Question

which statement is true concerning the light-dependent and light-independent reactions of photosynthesis?
○ carbon dioxide is required for the light-dependent reactions, and water is required for the light-independent reactions
○ oxygen is required for the light-dependent reactions, and glucose is required for the light-independent reactions.
○ glucose is required for the light-dependent reactions, and oxygen is required for the light-independent reactions.
○ water is required for the light-dependent reactions, and carbon dioxide is required for the light-independent reactions.

Explanation:

To solve this, we recall the processes of photosynthesis:

• Light - dependent reactions: Occur in the thylakoid membranes. Water ($H_2O$) is split here (photolysis) to release electrons, protons, and oxygen. So water is required for light - dependent reactions.
• Light - independent reactions (Calvin cycle): Occur in the stroma. Carbon dioxide ($CO_2$) is fixed (converted into organic compounds like glucose) here. So carbon dioxide is required for light - independent reactions.

Now let's analyze each option:

• Option 1: Carbon dioxide is not required for light - dependent reactions (water is), and water is not required for light - independent reactions (carbon dioxide is). So this is incorrect.
• Option 2: Oxygen is a by - product of light - dependent reactions, not a reactant. Glucose is a product of light - independent reactions, not a reactant. So this is incorrect.
• Option 3: Glucose is a product, not a reactant of light - dependent reactions. Oxygen is a by - product, not a reactant of light - independent reactions. So this is incorrect.
• Option 4: Water is required for light - dependent reactions (for photolysis), and carbon dioxide is required for light - independent reactions (for carbon fixation). This matches our understanding of photosynthesis.

Answer:

D. Water is required for the light - dependent reactions, and carbon dioxide is required for the light - independent reactions. (Here we assume the last option is labeled D, if the original options were labeled A - D in order as presented. If the original labeling was different, adjust the label accordingly, but the content about water and carbon dioxide requirements is correct.)