The cell part that controls the passage of nutrients into a cell is the cell membrane.

Here's why:

* Selective Permeability: The cell membrane acts like a gatekeeper, allowing some substances to pass through while blocking others. This is known as selective permeability.

* Phospholipid Bilayer: The cell membrane is made up of a double layer of phospholipids. These molecules have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. This structure helps control what enters and leaves the cell.

* Transport Proteins: Embedded within the membrane are various transport proteins. These proteins act as channels or carriers, helping specific molecules cross the membrane.

So, while other cell parts play important roles in cellular processes, the cell membrane is the primary barrier that controls the movement of nutrients into the cell.