Let's go. We had our test results. Aha, how did. You do. I got 41 out of 42. Brilliant. And what was on that test? Wait, I think it was the one about like the reflecting lights and the other one was about like the this like their leaves, cells and stuff. Was it animal nutrition? Yeah. Okay. So it's a bit of animal nutrition and then light that was no, I think it was a part nutrition, one part nutrition and waves and light. Oh, how come it was plant nutrition? I thought you were still doing that. Yeah, we were. But like we only we own Ned the test there was like only half this thing we learned, right? Okay, that's strange. Why did they give you a test with just half a topic on? Because like it was like at the end of the term, but like actually no classes have finished that lesson. So like Yeah so everybody's a bit behind Yeah Yeah. Well, sometimes lessons get cancelled because of other school events and things, don't they? So maybe that's why. Okay. So we're going to be a little bit ahead of you, but that's not a problem and you won't necessarily cover this part of the topic. I'm not sure sometimes it's left for gcse. But we're going to do it because you can cope with it. So we're looking at the limiting factors of photosynthesis. And can you read that, please, Linda? Learning objective to understand how limiting factors affect the rate of photosynicsis success criteria, to identify and describe the key limiting factors of photosynthesis, to draw a graph using experimental data, to evaluate the suitability of experimental methods used for measuring the rate of photosynthesis, and what do you think is meant by limiting factors? Like. Like maybe like for example, the carbon dioxide needed Mhmm. Or like the water they receive and like how much light and stuff good. So how much carbon dioxide, how much water and how much light they receive. Yeah. Sounds ds, very sensible suggestions. So we are going to look at the idea of baking a cake just for students who don't quite get this concept of limiting factors. So imagine you are baking a cake. Here is the recipe. These are the quantities of flour, sugar, butter, eggs and vanilla extrts. So you look in your cupboards, and this is what you find. So, 800 grams of flour, 500 of sugar, 250 of butter, four eggs and a whole bottle of vanilla extract, how many cakes can you make? One because because there's only four eggs exactly. So what is the limiting factor? The eggs the eggs what would the next limiting factor be? The butter, the butter Yeah plenty of flour not going to run out of that. And enough sugar for two cakes and plenty of vanilla extract. So eggs, and after you've made one cake, butter, they are the limiting factors for this cake baking. Okay, you got that. So it doesn't matter how much of the other ingredients you have, the amount of eggs limits how many cakes that you can make. So you buy six more eggs and 250 grams more of butter. How many cakes can you make? You can make. Two good two cakes Yeah and the Anshas already come up. This time it is sugar. You got enough sugar for two cakes, but not enough for three. And of course, you wouldn't quite have enough butter for three anyway. So that's with the cake. But we're talking about photosynthesis. So a limiting factor is something that restricts or dictates the rates of a chemical reaction. So this isn't just something for photosynthesis. This is a chemistry concept. So this will apply to all reactions. So can you read this next bit here? Plants to phosynthesis they require sunlight, and there is no sunlight does limit the rate at which a plant and photosynthesis photosynthesize. Ntheare you on a computer or are you on your phone today? On my iPad. Okay, so your screen is big enough. Like it's like a small one, so okay, so not huge, right? Fair enough, but you can you can zoom in onto things. Oh, you know Oh, you can't you can't do that, right? Okay. Yeah, right. So if anything is particularly small, you can tell me and I can zoom in on it for you. So what other factors might limit the rate of photosynthesis? Well, I think you said water and you said carbon dioxide, and you said light. What else that I said is sometimes written above or below the arrow. Chlorophyll, yes. So if we have got a plant with a nutrient deficiency like we saw last week with yellow leaves, that may become a limiting factor. Now obviously, the reactants products, sorry, it's just the reactants that are limiting factors, not the products. And another one that we haven't mentioned here, temperature. Now y temperature. Is it like if the temperature is like really high, there is less water? And b, it can also be to do with. The gases dissolved in the air are going to be lower at higher temperatures. And it can be to do with, if you think about enzymes, these require certain temperatures to work. Okay. Let me look at our first so what we're going to do. So we're going to look at two ways to investigate limiting factors in plants. So there's two different methods. I'm going to show you a quick video of one of the methods, and I think we'll start at that point if it will play. Let's see if it will play. Right, is that playing for you? No, okay, let me give it another minute. Right. I'm just going to turn the volume down. So it's very loud for me. So I haven't shared the volume. I'll do that. I'll share the volume and then I'll try again. And we'll just give it a minute because sometimes it might need your Internet to just catch up. What can you see at the moment? Creates a hypothesis. And now it's like materials. So is it just changing the screen but it's not actually playing? Right. The other thing I Yeah I think like there's like music. I've paused it now let me Press play again. Yeah, there's music. And is the screen moving? It's like appearing names. Like it's ping water. Yep. So it's working for you now. Okay. I'm going to go back to the beginning then. So this is one method. For calculating the itting factors in photosynthesis, I want you to think about the method and think about any shortcomings. I'm going to pause it every now and then to explain bits. So to quantify photosynthesis, so to give us actual data and figures to find out how much photosynthesis is taking place. Now it says bubbling plants. What do you think the bubbles are? Yeah, good. Now what type of plant is this? It looks like one of the plants that like can open and close, it's actually pondweed. So it's an aquatic plant, so you might not be able to see very clearly, but it's actually in a beaker with a bit of water in. So this is pond weed. So why would we do this experiment with an aquatic plant in water? The clue is in the. Why are we using an aquatic, so a plant that lives in water, to do this experiment? There's no like oxygen like there's no oxygen in water and like you can see oxygen like clearly in water, right? There is oxygen dissolved in water. Otherwise fish would not be able to live in water. So there is oxygen dissolved in water, but you don't see it as bubbles necessarily, but we will see it as bubbles when it is being released from the plant. So that's why it's so we can see the bubbles of oxygen being released because, of course, we wouldn't see it just in air. That's just the photosynthesis equation. So does the amount of light change the amount of photosynthesis a plant produces? Now that's not phrased very well. It doesn't exactly produce photosynthesis as it so carries out. I think would be better. Okay, we have got baking soda. And what this is, is something called sodium hydrogen carbonate. And that just gives a source of carbon dioxide in the water. So there is plenty of carbon dioxide and it won't become a limiting factor. So that's what that's for. Aged tap water, that is just tap water that has been sitting around so that the oxygen, the dissolved oxygen will leave it. And if you think about if you turn your tap on and pour yourself a glass of water, there are going to be some bubbles in it. So you want to let those rise to the surface and pop so that you're not counting those rather than oxygen released from your palm weed. Okay, so the baking soda is adding carbon dioxide. Just weighing it down with a rock so that it doesn't rise to the top. So that says we'll be quantifying the amount of photosynthesis that occurs in a given period of time by counting the bubbles that rise to the surface. But that was just giving it five minutes to acclimatize without the light on. And they said, you may not even see any bubbles in that time. And now you can start to see the bubbles. So this is quite a basic experiment. They had light and no light. How would they have made that a bit more quantitative? Like when they did like no light and stuturn like every single light, like make sure that there's like clip, like no light source, like appall okay. So then they've got Yeah Carry on. And like so maybe they should add like another kind of light, like a wine that's like light but like not that light. And what purpose would that have? Like I don't know. So we want to know whether the light intensity has an effect on the rate of photosynthesis. Sorry, I've still got a bit of cough. Ernie bothers me when I'm talking too much. So rate of photosynthesis, how is that affected by the light levels? So we can do the dark at the start, that's fine. But then to change the intensity of the light, we just need to alter the distance of the light from the pond weed. So we could start with it maybe half a metre away for five minutes and then 10 cm closer for five minutes, count the bubbles and so on, until we get to the situation they have where it's right on top of the beaker. Does that make sense, Linda? So that's going to give you a better set of results so that you can plot a graph because you can plot a graph with these results at the moment. Now what sort of errors can you think of in that setup? What you're having to do for five minutes, like wait. What you're looking at Yeah at first, but then when you put the light right over it, what you're doing for five minutes. What are you recording like? Count the number of bubbles. Count the number of bubbles. Now what if you look away? You you might get the experiment wrong. You're gonna miss gonna miss a bubble. It's quite a long time to be staring at something counting bubbles. Lots of people will get a little bit bored. And if you have got more than one bubble being formed at the same time, it's going to be very easy to count that incorrectly. So a lot of human error there. We're counting bubbles. Are the bubbles all going to be the same size? No, you might have already quite a big bubble with lots of oxygen in it and then a tiny one. So this isn't really telling us about how much oxygen is produced, is it? What would be more accurate? Like to count the bubbles, not counting the bubbles. We want to know the volume of oxygen. So that would be a more accurate way of doing it. Let me show you the setup for that because I don't don't think I have a picture of that. So this is. Okay. So this will give you an idea. So this is an improvement on the method. So we've just got an inverted, so an upside down funnel still got up onweed. And then we have got a test tube. And what you do is you use the principle of displacement. Do you understand what that means? So it's one thing pushing another thing out the way. So if you completely fill that test tube with water, the oxygen will push the water. So at the start, it was completely filled with water. As the bubbles rise up in there, they push the water out the way. So this level would rise very slightly and your tube would start to become filled with oxygen. Now what you can do is you can measure that with a ruler. Or an even better way of doing it should be on one of these worksheets. So let's get it. Here we go. And you see what we've got here? Yeah, like the method one and method two. Can you see what I've circled in the picture and make it bigger for you? Yeah. The syringe thing. The syringe, and there's little Marks on it. So if we attach that instead of the test tube and we collected the gas in that, we could actually get volume. So that's going to be more accurate. So let's just quickly go through these two methods. Right, just making that as big for you. So pond weed, sodium hydrogen carbonate solution that just adds carbon dioxide, boiling tube, clamp stand, etc. Let's find a picture for you. There we are. So they're just doing this on a slightly smaller scale than in a beaker, possibly make it a bit easier to count the bubbles. What do you notice at the bottom here? They got at the bottom here. Say that again, Linda ruler, they've got a ruler, so they can alter the distance of the lamp. Now on the second experiment. Exactly the same. But they have connected, Hey, we call this a gas syringe because it's a syringe for gases rather than a syringe for liquids. They have connected a gas syringe so they can measure the volume. Now, more than likely, that gas syringe is probably going to be too big. They would probably need one that would be much smaller than that because you're not going to get huge volumes of oxygen from that plant. So theyneed a thinner one. Right now, let's have a look at some results here. I'm going to show you something quickly and see if it will work. So usually I get students to do this themselves on their computer. But I'm not sure itwork for you today. Play. Hello, welcome to atomic lab. I'm al albe. Let's get started. Select you can access the. So this is just a simulation. I've opened the lab book on the overview. This explains what we are trying to do. This is the instructions section. You can select this to see the steps required to complete an experiment. When you complete an expite, that's the board. Okay. First we need to place the pond weed into the beaker. Is this showing on your screen? Lender? Yeah, okay, so I'll just set it up so that you can get an idea. Now move the lamp into position 30 cm away. Okay, so they're starting 30 cm. Tap on the lamp and let's slide it up. Okay. We need to leave the pond weed for five minutes to acclimatize. So this is the five minutes in the beginning to get it to acclimatize. And this is really just to get it starting to photosynthesize. The pond weed produces bubbles of oxygen during photosynthesis. For one minute, tap the clicker to count the number of bubbles reduced. Tap the clicker once for each bubble that is produced. And then it's just a case of counting the bubbles. And at this distance, there isn't very many bubbles. I won't go through the whole thing. I'll just show you the next one. Okay, time's up. We'll keep a record of your results in this table. Now we need to abto perfect. Let's. Okay, same process. Tap the clicker once for each. I think I tapped it then and there wasn't a bubble, so I won't tap it again. And obviously, because the light intensity is greater, you would expect there to be a higher number of bubbles. So I won't go through all that for you. I've got a set of results for you anyway, that's just to show you the setup. Okay, let's go on to our next one. Are you okay, Linda? Yeah, okay, brilliant. Just close a few of these. Right. Let me give you some results now. Are you able to write on the screen? Yeah, okay. Right. So first one, this is just when we're counting the bubbles with the test tube. Wait, that was the accident, all right? Right, 699. And that's given you an average of eight. Now notice they have not changed the distance of the light in this next one, same thing, but with the syringe. Two, three and a half. 22.5. Right, I don't need you to write today, you can just answer this for me. So can you suggest three variables that should be controlled in both of the methods? The temperature of the water good. Wait. Maybe like the size of the plant. Yeah, you can either share the length of it like we saw in the video, or I guess you could weigh it. One more carbon dioxide. Yep. So how much of the sodium hydrogen carbonate you add? And that's just a White powder. So same amount of that to each seup. The other thing is the distance of the lamp. So this wasn't changed. So whatever distance they picked had to be the same for both. And you could also say make sure that both experiments are acclimatized beforehand in the same way. Mate, don't need to comment on that next one because you didn't actually do it. Great advantages and disadvantages. So advantages of the counting the bubbles one. There are like no de like very like complicated steps and stuff. Yeah, so we can say easy to set up. Did it give some results? Yeah. Like it gives like the number of bubbles? Yeah. And if you changed the distance of the light, you would have been able to plottograph with that. What about disadvantages? Like it's hard to cathe bubbles. You might like miss small ones. Yeah. So a high chance of human error. And bubble sizes are not the same. Each bubble is going to contain a different volume of oxygen. So the next experiment. Order to set up Yeah possibility of breaking some of the delicate glassware as well. What did I say about Yeah like when you put the thing, there might be like oxygen getting out or like disappearing or like dissolving. So like you can't like get like a really accurate number. You mean if you haven't set it up properly and it's not airtight? Yeah, Yeah, that would be human error in setting it up. If you set it up properly, they shouldn't be anywhere to go rather than into the gas syringe. Remember, we said that we're dealing with very small volumes of gas. You're going to need quite a small syringe. And in one minute, maybe you wouldn't even be able to measure how much oxygen was given off. So this experiment with the syringe maybe needs to be left longer. What's advantages, though? It like give like a precise value Yeah. And all of the gas is counted as well. So which is the best method? Help the bubbles or the sysyge one? Yeah, absolutely. Okay. And we've said why, so we don't need to repeat that one. That's fine. Right. Let's have a look at our PowerPoint. Right. Just whizzing through a few slides here because we've seen these on the worksheet. Okay. And that's what we've just gone through there. So light is a limiting factor. So some students want to investigate how light intensity affects the rate of photosynthesis using method one. How might they measure how light intensity affects the rate? So this is the counting the bubbles one. So how are they going to measure how light intensity affects the rate of photosynthesis? Remember the thing that I said that they weren't actually changing. So there was only one set of results. Yeah, so moving the lamp. Oh, so what is the independent variable? The independent variable is like. The like. How much light it? Yeah distance of lamp from palm weed. Dependent variable. Water temperature. How like how many minutes of bubbles? Like view count? Yeah that's the control variables. Remember the dependent variable is the thing that you measure. What are you measuring the rate of photosynthesis by the number of bubbles? So number of bubbles per minute. And then the control, that's some of the things that you were set. So volume of sodium hydrogen carbonate, amount of pond wetemperature of solution. Right. We have got some results here. Let's see whether you can plot a graph. So can you calculate the mean? Let me cut this out. Have you got a calculator to do the mean? Okay, add that in then. I just like use my pen. Yeah, you should be able to use your pen. That's it. Brilliant. Let's try and get the right worksheet now. Okay. Going to make the table slightly smaller to give you more room. So design a suitable scale and label the axis, plot the mean number of bubbles per minute for each distance, and then draw a line of best fit. And this is actually going to be a curve of befit. I'm just going to change along the bottom and start at zero. Okay, okay. Why won't it let me rub that out? Oh, well, no, I think speais like this, like a straight line. Yeah, okay, just redo those starting at zero, please. I think they're fine, just like I think I put them in carplace. What's up? Thank you. I'll type in the labels for you because that will be it's tricky to write them in. Vickey. Now, can I turn this? No, I can't turn it on its side anyway. Why did I think that you could turn text on this? You can't. Wait, like maybe if you click it, it's going not work. I've tried. It's not working. Yeah, I don't think it works. No, that's a bit silly, isn't it? There we are. That's something that they need to improve. Unclass. Okay. So that is your curve of best fit. So explain to me how you draw a curve of best fit. Like you draw this line that's like like close, like all the points and like. Like kind of like there's like echo number of points on each side. That's it. You got it all. Right. Let's have an appropriate title. What do you think for the title of this graph? How loudistance affect the number of oxygen gen bubbles or the effect of light intensity on the rate of photosynthesis? Just wondering if you drew. Yeah, you can't. 好move that either that okay。So I'm not going to put that on our chat because I can't get the label from the y axis and that's bugging me, so I won't cut that on. Alright, let's have a look. Let's go back to our PowerPoint. Right. So you're ours are similar. Your line of best stfit or your curve of best stfit was slightly different. I think probably I would have moved that up a little bit more like yours. I think there's a bit bigger, too much of a gap on that one. So what happened to the light intensity as the lamp was moved further away? Light intensity decreased. So prior to the experiment, the students hypothesized as light intensity decreases, so does the rate of photosynthesis. So were they correct? Was their hypothesis correct? No. Why no? Because I thought the right of the photo sythis was like the bubble. Yeah so the brighter the light, the more the bubbles that saying and that's what happened. Yeah but like I think I got it the wrong way. Okay? Right? Light is a limiting factor. So let's just quickly have a little look at these. At a certain intensity of light, the rate of photosynthesis stops increasing because another factor will be limiting the rate of reaction, just like those ingredients in a cake. So this is not going to keep on increasing forever. You will get a point here where the graflattens out, where something else is limiting the rate. So what sort of shape would you expect for carbon dioxide? Would you expect it to be the same shape as light intensity? Different. Yeah. It's exactly the same shape. So these are limiting factor graphs and they will take this shape. So an increase. In photosynthesis, as the carbon dioxide increases up to a point where something else is limiting it, what about temperature? I'm the same ved. Not quite as simple for temperature, because as temperatures get too high, then we start to have damage to molecules. So we have got optimum temperature here. But then at higher levels, we basically get to the point where the plant has been cooked, it gets fried. And that's why you have cacti in the desert that have got special adaptations. So that's our three graphs. I'm rushing through this a little bit at the end. What I'm going to do is I'm going to set you some homework here just to go over and summariise this. So I'm going to do some homework, which will be about limiting factors. Okay, Linda and I will see you next week, Islander. Bye.