Sexual reproduction in plants

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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

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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