Question

Assertion: Regeneration of \(\mathrm{CO}_{2}\) acceptor molecule RuBP is crucial if the cycle is to continue uninterrupted. Reason: The regeneration steps require one ATP for phosphorylation to form RuBP.

Short answer

The assertion and reason are correct. The regeneration of \(\mathrm{CO}_{2}\) acceptor molecule RuBP is crucial for the Calvin Cycle, and it does require one ATP for phosphorylation to form.

Step-by-step solution

- Understand the Calvin Cycle

The Calvin Cycle is a series of biochemical redox reactions that occur in the stroma of chloroplast in photosynthetic organisms. It is crucial for fixing \(\mathrm{CO}_{2}\) into carbohydrates. The cycle consists of three stages: \(\mathrm{CO}_{2}\) fixation, reduction and regeneration of RuBP.

- Evaluate the role of RuBP

During the \(\mathrm{CO}_{2}\) fixation stage, RuBP combines with \(\mathrm{CO}_{2}\) to form two 3-carbon compound, 3-PGA (3-phosphoglycerate). Therefore, RuBP is crucial for the process as it 'accepts' \(\mathrm{CO}_{2}\). This reaction is catalyzed by the enzyme RuBisCO.

- Focus on the Need for Regeneration of RuBP

The last stage of Calvin Cycle is the regeneration of RuBP, which is crucial for the cycle to continue. The remaining five molecules of G3P are rearranged in a complex series of reactions that also involves one ATP, to form three RuBP. Thus RuBP is recreated to start another cycle.

- Assess the Reason

The reason given states that the regeneration of RuBP requires one ATP for phosphorylation. This is accurate and highlights the energy input needed for the cycle to continue, particularly for the regeneration of RuBP, affirming its critical role in the Calvin cycle.

Key concepts

RuBP regeneration

The regeneration of Ribulose bisphosphate (RuBP) is a crucial step within the Calvin Cycle, which takes place in the chloroplasts of plant cells during photosynthesis. Understanding this process is important because RuBP acts as the primary molecule that accepts carbon dioxide for the continuation of the cycle. Without the regeneration of RuBP, the entire photosynthetic process would come to a halt.

During the Calvin Cycle, RuBP is regenerated by converting glyceraldehyde-3-phosphate (G3P) molecules. Typically, it requires the rearrangement of five G3P molecules to generate three RuBP molecules. One ATP is utilized during this process for phosphorylation, which provides the necessary energy input to rearrange the molecules. This step ensures that RuBP is available again to bind with carbon dioxide, maintaining a continuous cycle of photosynthesis.

• RuBP is regenerated from G3P.
• One ATP is consumed in this process.
• Regeneration is vital for the continuity of the Calvin Cycle.

Therefore, the regeneration of RuBP, with its demand for energy, underscores its importance in the photosynthesis cycle, making it a pivotal component for the synthesis of organic compounds.

CO2 fixation

Carbon dioxide fixation is the initial stage of the Calvin Cycle where RuBP, a 5-carbon molecule, plays a key role. In this part of the cycle, RuBP combines with carbon dioxide ( CO2 ) from the atmosphere to create two molecules of 3-phosphoglycerate (3-PGA), which are three-carbon compounds. This process is catalyzed by the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase).

RuBisCO is one of the most abundant enzymes on Earth due to its essential role in the biosphere, aiding in the initial conversion of inorganic carbon ( CO2 ) into organic forms that can be utilized by plants and other photosynthetic organisms.

• CO2 combines with RuBP to form 3-PGA.
• The reaction is facilitated by RuBisCO.
• This step initiates the conversion of atmospheric CO2 to organic carbon.

This step is critical as it represents the entry of inorganic carbon into the living world, providing the building blocks for the synthesis of more complex carbohydrates that fuel plant growth and development.

Photosynthesis

Photosynthesis is the fundamental process through which plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, using water and CO2 . It takes place mainly in the leaves of plants where chloroplasts play a vital role. The overall process can be divided into two main stages: the light-dependent reactions and the Calvin Cycle.

The light-dependent reactions, also known as the photochemical phase, occur in the thylakoid membranes of chloroplasts. Here, sunlight is absorbed by chlorophyll, exciting electrons and splitting water molecules to release oxygen. This phase generates ATP and NADPH, which are then used in the Calvin Cycle. The Calvin Cycle, also known as the light-independent reactions, takes place in the stroma of the chloroplast. It utilizes ATP and NADPH from the light-dependent reactions to convert carbon dioxide into glucose through several steps including CO2 fixation, reduction, and RuBP regeneration.

• Photosynthesis consists of light-dependent and light-independent reactions.
• The Calvin Cycle is essential for converting CO2 into glucose.
• Photosynthesis is crucial for oxygen and organic molecule production.

Understanding photosynthesis provides insight into how plants produce energy, and how it sustains life on Earth by providing oxygen and serving as the foundation for food chains.