Assertion (A): Frogs have a three-chambered heart. Reason (R): This allows complete separation of oxygenated and deoxygenated blood. MCQ with Answer and Explanation

Explanation:
Plague is a severe zoonotic bacterial disease caused by Yersinia pestis. It is primarily transmitted to humans through the bite of infected rat fleas, most commonly Xenopsylla cheopis. The disease has three main forms: bubonic (swollen lymph nodes), pneumonic (lungs), and septicemic (blood). Tuberculosis is airborne, leprosy is transmitted via prolonged close contact, and tetanus enters through deep wounds.

Explanation:
Eukaryotic ribosomes are 80S and composed of a small 40S subunit and a large 60S subunit. Prokaryotic ribosomes are 70S with 30S and 50S subunits. The S (Svedberg) value is a measure of sedimentation rate, not simply additive. Both ribosome types synthesize proteins, but the structural difference allows selective antibiotic targeting (e.g., streptomycin acts on 70S).

Explanation:
Homologous organs share a common ancestral origin and structural plan but may have different functions (e.g., human arm, whale flipper, bat wing). This indicates divergent evolution. Analogous organs have different origins but similar functions (e.g., wings of birds and insects) due to convergent evolution. Vestigial organs are reduced and non-functional, like the human appendix.