An individual animal, plant, or single-celled life form. Population: A particular section, group, or type of organisms living in an area or region. Levels of organization in ecology include the population, community, ecosystem, and biosphere. An ecosystem is all the living things in an area interacting with all of the abiotic parts of the environment
One is like an impersonal pronoun, can be used for people or as an indefinite pronoun. Instead of saying stamps again, they use "one" to replace it. Hope that helps.
He was swayed by both these considerations: the marriage gave him personal satisfaction, and at the same time it was considered the right thing by the most highly placed of his associates.
