The disease 'pellagra' is caused by the deficiency of: MCQ with Answer and Explanation

Explanation:
Peroxisomes are single-membrane organelles involved in oxidative reactions, not plastids. Plastids (chloroplasts, chromoplasts, leucoplasts) are double-membrane organelles found in plants and algae, involved in photosynthesis, storage, and pigmentation. Chloroplasts contain chlorophyll, chromoplasts carotenoids, leucoplasts are colorless storage plastids.

Explanation:
A gene is a segment of DNA that codes for a functional product (protein or RNA) and is the basic unit of heredity. It determines traits. Chromosomes are structures containing many genes. DNA is the genetic material, and nucleotides are the building blocks. Genes are passed from parents to offspring.

Explanation:
B-lymphocytes (B cells) differentiate into plasma cells that secrete antibodies, providing humoral immunity. T-lymphocytes (T cells) are responsible for cell-mediated immunity, directly attacking infected or cancerous cells. Vaccines are prophylactic; they stimulate the immune system to develop memory and prevent future infections, but they do not cure active, ongoing viral infections. Thus, statements 1 and 2 are correct.