The vitamin that acts as an antioxidant and is important for immune function is: MCQ with Answer and Explanation

Explanation:
Myosin is the motor protein forming thick filaments; its heads bind to actin thin filaments and generate force via the cross-bridge cycle. Actin forms thin filaments, troponin and tropomyosin regulate contraction. The sliding filament theory describes muscle shortening without filament length change.

Explanation:
Fossils are direct evidence showing transitional forms. Lamarck proposed use and disuse, not natural selection. Analogous organs do not indicate common ancestry; homologous do. Appendix is vestigial.

Explanation:
Down syndrome (trisomy 21) is an autosomal aneuploidy caused by nondisjunction resulting in three copies of chromosome 21. It is characterized by intellectual disability, flat facial profile, protruding tongue, and simian crease. Turner's syndrome is monosomy X (45, X). Klinefelter's is 47, XXY. Phenylketonuria is an inborn error of metabolism (autosomal recessive) due to deficiency of phenylalanine hydroxylase.