Plants look wilted when they lose water because the cells in the plant lose their turgor pressure. Turgor pressure is the pressure exerted by the cell contents against the cell wall. When a plant cell is full of water, the turgor pressure is high and the cell is firm. When a plant cell loses water, the turgor pressure decreases and the cell becomes soft and wilted.

The loss of turgor pressure can also cause the leaves of a plant to droop. This is because the leaves are supported by the turgor pressure of the cells in the petioles (the stalks that connect the leaves to the stem). When the turgor pressure decreases, the petioles become soft and the leaves droop.

Wilting is a plant's natural response to water loss. It is a way for the plant to conserve water and prevent further damage to the cells. When a plant wilts, it closes its stomata (the pores on the leaves that allow for gas exchange) and reduces the rate of transpiration (the loss of water vapor from the leaves). This helps to slow down the rate of water loss and allows the plant to recover.