 Hi I'm Dr. Caitlin Burt from the Australian National University and our lab here works on a type of protein that's located in membranes of all kinds of kingdoms of life including plants and these little proteins help to facilitate the transport of water and nutrients across the membrane. It's part of a process that's really important for how cells manage to control both water and nutrient influx and efflux from cells. Materials that are in a gas form or a liquid form diffuse. They diffuse from where they are present in a higher concentration to where they find a lower concentration. For example the molecules of this dye that we dropped into a beaker of water start off close together and then they diffuse through the water which means that they move apart from each other towards areas of the beaker that are lower in dye concentration. Diffusion is the net movement of anything from a region of higher concentration to a region of lower concentration and diffusion is driven by the gradient in concentration. Diffusion is important for living things because substances move in and out of cells by diffusion. Cells are surrounded by a membrane which influences which substances move in and out and how fast. Cell membranes are made out of phospholipids and they contain proteins which can influence the type of substances that move in and out of the cell. Some small molecules such as water, oxygen and carbon dioxide can pass through the phospholipid membrane by diffusion. Substances can also move in and out of the cell through transport proteins present in the cell membrane such as channels or active transport proteins. Another way that substances can be moved in and out of the cell is by endocytosis or exocytosis which is where smaller membrane bound vesicles can form within or fuse with the cell membrane and these vesicles can contribute to transporting substances in or out of the cell. The movement of molecules across the cell membranes is influenced by the concentration gradient. Molecules will move in the direction of where there is a relatively lower concentration. The surface area to volume ratio of the cell influences the movement of molecules. For example, when there is more cell volume and less surface area diffusion takes longer and diffusion happens faster when there is more surface area relative to volume. One example of diffusion that is of great significance to life on earth is the diffusion of carbon dioxide from the air through plant leaves. Carbon dioxide moves by diffusion through small holes in leaves called stomata. Plant stomata have guard cells that control the opening and closing of the stomata so that the leaf does not lose too much water when the stomata open to take in carbon dioxide. The movement of carbon dioxide into leaf cells by diffusion is important because carbon dioxide is needed for photosynthesis. Photosynthesis keeps the plants and animals on earth alive because it is the process by which plants take water, carbon dioxide and light and make sugar and oxygen. The sugar and oxygen from plants gives us food to eat and air to breathe.