What does phototropism refer to?

Phototropism refers specifically to the growth of plants in response to light stimuli, where they bend or lean towards the light source. This phenomenon occurs because certain areas of the plant, usually the stems, have cells that elongate when exposed to light, causing the plant to grow towards it. This adaptation allows plants to maximize their exposure to sunlight, which is essential for photosynthesis—the process by which they convert light energy into chemical energy.

The other options highlight different plant responses or processes but do not relate directly to the concept of phototropism. For instance, the first option deals with disease defense mechanisms in plants, while the third touches on interactions with insects, which is a separate aspect of plant biology. The last option describes abscission, the natural process of shedding leaves, particularly in response to seasonal changes, but does not involve growth direction in response to light.