CBSE Questions for Class 8 Biology Microorganisms Friend And Foe Quiz 5 - MCQExams.com

• Mosaic of tobacco is caused by tobacco mosaic virus which causes mottling and discolouration on the tobacco leaves.
• So the correct answer is 'Virus'.

$$\textbf{Correct option: D}$$

$$\textbf{Solution:}$$

Option A:

$$\bullet$$ Smallpox is caused by the $$Variola$$ virus, not by any fungus.

$$\bullet$$ High fever and fatigue are early symptoms of smallpox. 

$$\bullet$$ The virus then causes a distinctive rash, most notably on the face, arms, and legs. 

$$\bullet$$ Firstly, these rashes fill with clear fluid, then form pus, and finally form a crust that eventually dries up and falls off.

Option B:

$$\bullet$$ Tuberculosis is caused by bacterium named $$Mycobacterium$$ $$tuberculosis$$. It is not caused by a fungus.

$$\bullet$$ The person suffering from tuberculosis will have a fever, cough, night sweats and weight loss.

Option C:

$$\bullet$$ Cancer occurs due to mutation in the DNA of an individual.

$$\bullet$$ The cancerous cells divide in an uncontrolled manner and form tumors.

Option D:

$$\bullet$$ Black rust of wheat is caused by a fungus named $$Puccinia$$ $$graminis$$.

$$\bullet$$ The disease affects the aerial parts like stems, upper and lower leaf surfaces, leaf sheaths, etc.

$$\bullet$$ Pustules (blisters containing pus) are formed in all of the aerial parts of the affected plant.

Hence the correct option is option D.

• Bacteria (except in spore stage) must be continuously metabolically active most of the time and thus a bacterial infection can be cured. Viruses are metabolically inert until they enter a host cell and thus they are not susceptible to the actions of antivirals until then. An exception would be drugs that block viral adhesion to host cells, thus preventing their entry.
  
• The virus often hijacks host genome, thus their protein can be closely related to host proteins. So it is difficult to distinguish between host and virus proteins.
• The virus does not have a cell wall as bacteria. Antibiotics stop the making of a cell wall in bacteria. Thus they remain unaffected by antibiotics.

• Plants can absorb nitrogen in the form of nitrites, nitrates, and ammonium ions during the assimilation process, after which they are converted into nitrogen-containing organic molecules, such as amino acids and DNA.

• Bacteria or germs are unicellular organisms that make people sick. Cholera, jaundice, anthrax, etc are caused by bacterial infections.
• While earthworms, frog and rose are multicellular organisms and are harmless.