Calvin cycle | Dark reaction | C3 Cycle | Photosynthesis | Home Revise

Summary

The dark phase of photosynthesis, known as the Calvin cycle, occurs in the stroma of chloroplasts and is a light-independent process where carbon dioxide is fixed into carbohydrates like glucose. Key enzymes, notably rubisco, catalyze this reaction, utilizing ATP and NADPH generated during the light reactions. The overall chemical equation summarizes the transformation of reactants, including ribulose bisphosphate (RuBP) and carbon dioxide, into glucose and other byproducts. The Calvin cycle runs continuously alongside the light reactions, showcasing the intricate interplay of these essential processes in photosynthesis.

Takeaways

• 🌱 The dark phase of photosynthesis is also known as the Calvin cycle.
• 🧪 This phase occurs in the stroma of chloroplasts and is a light-independent reaction.
• 🔬 Carbon dioxide fixation occurs through a series of enzyme-catalyzed steps during the biosynthetic phase.
• 📚 The reactions in this phase were discovered by Melvin Calvin and Andy Benson.
• 🔄 The Calvin Benson cycle begins with carbon dioxide entering through the compound ribulose bisphosphate (RuBP).
• ⚙️ The enzyme ribulose bisphosphate carboxylase (rubisco) catalyzes the fixation of carbon dioxide.
• 💡 ATP and NADPH produced during the light reaction provide the energy required for carbon fixation.
• 🌟 Hydrogen from NADPH combines with carbon dioxide to produce glucose (C6H12O6).
• 🧮 The overall chemical reaction can be summarized as: 6 RuBP + 6 CO2 + 18 ATP + 12 NADPH + 12 H+ → 6 RuBP + C6H12O6 + 18 Pi + 18 ADP + 12 NADP + 6 H2O.
• 🔄 RuBP is regenerated to restart the Calvin Benson cycle, which occurs simultaneously with the light reaction.

Q & A

What is the dark phase of photosynthesis?

The dark phase, also known as the Calvin cycle, is the biosynthetic phase of photosynthesis where carbon dioxide fixation occurs.

Where does the dark reaction take place?

The dark reaction occurs in the stroma of chloroplasts.

Why is the dark reaction called the light-independent reaction?

It is called the light-independent reaction because it does not directly require light to occur, unlike the light reactions of photosynthesis.

Who discovered the reactions involved in the Calvin cycle?

The reactions involved in the Calvin cycle were discovered by Melvin Calvin and Andy Benson.

What is the role of ribulose bisphosphate (RuBP) in the Calvin cycle?

RuBP acts as a carbon dioxide acceptor compound that enters the Calvin cycle, facilitating the fixation of carbon dioxide.

What enzyme catalyzes the fixation of carbon dioxide in the Calvin cycle?

The enzyme that catalyzes the fixation of carbon dioxide is ribulose bisphosphate carboxylase, commonly referred to as Rubisco.

What substances provide the energy needed to fix carbon dioxide in the Calvin cycle?

ATP and NADPH produced during the light reactions provide the necessary energy for fixing carbon dioxide.

What is the overall summary of the chemical reactions in the Calvin cycle?

The overall reaction can be summarized as: 6 RuBP + 6 CO2 + 18 ATP + 12 NADPH + 12 H+ ions → 6 RuBP + C6H12O6 + 18 Pi + 18 ADP + 12 NADP+ + 6 H2O.

How is RuBP regenerated in the Calvin cycle?

RuBP is regenerated to start the Calvin cycle again through a series of enzyme-catalyzed reactions after glucose is synthesized.

How do the light reactions and dark reactions interact during photosynthesis?

The dark reactions occur simultaneously with the light reactions, with a minimal time gap between the two processes, less than one thousandth of a second.