Video Transcript
Where in the chloroplast do the
light-dependent reactions take place? (A) In the stroma, (B) in the
thylakoid membrane, (C) in the cristae, (D) in the inner membrane.
The light-dependent reactions are a
series of reactions that make up the first part of photosynthesis. Photosynthesis is the process by
which plants produce glucose and oxygen from carbon dioxide and water, using light
energy. Plants contain specialized
organelles called chloroplasts, which are the site of photosynthesis. The fluid that fills the
chloroplast is called the stroma. This fluid contains many useful
enzymes, but it is not the site of the light-dependent reactions. So we can eliminate option (A).
The chloroplast is an organelle
with a double membrane. This means it has an outer and an
inner membrane. However, the light-dependent
reactions do not take place in either of these membranes. We can therefore eliminate option
(D).
Chloroplasts contain multiple
membrane-bound compartments called thylakoids. These thylakoids form stacks, which
are called grana. The membranes of these thylakoids
contain proton pumps, electron carriers, enzymes, and other proteins which form the
electron transport chain. The electron transport chain is
where the reactions associated with the light-dependent stage of photosynthesis take
place. So it looks like our correct answer
is (B), but let’s just check the final option.
The cristae actually refers to a
structure found in the mitochondria of cells and not in the chloroplast. So this choice is not correct.
Our correct answer is therefore
that the light-dependent reactions of photosynthesis take place in the thylakoid
membrane of the chloroplast.
