The mentioned event is an illustration of primary succession as the reason for the succession is the volcanic tendencies or eruptions that lead to the formation of poor soil for further development. The mosses and the lichens are known as the pioneer community, as they are the community that has colonize the area initially and are the life forms that developed first. While the pine trees are known as the climax community as post succession, they are the stable community.
The most important organelle in a cell is the nucleus. Because it contains DNA which is in control of directing all the activities of a cell. And all the RNAs needed for the cell are synthesized in the nucleus
Expendable can mean having little to no value when compared to the big picture or something that's designed to only be used once and then destroyed. Since I don't have any context, I can't decipher which one it would be.
