The smallest cellular microbes are __________.
a. Rickettsias
b. Mycoplasmas
c. Chlamydias
d. Both a and c

Verified step by step guidance

Step 1: Understand the question is asking about the smallest cellular microbes, which refers to the size of the organisms that have cellular structure (not viruses).

Step 2: Recall that rickettsias and chlamydias are small bacteria but are generally larger than mycoplasmas.

Step 3: Recognize that mycoplasmas are known as the smallest free-living cellular microbes because they lack a cell wall and have very small genomes and cell sizes.

Step 4: Compare the sizes of rickettsias, chlamydias, and mycoplasmas to confirm that mycoplasmas are indeed the smallest among them.

Step 5: Conclude that the correct answer is the group that includes the smallest cellular microbes, which is mycoplasmas.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Characteristics of Mycoplasmas

Mycoplasmas are the smallest free-living cellular organisms known, lacking a cell wall and having very small genomes. Their minimal size allows them to pass through filters that retain most bacteria, making them unique among cellular microbes.

Rickettsias and Chlamydias as Intracellular Parasites

Rickettsias and chlamydias are small, obligate intracellular bacteria that depend on host cells for survival. Although small, they are generally larger than mycoplasmas and have distinct life cycles involving host cell invasion.

Microbial Size and Classification

Microbial size varies widely and is a key factor in classification. Understanding the relative sizes of different bacteria helps in identifying them and their biological roles, with mycoplasmas being the smallest cellular microbes compared to rickettsias and chlamydias.

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