Section 1 Sexual Reproduction in Seedless Plants

1 OverviewBefore beginning this sectionreview with your students theobjectives listed in the lesson begins with adiscussion of alternation of genera-tions, which occurs in all Plants . Itcontinues with the life cycle of amoss to introduce the reproductivestructures and life cycles of non-vascular Plants . A fern is used toillustrate the reproductive structuresand life cycles of Seedless a moss and a fern on yourdesk. Instruct students to write ashort paragraph that describes amoss or fern plant. Tell them to beas descriptive as possible about theplant s general appearance andwhere it students that the sperm of anonvascular plant must swim to anegg cell for fertilization to students to describe environ-mental conditions that wouldenable nonvascular Plants to repro-duce sexually.

2 (Nonvascular plantsare able to reproduce sexually wher-ever moisture is abundant. Shadyareas near streams are ideal drier habitats, nonvascular plantscan reproduce sexually after a rainfallor heavy dew.) InterpersonalTAKS 2 Bio 6D (grade 10 only), 8C TAKS 3 Bio 7B, 13A; Bio 5A, 13 BLSM otivateMotivateBellringerFocusFocusSecti on 1530 chapter 24 Plant Reproduction Lesson Plan Directed Reading Active Reading Data Sheet for Quick LabGENERALGENERALGENERALC hapter Resource File Reading Organizers Reading Strategies Planner CD-ROMS ection 1 Sexual Reproduction in Seedless PlantsReproduction in Nonvascular Plants The carpet of green you often see near streams and in moist, shadyplaces is usually made up of mosses or liverworts. As you learned inthe previous chapter , these small, relatively simple Plants are non-vascular Plants .

3 They do not have a vascular system for distributingwater and nutrients. Mosses and liverworts do not usually thriveoutside moist places because they must be covered by a film ofwater to reproduce all Plants , nonvascular Plants have a life cycle called alterna-tion of generations. In this type of life cycle , a gamete-producingstage, or gametophyte, alternates with a spore-producing stage, orsporophyte. Gametophytes produce gametes (eggs and sperm) inseparate multicellular structures. The structure that produces eggsis called an (ark uh GOHN ee uhm).The structure thatproduces sperm is called an (an thuhr IHD ee uhm).Sporophytes produce spores in a sporangium. The gametophytes ofnonvascular Plants are larger and more noticeable than are thesporophytes.

4 This difference in size is very pronounced in the liver-worts, as you can see in Figure Summarizethe life cycle ofa moss. Summarizethe life cycle ofa fern. Compareand Contrastthe life cycle of a moss withthe life cycle of a fern. Key TermsarchegoniumantheridiumsorusThe gametophytes of Marchantia, a common liverwort,produce male and female gametes on separate stalks. Figure 1 Reproductive structures of a liverwortSporophytes, which grew from archegonia under the cap of a female stalkArchegonia under thecap of a female stalk FemalestalksSporophytesAntheridia on top of a male stalk Malestalks13B13B13B530 Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 13A TEKS Bio 7B, 8C, 13A, 13 BTeacher Edition TAKS Obj 2 Bio 6D, 8C TAKS Obj 3 Bio 7B, 13 ATEKS Bio 5A, 6D, 6E, 7B, 8C, 10C,13A, 13 Bpp.

5 530 531 TransparenciesTTLife cycle of a MossTTLife cycle of a FernChapter 24 Plant Reproduction531 GENERALU sing the Figure Walk students through the moss lifecycle shown in Figure 2,startingwith the zygote. Point out that thezygote divides mitotically. Repeatedmitotic cell divisions result in amulticellular, diploid organismcalled the sporophyte. In mosses,the sporophytes are not green, andthey consist of a bare stalk toppedwith a spore capsule. Reproductivecells in the spore capsule undergomeiosis, which reduces the chromo-some number from diploid tohaploid. Point out that the sporesgrow into either male or femalegametophytes, which are haploid. Inmosses, the gametophytes are greenand have leaflike structures. Finally,point out that when fertilization (theunion of an egg and a sperm) occursand a new zygote is formed, thediploid chromosome number isrestored, and a new sporophytegeneration begins.

6 VisualBrainstormingAsk students toidentify the haploid structures in aplant s life cycle (spores, male andfemale gametophytes, eggs, andsperm).Ask which are unicellular(spores, sperm, and eggs)and whichare multicellular (male and femalegametophytes).Ask students toidentify the haploid structures in ananimal s life cycle (egg and sperm).Ask if these are unicellular or mul-ticellular (unicellular).Ask studentsto identify the diploid structures ina plant s life cycle (sporophyte,zygote). Ask which is unicellular(zygote)and which is multicellular(sporophyte). Ask students to iden-tify the diploid structures in ananimal s life cycle (all stages ofdevelopment from the zygote to theadult). Ask which of these struc-tures is unicellular (zygote)andwhich are multicellular (all otherstages of development).

7 InterpersonalBio 6E, 10C, 13 BLSSKILLBUILDERREADINGREADINGBio 6E, 10C, 13 BLST eachTeachMISCONCEPTION ALERT Spores The term sporedoes not have a sin-gle, concise definition as students might things are generally true of spores. First,they are unicellular; second, they have a pro-tective outer covering. In some bacteria, sporesform from regular cells when environmentalconditions are harsh. These cells lose most oftheir water and develop a protective outercovering. Many of these bacteria also pro-duce toxins, which help the spores remainviable in harsh environments. The spores of fungi and Plants are haploid, drought-resistant, and easily transported by wind orwater. The spores of fungi and Plants developinto multicellular individuals (by mitotic celldivision) without fusing with another cycle of a MossThe life cycle of a moss is summarized in Figure reproduc-tion results in a fertilized egg, or zygote.

8 The diploid zygote grows intoa new diploid sporophyte. As you can see, a moss sporophyte growsfrom a gametophyte and remains attached to it. The sporophyteconsists of a bare stalk with a spore capsule (sporangium) at its form by meiosis inside the spore capsule. Therefore, as in allplants, the spores are haploid. The spore capsule opens when thespores are mature, and the spores are carried away by wind or a moss spore settles to the ground, it germinates and grows intoa leafy green gametophyte. Archegonia and antheridia form at thetips of the haploid gametophytes. Eggs and sperm form by mitosisinside the archegonia and antheridia. Remember, moss gametophytesgrow in tightly packed clumps of many individuals.

9 When watercovers a clump of mosses, sperm can swim to nearby archegonia andfertilize the eggs inside word archegoniumcomes from the Greekwords archegonos,meaning first of a race. Knowing this makes iteasier to remember that anew and geneticallydifferent individual growsfrom an archegonium whenits egg is 2 Moss life mosses, a sporophyte thatconsists of a spore capsule ona bare stalk alternates with a leafy, green adult sporophyte produces spores within its spore gametes inside antheridia and swim toand fertilize eggs inside the zygote develops into a new grow into male and female (2n)Haploid (n)GametophytesFemaleMaleAntheridiaSperm EggArchegoniaAdultsporophyteSporesSpore capsule(sporangium)Germinating sporeZygoteYoung sporophyteFertilizationMeiosisMitosisMit osis531532 chapter 24 Plant ReproductionGENERALO bserving a FernGametophyteSkills AcquiredObserving, makingcomparisons, makingconclusionsTeacher s Notes Tell students that fern gameto-phytes develop on moist soiland are very to will vary but shouldbe consistent with the dia-grams in Figure new sporophyte begins itsgrowth in an process occurs becausethe egg remains in the archego-nium, and a sperm cell swimsfrom an antheridium to thearchegonium where it fertilizesthe 1 Bio/IPC 2C, 2D; Bio 13 BMath SkillsAsk students to usethe information in Figure 3to esti-mate the number of spores that onefern plant might produce.

10 To helpthem with their calculations, havestudents assume that only half ofthe frond is visible in the photo,each sporangium produces 100spores, and one plant produces 12fronds. (A sample calculation wouldbe as follows: 260 sori per frond 30sporangia per sorus 100 spores persporangium 12 fronds per plant = 9,360,000 spores per plant.) LogicalTAKS 1 Bio/IPC 2C; Bio 13 BLSBUILDERSKILLT each, continuedTeach, continuedGarden centers and florists often receive callsabout insects on ferns and flower arrange-ments that include fern leaves. When the fernleaves have sporangia on them, people oftenmistake the sori or sporangia for insects. Aclose look at these spore-producing struc-tures reveals that they are lined up in rowsacross from each other.