Question

which statement best distinguishes the light-dependent (l-d) reactions from the light-independent (l-ind) reactions?
the l-d reactions occur in the thylakoid membrane, and the l-ind reactions occur in the stroma.
the l-d reactions occur in the cytoplasm, and the l-ind reactions occur in the chloroplast.
the l-d reactions occur in the chloroplast, and the l-ind reactions occur in the mitochondria.
the l-d reactions occur in the stroma, and the l-ind reactions occur in the cytoplasm.

Explanation:

To determine the correct answer, we analyze the locations of light - dependent (L - D) and light - independent (L - IND) reactions in photosynthesis:

1. Light - dependent reactions take place in the thylakoid membranes of chloroplasts. This is where the absorption of light energy, splitting of water, and generation of ATP and NADPH occur.
2. Light - independent reactions (Calvin cycle) occur in the stroma of the chloroplast. Here, the ATP and NADPH from the light - dependent reactions are used to fix carbon dioxide into glucose.

Now let's analyze each option:

• Option 1: "The L - D reactions occur in the thylakoid membrane, and the L - IND reactions occur in the stroma." This matches the correct locations of the two types of reactions.
• Option 2: Light - dependent reactions do not occur in the cytoplasm. They occur in the chloroplast's thylakoid membranes. So this option is incorrect.
• Option 3: Light - independent reactions do not occur in the mitochondria. They occur in the chloroplast's stroma. So this option is incorrect.
• Option 4: Light - dependent reactions occur in thylakoid membranes (not stroma) and light - independent reactions occur in the stroma (not cytoplasm). So this option is incorrect.

Answer:

The L - D reactions occur in the thylakoid membrane, and the L - IND reactions occur in the stroma.