Problem 5 - Campbell Biology

Question

Which of the following occurs during the Calvin cycle? (A) carbon fixation (B) reduction of NADP (C) release of oxygen (D) generation of \(\mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

Carbon fixation

Step 1: Understand the Calvin Cycle

The Calvin cycle, also known as the light-independent reactions or C3 cycle, takes place in the stroma of chloroplasts in photosynthetic organisms. It does not require light and occurs after the light-dependent reactions. The primary purpose of the Calvin cycle is to synthesize glucose from carbon dioxide.

Step 2: Analyze each option

Review each of the listed options to determine their relevance in the Calvin cycle.- (A) Carbon fixation: This is the first step of the Calvin cycle where carbon dioxide is incorporated into a 5-carbon sugar called ribulose bisphosphate (RuBP).- (B) Reduction of NADP: This occurs in the light-dependent reactions where NADP is reduced to NADPH, which then provides reducing power to the Calvin cycle.- (C) Release of oxygen: This happens during the light-dependent reactions, not during the Calvin cycle.- (D) Generation of \(CO_{2}\): This is not a function of the Calvin cycle but rather a result of cellular respiration.

Step 3: Identify the Correct Answer

After analyzing all options, (A) Carbon fixation is the correct process that occurs during the Calvin cycle.

Key Concepts

carbon fixation

The Calvin cycle begins with a crucial step called carbon fixation. During this stage, carbon dioxide from the atmosphere is captured and incorporated into a 5-carbon molecule called ribulose bisphosphate (RuBP). This reaction is facilitated by an enzyme known as RuBisCO. The result of this process is a 6-carbon compound, which is then immediately split into two 3-carbon molecules of phosphoglycerate (3-PGA). This step effectively traps atmospheric carbon in a form that can be used in the production of glucose, which is vital for the plant's energy and growth needs.

light-independent reactions

The Calvin cycle is often referred to as the light-independent reactions because they do not directly require light to proceed. They occur in the stroma of the chloroplasts after light-dependent reactions have provided the necessary energy carriers (ATP and NADPH). While the light-dependent reactions capture and convert solar energy into chemical energy, the light-independent reactions use this chemical energy to synthesize glucose from carbon dioxide and water. These reactions are crucial for the plant’s ability to store energy in the form of sugars, which can be used even when sunlight is not available.

photosynthesis process

Photosynthesis is the overall process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. It consists of two main stages: light-dependent reactions and light-independent reactions (Calvin cycle).
During the light-dependent reactions, chlorophyll absorbs sunlight and uses its energy to produce ATP and NADPH while splitting water molecules to release oxygen.
Afterward, the Calvin cycle occurs in the stroma of the chloroplasts. This cycle uses the energy from ATP and NADPH to convert carbon dioxide into glucose. Understanding the distinction between these two stages is essential as the Calvin cycle (light-independent reactions) fundamentally depends on the products generated by the light-dependent reactions to function efficiently.