Which of the following organisms lacks a cell wall? MCQ with Answer and Explanation

Explanation:
Vitamin D (calcitriol) stimulates the production of calcium-binding proteins in the intestinal lining, enhancing calcium absorption. Deficiency leads to rickets/osteomalacia. Vitamin A is for vision, C for collagen, B₁₂ for nerve function.

Explanation:
HIV is a retrovirus with two copies of single-stranded RNA as its genome. It uses reverse transcriptase to convert RNA into DNA upon infection. Double-stranded DNA is typical of many organisms. Single-stranded DNA viruses exist (e.g., parvovirus). Double-stranded RNA viruses include rotavirus. The viral RNA genome enables integration into host DNA via a DNA intermediate.

Explanation:
The cardiac conduction system ensures coordinated heartbeats. The sinoatrial (SA) node generates the electrical impulse, acting as the natural pacemaker. The impulse reaches the atrioventricular (AV) node, which delays it slightly to allow the atria to fully contract and empty into the ventricles. The impulse then travels down the Bundle of His to the Purkinje fibers, which rapidly distribute it throughout the ventricular myocardium, causing ventricular contraction. All statements are correct.