Question

vernon is using the diagram shown below to develop a model of photosynthesis. the letters a, b, and c each represent a reactant or product of the process.

what is the role of compound c?
standard addressed:

a product that forms along with sugars
a reactant that provides the carbon and oxygen for sugars
a reactant that provides the energy for assembling sugars
a reactant that provides the carbon and hydrogen for sugars

Explanation:

Identify the components of the photosynthesis model

The diagram illustrates the two main stages of photosynthesis occurring inside a chloroplast: the light-dependent reactions (on the left, taking place in the thylakoids) and the light-independent reactions or Calvin cycle (on the right, taking place in the stroma).

In Photosynthesis Reactions:

• A represents water (\(\text{H}_2\text{O}\)), which enters the light-dependent reactions.
• B represents oxygen (\(\text{O}_2\)), which is released as a byproduct of photolysis.
• C represents carbon dioxide (\(\text{CO}_2\)), which enters the Calvin cycle.

Analyze the role of compound C

Compound C is carbon dioxide (\(\text{CO}_2\)). In the Calvin cycle, carbon dioxide is a key reactant.

Using the Calvin Cycle Reactants knowledge point, we know that \(\text{CO}_2\) enters the cycle to undergo carbon fixation. The carbon and oxygen atoms from \(\text{CO}_2\) are used to build the backbone of the synthesized organic molecules (Sugars, such as G3P/glucose).

Evaluate the given multiple-choice options

• Option 1: "a product that forms along with sugars" — Incorrect, because compound C is an input (reactant) entering the cycle, not a product leaving it.
• Option 2: "a reactant that provides the carbon and oxygen for sugars" — Correct, because \(\text{CO}_2\) provides both the carbon and oxygen atoms that make up the carbohydrate molecules (\(\text{C}_6\text{H}_{12}\text{O}_6\)).
• Option 3: "a reactant that provides the energy for assembling sugars" — Incorrect, because the energy is provided by ATP and NADPH, which are generated in the light-dependent reactions.
• Option 4: "a reactant that provides the carbon and hydrogen for sugars" — Incorrect, because \(\text{CO}_2\) does not contain hydrogen; hydrogen is provided by NADPH.

Answer:

• a product that forms along with sugars
• a reactant that provides the carbon and oxygen for sugars (Correct answer)
• a reactant that provides the energy for assembling sugars
• a reactant that provides the carbon and hydrogen for sugars