﻿- Hi, everyone. Welcome back to unit four of bioenergetics. My name is Ms. Turmeck and I'm really excited to be teaching you biology today. Today, we're going to be having a look at the limiting factors of photosynthesis. During today's lesson all you will need is a pen and a piece of paper. I'll give you a moment now to pause the video and go collect the equipment if you don't have it already. Once you've got that, take a moment to make sure that you're in a distraction free environment and that your phone is on silent. When you're ready, let's begin. In today's lesson we're going to be looking at four different areas. The first section is going to be a quick recap on what the limiting factors of photosynthesis are. The second portion we're going to be interpreting the rate of photosynthesis by looking at different graphs and working out what the independent and dependent variables are. Thirdly, we'll be looking at some exam practise questions and seeing how to apply our knowledge to those questions. And finally, you'll hit next and continue to the final quiz. But first off, we're going to have a look at the limiting factors of photosynthesis. Try to have a think now. There are four of them. See if before I flip the page you'll be able to work out what they are. Right. They're now on screen. The first limiting factor is temperature. Second is light intensity. The third is carbon dioxide concentration and the fourth is chlorophyll. You should remember that the reason why we call these limiting factors is because if any one of those factors is being increased it will increase the rate of photosynthesis until a certain point. At that certain point is when one of the other factors limits how high the rate of photosynthesis can become. And we're going to be looking at what that looks like in graph form today. Now let's take a moment to do some quick fire practise questions. The first question is now on screen. I'll give you five seconds to shout out the answer and then I'll display the answer here. If you said temperature, light intensity, concentration of carbon dioxide and chlorophyll, you're correct, well done. Next question. Have a read, five seconds, and then I'll propose the answer. If you said constant, well done. That is correct. Third question. If you said true, you got it right. Well done. Now take a moment to do some independent practise questions. I'd like you to complete this with on a piece of paper with your pen. If you want some help and some hints at what the questions could be, then stay tuned and keep listening. Your hint for question one and two is to remember back to the photosynthesis equation that we learned in lesson one. Have a think about what the two reactants that go into the equation are and what the two products that are produced at the end are. Once you've worked out the word equation, now I'd like you to turn each of those words into their symbol forms. So for example, one of your reactants should have been water and the symbol equation for water is H two O. Hopefully question three is quite straightforward but make sure to remember T L C C. For number fours hint, you can use this sentence starter. As the light intensity increases, the rate of photosynthesis. And finally, for question five your hint is to remember to talk about what happens when the temperature gets too high. Give the video a pause and resume when you finish. Well done everybody. The answers are now on screen. So go ahead and pause the video and give yourself a tick for every one that you got correct. Be sure to feed back the ones that you got wrong. And for question number five, make sure you've got all of the parts included to get full marks for that answer. Well done. The next section of the lesson, we're going to have a look at how to interpret graphs that show the rate of photosynthesis. The first graph is now on screen. This one is going to look at light intensity. You should recognise light intensity as one of the limiting factors, because it's the one that we used for the required practical. From that required practical we determined that as the light intensity increases, the rate of photosynthesis increases. This is demonstrated very well in the graph because you can see that as the light intensity on the X axis moves towards the right, which has increased, the rate of photosynthesis is also increased. You will notice however that the increase is not proportional and that at some point the curve actually begins to flatten and form a bit of a plateau. Let's have a look at why that is. If we look at where the first arrow is pointing we can see that the graph is increasing steadily. As the light intensity increases, the rate of photosynthesis increases. This means that light intensity here is the limiting factor. And by increasing the light intensity the rate of photosynthesis will also increase. Let's look at the next part of the graph. Up here where it starts to flatten. At this point of the graph light intensity is not the limiting factor. We know this because the light intensity is continuing to increase but the rate of photosynthesis is not. It's staying at a constant rate. This tells us that one of the other factors is limiting how quickly that plant can photosynthesize. And one of those factors might be temperature, or chlorophyll, or concentration of carbon dioxide. Now let's have a look at another limiting factor and how this graph is interpreted. Carbon dioxide has the same pattern. As the concentration of carbon dioxide increases, the rate of photosynthesis increases. And you can see that on the graph here. As the X axis increases, the Y axis also increases. Let's see if we can recognise what's happening at this point in the graph. So at this point in the graph the rate of photosynthesis is increasing steadily. This means that the concentration of carbon dioxide is the limiting factor and that by adding more carbon dioxide we're going to have an increased rate of photosynthesis. In the next part of the graph. What do you think is happening here? Is carbon dioxide still the limiting factor? If by adding more carbon dioxide the rate of photosynthesis isn't increasing. No, carbon dioxide is now not the limiting factor and photosynthesis has plateaued or remained constant despite the fact that the amount or the concentration of carbon dioxide is still going up. So at this point in the graph, it means that one of the other factors is limiting how quickly this plant can photosynthesize. Now let's look at temperature. Temperature has a slightly different curve, so we can see that the rate of photosynthesis increases as the temperature increases, but we can also see that it hits an optimal point. And we'll talk about where that optimal point is in a moment. But beyond that optimal point, we can see that the graph has a very quick decline down. And that means that past the optimal point if the temperature continues to increase then the rate of photosynthesis will decrease. Let's look at this a bit more closely. We can see that in that first arrow on the left-hand side of the graph, temperature is the limiting factor. Meaning that when we add more temperature the rate of photosynthesis will increase. Now looking at the top of graph, we can see that temperature is no longer the limiting factor, and instead we're starting to hit the optimal point meaning the highest of the temperature likes to be before the rate of photosynthesis decreases. And now, if we look to the right side of the graph, that third arrow there, we can see that we're getting a decrease in the rate of photosynthesis. This is caused by the temperature being too hot and the enzymes and their reaction beginning to denature. Let's now have a look at the fourth limiting factor of photosynthesis. You should recall from lesson three that chlorophyll was the fourth limiting factor of photosynthesis, but chlorophyll is not very easy to understand by analysing a graph. Instead, it's important that we look at two different species of plants and consider how they differ. On the left-hand side on the screen, you'll see a completely green leaf and beside it on the right hand side you'll see what we call is a very gated leaf, very gated meaning that it's not completely green and it has white bits around the edge. Now, the only difference or one of the main differences between these two leaves is the fact that the very gated leaf would have a lower amount of chlorophyll. And that's because if you remember chlorophyll is a green pigment and this leaf is not completely green. So because it has a lower amount of chlorophyll it will absorb less sunlight. If it absorbs less light energy then it will have a decreased rate of photosynthesis. Let's take a moment to do some quick recall questions and see what you can remember. Question one is now on screen, have a read and I'll give you the answer in five seconds. If you said increases that's correct. Question two. The answer we're looking for here is optimal. Well done if you got that right. Next question. If you said less, well done. That's correct. Now let's put what we just learned into practise. I'd like you to pause your screen and complete questions one and two as listed below. Come back when you've completed it. Well done everyone. Let's have a look at the answers. For number one where the arrow is pointed at the steady increase. You should have said that carbon dioxide is the limiting factor. And as carbon dioxide increases, the rate of photosynthesis also increases. At point number two you should have said that carbon dioxide is now not the limiting factor and that in order to increase the rate of photosynthesis you should try to change either the light intensity or the temperature to increase the rate of photosynthesis. Feel free to pause your screen and correct your answers. Well done everyone. Let's have another look at some recall questions. I want you to have a look at the graph, make sure to look at the X axis so that you can see what limiting factors is being used here. And then I want you to look at what where the arrow is pointing to on the graph. Take a moment, read through the question, And I would like you to point to the answer that you think is correct. If you said concentration of carbon dioxide. Well done. You're correct. Next question. For this question I'm looking for two possible answers. If you said light intensity and temperature you're correct. Well done. Next question. Be sure to take note of the X axis that has now changed in this graph. I'm looking for one answer. Go ahead and point to it when you think you know If you said light intensity, you're correct. Well done. Now we're going to move into some more independent practise, this time looking at an exam style question. Go ahead and pause your screen here and have a go with the question. Great job, everyone. Let's have a look at the answers. The optimum temperature for photosynthesis according to this graph is answer C, 25 degrees Celsius. Excellent work. Next independent practise. Once again, give the screen a pause, read the question and resume when you're ready. Excellent work. Let's have a look at the answer. On the graph, the limiting factor of carbon dioxide is placed at the X. Give yourself a tick if you got that right. Well done. Great job for making it to the end of today's lesson. You should now feel more confident being able to identify the limiting factors of photosynthesis in graphs like the one that's shown here. Remember a couple pointers. Increasing any one of the limiting factors will have an increase in the rate of photosynthesis, but this will only happen to a certain point. As the next arrow shows when the graph begins to plateau or flatten then that's when we know that the limiting factor in the independent variable is no longer the limiting factor, and that instead we would have to try to manipulate one of the other factors. In the graph that's labelled here we're looking at the carbon dioxide concentration. At the point where the graph flattens, the carbon dioxide concentration is no longer the limiting factor, and in order to get the rate of photosynthesis to continue increasing we would have to try to change either the temperature, the light intensity, or the amount of chlorophyll. Well done everybody. Don't forget to hit next and complete the final quiz to show yourself all the excellent knowledge that you've learned today. Next lesson we'll be reviewing everything that you've learned in the first half of this unit about photosynthesis, so be sure to stay tuned for that. See you then.

In this lesson we will continue to investigate the limiting factors of photosynthesis and interpret the graphs that investigate when one factor becomes the limiting factor over another.

Biology

Y10 Biology

Key Stage 4

Year 10

Miss

Limiting factors of photosynthesis

Bioenergetics

UNIT

Photosynthesis

Photosynthesis required practical

Photosynthesis required practical results

Manipulating factors of photosynthesis HT

Review photosynthesis

Respiration

Anaerobic respiration

Consequences of anaerobic respiration

Metabolism

Synoptic links

End of topic review


Exam Skills

Maths Skills

Scientist case study-Ynes Mexia

Combined Science

Y10 Combined Science (Foundation)

Bioenergetics (FT)

Y10 Combined Science (Higher)

Bioenergetics (HT)

Lesson overview: Limiting factors of photosynthesis

Video

Presentation

Worksheet

Exit Quiz

Transcript

15 lessons in Bioenergetics:

13 lessons in Bioenergetics (FT):

15 lessons in Bioenergetics (HT):