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.
The theme is the writer's view of or comment about the subject. The answer to your question is D. I hope this is the answer that you are looking for and it comes to your help.
There is no choice? But if I was thinking it would be idk
