HOW DO ORGANISM REPRODUCE(SEXUAL METHOD IN FLOWERING PLANT)

SEXUAL REPRODUCTION- 

                        SEXUAL REPRODUCTION IS A NATURAL WAY OF REPRODUCTION AND TAKES PLACE IN ALL MULTI-CELLULAR ORGANISM. THIS PROCESS INVOLVE THE TWO INDIVIDUAL TO PRODUCE OFFSPRING. IN THIS THE MALE AND THE FEMALE GAMETES FUSE TOGETHER AND GIVE RISE TO A NEW CELL.

 WHY THE SEXUAL MODE OF REPRODUCTION ?

                                                        THE PRODUCTION OF TWO NEW CELL FROM INVOLVE COPYING OF THE DNA AS WELL AS OF THE CELLULAR APPARATUS. THE DNA COPYING MECHANISM , AS WE HAVE OBSERVED , CAN NOT BE COMPLETELY ACCURATE AND THE RESULTANT ERRORS ARE A SOURCE OF CHANGES IN POPULATIONS OF ORGANISMS. EVERY INDIVIDUAL ORGANISMS CAN NOT BE SAVED BY VARIATIONS, BUT IN A POPULATION, VARIATIONS ARE IMPORTANT FOR ENSURING THE SURVIVAL OF  THE SPECIES, IT WOULD HENCE MAKE SENSE IF ORGANISMS COME UP WITH REPRODUCTIVE MODES THAT PERMITTED MORE AND MORE VARIATIONS TO BE CREATED.  THUS, TO VARIOUS INDIVIDUAL IN A POPULATION WOULD HAVE QUITE DIFFERENT PATTERNS OF ACCUMULATED VARIATIONS.

                 THE SEXUAL MODE OF REPRODUCTION INCORPORATES SUCH A PROCESS OF COMBINING DNA FROM TWO VARIOUS INDIVIDUALS DURING REPRODUCTION . 

SEXUAL REPRODUCTION OF FLOWERING PLANT -  

                                                      IN ANGIOSPERMS, THE REPRODUCTIVE PART LOCATED IN THE FLOWER. DIFFERENT PART OF FLOWER , PETALS,SEPALS, CARPELS AND STAMENS .CARPELS AND STAMENS ARE THE REPRODUCTIVE PART OF THE FLOWER WHICH CONTAINS THE GERM - CELLS.THE FLOWER MAY BE ASEXUAL ( PAPAYA , WATERMELON) WHEN IT HAVE EITHER CARPELS OR STAMENS OR BISEXUAL(HIBISCUS ,MUSTARD ) WHEN IT CONTAINS BOTH CARPELS AND  STAMENS STAMEN IS THE MALE REPRODUCTIVE PART AND ITS GIVES POLLEN GRAINS THAT ARE YELLOWISH IN COLOUR . 

                      CARPEL IS LOCATED IN THE CENTRE OF THE FLOWER AND IS THE FEMALE REPRODUCTIVE PART. IT IS MADE OF THREE PARTS.THE SWOLLEN BOTTOM PART IS CALLED OVARY.MIDDLE ELONGATED PART IS CALLED STYLE AND THE TERMINAL PART WHICH MAY BE STICKY IS THE STIGMA. THE OVARY HAVE THE OVULE AND EACH OVULE  CONTAINS AN EGG CELL. THE MALE GERM CELL PRODUCED BY POLLEN GRAINS FUSES WITH THE FEMALE GAMETE PRESENT IN THE OVULE . THIS FERTILISATION OR FUSION OF GERM CELL GIVES US THE ZYGOTE WHICH IS ABLE OF GROWING  INTO A NEW PLANT. THUS THERE IS A NEED TO BE TRANSFERRED THE POLLEN FROM THE STAMEN TO THE STIGMA . ON IF THIS TRANSFER OF POLLEN HAPPENS IN THE SAME FLOWERS , IT IS REFERRED TO AS SELF POLLINATION . ON THE OTHER HAND , IF THE POLLEN IS TRANSFERRED FROM ONE FLOWER TO ANOTHER , IT IS CALLED A CROSS-POLLINATION . THIS TRANSFER OF  POLLEN FROM ONE FLOWER TO ANOTHER IS OCCURED BY AGENTS SUCH AS WIND, WATER AND ANIMALS. 

             AFTER THE POLLEN TRANSFERRED TO A SUITABLE STIGMA , IT HAS TO REACH THE FEMALE GERM-CELLS WHICH ARE PRESENT IN THE OVARY . FOR THIS, A TUBE GROWS OUT OF THE POLLEN GRAINS AND TRAVEL ACROSS THE STYLE TO REACH THE OVARY . 

 AFTER FERTILISATION, THE ZYGOTE DIVIDES SEVERAL TIMES TO PRODUCE AN EMBRYO WITHIN THE OVULE . THE OVULE DEVELOPS A TOUGH COVERING AND IS GRADUALLY CHANGED INTO A SEED . THE SEED CONTAINS A EMBRYO OR FUTURE PLANT WHICH DEVELOPS INTO A SEEDLING UNDER APPROPRIATE CONDITIONS. THIS PROCESS IS CALLED GERMINATION .

 

   THE OVARY GROWS RAPIDLY TO PRODUCE A FRUIT,MEANWHILE, THE SEPALS,PETALS, STAMENS,STIGMA AND STYLE MAY SHRIVEL AND FALL OFF.