Advanced Placement (AP) Biology Practice Exam

Which part of the chloroplast is specifically associated with light-independent reactions?

1. Thylakoid Space

2. Stroma

3. Outer Membrane

4. Granum

The correct answer is: Stroma

The part of the chloroplast that is specifically associated with light-independent reactions, also known as the Calvin cycle, is the stroma. The stroma is the liquid-filled space surrounding the thylakoids, and it contains enzymes, metabolites, and the necessary substrates for the synthesis of glucose during the light-independent reactions. During photosynthesis, the light-dependent reactions occur in the thylakoid membranes, where light energy is converted into chemical energy in the form of ATP and NADPH. These energy carriers are then utilized in the stroma during the light-independent reactions to convert carbon dioxide into glucose. The stroma's environment is optimal for these reactions, providing the necessary conditions and molecules for the assembly and reduction of carbon compounds. The other options are involved in different functions within the chloroplast. The thylakoid space is where the light-dependent reactions take place, the outer membrane provides a boundary for the chloroplast but does not participate in photosynthesis, and the granum is a stack of thylakoids where the light-dependent reactions happen but not the light-independent reactions. Thus, the stroma is the critical site for the light-independent reactions, making it the most accurate answer to the question.