General Microbiology Practice Questions

Q: Diatoms are classified as which of the following?

Algae. **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**.

Q: Which of the following organisms does not fulfill Koch's postulates?

T. pallidum. ***T. pallidum*** - **_Treponema pallidum_**, the causative agent of **syphilis**, cannot be cultured on artificial media, failing the third Koch's postulate. - Its inability to grow in pure culture makes it difficult to reproducibly cause disease in an experimental host by direct inoculation of a cultured organism. *M. tuberculosis* - **_Mycobacterium tuberculosis_** can be isolated and grown in **pure culture** on specific media like Löwenstein-Jensen medium. - It also consistently causes tuberculosis when inoculated into susceptible animals, fulfilling Koch's postulates. *E.coli* - **_Escherichia coli_** is readily cultured in various laboratory media and can be isolated from infected hosts. - Specific pathogenic strains of _E. coli_ (e.g., EHEC) fulfill Koch's postulates by reproducing disease in animal models. *All of the options* - This option is incorrect because both **_M. tuberculosis_** and **_E. coli_** largely fulfill Koch's postulates. - The primary exception among the given options is **_T. pallidum_** due to its unculturable nature.

Question 1

Diatoms are classified as which of the following?

Accepted Answer

Algae

Answer

Parasites

Answer

Bacteria

Answer

Fungi

Question 2

Which of the following organisms does not fulfill Koch's postulates?

Accepted Answer

T. pallidum

Answer

E.coli

Answer

M. tuberculosis

Answer

All of the options

Question 3

Which of the following statements most accurately describes the characteristics of exotoxins?

Accepted Answer

Secreted by certain bacteria into the surrounding environment

Answer

Can provoke a strong immune response

Answer

Generally heat-stable and resistant to antibodies

Answer

A component of the outer membrane of gram-negative bacteria

General Microbiology — MCQs

General Microbiology — MCQs

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