Final answer:
The photosynthetic membranes are found in chloroplasts in plant cells, specifically within the thylakoid membranes, which contain chlorophyll and where the light-dependent reactions of photosynthesis occur.
Step-by-step explanation:
The photosynthetic membranes are found in the chloroplasts in plant cells. These organelles are where photosynthesis occurs, harnessing sunlight to produce energy.
Chloroplasts have a double membrane envelope composed of an outer membrane and an inner membrane. Within these membranes is a third membrane system called the thylakoid membrane, which contains chlorophyll and is the site of the light-dependent reactions of photosynthesis. In most plant chloroplasts, the thylakoids are organized in stacks called grana.
Outside the thylakoid membranes is the stroma, a dense fluid where the light-independent reactions of photosynthesis take place. Embedded within the thylakoid membranes are molecules of chlorophyll which capture light energy and initiate photosynthesis, giving plants their characteristic green color.