Video Transcript
Which of the following is not an
adaptation chloroplasts have to carry out photosynthesis? (A) The thylakoids contain
photosystems within their membranes to capture and absorb light. (B) The highly folded inner
membrane of the chloroplast, called the cristae, increases the surface area
available for photosynthetic reactions to take place. (C) The stroma contains enzymes
that are essential for the light-independent reactions of photosynthesis to take
place. (D) Photosystems can contain a
range of photosynthetic pigments, e.g., chlorophyll A, chlorophyll B, and
carotenoids, to absorb a range of wavelengths of light.
Chloroplasts are specialized
organelles within the plant cell that have adapted to carry out photosynthesis. You might recall that
photosynthesis is a process that uses light energy to synthesize glucose from carbon
dioxide and water. Chloroplasts have many adaptations
that allow them to carry out this process.
First, let’s have a look at the
structure of a chloroplast. A chloroplast has two main
components on its inside: the stroma and the thylakoids. The stroma is the fluid matrix
contained by the chloroplast membranes. The thylakoids are disklike
structures which are piled up into stacks and are suspended within the stroma. The light-dependent stage of
photosynthesis occurs in the thylakoids.
Photosystems are structures that
are located in the thylakoid membrane. They absorb and utilize light
energy in the first stage of photosynthesis. The absorption of light is
performed by a range of pigments, such as chlorophylls and carotenoids. So answers (A) and (D) correctly
describe two adaptations of the chloroplast and can be excluded from the answer
pool.
The stroma is the site of the
light-independent reactions of photosynthesis. These reactions require certain
enzymes, as well as carbon dioxide and water from the environment, to synthesize
glucose. So answer (C) correctly describes
an adaptation as well.
So what is wrong in answer option
(B)? First, while the chloroplast does
have a double membrane, the inner membrane is not folded. In addition, the cristae are
structures found within a mitochondrion, which is the organelle that is responsible
for cellular respiration, not photosynthesis. So the answer to the question
“Which of the following is not an adaptation chloroplasts have to carry out
photosynthesis?” is found in answer option (B): the highly folded inner membrane of
the chloroplast, called the cristae, increases the surface area available for
photosynthetic reactions to take place.
