A process whereby two sex cells (gametes), egg and sperm, fuse together to form an entirely new. organism. the number of chromosomes.

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1 UNIT15: REPR()DUCTION IN PTANTS Lerning Objectives: g Define sexul reprocluction nd sexul reproduction g ldentify, drw nd stte the sepls, petls, srmens nd crpels ofn insect-pollinted, dicotyledonous fiower A ldentify rul describe the stmens nd stigms of n insect-pollintecl, dicotyledonous flower 9 Outline the process of pollintion nd distinguish self-pollintion nd cross-pollintion A Compre insect-pollinted ndwincl-pollinted.flowers g Describe the growth of the pollen tube nd its entty into the ovule fter fertilistion TYPES OF REPRODUCTION ' Reproduction refers to the process by which n orgnism produces others of its sme kind. The purpose of reproduction is to mke sure the continuity of species.. There re two types of reproduction-sexul nd sexul. Asexul A process whereby one prent produces geneticlly identicl offspring lnvolves mitosis: A cell divides to produce two identicl dughter cells with the sme number of chromosomes. As result, the dughtercells hve identicl hereditry mterils s the prent cell. SEXUAL REPRODUCTION!N FLOWERING PIANTS Structure of flower. Flower is the reproductive orgn for flowering plnts. stmen (mle reproductive system) filment nther petl stigm style ovry Sexul A process whereby two sex cells (gmetes), egg nd sperm, fuse together to form n entirely new orgnism Sexul reproduction results in offspring tht re geneticlly different from the prents. lnvolves meiosis process tht cell divides to produce the dughter cells with hploid (n) of the number of chromosomes. During fertilistion, the combintion of two gmetes restores the diploid (2n) number of chromosomes. For humns, the hploid number (n) is 23 nd the diploid number (2n) is 46. crpel or pistil (femle reproductive system) ovule I receptcle sepl nectry 262 O GLM Pte Ltd

2 Prt Description nd function Petl Stmen Receptcle Sepl Nectry Usully brightly coloured nd sometimes scented to ttrct insects to bring bout pollintion for insect-pollinted flowers Wind-pollinted flowers hve dull, unscented petls Arrnged in circle or cylinder (collective nme: Coroll) Flowers of grsses hve smll lef-like structures (brcts), which enclose the reproductive orgns Mle reproductive orgn of flower (collective nme: Androecium) Ech stmen hs stlk clled the filments, with n nther t the end. The chrcteristics of filment nd nther: Filment Anther A long stem-like structure Position the nther so tht pollen grins cn be pollinted by gents Meiosis tkes plce to produce mle gmetes in pollen Mde up of two or four pollen lobes Ech lobe contins two pollen scs where the pollen grins re formed Ech pollen grin hs two nuclei in its cytoplsmgenertive nucleus nd pollen tube nucleus Pollen grins contin mle gmetes produced by meiosis (hploid cells which will fuse with hploid femle ovum during fertilistion) Anther lso hs vsculr bundle-phloem nd xylem./ Phloem trnsports sugr s energy needed for cell division nd mino cids for synthesising proteins nd new protoplsm,/ Xylem trnsports wter nd minerl slts Expnded end of flower stlk to which ll flower structures re ttched Sometimes fter fertilistion, it becomes fleshy nd edible. For exmple, pple, per nd strwberry Outside the ring of petls, green in colour nd much smller (col lective nme: Clyx) Protect the flower when it is in the bud Found in the insect-pollinted flowers only Produce sugry nectr which ttrcts insects =' q, o GIM Pte Ltd BIOLOGY O Level Conceptul Lerning I lf$

3 o REVTST0N 1 Crpel 1,. Definereproduction. 2 Femle reproductive orgn (Collective nme: Gynecium) Ech crpel hs n ovry, with the style nd stigm. lnside the ovry re one or numerous ovules, which will become seeds fter fertilistion. The chrcteristics of structures in the crpel: Stigm Style Ovry Ovule Hs sticky or fether-like surfce for pollen grins to ttch to Secretes sugry fluid to stimulte the germintion of pollen grins fter pollintion Joins the stigm to the ovry Mde up of soft tissues tht llows the pollen tube to grow down towrds the ovule Attched to the receptcle of the flower Contins nd protects the ovules Meiosis tkes plce to produce egg cells in ovule Attched to the plcent through funicle in the ovry Contins femle gmetes clled ov (singulr: ovum) produced by meiosis (lso hploid cells)nd the definitive nucleus There re two types of reproduction-sexul nd sexul. Describe these two types of reproduction. () Asexulreproduction (b) Sexulreproduction 264 O 0[M Ple Lld

4 3. The digrm below shows the structure of flower () Lbel the prts nd one function of ech prt Lbel Nme Function L t LL L2 O 0[M Pte ttd BIOLOGY O LevelConceptul Lerning I lf,!

5 (b) Wht is the collective nme for the prt tht mkes up of (i) Structures 2 nd 3 (ii) Structures 4, 5 nd 6 4. Explin the following terms. () Coroll (b) Androecium (plurl:ndroeci) (c) Gynoecium (plurl: gynoeci) POLLINATION. Pollintion is the trnsfer of pollen grins from the nther to the stigm. ' When pollen grins re trnsferred to the stigm of the sme flower or ditferent ftower of the sme plnt, it is clled self-pollintion. ' When pollen grins re trnsferred to the stigm of flower on nother plnt of the sme kind, it is clled cross-pollintion. Advntges nd disdvntges of types of pollintion Type of pollintion Selfpollintion Crosspollintion Advntge It is dvntgeous where externl gents, for exmple, wind or insects, re not relible. Less energy is needed to ttrct nd rewrd pollintors. lf given trit is well-dpted to the environment, it helps keep this fvourble trit in the species. Allows prticulr species to colonise certin re. lncreses genetic vribility so tht there is higher chnce for the species to survive in chnging envi ronmentl conditions Offspring cn obtin fvourble trits from both prents to ensure its vibility. Disdvntge It is similr to sexul reproduction becuse it produces offspring tht re geneticlly identicl to the prent. Therefore, there will be loss of genetic diversity. Due to constnt chnging environmentl conditions, the fvourble trit my not be ble to dpt in the future. Complete nd continuous self-poll intion mens certin extinction. Cn destroy well-dpted trits, so offspring re not gurnteed to be vible Rel ies on effective cross-pollintion strtegies to ensure tht the pollen is ctully trnsferred to different plnt of the sme species. 266 o OLM Ple ltd

6 Differences in the fetures of cross-pollinted flowers. For plnts tht crry out cross-pollintion, there re differences in theirflowers.. They cn be clssified s wind-pollinted flowers nd insect pollinted flowers. The digrms below show the wind- nd insect-pollinted flowers. fethery stigm lodicules non-flowering petl ovry wind-pollinted flower filment stigm nther style nther insect-pollinted flower Feture Wind-pollinted Insect-pollinted Significnce Petls I nconspicuous, smllflowers Petls re green usully Reltively lrge nd conspicuous flowers Petls brightly coloured Scent No scent Scented Nectry guide Pollen Absent Present Lrge quntities Smll, dry nd smooth pollen grins Smller quntities Lrger, sticky nd hevy pollen with rough surfce petl nectr guide ovule ovry lnsects respond to the stimulus of colour nd scent nd re ttrcted to the i nsect-pollinted f lowers. I n insect-pollinted f lowers, the nectr guides led the insects to the nectries. When they collect or feed on the nectr, they brush ginst the nthers to dislodge pollen grins in the process. ln wind-pollintion, only very smll portion of pollen grins is likely to lnd on ripe stigm. lf lrge quntities of pollen grins re not produced, the chnces of successful pollintion re very low. Smooth, light grins re esily crried by wind nd do not stick together. ln insect-pollintion, fewer pollen grins will be wsted. The rough surfces of the grins re more likely to stick to the body of the SIM Pte ltd BIOLOGY O Level Conceptul Lerning!f,f

7 Anthers Stigm Lrge, loosely ttched to filment Stmens hngout of the flower nd re exposed to the wind Lrge nd fethery Projects outside the flower Smll, firmly ttched to filment lnside the flower where insects re likely to brush ginst Sticky lnside the flower The wind is more likely to dislodge pollen grins from exposed, dngling nthers thn from those enclosed in petls. The fethery stigms ct s 'net' with lrge surfce re to trp pollen grins in the ir. FERTILISATION. When pollen grin from n nther lnds on stigm, pollintion tkes plce.. After pollintion, fertilistion will follow.. Fertilistion is process tht involves the fusion of the mle nd femle gmetes in the ovule inside the ovry of flower. Process of fertilistion. After pollintion, the pollen grin bsorbs sugry liquid from the stigm nd germintes pollen tube nucleus genertive nucleus mture pollen grin stigm ovule definitive nucleus ovum style mle gmetes...- ovry wll micropyle pollen tube plcent \ 268 O GIM Pte hd

8 A microscopic pollen tube grows out of the grins. lts growth is controlled by the pollen tube nucleus. The tube secretes enzymes to brek down the surrounding tissue of the stigm nd style so tht it grows down the style nd into the ovry where it enters the micropyle in n ovule. The pollen tube nucleus eventully disintegrtes. However, the genertive nucleus divides to form two mle gmetes. The mle gmetes within the pollen grin enters the ovule when the tip of the tube bursts by bsorbing the sp. One of the mle gmetes combines with the nucleus of the ovum../ First mle gmete * Ovum -+ Zygote./ Second mle gmete + Definitive nucleus -+ Endosperm nucleus The zygote undergoes cell division to form embryo in the seed. The endosperm nucleus develops into endosperm which is the food storge tissue. After fertilistion,./ ovry develops into the fruit./ ovule develops into the seed 2 L. Define pollintion. 2 The digrm below shows the pollintion process between the flowers of the sme plnt nd of different plnts of sme species. B Plnt 1 Plnt 2 () (D Nme the type of pollintion A, B nd C shown in the digrm (ii) A C A Hence, explin the difference between the types of pollintion t B L o olm Ple Ltd BIOLOGY O LevelConceptul Lerning I lf,

9 (b) Using your biologicl knowledge, stte two common fetures tht most likely be found in flowers tht crry out pollintion through (i) process A (ii) process C (c) (i) Stte three dvntges of process A in plnt. (ii) Stte two disdvntges of process A in plnt. (d) (i) Stte three dvntges of process C in plnts (ii) Stte two disdvntges of process C in plnts. 270 o 6lM Ple ltd

10 3. The digrm below shows two types of flowers, A nd B stigm Flower A nectry nther () (i) Nme the gent of pollintion for flowers A nd B. Flower B nther stigm (ii) Stte three resons for your nswer in ()(i) bsed on the structures of these two flowers shown in the digrm. (b) Complete the tble below to show the other chrcteristics of these flowers. Chrcteristics Flower A Flower B Petls Pollen grins Odour C O StM Pte ttd B OI-OGY O Level Conceptul Lerning I l/l

11 4. The digrm below shows prts of stmen P () ldentify prts P to S P R (b) The digrm below shows the component found in one of the structure Q. X secretes n enzyme to digest prt of the tissues of the femle reproductive orgn of flower. (i) Nme the components X nd Y (ii) Wht is the function of Y? (c) (i) Nme the structure tht contins structure R. (id Explin the importnce of this structure R S X Y R S 2t2 o Sl${ Pte Ltd

12 5. The digrm below shows the fertilistion in flower, genertive nucleus pollen tube nucleus pollen tube germintion of pollen grin ovu le ov ry mle gmetes () Describe in detils how this process tkes plce in the flower, (b) Wht would hppen to the ovule nd ovry fter fertilistion? stigm style definitive nucleus ovum micropyle

Check your understanding 3

Check your understanding 3 1 Wht is the difference etween pssive trnsport nd ctive trnsport? Pssive trnsport is the movement of prticles not requiring energy. Movement of prticles in ctive trnsport uses energy. 2 A gs tp in the