Video Transcript
What is the primary role of the
stroma in the chloroplast? (A) To provide the site for the
light-dependent stage of photosynthesis. (B) To provide the site for the
light-independent stage of photosynthesis. (C) To provide a membrane to which
photosynthetic pigments can attach. (D) To connect and allow
communication between the thylakoids.
The stroma is the fluid matrix
inside the chloroplast. It contains many enzymes and the
DNA of the chloroplast, as well as ribosomes for protein synthesis. Also suspended in the stroma are
the thylakoids. The thylakoid membranes contain
photosynthetic pigments that absorb light. Thylakoids are the site for the
light-dependent stage of photosynthesis. In the light-dependent stage of
photosynthesis, the energy absorbed from light is stored in ATP.
So, looking at our answer choices,
we can exclude answer (A), as this answer describes the thylakoid, not the
stroma. We can eliminate answer option (C)
as well because we know that the stroma is a fluid, not a membrane, and that
pigments attach to the thylakoid membranes.
Let’s discuss answer option (D)
next. Although the stroma can and does
transport molecules between thylakoids, this is not its primary function. So answer (D) is incorrect. This suggests that the correct
answer is given by option (B). In the light-independent stage of
photosynthesis, the energy stored in ATP is used to build up carbohydrates for
long-term energy storage and as building material for the plant. This process indeed happens in the
stroma as the enzymes needed for the reactions of the light-independent stage of
photosynthesis are located in the stroma.
So the correct answer is “To
provide the site for the light-independent stage of photosynthesis.”
