Which of the following prokaryotes is not pathogenic?
a. Chlamydia
b. Rhizobium
c. Streptococcus
d. Salmonella

Verified step by step guidance

1. Step 1: Understand the term 'pathogenic.' Pathogenic organisms are those that cause disease in their host. In this case, we are identifying which prokaryote does not cause disease.
2. Step 2: Review the characteristics of each prokaryote listed in the options. For example: Chlamydia is a genus of bacteria known to cause infections in humans, such as Chlamydia trachomatis. Streptococcus includes species that cause diseases like strep throat. Salmonella is a genus of bacteria that causes foodborne illnesses.
3. Step 3: Learn about Rhizobium. Rhizobium is a genus of bacteria that forms a symbiotic relationship with leguminous plants. It helps fix nitrogen in the soil, which benefits plant growth. It is not known to cause disease, making it non-pathogenic.
4. Step 4: Compare the pathogenicity of the other options (Chlamydia, Streptococcus, and Salmonella) with Rhizobium. Since Rhizobium does not cause disease, it stands out as the non-pathogenic option.
5. Step 5: Conclude that Rhizobium is the correct answer because it is beneficial to plants and does not cause harm to its host, unlike the other prokaryotes listed.

Key Concepts

Prokaryotes

Prokaryotes are single-celled organisms that lack a nucleus and membrane-bound organelles. They are classified into two main domains: Bacteria and Archaea. Prokaryotes are characterized by their simple cell structure, typically consisting of a cell membrane, cytoplasm, and genetic material in the form of a single circular DNA molecule. Understanding prokaryotic biology is essential for distinguishing between pathogenic and non-pathogenic species.

Pathogenicity

Pathogenicity refers to the ability of an organism to cause disease in a host. Pathogenic organisms can invade host tissues, evade the immune system, and produce toxins or other harmful substances. Not all prokaryotes are pathogenic; some, like Rhizobium, play beneficial roles in ecosystems, such as nitrogen fixation in plants. Recognizing which prokaryotes are pathogenic is crucial for understanding their impact on health and disease.

Examples of Prokaryotes

Different prokaryotes exhibit varying characteristics and roles in the environment. For instance, Chlamydia, Streptococcus, and Salmonella are known pathogenic bacteria that can cause infections in humans. In contrast, Rhizobium is a non-pathogenic bacterium that forms symbiotic relationships with legumes, aiding in nitrogen fixation. Familiarity with specific examples helps in identifying which prokaryotes are harmful and which are beneficial.