Which complex biochemical cycle fixes carbon dioxide into organic sugars inside the stroma of plant chloroplasts?

The process of converting carbon dioxide into organic sugars (like glucose) in plant chloroplasts is known as photosynthesis. Specifically, the "fixing" of carbon dioxide occurs during the light-independent reactions.

• A. The Cori Cycle: This cycle is involved in glucose metabolism between muscle and liver in animals.
• B. The Calvin Cycle: This cycle is the set of light-independent reactions of photosynthesis that take place in the stroma of chloroplasts, where carbon dioxide is converted into glucose.
• C. The Urea Cycle: This cycle occurs in the liver of animals and converts ammonia into urea.
• D. The Krebs Cycle (Citric Acid Cycle): This cycle is part of cellular respiration and occurs in the mitochondria, breaking down glucose derivatives, not synthesizing them from carbon dioxide.

Based on the description, the Calvin Cycle is responsible for fixing carbon dioxide into organic sugars in the stroma of plant chloroplasts.

The correct answer is B.
$\boxed{\text{B. The Calvin Cycle}}$