Spirillum is not classified as a spirochete because spirochetes
a. do not cause disease.
b. possess axial filaments.
c. possess flagella.
d. are prokaryotes.
e. none of the above

Verified step by step guidance

Step 1: Understand the key terms in the question. 'Spirillum' and 'spirochetes' are both types of spiral-shaped bacteria, but they differ in certain structural features.

Step 2: Recall that spirochetes are characterized by the presence of axial filaments (also called endoflagella), which are flagella located in the periplasmic space that allow them to move in a corkscrew motion.

Step 3: Recognize that Spirillum bacteria have external flagella rather than axial filaments, which is a major reason they are not classified as spirochetes.

Step 4: Evaluate each answer choice in the context of these structural differences: (a) disease causation is not a defining feature, (b) possession of axial filaments is unique to spirochetes, (c) possession of flagella is common to many bacteria including spirilla, (d) being prokaryotes applies to both groups, and (e) none of the above.

Step 5: Conclude that the correct distinguishing feature is the possession of axial filaments by spirochetes, which Spirillum lacks.

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Key Concepts

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

Differences Between Spirillum and Spirochetes

Spirillum and spirochetes are both spiral-shaped bacteria, but they differ in structure and motility. Spirilla have external flagella for movement, while spirochetes move using internal axial filaments, which are unique to their morphology.

Axial Filaments in Spirochetes

Axial filaments, also called endoflagella, are specialized structures located between the cell wall and outer membrane of spirochetes. These filaments enable a corkscrew-like motion, allowing spirochetes to move efficiently through viscous environments.

Flagella in Bacterial Motility

Flagella are whip-like appendages that extend outside the cell and facilitate bacterial movement. In spirilla, flagella are external and rotate to propel the cell, contrasting with the internal axial filaments of spirochetes.

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