Environmental Microbiology — MCQs

Environmental Microbiology Indian Medical PG Practice Questions and MCQs

Question 11: Which test is most commonly used for rapid quantitative detection of coliform bacteria in water samples?

A. Multiple-tube fermentation technique
B. Membrane filtration method (Correct Answer)
C. Oxidase test
D. Gram staining

Explanation: ***Membrane filtration method*** - This method is the **most widely used technique** for rapid quantitative detection of coliforms in water quality testing. - A water sample is passed through a sterile membrane filter (0.45 μm pore size), which traps bacteria, and the filter is then cultured on a selective medium (like m-Endo agar). - Results are obtained in **24 hours**, and colony counts provide a direct quantitative measure. - It is the **preferred method** for routine water quality monitoring in modern laboratories. *Multiple-tube fermentation technique* - This is the traditional **Most Probable Number (MPN) method**, consisting of presumptive, confirmed, and completed tests. - While it is a **standard reference method** and still widely used, it requires **multiple serial dilutions** and takes **48-96 hours** for complete results. - It provides a statistical estimate rather than direct counts, making it less convenient for routine screening compared to membrane filtration. *Oxidase test* - The oxidase test identifies bacteria that produce **cytochrome c oxidase enzyme**. - It is used to differentiate *Pseudomonas* (oxidase-positive) from enteric bacteria like coliforms (oxidase-negative). - It is **not a primary method** for detecting coliforms in water samples. *Gram staining* - Gram staining differentiates bacteria based on **cell wall composition** (Gram-positive vs. Gram-negative). - While coliforms are Gram-negative, this technique is for **bacterial identification**, not for quantitative detection of coliforms in water samples.

Question 12: A bacterium that can thrive at temperatures around 60-70 degrees Celsius is classified as

A. Thermophilic (Correct Answer)
B. Mesophilic
C. Cryophilic
D. Halophilic

Explanation: ***Thermophilic*** - **Thermophilic** bacteria are heat-loving organisms that thrive at high temperatures, typically in the range of **45°C to 80°C**, with optimal growth around 50-70°C - These organisms are commonly found in hot springs, compost heaps, and industrial processes - **Note**: Extreme thermophiles (hyperthermophiles) can grow at temperatures exceeding 80-100°C, found in hydrothermal vents and geothermal environments *Mesophilic* - **Mesophilic** bacteria grow best at moderate temperatures, typically between **20°C and 45°C** - This includes most human pathogens and bacteria found in normal body temperature environments - These organisms cannot survive the high temperatures characteristic of thermophiles *Cryophilic* - **Cryophilic** (or psychrophilic) bacteria are cold-loving organisms that thrive at low temperatures, typically **below 20°C** - These organisms are adapted to cold environments like polar regions, deep oceans, and refrigerated foods - They would be rapidly killed at thermophilic temperature ranges *Halophilic* - **Halophilic** bacteria require high concentrations of salt (NaCl) for growth - This classification is based on **salt tolerance**, not temperature preference - Halophiles can be mesophilic, thermophilic, or psychrophilic depending on their temperature requirements

Question 13: Diatoms are classified as which of the following?

A. Algae (Correct Answer)
B. Parasites
C. Bacteria
D. Fungi

Explanation: **Correct: Algae** - Diatoms are a major group of **algae**, specifically **single-celled eukaryotic microorganisms** characterized by unique silica cell walls called frustules. - They are significant primary producers in aquatic environments, contributing substantially to the **global oxygen supply** and forming the base of many food webs. - Diatoms are **photosynthetic** organisms belonging to the class Bacillariophyceae. *Incorrect: Parasites* - **Parasites** are organisms that live in or on another organism (their host) and benefit by deriving nutrients at the host's expense. - Diatoms are **photosynthetic** and generally **free-living**, not dependent on a host for survival. *Incorrect: Bacteria* - **Bacteria** are prokaryotic microorganisms, meaning they lack a membrane-bound nucleus and other organelles. - Diatoms are **eukaryotic**, possessing a true nucleus and complex internal structures. *Incorrect: Fungi* - **Fungi** are eukaryotic organisms that are heterotrophic, meaning they obtain nutrients by absorbing organic compounds from their environment. - Diatoms are **autotrophic**, producing their own food through **photosynthesis**.

Practice by Chapter

Microorganisms in Soil

Practice Questions

Aquatic Microbiology

Practice Questions

Air Microbiology

Practice Questions

Microbial Biofilms

Practice Questions

Microbial Ecology

Practice Questions

Microbes in Waste Treatment

Practice Questions

Bioremediation

Practice Questions

Microbial Interactions in Environment

Practice Questions

Environmental Monitoring

Practice Questions

Microbial Biodegradation

Practice Questions

Extremophiles

Practice Questions

Environmental Transmission of Pathogens

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free