The Calvin Cycle

Summary

This tutorial explains the Calvin cycle, a crucial part of photosynthesis that converts atmospheric carbon dioxide into carbohydrates. Occurring in the stroma of chloroplasts, the Calvin cycle is divided into three phases: carbon dioxide fixation, reduction, and regeneration of RuBP. The enzyme Rubisco captures CO2, which is transformed into G3P, a carbohydrate. ATP and NADPH, produced by light reactions, provide the energy for this process. The cycle must turn six times to form one glucose molecule, demonstrating its dependence on the light reactions for energy and electrons.

Takeaways

• 🌿 The plant's leaves have cells that carry out photosynthesis.
• 🔬 Chloroplasts are the organelles where the reactions of photosynthesis occur.
• 💡 Photosynthesis consists of two primary steps: the light reactions and the Calvin cycle reactions.
• 🌞 The Calvin cycle's main purpose is to convert atmospheric carbon dioxide into carbohydrates (sugars) for the plant's cellular activities.
• 🌀 The Calvin cycle takes place in the stroma of the chloroplast and uses ATP and NADPH from the light reactions.
• 🌿 The Calvin cycle has three phases: carbon dioxide fixation, carbon dioxide reduction, and regeneration of RuBP.
• 🌱 In the carbon dioxide fixation phase, CO2 is attached to RuBP, producing an unstable 6-carbon molecule that quickly splits into two 3PG molecules.
• ⚡ During carbon dioxide reduction, electrons from NADPH and energy from ATP are used to convert 3PG into G3P, a carbohydrate.
• 🍬 One G3P molecule is set aside as a building block for glucose, while the rest move forward into the regeneration phase.
• 🔄 To form one glucose molecule, the Calvin cycle must turn six times, adding one carbon atom per cycle, relying on the light reactions for ATP and NADPH.

Q & A

What is the primary purpose of the Calvin cycle?

The primary purpose of the Calvin cycle is to convert carbon dioxide from the atmosphere into carbohydrates (or sugars) that the plant needs to power its cellular activities and build new plant structures.

Where do the Calvin cycle reactions occur within the chloroplast?

The Calvin cycle reactions occur within the stroma of the chloroplast.

What molecules produced by the light reactions are used in the Calvin cycle?

The Calvin cycle uses ATP and NADPH produced by the light reactions to convert carbon dioxide into carbohydrates.

What are the three phases of the Calvin cycle?

The three phases of the Calvin cycle are carbon dioxide fixation, carbon dioxide reduction, and regeneration of RuBP.

What enzyme is involved in the carbon dioxide fixation phase of the Calvin cycle?

The enzyme involved in the carbon dioxide fixation phase is called Rubisco.

What is the initial product formed after carbon dioxide fixation?

The initial product is an unstable 6-carbon molecule that quickly splits into two 3-carbon molecules called 3-phosphoglycerate (3PG).

What happens during the carbon dioxide reduction phase?

During the carbon dioxide reduction phase, NADPH and ATP from the light reactions supply electrons and energy to reduce 3PG into G3P, a carbohydrate.

What is G3P, and what role does it play in the Calvin cycle?

G3P is a 3-carbon carbohydrate formed during the carbon dioxide reduction phase. One G3P molecule is set aside to build glucose, while the rest are used in the regeneration of RuBP.

How many turns of the Calvin cycle are required to form one glucose molecule?

Six turns of the Calvin cycle are required to form one glucose molecule because each turn adds only one carbon atom from the incoming carbon dioxide.

Why is the Calvin cycle dependent on the light reactions?

The Calvin cycle is dependent on the light reactions because they provide NADPH and ATP, which supply the electrons and energy needed to reduce carbon dioxide and form carbohydrates.