What is the function of the structure identified by the red arrow?

The structure shown by the red arrow is cell membrane.  

In biology, cell membrane refers to the thin layer, which develops the external boundary of a living cell. It has three primary functions, which are as follows:  

1. It comprises channels and receptors, which permits particular molecules like nutrients, ions, metabolic components, and wastes to pass between the cell and the outside environment.  

2. It prevents toxic components from entering the cell.  

3. They distinguish essential but incompatible metabolic procedures conducted within the cell.  

Explanation: