Mitochondria is described as the power house of the cell, because it is the cell organelle that process the production of ATP, which is the energy source of the cell. Kreb's cycle occurs in the mitochondria, it is the process by which energy is generated inside the cell, leading to the production of ATP and carbon dioxide and water are given up as waste products.
This is to prevent water loss by the trees. Under drought or dry conditions, plants may close their stomata to limit the amount of water that evaporates from their leaves a process called transpiration. In this process water diffuses through the stomata into the atmosphere, in a bid to preserve water plants may close their stomata, especially during very dry climates.