biology notes

CENTRIOLES DEFINITION; ANIMALS AND MANY UNICELLULAR ORGANISMS HAVE HOLLOW  AND CYLINDRICAL ORGANELLES KNOWN AS CENTRIOLES. LOCATION;  ANIMALS CELLS, AND CELLS OF SOME MICROORGANISMS AND  LOWER PLANTS CONTAIN TWO CENTRIOLES LOCATED NEAR THE  EXTERIOR SURFACE OF THE NUCLEUS .  CONSIST OF; IN CROSS SECTION EACH CENTRIOLE CONSISTS OF A CYLINDRICAL ARRAY OF NINE MICROTUBULES . HOWEVER, EACH OF THE NINE MICROTUBULES IS FURTHER COMPOSED  OF THREE TUBULES. PLACED ON;  THE TWO CENTRIOLES  ARE USUALLY PLACED AT RIGHT ANGLE TO  EACH OTHER.   WORKING; JUST BEFORE A CELL DIVIDES, ITS CENTRIOLES DUPLICATE AND ONE  PAIR MIGRATES TO THE OPPOSITE SIDE OF THE NUCLEUS. THE SPINDLE  THEN FORMS BETWEEN THEM. THEY ARE ABSENT IN HIGHER PLANTS. FUNCTION;  CENTRIOLES PLAY IMPORTANT ROLE IN THE FORMATION OF CILIA  AND FLAGELLA. THE END