A rainforest plant would be least affected by the loss of the guard cell function that closes stomata.
Plants may control the quantity of water and solutes they contain by using guard cells, which use osmotic pressure to open and close stomata. Even though a plant needs an open stoma to engage in photosynthesis, it has a drawback in the form of water loss.
Water vapour from the stoma accounts for almost 95% of a plant's water loss. Therefore, it is important to maintain a delicate equilibrium that permits the passage of light and gases between cells without endangering the plant's ability to retain water.
With guard cells, this issue is reduced. A rise in solute concentration causes water to flow past the guard cell membrane. The guard cells "inflate" into two kidney-bean-like forms as their volume rises.
They open up to disclose the stoma opening in the middle of the two guard cells as they do so (similar to a hole in the centre of a doughnut). The stoma becomes open after it has fully expanded, allowing gases to flow between the cell and its surroundings.
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