Nutritional requirements of bacteria MCQs With Answer: This concise introduction covers microbial nutrition tailored for B. Pharm students, focusing on the nutritional requirements of bacteria, microbial nutrition, growth factors, and culture media. Understand macronutrients (carbon, nitrogen, phosphorus, sulfur), micronutrients (iron, magnesium, trace elements), vitamins as coenzymes, and the role of growth factors and energy sources in bacterial metabolism. Learn about defined vs. complex media, fastidious organisms, auxotrophy, and factors that influence in vitro growth like pH, temperature, and oxygen. These MCQs emphasize clinical and pharmaceutical relevance to help you master bacterial culture and formulation considerations. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which macronutrient is required in the largest amount by bacteria and serves as the primary building block for biomass?
- Carbon
- Nitrogen
- Phosphorus
- Sulfur
Correct Answer: Carbon
Q2. Which nitrogen source is most readily assimilated by many bacteria for amino acid and nucleotide synthesis?
- Atmospheric nitrogen (N2)
- Nitrate (NO3−)
- Ammonium (NH4+)
- Organic nitrogen (amino acids)
Correct Answer: Ammonium (NH4+)
Q3. Which of the following is a macronutrient required for nucleic acid backbone and energy metabolism?
- Iron
- Phosphorus
- Magnesium
- Potassium
Correct Answer: Phosphorus
Q4. Fastidious bacteria are best described as organisms that:
- Grow on minimal defined media without supplements
- Require multiple specific growth factors or enriched media
- Grow only at high temperatures
- Do not require vitamins
Correct Answer: Require multiple specific growth factors or enriched media
Q5. Which vitamin commonly acts as a coenzyme in redox reactions (NAD+/NADH) in bacteria?
- Biotin
- Riboflavin
- Niacin (nicotinamide)
- Folic acid
Correct Answer: Niacin (nicotinamide)
Q6. A defined (synthetic) medium is characterized by:
- Unknown exact chemical composition
- Complex extracts like yeast or meat
- Precisely known amounts of each chemical component
- Use only for eukaryotic cells
Correct Answer: Precisely known amounts of each chemical component
Q7. Which trace element is critical for many bacterial enzymes and often limits growth in natural environments?
- Sodium
- Iron
- Calcium
- Chloride
Correct Answer: Iron
Q8. Which class of bacteria uses organic compounds both as carbon source and electron donor?
- Autotrophs
- Phototrophs
- Organotrophs (heterotrophs)
- Lithotrophs
Correct Answer: Organotrophs (heterotrophs)
Q9. The term “auxotroph” refers to a bacterium that:
- Can synthesize all growth factors
- Requires a specific growth factor it cannot synthesize
- Is independent of nutrient sources
- Grows only on selective media
Correct Answer: Requires a specific growth factor it cannot synthesize
Q10. Which of the following is a common carbon source used in culture media that many bacteria can metabolize aerobically?
- Cellulose
- Glucose
- Lignin
- Rubber
Correct Answer: Glucose
Q11. Which oxygen requirement classification describes bacteria that cannot tolerate oxygen and lack superoxide dismutase and catalase?
- Obligate aerobe
- Facultative anaerobe
- Microaerophile
- Obligate anaerobe
Correct Answer: Obligate anaerobe
Q12. Which growth factor is often required by Haemophilus influenzae for heme-containing enzymes?
- Vitamin B12
- Factor X (hemin)
- Glucose
- Magnesium
Correct Answer: Factor X (hemin)
Q13. Complex media differ from defined media mainly because they contain:
- Only inorganic salts
- Precisely measured pure chemicals
- Extracts or digests of biological materials with unknown composition
- No carbon source
Correct Answer: Extracts or digests of biological materials with unknown composition
Q14. Which ion often stabilizes ribosomes and nucleic acids and is essential for many bacterial enzymes?
- Magnesium (Mg2+)
- Sodium (Na+)
- Chloride (Cl−)
- Fluoride (F−)
Correct Answer: Magnesium (Mg2+)
Q15. Sulfur in bacterial media is primarily required for the synthesis of:
- Nucleic acids
- Fatty acids
- Amino acids like cysteine and methionine
- Carbohydrates
Correct Answer: Amino acids like cysteine and methionine
Q16. Which culture medium component supplies both nitrogen and growth factors and is commonly found in enriched media?
- Sodium chloride
- Yeast extract
- Crystal violet
- Agar
Correct Answer: Yeast extract
Q17. Which electron acceptor is used by many facultative anaerobes under anaerobic respiration to generate energy?
- Oxygen only
- Nitrate (NO3−)
- Hydrogen gas
- Glucose
Correct Answer: Nitrate (NO3−)
Q18. Quorum sensing influences bacterial growth and metabolism by regulating:
- Only DNA replication fidelity
- Population-density dependent gene expression
- Abiotic nutrient composition
- Temperature tolerance exclusively
Correct Answer: Population-density dependent gene expression
Q19. Which of the following is a bacterial growth factor often required in purine and pyrimidine biosynthesis?
- Folic acid (folate)
- Vitamin C
- Cholesterol
- Vitamin D
Correct Answer: Folic acid (folate)
Q20. Osmotic pressure in media is most directly controlled by adjusting the concentration of:
- Trace metals
- Salts such as NaCl
- Vitamins
- Protein hydrolysates
Correct Answer: Salts such as NaCl
Q21. Which type of bacteria can fix atmospheric nitrogen (N2) into bioavailable forms?
- Nitrogen-fixing bacteria like Rhizobium
- All obligate aerobes
- Pathogenic streptococci only
- All heterotrophs
Correct Answer: Nitrogen-fixing bacteria like Rhizobium
Q22. Which pigment-binding growth factor is required by certain bacteria for cytochromes and electron transport?
- Hemin
- Carotene
- Cellulose
- Starch
Correct Answer: Hemin
Q23. Bacterial generation time is defined as:
- Time to form a colony on agar
- Time for the population to decrease by half
- Time required for the population to double
- Time between two consecutive measurements of OD
Correct Answer: Time required for the population to double
Q24. Which method directly measures bacterial turbidity as an indirect estimate of growth in liquid culture?
- Viable plate count
- Optical density (spectrophotometry)
- ATP bioluminescence
- Gram staining
Correct Answer: Optical density (spectrophotometry)
Q25. Which of the following best describes lithotrophs?
- Use inorganic molecules as electron donors
- Use organic molecules as carbon sources exclusively
- Require light as an energy source only
- Cannot grow on mineral salts media
Correct Answer: Use inorganic molecules as electron donors
Q26. Which amino acid or derivative is commonly supplied externally for bacteria that cannot synthesize it and is a common auxotrophic requirement?
- Alanine
- Methionine
- Glucose
- Fructose
Correct Answer: Methionine
Q27. Selective media contain agents that:
- Support the growth of all microbes equally
- Suppress unwanted microbes while allowing target organisms to grow
- Provide defined chemical composition for metabolic studies
- Eliminate the need for incubation
Correct Answer: Suppress unwanted microbes while allowing target organisms to grow
Q28. Which compound serves as a key sulfur source in defined media for bacterial growth?
- Sodium sulfate or ammonium sulfate
- Sodium nitrate
- Calcium carbonate
- Glycerol
Correct Answer: Sodium sulfate or ammonium sulfate
Q29. Which of the following terms describes bacteria that derive energy from light?
- Chemotrophs
- Phototrophs
- Organotrophs
- Barotrophs
Correct Answer: Phototrophs
Q30. Which assay quantifies viable bacterial cells capable of forming colonies on solid media?
- Direct microscopy count
- Viable plate count (CFU)
- Turbidimetric measurement only
- pH indicator test
Correct Answer: Viable plate count (CFU)
Q31. Siderophores secreted by bacteria function to:
- Digest complex carbohydrates
- Sequester and import iron from the environment
- Act as antibiotics against other bacteria
- Stabilize membrane lipids
Correct Answer: Sequester and import iron from the environment
Q32. Which condition in media most influences the ionization state of nutrients and enzyme activity in bacteria?
- Color
- pH
- Viscosity
- Transparency
Correct Answer: pH
Q33. Which organism type uses carbon dioxide as its sole carbon source?
- Heterotrophs
- Autotrophs
- Facultative anaerobes
- Organotrophs
Correct Answer: Autotrophs
Q34. Which compound is an essential cofactor for carboxylation reactions and is often supplied in media as a vitamin?
- Biotin
- Thiamine
- Riboflavin
- Vitamin K
Correct Answer: Biotin
Q35. Minimal medium is best defined as a medium that:
- Contains only the compounds essential for growth of a wild-type organism
- Contains rich organic supplements
- Lacks a carbon source
- Is selective for Gram-negative bacteria
Correct Answer: Contains only the compounds essential for growth of a wild-type organism
Q36. Which environmental factor most directly affects membrane fluidity and enzyme function in bacteria?
- Light intensity
- Temperature
- Magnetic field
- Ultraviolet radiation
Correct Answer: Temperature
Q37. Which metabolic pathway supplies precursors for amino acid and nucleotide biosynthesis and is central to bacterial anabolism?
- Glycolysis and pentose phosphate pathway
- Urea cycle
- Beta-oxidation exclusively
- Photosynthetic light reactions only
Correct Answer: Glycolysis and pentose phosphate pathway
Q38. Which media additive is often included to neutralize toxic peroxides for supporting growth of microaerophiles?
- Catalase or cysteine
- Phenol red
- Metal ions like mercury
- SDS (sodium dodecyl sulfate)
Correct Answer: Catalase or cysteine
Q39. Which phosphorus-containing molecule is directly used as an energy currency in bacterial cells?
- DNA
- ATP
- Peptidoglycan
- Cellulose
Correct Answer: ATP
Q40. Which of the following best explains why some bacteria require vitamins in their growth media?
- Vitamins act as structural cell wall components
- Vitamins serve as precursors/cofactors for essential enzymatic reactions
- Vitamins directly provide ATP
- Vitamins are the primary carbon source
Correct Answer: Vitamins serve as precursors/cofactors for essential enzymatic reactions
Q41. In pharmaceutical microbiology, understanding bacterial nutritional requirements helps to:
- Design culture-independent sequencing only
- Optimize isolation, formulation, and stability testing of microbial products
- Eliminate need for sterility testing
- Predict human dietary needs
Correct Answer: Optimize isolation, formulation, and stability testing of microbial products
Q42. Which type of agar medium differentiates bacteria based on lactose fermentation and pH indicator changes?
- Blood agar
- MacConkey agar
- Nutrient agar
- Minimal salts agar
Correct Answer: MacConkey agar
Q43. Which biochemical requirement is directly assessed by supplying nucleotides or nucleosides in the medium?
- Lipid synthesis
- Nucleotide auxotrophy or inability to synthesize purines/pyrimidines
- Carbohydrate fermentation
- Motility determination
Correct Answer: Nucleotide auxotrophy or inability to synthesize purines/pyrimidines
Q44. Which ion is often required for DNA polymerase function and stabilization of the replication complex?
- Iron (Fe2+/Fe3+)
- Magnesium (Mg2+)
- Potassium (K+)
- Chloride (Cl−)
Correct Answer: Magnesium (Mg2+)
Q45. Which metabolic strategy do obligate chemolithoautotrophs use?
- Use inorganic electron donors and CO2 as carbon source
- Use organic compounds for both carbon and electrons
- Require light for energy
- Grow only in host tissues
Correct Answer: Use inorganic electron donors and CO2 as carbon source
Q46. Which compound is commonly added to media to chelate iron and thereby make it less available to bacteria for selective inhibition?
- EDTA
- NaCl
- Glucose
- Agar
Correct Answer: EDTA
Q47. Which measurement provides information about metabolic activity and live biomass rather than just turbidity?
- Optical density at 600 nm
- ATP assay (bioluminescence)
- Colony morphology
- Gram stain color
Correct Answer: ATP assay (bioluminescence)
Q48. Which factor would most likely increase bacterial growth rate in vitro for a strain limited by oxygen diffusion?
- Decrease temperature below optimum
- Increase aeration or agitation
- Remove carbon source
- Add bacteriostatic antibiotic
Correct Answer: Increase aeration or agitation
Q49. Which of the following is a primary reason some pathogens are difficult to culture in the lab?
- They grow too fast on simple media
- They require specific host-derived growth factors and complex conditions
- They are all obligate phototrophs
- They do not need water
Correct Answer: They require specific host-derived growth factors and complex conditions
Q50. In designing a minimal medium to study auxotrophy, what is the most appropriate first step?
- Add random vitamins until growth occurs
- Determine the wild-type organism’s essential nutrients and systematically add defined components
- Use undiluted blood as the only supplement
- Exclude carbon and nitrogen sources
Correct Answer: Determine the wild-type organism’s essential nutrients and systematically add defined components
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