Explain how a symbiotic relationship like the one described in the endosymbiotic theory would have benefited each cell. Please I need help for Biology.

5. what might happen if you were to remove all light from the setup after the discs have all become buoyant? describe what you would see. explain why this would occur with relation to cellular processes like respiration. [referring to an ap biology lab in which spinach discs are placed in a sodium bicarbonate solution and exposed to light.]