Short answers, pulled from the story.
An egg cell, also called an ovum, is the female reproductive cell, or gamete, in sexually reproducing organisms. When it fuses with a male sperm cell during fertilisation, a diploid cell called the zygote is formed, which grows into a new organism.
Karl Ernst von Baer discovered the mammalian ovum in 1827. The fusion of spermatozoa with ova was later observed by Oskar Hertwig in 1876, using starfish eggs.
The human ovum measures approximately 120 micrometers in diameter, making it one of the largest cells in the human body and visible to the naked eye without magnification.
This was the accepted scientific view for most of the twentieth century, established through studies in the 1870s and reinforced by zoologist Solomon Zuckerman's review of reports from 1900 to 1950. Since 2004, multiple studies have challenged this dogma, suggesting ovarian stem cells may exist, but whether mature mammals can create new egg cells remains an open research question.
The ooplasm is the central cell substance of the ovum, similar to the yolk. It contains the nucleus (called the germinal vesicle) and the nucleolus (called the germinal disc), along with formative and nutritive yolk components made of fatty and albuminoid granules.
In flowering plants, the female gametophyte is reduced to eight cells inside the ovule. The cell nearest the micropyle opening becomes the egg cell. During pollination, a pollen tube delivers sperm into the gametophyte, and one sperm nucleus fuses with the egg nucleus to form a zygote that develops into an embryo inside the seed.