Video Transcript
What is the primary role of the
proton pumps in the thylakoid membrane? (A) To allow the diffusion of H+
ions from the thylakoid lumen into the stroma. (B) To absorb wavelengths of light
to provide the energy needed for the light-dependent reactions. (C) To actively transport H+ ions
from the stroma into the interior of the thylakoid, the lumen. Or (D) to transport electrons along
the electron transport chain.
Thylakoids are structures found
within the chloroplasts of plant and some algae cells. Within the membrane of the
thylakoids are a series of enzymes, proton pumps, and electron carriers that
collectively make up the electron transport chain. The electron transport chain plays
a key role in the light-dependent reactions. Let’s take a closer look at
how.
In the electron transport chain,
there are two photosystems. These photosystems absorb the light
energy needed for the light-dependent reactions of photosynthesis to occur. Therefore, we could already
eliminate option (B) as the correct answer, as absorbing wavelengths of light is the
primary role of the photosystems and not the proton pumps.
When the photosystems absorb this
light energy, the electrons within them become excited. These electrons then move down the
electron transport chain. As they do so, they release
energy. This energy is used by the proton
pumps to actively transport hydrogen ions from the stroma of the chloroplast and
into the interior of the thylakoid. Although proton pumps do play a
role in transporting electrons along the electron transport chain, this is not their
primary role. So we can eliminate option (D) as a
correct answer.
Proton pumps do not facilitate the
diffusion of hydrogen ions, but rather the active transport of them. Active transport of ions requires
energy, unlike diffusion, which is a passive process. So we can eliminate option (A) as
our correct answer.
We know that hydrogen ions can be
actively transported across the thylakoid membrane by proton pumps. So our correct answer must be
(C). The primary role of the proton
pumps in the thylakoid membrane is to actively transport H+ ions from the stroma
into the interior of the thylakoid.
