Step 1: Understanding the Concept
Levels of organisation go from organism to population, community, ecosystem, biome and biosphere.
Step 2: Match the description
A biome is a large terrestrial region set by climate, with its own main vegetation zone and the associated animals, for example rain forest, desert, grassland or tundra.
Step 3: Why the other options fail
Organisms, populations and communities are much smaller units and are not defined by a climatic zone.
Final Answer:
The unit described is a biome.
\[ \boxed{\text{(C) }\text{Biome}} \]