What physical change occurs in a wilting plant?

Wilting in plants primarily involves the loss of turgor pressure in the cells, which is the internal pressure exerted by the fluid in the central vacuole against the cell wall. This pressure helps maintain the plant's structure and rigidity. When a plant wilts due to insufficient water, the cells lose their turgor, causing the leaves and stems to droop. This drooping is a visible sign that the plant is not receiving adequate water to maintain its normal upright posture.

In contrast, standing leaves and stems would indicate a healthy plant receiving enough water and nutrients. Yellowing of leaves is typically related to nutrient deficiency or stress factors, not wilting itself, and thickening of leaves is a process that can occur in plants as an adaptation to certain environmental conditions, rather than as a direct result of wilting. Therefore, the characteristic drooping of leaves and stems is the clearest indication of physical change associated with a wilting plant.