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Reproductive apparatus

Reproductive-1.serving to reproduce. 2. cocerned with pertaining to reproduction:a reproductive process; reproductive organs.-n.3.Entomol.a sexually mature male or female termite;a member of reproductive caste.( RE+PRODUCTIVE) APPARATUS- 4. Physiol. a group of structurally different organs working together in the performance of a particular function:the degistive apparatus.(<L<apparatus (ptp. of apparare)provided,equiv.to ap-AP-+par-prepare+atus-ATE) F-2.Phylum Oomycota (water molds) The water molds are a group of organisms consisting of long filaments,or hyphae ,filled with nuclei.Members of this division possess flagellated stages and cell walls made of cellulose (unlike the true fungi).Sexual reproduction in this group is oogamous .Although most members of the phylum are aquatic,a few are terrestrial.Among the terrestrial group are some important plant pathogens such as Phytophthora (potato blight),the cause of the potato famine in Ireland,and Plasmopara (downy mildew),which almost caused the destruction of the wine industry in France in the late 1800 ’s. Saprolegnia is an aquatic organism that is very common locally,and is an important pathogen on fish and amphibians (it may be linked to the global decline in amphibian populations).The prepared slides of Saprolegnia have two different regions:one containing the structures associated with sexual reproduction,and the other containing the asexual reproduction structures.You will need to examine both regions of the slide to find the following structures. Saprolegnia is diploid in its vegetative state. Female gametes (eggs)are produced by meiosis in round structures termed oogonia (sing.oogonium).Sperm are produced by meiosis in antheridia (sing.antheridium), small filaments closely associated with,and penetrating the oogonia.Fertilization results in the production of diploid spores that germinate to produce a new mass of filaments. Asexual reproduction is very common in this group.In this case,diploid spores are produced by mitosis in elongate sporangia, which are somewhat wider and more darkly stained than the other filaments visible on the slide. B.Life Cycles and Sexual Reproduction: When looking at multicellular algae,plants,and to some extent,the fungi and animals,it is essential to have some understanding of life cycles.The information outlined for you here will prove to be useful in the completion of this exercise as well as others throughout the remainder of the term.You should refer back to this section repeatedly over the next several weeks. There are three basic types of life cycles (exhibiting zygotic ,sporic ,or gametic meiosis)which can be used to describe all organisms (Figure 1).Each of the three cycles is similar in that (i)a haploid (n)phase alternates with a diploid (2n)phase;(ii)to get to the haploid phase from the diploid phase,meiosis has to occur;and (iii)to get to the diploid phase from the haploid phase,fusion of gametes (syngamy )must take place.The life cycles differ with respect to the timing of meiosis and fertilization,and what the products of meiosis are. 1.Life Cycle Exhibiting Zygotic Meiosis: Zygotic meiosis is very common in organisms like green algae and fungi.In this type of life cycle, the organism exists for most of the cycle as a multicellular,haploid organism.This organism at some point produces gametes via mitosis,which then unite to form a diploid zygote.The zygote undergoes a meiotic division and haploid spores are the result.These spores germinate to produce a new multicellular gametophyte.Hence,the only multicellular stage is the gametophyte,and meiosis takes place in the zygote to produce spores. 2.Life Cycle Exhibiting Sporic Meiosis: Some green and brown algae,as well as the red algae and all plants exhibit life cycles with sporic meiosis.All organisms possessing this life cycle exhibit alternation of generations ,where a multicellular,haploid form of the organism (the gametophyte )alternates with a multicellular diploid form (the sporophyte ).If the two generations appear to be identical,then the organism is said to exhibit isomorphic alternation of generations.If the gametophyte and sporophyte stages are phenotypically distinct,then heteromorphic alternation of generations is the result.At first glance,this life cycle may seem to be much more complicated than life cycles with zygotic meiosis, but in reality,little has changed.The multicellular gametophyte still produces gametes via mitosis,and these gametes will again fuse to form the zygote.However,the zygote then divides mitotically to produce a multicellular sporophyte,rather than immediately undergoing meiosis. At some point,cells in the multicellular sporophyte will undergo meiosis to produce spores which then germinate to form a new multicellular gametophyte.In sporic meiosis then,there is an alternation of multicellular sporophytic and gametophytic generations,and the products of meiosis are spores.This alternation of generations is found only in organisms that exhibit sporic meiosis. 3.Life Cycle Exhibiting Gametic Meiosis: Gametic meiosis is exhibited by some brown algae and all animals.In this life cycle,only the gametes are haploid.All other stages are diploid (think of your own bodies:every cell in your body has two sets of chromosomes,except for the eggs or sperm that you produce.These only contain one set of chromosomes).This life cycle is also somewhat similar to a sporic meiosis life cycle.Imagine a reduction in the size of the multicellular haploid stage to just one cell;a gamete, while the diploid stage remains large and dominant.This is a trend that occurs in plants.The most advanced plants have very reduced gametophytes and large,dominant sporophytes. Conversely,you can get sporic meiosis from gametic meiosis by making the product of meiosis a spore,rather than a gamete and having the spore grow to produce a multicellular haploid stage. Thus,in gametic meiosis,the only multicellular stage is diploid,and the products of meiosis are always gametes. 4.Spore Types: Spores are always produced in specialized structures called sporangia (from the Greek “angium ”, meaning container).For the sake of simplicity,Figure 1 shows only a single type of spore produced in each type of life cycle.Plants that produce only one type of spore are said to be homosporous .However some plants,including all conifers and flowering plants,are heterosporous ;that is,they produce two different kinds of spores,megaspores and microspores , in two different kinds of sporangia,megasporangia and microsporangia .The spores germinate to produce megagametophytes and microgametophytes,the sites of female and male gamete production respectively.Only one type of gametophyte is produced in homosporous plants. Homosporous organisms always have free-living,bisexual gametophytes (both male and female gametes are produced on the same gametophyte),while in heterosporous organisms,unisexual gametophytes (those that produce only one kind of gamete,either male or female)always develop within the spore wall.What is the evolutionary advantage of having gametophyte development occur within the spore? 5.Gamete types: Gametes are produced in structures called gametangia .Although the diagrams in Figure 1 show the gametes as always being the same size,this is not always the case.Organisms that practice isogamy produce gametes that are motile and morphologically similar.Anisogamous organisms produce motile gametes as well,but one is large and the other is small.Oogamous organisms produce large,nonmotile gametes (the eggs)and small,motile gametes (the sperm).You will see examples of all of these throughout the semester. sources:Webster's Encyclopedic Unabridged Dictionary of the English Language Biology 1020,Diversity of life, laboratory Manual,Spring 2003, Written by Helena Danyk, Teresa Dolman



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