In genetics, the 'Operon model' was proposed by: MCQ with Answer and Explanation

Explanation:
Fats provide about 9 kcal per gram, while carbohydrates and proteins provide about 4 kcal/g each. Vitamins are not energy-yielding. Therefore, fats are the most energy-dense macronutrient, serving as long-term energy storage. However, carbohydrates are the primary fuel. Excess fat storage leads to obesity. Fats also aid in absorption of fat-soluble vitamins.

Explanation:
The skin and mucous membranes form the first line of defense (innate immunity), acting as physical barriers that prevent pathogens from entering the body. White blood cells (leukocytes), including phagocytes and lymphocytes, are the cellular components of the immune system that identify, attack, and destroy pathogens. Antibiotics are drugs designed to kill or inhibit the growth of bacteria; they are completely ineffective against viruses, which lack the cellular machinery targeted by antibiotics. Thus, statements 1 and 2 are correct.

Explanation:
Alexander Fleming discovered penicillin in 1928 from the mold Penicillium notatum (later renamed P. chrysogenum). Aspergillus niger is used for citric acid production, Saccharomyces is yeast, Rhizopus is a bread mold. Penicillin was the first true antibiotic and its mass production during WWII saved countless lives. It inhibits bacterial cell wall synthesis.