B1101 plant reproduction 2023 2022_251214_103225.pdf

# Reproduction of Myocota Fungal reproduction encompasses diverse asexual and sexual strategies, involving haploid and diploid stages, with Ascomycetes and Basidiomycetes also featuring a dikaryotic phase where parental nuclei remain separate before fusion [25](#page=25). ### 4.1 Asexual reproduction Asexual reproduction in fungi occurs through budding, fragmentation, or spore formation [25](#page=25). #### 4.1.1 Budding This method is characteristic of single-celled yeasts, such as *Saccharomyces* [25](#page=25). #### 4.1.2 Fragmentation Mycelial fragmentation involves the separation of a fungal mycelium into pieces, with each fragment capable of developing into a new, independent mycelium. This is observed in groups like Basidiomycota [25](#page=25). #### 4.1.3 Spore formation Spores are minute, wind-dispersed reproductive units that serve as the primary means of reproduction, dispersal, and survival for fungi. They can act as resistant resting stages (cysts) during unfavorable conditions and become active under favorable conditions. Spores are typically non-flagellated (aplanospores) [25](#page=25). * **Exogenous spores:** These spores, known as conidia, develop externally. *Penicillium* is an example that produces conidia [25](#page=25). > **Example:** Figure 24a depicts exogenous spores (conidia) of *Penicillium*. * **Endogenous spores:** These spores are produced internally within structures called sporangia, which are typically located at the tips of hyphae and separated by complete septa. *Rhizopus* is an example of a fungus that produces endogenous spores [25](#page=25). > **Example:** Figure 24b illustrates endogenous spores of *Rhizopus*. * **Deuteromycetes (Imperfect fungi):** This group reproduces exclusively asexually through the production of conidia, and no sexual reproduction has been observed in them [25](#page=25). ### 4.2 Sexual reproduction #### 4.2.1 Zygomycota *Rhizopus* species, commonly known as black bread mold, are characteristic zygomycetes. Sexual reproduction involves the interaction between a plus (+) strain and a minus (-) strain [26](#page=26). 1. **Gametangial contact:** When hyphae of opposite mating types meet, their tips, called gametangia, fuse (cystogamy) [26](#page=26). 2. **Plasmogamy:** This fusion results in plasmogamy, leading to the formation of a heterokaryotic zygosporangium [26](#page=26). 3. **Zygospore formation:** Zygosporangia possess a thick, protective wall and exhibit resistance to dry and cold conditions [26](#page=26). 4. **Karyogamy and zygospore:** Under favorable conditions, nuclear fusion (karyogamy) occurs within the zygosporangium, producing a diploid zygospore with a thick wall [26](#page=26). 5. **Meiosis and germination:** Meiosis likely takes place at or just before the zygospore germinates [26](#page=26). 6. **Sporangium development:** Upon germination, an erect (aerial) haploid hypha develops, bearing a sporangium at its apex [26](#page=26). 7. **Spore dispersal:** Mitosis within the sporangium generates haploid spores, which are then dispersed [26](#page=26). 8. **New cycle:** These dispersed spores eventually germinate, initiating a new life cycle [26](#page=26). > **Example:** Figure 25 illustrates the life cycle of *Rhizopus nigricans* (Zygomycota). #### 4.2.2 Ascomycota Sexual reproduction in Ascomycetes begins with the close association of hyphae from two different strains [27](#page=27). 1. **Gametangial formation:** Antheridia develop on the mycelium of one strain (typically '-'), and oogonia on the other ('+') [27](#page=27). 2. **Plasmogamy and trichogyne:** Male nuclei from the antheridium migrate into the ascogonium through a trichogyne, an outgrowth of the ascogonium. Here, they pair with the female nuclei, but do not fuse immediately (plasmogamy occurs) [27](#page=27). 3. **Dikaryotic hyphae formation:** New dikaryotic hyphae (dikaryons) develop from this fused structure [27](#page=27). 4. **Ascus development and karyogamy:** Cells at the tips of these dikaryotic hyphae differentiate into asci (singular: ascus), which are sac-like structures where karyogamy (nuclear fusion) takes place. These asci, along with sterile filaments called paraphyses, are embedded within an ascocarp, the fruiting body of the fungus [27](#page=27). 5. **Meiosis and ascospore production:** Karyogamy within the asci is immediately followed by meiosis, resulting in the production of endogenous ascospores [27](#page=27). 6. **Dispersal and germination:** The ascospores are disseminated and subsequently germinate to form new haploid mycelium [27](#page=27). 7. **Asexual reproduction:** The haploid mycelium may also produce asexual conidia [27](#page=27). > **Key Feature:** In the Ascomycota life cycle, plasmogamy and karyogamy are separated in time and space by a distinct dikaryotic phase [27](#page=27). > **Note:** In many Ascomycete species, antheridia and oogonia can be produced on the same mycelium [27](#page=27). > **Example:** Figure 26 illustrates the Ascomycota life cycle. #### 4.2.3 Basidiomycota Sexual reproduction in Basidiomycetes shares similarities with Ascomycetes [28](#page=28). 1. **Plasmogamy:** Somatic cells of sexually compatible haploid hyphae fuse through plasmogamy, leading to the formation of a dikaryotic mycelium [28](#page=28). 2. **Fruiting body (Basidiocarp) development:** This dikaryotic mycelium gives rise to a fruiting body called a basidiocarp [28](#page=28). 3. **Basidia formation:** The basidiocarp is lined with terminal dikaryotic cells known as basidia [28](#page=28). 4. **Karyogamy and meiosis:** Karyogamy occurs within each basidium, producing a diploid nucleus, which then undergoes meiosis [28](#page=28). 5. **Basidiospore production and germination:** Meiosis generates haploid exogenous basidiospores, which subsequently germinate to form new haploid mycelium [28](#page=28). > **Key Feature:** Similar to Ascomycota, the Basidiomycota life cycle also features a plasmogamy and karyogamy separated in time and space by a dikaryotic phase [28](#page=28). > **Example:** Figure 27 depicts the life cycle of a typical Basidiomycete. #### 4.2.4 Deuteromycota Deuteromycetes are classified as imperfect fungi because their sexual reproductive phase has never been observed. They reproduce asexually by producing conidia on specialized hyphae called conidiophores [28](#page=28). --- # Reproduction of pteridophytes The life cycle of pteridophytes, vascular seedless plants, is characterized by alternation of generations (haplodiplontic) with a dominant sporophyte phase and a reduced gametophyte phase [35](#page=35). ### 6.1 Asexual reproduction Pteridophytes can reproduce asexually through the fragmentation of their rhizomes [35](#page=35). ### 6.2 Sexual reproduction Sexual reproduction in pteridophytes involves both homosporous and heterosporous species, with the gametophyte developing independently or endoprothally within spore structures [35](#page=35) [36](#page=36). #### 6.2.1 Reproduction of Filicopsida (Ferns) Ferns, such as *Polypodium vulgare*, are typically homosporous. The diploid sporophyte plant produces haploid spores via meiosis within sporangia. A spore germinates to form a free-living gametophyte, often a heart-shaped prothallus, bearing both antheridia (producing motile sperm) and archegonia (containing an egg). Sperm swim through water to fertilize the egg (oogamy), forming a diploid zygote that develops into a new sporophyte, while the prothallus withers. The sporophyte generation is dominant due to its larger size and longer persistence [35](#page=35) [36](#page=36). > **Tip:** The life cycle of ferns clearly demonstrates the alternation between the diploid sporophyte and the haploid gametophyte, with the sporophyte being the more prominent phase [36](#page=36). #### 6.2.2 Reproduction of Lycopodiopsida (e.g., Selaginella) *Selaginella* is a heterosporous example within Lycopodiopsida. The sporophyte produces two types of sporangia within a strobilus: megasporangia (female) on lower sporophylls and microsporangia (male) on upper sporophylls. Microsporocytes in microsporangia undergo meiosis to form microspores, each developing into a male gametophyte endoprothally within the microsporangium. Similarly, megasporocytes in megasporangia undergo meiosis to form megaspores, each initiating the development of a female gametophyte while still inside the megasporangium. Male gametophytes produce flagellated sperm, and female gametophytes produce an egg. Fertilization occurs via oogamy when sperm reach the egg, forming a zygote that develops into a new sporophyte. This life cycle is haplodiplontic with sporophyte dominance [36](#page=36) [37](#page=37). > **Example:** In *Selaginella*, the development of both male and female gametophytes within their respective spore walls is termed endoprothally [36](#page=36). #### 6.2.3 Reproduction of Gymnosperms (Contextual Information) While the document focuses on pteridophytes in pages 35-42, it briefly introduces gymnosperms in pages 38-41 as a transition to seed plants. Gymnosperms are heterosporous with reduced gametophytes that develop within sporophyte structures. Their seeds are exposed, and pollination, rather than swimming sperm, is the mechanism for delivering male gametes to the egg. This section provides contrast to the spore-based reproduction of pteridophytes [38](#page=38) [41](#page=41). --- # Artificial vegetative reproduction techniques Artificial vegetative reproduction involves human intervention to propagate plants, primarily for the large-scale cultivation of economically valuable species. This method bypasses sexual reproduction, ensuring the creation of genetically identical individuals to the parent plant (clones) [49](#page=49) [51](#page=51). ### 3.1 Cutting Cutting is a technique where any vegetative part of a plant, such as a leaf, stem section, or root piece, is used to generate a new plant. When a cutting is planted and appropriately covered, it develops the missing organs [51](#page=51). * **Leaf cuttings:** A partially buried leaf, stimulated by hormones like auxins, can develop roots and stems. An example is the begonia [51](#page=51). * **Stem cuttings:** A buried portion of a stem can develop roots. Roses are commonly propagated this way [51](#page=51). * **Root cuttings:** A piece of root can form stems and leaves above the soil surface. The olive tree is an example [51](#page=51). > **Tip:** Hormones, particularly auxins, play a crucial role in stimulating root and shoot development in cuttings [51](#page=51). ### 3.2 Layering Layering involves inducing root formation on a stem while it is still attached to the parent plant. A stem is bent over and a portion is covered with soil. Once roots develop on the covered section, the new shoot can be detached from the parent plant to become an independent organism. This method is naturally employed by some species, like the grape vine [52](#page=52). * **Tip layering:** The tip of a shoot is inserted into the soil and covered [52](#page=52). * **Simple layering:** A stem is bent downwards, and the target section is buried in the soil [52](#page=52). > **Example:** Grape vines can naturally reproduce through simple layering as their flexible stems spread and root when in contact with the soil [52](#page=52). ### 3.3 Grafting Grafting is a technique where a stem or bud from one plant is joined permanently to the stem of a closely related plant. The rooted portion of the combined plant is termed the "stock," while the upper portion that develops into the aerial parts is called the "scion". The tissues of both the stock and scion fuse, forming a single plant. The scion contributes the stems, leaves, and flowers, while the stock provides the root system and nourishes the scion [52](#page=52). Grafting is advantageous for combining desirable traits from two different plants. The stock is chosen for its vigor, adaptation to soil conditions, and resistance to diseases and parasites. The scion is selected for its desired marketable qualities, such as fruit or flower production, and importantly, it preserves the performance of selected varieties [52](#page=52). * **Bud grafting:** A specific type of grafting where only a single bud is removed from a stem and grafted onto the stock. This method is faster than other forms of grafting and is widely used in the nursery industry for mass plant propagation [52](#page=52). ### 3.4 Plant tissue culture Plant tissue culture, also known as micropropagation, is a laboratory technique used to grow new plants from small pieces of plant material, such as cells, tissues, or organs. This process occurs *in vitro* in sterilized nutrient media under controlled aseptic conditions [53](#page=53). The procedure involves placing tiny plant fragments onto a gel-like medium enriched with hormones and nutrients, which stimulates their development into plantlets. These young plants are then transferred to pots with soil, acclimatized in specific greenhouses, and eventually moved outdoors to mature. This method enables the generation of numerous identical plants (clones) year-round [53](#page=53). Key characteristics of plant tissue culture include: * **Artificial media:** The presence of nutrients and hormones in the growth medium [53](#page=53). * **Controlled conditions:** Regulated temperature and light [53](#page=53). * **Aseptic conditions:** Strict sterile environments to prevent contamination [53](#page=53). The objectives of plant tissue culture are: * **Large-scale propagation:** Producing numerous plants true to type (clones) in very short durations, used for commercial production of important plants like tomatoes, bananas, potatoes, and roses [53](#page=53). * **Production of healthy plants:** Generating plants free from viruses [53](#page=53). * **Storing germplasm:** Creating gene banks for genetic conservation [53](#page=53). * **Quick generation of clones:** Rapidly producing numerous clones year-round in greenhouses [53](#page=53). > **Tip:** Tissue culture can produce hundreds of thousands of plants from a single rose plant in a year, significantly exceeding the output of dozens of plants from cuttings in the same period [53](#page=53). --- # Reproduction of Bryophytes Bryophytes exhibit adaptations for terrestrial life, including a waxy cuticle and gametes developed within gametangia, and reproduce both asexually and sexually [29](#page=29). ### 5.1 Asexual reproduction Asexual reproduction in bryophytes occurs through fragmentation or the formation of gemmae [29](#page=29). - **Fragmentation:** Involves the breaking off of parts of the gametophyte, which then develop into new bryophyte plants [29](#page=29). - **Gemmae:** These are small, multicellular propagules, often cup-shaped, found on the gametophytes. They are dispersed by raindrops, allowing them to spread and initiate new gametophytes. For example, gemmae are found in *Marchantia*, a member of the class Hepaticopsida [29](#page=29). > **Tip:** Asexual reproduction allows for rapid propagation and is advantageous when sexual reproduction is not possible or less efficient. ### 5.2 Sexual reproduction Bryophytes have a haplodiplontic life cycle where the gametophyte generation is dominant and conspicuous, while the sporophyte is dependent on the gametophyte [29](#page=29). #### 5.2.1 Gametangia and gametes Gametophytes produce gametes within specialized structures called gametangia [29](#page=29). - **Antheridia:** These are the male reproductive structures that produce numerous flagellated, motile sperm cells through mitosis [29](#page=29). - **Archegonia (sing. archegonium):** These are the female reproductive structures that produce a single egg cell through mitosis [29](#page=29). Some bryophytes can bear both antheridia and archegonia on the same gametophyte [29](#page=29). #### 5.2.2 Fertilization Fertilization in bryophytes is oogamous, meaning it involves the fusion of a large, non-motile egg with a smaller, motile sperm. This process requires the presence of water for the sperm to reach the egg [29](#page=29). #### 5.2.3 Zygote and sporophyte development Following fertilization, a diploid zygote is formed. This zygote undergoes mitosis to develop into a multicellular embryo, which then matures into the sporophyte. The sporophyte remains attached to and nutritionally dependent on the gametophyte throughout its existence. The sporophyte is typically not photosynthetic, meaning it relies on the gametophyte for nourishment [29](#page=29) [30](#page=30). #### 5.2.4 Spore production and dispersal Within the sporophyte's capsule, diploid sporocytes (spore mother cells) undergo meiosis to produce haploid spores. Once mature, the capsule opens, and the spores are dispersed by wind or rain [30](#page=30). > **Tip:** The dependence of the sporophyte on the gametophyte is a key characteristic distinguishing bryophytes from vascular plants. ### 5.3 Class Bryopsida — Mosses (e.g., *Mnium*) Mosses exhibit a typical haplodiplontic life cycle where the sporophyte grows on and is nutritionally dependent on the female gametophyte [30](#page=30). - **Fertilization:** Flagellated sperm cells are chemically attracted to the archegonium on a neighboring plant after traveling via water droplets. Fertilization occurs when a sperm fuses with the egg [30](#page=30). - **Sporophyte:** The resulting diploid zygote develops into a sporophyte that remains attached to the gametophyte [30](#page=30). - **Spore formation:** Meiosis of sporocytes in the sporophyte's capsule produces haploid spores [30](#page=30). - **Germination and gametophyte development:** Dispersed spores germinate on suitable substrates, forming a filamentous thread called a protonema. Buds on the protonema grow into leafy gametophyte plants, thus completing the life cycle [30](#page=30). ### 5.4 Class Hepaticopsida — Liverworts (e.g., *Marchantia polymorpha*) Liverworts share a similar haplodiplontic life cycle with mosses, characterized by gametophyte dominance and sporophyte parasitism [31](#page=31). - **Gametangia:** In *Marchantia*, antheridia and archegonia are borne on specialized stalked structures: antheridiophores (male receptacles) and archegoniophores (female receptacles), respectively [31](#page=31). - **Fertilization:** Flagellated sperm swim to the archegonia for oogamous fertilization of the egg [31](#page=31). - **Sporophyte:** The zygote develops into an embryo that is entirely dependent on the gametophyte, with the mature sporophyte anchored within the archegoniophore tissue [31](#page=31). - **Spore and elater formation:** Sporocytes within the sporophyte capsule undergo meiosis to produce haploid spores. Diploid elater cells, which do not undergo meiosis, are also present in the capsule and aid in spore dispersal through their coiling and uncoiling movements in response to humidity changes [31](#page=31). - **Gametophyte development:** Liverwort gametophytes develop directly from spores, without a protonema stage [31](#page=31). > **Example:** In *Marchantia*, the thallus is the photosynthetic gametophyte, and the archegoniophores and antheridiophores are structures specialized for sexual reproduction [32](#page=32). ### 5.5 Class Anthoceropsida — Hornworts (e.g., *Anthoceros* sp.) Hornworts also possess a haplodiplontic life cycle with a dominant gametophytic phase and oogamy [33](#page=33). - **Gametangia:** Archegonia and antheridia are produced in rows just below the upper surface of the gametophytes [33](#page=33). - **Fertilization:** Flagellated sperm swim to the archegonia and fertilize the egg [33](#page=33). - **Sporophyte:** The zygote develops into a sporophyte that grows from the gametophyte in a horn-like fashion [33](#page=33). - **Spore and elater association:** As the sporophyte grows, sporocytes within it undergo meiosis to produce spores. Elaters, similar in function to those in liverworts, are associated with the spores and aid in their dispersal [33](#page=33). - **Spore release:** At maturity, the tip of the horn-like sporophyte splits open, releasing the spores [33](#page=33). --- # Angiosperm reproductive structures and life cycle Angiosperms, or flowering plants, have reproductive structures within flowers and a unique life cycle characterized by double fertilization [43](#page=43). ### 5.1 Typical flower structure A typical angiosperm flower possesses four main whorls of organs: the calyx, corolla, stamen, and carpel [43](#page=43). #### 5.1.1 Sterile floral organs * **Calyx:** Composed of sepals, which are typically green and enclose the flower bud before it opens [43](#page=43). * **Corolla:** Composed of petals, which are usually brightly colored to attract pollinators [43](#page=43). * Both sepals and petals are sterile floral organs, not directly involved in reproduction [43](#page=43). #### 5.1.2 Reproductive organs * **Stamen:** The male reproductive structure, consisting of a filament (stalk) and an anther (terminal sac where pollen is produced) [43](#page=43). * **Carpel:** The female reproductive structure, typically comprising: * **Stigma:** The sticky tip that receives pollen [43](#page=43). * **Style:** A stalk connecting the stigma to the ovary [43](#page=43). * **Ovary:** Located at the base of the carpel, containing ovules that develop into seeds after fertilization [43](#page=43). ### 5.2 The life cycle of an angiosperm The angiosperm life cycle involves the alternation of generations, with distinct gametophyte and sporophyte phases [43](#page=43) [48](#page=48). #### 5.2.1 Gametogenesis: Formation of egg cells and pollen grains Gametogenesis is the process of forming gametes (egg cells and sperm cells), which leads to the development of the female and male gametophytes [44](#page=44). ##### 5.2.1.1 Female gametophyte (embryo sac) formation 1. A diploid megasporocyte cell within the ovule undergoes meiosis to produce four haploid megaspores [44](#page=44). 2. In most angiosperms, three megaspores degenerate, while the nucleus of the surviving megaspore undergoes three rounds of mitosis [44](#page=44). 3. This results in an embryo sac containing eight haploid nuclei within seven cells [44](#page=44). 4. The integuments of the ovule develop, leaving a pore called the micropyle [44](#page=44). 5. The mature embryo sac, also known as the female gametophyte (megagametophyte), consists of: * An egg cell and two synergids located near the micropyle [44](#page=44). * A central cell with two polar nuclei [44](#page=44). * Three antipodal cells opposite the micropyle [44](#page=44). * Synergids and antipodal cells do not play a direct role in fertilization [44](#page=44). ##### 5.2.1.2 Male gametophyte (pollen grain) formation 1. Within the anther's microsporangia (pollen sacs), diploid microsporocyte cells undergo meiosis to produce tetrads of haploid microspores [44](#page=44). 2. Each microspore divides once by mitosis to form two cells: * **Generative cell:** Will divide to produce two sperm cells [44](#page=44). * **Vegetative cell:** Will form the pollen tube [44](#page=44). 3. These microspores develop into pollen grains, which constitute the male gametophyte (microgametophyte) [44](#page=44). #### 5.2.2 Pollination and fertilization Pollination is the transfer of pollen from an anther to a stigma, while fertilization is the fusion of gametes [45](#page=45) [46](#page=46). ##### 5.2.2.1 Pollination * Pollen is transferred from the anther to the receptive stigma, typically by wind, insects, or animals [45](#page=45). * **Self-pollination:** Occurs when pollen is transferred to the stigma of the same flower or another flower on the same plant [45](#page=45). * **Cross-pollination:** Occurs when pollen is transferred from a flower on one plant to the stigma of a flower on another plant of the same species [45](#page=45). ##### 5.2.2.2 Fertilization and double fertilization 1. After landing on the stigma, a pollen grain germinates, forming a pollen tube that grows down through the style towards the ovule [45](#page=45). 2. The pollen tube, containing the vegetative nucleus and two sperm cells, reaches the micropyle of the ovule [45](#page=45). 3. The pollen tube penetrates the ovule and discharges its two sperm cells into the embryo sac [46](#page=46). 4. **Double fertilization:** * One sperm nucleus fuses with the egg cell to form a diploid zygote ($2n$) [46](#page=46). * The second sperm nucleus fuses with the two polar nuclei in the central cell to form a triploid nucleus ($3n$) [46](#page=46). * This process is unique to angiosperms [46](#page=46). #### 5.2.3 Seed and fruit formation Following double fertilization, the ovule develops into a seed, and the ovary matures into a fruit [46](#page=46) [47](#page=47). ##### 5.2.3.1 Seed formation * The diploid zygote develops into a sporophyte embryo, which possesses a rudimentary root and one or two seed leaves called cotyledons [46](#page=46). * Monocots have one cotyledon [46](#page=46). * Dicots have two cotyledons [46](#page=46). * The triploid nucleus develops into endosperm, a nutrient-rich tissue that nourishes the developing embryo [46](#page=46). * The mature seed consists of the embryo, endosperm, and a protective seed coat derived from the integuments [47](#page=47). * Upon dispersal and under favorable conditions, the seed germinates, the coat ruptures, and the embryo emerges as a seedling [47](#page=47). ##### 5.2.3.2 Fruit formation * The ovary wall develops into the pericarp, the fruit layer [47](#page=47). * The fruit encloses and protects the developing seeds, often aiding in their dispersal [47](#page=47). > **Tip:** The enclosure of seeds within an ovary is a defining characteristic of angiosperms that distinguishes them from gymnosperms [43](#page=43). > > **Tip:** The development of the triploid endosperm is a consequence of double fertilization and is crucial for providing nourishment to the embryo [46](#page=46). --- # Life cycle patterns in sexually reproducing organisms A life cycle in sexually reproducing organisms represents the series of developmental changes from one generation to the next, characterized by an alternation of meiosis and fertilization [14](#page=14). ### 6.1 Types of sexual reproduction based on fertilization mode Several modes of fertilization exist in sexually reproducing organisms: * **Somatogamy:** Involves the fusion of somatic cells of two haploid filaments of opposite mating types (+ and -), leading to plasmogamy. Karyogamy is delayed, resulting in a dikaryotic phase (n+n). This is observed in organisms like Basidiomycota [13](#page=13). * **Conjugation (Cystogamy):** A donor cell (- mating type) forms a temporary connection with a recipient cell (+ mating type) via a conjugation tube (e.g., *Spirogyra*) or a protuberance (e.g., *Mucor*). Genetic material is directly transferred from the donor to the recipient for fusion [13](#page=13). * **Trichogamy:** Occurs when a male, non-motile spermatium fuses with a trichogyne, a hair-like extension of the female gametangia. Cytoplasmic fusion is followed by the migration of the spermatium nucleus to fuse with the egg nucleus. This is seen in red algae [13](#page=13). * **Siphonogamy:** A process where non-motile sperms are conveyed to a non-motile egg via a tube for fertilization. This is characteristic of angiosperms [13](#page=13). ### 6.2 Life cycle classifications Life cycles in sexually reproducing organisms are classified based on the timing of meiosis and fertilization, leading to three main types: monobiontic, haplodiplontic, and triplobiontic [14](#page=14). #### 6.2.1 Monobiontic life cycles (monogenetic) Monobiontic life cycles involve only a single independent generation. * **Haplontic:** This cycle consists of a single generation of haploid organisms. Meiosis occurs immediately after fertilization, forming a zygote which is the only diploid cell. The resulting haploid cells undergo mitosis to form a multicellular haploid organism (gametophyte). Mitosis exclusively occurs in the haploid phase. Examples include some fungi and green algae like *Chlamydomonas* and *Spirogyra* [14](#page=14). * **Example: *Chlamydomonas*** Haploid cells divide mitotically to produce motile gametes of the same size, differentiated into "+" and "-" mating types. Fusion of these gametes (isogamous planogamy) forms a diploid zygote. The zygote develops into a thick-walled zygospore that can withstand unfavorable conditions. Upon favorable conditions, the zygospore undergoes meiosis to produce four haploid motile tetraspores (zoospores), which emerge and develop into new haploid organisms [18](#page=18). * **Example: *Spirogyra*** This filamentous haploid green alga undergoes sexual reproduction through conjugation. Adjacent filaments of different mating types form protuberances that fuse to create a conjugation tube. The protoplast of one cell migrates through the tube and fuses with the protoplast of the cell in the adjacent filament, forming a zygote. This zygote develops into a resistant zygospore. After dormancy and favorable conditions, the zygospore undergoes meiosis, germinating into new haploid filaments [18](#page=18). * **Diplontic:** This cycle involves a single generation of diploid organisms. Organisms produce haploid gametes, which fuse during fertilization to form a diploid zygote that develops into a sporophyte. Meiosis occurs only during gamete formation, and gametes do not undergo further mitotic division before fertilization. Gametes are the only haploid cells in the cycle. The diploid multicellular individual is a diplont. This is observed in some brown algae, such as *Fucus* [15](#page=15). * **Example: *Fucus*** *Fucus* is a brown alga with a branched diploid sporophyte. Specialized structures called conceptacles, located at the tips of the fronds, contain gametangia (oogonia and antheridia) and sterile paraphyses. Oogonia produce haploid non-motile eggs by meiosis, while antheridia produce haploid biflagellated sperm by meiosis. Eggs and sperm are released into the water, with eggs releasing a pheromone to attract sperm. Fertilization is external (oogamy), and the resulting zygote develops by mitosis into a mature diploid sporophyte [20](#page=20). #### 6.2.2 Haplodiplontic life cycles (digenetic) Haplodiplontic life cycles, also known as digenetic or diplobiontic, are characterized by alternation of generations, including both a multicellular sporophyte (diploid generation) and a multicellular gametophyte (haploid generation) [15](#page=15) [21](#page=21). * **Isomorphic haplodiplontic:** This type features sporophytic and gametophytic life stages with similar morphologies [22](#page=22). * **Example: *Ulva*** *Ulva* species exhibit isomorphic alternation of generations. The gametophytes are haploid, and the sporophytes are diploid. Both male and female gametes are motile (zoogamy, planogamy) and anisogamous (female gamete is larger). Fertilization produces a quadriflagellate zygote, which develops into a sporophyte. Mature sporophytes produce haploid quadriflagellate zoospores by meiosis. These zoospores develop into gametophytes [22](#page=22). * **Heteromorphic haplodiplontic:** This type involves sporophyte and gametophyte generations with distinct morphologies [22](#page=22). * **Example: *Laminaria*** *Laminaria* displays heteromorphic alternation of generations. The sporophyte is a large multicellular alga, while the male and female gametophytes are microscopic and composed of few cells. Sporophytes produce motile flagellated zoospores (n) by meiosis from sporangia. These zoospores develop into male and female gametophytes. Male gametophytes release motile male gametes, and female gametophytes produce eggs. Fertilization is oogamous, with male gametes fertilizing the eggs [22](#page=22). #### 6.2.3 Triplobiontic life cycles (trigenetic) Triplobiontic life cycles, also referred to as trigenetic, involve three successive generations. This pattern is common in most red algae (Rhodophytes) [16](#page=16) [23](#page=23). * **Example: *Polysiphonia*, *Nemalion*** The trigenetic cycle comprises three generations: 1. **Gametophyte:** Isomorphic haploid male and female gametophytes bear gametangia. Spermatangia produce non-motile sperm cells (spermatia), and carpogonia are female gametangia with a trichogyne that receives spermatia. Fertilization is trichogamy. The resulting zygote develops parasitically on the female gametophyte [23](#page=23) [24](#page=24). 2. **Carposporophyte (Sporophyte I):** The diploid zygote divides mitotically to form the carposporophyte, which produces diploid carpospores in carposporangia [24](#page=24). 3. **Tetrasporophyte (Sporophyte II):** Released carpospores germinate and grow into a diploid tetrasporophyte. Tetrasporangia on the tetrasporophyte undergo meiosis to produce four haploid tetraspores. These tetraspores develop into male and female gametophytes, thus completing the cycle [24](#page=24). In this life cycle, the male gametophyte, female gametophyte, and tetrasporophyte thalli outwardly resemble each other [24](#page=24). ### 6.3 Definitions * **Gametangium (pl. gametangia):** A cell or structure where gametes are produced [24](#page=24). * **Sporangium (pl. sporangia):** A structure in which spores are produced; it can be unicellular or multicellular [24](#page=24). --- # Types of sexual reproduction based on gamete characteristics Sexual reproduction is a biological process characterized by the fusion of gametes, leading to genetic diversity in offspring. This section details the classification of sexual reproduction based on the characteristics of these gametes, focusing on their size, motility, and the resulting modes of fertilization. ### 7.1 Types of sexual reproduction related to gamete size and motility Sexual reproduction can be categorized based on whether the fusing gametes are similar or different in morphology and movement [12](#page=12). #### 7.1.1 Isogamy Isogamy, derived from Greek words meaning "equal" and "marriage," describes the fusion of gametes that are identical in morphology (size and form) but differ in their mating type, typically designated as male/female or "+" and "−" strains [12](#page=12). * **Example:** *Chlamydomonas* exhibits isogamy [12](#page=12). #### 7.1.2 Anisogamy or heterogamy Anisogamy or heterogamy, using Greek terms for "different" and "marriage," refers to the fusion of two gametes that differ in size and/or form. In this type, the female gamete is characteristically larger than the male gamete [12](#page=12). * **Example:** *Ulva* is an example of anisogamy [12](#page=12). #### 7.1.3 Planogamy Planogamy involves the fusion of two motile gametes, also known as planogametes or zoogametes [12](#page=12). * Planogamy can be either isogamous or anisogamous [12](#page=12). * **Example:** *Chlamydomonas* demonstrates isogamous planogamy [12](#page=12). * **Example:** *Ulva* exhibits anisogamous planogamy [12](#page=12). #### 7.1.4 Aplanogamy (or heterogamy) Aplanogamy, sometimes referred to as heterogamy, is the fusion of two non-motile gametes (aplanogametes) [12](#page=12). * **Example:** Red algae undergo aplanogamy [12](#page=12). #### 7.1.5 Oogamy Oogamy is a specific type of fertilization characterized by the fusion of a large, non-motile female gamete (macrogamete) with a small, motile male gamete (microgamete) [12](#page=12). * **Example:** *Fucus* exemplifies oogamy [12](#page=12). > **Tip:** While "heterogamy" can refer to the fusion of different-sized gametes (anisogamy), it is also used here to describe the fusion of non-motile gametes (aplanogamy). Pay close attention to the context provided by the descriptions. ### 7.2 Types of sexual reproduction related to the mode of fertilization Sexual reproduction can also be classified by how the fertilization process is achieved, particularly concerning the origin of the fusing cells and the pathways of gamete transfer [13](#page=13). #### 7.2.1 Somatogamy Somatogamy occurs when somatic (vegetative) cells of two haploid filaments of opposite mating types come into contact and fuse. This process primarily involves plasmogamy (cytoplasmic fusion), with karyogamy (nuclear fusion) being delayed, leading to a dikaryotic phase (n+n) [13](#page=13). * **Example:** This mode is observed in Basidiomycota [13](#page=13). #### 7.2.2 Conjugation (Cystogamy) Conjugation, also known as cystogamy, is a process where a donor cell of one mating type makes temporary direct contact with a recipient cell of the opposite mating type. This connection is typically facilitated by a conjugation tube (e.g., in *Spirogyra*) or a protuberance (e.g., in *Mucor*). Genetic material is transferred directly from the donor to the recipient, leading to fusion [13](#page=13). * **Example:** *Spirogyra* and *Mucor* species utilize conjugation for sexual reproduction [13](#page=13). #### 7.2.3 Trichogamy Trichogamy is a fertilization mode where a male, non-motile gamete (spermatium), often transported by water currents, encounters a hair-like extension of the female gametangium called a trichogyne. After cytoplasmic fusion between the spermatium and trichogyne, the nucleus of the spermatium migrates through the trichogyne to fuse with the egg nucleus [13](#page=13). * **Example:** This process is seen in Red algae [13](#page=13). #### 7.2.4 Siphonogamy Siphonogamy describes a process of gamete fusion where non-motile sperm are transferred and guided to the egg (which is also non-motile) via a specialized tube [13](#page=13). * **Example:** Angiosperms (flowering plants) utilize siphonogamy [13](#page=13). > **Tip:** While both conjugation and somatogamy involve the fusion of somatic cells or hyphae in some fungi, conjugation specifically refers to the direct transfer of nuclear material through a connecting tube, often between distinct cells. Somatogamy is a broader term for the fusion of vegetative cells. ### 7.3 Fertilization and Syngamy in Sexual Reproduction Syngamy is the fundamental process in sexual reproduction, involving the fusion of two gametes to produce a diploid zygote, which subsequently develops into a new individual. Syngamy is typically divided into two sequential stages [12](#page=12): 1. **Plasmogamy:** The fusion of the cytoplasm of two parent cells [12](#page=12). 2. **Karyogamy:** The fusion of two haploid nuclei to form a diploid nucleus [12](#page=12). Often, plasmogamy is immediately followed by karyogamy. However, in some reproductive systems, karyogamy is delayed, allowing the two haploid parental nuclei to coexist within the same cell without fusing for a period. This results in a dikaryotic cell (denoted as n+n) or a dikaryon, which arises after plasmogamy [12](#page=12). ### 7.4 Examples of Gamete Characteristics in Algae * **Chlamydomonas:** Produces "plus" and "minus" motile gametes of the same size, exhibiting isogamous planogamy [18](#page=18). * **Ulva:** Features both gametophytic and sporophytic life stages, with gametes that are biflagellated (motile). The female gamete is larger than the male gamete, demonstrating anisogamous planogamy [22](#page=22). * **Fucus:** The female gametangia (oogonia) produce non-motile eggs, and the male gametangia (antheridia) produce biflagellated (motile) sperm. Fertilization occurs via oogamy [20](#page=20). * **Red algae:** Exhibit aplanogamy, the fusion of non-motile gametes and utilize trichogamy for fertilization [12](#page=12) [13](#page=13). ### 7.5 Gamete Characteristics in Fungi and Bryophytes * **Zygomycota (e.g., Rhizopus):** Sexual reproduction can occur between hyphae of opposite mating types (+ and -) where their tips (gametangia) fuse, leading to plasmogamy and the formation of a heterokaryotic zygosporangium. Karyogamy and meiosis follow, preceding germination [26](#page=26). * **Ascomycota:** Involves the union of hyphae from different strains. Male nuclei from an antheridium pass to the ascogonium via a trichogyne. Plasmogamy occurs, followed by the development of dikaryotic hyphae. Karyogamy takes place within asci, followed by meiosis [27](#page=27). * **Basidiomycota:** Somatic cells of compatible haploid hyphae fuse (plasmogamy) to form a dikaryotic mycelium. Karyogamy occurs in basidia, producing a diploid nucleus that undergoes meiosis [28](#page=28). * **Bryophytes (Mosses, Liverworts, Hornworts):** Male gametophytes produce motile, flagellated sperm by mitosis in antheridia. Female gametophytes produce eggs by mitosis in archegonia. Fertilization is oogamous and requires the presence of water [29](#page=29). --- Sexual reproduction in plants can be classified based on the characteristics of the gametes involved. The primary distinctions lie in whether the gametes are morphologically similar or dissimilar, and the mechanism of sperm delivery to the egg. ### 7.1 Isogamy, Anisogamy, and Oogamy Sexual reproduction is fundamentally the fusion of gametes. The morphological appearance of these gametes dictates the type of sexual reproduction. Isogamy, where the fusing gametes are morphologically identical, is a less common form of sexual reproduction observed in some algae and fungi. In this type, both gametes are motile and indistinguishable from each other in size and shape [31](#page=31). #### 7.1.2 Anisogamy Anisogamy, also known as heterogamy, involves the fusion of gametes that are morphologically dissimilar but not greatly different in size. One gamete is typically larger and less motile than the other. This form is found in some algae and protozoa. #### 7.1.3 Oogamy Oogamy is the most widespread type of sexual reproduction in plants and is characterized by the fusion of a large, non-motile female gamete (egg) with a small, motile male gamete (sperm). The male gamete is typically flagellated and swims to the female gamete for fertilization. This mode of fertilization is observed in bryophytes (mosses, liverworts, hornworts), pteridophytes (ferns, *Selaginella*), gymnosperms, and angiosperms [31](#page=31) [33](#page=33) [35](#page=35) [36](#page=36) [37](#page=37) [41](#page=41). > **Tip:** Oogamy is the basis for sexual reproduction in most familiar plants, leading to the formation of a zygote which develops into a new sporophyte generation. ### 7.2 Types of Sexual Reproduction based on Gamete Production and Delivery Beyond the morphology of gametes, the mode of their production and delivery to the site of fertilization also defines different reproductive strategies in plants. #### 7.2.1 Homospory Homospory is the production of a single type of spore by the sporophyte. This spore, upon germination, develops into a bisexual gametophyte, which produces both male and female gametangia (antheridia and archegonia). This is common in many ferns and some other seedless vascular plants. For example, *Polypodium vulgare* is homosporous, producing a single type of spore that grows into a gametophyte with both antheridia and archegonia [35](#page=35). > **Example:** In homosporous ferns, the heart-shaped prothallus (gametophyte) typically bears both antheridia and archegonia on its underside [35](#page=35). #### 7.2.2 Heterospory Heterospory is the production of two different types of spores by the sporophyte: megaspores and microspores [36](#page=36). * **Megaspores:** Larger spores that develop into female gametophytes (megagametophytes). * **Microspores:** Smaller spores that develop into male gametophytes (microgametophytes). This condition is found in *Selaginella*, all gymnosperms, and all angiosperms. The development of gametophytes within their respective spore walls is termed endosporic development [36](#page=36) [38](#page=38) [43](#page=43). > **Tip:** Heterospory is considered an evolutionary advancement, leading to greater efficiency in sexual reproduction and paving the way for seed formation. ##### 7.2.2.1 Microspore Development in Heterosporous Plants Microsporocytes (microspore mother cells) within microsporangia undergo meiosis to produce haploid microspores. In heterosporous plants, each microspore develops into a male gametophyte [36](#page=36) [39](#page=39) [44](#page=44). * **In *Selaginella*:** The microspore develops into a male gametophyte within the microsporangium. This male gametophyte produces flagellated sperm cells within antheridia [36](#page=36). * **In Gymnosperms (e.g., Pines):** Each microspore develops into a pollen grain, which consists of several cells including generative cells that will form sperm and a tube cell that forms the pollen tube. The pollen grain is the immature male gametophyte. In pines, the sperms lack flagella and are delivered via the pollen tube [39](#page=39) [41](#page=41). * **In Angiosperms:** Each microspore divides by mitosis to form a generative cell and a vegetative cell, becoming a pollen grain (male gametophyte). The generative cell will later divide to form two sperm cells, and the vegetative cell forms the pollen tube. The mature male gametophyte consists of the pollen grain, pollen tube, and two sperm cells [44](#page=44) [45](#page=45). ##### 7.2.2.2 Megaspore Development in Heterosporous Plants Megasporocytes (megaspore mother cells) within megasporangia undergo meiosis to form haploid megaspores [36](#page=36) [40](#page=40) [44](#page=44). * **In *Selaginella*:** Each megaspore begins the development of a female gametophyte while still inside the megasporangium. The female gametophyte produces an egg within an archegonium [36](#page=36). * **In Gymnosperms (e.g., Pines):** A single megasporocyte within the ovule's megasporangium (nucellus) undergoes meiosis, producing four megaspores, three of which degenerate. The remaining megaspore develops into a female gametophyte by mitosis, utilizing the nucellus as a food source. This female gametophyte develops archegonia, each containing a single large egg [40](#page=40). * **In Angiosperms:** A diploid megasporocyte within the ovule undergoes meiosis, producing four haploid megaspores. Three megaspores degenerate, and the nucleus of the fourth undergoes several mitotic divisions to produce eight haploid nuclei within seven cells, forming the embryo sac (female gametophyte). The embryo sac contains an egg cell, synergids, a central cell with polar nuclei, and antipodal cells [44](#page=44). #### 7.2.3 Siphonogamy Siphonogamy is a mode of fertilization where the pollen tube delivers the male gametes to the egg without the need for external water. This is characteristic of gymnosperms and angiosperms. The pollen grain germinates on the stigma (in angiosperms) or near the ovule (in gymnosperms), and a pollen tube grows towards the ovule, carrying the sperm cells [41](#page=41) [45](#page=45). > **Example:** In pines, the pollen tube grows through the nucellus to reach the archegonium, delivering the non-motile sperm to the egg [41](#page=41). #### 7.2.4 Double Fertilization Double fertilization is a unique process in angiosperms where two male gametes from a single pollen grain participate in fertilization. One sperm nucleus fuses with the egg to form a diploid zygote (which develops into the embryo), and the other sperm nucleus fuses with the two polar nuclei in the central cell to form a triploid nucleus (3n). This triploid nucleus develops into the endosperm, a nutritive tissue for the developing embryo [46](#page=46). > **Tip:** Double fertilization ensures that the embryo develops only after successful fertilization of the egg, and the nutritive tissue (endosperm) is formed simultaneously. --- ## Common mistakes to avoid - Review all topics thoroughly before exams - Pay attention to formulas and key definitions - Practice with examples provided in each section - Don't memorize without understanding the underlying concepts

| Term | Definition | |------|------------| | Asexual Reproduction | A method of reproduction that does not involve the fusion of gametes, occurring in fungi through processes like budding, fragmentation, or spore formation. | | Budding | A form of asexual reproduction where a new organism develops from an outgrowth or bud due to cell division at one particular site, commonly observed in single-celled fungi like yeast. | | Fragmentation | A type of asexual reproduction in fungi where a piece of the mycelium breaks off and develops into a new, independent mycelium. | | Spore Formation | The production of spores, which are small, easily dispersed reproductive units, as a primary means of reproduction, dispersal, and survival for fungi. | | Sporangia | Specialized reproductive structures, typically found at the tips of hyphae and separated by septa, that are involved in the production of endogenous spores. | | Conidia | Exogenous spores produced by fungi, which are released from specialized hyphae called conidiophores and serve in reproduction and dispersal. | | Deuteromycetes | A group of fungi, also known as imperfect fungi, characterized by their asexual reproduction through conidia, with no observed sexual reproductive stage. | | Sexual Reproduction | A reproductive process in fungi that involves the fusion of genetic material from two parent individuals, typically involving a haploid and a diploid stage, and often a dikaryotic phase. | | Zygomycota | A phylum of fungi exemplified by *Rhizopus* (black bread mold), which undergoes sexual reproduction involving the fusion of gametangia to form a zygosporangium. | | Gametangia | Specialized structures in fungi that contain gametes or nuclei destined to fuse during sexual reproduction; in Zygomycota, these are the tips of meeting hyphae. | | Cystogamy | The initial stage of sexual reproduction in some fungi where the tips of hyphae (gametangia) come into close contact before fusion. | | Plasmogamy | The fusion of the cytoplasm of two parent cells during sexual reproduction, which precedes nuclear fusion and can lead to a dikaryotic stage. | | Pteridophytes | A group of vascular plants that reproduce via spores and lack seeds and flowers. Their life cycle exhibits alternation of generations, with the sporophyte being the dominant phase. | | Alternation of Generations | A life cycle pattern, also known as haplodiplontic, characterized by a regular alternation between a haploid gametophyte generation and a diploid sporophyte generation. | | Sporophyte | The diploid generation in the life cycle of plants that reproduce via alternation of generations. It is the generation that produces spores through meiosis. | | Gametophyte | The haploid generation in the life cycle of plants that reproduce via alternation of generations. It is the generation that produces gametes through mitosis. | | Homosporous | Producing only one type of spore, which typically develops into a bisexual gametophyte. This is characteristic of many ferns. | | Sporangium | A structure found in plants where spores are produced through meiosis. In pteridophytes, these are typically found on the sporophyte. | | Prothallus | The heart-shaped, free-living gametophyte of a fern, typically a small, thalloid structure that bears the antheridia and archegonia. | | Archegonium | The female reproductive structure in plants, such as pteridophytes and gymnosperms, that produces and contains a single egg cell. | | Antheridium | The male reproductive structure in plants, such as pteridophytes and some gymnosperms, that produces numerous sperm cells. | | Oogamy | A type of sexual reproduction in which a large, non-motile egg is fertilized by a small, motile sperm. | | Zygote | The diploid cell formed by the fusion of two haploid gametes (egg and sperm) during fertilization. | | Heterosporous | Producing two different types of spores: megaspores (which develop into female gametophytes) and microspores (which develop into male gametophytes). | | Vegetative Reproduction | A form of asexual reproduction in plants that does not involve genetic recombination, resulting in offspring that are genetically identical to the parent plant (a clone). This process utilizes vegetative organs such as roots, stems, and leaves. | | Artificial Vegetative Propagation | A method of plant reproduction achieved through human intervention, often employed by horticulturists to propagate economically important plants on a large scale. | | Cutting | A vegetative part of a plant, such as a leaf, stem section, or root piece, that is detached and used to produce a new, independent plant by developing the missing parts. | | Layering | A propagation technique where a stem is bent and partially covered with soil to induce root formation. Once roots develop, the new shoot can be separated from the parent plant to form an independent individual. | | Grafting | A technique involving the joining of a stem or bud from one plant onto the stem of a closely related plant. The rooted part is called the stock, and the upper portion that develops into the aerial part is called the scion. | | Stock | In grafting, the part of the combination that provides the root system for the new plant. It is selected for vigor, adaptation to soil conditions, and disease resistance. | | Scion | In grafting, the added piece (upper portion) that will develop the aerial parts of the new plant, including stems, leaves, and flowers. It is chosen for its desirable market qualities. | | Bud Grafting | A specific type of grafting where a single bud is removed from a stem and grafted onto the stock, allowing for rapid mass propagation of plants. | | Plant Tissue Culture | A laboratory technique for growing new plants from plant material (cells, tissues, or organs) cultured in vitro on sterilized nutrient media under controlled aseptic conditions to stimulate development into plantlets. | | Micropropagation | A synonym for Plant Tissue Culture, referring to the process of propagating plants on a small scale, often in laboratories, to produce numerous identical plants (clones). | | Clone | An organism that is genetically identical to the parent organism from which it was derived, typically through asexual reproduction. | | Bryophytes | Non-vascular plants that include mosses, liverworts, and hornworts, characterized by adaptations like a waxy cuticle for water retention and gametes developing within gametangia. | | Gemmae | Tiny, multicellular structures produced on the gametophytes of some bryophytes, such as liverworts, that serve as propagules for asexual reproduction, detaching and forming new gametophytes. | | Haplodiplontic Life Cycle | A life cycle that alternates between a haploid gametophyte generation and a diploid sporophyte generation, with the gametophyte being the dominant and conspicuous phase in bryophytes. | | Antheridia | The male gametangia in bryophytes that produce flagellated sperm cells through mitosis. | | Archegonia (sing. Archegonium) | The female gametangia in bryophytes that produce egg cells through mitosis. | | Angiosperm | A plant belonging to the group Spermatophytes, characterized by seeds that develop within ovaries, which subsequently mature into fruits. | | Spermatophyte | A plant that produces seeds, encompassing both angiosperms and gymnosperms. | | Flower | The reproductive structure of angiosperms, typically containing sepals, petals, stamens, and carpels. | | Calyx | The outermost whorl of a flower, composed of sepals, which usually enclose the flower bud before it opens. | | Sepal | Individual leaf-like structures that collectively form the calyx, typically green and protective of the developing flower. | | Corolla | The whorl of petals within a flower, usually brightly colored to attract pollinators. | | Petal | Individual, often brightly colored, structures that collectively form the corolla, serving to attract pollinators. | | Stamen | The male reproductive organ of a flower, consisting of a filament and an anther where pollen is produced. | | Filament | The stalk that supports the anther in a stamen. | | Anther | The part of the stamen that contains the microsporangia and produces pollen. | | Carpel | The female reproductive organ of a flower, typically consisting of a stigma, style, and ovary. | | Stigma | The receptive tip of a carpel, where pollen grains adhere. | | Somatogamy | A type of sexual reproduction where somatic cells of two haploid filaments of opposite mating types fuse, involving only plasmogamy. Karyogamy is delayed, resulting in a dikaryotic phase (n+n). | | Conjugation | A process where a donor cell of one mating type makes temporary contact with a recipient cell of the opposite mating type, transferring genetic material directly through a conjugation tube or protuberance. | | Trichogamy | A mode of fertilization where a non-motile male spermatium collides with a trichogyne, a hair-like extension of the female gametangium. Their cytoplasms fuse, and the spermatium nucleus migrates to fuse with the egg nucleus. | | Siphonogamy | A process of gamete fusion where non-motile sperm are transferred and conducted to a non-motile egg via a tube, commonly observed in angiosperms. | | Life Cycle | The series of developmental changes an organism undergoes from the beginning of a specific stage to the inception of that same stage in the next generation. | | Meiosis | A type of cell division that reduces the number of chromosomes by half, essential for sexual reproduction to produce gametes or spores. | | Fertilization | The fusion of male and female gametes to form a zygote, restoring the diploid number of chromosomes. | | Monobiontic Cycle | A life cycle characterized by a single independent generation, which can be either entirely haploid (haplontic) or entirely diploid (diplontic). | | Haplontic Cycle | A monobiontic life cycle where the organism's cells are haploid, with meiosis occurring immediately after zygote formation. Mitosis occurs only in the haploid phase. | | Diplontic Cycle | A monobiontic life cycle where the organism's cells are diploid. Meiosis occurs only during gamete formation, and gametes are the only haploid cells. | | Syngamy | The process of fusion of two gametes, typically from different sexes (male and female), to produce a diploid zygote that will develop into a new individual. | | Karyogamy | The stage of syngamy where the two haploid parental nuclei fuse to form a single diploid nucleus, completing fertilization. | | Dikaryotic Cell | A cell that contains two distinct haploid nuclei, which have fused cytoplasm but have not yet fused nuclei. This phase (n+n) can persist for a period before karyogamy. | | Isogamy | A type of sexual reproduction characterized by the fusion of gametes that are similar in morphology (size and form) but differ in mating types, often designated as "+" and "−" strains. | | Anisogamy | A type of sexual reproduction involving the fusion of two gametes that differ in size and/or form, where the female gamete is typically larger than the male gamete. Also known as heterogamy. | | Planogamy | The fusion of two motile gametes, referred to as planogametes or zoogametes. This process can be either isogamous or anisogamous. | | Aplanogamy | The fusion of two non-motile gametes, known as aplanogametes. This type of fertilization is also referred to as heterogamy in some contexts. |