Question 17

Non-pathogenic bacteria are harmless.

Non-pathogenic bacteria are those that do not cause disease in their host. They play essential roles in various ecological and biological processes, making them harmless in contrast to pathogenic bacteria.

A) pathogenic

Pathogenic bacteria are known to cause disease in their hosts, including humans, animals, and plants. This characteristic makes them harmful and directly contradicts the question regarding harmless bacteria.

B) non-pathogenic

Non-pathogenic bacteria are defined by their inability to cause disease. They are typically beneficial, aiding in processes such as digestion and nutrient cycling, which exemplifies their harmless nature.

C) cocci

Cocci refer to a shape classification of bacteria that can be either pathogenic or non-pathogenic. Therefore, while some cocci may be harmless, the term itself does not specifically indicate harmlessness, making it an incorrect option.

D) spirilla

Spirilla are another shape classification of bacteria, characterized by their spiral form. Similar to cocci, spirilla can include both pathogenic and non-pathogenic types; thus, this option does not inherently represent harmless bacteria.

Conclusion

Non-pathogenic bacteria are the only type explicitly recognized as harmless due to their lack of disease-causing ability. In contrast, pathogenic bacteria are harmful, while the shape classifications of cocci and spirilla do not guarantee harmlessness. Therefore, option B is the definitive correct answer.