Know All About Gymnosperms And Angiosperms

                  Gymnosperms :- 

The gymnosperms (gymno ; Naked , Sperma ; seeds ) are plants in which the ovules are not enclosed by any ovary walls & remain exposed. 

• The giant redwood free sequoia is one of the tallest trace species. 

• Mycorrhiza (Pinus). 

• (Cycas) small specialised roots called coralloid roots. 

• Stems are unbranched ( cycas ) or branched ( pInus, Cedrus). 

The leaves may be simple or compound. In cycas the pinnate leaves persist for a few years . 

• The leaves in gymnosperms are well- adopted to withstand extrems of tempreture, humidity and wind. In conifers , the needle – like leaves reduce the surface area. Their thick cuticle & sunken stomata also helps to reduces water loss. 

• The gymnosperms are heterosperes , they produce haploid microsproes and megaspores. 

• The males or female cones or strobli may be borone on the same tree ( Pinus). However, in cycas male cones and megasporophylls are borone on different trees. 

• The megaspores mother cells divides meiotically to forms four megaspores. 

• Two or more Archegonium. 

Unlike bryophytes & pteriodphytes , in gymnosperms the male & the female gametophytes do not have and independent free-living existence. 

                      Angiosperms :- 

• The seeds are enclosed in fruits. 

• Smallest Walffia to tall trees or Ecualyptus ( over 100 meters). 

• The dicotyledons are characterized by seeds having two cotyledons, reticulate venations in leaves, and tetramerous or pintamerous flowers, i.e, having four or five members in each floral whorls. 

• The mono cotyledons on the other hand are characterized is single cotyledons seeds, parallel venation in leaves, & trimerous flowers having three members in each floral whorls. 

Each ovule has a megaspores mother cell that undergoes meiosis to form four haploid megaspores. 

Three of them degenerate and one divide to form the embryo sac. Each embryo – sac has a three – called Egg Apparatus – one egg cell & two synergids, three antipodal cells and two polar nuclei. 

• One of the male gamete fuses with the egg cell ( Syngamy) to form a zygote. 

• Produces the triploid primary endosperms nucleus ( PEN) . because of the occurrence of two fusions, i.e, syngamy & triple fusion, this event is termed as double fertilization , as event unique to angiosperms. 

Plants life cycles and Alternation of Generations :- 

• Meiosis in the zygote results in the formation of haploid spores. 

Many algae such as Volvox, Spirogyra & some species of Chlamadomonas. \

• An Algae, focus sp, all seed bearing plants gymnosperms & angiosperms. 

• Bryophytes and pteriodophytes , interstingly , exhibits an intermediate conditions (haplo – diploid ) both phases are multicellular . however, they differ in their dominant phases.

• All bryophytes represent this pattern. 

• While most algal genera & haplontic. 

• Ectocarpus , Polysiphonia , kelps are haplo- diplontic. Focus , an algae is diplontic.