the final part of this chapter is going to be focusing about something known as the respiratory quotient also referred to as the RQ you must know the definition of RQ they may ask this in the exam there can be two definitions you can give in the exam which means the mole of carbon dioxide produced during respiration divided by the mole of oxygen used up during respiration in a period of time or the second definition is the volume of CO2 produced during respiration divided by the volume of oxygen used up uh during respiration in a period of time so for example let's look at the first definition which is using the mole of CO2 produced divided by the mole of oxygen used up so in the aerobic respiration of glucose as you can see here C6 h126 which is glucose molecules requires six oxygen molecules and when it's broken down completely it will produce six molecules of carbon dioxide and six molecules of water you can represent the six oxygen six carbon dioxide and 6 H2O as moles as well six moles so the RQ of glucose equals to remember mole of carbon dioxide produced and what was the mole of carbon dioxide produced in that case it was six in that case six moles of carbon dioxide so and then the mole of oxygen used up is basically six as well based on the chemical equation and therefore the RQ of glucose is 1.0 quite simple that way let's take another one what about aerobic respiration of fatty acids c18 h342 is a particular type of fatty acid and it requires 25.5 molecules or moles of oxygen and when it's broken down completely it gives gives you 18 moles or 18 molecules of carbon dioxide and 17 moles of Water by the way you do not need to memorize the chemical formula they will usually give you the chemical formula and they may just fill in the they may just ask you to balance the chemical equation certain exam questions would do that so uh the RQ of fatty acid in this case is 18 moles of carbon dioxide produced so 18 is the numerator and 25.5 mol of oxygen would be the denominator at and therefore 18 ID 25.5 is around 0.7 now you do have to memorize the respiratory substrates and also their matching RQ values remember when we studied the previous video I told you that your cells can use carbohydrates proteins and lipids or fats as respiratory substrates the RQ value of most carbohydrates will be around 1.0 proteins will be about about 0.9 and lipids about 0.7 this needs to be memorized especially carbohydrates and lipids they love asking that in the exam too I also want you to understand that uh we cannot calculate the RQ value for anerobic respiration for example if you look at this anerobic respiration in yeast where the yeast breaks down the glucose without the presence of oxygen it produces two molecules of carbon dioxide so two two will with the numerator but did it use any Oxygen it didn't so there are zero moles of oxygen so two may not be divided by zero it is impossible in this case that is why RQ or the respiratory quoti is only specifically used for aerobic respiration imagine for a second the person is standing on a treadmill you know those threadmill are those stationary machines that people run on it looks like a hamster wheel um yeah so so uh imagine in this case here the person has a mask attached to their um face and the mask is attached to a machine and the Machine is able to calculate the volume of CO2 the person produces and the volume of oxygen the person uses up and the Machine will then be able to immediately calculate the RQ value and based on certain activities a graph of RQ over time was plotted so for examp example in this case over here the person was asked to do four types of activity stand on the threadmill slow jog on the threadmill walk on the threadmill and Sprint on the threadmill and the Machine would calculate the person's RQ value in this case and let's look at the changes of the RQ value when the person was standing the RQ value was one and when the person started to do a slow jog the RQ value quickly decreased to 0.7 when the person was asked to walk it switches back to 1.0 but when the person was asked to Sprint the RQ value suddenly started going up so this is quite peculiar now you might be thinking oh I thought RQ values are only supposed to be between 1.0 and 0.7 why is it suddenly going above 1.0 well let's talk about it so in this case over here when the person was standing the cells were mostly using carbohydrates as a source of energy because carbohydrates can be easily broken down like glucose and such now but when the person was doing a slow jog perhaps the muscles needed more energy and the muscles switched the source of energy to lipids so more fatty acids were broken down during respiration in that case but when the person started to walk again perhaps in that case the body switched back to carbohydrates because you do not need that much energy in that case but the sprinting is the interesting one because during sprinting the RQ value goes above one remember RQ value is volume or mole of carbon dioxide produced divided by volume or mole of oxygen produced so to have a very high RQ value because the RQ value in this case is quite High either the mole of volume of carbon dioxide increases or the mole of volume of oxygen taken up decreases so in this case perhaps we can assume that the oxygen level taken used up is decreasing because that's the relationship in mathematics right when the numer when the denominator decreases the value increases so why would the oxygen level decrease in this case perhaps in that situation the person is doing more anerobic respiration there is a lack of oxygen used up so while sprinting the person switches to more anerobic respiration causing the RQ value to go up reaching a limit that does not exist so that is what we have to understand for this now let's look at a few experiments now the first experiment over here that we have to see is how to measure the RQ value this is extremely important to know so for the RQ value we start off with germinating seeds germinating seeds are just seeds that are respiring they are producing ATP and they are growing okay okay so the question over here is what are they breaking down when they are growing are they breaking down carbohydrates as a source of energy or are they breaking down lipids as a source of energy you can't ask the seeds now can you so you will have to do an experiment the experiment looks something like this you put the seeds into like a chamber and you seal the chamber but there is a capillary tube connected to the inside of the chamber all right and then after that you also have sodal lime or potassium I hydroxide or sodium hydroxide and the function of the sodal lime K or n AOH is to absorb the CO2 in the chamber so that inside the chamber only oxygen is present I mean oxygen and nitrogen will be present along with other you know uh inert gases but we don't care about the other gases we are just focused on oxygen in this case so there are no carbon dioxide molecules in there at all and of course because in the capillary tube we also put a liquid droplet all right now how does this experiment actually work now let's represent the oxygen as those dots okay you cannot see oxygen molecules obviously but I'm going to represent those dots as oxygen molecules the small little dots inside the chamber now as the seed starts using up oxygen because the seed is carrying out aerobic respiration so the seed will absorb the oxygen from the surrounding so what happens to the volume of oxygen it decreases and as the amount of oxygen in the chamber decreases what happens the droplet starts moving towards the seeds or it moves towards the left the reason why is because as the amount of oxygen in the chamber decreases the pressure also decreases in the chamber it creates a suction effect and that suction effect will pull the droplet inwards so the movement of the droplet should shows that oxygen is being used up so you're like oh okay that's good but the question here is very important how much oxygen or what's the volume of oxygen that is being used up because you can't see the oxygen you could not count the oxygen molecules could you I mean of course in my in my diagram here you can count the dots but in reality you can do that right so how would we measure the volume of oxygen used up by the seeds the answer is actually quite interesting the first thing we do is we measure the distance the droplet moves for example over the course of the experiment the droplet moves 5 mm as an example by the way and what was the reason the droplet moved 5 mm because oxygen is used up so that part where I've highlighted in pink is basically the volume of oxygen used up by the seeds but how do we measure the volume of oxygen the answer is very simple you must know the radius of the tube because the radius of the tube there as I'm giving you is 1 mm this is just an example 1 mm and the distance the droplet moves was 5 mm right so how do you calculate the volume of a cylinder in that case p r² r being the radius times or multiply It by L which is the distance the droplet moves so so < r² which is PK 1 s multiplied by 5 and when it's multiplied by 5 in this case it will give you 15.7 mm cube of oxygen was used up that was the volume of oxygen the seed used up by the way so you like oh okay so the seed used up 15.7 mm Cub of oxygen that's fine the problem is we know now know the volume of oxygen used up but we do not know the volume of carbon dioxide that was produced by the seeds why because whatever carbon dioxide that the seeds produced were absorbed by the soda line so how do we find out the volume of CO2 produced you have to repeat the experiment again but in this case you have to repeat the experiment without the soda lime potassium hydroxide or sodium hydroxide question is why so let's look at this think about it logically so let's let's imagine that as the seed uses up oxygen what happens to the liquid droplet the liquid droplet moves to the left as you can see over there so that's fine but now the seed as it carries out aerobic respiration it also produces carbon dioxide is the carbon dioxide going to be absorbed by anything no and that carbon dioxide will push the liquid vet so as it pushes the liquid vet it goes back to its original place as you can see here Oxygen's being used up by the seed again uh taken up by the seed again the seed produces carbon dioxide the carbon dioxide pushes the liquid droplet now how do we calculate the volume of CO2 produced that when you do the experiment let's say at the end of this experiment the liquid droplet only moved 0.3 mm it only moved a net movement of 0.3 mm towards the seed so how do we calculate the volume of CO2 so in this case over here the with soda lime the droplet moved 5 mm correct but without sodar lime the droplet only moved 0.3 mm the reason was because it was being pushed by the CO2 so we can assume that 4.7 mm over there 4.7 mm worth of C2 was actually produced okay so that is why the droplet did not move so much because the CO2 was also pushing back against it so in this case over here what is the volume of CO2 produced in this case you basically do the formula where the formula is PK r² * L where PK r² is just basically um Pi is Pi obviously right R in this case is one and then times L which is 4.7 mm and in this case it produces 14.8 mm Cub of carbon dioxide so in this case we have the volume of CO2 produced and we also have the volume of oxygen used up therefore the respiratory quotient in this case is 14.8 / 15.7 which gives you an answer of 0.94 so you can assume that during this respiration the seeds are using up proteins or carbohydrates as respiratory substrates because 0.94 Falls between proteins and carbohydrate proteins were 0.9 carbohydrates 1.0 so we can assume that the seed was using a lot of carbohydrates or proteins that were being broken down to be to produce use ATP as the seeds are growing okay if you're not so sure let's try another simple one in this case now this simple one over here is with soda lime and without soda lime all right so in this situation over here let's say with soda lime on the one on the left the liquid droplet moved 8 mm all right and the radius of the tube as I'm cing over there the radius is 0.3 mm right now okay the radius will be given in the exam do not worry so what is the volume of oxygen used up the volume of oxygen used up in this case is 2.3 mm Cub of oxygen that was being used up in the second experiment the without sodal lime or potassium hydroxide or sodium hydroxide the liquid droplet did move to the left but it only moved a total of uh let's say 2 mm so why did it move a total of 2 mm because the one on the left moved 8 mm the one on the right only moved 2 mm the reason is because imagine if the liquid droplet moved 8 mm because it uses up oxygen but because the carbon dioxide was being produced it pushed it back over there by a total of 6 mm which means means the net movement is only 2 mm overall by the way okay so in this case we can assume that the this is the volume which I'm highlighting here this is the volume of carbon dioxide that was being produced by the um insect so in this case what's the volume of carbon dioxide it will be pi r² r being 0.3 uh 0.3 squ * L which is 6 mm so so the volume of carbon dioxide produced by the insect is 1.7 mm Cub okay so what's the respiratory quotient of the insect in this case the respiratory quo is 1.7 divided by 2.3 and it will give you 0.74 so we can assume that in this case maybe for some reason the insect at 32° C because that's when the experiment was being done is respiring but it's not really breaking down carbohydrates is it because the RQ is 0.74 so we can assume that in this case the insects might be breaking down more lipids as a source of energy to produce ATP these are how the experiments are usually done to determine the RQ value