okay so the next thing that we actually have to talk about uh as a quick video is the factors affecting transpiration rate so what environmental factors will increase the rate of transpiration or decrease the rate of transpiration so the first factor that can affect transpiration rate is obviously temperature so you can see my cross-section of the leaf over here I have two cross-sections one cross-section has the leaf in lower temperature and one has the leave at a higher temperature so obviously in this case if the plant is exposed to a higher temperature more evaporation of water happens through the mesophile cell wall it will form more water vapor in the air space and because it has a higher temperature the water vapor has a higher kinetic energy and you remember that if the particles have a higher kinetic energy diffusion rate increases thus the the plant loses more water and in this case plants subjected to a higher temperature will have a higher rate of transpiration simple stuff light intensity is a rather interesting one as well light intensity just means the strength of the light so immediately students will go oh well the brighter the light the higher the temperature I don't want you to assume that it's due to the temperature by the way in fact what I'm to say is Imagine three different plants exposed to three different light intensity dark low light intensity and high light intensity but all their temperatures are exactly the same okay imagine that all their temperatures are exactly the same so temperature is not a factor here we are focusing more on the light intensity which Leaf will have a higher rate of transpiration well when it's dark the leaf does not do any photosynthesis because they need light to undergo photosynthesis right so in that case what just needs to happen is the stomata or the sto will be closed because they do not need to take any carbon dioxide in from the outside air so when the stomata is closed water vapor inside the leaf air space cannot diffuse out thus the leaf will not lose any water through transpiration when it has a low light intens it the stomata are slightly open and when the stomata are slightly open to allow some carbon dioxide to go inside the leaf why does it need a little bit of carbon dioxide well because it's doing a little bit of photosynthesis because there is a little bit of light they can't do they can't they don't need a lot of carbon dioxide in that case so the stomata just opens very slightly and because the stomata opens very slightly uh not a lot of water vapor can also diffuse out through the very tight space so the leaf will lose a little bit of water vapor transpiration is happening but the leaf is not losing too much water in the process so that's fine however when the leaf is exposed to a high light intensity the stomata opens much wider the reason why it opens much wider is because the plant needs more CO2 so that it can do more photosynthesis more water vapor can actually def use out through the Gap and thus the plant loses a lot more water in the process so light intensity is actually correlated to how wide the stomata will open and The Wider the stomata open more transpiration takes place in the process another factor that we want to talk about is something known as humidity now I do get a lot of students asking me the question as to what exactly is humidity all about so humidity itself what I'm going to do is I'm going to show you two images right now okay and the two images over here as you can see one in the forest one sort of like a desert which area is more humid immediately A lot of my students will be like yeah I know what humidity they can kind of have a sense of what humidity is but they don't know how to explain it so a lot of my students will say the image on the right is very humid and the image on the left is not humid at all in fact we say it's very arid all right although an area of low humidity okay humidity is just the measure of moisture or water vapor in the air so on the image on the right there's a lot of moisture in the air because you can see the Mist it's so Misty right and foggy which is formed due to the condensation of the water vapor and on the image on the left you can kind of imagine the air is extremely dry because there's not much moisture so the image on the left has a low humidity and the image on the right has a high humidity and humidity is not necessarily related to temperature because for example you can have a very cold environment too as I've shown as I'm showing you here and that very cold environment can be quite dry as well so humidity is not necessarily linked with temperature all the time by the way therefore humidity is just the measure of moisture in the air so what does this have to do with transpiration so imagine a leaf exposed to low humidity as I've shown you there the amount of moisture or water vapor in the air is very low and in the high humidity Leaf the amount of moisture or water vapor in the air is very high now imagine for a second that both Leaf under go evaporation of water from the mesop cell wall and they form water vapor inside the leaf asir space as I'm circling over there for you in which Leaf will it undergo a higher rate of transpiration so you have to mold this over and consider something known as a concentration gradient you must compare the water vapor concentration inside the leaf and outside the leaf for the diagram on the left the amount of water vapor inside the leaf is very high and the concentration of water vapor outside the leaf is very low thus they will have something referred to as a very steep concentration gradient and when the concentration gradient is extremely steep diffusion will happen at a higher rate and therefore the plant loses more water through transpiration but on the right side however the the concentration of water vapor inside the leaf is high and outside the leaf is also quite high as well therefore the concentration gradient is not as steep in fact it has something called a less steep concentration gradient therefore defusion rate in this case is lower so the plant will undergo less transpiration in the process these are the three environmental factors that can actually affect transpiration rate you must know all three factors and how they affect transpiration rate in detail