Gas Exchange in Plants Structure and function of stomata and guard cells.

Gas Exchange in Gas Exchange in PlantsPlantsStructure and function of stomata Structure and function of stomata and guard cellsand guard cells

Structure and function of Structure and function of stomatastomata

Generally stomata open during day and Generally stomata open during day and close during the night. The guard cells on close during the night. The guard cells on each side of the stoma pore control the each side of the stoma pore control the size of the poor by changing their shape.size of the poor by changing their shape.


Make your own clear and labelled Make your own clear and labelled diagram of the stomata and guard cells diagram of the stomata and guard cells from p28 of Systems & Their from p28 of Systems & Their MaintenanceMaintenance

The process of drawing these structures The process of drawing these structures will help you learn them!will help you learn them!


If water enters the guard cells, they swell If water enters the guard cells, they swell up and the stoma pore opens.up and the stoma pore opens.

If water leaves the guard cells, they If water leaves the guard cells, they become flaccid and the stoma pore become flaccid and the stoma pore closes.closes.


These changes are thought to be These changes are thought to be due to a reversible uptake and due to a reversible uptake and loss of loss of potassiumpotassium ions by the ions by the guard cells.guard cells.


During the day the chloroplasts inside the During the day the chloroplasts inside the guard cells photosynthesise.guard cells photosynthesise.

As a result they produce ATP, which As a result they produce ATP, which fuels an active transport mechanism that fuels an active transport mechanism that takes up potassium ions from the takes up potassium ions from the surrounding epidermal cells.surrounding epidermal cells.


This lowers the water potential in the This lowers the water potential in the guard cells and water enters by osmosis, guard cells and water enters by osmosis, the guard cells become turgid and the the guard cells become turgid and the stoma pore opens.stoma pore opens.


At night the chloroplasts in the guard At night the chloroplasts in the guard cells do not photosynthesise.cells do not photosynthesise.

Less ATP is available for the active Less ATP is available for the active uptake of potassium ions, which then uptake of potassium ions, which then leave the guard cells by diffusion.leave the guard cells by diffusion.


The loss of the potassium ions raises the The loss of the potassium ions raises the water potential of the guard cell, water water potential of the guard cell, water passes out into the epidermal cells, passes out into the epidermal cells, which have a more negative water which have a more negative water potential.potential.

The guard cells become flaccid and the The guard cells become flaccid and the stoma pore closes.stoma pore closes.

Gas Exchange in Plants Structure and function of stomata and guard cells.

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