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Double fertilization,formation of fruit and seed
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7/21/2019 Sexual reproduction in plants
http://slidepdf.com/reader/full/sexual-reproduction-in-plants-56d9615252c5f 1/2
Review sheet
Group 7
Module 3
Objectives
2.6 -explain the sequence of events from pollination to fertiliation
2.7 -explain the si!nificance of double fertiliation in the embr"o sac
2.# -discuss the development of the seed and the fruit from the embr"o sac and its contents$ the
ovule and the ovar".
Objective 2.6
%. &ollen !ermination- Once pollination has occurred and the pollen !rain lands on the
sti!ma$ the pollen !rains stic' to the surface of the sti!ma$ absorb (ater and be!in to
!erminate )onl" if it is compatible*.
2. +he pollen !rain then s(ells and it contents push throu!h its (all resultin! in the
formation of a pollen tube that !ro(s to(ards the ovule.
3. +he pollen !rain contains t(o nuclei, the !enerative nucleus and the tube nucleus both of
(hich are haploid. s the tube !ro(s$ the !enerative nucleus divides b" mitosis to
produce t(o haploid nuclei (hich represents the male !ametes
. +he pollen tube then enters the ovule usuall" throu!h the microp"le then penetrates the
embr"o sac (all. +he tube nucleus then de!enerates (hile the t(o male !ametes enter the
embr"o sac.
Objective 2.7
/ouble fertiliation- is a fertiliation mechanism unique to an!iosperms (hich involves the
fusion of t(o male !ametes$ one (ith the female !amete formin! the "!ote$ and the other (ith
the primar" endosperm nucleus formin! the endosperm.
Its significance:
s a result of double fertiliation$ an endosperm is formed that (ill provide the embr"o
(ith the necessar" nutrients durin! the first fe( da"s of !ro(th or (here food is scarce.
0t results in the formation of a "!ote$ (hich develops into an embr"o and !ives rise to a
ne( plant
0t results in variation amon! the offsprin!s
0t stimulates the plant1s ovar" to develop into fruit and the ovule to develop into the seed
7/21/2019 Sexual reproduction in plants
http://slidepdf.com/reader/full/sexual-reproduction-in-plants-56d9615252c5f 2/2
Objective 2.8
Seed development
fter fertiliation$ the ovule becomes the seed and remains attached to the parent from
(hom it receives its nutrients. +he "!ote divides b" mitosis to form the embr"o and is
attached to the (alls of the ovule b" a lar!e basal cell and a little column of cells calledthe suspensor. +he radicle )embr"o root*$ plummule )embr"o shoot* and the
cot"ledon)one or t(o* (ill then develop in the seed.
+he triploid endosperm nucleus also divides b" mitosis to become the endosperm
tissue (hich surrounds the embr"o. 0t mi!ht become the main food stora!e )as in cereal
!rains* or it mi!ht disappear (ithin a fe( da"s of fertiliation.+he inte!uments lose their
protoplasm $tou!hen and thic'en to become the testa. Moisture content decreases to about
%-%4. /ormanc" occurs )state of inactivit"*.+he microp"le remains to allo( ox"!en
and (ater to enter durin! !ermination
F!it development
+he ovar" becomes the fruit
+he (all of the ovar" becomes the pericarp of the fruit (hich is adapted for dispersion
+he pericarp contains three parts,
%. 5xocarp- the outermost s'in or coverin!
2. Mesocarp- middle part of the fruit )usuall" flesh" and edible*
3. 5ndocarp- the inner part of the fruit
+he other parts of the flo(er (ither and fall off