BIOL220 Development: Reproduction
Embryo Sac (definition, other)
*Definition:* The female gametophyte in flowering plants. *Other:* This is the female gameto- phyte—usually known as the embryo sac. It has haploid nuclei.
Carpel (Also called Pistol) (definition, other)
*Definition:* The female reproductive organ in a flower. Consists of the stigma, to which pollen grains adhere; the style, through which the pollen tube grows; and the ovary, which houses the ovule. *Other:* reproductive structure in flowers which produces female gametophytes.
Apomixis (definition, other)
*Definition:* The formation of mature seeds without fertilization occurring; a type of asexual reproduction. *Other:* - Mature seeds can form without fertilization occurring. This phenomenon, known as apomixis, results in seeds that are genetically identical to the parent. - Ex plant: Dandelion
Self-Fertilization (Selfing) (definition, other)
*Definition:* The fusion of two gametes produced by the same individual to form offspring. Also called selfing. *Other:*
Stamen (definition, other)
*Definition:* The male reproductive structure of a flower. Consists of an anther, in which pollen grains are produced, and a filament, which supports the anther. *Other:* Stamens are reproductive structures that produce male gametophytes—also known as pollen grains. The male gametophytes, in turn, produce sperm.
Anther (definition, other)
*Definition:* The pollen-producing structure at the end of a stamen in flowering plants (angiosperms). *Other:* The anther is the business end of the stamen—where meiosis and pollen formation take place.
Germination (definition, other)
*Definition:* The process by which a seed becomes a young plant. *Other:*
Pollination (definition, other)
*Definition:* The process by which pollen reaches the carpel of a flower: (1) in flowering plants, it is trans- ferred from anther to stigma; (2) in gymnosperms, it reaches the ovule directly. *Other:*
Style (definition, other)
*Definition:* The slender stalk of a flower carpel connecting the stigma and the ovary. *Other:* The style is a slender stalk.
Stigma (definition, other)
*Definition:* The sticky tip at the end of a flower carpel; pollen grains adhere to it. *Other:* The stigma is a sticky tip that receives pollen.
Whorl (definition)
A whorl or verticil is an arrangement of leaves, sepals, petals, stamens, or carpels that radiate from a single point and surround or wrap around the stem or stalk.
Fruit (definition)
In flowering plants (angiosperms), a mature, ripened plant ovary (or group of ovaries), along with the seeds it contains and any adjacent fused parts; often functions in seed dispersal.
Pollen Tube (definition)
In flowering plants, a structure that grows out of a pollen grain after it reaches the stigma. The tube extends down the style, and two sperm cells travel through it to the ovule.
Pollen Grain (definition)
In seed plants, a male gametophyte enclosed within a protective coat of sporopollenin.
What are the three types of fruits ?
• *Simple fruits:* like the cherry develop from a single flower that contains a single carpel or several carpels that are fused together. This is the most common type of fruit. • *Aggregate fruits:* like the blackberry also develop from a single flower, but one that contains many separate carpels. • *Multiple fruits:* like the pineapple develop from many flowers and thus many carpels.
What are the three mechanisms to prevent Self-Fertilization (Selfing)?
• *Temporal avoidance:* In some species that have perfect flowers, male and female gametophytes mature at different times. Thus, selfing does not occur. • *Spatial avoidance:* Selfing isn't possible in dioecious species and may be rare in monoecious species, unless pollinators transfer pollen between "different-sexed" flowers on the same individual. And in some species with perfect flowers, the anthers and stigma are so far apart that self-pollination is extremely unlikely—if pollen falls inside the flower, it has almost no chance of landing on the stigma. • *Molecular matching:* In many species that produce both pollen and ovules on the same plant, molecular interactions occur that prevent pollen grains from delivering sperm to the female gametophytes produced on the same plant. Such species are said to be self-incompatible. Many plants, just like animals, have the ability to recognize self and non-self cells and tissues.
Endosperm (definition, other)
*Definition:* A triploid (3n) tissue in the seed of a flowering plant (angiosperm) that serves as food for the plant embryo. Functionally analogous to the yolk in some animal eggs. *Other:*
Sporopollenin (definition, other)
*Definition:* A watertight material that encases spores and pollen of modern land plants. *Other:* - The wall of a pollen grain develops a tough outer coat that includes the watertight compound called sporopollenin. - This coat protects the male gametophyte when the pollen is released from the parent plant into the environment. Depending on the species, pollen grains may be dispersed by an animal, the wind, or water currents.
Corolla (definition, other)
*Definition:* All of the petals of a flower. *Other:* The entire group of petals in a flower is collectively called the corolla.
Calyx (definition, other)
*Definition:* All of the sepals of a flower. *Other:* The entire group of sepals in the flower is collectively called the calyx.
Sexual Reproduction (definition, other)
*Definition:* Any form of reproduction in which genes from two parents are combined via fusion of gametes, producing offspring that are genetically distinct from both parents. *Other:*
Asexual Reproduction (definition, other)
*Definition:* Any form of reproduction where offspring inherit DNA from only one parent. Includes binary fission, budding, and parthenogenesis. *Other:* - Asexual reproduction does not involve fertilization and results in the production of clones—genetically identical copies of the parent plant. - Some plants extend their life indefinitely by asexual reproduction.
Petal (definition, structure, function)
*Definition:* Any of the leaflike organs arranged around the reproductive organs of a flower. Often the color and scent of petals attract pollinators. *Structure:* Petals are arranged around the receptacle in a whorl. Often brightly colored and scented. *Function:* - Petals function to advertise the flower to bees, flies, hummingbirds, and other pollinators. - In some cases, the color of the petals correlates with the visual abilities of particular animals. Bees respond to blue, purple, and yellow wavelengths.
Filament (definition, other)
*Definition:* Any thin, threadlike structure, particularly (1) the threadlike extensions of a fish's gills or (2) part of a stamen: the slender stalk that bears the anthers in a flower. *Other:* The filament holds the stamen in a place where wind, insects, hummingbirds, bats, or other agents can make contact with the pollen grains produced in the anther.
Monoecious (definition, other)
*Definition:* Describing an angiosperm species that has both male and female reproductive structures on each plant. *Other:* - In some cases, separate stamen- or carpel-producing flowers occur on the same individual. - Ex: Corn plants. In corn, the tassel is a collection of stamen-producing "male" flowers, and the ear contains a group of carpel-producing "female" flowers.
Dioecious (definition, other)
*Definition:* Describing an angiosperm species that has male and female reproductive structures on separate plants. *Other:* - Some species with imperfect flowers are dioecious meaning that each individual plant produces either stamen-bearing flowers only or carpel-bearing flowers only. - Ex Plant: Cannabis sativa is a dioecious species.
Synergids (definition, other)
*Definition:* One of two cells flanking the egg in the female gametophyte; releases chemical attractants that direct pollen-tube growth. *Other:* Two haploid cells called synergids lie close to the egg. They are important for fertilization.
Self-Incompatible (definition, other)
*Definition:* Plants that are unable to form viable seed when carpels are pollinated with pollen from the same plant. *Other:*
Cross-Pollination (definition, other)
*Definition:* Pollination of a flower by pollen from another individual, rather than by self-fertiliza- tion. Also called crossing. *Other:*
Outcross (definition, other)
*Definition:* Reproduction by fusion of gametes produced by different individuals. *Other:*
Plantlets (loose definition)
*Definition:* Small plants produced from meristematic tissue located along the margins of its leaves. When the plantlets mature, they drop off the parent plant and grow into independent individuals.
Pollination Syndrome (definition, other)
*Definition:* Suites of flower characters that are associated with certain types of pollinators and that have evolved through natural selection imposed by the interaction between flowers and pollinators. *Other:*
Zygote (definition, other)
*Definition:* The cell formed by the union of two gametes; a fertilized egg. *Other:* - Fertilization occurs when two gametes fuse to form a diploid zygote. - The zygote undergoes mitosis and grows into a multicellular, diploid embryo (sporophyte).
Ovary (definition, other)
*Definition:* The egg-producing organ of a female animal, or the fruit- and seed-producing structure in the female part of a flower. *Other:* The ovary is an enlarged structure at the base of the carpel
What are the two structures of stamens?
1. A slender stalk termed the filament. 2. The pollen-producing organs called anthers.
Fertilization Steps
1. After landing on the stigma of a mature flower from the same species, a pollen grain absorbs water and germinates on the stigma. Germination is a resumption of growth and development. This step is blocked in many self-incompatible species if the pollen came from the same plant. Pollen grain behind growing down the style. 2. When the male gametophyte germinates, a long tubular cell called a pollen tube grows through the stigma and down the length of the style. The direction of growth is affected by chemical attractants, called LUREs, which are small proteins released by the synergids. In most species, the tube-cell nucleus and the generative cell travel down the length of the tube, and the generative cell divides to form two sperm. In other species, the generative cell forms sperm before the pollen is shed. 3. Pollen tube completes growth toward the egg by passing through micripyle and I'd charging the two sperm into a synergid. When the pollen tube reaches the micropyle of the ovule, it grows through it and enters a synergid within the female gametophyte. The synergid degenerates and two sperm are released—each with a different fate. 4. In most plant groups, fertilization is straightforwar— sperm and egg simply combine, and a diploid zygote is formed. In angiosperms, however, an unusual event called double fertilization takes place. One sperm unites with the egg to form the zygote. The other sperm moves through the female gametophyte and fuses with the polar nuclei in the central cell to form endosperm (nutrient tissue). In most cases, two polar nuclei are present and a large triploid (3n) cell forms.
What are the five key processes that are common to all land plant life cycles?
1. Meiosis occurs in sporophytes and results in the production of haploid spores. Meiosis and spore production occur inside structures called sporangia. 2. Spores undergo mitosis and develop into multicellular, haploid gametophytes. 3. Gametophytes produce sperm (male gametes) and eggs (female gametes) by mitosis. 4. Fertilization occurs when two gametes fuse to form a diploid zygote. 5. The zygote undergoes mitosis and grows into a multicellular, diploid embryo (sporophyte).
What are some mechanisms of asexual reproduction?
1. Rhizomes 2. Corms 3. Plantlets 4. Apomixis
Four important points about formation of female gametophytes
1. The megasporocyte divides by meiosis. 2. Four haploid megaspores result from meiosis, but three degenerate. 3. The surviving megaspore divides by mitosis to produce a structure with haploid nuclei. This is the female gametophyte—usually known as the embryo sac. 4. The haploid nuclei segregate to different positions in the embryo sac, and cell walls form around some of them. One of these cells becomes the haploid egg.
What three regions does the carpel consist of?
1. The stigma is a sticky tip that receives pollen. 2. The style is a slender stalk. 3. The ovary is an enlarged structure at the base of the carpel
Simple Fruit (definition, other)
A fruit (e.g., apricot) that develops from a single flower that has a single carpel or several fused carpels.
Multiple Fruits (definition, other)
A fruit (e.g., pineapple) that develops from many separate flowers and thus many carpels.
Aggregate Fruit (definition, other)
A fruit (e.g., raspberry) that develops from a single flower that has many separate carpels.
Accessory Fruit (definition, other)
A fruit-like structure (e.g., strawberry) that develops not from an ovary, but from some tissue exterior to the carpel.
Clone (definition, other)
*Definition:* (1) An individual that is genetically identical to another individual. (2) A lineage of genetically identical individuals or cells. (3) As a verb, to make one or more genetic replicas of a cell or individual. *Other:* Asexual reproduction does not involve fertilization and results in the production of clones—genetically identical copies of the parent plant.
Corm (definition, other)
*Definition:* A rounded, thick underground stem that can produce new plants via asexual reproduction. *Other:* - Corms are modified stems - Corms grow under the surface of the soil - Plants can propagate themselves via Corms - Ex plant: Gladiolus Plant
What are the four basic organs of flowers that are essentially modified leaves?
(1) Sepals (2) Petals (3) Stamens (4) One or more carpels Note: These organs are attached to a compressed portion of stem called the receptacle.
Spore (definition, other)
*Definition:* (1) In bacteria, a dormant form that generally is resistant to extreme conditions. (2) In eukaryotes, a single haploid cell produced by meiosis; it is distinct from a gamete, however, in being able to grow into a multicellular, haploid organism through mitotic divi- sions directly (no fertilization required). *Other:* - Meiosis occurs in sporophytes and results in the production of haploid spores. - Meiosis and spore production occur inside structures called sporangia. - Spores undergo mitosis and develop into multicellular, haploid gametophytes.
Mutualism (definition, other)
*Definition:* (adjective: mutualistic) A species relationship between two organisms (mutualists) that benefits both. *Other:*
Megasporangium (definition)
*Definition:* (plural: megasporangia) In hetero- sporous species of plants, a spore-producing structure that produces megaspores; these develop into female gametophytes. *Other:* - Each ovule contains a structure called the megasporangium, inside which there is a diploid cell called the megasporocyte. - The megasporangium is comparable to spore-producing structures found in other plants, such as those on the back of fern leaves. - During female gametophyte formation four haploid megaspores result from meiosis, but three degenerate.
Microsporangia (definition, other)
*Definition:* (plural: microsporangia) In heterosporous species of plants, a spore-producing structure that produces microspores; these develop into male gametophytes. *Other:* A stamen consists of two major parts: an anther and a filament. Inside the anther, structures known as microsporangia contain diploid cells called microsporocytes.
Sporangium (definition, other)
*Definition:* (plural: sporangia) A spore-producing structure found in seed plants, some protists, and some fungi (e.g., chytrids). *Other:* Meiosis occurs in sporophytes and results in the production of haploid spores. Meiosis and spore production occur inside structures called sporangia.
Microsporocyte (definition, other)
*Definition:* A diploid cell that undergoes meiosis to produce microspores as part of male gametophyte formation. *Other:* - A stamen consists of two major parts: an anther and a filament. Inside the anther, structures known as microsporangia contain diploid cells called microsporocytes. - They are diploid. - During male gametophyte formation microsporocytes undergo meiosis, which results in four haploid microspores.
Perfect Flower (definition, other)
*Definition:* A flower that contains both male parts (stamens) and female parts (carpels). *Other:* - Flowers that contain both stamens and carpels are referred to as perfect.
Imperfect Flower (definition, Sex)
*Definition:* A flower that contains male parts (stamens) or female parts (carpels) but not both. *Sex:* - Male (Staminate): Contain only stamens. Staminate flowers produce stamens, which produce pollen grains, which produce male gametes (sperm). - Female (Carpellate): contain only carpels. Carpellate flowers produce carpels, which contain ovaries. Female gametophytes develop inside ovaries and produce female gametes (eggs).
Double Fertilization (definition, other)
*Definition:* A form of reproduction seen in flowering plants, in which one sperm cell fuses with an egg to form a zygote and the other sperm cell fuses with two polar nuclei to form the triploid endosperm. *Other:*
Gamete (definition, other)
*Definition:* A haploid reproductive cell that can fuse with another haploid reproductive cell of the opposite sex to form a diploid zygote. Exceptions to the haploid and diploid rule are seen in polyploid species. Most multi- cellular eukaryotes have two distinct forms of gametes: egg cells (ova) and sperm cells. *Other:*
Alternation of Generations (definition, other)
*Definition:* A life cycle involving alternation of a multicellular haploid stage (gametophyte) with a multicellular diploid stage (sporophyte). Occurs in most plants and some protists. *Other:* - Land plants are characterized by a life cycle with two distinct multicellular forms—one diploid and one haploid. - An individual in the diploid phase of the life cycle is called a sporophyte, while an individual in the haploid phase of the life cycle is called a gametophyte.
Egg (definition, other)
*Definition:* A mature female gamete and any associated exter- nal layers (such as a shell). In animals, also called ovum. *Other:* Gametophytes produce sperm (male gametes) and eggs (female gametes) by mitosis.
Sperm (definition, other)
*Definition:* A mature male gamete. *Other:* Gametophytes produce sperm (male gametes) and eggs (female gametes) by mitosis.
Rhizome (definition, other)
*Definition:* A modified stem that runs horizontally underground and produces new plants at the nodes (a form of asexual reproduction). *Other:* - Rhisome is a horizontal stem, which shoots and roots can emerge from - Rhizome grow underground - If the emerging individuals become separated from the parent plant, they represent asexually produced offspring.
Nectary (definition, structure, function, other)
*Definition:* A nectar-producing structure in a flower. *Structure:* The base of the petals contains a gland called a nectary *Function:* - The nectary produces the sugar-rich fluid nectar, which many of the animals that visit flowers harvest along with pollen. - In the process of collecting pollen or nectar, the visiting animal usually deposits on the female parts pollen from a different plant— accomplishing pollination. *Other:* Blue, Purple, and yellow petals that attract bees highlight the center of the flower, where the nectary is.
Coevolution (definition, other)
*Definition:* A pattern of evolution in which two interacting species reciprocally influence each other's adaptations over time. *Other:*
Seed (definition, other)
*Definition:* A plant reproductive structure consisting of an embryo, associated nutritive tissue (endosperm), and an outer protective layer (seed coat). In angiosperms, develops from the fertilized ovule of a flower. *Other:* Seeds consist of an embryo and nutrient stores surrounded by a protective coat.
Seed Coat (definition, other)
*Definition:* A protective layer around a seed that encases both the embryo and the endosperm. *Other:* As a seed matures, the embryo and endosperm develop inside the ovule and become surrounded by a covering called a seed coat.
Fertilization (definition, other)
*Definition:* Fusion of the nuclei of two gametes (often haploid) to form a zygote with a nucleus (often diploid). Exceptions to the haploid and diploid rule are seen in polyploid species. *Other:* - Is the fusion of haploid cells termed gametes. - In land plants, meiosis and fertilization occur in alternate phases of a life cycle.
Fertilization (definition, other)
*Definition:* Fusion of the nuclei of two gametes (often haploid) to form a zygote with a nucleus (often diploid). Exceptions to the haploid and diploid rule are seen in polyploid species. *Other:*
Flower (definition, other)
*Definition:* In angiosperms, the part of a plant that contains reproductive structures. Typically includes a calyx, a corolla, and one or more stamens and/or carpels. *Other:* A flower is a reproductive structure in angiosperms that produces gametes, attracts pollinators, receives gametes from other individuals, nourishes embryos, and develops seeds and fruits.
Fruit (definition, other)
*Definition:* In flowering plants (angiosperms), a mature, ripened plant ovary (or group of ovaries), along with the seeds it contains and any adjacent fused parts; often functions in seed dispersal. *Other:* Fruits develop from the flower's seed-producing organ and contain seeds.
Pollen Tube (definition, other)
*Definition:* In flowering plants, a structure that grows out of a pollen grain after it reaches the stigma. The tube extends down the style, and two sperm cells travel through it to the ovule. *Other:*
Polar Nuclei (definition, other)
*Definition:* In flowering plants, the nuclei in the female gametophyte that fuse with one sperm nucleus to produce the endosperm. Most species have two. *Other:* - In many angiosperms, the embryo sac contains eight haploid nuclei and seven cells. Typically, two polar nuclei stay together within one central cell—the largest cell in the ovule. - The number of polar nuclei varies among species. - The polar nuclei play an important role in seed development after pollination and fertilization take place.
Ovules (definition, other)
*Definition:* In flowering plants, the structure inside an ovary that contains the female gametophyte and eventually (if fertilized) becomes a seed. *Other:* - Inside the ovary, female gametophytes are produced in structures called ovules. An ovary may contain more than one ovule. When the female gametophytes that are produced inside ovules mature, they produce eggs. - Each ovule contains a structure called the megasporangium, inside which there is a diploid cell called the megasporocyte.
Sporophyte (definition, other)
*Definition:* In organisms undergoing alternation of generations, the multicellular diploid form that devel- ops by mitotic divisions after fertilization produces a zygote. *Other:* - Land plants are characterized by a life cycle with two distinct multicellular forms—one diploid and one haploid. - An individual in the diploid phase of the life cycle is called a sporophyte. - The zygote undergoes mitosis and grows into a multicellular, diploid embryo (sporophyte).
Gametophyte (definition, other)
*Definition:* In organisms undergoing alternation of generations, the multicellular haploid form that arises from a single haploid spore and produces gametes by mitosis and cell division. *Other:* - Land plants are characterized by a life cycle with two distinct multicellular forms—one diploid and one haploid. - An individual in the haploid phase of the life cycle is called a gametophyte. - Gametophytes produce sperm (male gametes) and eggs (female gametes) by mitosis.
Megaspore (definition, other)
*Definition:* In seed plants, a haploid (n) spore that is produced in a megasporangium by meiosis of a diploid (2n) megasporocyte; develops into a female gametophyte. *Other:* During gametophyte formation, four haploid megaspores result from megasporocyte undergoing meiosis, but three degenerate.
Microspore (definition, other)
*Definition:* In seed plants, a haploid (n) spore that is produced in a microsporangium by meiosis of a diploid (2n) microsporocyte; develops into a male gametophyte. *Other:* - They are haploid - During male gametophyte formation microsporocytes undergo meiosis, which results in four haploid microspores. - During male gametophyte formation each of the four haploid microspore divides once by mitosis forming the tube cell and generative cell.
Pollen Grain (definition, other)
*Definition:* In seed plants, a male gametophyte enclosed within a protective coat of sporopollenin. *Other:* The result of male gametophyte formation is a gametophyte, also called a pollen grain.
Meiosis (definition, other)
*Definition:* In sexually reproducing organisms, a special two-stage type of cell division in which one diploid (2n) parent cell produces haploid (n) cells (gametes); results in halving of the chromosome number. Also called reduction division. *Other:* - Meiosis is a type of nuclear division that results in four daughter cells, each made up of half the number of chromosomes present in the original parent cell. - Meiosis results in offspring that are genetically different from each other and different from their parents. - In land plants, meiosis and fertilization occur in alternate phases of a life cycle.
Megasporcyte (loose definition)
*Definition:* Is a diploid cell in plants in which meiosis will occur, resulting in the production of four haploid megaspores. At least one of the spores develop into haploid female gametophytes (megagametophytes). The megaspore mother cell arises within the megasporangium tissue. *Other:* - During female gametophyte formation the megasporocyte divides by meiosis. - Each ovule contains a structure called the megasporangium, inside which there is a diploid cell called the megasporocyte.
Sepal (definition, structure, function)
*Definition:* One of the protective leaflike organs enclosing a flower bud and, after blooming, the outermost portion of the flower. *Structure:* - Sepals are leaflike structures that make up the outermost parts of a flower. - Sepals are usually green and photosynthetic, and they are relatively thick compared with other parts of the flower. - Sepals are attached to the receptacle in a circle or whorled arrangement, enclosing the flower bud as it develops. - The entire group of sepals in the flower is collectively called the calyx. *Function:* Because sepals are attached to the receptacle in a circle or whorled arrangement, sepals enclose the flower bud as it devel- ops and grows—protecting young buds from damage by desiccation, insects, or disease-causing agents.
Nectar (definition, other)
*Definition:* The sugary fluid produced by flowers that attracts and rewards pollinating animals. *Other:* - The nectary produces the sugar-rich fluid nectar, which many of the animals that visit flowers harvest along with pollen. - In the process of collecting pollen or nectar, the visiting animal usually deposits on the female parts pollen from a different plant— accomplishing pollination.
Micropyle (definition, other)
*Definition:* The tiny pore in a plant ovule through which the pollen tube reaches the embryo sac. *Other:*
Micropyle (definition, other)
*Definition:* The tiny pore in a plant ovule through which the pollen tube reaches the embryo sac. *Other:* The egg cell is located at one end of the female gametophyte, near an opening in the ovule called the micropyle. The micropyle is where sperm will enter the ovule before fertilization.
Female Gametophyte Formation (Steps)
*TL;DR:* In the carpel, then, a diploid megasporocyte divides by meiosis to form a megaspore, which then divides by mitosis to form the female gametophyte. Female gametophytes are encased in an ovary, are retained in the flower, and produce an egg. *0.* The ovary contains one or more ovules. Each ovule contains a structure called the megasporangium, inside which there is a diploid cell called the megasporocyte. The megasporangium is comparable to spore-producing structures found in other plants, such as those on the back of fern leaves. *1.* The diploid megasporocyte inside the ovule undergoes meiosis, resulting in four megaspores. *2.* Four haploid megaspores result from meiosis, but three degenerate. *3.* The surviving megaspore divides by mitosis to produce a structure with eight haploid nuclei. This is the female gametophyte—usually known as the embryo sac. *4.* The eight haploid nuclei segregate to different positions in the embryo sac, and cell walls form around some of them. One of these cells becomes the haploid egg. Typically two polar nuclei stay together within one central cell— the largest cell in the ovule. *5.* The egg cell is located at one end of the female gametophyte, near an opening in the ovule called the micropyle. The micropyle is where sperm will enter the ovule before fertilization. Two haploid cells called synergids lie close to the egg which are important for fertilization.
Male Gametophyte Formation (steps)
*TLDR:* In the anther, then, diploid microsporocytes divide by meiosis to form microspores, which then divide by mitosis to form male gametophytes (pollen grains). Each diploid microsporocyte ultimately yields four haploid pollen grains. The production of male gametophytes is pollen. Male gametophytes are dispersed from the flower and eventually produce sperm. *0.* A stamen consists of two major parts, an anther and a filament. Inside the anther structures known as Microsporangia contain diploid cells called Microsporocytes. *1.* Microsporocytes undergo meiosis resulting in four Microspores. *2.* Each of the four Microspores divide by mitosis, forming the tube cell and generative cell. *3.* The two nuclei that result from mitotic division in a microspore form a haploid, immature male gametophyte, also known as a pollen grain. The generative cell will later divide to form sperm cells. The male gametophyte is considered mature when the haploid generative cell undergoes mitosis and produces two sperm cells. *4.* In some species, this maturation step occurs while pollen is still in the anther. In other species, maturation and sperm produc- tion don't occur until after the pollen grain lands on a stigma and begins to grow. The reasons for this difference are not understood.
What is the downside of Asexual Reproduction?
- A fungus or other disease-causing agent that infects an individual plant will probably succeed in infecting the plant's cloned offspring as well, even if they are no longer physically connected. - Plants fight disease with a wide variety of molecules. Populations of asexually produced individuals can lack the genetic diversity needed to generate an arsenal of effective disease-fighting compounds.
Flower organ diversity
- Not all four organs are present in all flowers. - The colors, sizes, and shapes of these four components are
Aesexual Reproduction Efficiency
- The key characteristic of asexual reproduction is efficiency. - If an herbivore or a disease wipes out other plants that surround a grass plant, the grass can quickly send out rhizomes. - Its asexually produced offspring are likely to fill the unoccupied space before seeds from competitors can establish themselves and grow. The parent plant can also nourish these progeny as they become established.
Eudicot (definition)
A member of a monophyletic group (lineage) of angiosperms that includes complex flowering plants and trees (e.g., roses, daisies, maples). All eudicots have two cotyledons, but not all dicots are members of this lineage.
Monocot (definition)
Any flowering plant (angiosperm) that has a single cotyledon (embryonic leaf ) upon germination. Monocots form a monophyletic group. Also called a monocotyledonous plant.
Dicot (definition)
Any flowering plant (angiosperm) that has two cotyledons (embryonic leaves) upon germination. The dicots do not form a monophyletic group. Also called dicotyledonous plant.
Receptacle (loose definition)
The compressed portion of stem where the organs of a flower are attached.
Cotyledon (definition)
The first leaf, or seed leaf, of a plant embryo. Used for storing and digesting nutrients and/or for early photosynthesis.
Pericarp (definition)
The part of a fruit, formed from the ovary wall, that surrounds the seeds and protects them. Corresponds to the flesh of most edible fruits and the hard shells of most nuts.
Petal Diversity
• Flattened petals may provide a landing pad for flying insects. • Elongated, tubelike petals frequently have a nectary at their base that can be reached only by animals with a long beak or tongue-like proboscis. • Some petals protect the reproductive organs located inside the corolla. • Specialized cells in some petals synthesize and release molecules that provide a scent attractive to certain species of pollinating animals. • Wind-pollinated angiosperms such as oaks, birches, pecans, and grasses have flowers that have small petals or no petals at all, and they lack nectaries. These species do not invest in structures that aren't required for pollination.
