[Music] hi and welcome back to three sighs lessons cold dot uk' by the end of this video you should be able to interpret graphs to determine the limiting factor in photosynthesis you should then be able to explain how greenhouses are used to increase the rate of photosynthesis now this topic is for higher-tier students only it can look difficult but please stick with it and you will get it in the last video we looked at the equation for photosynthesis we saw that light energy is absorbed by chlorophyll and used to react carbon dioxide with water to make the sugar glucose oxygen is also a product in this reaction we then saw that if we increase the light intensity and measure the rate of photosynthesis we get a graph like this initially the rate of photosynthesis increases as we increase the light intensity this tells us that light intensity is the limiting factor at this point in other words the rate of photosynthesis is limited by the light intensity however at a certain point the rate of photosynthesis stops increasing now light intensity is no longer the limiting factor so something else must be limiting so the question is how would we determine the limiting factor now well as we saw in the last video there are three other factors that limit photosynthesis these are the carbon dioxide concentration the temperature and the amount of chlorophyll in the leaves now we can't do much to change the amount of chlorophyll but we can change the temperature on the concentration of carbon dioxide so this graph shows the same experiment but with a higher concentration of carbon dioxide as you can see when the concentration of carbon dioxide is increased the rate of photosynthesis increases this tells us that the concentration of carbon dioxide was the limiting factor so the question is once again what's the limiting factor this time well if we increase the concentration of carbon dioxide one more time we get this graph as you can see the rate of photosynthesis hasn't changed so carbon dioxide concentration was no longer the limiting factor in this case that's because at the higher concentration there was plenty of carbon dioxide available so what happens if we now increase the temperature well here's the graph and as you can see at the higher temperature the rate of photosynthesis has increased so that tells us that temperature was a limiting factor however as we said in the last video if we increase the temperature too much then the enzymes in the leaf will start to denature armed the rate of photosynthesis will fall so as we've seen light intensity carbon dioxide concentration and temperature can all act as limiting factors so can the amount of chlorophyll in the leaf now the idea of limiting factors can be exploited to increase the way to photosynthesis and to do that we use a greenhouse like this one farmers want to increase the rate of photosynthesis as this increases the yield of crops they produce to do this farmers light and heat their greenhouses they also add extra carbon dioxide now there was a problem here because it's actually quite expensive to do this so the extra cost has to be justified by the increase in yield some gardeners use oil burners as these release heat and carbon dioxide at the same time remember you'll find plenty of questions on limiting factors in my vision workbook and you can get that by clicking on the link above ok so hopefully now you should be able to interpret graphs to determine the limiting factor in photosynthesis you should then be able to explain how greenhouses are used to increase the rate of photosynthesis [Music]