Problem 5 - Campbell Biology

Question

Which of the following does not occur during the Calvin cycle? \begin{equation}\begin{array}{l}{\text { (A) carbon fixation }} \\ {\text { (B) oxidation of NADPH }} \\ {\text { (C) release of oxygen }} \\ {\text { (D) regeneration of the CO }_{2} \text { acceptor }}\end{array} \end{equation}

Step-by-Step Solution

Answer

The release of oxygen (Option C).

Step 1 - Understand Calvin Cycle Activities

The Calvin Cycle involves several main activities: carbon fixation, reduction of 3-phosphoglycerate into G3P using NADPH, and regeneration of RuBP, the CO2 acceptor.

Step 2 - Evaluate Each Option

Identify which of the provided activities do or do not happen during the Calvin Cycle.

Step 3 - Analyze Option (A)

Carbon fixation occurs in the first step of the Calvin Cycle where CO2 is fixed into a 3-carbon compound. This step does occur during the Calvin Cycle.

Step 4 - Analyze Option (B)

Oxidation of NADPH happens during the Calvin Cycle as NADPH donates electrons for the reduction reactions. This step occurs during the Calvin Cycle.

Step 5 - Analyze Option (C)

Release of oxygen does not occur during the Calvin Cycle. Oxygen is released during the light-dependent reactions of photosynthesis, not during the Calvin Cycle.

Step 6 - Analyze Option (D)

Regeneration of the CO2 acceptor (RuBP) takes place in the final steps of the Calvin Cycle. This step does occur during the Calvin Cycle.

Step 7 - Conclusion

The activity that does not occur during the Calvin Cycle is the release of oxygen.

Key Concepts

carbon fixation

Carbon fixation is the first step of the Calvin Cycle. During this phase, the enzyme RuBisCO catalyzes the reaction between carbon dioxide (CO2) and ribulose-1,5-bisphosphate (RuBP). This reaction produces a six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate. This process is crucial because it converts inorganic CO2 into a form that can be used by plants to make sugars and other organic molecules. Without carbon fixation, the plant wouldn't be able to synthesize the organic compounds needed for energy and growth.

oxidation of NADPH

NADPH plays an essential role in the Calvin Cycle by providing the reducing power needed for the conversion of 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P). This occurs in the reduction phase of the Calvin Cycle. During this phase, NADPH donates electrons and hydrogen ions, becoming oxidized to NADP+. The energy stored in NADPH is used to convert ATP and 3-phosphoglycerate into G3P, which is then used to synthesize glucose and other carbohydrates. Thus, the oxidation of NADPH is a critical step in the Calvin Cycle.

regeneration of RuBP

Regeneration of RuBP is the final phase of the Calvin Cycle. After producing G3P, some of this molecule is used to regenerate RuBP. This process requires ATP, which also comes from the light-dependent reactions of photosynthesis. The regeneration process involves a series of complex reactions that convert G3P back into RuBP, enabling the cycle to continue. Regenerating RuBP ensures that the Calvin Cycle can keep fixing CO2 and synthesizing sugars, maintaining the plant's productivity.

photosynthesis

Photosynthesis is the process through which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. This process comprises two major stages: light-dependent reactions and the Calvin Cycle (light-independent reactions). During the light-dependent reactions, which occur in the thylakoid membranes, sunlight is captured and used to produce ATP and NADPH while splitting water molecules to release oxygen. The Calvin Cycle uses ATP and NADPH produced in the light-dependent reactions to fix CO2 into organic molecules. Ultimately, photosynthesis is essential for producing the oxygen we breathe and the organic compounds that form the base of the food chain.