التعريف: An oceanic island, often having a characteristic ring-like shape surrounding a lagoon. Atolls are formed when coral reef grows around a volcanic island that later subsides into the ocean.
التعريف: number of homologous sets of chromosomes in the nucleus or primary chromosome-containing compartment of the cell, each set essentially coding for all the biological traits of the organism.
التعريف: A group of species that exploit the same food resources, and/or use the same feeding or foraging methods. http://en.wikipedia.org/wiki/Guild_(ecology)
