Video Transcript
What is the primary function of a
photosystem in a chloroplast? (A) To reflect visible light and
attract pollinators. (B) To absorb heat energy for
metabolic reactions. (C) To act as the site of
light-independent photosynthetic reactions. Or (D) to absorb light energy for
photosynthesis.
The chloroplast is the site of
photosynthesis in plant cells. We will repeat the process of
photosynthesis in a moment, but let’s first discuss the structures of a
chloroplast.
A chloroplast has multiple
specialized structures, including the stroma, thylakoids, and a double membrane. The thylakoid membranes contain
pigments such as chlorophylls, which are responsible for absorbing light energy. The absorbed light energy is used
to build up glucose and bigger carbohydrates, which are used as long-term energy
storage and as building materials. Photosystems in chloroplasts play a
role in photosynthesis. But what is this role? Let’s go through the answer choices
to see if we can find a good description of the role of photosystems.
Answer (A) does not give a correct
description of the role of photosystems in the chloroplast. While some plants do adopt brightly
colored pigments in flowers to attract pollinators, this does not play a role in
photosynthesis. And so, it cannot be the primary
function of a photosystem. In addition, photosystems do not
absorb heat energy. In fact, heat energy is a byproduct
of absorbing light energy. So, answer (B) is incorrect as
well.
Photosystems are located in the
thylakoid membranes of a chloroplast. This is where the light-dependent
photosynthetic reactions, in which light energy is absorbed, take place. The light-independent stage of
photosynthesis, which uses the absorbed light energy to build up carbohydrates,
occurs in the stroma. The stroma is the fluid matrix
within the chloroplast that contains enzymes, which play a role in this
reaction. As photosystems are located in the
thylakoid membranes, they are involved in the light-dependent photosynthetic
reactions, not light-independent. So, answer (C) is incorrect.
The correct answer is given by
option (D). The primary function of
photosystems in chloroplasts is to absorb light energy for photosynthesis.
