Identify the correct statement regarding the human respiratory system: MCQ with Answer and Explanation

Explanation:
Pleiotropy occurs when a single gene affects two or more distinct phenotypic traits. This happens because the gene product (protein) may be used in multiple biological pathways or expressed in different tissues. Examples include phenylketonuria (PKU), sickle cell anemia, and Marfan syndrome. Epistasis involves the interaction of different genes, polygenic inheritance involves multiple genes affecting one trait, and incomplete dominance is a single gene interaction.

Explanation:
Vitamin B₁ (thiamine) is water-soluble and functions as a coenzyme (thiamine pyrophosphate) in carbohydrate metabolism, particularly in decarboxylation reactions. Vitamins A, D, E, and K are fat-soluble. B₁ deficiency causes beriberi and Wernicke-Korsakoff syndrome. Being water-soluble, excess is excreted in urine and toxicity is rare.

Explanation:
The liver is the largest internal organ and gland, weighing about 1.5 kg in an adult. It performs over 500 functions, including bile production, detoxification, metabolism of carbohydrates, lipids, and proteins, and synthesis of plasma proteins. The pancreas and thyroid are smaller glands, the spleen is not a gland.