The common cold is primarily caused by which virus? MCQ with Answer and Explanation

Explanation:
Pleiotropy is a phenomenon where a single gene influences multiple, seemingly unrelated phenotypic traits. Phenylketonuria (PKU) is an autosomal recessive metabolic disorder caused by a mutation in a single gene (PAH) that codes for the enzyme phenylalanine hydroxylase. This single mutation leads to multiple effects: intellectual disability, reduced hair and skin pigmentation, and musty odor.

Explanation:
Simple (endemic) goiter is caused by iodine deficiency, leading to low production of thyroid hormones. The pituitary secretes excess TSH, stimulating the thyroid to enlarge in an attempt to produce more hormones. Cretinism is congenital hypothyroidism, Graves' disease is autoimmune hyperthyroidism, Hashimoto's is autoimmune hypothyroidism. Iodized salt prevents goiter.

Explanation:
The bacterial cell wall is a rigid structure that provides shape and protection. It is primarily composed of peptidoglycan (also known as murein), a polymer consisting of sugars and amino acids. Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane. Cellulose is in plant walls, and chitin is in fungal walls.