ch20

BRYOPHYTES

Chapter 20

ADAPTATIONS ENABLING THE MOVE TO LAND

1. A layer of of sporopollenin protects charophytes from desiccation; sporopollenin is found in the spore wall of land plants. 2. Danger Danger of desiccation desiccation required required new adaptatio adaptations: ns: transport transport tissue, tissue, cuticle, cuticle, large large compact multicellular ody, etc. !. "imultane "imultaneous ous e#oluti e#olution on of cuticle cuticle and and stomata stomata with with guard guard cells. cells. $. "upp "uppor ortt again against st gra gra#i #ity ty.. %. &eproduct &eproduction ion ecame ecame adapted adapted to to periods periods of moistu moisture re so sperms sperms could could swim. swim. '. (ametes (ametes and spore spore mother mother cells ecame ecame protecte protected d from dryness dryness y layers layers of cells. cells. ). *#olutio *#olution n of +ylem and phloem phloem to transport transport materia materials ls to and from different different parts parts of the plant, plant, the atmosphere and the soil. . Alternation of generations: a characteristic life cycle. •

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Alternation of generation does not occur in the charophyceans. -his suggests that alternation of generation arose independently in land plants. A life cycle characteried y a multicellular haploi ga!etoph"te stage followed y a multicellular iploi sporoph"te stage. M#lti$ell#lar% M#lti$ell#lar% epenent e!&r"os' -he ("gote is retained surrounded y tissues of the gametophyte. gametophyte. -he parental tissue pro#ides the emryo with nutrients. Pla$ental transfer $ells present in the emryo and sometimes in the gametophyte as well, enhance the transfer of  nutrients.

/. Spores pro#$e in sporangia: haploid reproducti#e cells that ecome a multicellular haploid gametophyte y mitosis. •

-he multicellular sporangium contains sporocytes, the cells that undergo meiosis to form spores.

10. lants are euaryotic, euaryotic, multicellular, mostly mostly autotrophic organisms, organisms, with haploiddiploid haploiddiploid life cycles, which retain emryo within female se+ organ on parent plant; the cell wall contains cellulose.

)HARA)TERS O* NONVAS)+LAR PLANTS Aout 1),000 species worldwide di#ided into three Di#isions: Br"oph"ta, the mosses; Hepatoph"ta, the li#erworts; and Antho$eroph"ta, the hornworts. -heir life cycle is similar ut the three groups may not e closely related. -he ryophytes may form a  polyphyletic  polyphyletic group.

3ryophyt a refers to the phylum of mosses only; ryophyt es refer to the three phyla mentioned ao#e. 4n many respects, ryophytes are transitional etween charophycean green algae and the #ascular plants discussed later in the course. )hara$teristi$s:

1. "mall emryo emryophyt phytes es found in moist moist en#ironmen en#ironments, ts, lac woody woody tissue tissue and +ylem +ylem and phloem; phloem; they usually form mats spread o#er the ground. 2. (ametophy (ametophyte te generation generation is dominant dominant;; sporophyt sporophytee is parasitic parasitic on the gametophy gametophyte. te. !. 3ryophy 3ryophytes tes ha#e cuticle, cuticle, stomata stomata and multicell multicellular ular gametang gametangia ia and sporangia sporangia that that allow them them to sur#i#e on land. $. -heir odies odies are composed composed of true true parenchyma parenchyma deri#ed deri#ed from threedim threedimensio ensional nal growth growth usually usually from an apical meristem. %. 3ryophy 3ryophytes tes need water to reprodu reproduce ce and most species species lac lac #ascular #ascular tissue tissue 5+ylem and phloem phloem6. 6. '. 7ater 7ater transport transport is mostly through through capillary capillary action, action, diffusion diffusion and cytoplasmic streaming. -hey lac true roots, stems and lea#es. -he gametophyte of mosses is a onecellthic filament nown as the protonema that e#entually produces  uds ha#ing meristematic meristematic tissue. -hese -hese meristems produce an upright upright structure called the the ga!etophore. -hese gametophytes are one to a few cells thic and otain nutrients and water y direct asorption from the en#ironment. 8ost mosses do not ha#e conducting tissue. "ome species ha#e specialied cells that conduct water and nutrients ut lac lignin in their cell walls. -he gametophores are anchored y fragile rhi(ois. &hioids are either single elongated cells as those found in li#erworts and hornworts, or filaments of cells as those of mosses. &hioids are not made of tissues and do not asor any significant amount of water. 4n that way they differ from roots. 3ryophytes ha#e smallest and simplest sporophyte of any group. -he sporophyte remains attached to the gametophyte throughout its lifetime, dependent of the gametophyte gametophyte for food, water and minerals. -he mature sporophyte of mosses consists of a foot emedded in the archegonium, a seta or stal is  present in the phylum phylum 3ryophyta, and a $aps#le or sporangium. -he cap or $al"ptra closes the peristo!e or opening or the capsule.

Di,ision Br"oph"ta 8osses are a large phylum containing aout 12,000 species.

8any new species are disco#ered e#ery year in the tropics. -he phylum is di#ided into three classes, "phagnosida 5peat mosses6, Andreaeopsida 5granite mosses6 and 3ryopsida 5true mosses6. -he class 3ryidae contains aout /,%00 species. )HARA)TERISTI)S

rotonema gi#es rise to gametophores, leafy shoots that produce gametangia. rotonema chlorophyllous with multicellular rhioids. (ametophyte (ametophyte may or may not ranch. (ametophores deri#e from an apical meristem that has a large apical cell. Deri#ati#e cells sudi#ide and  produce the tissues of stems and lades in rather rather precise arrangement. (ametophore leafy with more than three rans of lades. A+is with thic walled outer cortical cells and a central strand of smaller cells. 9amina sessile, entire, seldom loed, one cell thic. 8idri composed of se#eral layers. la yers. 9aminar cells elongated; hyaline cells: dead, large, arrelshaped, retain large quantities of water... 4n the family olytrichaceae, the lamina ears long sheets of cells 5lamellae6 on the upper surface that greatly increases the #olume of photosynthetic tissue. Cuticle e+ists only on the upper surface of the lades; the underside lacs cuticle and is capale of asoring water directly from the en#ironment. "tomata are asent on lades ut present on the sporangial wall. araphyllia present in some species: small, ranched, uniseriate structures. -ater transport

1. 4n some mosses, mosses, primarily primarily in the family family olytricha olytrichaceae, ceae, the innermo innermost st corte+ is composed composed of cells cells called h"rois that conduct water and dissol#ed minerals. • • •

*longated cells that loose their c ytoplasm at maturity. maturity. *nd walls are partially digested ut are not remo#ed completely. completely. *ach hydroids are aligned with those ao#e and elow it

2. "pecie "peciess that that ha#e ha#e hydroi hydroids ds typic typicall ally y ha#e ha#e leptois. 9eptoids resemle sie#e cells. •

*longated cells.

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9ac nuclei at maturity ut retain some c ytoplasm. ytoplasm. a#e prominent interconnections with adacent cells.

!. Adacent Adacent parenchy parenchyma ma cells are unusually unusually cytoplas cytoplasmic mic and rich in enymes enymes ust as are companion companion cells. -he maority of mosses lac hydroids and leptoids. 7ater 7ater is conducted long the e+terior of their stems y capillary action. 4n species that lac leptoids, sugar is transported y slow transport etween the cells. At the ase of the a+is, rhi(ois anchor the plant ut do not asor water or nutrients. • •

8ulticellular filaments -hey lac chloroplasts

De,elop!ent

"pores germinate and send out a long chlorophyllous chlorophyllous cells. -his cells undergoes mitosis and produces a ranched system of similar cells called the protone!a.