double fertilisation

Question 1

define fertilisation

Answer 1

the fusion of a female and male gamete producing a zygote

Question 2

outline the process of double fertilsiation

Answer 2

1) a compatible pollen grain lands on the stigma and germinates in the sucrose solution secreted by the stigma producing a pollen tube
2) the pollen tube is controlled by the tube nucleus and produces hydrolytic enzymes which digest their way through the nucellus and style
3) pollen tube grows down the style following a gradient of chemo attractants ( GABA) secreted by the ovule
4) the generative nucleus divides by mitosis forming 2 male gametes- at the tip of the pollen tube are three nuclei
5) ) the pollen tube enters the micropyle and the tube nucleus disintegrates
6) the tip of the pollen tube bursts open releasing 2 male gametes into embryo sac
7) one male gamete fuses with the oosphere to form a diploid zygote
8) the other fuses with the polar nuclei forming a triploid endosperm nucleus

Question 3

why is it referred to as double fertilisation

Answer 3

1) 2 male nuclei fuse with two separate female gametes
the first fertilisation = male gamete with oosphere
2nd= fusion of male gamete with polar nucleus

Question 4

what does the first fertilisation form

Answer 4

a diploid zygote which eventually forms the embryo of the new plant

Question 5

what does the second fertilisation form

Answer 5

a triploid ( 3 complete sets of chromosomes) endosperm

Question 6

what does the triploid endosperm do

Answer 6

divides by mitosis to form endosperm tissue which takes over from the nucellus in providing nutrients for developing embryo