Location of ovules inside a Helleborus foetidus flower

Ovule literally means "small egg. Helleborus foetidus, known variously as Stinking hellebore, Dungwort, or Bear's foot, is a member of the buttercup family Ranunculaceae An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. " In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. The spermatophytes (from the Greek word "Σπερματόφυτα" (also known as phanerogams) comprise those Plants that produce Seeds They are It consists of three parts: The integuments forming its outer layer, the nucellus (or megasporangium), and the megaspore-derived female gametophyte (or megagametophyte) in its center. A sporangium (pl sporangia) is a Plant or fungal structure producing and containing Spores Sporangia occur in angiosperms, The megagametophyte (also called embryo sac in flowering plants) produces the egg cell for fertilization. An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. For soil improvement see Fertilization (soil. After fertilization, the ovule develops into a seed. A seed (in some plants referred to as a kernel) is a small embryonic Plant enclosed in a covering called the seed coat usually with some stored

Location within the plant

In flowering plants, the ovule is located within the actual flower, the part of the carpel known as the ovary, which ultimately becomes the fruit. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group A flower, also known as a bloom or Blossom, is the reproductive structure found in Flowering plants (plants of the division Magnoliophyta, also A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. In the Flowering plants an ovary is a part of the female reproductive organ of the flower or Gynoecium. The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. Depending on the plant, flowers may have one or multiple ovules per ovary. The ovule is attached to the placental wall of the ovary through a structure known as the funiculus, the plant equivalent of an umbilical cord. In placental Mammals the umbilical cord (also called the birth cord or funiculus umbilicalis) is the connecting cord from the developing Embryo Different patterns of ovule attachment, or placentation, can be found among plants: In parietal placentation, the ovules are attached to the outer ovary wall, whereas in free central placentation, they are attached to a central column within the ovary. In biology placentation refers to the formation type and structure or arrangement of Placentas The function of placentation is to transfers nutrients from maternal tissue In axile placentation, they are attached to radial spokes within the ovary.

In gymnosperms such as conifers and similar plants, the ovules are borne unenclosed on the surface of an ovuliferous (ovule-bearing) scale, usually within an ovulate cone (also called megastrobilus). Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are A cone (in formal botanical usage Strobilus, plural strobili is an organ on Plants in the division Pinophyta ( Conifers A strobilus (plural strobili is an organ of many Plants that contains the reproductive structures

Ovule parts and development

Plant ovules: Gymnosperm ovule on left, angiosperm ovule (inside ovary) on right

The ovule is composed of diploid maternal tissue that gives rise to the haploid tissue of the female gametophyte. "Haplo" redirects here For the fictional character see The Death Gate Cycle. "Haplo" redirects here For the fictional character see The Death Gate Cycle. The maternal tissues of the ovule include the integuments and the nucellus. The next "generation" formed within the ovule are the haploid megaspore and megagametophyte, or embryo sac. After fertilization of the egg cell and formation of a zygote, the ovule contains the embryo of the next sporophyte generation and, in flowering plants, the triploid endosperm. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular All land plants and some Algae, have life cycles in which a haploid Gametophyte generation alternates with a Diploid sporophyte, the generation of a Endosperm is the tissue produced in the Seeds of most Flowering plants around the time of fertilization

Integuments, micropyle and chalaza

The integuments are the outer cell layers of the ovule enclosing the nucellus. Gymnosperms typically have one integument layer while angiosperms typically have two. The integuments develop into the seed coat when the ovule matures after fertilization.

The integuments do not enclose the nucellus completely but leave an opening at its apex referred to as the micropyle. The micropyle opening allows the pollen tube to enter the ovule for fertilization. The pollen tube of most Seed plants acts as a conduit to transport sperm cells from the Pollen grain, either from the stigma (in Flowering plants In gymnosperms (e. g. conifers), the pollen itself is drawn into the ovule and the micropyle opening closes after pollination. Pollen is a fine to coarse powder consisting of microgametophytes ( pollen grains) which produce the male Gametes (sperm cells of During germination, the seedling's radicle emerges through the micropyle. Germination is the process whereby growth emerges from a period of dormancy A seedling is a young plant Sporophyte developing out of a plant embryo from a Seed. In Botany, the radicle is the first part of a Seedling (a growing plant Embryo) to emerge from the Seed during the process of

Located opposite from the micropyle is the chalaza where the nucellus is joined to the integuments. The chalaza (from Greek - khalaze - meaning "hailstone" is a structure inside animal eggs and plant Ovules It attaches or suspends the Yolk Nutrients from the plant travel through the phloem of the vascular system to the funiculus and outer integument and from there apoplastically and symplastically through the chalaza to the nucellus inside the ovule. In Vascular plants phloem is the living tissue that carries organic Nutrients (known as photosynthate particularly Sucrose, a sugar to The symplast of a Plant is the inner side of the Plasma membrane in which water (and low molecular solutes) can freely diffuse. In chalazogamous plants, the pollen tubes enter the ovule through the chalaza instead of the micropyle opening.

Nucellus, megaspore and perisperm

The nucellus (plural: nucelli) is the central portion of the ovule inside the integuments. It consists of diploid maternal tissue and has the function of a megasporangium. "Haplo" redirects here For the fictional character see The Death Gate Cycle. A sporangium (pl sporangia) is a Plant or fungal structure producing and containing Spores Sporangia occur in angiosperms, In immature ovules, it contains a megasporocyte (megaspore mother cell), which undergoes sporogenesis via meiosis. Sporogenesis is the production of Spores in Biology. The term is also used to refer to the process of Reproduction via spores In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half Three of the four haploid cells produced in meiosis degenerate, leaving one surviving megaspore inside the nucellus. "Haplo" redirects here For the fictional character see The Death Gate Cycle. After fertilization, the nucellus develops into the perisperm that feeds the embryo. In some plants, the diploid tissue of the nucellus can give rise to a seed through a mechanism of asexual reproduction called nucellar embryony. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. Nucellar embryony (notated Nu+) is a form of Seed Reproduction that occurs in certain plant species including many Citrus varieties

Megagametophyte and embryo sac

Ovule with embryo sac: egg cell (yellow), synergids (orange), central cell with two polar nuclei (bright green), and antipodals (dark green)

The haploid megaspore inside the nucellus gives rise to the female gametophyte (megagametophyte). In Plants and Algae that undergo Alternation of generations, a gametophyte is the multicellular structure or phase that is Haploid, containing In gymnosperms, the female gametophyte consists of around 2000 nuclei and forms archegonia which produce the egg cells for fertilization. An archegonium (pl archegonia) from the Ancient Greek ἀρχή ("beginning" and γόνος ("offspring" is a multicellular In flowering plants, the megagametophyte, also referred to as embryo sac, is much smaller and typically consists of only seven cells and eight nuclei. Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells The embryo sac develops from the megaspore through three rounds of mitotic divisions. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei The cell closest to the micropyle opening of the integuments differentiates into the egg cell, with two synergid cells by its side that may be involved in the production of signals that guide the pollen tube. Three antipodal cells form on the opposite (chalazal) end of ovule and later degenerate, serving no obvious function. The large central cell of the embryo sac contains two polar nuclei.

Zygote, embryo and endosperm

The pollen tube releases two sperm nuclei into the ovule. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. In gymnosperms, fertilization occurs within the archegonia produced by the female gametophyte. For soil improvement see Fertilization (soil. While it is possible that several egg cells are present and fertilized, typically only one zygote will develop into a mature embryo as the resources within the seed are limited. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular

In flowering plants, one sperm nucleus fuses with the egg cell into a zygote, the other fuses with the two polar nuclei of the central cell to give rise to the triploid endosperm. Endosperm is the tissue produced in the Seeds of most Flowering plants around the time of fertilization This double fertilization is unique to flowering plants. The plant stores nutrients such as starch, proteins and oils in the endosperm as a food source for the developing embryo and seedling, serving a similar function to the yolk of animal eggs. Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl An oil is a substance that is in a viscous Liquid state ( "oily") at ambient temperatures or slightly warmer and is An egg yolk is the part of an egg which serves as the Food source for the developing Embryo inside The endosperm is also called the albumen of the seed. Albumen redirects here For other uses see Albumen (disambiguation.

References

• P. H. Raven, R. F. Evert, S. E. Eichhorn (2005): Biology of Plants, 7th Edition, W. H. Freeman and Company Publishers, New York, ISBN 0-7167-1007-2

See also

• Carpel
• Ovum
• Alternation of generations