 In today's experiment we're looking at photosynthesis and different kinds of plants, in particular plants that have adapted to live in the shade and plants that are adapted to live in the sunlight. And the focus is on the different traits that those plants have, the properties that allow them to thrive, for example, on the forest floor or in the direct sun. What we're looking at is what's the difference between sun and shade plants. So you're going to need leaves. Now, these are geranium plants, these like full sunlight, but you can use things like crests if you allow the leaves to grow big enough. Shade plants, there's something called a cast iron plant you can use, but we used ivy, which is very easy to get a hold off, or laurel. You need a sodium hydrogen carbonate solution. You just make this up using bicarb. So this is a 0.2 molar sodium hydrogen carbonate. How would you make that? So you need 84.01 grams sodium hydrogen carbonate powder, and you put that into a thousand millilitres, one litre of water. You get your one mole solution, and then you have 200 mils of that, 800 mils of water, so diluting down a fifth to get your 0.2 mole. And once you've made up a litre of it, you just need about four or five drops of detergent to go into the solution. It just stops the leaf disc from sticking. And then you need your white tile so you can cut your leaf discs out. Now, cutting the leaf discs, you have a few different options. So lots of schools will have one of these. It's called a cork borer. You can use a metal drinking straw. You can hole punch as well. What you want is three or four leaf discs, which are as similar as possible. Yeah, where do we go from there? Once you've got your discs, you would pour your sodium hydrogen carbonate. You can put it into be because it makes it easier for the students to pour it. Now, this is not harmful. This is baking soda diluted with water. So put your finger or your thumb, whatever is comfortable. And you just pour, if you're using a five centimetre, keeps your hinge just up to the five centimetres. So you can either pick the leaf discs up with your fingers or with a pair of forceps, either metal or plastic, whatever you have. Right. If you just want to pop three in, perfect. And then put the plunger in. This is the tricky part. Make sure your students have goggles on for this. And then you want to get rid of the air. So put your finger on the top. Pull down. You're forcing the air out of the leaves. So making them denser. And then tap. This is a bit where you have to be persistent. And they should start to descend. You may get the old stub on one at the top. And so you could put it in a clamp stand with a boss and a clamp. Or you can just leave it on the white tile. And then because we're looking at the difference between white light and green light, just green filter paper. Now, you just need to cut it to a size which you can wrap around the syringe. And what are the key messages or the most important bits of science that you want them to take away? Comparing the sun and the shade plants is that under the white light, both of them will photosynthesize. The idea is that they produce oxygen. This makes the leaf disc less dense, causing it to rise. Green filters on. The plant was just in the full sunshine usually. Now it's only exposed to the green. You would see a very slow rate of photosynthesis, if any at all. The shade plant should rise with the green filter on because it's used to having to photosynthesize using only the green light which is left by all the other plants. Now, when you're doing the practical and you're trying to push the air out, I would make sure my students had goggles on because you don't want to be squirting sodium hydrogen carbonate solution into your eyes. It's not going to hurt you, but it's better to have the safety goggles on. Four steps would be good. All right, okay, so we've got one sinking, one at the bottom and one at the top. So, as we were. No, no, no, no, air out, so push up. Okay, there at the bottom now, boys. Good tapping, well done. And that's what you have to be careful of. So you're ready to start the experiment? So that would be turn the light on, I suppose, wouldn't it? And start timing. So what have you done to make sure this is a fair test? We've done three discs of leaves, so we can take the average from all of them, so we can work out what's the average time of how long it would take to rise. You ready? Three, two, one. They're moving yet? They're not moving yet, are they? No, they're only eight minutes. Yeah. Excuse me, it might take a while. Yeah. What did you see happen? Well, first we saw bubbles forming on the top and bottom and then they kept on growing and growing and just lifted it eventually. For our first geranium it only took eight minutes, but for the group over there it took like over 20. So I don't know if it was about the power of light. Because that's important for the fair test, isn't it? Yeah. That the light is the same brightness and the same bulb and the same distance. So what are you doing now? We're putting the green filter onto the syringe so that there's a different colour of light going on to the leaf discs and we're going to see if that makes a difference at the time it takes to rise. What do you expect will be the difference? For the shade part, because it uses less light, it will go much quicker than the geranium with the filter. Right, boys, so we've done our experiment. We need to talk about what actually happened with our results. I found that some leafs took a significant amount more time than other leafs did. For us, I think we might have done something wrong because the laurel came up the quickest, but then for us the geranium and the ivy didn't come up. Plants can be temperamental. So it might be that you had the syringe in the one which was quicker, you might have had the syringe closer to the light. You might find that the solution, the sodium hydrogen carbonate that you were using may have been slightly warmer than the previous experiment. The leaf discs may have in the syringe been facing the light more than they weren't facing the light. There's all kinds of variables that if we were to repeat this experiment again, that we would need to make sure we kept the same. Often the leaf discs didn't rise for quite a long time, but then when they did rise they rose quite quickly. Did you see the moving at all? So what you get is obviously whilst they're photosynthesising they're producing that oxygen and the bubbles are beginning to collect and then finally when that leaf disc is less dense than the solution they're in then they will lift. So why do you think that the plants behave differently in the different lights? So maybe the plants have adapted to absorb more of say green light than the other types of light. So ones which are more adapted to sunlight would not really focus on green light they would focus more on red and blue light to the ones which usually you can find in the shade. What I would say is so they all absorb red and blue light which is so they're green but you're right that the darker green plant is absorbing more of the green light and that's what you saw. Chlorophyll makes the plants green but did you know that there are two types of chlorophyll? You have chlorophyll A which absorbs at both ends of the spectrum and you have chlorophyll B which is a little bit more in the middle so the chlorophyll B is absorbing towards the green light a little bit more than chlorophyll A. You would have more chlorophyll B present in the shade ones because they simply aren't getting the red and the blue light whereas the geranium would be getting the white light so it would be absorbing the red and the blue so it would probably have more A than B. I enjoyed watching the experiment actually it is I think it's really cool. It is tricky but when you've set it up and you're sitting there watching it actually seeing leaf discs rise as they're supposed to you see the oxygen bubbles form and you can hear the students they're all quite excited about it whose leaf disc is rising first which one's going to get to the top first one goes up then it comes down but it's fun and it's not often photosynthesis experiments are fun so actually be able to do this and see it actually working in front of you yeah it's kind of cool. What are the pitfalls what are the things to avoid? Keep a close eye on them and the syringes make sure they have their goggles on do it in the warmer months of the year because that is going to have a profound effect on the results. Yeah so it is quite it's quite sensitive to the temperature just the air temperature most definitely I would be aiming for the summer term if you're going to do photosynthesis practical doesn't always work out that way but if you can do it in the summer term photosynthesis practicals do tend to work better because it's just warmer. Now if researchers can identify the specific genes responsible for a certain trait for example as we've seen today the traits that allow plants to thrive in shady environments then we could take those genes and put them into crops so those crops would grow all year round or in places where there is little sunlight.