No, the dark reactions of photosynthesis do not occur only at night. They are actually called "dark reactions" because they do not directly require sunlight to proceed. However, they still depend on the products of the light reactions, which do require sunlight.

Here's a breakdown:

* Light Reactions: These occur in the thylakoid membranes of chloroplasts and use sunlight to:

* Split water molecules, releasing oxygen as a byproduct.

* Produce ATP (energy) and NADPH (reducing power).

* Dark Reactions (Calvin Cycle): These occur in the stroma of chloroplasts and use the ATP and NADPH produced in the light reactions to:

* Fix carbon dioxide from the atmosphere into organic molecules like glucose.

Therefore, the dark reactions can occur both during the day and night, as long as there is a sufficient supply of ATP and NADPH from the light reactions.

In summary:

* The light reactions require sunlight.

* The dark reactions require the products of the light reactions (ATP and NADPH).

* Both reactions are essential for photosynthesis and occur continuously in plants.