The part of the cell that is in most direct contact with the environment is the cell membrane, also known as the plasma membrane.

Here's why:

* Outermost layer: The cell membrane is the outermost layer of the cell, acting as a barrier between the cell's internal environment and the external environment.

* Selective permeability: The cell membrane is selectively permeable, meaning it controls what substances can enter and leave the cell. This is crucial for maintaining the cell's internal balance and responding to changes in the external environment.

* Communication: The cell membrane also plays a role in cell communication, allowing the cell to receive signals from its surroundings and respond accordingly.

While other structures, like the cell wall in plants and some bacteria, can be in contact with the environment, the cell membrane is the primary interface for communication and exchange with the external world.