Where are clusters of light Gathering pigments in a photosystem

What are the doorways into and out of cells, attached to the membrane, and built in the rough er.

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins? a. pressure applied by the heart b. one–way valves in veins c. thin muscular walls of veins