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Angiosperm Reproduction
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• In angiosperms, the dominant sporophyte
– Produces spores that develop within flowersinto male gametophytes (pollen grains) – Produces female gametophytes (embryo sacs)
• lowers – Are the reproductive shoots of the angiosperm
sporophyte – Are composed of four floral organs! sepals,
petals, stamens, and carpels• "any variations in floral structure – #ave evolved during the $%& million years of
angiosperm history
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• An overview of angiosperm reproduction
Figure 38.2a, b
Anther attip of stamen
ilament
Anther 'tamen
Pollen tube
erminated pollen grain(n) (male gametophyte)
on stigma of carpel
vary (base of carpel)
vule
*mbryo sac ( n)(female gametophyte)
FERTILIZATION*gg ( n)
'perm ( n)
PetalReceptacle
'epal
'tyle
vary
Key
#aploid ( n)
+iploid ( n)
(a) An idealized l!"er.
(b) #i$%li ied angi!&%er$ li e 'y'le.'ee igure -&.$& for a more detailedversion of the life cycle, including meiosis.
"ature sporophyteplant ( 2n ) withflowers
'eed(developsfrom ovule)
/ygote( n)
*mbryo ( n)(sporophyte)
'imple fruit(develops from ovary)
erminatingseed
'eed
0arpel'tigma
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ametophyte +evelopment andPollination
• In angiosperms – Pollination is the transfer of pollen from an anther to a
stigma
– If pollination is successful, a pollen grain produces astructure called a pollen tube, which grows down intothe ovary and discharges sperm near the embryo sac
• Pollen – +evelops from microspores within the sporangia of
anthers
• *mbryo sacs – +evelop from megaspores within ovules
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• Pollen – +evelops from microspores within
the sporangia of anthers
3 A pollen grain becomes amature male gametophytewhen its generative nucleusdivides and forms two sperm.1his usually occurs after apollen grain lands on the stigmaof a carpel and the pollentube begins to grow. ('ee
igure -2. b.)
e el!%$en* ! a $ale ga$e*!%+y*e(%!llen grain)
(a)
2*ach microsporo3cyte divides bymeiosis to producefour haploidmicrospores,each of whichdevelops intoa pollen grain.
Pollen sac
(microsporangium)
"icro3sporocyte
"icro3
spores (%)
*ach of %microspores
enerativecell (willform
sperm)
ale-a$e*!%+y*e
(pollen grain)
4ucleusof tube cell
*ach one of themicrosporangiacontains diploidmicrosporocytes(microsporemother cells).
56 m
& m
Ragweedpollengrain
Figure 38./a
"*I 'I'
"I1 'I'
7*8to labels
#aploid ( 2n )
+iploid ( 2n )
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Key*! label&
ITO#I#
EIO#I#
vule
vule
Integuments
*mbryosac
"ega3
sporangium"ega3sporocyte
Integuments"icropyle
'urvivingmegaspore
Antipodel0ells (-)
Polar 4uclei ( )
*gg ($)
'ynergids ( )
e el!%$en* ! a e$ale ga$e*!%+y*e(e$bry! &a')
(b)
9ithin the ovule:s
megasporangiumis a large diploidcell called themegasporocyte(megasporemother cell).
1hree mitotic divisionsof the megaspore formthe embryo sac, amulticellular femalegametophyte. 1heovule now consists ofthe embryo sac alongwith the surroundinginteguments (protectivetissue).
3
Fe$ale ga$e*!%+y*e(embryo sac)
+iploid ( 2n )
#aploid ( 2n )
Figure 38./b $ & &
m
1he megasporocyte divides bymeiosis and gives rise to four haploid cells, but in mostspecies only one of thesesurvives as the megaspore.
2
• *mbryo sacs – +evelop from megaspores within ovules
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e'+ani&$& T+a* 0re en* #el 1Fer*iliza*i!n
• "any angiosperms – #ave mechanisms that ma;e it difficult or impossible for a flower to fertili
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+ouble ertili
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'tigma
Polar nuclei
*gg
Pollen grain
Pollen tube
sperm
'tyle
vary
vule (containingfemalegametophyte, or embryo sac)
"icropyle
vule
Polar nuclei
*gg
1wo spermabout to bedischarged
*ndosperm nucleus (- n)( polar nuclei plus sperm)
/ygote ( n)(egg plus sperm) Figure 38.
• rowth of the pollen tube and doublefertili
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rom vule to 'eed• After double fertilisually precedes embryo development• In most monocots and some eudicots
– 1he endosperm stores nutrients that can be usedby the seedling after germination
• In other eudicots – 1he food reserves of the endosperm are completely
e=ported to the cotyledons
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Structure of the Mature Seed
• 1he embryo and its food supply – Are enclosed by a hard, protective seed coat
• In a common garden bean, a eudicot –
1he embryo consists of the hypocotyl, radicle, andthic; cotyledons
Figure 38.8a
(a) 4!$$!n garden bean, a eudi'!* "i*+ *+i'5 '!*yled!n&. 1he fleshy cotyledons store food absorbed from the endosperm before
the seed germinates.
'eed coat
Radicle
*picotyl
#ypocotyl
0otyledons
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• 1he embryo of a monocot – #as a single cotyledon, a coleoptile, and a
coleorhi
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rom vary to ruit
• A fruit – +evelops from the ovary – Protects the enclosed seeds – Aids in the dispersal of seeds by wind or
animals
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• ruits are classified into several types – +epending on their developmental origin
Figure 38.6a7'
#i$%le rui*. A simple fruitdevelops from a single carpel (orseveral fused carpels) of one flower(e=amples! pea, lemon, peanut).
(a) Aggrega*e rui*. An aggregate fruitdevelops from many separatecarpels of one flower (e=amples!raspberry, blac;berry, strawberry).
(b) ul*i%le rui*. A multiple fruitdevelops from many carpelsof many flowers (e=amples!pineapple, fig).
(')
0inea%%le rui*Ra&%berry rui*0ea rui*
'tamen
0arpel(fruitlet) 'tigma
vary
Ra&%berry l!"er
*achsegmentdevelopsfrom thecarpel of
one flower
0inea%%le in l!re&'en'e
'tamen
0arpelslower
vary'tigma
'tamen
vule
0ea l!"er
'eed
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From Seed to Seedling
• ermination of seeds depends on thephysical process called imbibition – 1he upta;e of water due to low water potential
of the dry seed
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Figure 38. a
oliage leaves
0otyledon
#ypocotyl
Radicle
*picotyl
'eed coat
0otyledon#ypocotyl 0otyledon
#ypocotyl
4!$$!n garden bean. In common gardenbeans, straightening of a hoo; in the
hypocotyl pulls the cotyledons from the soil.
(a)
• 1he radicle
– Is the first organ to emerge from the germinatingseed
• In many eudicots – A hoo; forms in the hypocotyl, and growth pushes
the hoo; above ground
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• "onocots – >se a different method for brea;ing ground when
they germinate
• 1he coleoptile – Pushes upward through the soil and into the air
Figure 38. b
oliage leaves
0oleoptile0oleoptile
Radicleaize. In mai
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e'+ani&$& ! A&e9ual ( ege*a*i e)Re%r!du'*i!n
• ragmentation – Is the separation of a parent plant into parts that develop into
whole plants – Is one of the most common modes of ase=ual reproduction
4l!ne& r!$ 'u**ing and gra *ing• "any ;inds of plants
– Are ase=ually reproduced from plant fragments called'u**ing& .
• -ra *ing !In a modification of vegetative reproductionfrom cuttings – A twig or bud from one plant can be grafted onto a plant of a
closely related species or a different variety of the samespecies
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• Begetative Reproduction – Involve the emergence and separation a part of the parent or
plant. – 1he vegetative reproduction (fragmentation) are
• #ori
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