how do seeds from after fertilization?

Question

form*
in gymnosperms

Answer 1

Gymnosperm Fertilization


The female gametophyte contains several archegonia, where the egg cells originate and develop. The gametophyte itself is surrounded by layers of sporangia and integument; all of these elements comprise an ovule, which is found on the surface of a female cone. Fertilization occurs when pollen grains (male gametophytes) are carried by the wind to the open end of an ovule, which contains the eggs, or female gametophyte. There, the pollen grain develops an outgrowth called a pollen tube, which eventually penetrates to the egg cell within one of the archegonia. The sperm cells within the pollen tube then vie to fertilize the egg. Once fertilization has occurred, the embryo develops within the female gametophyte, and the ovule becomes the seed, complete with a food source (the gametophyte tissue) and a seed coat (the integument). This embryo, which will eventually become a new sporophyte, consists of two embryonic leaves, the epicotyl and hypocotyl.

The following links will be helpful , just click on them--

1)http://www.sparknotes.com/biology/plants/lifecycle/section2.rhtml

2) http://www.science.siu.edu/plant-biology/PLB304/Gymnosperms.html

3) http://www.rngr.net/Publications/ttsm/pdf.2005-01-11.8804416357/file

Answer 2

the process differs in gmnosperms vs. angiosperms. In angiosperms, double fertilization occurs. One sperm fuses with the egg froming the zygote; the other with the endosperm nucleus forming a 3N endosperm. The zygote gives rise to the embryo which is embedded in the endospem. The wall of the megasporangium (nucellus) surrounds the endosperm. The integuments outside the nucelus form the seed coat.