question_answer 38)

  With the help of a schematic diagram describe the hapiodiptontic life cycle pattern of a plant group.

Answer:

                  Hapio diplontic life cycle (is also referred as diplohaplontic, dipio biontic or dibiontic)shows multicellular diploid and haploid stages as dipicted in the following figure. Schematic diagram represent the life cycle of a pteridophyte (homosporous one) haplo-diplontic type of life cycle Life Cycle of a Pteridophyta The life cycle of a pteridophyte consists of two morphologically distinct phases (i ) The gametophytic phase (ii) The saprophytic phase These two phases come one after another in the life cycle of a pteridophyte. This phenomenon is called alternation of generation. The gametophyte is haploid with single set of chromosomes. It produces male sex organs antheridia and female sex organs archegonia. (i) The antheridia may be embedded or projecting type. Each antheridium has single layered sterile jacket enclosing a mass of androcytes. (ii) The androcytes are flask-shaped, sessile or shortly stalked and differentiated into globular venter and tubular neck. (iii) The archegonium contains large egg, which is non-motile. (iv) The antherozoids after liberation from antheridium, reaches up to the archegoniumfuses with the egg and forms a diploid structure known as zygotes. (v) The diploid zygote is the first cell of saprophytic generation. It is retained inside the archegonium and forms the embryo. (vi) The embryo grows and develop to form saprophyte which is differentiated into roots, stem and leaves. (vii) At maturity the plant bears sporangia, which encloses spore mother cells. (viii) Each spore mother cell gives rise to four haploid spores which are usually arranged in tetrads. (ix) The saprophytic generation ends with the production of spores. (x) Each spore is the first cell of gametophytic generation. It germinates to produce gametophyte and completes its life cycle.