Which leaf shape predominates in rainy regions? Explain?

Explain why a lettuce leaf in contact with salad dressing containing salt and vinegar becomes wilted and limp,

• explain why a lettuce leaf in contact with salad dressing containing salt and vinegar becomes wilted and limp, whereas another leaf in contact with plain water remains crisp.

• Answer:

  It's a function of osmosis. When there is pure water around the leaf, then the moisture inside the cells have a lower concentration of water inside them then outside (they have more big molecules, and so are called hypertonic), and the water flows into the cells to balance the concentration. When there is salt and vinegar outside the leaf cells, then the concentration of water is higher in the cells than outside (hypotonic), and so the water flows out to equalize the water concentration. Cells are like balloons that are stiff and firm when full, but limp and slack when nearly empty. So, putting non-watery liquids around the leaf causes it to lose water and become limp. You can read all about osmosis at Wikipedia.