Leaves and green stems of plants make food during the day, specifically when they are exposed to sunlight. This process is called photosynthesis.

Here's a breakdown:

* Sunlight: Provides the energy needed for photosynthesis.

* Chlorophyll: The green pigment in leaves and stems absorbs sunlight.

* Carbon dioxide: Plants take in carbon dioxide from the air.

* Water: Plants absorb water from the soil through their roots.

Using these ingredients, plants convert light energy into chemical energy stored in the form of sugars (glucose). This glucose is the plant's food, providing energy for growth and other processes.

So, while leaves and stems are constantly working, they only produce food when sunlight is present.