Specialised cells- Guard cells

Guard cells are at bottom of leaf to stop excess loss of water. They react to changes in sunlight, gases and humidity.

• The Lower Epidermis of the leaf contains Pores known as Stomata, which allow the movement of gases in and out of the leaf. A Stoma is made from two Guard Cells. These have spiral thickenings of Cellulose which mean that when the Cells are Turgid, the Stoma opens, and when they are Flaccid, the Stoma closes.

When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity), a proton pump drives protons (H+) from the guard cells. This means that the cells' electrical potential becomes increasingly negative. The negative potential opens potassium voltage - gated channels and so an uptake of potassium ions (K+) occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. in some cases chloride ions enter, while in other plants the organic ion…