The two steps in photosynthesis are the light-dependent reactions and the Calvin cycle.
Which of the following is true regarding these two steps?
a
During the light-dependent reactions, carbon dioxide is fixed to produce sugars that form glucose.
b
The light-dependent reactions take place in the thylakoid membrane, and the Calvin cycle takes place in the stroma.
c
The light-dependent reactions use ATP from the Calvin cycle, and the Calvin cycle uses energy from absorbed sunlight.
d
The Calvin cycle converts water molecules into oxygen gas as a byproduct of its reactions.
b
The light-dependent reactions take place in the thylakoid membrane, and the Calvin cycle takes place in the stroma.
b) The light-dependent reactions take place in the thylakoid membrane, and the Calvin cycle takes place in the stroma.
To determine which statement is true regarding the two steps in photosynthesis, let's examine each option:
a) "During the light-dependent reactions, carbon dioxide is fixed to produce sugars that form glucose."
This statement is not entirely accurate. During the light-dependent reactions, carbon dioxide is not fixed or converted into sugars. Instead, in the light-dependent reactions, light energy is absorbed by chlorophyll and converted into chemical energy in the form of ATP and NADPH.
b) "The light-dependent reactions take place in the thylakoid membrane, and the Calvin cycle takes place in the stroma."
This statement is correct. The light-dependent reactions occur in the thylakoid membrane of the chloroplasts, specifically in structures called photosystems. On the other hand, the Calvin cycle takes place in the stroma of the chloroplasts, which is the fluid-filled region that surrounds the thylakoid membranes.
c) "The light-dependent reactions use ATP from the Calvin cycle, and the Calvin cycle uses energy from absorbed sunlight."
This statement is incorrect. The light-dependent reactions directly utilize absorbed sunlight to generate ATP and NADPH. These energy-carrying molecules are then used in the Calvin cycle to convert carbon dioxide into glucose.
d) "The Calvin cycle converts water molecules into oxygen gas as a byproduct of its reactions."
This statement is also incorrect. The Calvin cycle does not involve the direct conversion of water into oxygen gas. Instead, during the light-dependent reactions, water molecules are split, producing oxygen gas as a byproduct, while releasing electrons that are used to replenish electron carriers in the photosystems.
Based on the analysis, the correct statement is option b: "The light-dependent reactions take place in the thylakoid membrane, and the Calvin cycle takes place in the stroma."