CH6 Flashcards
Process of development of pollen grain
A group of tissue grows inside each lobe of anther during development of anther to form 4 pollen sacs
In each pollen sac contained hundreds of microspore mother cells (2n)
Microspore mother cells undergoes cell division through meiosis to form 4 microspore cells (n) that are collectively known as tetrad
Each cell in the tetrad develops into a pollen grain
Nucleus in the pollen grain divides through mitosis to form 2 nuclei, tube nucleus and generative nucleus
Formation of embryo sac
Megaspore mother cell (2n) undergoes cell division through meiosis to produce 4 megaspore cells (n)
3 Megaspore cells degenerate, 1 develops
Nucleus of developed megaspore cell divides through mitosis 3 times to form a cell with 8 nuclei
3 Nuclei move to end of embryo sac forming 3 antipodal cells
3 Nuclei move to opposite end of embryo sac form 2 synergid and 1 egg cell
2 nuclei in the centre of embryo form polar nuclei
Formation of pollen tube and male gametes
Walls of matured anther shrink dry and split
Pollen grains in pollen sacs are released
Released pollen grain is trasnferred to the stigma of same or different or different flowers by pollinating agent
Transferred pollen grain germinate to form a pollen tube.
Pollen tube grows down to the ovule through the style
Generative nucleus move along the pollen tube towards the ovule
while generative divides through mitosis to form 2 male gametes (n)
End of pollen tube will secrete an enzyme to digest tissues of the style
When it reaches embryo sac, pollen tube penetrate ovule through the micropyle
Tube nucleus degenerate and both male gametes enter embryo sac, double fertilisation occur
One male nucleus fuses with egg cell to form diploid zygote
Another male nucleus fuses with polar nuclei to form triploid endosperm cell.
