Plant Reproduction
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| What is reproduction? | Reproduction is a biological process by which cells or living organisms give rise to offsprings. Species are maintained in existence through this vital process. Reproduction is not necessary to the life of an individual, yet it is a prerequisite for the continuity of any species. |
| What are the two basic types of reproduction? | Asexual and sexual. In asexual reproduction, offspring arise from a single parent even without special reproductive cells or organs. The new individual is a separated part of the parent organism. Sexual reproduction, however, involves the union of two nuclei from special cells, which are usually produced by two separate parents. Some organisms reproduce only asexually, others reproduce only sexually, and still others can reproduce by either of these methods. |
| Talk in general about asexual reproduction. | Asexual reproduction (also known as agamogenesis) is the biological process by which an organism creates a genetically-similar or identical copy of itself without a contribution of genetic material from another individual (lack of genetic recombination). It is a form of reproduction which does not involve meiosis, gamete formation, or fertilization. |
| How is asexual reproduction performed? | Asexual reproduction may be as simple as cell division, resulting in two separate individual cells, as in Prokaryotes and simpler Eukaryotes, or it may involve the production of spores, special reproductive cells, each capable of producing a new organism, common in Algae and Fungi. At a more complex level, as in higher plants (also reproduce sexually), asexual reproduction involves the formation of a complete multicellular individual, which becomes detached from its parent. This way of reproducing is called vegetative reproduction as it is accomplished without seeds or spores. |
| Talk about asexual cell division. | Asexual reproduction involves only mitotic cell division, therefore each offspring has exactly the same hereditary information as its parent: each daughter cell receives an exact copy of the chromosomes of the mother cell (clones). Thus asexual reproduction results in stable characteristics within a species from generation to the next: the same chromosome number is retained from generation to generation. Asexual reproduction is efficient in that it is generally rapid and often results in the production of large numbers of identical offsprings. |
| Talk in general about sexual reproduction | Sexual reproduction is a biological process by which organisms generate heterogeneous offsprings (descendants) that have a combination of genetic material contributed from two different members of the species (typically one of each sex), thus leading to genetic diversity. |
| What are the characteristics of sexual reproduction? | This type of reproduction is characterized by two processes. The first, meiosis, involves the halving of the number of chromosomes. The second process, fertilization, leads to the fusion of two gametes and the restoration of the original number of chromosomes. |
| Can plants reproduce sexually and asexually? | Many organisms can reproduce sexually as well as asexually. Bryophytes, Pteridophytes and many plants are examples. |
| Talk about when plants that can reproduce sexually and asexually become asexually reproducing. | When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supplied resources. |
| When do sexual/asexual plants reproduce sexually | When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, cysts or other “dormant or quiescent” and resistant form ensure the survival during unfavorable times and the organism can “wait out” adverse situations until a swing back to suitability occurs in order to carry on its asexual reproduction. |
| Talk about endospores of bacteria. | Several types of bacteria are able to form resistant spores when the conditions are hostile. Endospores are spores formed within the cell wall of a parent cell. Endospores are resistant resting cells, protected by several thick layers. The spore will remain dormant for a period of time before it can be induced to germinate and to revive the vegetative state in hospitable environments. |
| Talk about akinetes. | Under unfavorable conditions, some Cyanobacteria form resistant spores called akinetes - enlarged vegetative cells with a thickened outer wall. Akinetes are dormant cells. They are resistant to cold and drought (desiccation). They also accumulate and store various essential materials, thus allow the Cyanobacteria to survive under unfavorable environmental conditions. Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell. |
| Talk about heterocysts. | Within the filament, heterocysts are specialized enlarged thick cell wall that fix nitrogen. When environmental conditions trigger reproduction, certain heterocysts in the filament die causing the defragmentation of the trichome into multicellular fragments. Each fragment is capable of growing into a new filament. |
| Talk about hormogonia. | Filamentous cyanobacteria reproduce by fragmentation of their filaments (trichomes) at more or less regular intervals to form short pieces of filaments. These pieces of filaments (surrounded by a mucilaginous sheath) are called hormogonia. The latter show gliding motility and develop into new filaments. |
| Talk in general about asexual reproduction of cyanobacteria. | All cyanobacteria are unicellular, though many grow in colonies or filaments (trichomes), often surrounded by a gelatinous or mucilaginous sheath. Cyanobacteria present several forms of asexual reproduction: - Unicellular cyanobacterial cells divide and reproduce by binary fission and spore formation. - Filaments may fragment, often at weak points where a cell has collapsed (hormogonia) or near a nitrogen-fixing site (heterocysts). |
| Talk about budding of bacteria. | Rare form of bacterial division where a cell bulges and forms a protuberance that grows to equal volume of the mother cell, and then becomes detached to form a daughter cell. |
| Talk about binary fission of bacteria. | Most bacteria reproduce by a process called binary fission or scissiparity. Binary fission is basically an asexual mode of cell division where a single parent bacterial cell replicates its DNA before splitting into two new daughter cells. Under ideal conditions, bacteria divide (reproduce) rapidly, doubling their numbers every 20 minutes. |
| How is the mode of reproduction of bacteria? | Bacteria are organisms which reproduce through asexual reproduction; they are not able to reproduce by mitosis or meiosis because they lack a true nuclei. They do not have different sexes, and they are capable of “splitting” themselves into two or more individuals. |
| Talk in general about bacteria | Bacteria are considered as the most ancient living forms on earth. They can colonize many environments even the harshest ones. They are divided into Eubacteria and Archaebacteria. Bacteria are prokaryotes; they are unicellular organisms that lack membrane-bound organelles and a defined nucleus. |
| Talk about the conjugation type of sexual reproduction related to fertilization mode. | Conjugation (Cystogamy) is a process by which a donor cell (- mating type) makes a temporary contact with a recipient cell (+ mating type) through a conjugation tube (e.g. Spirogyra) or a protuberance (e.g. Mucor) to transfer and fuse its content and its genetic material directly from the donor into the recipient cell. |
| Talk about triplobiontic cycle | In most red algae (e.g. Rhodophytes), the life cycle includes three phases. Such multigenerational cycles are said to be “trigenetic” because they produce three successive generations : the gametophyte (haploid), the carposporophyte (diploid) and the tetrasporophyte (diploid). |
| Talk about digenic cycle | AKA haplodiplotonic In some protists and some fungi as well as in plants, the life cycle is, by contrast, multigenerational, characterized by an alternation of generations - it includes both a multicellular sporophyte (diploid generation) and a multicellular gametophyte (haploid generation). Life cycles that present two phases are called digenetic (also known as diplobiontic, diplohaplontic, haplodiplontic, or dibiontic): A diploid (2n) sporophyte produce through meiosis, haploid (n) cells, called spores. The germination of a haploid spore undergoes mitosis and grows into a gametophyte (gamete-producing organism). The gametophyte reaches maturity and produces haploid (n) gametes by mitosis, which following fertilization, grow into a zygotic sporophyte (spore-producing organism). |
| Talk about diplobiontic monogenic cycle | When the cycle encompasses a single generation of organisms whose cells are diploid. Organisms produce sex cells that are haploid, and each of these gametes must combine with another gamete in order to obtain the double set of chromosomes necessary to grow into a complete organism, the sporophyte. Meiosis occurs only during the formation of gametes and the gametes undergo no further cell division (by mitosis) until fertilization occurs. In the whole cycle, gametes are the only haploid cells. The diploid multicellular individual is a diplont; this is the case of some brown algae, e.g. Fucus. |
| Talk about haplotonic monobiontic cycle | When it encompasses a single generation of organisms whose cells are haploid (absence of a sporophytic phase). In this case, meiosis occurs immediately after fertilization and the formation of the zygote. The produced haploid cells undergo mitosis and produce a multicellular haploid organism, the gametophyte. In the whole cycle, zygotes are the only diploid cell; mitosis occurs only in the haploid phase. The individuals or cells that result from the mitosis are called haplonts; e.g.: some fungi and some green algae - e.g. |
| Talk in general about monobiontic cycle | AKA monogenic It describes a life cycle in which there is only a single independent generation (monogenetic). |
| Talk in general about the life cycle. | A life cycle represents the series of changes that an organism undergoes as it passes from the beginning of a given developmental stage to the inception of that same developmental stage in a subsequent generation. The life cycle of every sexually reproducing group of organisms has a characteristic pattern. Alternation of meiosis and fertilization is common to all sexually reproducing organisms; however, the timing of these two events in the life cycle varies among species. When fertilization is followed by mitosis, a diploid sporophyte is produced. When meiosis is followed by mitosis, a haploid gametophyte is produced. |
| Talk about sphenogamy. | Siphonogamy is a process of gametes fusion in which non motile sperms are transferred and conducted to the egg (non motile) via a tube. e.g. Angiosperms |
| Talk about trichogamy | Trichogamy is a mode of fertilization that occurs when a male, non-motile spermatium (carried by water currents) collides with a hair-like extension of the female gametangia, the trichogyne. The spermatium and the trichogyne fuse their cytoplasms then the nucleus of the spermatium migrates through the trichogyne and fuse with the egg nucleus. e.g. Red algae |
| Talk about the somatogamy type of sexual reproduction | Somatic cells of two haploid filaments of opposite mating types (+ and -) come in contact and fuse (without the fusion of nuclei) involving only plasmogamy. Karyogamy is delayed and is separated from plasmogamy by a dikaryotic phase (n+n). e.g. Basidiomycota. |
| What does Aplanogamy mean? | The fusion of two non-motile gametes (aplanogametes). e.g. Red algae. AKA heterogamy. |
| What does planogamy mean? | The fusion of two motile gametes (planogametes, zoogametes). Planogamy can be isogamous or anisogamous. e.g. Chlamydomonas (Isogamous planogamy) Ulva (Anisogamous planogamy) |
| What does anisogamy mean? | AKA heterogamy The fusion of two different gametes (different sizes and/or forms). The female gamete is larger than the male gamete. e.g. Ulva. |
| What does isogamy mean? | The fusion of gametes of similar morphology (same size and form) but of different mating types, most commonly noted as male and female gametes or as "+" and "−" strains e.g. Chlamydomonas. |
| Talk about oogamy. | The evolutionary tendancy progresses further towards oogamy. Oogamous organisms - e.g. some Algae such as Fucus, Laminaria) produce a nonmotile female macrogamete (egg or oogonium) and a flagellated male microgamete (spermatozoid). In oogamy, more male than female gametes are produced. |
| What do we call different types of gamete cells reproducing? | Most organisms form two different types (and sizes) of gametes (anisogametes). In these anisogamous species, (e.g. Ulva) the two sexes are referred to as male (producing sperm) and female (producing ovules). The female gamete is larger than the male gamete, a state called heterogamy or anisogamy |
| What do we call similar gamete cell types reproducing? | In isogamous species, the gametes (the female and the male, or the + and the – gametes as for example in the green algae, Chlamydomonas) are similar or identical in form and size . Such type of reproduction is called isogamy. |
| Talk about the formation of motile and non-motile gametes during sexual reproduction. | Sexual reproduction involves formation of gametes in gametangia. When these gametes are capable of moving - flagellated - they are called planogametes (zoogametes); planogamy refers to the type of reproduction that involves such gametes. Aplanogamy refers to the type of reproduction that involves non motile gametes (aplanogametes). |
| Talk about syngamy. | Syngamy is the process of fusion of two gametes (of different sexes, male and female) to produce a diploid zygote which later becomes the new individual. Syngamy can be divided into two sequential stages: plasmogamy (fusion of the cytoplasm of two parent cells) and karyogamy (fusion of two haploid nuclei to produce a diploid cell). Usually, plasmogamy is immediately followed by karyogamy. In some systems of reproduction, karyogamy is delayed; the two haploid parental nuclei cohabit without fusing the cell (dikaryotic cell (n+n) or a dikaryon) that results from plasmogamy. |
| Talk about the simplest kind of sexual reproduction | The simplest form of reproduction, in which two eukaryotes unicellular organism or some multicellular algae (e.g. Spirogyra), link together joined by the outgrowth of conjugation tubes, exchange genetic information, and then separate. This type of reproduction is termed conjugation (cystogamy) when there is a complete transfer of one organism’s (or cell’s) contents to the other organism. If the process involves only the transport of the sperm through a tube it is then termed siphonogamy. |
| What does oogamy mean? | Fertilization by the fusion of a large, non-motile, female gamete (macrogametes) with a small, motile, male gamete (microgametes) e.g. Fucus. |
| Talk about digenetic cycle of algae *heteromorphic* | Laminaria exhibits an alternation of heteromorphic generations. The sporophyte plant is a large multicellular alga whereas the microscopic female and male gametophytes are composed of few cells. The sporophyte generation (2n) develops on the surface of its blades sori containing sporangia and paraphyses; sporangia produce by meiosis motile flagellated zoospores (n ch), which develop into male and female gametophytes (n ch). Male gametophytes release motile male gametes. Female gametophytes produce eggs which remain attached to it. Male gametes fertilize the eggs; the fertilization of Laminaria is oogamous. |
| Talk about the third generation of red algae | Tetrasporophyte stage. When a carpospore lodges in a suitable location, it germinates and grows into a diploid tetrasporophyte (Sporophyte II). Tetrasporangia are formed along the branches of the tetrasporophyte. Mother cells of each tetrasporangium undergoe meiosis, giving rise to four haploid tetraspores. When tetraspores germinate, they develop into male and female gametophyte, thereby completing the life cycle. In this life cycle, the three types of thalli (male gametophyte, female gametophyte and tetrasporophyte) all outwardly resemble one another. |
| Talk about the second generation of red algae | Carposporophyte stage (parasitic on the gametophyte). The zygote, divides repeatedly by mitosis and gives birth to the carposporophyte (diploid, Sporophyte I), producing then diploid carpospores in the carposporangia. These carpospores are released and carried away by ocean currents. |
| Talk about the first generation of red algae | The male and female gametophytes are isomorphic haploid generations and bear the gametangia. The male gametangia called spermatangia produce non motile sperm cells called spermatia. The female gametangia are called carpogonia. Each carpogonium consists of a single large cell and has a long tubular hair-like extension the trichogyne that basically acts as a receptor of drifting spermatia. Since reproductive organs of Rhodophyta are non-motile, the spermatia are carried to the trichogyne of carpogonium by water currents. If a spermatium should brush against a trichogyne, it may become attached, and plasmogamy occurs. Then the nucleus of the spermatium migrates to the egg nucleus and fuses with it, forming a zygote. This type of fertilization is trichogamy. The produced zygote goes on to develop parasitically on the female gametophyte. |
| Talk in general about trigenic algae cycle | Most red algae (Rhodophyta) have a trigenetic life cycle. A typical example of trigenetic life cycle of Algae is the one of Polysiphonia and Nemalion… The Trigenetic cycle include three successive generations |
| Talk about monobiotic diplontic cycle of algae | Fucus is a brown alga presenting a branched thallus (diploid sporophyte). At the tips of the frond, the receptacles bear many small cavities called conceptacles. Each conceptacle contains the gametangia (structures where gametes are produced) and sterile hairlike filaments called paraphyses. Some species develop male and female gametangia inside the same conceptacle, whereas other species have separate male and female conceptacles on separate thallus The female gametangia, oogonia, produce by meiosis haploid non motile female gametes (eggs). The male gametangia, antheridia, produce by meiosis haploid biflagellated (motile) male gametes (sperm). Eggs and sperm are released simultaneously into water; the eggs release a pheromone that attracts the sperm (chemotaxis). Fertilization occurs externally (in water), by oogamy. The fertilized egg settles to the substrate where it becomes attached. The zygote develops by mitosis a mature diploid sporophyte. |
| Talk about monobiontic haplontic sexual reproduction of algae | Spirogyra is a filamentous haploid green alga (gametophyte) which is common in freshwater habitats. When sexual reproduction begins, the individual cells of adjacent aligned filaments (of two different mating types) form protuberances which grow and fuse to form a conjugation tube connecting the opposite pair of cells. Fertilization occurs when the condensed protoplast of cells of one filament, migrates through a conjugation tube and fuses with the protoplast of the adjacent cells of the second mating filament, forming a zygote. Each filament of protoplast moving cells is considered as a male filament, while the stationary one functions as a female filament. Sexual reproduction is done by conjugation. The resulting zygote forms a zygospore with a tough resistant outer covering within the cells of the female filament. The zygospores break away from the parent when the filament cell walls rupture. After a period of dormancy, on return of favorable conditions, these zygotes undergo meiosis and germinate, resulting in new haploid filaments of Spirogyra |
| Talk about Asexual reproduction of algae | - Mitotic division for single-celled forms ex. Diatoms. - Fragmentation for multicellular organisms. Some multicellular algae, e.g. Sargassum reproduce asexually through fragmentation, in which fragments of the parent develop into new individuals. -Budding, a process similar to fragmentation, where the parent organism divides into two unequal parts. New individuals develop as buds on the outer surface of the parent organism. The buds may break off and live independently or they may remain attached, forming a colony. - Spore formation. Many algae produce spores asexually by mitosis. If these spores are flagellated and motile, they are called zoospores or planospores. The majority of algae produce zoospores except red algae. |
| Talk about algae reproduction in general | Algae (Protists) comprise a large heterogenous assemblage of photoautotrophic organisms which vary vastly in size, shape and mode of life. Algae show morphological, cytological, physiological differences. The reproductive systems of algae also show similar diversity. Algae reproduce in astoundingly diverse ways; some reproduce asexually, others use sexual reproduction, and many use both mode of reproduction. |
| Talk about digenetic life cycle of algae *isomorphic* | All Ulva species alternate between gametophytic and sporophytic life stages (haplodiplontic life cycle n/2n) with similar morphologies (isomorphic generation). The gametophytes are haploid and the sporophytes are diploid. Both gametes (biflagellated) are motile (zoogamy, planogamy) and the female gamete is larger than the male (anisogamous). The gametes fuse to produce a quadriflagellate zygote. The zygote swims for a short time then comes to rest, withdraws its flagella and grows into a new sporophyte. The mature sporophyte forms sporangia and produces by meiosis haploid quadriflagellate zoospores. Zoospores withdraw their flagella and develop into gametophytes. |
| Talk about deuteromycota reproduction | Deuteromycetes (Imperfect fungi) reproduce asexually by producing conidia. They have no known sexual reproduction. |
| Talk about deuteromycota sexual/asexual reproduction | They are referred to as imperfect fungi; their sexual form of reproduction has never been observed. Imperfect fungi reproduce asexually by producing conidia on specialized hyphae called conidiophores. |
| Talk about ascomycota reproduction | In Ascomycetes, sexual reproduction begins when the hyphae of two different strains of sac fungi become closely associated. Antheridia are formed on the mycelium of (-) strain and oogonia on the other one (+). The male nuclei of the antheridium pass into the ascogonium via the trichogyne which is an outgrowth of the ascogonium (2) and pair with the female nuclei present but do not unite - Plasmogamy takes place. New dikaryotic hyphae (= dikaryon) develop from this fused structure (3). The cells at the tip of these hyphae form asci (sing. ascus), sac like structure (4), in which karyogamy (nuclear fusion) occurs. These asci (along with the sterile filaments paraphyses) are embedded in an ascocarp, the fruiting body of the fungus. Karyogamy in the asci is followed immediately by meiosis (5) and the production of ascospores (endogenous) (6, 7). The ascospores are disseminated (8) and germinate (9) to form new haploid mycelium. Asexual conidia may be produced by the haploid mycelium (10). In this life cycle, plasmogamy and karyogamy are separated in time and space by a dikaryotic phase. |
| Talk about asexual reproduction of fungi (spore formation) | Spores are quite small and easily carried by wind. Reproductive structures involved in the production of spores are called sporangia. These sporangia are located at the tip of hyphae from which they are separated by complete septa. Spores are the primary means of reproduction, dispersal and survival. Spores are resting resistant stages (cysts) under unfavorable conditions and are in an active stage under favorable conditions. Spores could be exogenous, called conidia, (e.g. Penicillium) or endogenous, produced inside sporangia (e.g. Rhizopus). Spores of fungi are non-flagellated (aplanospores). |
| Talk about Asexual reproduction of fungi (Budding and fragmentation) | Asexual reproduction is carried out by budding, fragmentation, or, most commonly, by spore formation. - Budding: as in single celled yeast (Saccharomyces) - Fragmentation: Mycelial fragmentation occurs when a fungal mycelium separates into pieces with each component growing into a separate new mycelium. e.g. Basidiomycota |
| Talk in general about fungal reproduction | Fungal reproduction occurs in a variety of ways asexually and sexually using different strategies. Fungi that reproduce sexually have a haploid stage and a diploid stage (short-lived) in their life cycles. Ascomycetes and Basidiomycetes also go through a dikaryotic stage, in which the nuclei inherited by the two parents do not fuse right away, but remain separate in the hyphal cells. |
| Talk in general about bryophyte reproduction | Bryophytes display two adaptations that first made the move onto land possible. They are covered by a waxy cuticle that helps the body retain water, and their gametes develop within gametangia. Bryophytes include mosses, liverworts and hornworts. |
| Talk about asexual reproduction of bryophytes. | Asexual reproduction in Bryophyta (mosses, liverworts and hornworts) may occur by fragmentation or by gemmae. - Fragmentation: Pieces of a gametophyte can break off and form new bryophyte plants. - Gemmae (e.g. Marchantia: class Hepaticopsida) are tiny, multicellular propagules, cup-shaped structures on the gametophytes. Raindrops separate gemmae from the parent plant so they can spread and form new gametophytes. |
| Talk in general about bryophyte sexual reproduction | Bryophytes are characterized by a haplodiplontic life cycle. The gametophyte generation (conspicuous vegetative plant) is dominant and the sporophyte is dependent on the gametophyte. |
| Talk about steps of bryophytes sexual reproduction | Gametophytes can form multiple gametangia, each of which produces gametes. Male gametophytes develop reproductive structures called antheridia (flagellated, motile) that produce sperm cells by mitosis. Female gametophytes develop archegonia (sing. archegonium) that produce eggs by mitosis. Each archegonium produces one egg, whereas each antheridium produces many flagellated sperm. Some bryophytes bear antheridia and archegonia within the same gametophyte. Fertilization occurs in the presence of water. The type of reproduction is oogamy. |
| Talk about bryopsida (Mnium) sexual reproduction | Mosses have an alternation of generations (haplodiplontic cycle), the sporophyte grows on the female gametophyte and remains attached and nutritionally dependent on the gametophyte throughout its existence |
| Talk about steps of bryopsida sexual reproduction | Flagellated sperm cells travel to a neighboring plant via a water droplet and are chemically attracted to the entrance of the archegonium. Fertilization occurs when one of the sperm cells fuses with the egg (oogamy). The diploid zygote formed as a result of fertilization grows into a multicellular embryo by mitosis, and matures into a moss sporophyte. The embryonic sporophyte develops within the archegonium, and the mature sporophyte stays attached to the female gametophyte throughout its existence. The sporophyte is not photosynthetic. Thus both the embryo and the mature sporophyte are nourished by the photosynthetic gametophyte. Meiosis of the sporocytes (spore mother cells), within the capsule of the sporophyte, forms haploid spores. When the spores are mature, the capsule opens and the spores are dispersed by wind or rain. If a moss spore lands on a suitable spot, it germinates and grows into a filamentous thread of cells called protonema. The protonema forms buds, each of which grows into a leafy gametophyte plant, and the life cycle continues. |