What is dominant gametophyte?
The term dominant refers to how often a plant uses the gametophyte or sporophyte stage in their life cycle. More primitive, non-vascular plants such as mosses are dominant gametophytes, whereas higher vascular plants and some algae are dominant sporophytes. Also, what is the dominant life stage of moss?
Why is gametophyte dominant in Moss?
Why is Gametophyte dominant in Moss? Alternation of Generations. In bryophytes (mosses and liverworts), the dominant generation is haploid, so that the gametophyte comprises what we think of as the main plant. The opposite is true for tracheophytes (vascular plants), in which the diploid generation is dominant and the sporophyte comprises the ...
Is the gametophyte generation haploid or diploid?
There is a regular feature of alternation of generations. The gametophyte of sexual generation intervenes between meiosis and syngamy while the sporophyte or asexual generation intervenes between syngamy and meiosis. The haploid phase (n) is the gametophyte and the diploid phase (2n) is the sporophyte.
Are mosses gametophyte or sporophyte dominant?
Similar to plants, the moss lifecycle is completed in two distinct stages - the gametophyte and the sporophyte. The term that describes this type of life history is called alternation of heteromorphic generations. In vascular plants the dominant stage of this lifecycle is the diploid generation. In mosses, the dominant stage is the haploid generation (the gametophyte).
How does gametophyte develop?
For the formation of spores, the mother cell goes through meiosis to produce haploids whereas gametes undergo fusion for the formation of diploid(2n), the zygote. The meiospore grows to develop into the gametophyte.
How does male and female gametophyte develop?
The haploid gametophyte produces the male and female gametes by mitosis in distinct multicellular structures. Fusion of the male and females gametes forms the diploid zygote, which develops into the sporophyte.
What does the female gametophyte contain and what does it produce?
It contains the egg cell and central cell that become fertilized and give rise to the embryo and endosperm of the seed, respectively. Female gametophyte development begins early in ovule development with the formation of a diploid megaspore mother cell that undergoes meiosis.
What is the female gametophyte called?
3.1 Initiation of female gametophyte development. In angiosperms, the female gametophytes, known as megagametophytes or embryo sacs, develop within the ovule (Grossniklaus and Schneitz, 1998).
What is the difference between male and female gametophytes?
Male gametophyte is the haploid stage that produces male gametes. It derives from the microspore. Female gametophyte is the haploid stage that produces female gametes. It derives from the megaspore. Male gametophyte is inside the pollen grain while female gametocyte is inside the ovule.
What is the first cell of female gametophyte?
functional megasporeSo, the functional megaspore serves as the first cell of the female gametophyte.
What is the role of female gametophyte in angiosperms?
The angiosperm female gametophyte is critical to the reproductive process. It is the structure within which egg cell production and fertilization take place. In addition, the female gametophyte plays a role in pollen tube guidance, the induction of seed development, and the maternal control of seed development.
Is a female gametophyte haploid or diploid?
The female gametophyte forms from a diploid megaspore that undergoes meiosis and starts being singled celled. The size of the mature female gametophyte varies drastically between gymnosperm orders.
How does the male gametophyte develop in gymnosperms?
The male gametophyte containing the generative cell splits into two sperm nuclei, one of which fuses with the egg, while the other degenerates. After fertilization of the egg, the diploid zygote is formed, which divides by mitosis to form the embryo. The scales of the cones are closed during development of the seed.
How are male gametophytes formed in angiosperms?
Abstract. The male gametes of angiosperms consist of two sperm cells within a pollen grain or a pollen tube. They are derived from a single generative cell, which is formed as the smaller cell by unequal cell division in the microspore after meiosis.
What is the development of male gametophyte in angiosperms?
Male Gametophyte development in Angiosperms The male gametophyte is found in the stamens' anthers, whereas the female gametophyte is found in the pistil's ovules. Four pollen sacs (locules) in the anther contain many microspore mother cells, each of which goes through meiosis to create four microspores in a tetrad.
How do female gametophytes develop?
Different stages of development of female gametophyte are: 1) In the nucleus of a developing ovule, one diploid cell develops into a diploid megaspore mother cell. 2) This megaspore mother cell divides by meiosis to produce four haploid megaspores which are arranged in a linear tetrad.
Which megaspore produces the female gametophyte?
3) One of the megaspores is functional, while the other three degenerate in angiosperms. The lower chalazal megaspore produces the female gametophyte (embryo sac).
What are the carpels of an angiosperm?
Answer. The carpels of an angiosperm is known as megasporophyll. It is differentiated into three regions-ovary, style and stigma. The ovary contains ovules or megasporangium. Megasporogenesis is the process of formation of megaspores from the megaspore mother cell (MMC).
How many nuclei are formed in the third division?
The third division results in the formation of 4 nuclei at each pole. 6) One nucleus from each pole then migrates towards the centre to become polar nuclei, which fuse together and give rise to the secondary nucleus (2n). Out of these, the central one is the egg cell while the two lateral cells are called synergids.
How many nuclei are in a female gametophyte?
With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
Which cell develops into a diploid megaspore?
1) In the nucleus of a developing ovule, one diploid cell develops into a diploid megaspore mother cell.
How many cells are in an angiosperm sac?
9) Thus, a typical angiosperm embryo sac, at maturity is 8-nucleate and 7-celled.
Where is the gametophyte located?
Female gametophyte or embryo sac is embedded in the micropylar region of nucellus. Depending upon the thickness of the nucellus, ovules are called tenuinucellate (nucellus thin) and crassinucellate (nucellus massive).
How many integuments are there in a gymnosperm?
In gymnosperms, family Compositae and few other families with gamopetalous corolla, there is one integument . The ovules with one integument are called unitegmic and with two integuments are known as bitegmic. A small opening is left at the apex of integuments known as micropyle. ADVERTISEMENTS:
What is the part of the ovule that remains attached to the hilum?
The inverted ovule, the part of funicle remain attached beyond the hilum alongside of the body of the ovule forming a sort of ridge called raphe (Fig. 2.11). The ovule contains a mass of thin walled parenchymatous cells called nucellus. The nucellus is protected by one or two multicellular coats called integuments.
What are the different types of ovules?
orthotropous—upright or erect ovule and variously curved like anatropous, campylotropous, amphitropous and circinotropous) (Fig. 2.14).
What is the name of the way the placentae are distributed in the cavity of an ovary?
The manner in which the placentae are distributed in the cavity of an ovary is called placentation. Each ovule is attached to the placenta by a slender stalk called funicle. The point of attachment of the body of the ovule to its stalk or funicle is known as hilum.
How many nuclei are in a megaspore?
The nucleus of megaspore divides into two, four and finally eight daughter nuclei. Four of which are located at each pole. One nucleus from each pole migrates to the centre to form two polar nuclei which further fuse to form a diploid fusion or secondary nucleus. Thus, central cell bears two polar nuclei.
Do synergids get disorganized after fertilization?
The egg cell on fertilization gives rise to zygote, while synergids get disorganized soon after fertilization. The antipodal cells sooner or later also get disorganized. They may, however, be nutritive m function. Thus, a typical angiospermic embryo-sac, at maturity though eight nucleate is seven celled.
What is the first cell of a gametophyte?
The microspore is the first cell of the male gametophyte. It has a haploid nucleus. The microspore starts germinating while it is still within the microsporangium or pollen sac.
Where does the ovule come from?
Each ovule is attached to the placenta by a stalk called funicle. The point of attachment of the ovule to the funicle is known as hilum. The funicle continues beyond the hilum along the body of the ovule and forms a ridge called raphe.
How does a microsporangial cell divide?
Each microsporangial initial divides by periclinal division to form outer primary parietal cell and inner primary sporogenous cell. The primary parietal cell repeatedly divides to form the wall layers as described below :
How many microspores are produced in a sporogenous cell?
The primary sporogenous cells undergo several divisions to form microspore mother cells. Each microspore mother cell divides meiotically to produce four microspores or pollengrains which will have half the (n) number of chromosomes.
What is the outer layer of pollengrain?
Each pollengrain is unicellular and uninucleate having a two layered wall. The outer layer is called exine and the inner wall is called intine. The exine is provided with spinous outgrowth or different types of ornamentation. The intine is thin, delicate and made up of cellulose.
Why is the pollen grain on the stigma of a flower three-celled?
The two celled pollen grain on the stigma of a flower becomes three celled as a result of the division of the generative cell into two male cells or two male gametes. The pollen grain absorbs water and the intine grows out through a germpore to form a pollen tube, which discharges the two male gametes into the embryosac.
What are the three regions of angiosperm?
The carpels of angiosperm is known as megasporophyll. It is differentiated into three regions-ovary, style and stigma. The ovary contains ovules or megasporangium.
What is the female gametophyte generation?
The female gametophyte generation consists of the megaspores with embryo sac. The male gametophyte generation consists of microspores and pollen. The sporophyte generation consists of the plant body and seeds.
Which generation of gametophytes produces both male and female spores?
In flowering plants, the sporophyte generation produces both male and female spores. Male microspores (sperm) form in microsporangia (pollen sacs) in the flower stamen. Female megaspores (eggs) form in megasporangium in the flower ovary. Many angiosperms have flowers that contain both microsporangium and megasporangium.
What is the term for the haploid gametophyte?
The term gametophyte may refer to the gametophyte phase of the plant life cycle or to the particular plant body or organ that produces gametes. It is in the haploid gametophyte structure that gametes are formed. These male and female sex cells, also known as eggs and sperm, unite during fertilization to form a diploid zygote.
What is the sporophyte phase of ferns?
In ferns, the sporophyte phase consists of the leafy fronds, sporangia, roots, and vascular tissue. The gametophyte phase consists of the small, heart-shaped plants or prothallia.
How do haploid cells form?
In plants, the gametophyte phase ends with the formation of a diploid zygote by sexual reproduction . The zygote represents the sporophyte phase, which consists of the plant generation with diploid cells. The cycle begins anew when the diploid sporophyte cells undergo meiosis to produce haploid spores.
Why is the sporophyte dependent on the gametophyte?
The sporophyte structure is dependent upon the gametophyte of nourishment because only the gametophyte is capable of photosynthesis. The gametophyte generation in these organisms consists of the green, leafy or moss-like vegetation located at the base of the plant.
What is the name of the sex cell that forms during fertilization?
These male and female sex cells, also known as eggs and sperm, unite during fertilization to form a diploid zygote. The zygote develops into a diploid sporophyte, which represents the asexual phase of the cycle. Sporophytes produce the haploid spores from which haploid gametophytes develop.
How do gametophytes form?
Usually while the megagametophyte is developing, a parallel process that leads to the formation of male gametophytes takes place in the anthers. As an anther develops, four patches of tissue differentiate from the main mass of cells. These patches of tissue contain many diploid microsporocyte cells, each of which undergoes meiosis, producing a quartet (also referred to as a tetrad) of microspores. Four chambers or cavities (pollen sacs) lined with nutritive tapetal cells are visible in an anther cross section by the time the microspores have been produced. As the anther matures, the walls between adjacent pairs of chambers break down so that only two larger sacs remain.
How do megasporocytes differentiate?
While the flower is developing in the bud, a diploid megasporocyte cell differentiates from all the other cells in the ovule (Fig. 23.3). This megasporocyte undergoes meiosis, producing four haploid megaspores. Soon after they are produced, three of these megaspores degenerate and disappear, but the nucleus of the fourth undergoes mitosis, and the cell enlarges. While the cell is growing larger, its two haploid nuclei divide once more. The resulting four nuclei then divide yet another time. Consequently, eight haploid nuclei in all are produced (without walls being formed between them). By the time these three successive mitotic divisions have been completed, the cell has grown to many times its original volume. At the same time, two outer layers of cells of the ovule differentiate. These layers, called integuments, later become the seed coat of the seed. As they develop, they leave a pore, or gap, called the micropyle, at one end.
How many divisions of the remaining megaspore nucleus take place?
three successive divisions of the remaining megaspore nucleus take place the eight nuclei produced by the three successive divisions of the megaspore nucleus become rearranged in what is now called the megagametophyte. It constitutes the female gametophyte.
How often does the nucleus divide in microspores?
1. the nucleus in each microspore divides once by mitosis;
What is the 3/7 endosperm tissue?
3/7 endosperm tissue, which develops from a cell formed when the two central cell nuclei and one sperm nucleus unite
How many nuclei are there in a haploid cell?
At this stage, there are eight haploid nuclei in two groups, four nuclei toward each end of the large cell. One nucleus from each group then migrates toward the middle of the cell. These two central cell nuclei may become a binu-cleate cell, or they may fuse together, forming a single diploid nucleus. Cell walls also form around the remaining nuclei. In the group closest to the micropyle, one of the cells functions as the female gamete, or egg. The other two cells, called synergids, either are destroyed or degenerate during or after events that occur later. At the other end, the remaining three cells, called antipodals, have no apparent function, and later they also degenerate. The large sac, usually containing eight nuclei in seven cells, constitutes the female gametophyte (megagametophyte), formerly known as the embryo sac (Fig. 23.4).