[Music] hi and welcome back to free science lessons by the end of this video you should be able to describe the structure and function of the cell walls found in Plants algae and fungi okay I'm showing you here a plant cell and one of the key features of plant cells is that they're bounded by a cellulose cell wall now the cellulose cell wall has a number of functions firstly the cell wall provides strength to the plant cell this is really important because plant cells face a significant challenge due to water is an essential reactant for photosynthesis and for other reactions taking place in the plant cell so this means that water molecules have to enter and leave the plant cell now if the water potential outside the plant cell is greater than inside then there'll be a net inflow of water molecules by osmosis this creates a great deal of hydrostatic pressure inside the plant cell pushing outwards so the plant cell wall must be mechanically strong enough to resist this hydrostatic pressure now when a plant cell is filled with water the outward hydrostatic pressure makes the cell wall rigid and this helps to support the whole plant now we can see the importance of this by looking at a plant which is wilted under certain conditions plants can lose too much water now the individual plant cells are no longer filled with water and this reduces the hydrostatic pressure pressing on the cell wall now the plant cell walls are no longer rigid and the plant can no longer maintain its structure and this causes the plant to wilt so mechanical strength is a key feature of the plant cell wall now as we said before water molecules must be able to enter and leave the plant cells so as well as being mechanically strong the plant cell wall is also permeable to water molecules the plant cell wall is made of the polysaccharide cellulose now we're going to be looking at cellulose in detail in the topic on biological molecules an individual cellulose molecule is a polymer of beta glucose cellulose molecules can form hydrogen bonds with each other forming larger structures called microfibrils and these cellulose microfibrils form a mesh-like structure in the plant cell wall this microfibril mesh is extremely strong and contributes to the mechanical strength of the plant cell wall now in between plant cells we find a layer of material called The Middle lamella the middle lamella consists of polysaccharides as well as calcium and magnesium ions and the job of the middle lamella is to act as a glue between plant cells okay now apart from in plant cells we also find cell walls in algae and in fungi and again the cell walls give the cells rigidity and contribute to the cell shape in algae the cell walls can contain both cellulose and glycoproteins whereas in fungi the cell walls are made of the polysaccharide chitin as well as other polysaccharides and glycoproteins okay so hopefully now you can describe the structure and function of the cell walls found in Plants algae and fungi [Music] oh [Music]