Recommended Content

Page 1 :
1:06 PM cin 4G:, , < CBTAFA-2.pdf Qa :, , CBTA FOCUS AREA NOTES Chapter 2-~SEXUAL REPRODUCTION IN FLOWERING PLANTS, 2.2.1, STRUCTURE OF MICROSPORANGIUM, , - A typical stamen consists of the long filament, and the terminal bilobed anther, , -The anther is a four-sided structure consisting of 4 microsporangia located at the corners., , Stigma Anther, — P,, , ‘Stamen, , , , , , , Style, , etal, Wilatmasit oe, Microsperangum, Sepal, Nectarifercus. ™ OMY, , area, Structure of microsporangium:, ¢ Microsporangium is surrounded by four wall layers, ¢ Epidermis, Endothecium, Middle layers & Tapetum., e The outer three wall layers perform the function of protection and help in dehiscence of anther to, release the pollen., , , , , , e The innermost wall layer is the Tapetum. It nourishes the pollen grains., e Inner to the Tapetum lies a group of sporogenous cells which mature into Microspore Mother Cells., e Later Meiosis takes place in these cells to form Microspores or Pollen grains, , Structure of Microspore / Pollen grain, , Pollen grains are the Male gametophytes, , It has a two-layered wall., , The hard outer layer is called the Exine which is made up of Sporopollenin, , Pollen grains are well preserved as fossils due to the presence of sporopollenin. It is one of the, , most resistant organic material which can withstand high temperatures and strong acids and alkali., , It cannot be degraded by any enzymes, , e The inner wall of the pollen grain is called the Intine which is made up of cellulose and pectin, , e Exine has apertures called germpores where sporopollenin is absent, through which the pollen, tube comes out during germination, , ¢ When the pollen grain matures it has two cells, a large vegetative cell and a small generative cell, , Vacuoles—, Nucleus, Vegetative, cell, Asymmetric, ‘splindle Geperauve, , ‘Stages of a microspore maturing into a pollen grain, , - Over 60% angiosperms shed their pollen grains at 2-celled stage. In others, generative cell divides, mitotically to give 2 male gametes. Thus pollen grains are shed at 3-celled stage.