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:
Edward Jenner developed the first successful smallpox vaccine (1796). Pasteur invented pasteurization and rabies vaccine, not penicillin. Fleming discovered penicillin. Hooke coined the term 'cell' but did not discover bacteria; Leeuwenhoek observed bacteria. Thus, the correct match is Jenner - smallpox vaccine.

Explanation:
Excretion is the elimination of nitrogenous waste products (urea, uric acid, ammonia) and other metabolic wastes from the body, primarily by the kidneys. Digestion is breakdown of food, circulation is transport, respiration is gas exchange and energy release. Excretion maintains homeostasis of body fluids and prevents toxic accumulation.

Explanation:
Genetic variation within a population provides the raw material upon which evolutionary forces act; without variation, evolution cannot occur. Natural selection acts directly on the phenotype (observable traits) of an organism, determining its survival and reproductive success. However, evolution is a population-level phenomenon; it involves changes in allele frequencies over generations, not changes occurring within a single individual's lifetime. Thus, statements 1 and 2 are correct.