Consider the following statements about cell theory: 1. All living organisms are composed of cells. 2. The cell is the basic structural and functional unit of life. 3. All cells arise from pre-existing cells. Which of the statements above are correct? MCQ with Answer and Explanation

Explanation:
Charles Darwin, in 'On the Origin of Species' (1859), proposed natural selection as the mechanism for evolution, based on variation, inheritance, and differential survival. Mendel discovered genetics, Pasteur disproved spontaneous generation, Lamarck proposed inheritance of acquired characters. Wallace independently arrived at natural selection.

Explanation:
Plasma cells, differentiated from B lymphocytes, are the factories that produce and secrete large amounts of antibodies (immunoglobulins) specific to an antigen. Macrophages phagocytose, T cells regulate or directly kill, neutrophils phagocytose bacteria.

Explanation:
Testosterone, secreted by Leydig cells of the testes, is responsible for the development of male secondary sexual characteristics like facial hair, deepening of voice, and muscle growth. Estrogen and progesterone are female hormones.