 Hi, I'm Ross and I'm a researcher at ANU and I study tiny pores on the surface of leaves called stomata that have a global impact. Plants make their own food by photosynthesis. Photosynthesis takes light energy, carbon dioxide and water to produce sugars and as a byproduct also produces oxygen. For photosynthesis to occur, plants need to get the carbon dioxide from the air outside of the leaf into the leaf. Where photosynthesis occurs. As photosynthesis occurs the carbon dioxide concentration inside of the leaf decreases and this sets up a concentration gradient. Carbon dioxide then diffuses from the higher concentration outside of the leaf to the lower concentration inside of the leaf. However, at the same time inside of the leaf is very wet whereas the air outside of the leaf is typically fairly dry. And so water evaporates from the leaf and is lost to the air. Water is often a limiting resource for the plant and so if they lose too much water they can die. So plants need to control the amount of water they lose for the amount of carbon dioxide that they take up. To do this plants have evolved a pair of special elongated cells called guard cells on the surface of the leaves that surround the central pore and these pores are called stomata. Under different conditions the guard cells can inflate and deflate like a balloon increasing and decreasing the size of the central pore. The opening and closing of stomata allows plants to actively regulate the uptake of carbon dioxide for the loss of water. The rest of the surface of the leaf is covered with epidermal cells which are further covered by a thick waxy cuticle. This stops water vapour and carbon dioxide from diffusing through the surface of the leaf other than through the stomata so that all the gases move through the stomata. I investigate how plants best use their limited water resource to maximise the uptake of carbon dioxide. I do this by studying the movements of stomata under different environmental conditions. Over an uptake by land plants has been estimated at 120 gigatons of carbon per year, almost all passing through stomata. That's a lot of carbon passing through these tiny little pores. Research on stomata is important to understand the impact of plant responses to the environment on the world's carbon and water cycles as well as helping us develop better water use in crops.