Which of the following statements about viruses is INCORRECT?
A. They can have either DNA or RNA as genetic material.
B. They reproduce by binary fission.
C. They are obligate intracellular parasites.
D. They lack metabolic machinery.
Answer: Option B
Solution (By JKSSB Mock Tests)
Viruses do not reproduce by binary fission; they replicate by hijacking host cell machinery. Binary fission is a method of asexual reproduction in bacteria. All other statements are correct.
Explanation:
The 'lub' sound occurs at the beginning of ventricular systole when the atrioventricular valves (mitral and tricuspid) close to prevent backflow of blood into the atria. The 'dub' sound occurs at the beginning of diastole due to closure of the semilunar valves (aortic and pulmonary). Valve closure is passive, resulting from pressure gradients.
Explanation:
The cell wall is porous and does not regulate entry; the plasma membrane is selectively permeable. Thus, the wall is freely permeable, and the reason explains it.
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