(a) : The centrioles occur in nearly all animal cells and in motile plant cells, such as zoospores of algae, sperm cells of ferns, and motile algae. They are absent is amoebae, prokaryotic cells, higher gymnosperms and all angiosperms. An interphase (undividing) cell has a pair of centrioles (diplosome) usually near the nucleus. They lie in a small mass of specialized, distinctly staining cytoplasm that lacks other cell organelles. The centrioles and the centrosphere are together referred to as centrosome. Before cell division, the centrioles duplicate so that a dividing cell has a pair of centrioles at each pole of the spindle. Spindle fibre, cell plate and centromere are present in all plant cells.