question_answer 41)

  Cell theory was given by (a) Schleiden and Schwann                                          (b) Virchow (c) Hooke                                                                            (d) Haeckel

Answer:

  (a) Schleiden (1836) and Schwann (1834) gave the cell theory, which was further refined by R. Virchow (1855). The main postulates of cell theory are (i) All organisms are composed of cells and cell products. (ii) All metabolic reactions take place in cells. Thus cell are structural and functional units of life. (iii) All cell arise from pre-existing cells only. No cell can originate spontaneously but they comes into being only by division of pre-existing cells. (iv) Every organism starts its life as a single cell.