The part of the biosphere that surrounds an organism is its environment.

Here's why:

* Biosphere: This refers to the entire region of Earth where living things exist, including the atmosphere, hydrosphere (water), and geosphere (land).

* Environment: This refers to the specific surroundings of an organism, encompassing all the living and non-living factors that influence its life.

So, the environment encompasses everything an organism interacts with, from the air it breathes to the food it eats, the predators it avoids, and the temperature it experiences.