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In both gymnosperms and angiosperms, the young plant contained in the seed, begins as a developing egg-cell formed after fertilization (sometimes without fertilization in a process called apomixis) and becomes a plant embryo. This embryonic condition also occurs in the buds that form on stems. The buds have tissue that has differentiated but ...
The gametophyte produces an egg cell. After fertilization, the ovule develops into a seed containing the embryo. [14] In flowering plants, the female gametophyte (sometimes referred to as the embryo sac) has been reduced to just eight cells inside the ovule. The gametophyte cell closest to the micropyle opening of the ovule develops into the ...
Location of ovules inside a Helleborus foetidus flower. In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the integument, forming its outer layer, the nucellus (or remnant of the megasporangium), and the female gametophyte (formed from a haploid megaspore) in its center.
In seed plants, the microgametophyte (pollen) travels to the vicinity of the egg cell (carried by a physical or animal vector) and produces two sperm by mitosis. In gymnosperms, the megagametophyte consists of several thousand cells and produces one to several archegonia, each with a single egg cell. The gametophyte becomes a food storage ...
An endosperm is formed after the two sperm nuclei inside a pollen grain reach the interior of a female gametophyte or megagametophyte, also called the embryonic sac.One sperm nucleus fertilizes the egg cell, forming a zygote, while the other sperm nucleus usually fuses with the binucleate central cell, forming a primary endosperm cell (its nucleus is often called the triple fusion nucleus).
The three cells left at the end of the cell near the micropylar become the egg apparatus with an egg cell in the center and two synergids. A cell wall forms around the other set of nuclei and forms the antipodals. The cells in the center develop into the central cell. This entire structure with its eight nuclei is called the embryonic sac.
These initial cells form, divide, and expand. C) The nucellar embryos are developed. If and when a zygote is present, the nucellar embryos supersede the zygote. D) The presence of extra embryos formed from the nucellar tissue gives rise to polyembryonic seeds. E) Polyembryonic seeds germinate and develop. [1]
In Ephedra nevadensis, a single binucleate sperm cell is deposited into the egg cell. Following the initial fertilization event, the second sperm nucleus is diverted to fertilize an additional egg nucleus found in the egg cytoplasm. In most other seed plants, this second 'ventral canal nucleus' is normally found to be functionally useless. [8]