The outer layer of a cell that acts as a gatekeeper to a cell is the

The outer layer of a cell that acts as a gatekeeper to a cell is the Cell Membrane or Plasma Membrane.

The cell membrane made up of mostly phospholipids and proteins and is known as selectively permeable membrane as it allows the entry of some selective molecules into it.

The plasma membrane is the layer present between  the cell and its external  environment. As the gatekeeper takes care of entry, cell membrane also regulates the molecules that enters and exits the cell from external environment.

Cells membrane helps in maintaining appropriate amount of molecules to function inside them.

Hence, the correct option is Cell Membrane.

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation:

c.more precipitation,but only when emission levels.