Which of the following is a correct statement about the structure of a neuron? MCQ with Answer and Explanation

Explanation:
The common cold is a viral infection of the upper respiratory tract, primarily caused by rhinoviruses. Typhoid fever, caused by Salmonella typhi, is transmitted via the fecal-oral route through contaminated food and water. Plague, caused by Yersinia pestis, is a zoonotic disease transmitted to humans primarily by the bite of infected rat fleas (Xenopsylla cheopis). All three statements are correct.

Explanation:
Vitamin A (retinol) is essential for the synthesis of rhodopsin, the visual pigment in rod cells responsible for low-light vision. Deficiency leads to night blindness (nyctalopia) and, if severe, xerophthalmia and permanent blindness. Vitamin B₁ deficiency causes beriberi, C scurvy, D rickets.

Explanation:
Vaccination involves the introduction of a weakened, killed, or partial pathogen (antigen) into the body. This stimulates the immune system to produce its own antibodies and memory cells without causing the disease. Since the body actively produces the immune response due to an artificial stimulus, it is called artificial active immunity.