cool, dry, airtight container away from light
- Open shelf in humid area
- Refrigerated at −20°C with high humidity
- Stored in direct sunlight to prevent microbial growth
Correct Answer: Cool, dry, airtight container away from light
Q11. Why is agar widely used as a solidifying agent in microbiology?
- It remains solid at incubation temperatures and is not metabolized by most bacteria
- It melts at room temperature enabling easy colony mixing
- It is readily digested by bacteria, providing nutrients
- It reacts chemically with bacterial cell walls
Correct Answer: It remains solid at incubation temperatures and is not metabolized by most bacteria
Q12. Which feature distinguishes agar from gelatin in pharmaceutical use?
- Agar is plant-derived with higher melting point and thermostability
- Agar is animal-derived and sensitive to bacterial enzymes
- Agar forms irreversible covalent gels
- Agar cannot form gels in aqueous systems
Correct Answer: Agar is plant-derived with higher melting point and thermostability
Q13. Agarose is particularly useful in electrophoresis because it:
- Forms a porous matrix for size-based separation of nucleic acids
- Contains proteins that bind DNA selectively
- Is electrically conductive without buffer
- Degrades quickly during electrophoresis
Correct Answer: Forms a porous matrix for size-based separation of nucleic acids
Q14. Which analytical test is used to detect sulfate groups in agaropectin?
- Barium chloride turbidity (sulfate) test
- Kjeldahl nitrogen test
- Biuret protein test
- Phenol-sulfuric acid carbohydrate test only
Correct Answer: Barium chloride turbidity (sulfate) test
Q15. In the food industry, agar is primarily used as a:
- Gelling and stabilizing agent in food and confectionery
- Primary sweetener in beverages
- Preservative replacing sodium benzoate
- Coloring agent for confectionery
Correct Answer: Gelling and stabilizing agent in food and confectionery
Q16. Which therapeutic or health-related use is associated with agar when consumed?
- Dietary fiber/bulk-forming laxative and weight-loss aid
- Antibiotic for systemic infections
- Systemic anticoagulant
- High-calorie nutritional supplement
Correct Answer: Dietary fiber/bulk-forming laxative and weight-loss aid
Q17. Best practice to prevent microbial contamination of powdered agar during long-term storage is to:
- Keep it dry in an airtight container with desiccant
- Store it in a bowl uncovered at room temperature
- Mix it with glucose to inhibit microbes
- Expose it to sunlight periodically
Correct Answer: Keep it dry in an airtight container with desiccant
Q18. Which analytical indicator suggests high purity of commercial agar?
- Low ash content indicating minimal inorganic impurities
- High protein content
- High turbidity of a 1% solution
- High moisture content over 20%
Correct Answer: Low ash content indicating minimal inorganic impurities
Q19. Which technique is appropriate for determining the molecular weight distribution of agarose?
- Gel permeation (size exclusion) chromatography
- Gas chromatography with flame ionization detector
- UV-visible spectrophotometry without standards
- Atomic absorption spectroscopy
Correct Answer: Gel permeation (size exclusion) chromatography
Q20. What effect does alkali treatment of seaweed have during agar extraction?
- Converts L-galactose to 3,6-anhydro-L-galactose increasing gel strength
- Removes all agarose converting it to starch
- Makes agar completely soluble in organic solvents
- Eliminates carbohydrate content entirely
Correct Answer: Converts L-galactose to 3,6-anhydro-L-galactose increasing gel strength
Q21. Which fraction of agar contains the sulfated branched polysaccharide?
- Agaropectin
- Agarose
- Cellulose fraction
- Starch fraction
Correct Answer: Agaropectin
Q22. The recommended sterilization method for prepared agar media in labs is:
- Autoclaving at 121°C and 15 psi
- Dry heat at 160°C for 15 minutes
- Filtration through 0.45 μm membrane
- Exposure to UV light only
Correct Answer: Autoclaving at 121°C and 15 psi
Q23. In pharmaceutical formulations agar is commonly used as an:
- Excipient: gelling agent and matrix for drug delivery
- Primary active pharmaceutical ingredient for infections
- Solvent for nonpolar drugs
- Preservative for injectable solutions
Correct Answer: Excipient: gelling agent and matrix for drug delivery
Q24. Commercial grades of agar typically include which categories?
- Bacteriological, pharmaceutical and food-grade
- Industrial metal-grade only
- Pharmaceutical grade only
- Agricultural feed-grade exclusively
Correct Answer: Bacteriological, pharmaceutical and food-grade
Q25. Which analytical method provides sensitive quantification of sulfate groups in agar?
- Ion chromatography
- Infrared spectroscopy without standards
- Polarimetry
- Refractometry
Correct Answer: Ion chromatography
Q26. Maximum recommended moisture content for good-quality powdered agar is typically:
- Not more than 12% (w/w)
- More than 25% (w/w)
- Exactly 50% (w/w)
- Less than 0.1% (w/w)
Correct Answer: Not more than 12% (w/w)
Q27. Which term best describes the thermal behavior of agar gels?
- Thermoreversible (they set on cooling and remelt on heating)
- Thermosetting (irreversible crosslinked gels)
- Photoreactive gels only
- Non-thermal gels that form in organic solvents
Correct Answer: Thermoreversible (they set on cooling and remelt on heating)
Q28. Which statement about agarose gels at incubation temperatures (e.g., 37°C) is true?
- They set on cooling and remain stable at incubation temperatures commonly used in microbiology
- They completely dissolve at 25°C
- They are liquefied at 4°C
- They polymerize further at 37°C forming covalent bonds
Correct Answer: They set on cooling and remain stable at incubation temperatures commonly used in microbiology
Q29. After full acid hydrolysis of agar, which sugar is detected?
- D-galactose
- D-fructose
- D-xylose
- L-arabinose
Correct Answer: D-galactose
Q30. Which quality control test assesses microbial contamination of commercial agar powder?
- Total aerobic microbial count (plate count)
- Colorimetric protein assay only
- Viscosity at 200°C
- pH measurement without culture
Correct Answer: Total aerobic microbial count (plate count)
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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