3.1 Angiosperm Reproduction-MNR

8/18/2019 3.1 Angiosperm Reproduction-MNR

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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

3.1 Angiosperm Reproduction-MNR

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