Which part of the cell controls what enters and exits?

The cell membrane is the part of the cell that controls what enters and exits. It serves as a selective barrier, ensuring that specific substances can pass into and out of the cell while keeping others out. This selectivity is crucial for maintaining the appropriate environment for cellular functions, allowing essential nutrients to enter and harmful substances to be expelled.

The cell membrane is composed of a phospholipid bilayer with embedded proteins that assist in transporting materials. This organization enables the cell to maintain homeostasis, which is the balance of internal conditions. Additionally, the fluid nature of the membrane allows it to adjust and respond to changes in the environment.

In contrast, the cell wall provides structural support and protection but is not involved in the selective transport of materials. The cytoplasm is the jelly-like substance within the cell that houses organelles and where many metabolic reactions occur, but it does not control movement across the cell’s boundaries. The nucleus, while essential for housing genetic material and controlling cellular activities, does not play a direct role in the transport of substances across the cell's outer limits.