When the daylight hours are increased, the rate of photosynthesis: 

In the presence of sunshine and chlorophyll, plants create their own nourishment through a process called photosynthesis. It happens in the leaves' chloroplast cells.

Photosynthesis is a reaction that requires light. The light activates the chloroplast (leaves). It is a chemical process that converts carbon dioxide and water into organic food and oxygen. Organic food is used by plants to help them grow and develop.

Hence, the correct answer is option A.