The correct option is C organism
An ecosystem is an integrated functional unit that consists of many successive levels of organisation, which can be called the ecological hierarchy.
The basic component or the lowest level in this hierarchy is the organism.
An interbreeding group of organisms of the same species is called a population.
A group of interacting populations forms a community. A community and its physical environment together forms the ecosystem.
When many ecosystems that are similar to each other interact with each other on a large scale, it is called a biome.