stamata are little openings or pores on the lower epidermis of the leaf this diagram shows a leaf cross-section at the bottom of the leaf you can see a gap which is called a sto bear in mind that we use the word sto when it's just one this is the singular when there's more than one sto we use the plural which is stomata so remember one sto lots of stomata so what type of cells surround stomata the stamata are surrounded by cells known as guard cells allowing the plant to open and close the pores you need to be aware of stamata and the guard cells that surround them this image shows a leaf cross-section notice that the opening underneath is surrounded by guard cells these guard cells control the size of the opening or the pore that we call the sto this is the view that we would get of the Guard cell if we were looking into the leaf from the underside here we see a single open sto and one closed so what is the function of the stomata when the stamata are open carbon dioxide diffuses into the airspace and into the cells down a concentration gradient you need to learn that the role of the stamata and the guard cells are to control gas exchange and water loss within the leaf in this diagram you can see the inside of the leaf in this area and the outside Beyond these cells carbon dioxide moves from an area of high concentration to an area of lower concentration inside the leaves as CO2 is being used for photosynthesis within the leaf oxygen the product of photosynthesis moves in the opposite direction so as CO2 moves in oxygen moves out remember that in photosynthesis we have carbon dioxide going into the system and then oxygen comes out as a waste product what about water water vapor will diffuse out of the leaf when the stata are open once again this diagram shows the inside of the leaf here and the outside just beyond the bottom cells water is also diffusing to an area of lower water vapor which should be outside of the leaf this movement of water is called transpiration what's the role of the guard cells of the stamata to control this gas exchange and water loss it's important for the plant to be able to control the size of the pores this open sto on the left has occurred because the guard cells are swollen and they also have a thick inner wall which creates an open pore however guard cells lacking in water water become shriveled and as a result give a closed sto you need to be able to explain that the stata have guard cells that allow for the control of the size of the pores and therefore control gas exchange and water loss from the plant thanks for watching if you want to take your gcsc revision to the next level head over to Launchpad learning.com and check out our Smart Learning platform that's been designed to get you top results in your exams we cover your whole specification and make revision fun with interactive quizzes easy to follow videos and more you'll be kept motivated by your own AI tutor who's here to support you every step of the way to check it out for yourself click here or click here to keep watching a selection of the videos from our full gcsc biology course see you there