Egg Cell


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Egg Cell

 

(also ovicell), in plants, the female sex cell; the relatively large nonmotile cell that is the parent cell of a new organism. The egg cell occurs in all higher plants and in certain algae and fungi (in oogamous species it is formed in the oogonia). In bryophytes, Lycopodiales, and gymnosperms the egg cell originates in the archegonia; in angiosperms it is a component of the egg apparatus of the embryo sac.

The shape and size of the egg cell vary in different plants. The egg cell is considerably larger than the sperm. There is a vacuole in the upper part. An external cellulose membrane is absent. There is, however, a thin plasma membrane, which promotes the exchange of matter between the egg cell and the cytoplasm of the embryo sac surrounding it. The plasma membrane also facilitates penetration by the sperm during fertilization, after which the zygote develops a typical external egg membrane.

The egg cell has marked morphological and physiological polarity, which is manifested in the varied activity of metabolism. Physiological activity is higher in the upper part of the cell than in the lower. The fertilized egg cell forms the zygote, from which the embryo develops. The cytoplasm of the egg cell contains organelles and inclusions characteristic also of other cells (mitochondria, leucoplasts, chloroplasts, chromoplasts).

REFERENCES

Gerasimova-Havashina, E. N. “Pyl’tsevoe zerno, gamety i polovoi protsess u pokrytosemennykh.” Trudy Botanicheskogo instituia. Morfologiia i anatomiia rastenii, 1951, issue 2.
Iakovlev, M. S. “Gametogenez, zarodyshevyi meshok i pyl’tsevoe zerno.” Botanicheskii zhurnal, 1974, vol. 59, no. 12.
Poddubnaia-Arnol’di, V. A. Tsitoembriologiia pokrytosemennykh rastenii. Moscow, 1976.
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