Which of the following statements about genes and alleles is correct? MCQ with Answer and Explanation

Explanation:
Folic acid (vitamin B₉) is crucial for DNA synthesis and cell division; its deficiency during early pregnancy increases the risk of neural tube defects like spina bifida. Many countries fortify flour with folic acid. Vitamin A is for vision, C for collagen, D for calcium. Women of childbearing age are advised to take supplements.

Explanation:
Pepsin, activated from pepsinogen by HCl, initiates protein digestion in the stomach, breaking proteins into smaller peptides. Trypsin and chymotrypsin are pancreatic enzymes active in the small intestine. Carboxypeptidase is also pancreatic. Pepsin is an endopeptidase active at acidic pH.

Explanation:
The skin and mucous membranes act as primary physical barriers in innate immunity, preventing pathogen entry. Phagocytosis by macrophages and neutrophils is a non-specific (innate) cellular defense mechanism, not a specific immune response. Memory B and T cells are produced during the primary specific immune response and provide rapid, long-lasting immunity upon re-exposure. Thus, statements 1 and 3 are correct.