Lesson video

This lesson is called "Climate change and photosynthesis," and is from the unit, "Photosynthesis: Factors affecting the rate." Hi there, my name's Mrs. McCready, and I'm here to guide you through today's lesson.

So thank you very much for joining me today.

In our lesson today, we're going to explain how photosynthesis and food security could be affected by climate change.

And in our lesson today, we're gonna come across a number of keywords which are shown on the screen for you now.

You may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

So in our lesson today, we're going to, first of all, look at making predictions about photosynthesis before we predict how climate change and photosynthesis might interact.

So, are you ready to go? I certainly am.

Let's get started.

So I'm gonna take you back, first of all, to photosynthesis, and let's just pull out some of the key details from that process.

But before we do that, I just want you to take an imagination stroll and imagine a machine that is making cakes.

So what we're putting into that machine is cake mix and icing powder.

And what's coming out, the products, are the cakes themselves.

So if we provide more cake mix, we could predict that the machine would make more cakes.

In other words, the rate of production of cakes would increase.

We would see an increase in the rate, unless there is a limiting factor.

And a limiting factor is something that inhibits the rate from going any faster.

So for instance, there isn't sufficient amounts of icing powder, for instance, that would limit the rate of cake production.

So cake production could increase to a point up until that limiting factor prevents it from going any faster.

Right, we've now got that.

Let's transfer that idea across into photosynthesis.

So, photosynthesis has taken place in chloroplasts within plant cells.

And chloroplasts are like little microscopic machines within the plant, which are designed to produce vast quantities of glucose through the process of photosynthesis.

So chloroplasts taking carbon dioxide, water, and using the energy from light, turn those inputs into the products, glucose and oxygen.

So the inputs of carbon dioxide and water with light energy, and the outputs are glucose and oxygen.

And I'm sure you're fairly familiar with that.

Photosynthesis is a really important subject in biology.

So what are the inputs? Which ones do you think are correct? I'll give you five seconds to decide.

Okay.

So you should have chosen that the inputs for photosynthesis are carbon dioxide, light, and water.

Well done if you've got all three of those correct.

And what about the products or the outputs of photosynthesis, which are correct for those? Again, five seconds to consider.

Okay, so you should have chosen glucose and oxygen.

Well done again.

Okay, so we've seen what the inputs and the outputs are of photosynthesis.

So just like the cake idea, we can then make some predictions about what would happen if we increase the quantity of one of the inputs, what would happen to the amount of output.

So if we increase the amount of carbon dioxide that was being provided, we could predict that the chloroplast would make more glucose and oxygen, and therefore the rate of photosynthesis would increase unless there was a limiting factor restricting the degree to which the product output could be increased by.

And the things that could limit the rate of photosynthesis include the amount of water, the amount of light, and the number of chloroplasts present within the plant.

So, if the amount of available water increased, whose prediction is correct? Alex predicts the rate of photosynthesis could keep increasing forever.

Aisha predicts more products would be made until another factor became limiting.

And Lucas predicts the amounts of carbon dioxide and light would also increase.

But who is correct? I'll give you five seconds to decide.

Okay, so you should have said that Aisha is correct.

More products would be made until another factor became limiting.

Well done if you chose her prediction.

So we've seen how the rate of photosynthesis is affected by the quantity or the concentration of the inputs, the substrates going into this chemical reaction.

But photosynthesis is also affected by temperature, and that is because photosynthesis is controlled by a series of enzymes present within the chloroplasts, which are catalysing the reactions of photosynthesis.

And enzymes, as they are catalysts, they speed up the chemical reaction rate, they are affected by the temperature of their environment.

So at low temperatures, the particles involved in the chemical reaction, that's the substrates, so water and carbon dioxide, and the enzymes which are catalysing these reactions, are moving slower because there is less kinetic energy because the temperature is lower.

And this means that the number of collisions that are taking place between the substrates and the enzyme is lower, and therefore the rate of photosynthesis will also be lower.

So at lower temperatures, we would expect to see a lower rate of photosynthesis.

Now, as temperature increases, so does the available kinetic energy, and therefore the particles start to increase the speed at which they are moving, and therefore the number of times they hit into each other, and therefore the number of successful collisions that are formed as well between the substrates and the active site of the enzyme.

And the more successful collisions there are between the substrates and the enzymes' active site, the more reactions will be able to be catalysed by the enzyme and therefore the rate will increase.

So as temperature increases, we expect to see the rate of photosynthesis also increasing because the enzymes are able to function faster because there is more energy available in the system.

Now, at temperatures beyond the optimum temperature, so the temperature at which these chemical reactions are working at their fastest, at temperatures beyond the optimum, the enzyme starts to denature.

That means it starts to change shape.

And denaturing means that the active site changes shape, which means that the substrates no longer fit as well into that space, and therefore the enzyme is less able to catalyse the reaction.

And denaturing happens over a period of temperature range, but ultimately it causes a complete loss at high enough temperatures, a complete loss of chemical reaction because the enzyme will have become so completely denatured that it is now no longer able to catalyse the reaction.

So we would expect to see the rate of chemical reaction, the rate of photosynthesis, decreasing beyond the optimum temperature because of denaturing that is happening to the enzyme.

Now, therefore, when it's cold, but if it's bright and sunny and there's plenty of carbon dioxide available, plenty of water, we would still expect to see low rates of photosynthesis because temperature is the limiting factor in that scenario.

And therefore, we could also predict what will happen if temperature increases.

So we could say that as temperature increases, we would expect to see the rate of photosynthesis increasing as well until the optimum temperature was reached or another factor becomes limiting, such as the amount of light or the concentration of carbon dioxide, the availability of water, or the number of chloroplasts within the plant.

And we could say that the rate of photosynthesis will continue to increase up to the optimum temperature and then beyond that, beyond the optimum, the rate will decrease because the enzymes will be denatured.

So the rate will increase up to the optimum temperature or whenever another limiting factor is reached, whichever one happens first.

And then if another limiting factor hasn't reduced or impeded the rate of photosynthesis, then beyond the optimum temperature, assuming temperature is the limiting factor, the rate will decrease from that point onwards because the enzymes will start to become denatured.

So, true or false? The rate of photosynthesis is affected by the availability of oxygen.

Okay, so you should have said that that is false.

But can you explain why? So you should have explained that by saying that oxygen is not used for photosynthesis, it is made by photosynthesis.

So the rate of photosynthesis will be the same no matter how much oxygen is present.

Well done if you spotted that.

So what I'd like you to do is to summarise this first part of the lesson, please, by explaining in your own words what would happen to the growth of the crops that a farmer is growing in a greenhouse if the farmer increased the concentration of carbon dioxide inside the greenhouse.

And then what would happen to the growth of the crops if the farmer increased the temperature inside the greenhouse.

So pause the video and come back to me when you're ready.

Okay, let's check our work.

So what would happen to the growth of the crops if the farmer increased the carbon dioxide concentration inside the greenhouse? Well, you might have said that growth will increase as more carbon dioxide can increase the rate of photosynthesis, which is used to produce glucose to build the biomass within the plant which is necessary for growth.

But, that will only happen if other factors such as temperature or the availability of light or water are not limiting the rate of photosynthesis.

Well done if you got both of those points.

And then for the second question, "What would happen to the growth of the crops if the farmer increased the temperature inside the greenhouse?" You might have said that the growth will increase as the higher temperatures can increase the rate of photosynthesis, again, used to produce glucose, which is used to build biomass within the plant which enables growth.

But only if other factors such as the availability of light, water, or carbon dioxide are not limiting the rate of photosynthesis, and also, only up to the optimum temperature.

And if the temperature increases above the optimum temperature, the rate of photosynthesis will decrease as the enzymes will become denatured.

So make sure you've got all three aspects of that because it's important that you also talk about the impact that above optimum temperature will have on the rate of photosynthesis as well as what will happen in the lead up to the optimum temperature.

And well done.

Okay, let's move on to have a look at how we might predict what would happen with climate change and photosynthesis.

So we've seen how photosynthesis is a chemical reaction, which is produced by chloroplast within the plants.

And plants are one of a group of producers, and all food chains start with producers.

So you can see here on the screen three different types of producers shown.

So we've got strawberries, wheat, and we've got algae.

And these are producers because they are producing their own food.

They are using sunlight, carbon dioxide, and water to make their own biomass.

Now, human nutrition and the survival of humans therefore, depends on food chains.

So how this biomass is passed from one organism to the next.

And that is because we are consumers.

We cannot make our own food.

We have to obtain it from other organisms. So for instance, we could be a primary consumer if we eat fruit and vegetables plants directly.

So for instance, if Sam eats the strawberries, they are a primary consumer.

If a chicken eats the wheat, and then Sam eats the chicken, then Sam is a secondary consumer because they have eaten the chicken which has eaten the producer, the wheat.

And if the producer is eaten by a small fish, a primary consumer, which is then eaten by tuna, for instance, the secondary consumer, and then Sam eats tuna, then Sam is a tertiary consumer because they are the third consumer within that food chain.

So depending on where in the food chain we are, would depend on whether we're a primary consumer, a secondary consumer, or a tertiary consumer.

But regardless, we are always a consumer.

And as you can see from this very simplified diagram, all consumers require and rely upon producers in order to survive.

and no consumers could survive if there weren't producers present in the first place.

Now, as we've seen, producers are using carbon dioxide and water from their surroundings to produce glucose using the process of photosynthesis.

So, in a little bit more detail, we would take six carbon dioxide molecules and six water molecules, and that is converted into C6H12O6, which is glucose, and 6 lots of oxygen.

Now, this is a very beautifully balanced chemical equation because it's essentially all the sixes, you can see that.

And it's worth learning, especially if you are doing higher, because it's a two for one equation.

If you reverse the arrow, you get respiration.

And those of you doing higher will need to know the balanced symbol equation as well as the word equation.

Now, glucose is then used by the producer to build their own biomass, to build their bodies, so to put together in lots of different ways to make a range of biological molecules required and necessary for their growth.

And all of this biomass, including all of the carbon that is transferred through the food chain, comes from photosynthesis, which is completed by producers in order to make their own body.

So, humans could survive without photosynthesis in producers.

True or false? Okay, so you should have said that that is false.

But why? So you should have explained that by saying that humans are consumers and consumers get their food and their carbon by eating producers or consumers that have already eaten producers such as the chicken and the fish.

Now, human food security, as you could hopefully predict, entirely depends on photosynthesis in producers.

Because if photosynthesis in producers is not occurring, then food chains are disrupted and food security is threatened.

Now the rate of photosynthesis is affected by a number of different factors.

It is affected, as we've seen already, by the amount of carbon dioxide available in the atmosphere, the amount of water available in the soil, and the temperature that the producer is in because of enzyme chemical reactions.

And climate change is having an impact on all of these factors.

So which of these factors are being affected by climate change? The amount of oxygen in the atmosphere, the availability of water, or the average temperature? I'll give you five seconds to decide.

Okay, so you should have chosen, the availability of water and the average temperature.

Well done if you selected both of those.

So I've said that climate change is affecting the concentration of carbon dioxide, the availability of water, and the average temperature.

So let's look at those in a little bit more detail.

So let's start with atmospheric carbon dioxide, because measurements over many years, over the last 60 years or so, have shown that the concentration of carbon dioxide in the atmosphere is increasing, and not even steadily.

It is increasing at an increasing rate.

So the amount of carbon dioxide present in the atmosphere is going up, and going up at a faster rate as the years pass.

If we look at how much carbon dioxide is being emitted by burning fossil fuels and industry, we can see that the amount of carbon dioxide being emitted by these industries has been on a very steep increase since 1950.

And the concentration of carbon dioxide that has been emitted has been increasing since the industrial revolution, since about 1850.

Now, 99.

9% of scientists agree that the increase in atmospheric carbon dioxide is directly caused by human activities including burning fossil fuels and industrial processes that use fossil fuels for energy.

So there is a direct link between the amount of carbon dioxide in the atmosphere and how we are using fossil fuels, and the fact that we're burning them and releasing carbon dioxide in the process of doing so.

Now, carbon dioxide is a greenhouse gas, and that means that increasing the quantity of greenhouse gases, including carbon dioxide in the atmosphere, will increase the greenhouse effect.

So the greenhouse effect is caused by sunlight being beam from the sun to the earth.

And some of that sunlight is reflected straight back into space, but some of it is absorbed by the surface of the earth and then radiated back into the atmosphere.

And the greenhouse gases bounce that heat around the atmosphere, warming the atmosphere, and therefore warming the earth.

So this process naturally occurs, and it's actually very important because it helps to maintain a pleasant ambient temperature across the earth of, on average 15 degrees, which is exactly what is required for life to be so abundant on earth.

However, increasing the quantity of greenhouse gases in the atmosphere makes the greenhouse effect stronger.

And by increasing artificially the greenhouse effect, what it is causing is climate change changes to long-term weather patterns because of the increased temperature on earth, because of the amount of extra carbon dioxide present within the atmosphere.

Because extra carbon dioxide, extra methane, extra greenhouse gases, means that more heat is trapped and radiated around the atmosphere, not less.

And that means there's a greater warming effect on earth, and that is driving climate change.

Now, Jun says, "Isn't this all a good thing? If there's more carbon dioxide and it's warmer, there'll be more photosynthesis and producers, so we'll get higher yields of crops, and that means there'll be more food for farm animals and for us." Well, what do you think? Well, to an extent he's correct, but only partly so.

So let's see why.

So a higher concentration of carbon dioxide in the atmosphere could well increase the rate of photosynthesis, because carbon dioxide will become less of a limiting factor.

But that is true only if no other factors limit the rate of photosynthesis.

Now, if atmospheric carbon dioxide doubles from pre-industrial levels, then the rate of photosynthesis could increase by 23% in trees, 11.

5% in wheat, and 8.

4% in corn, which, on balance, would be a good thing, would improve food security because over a third of the world's population depend on staple foods such as wheat and corn in order to survive.

So a third of the world's population is going to directly benefit from an increase in carbon dioxide in the atmosphere because of the increase in photosynthesis, you think.

However, in reality, it is unlikely that the crop yields will go up to that extent.

But why is that? Well, there will be other limiting factors that will restrict the ability for that increase to occur to that extent.

For instance, plant growth would be limited by the lack of nitrogen or nitrate ions in the soil.

Now, nitrate ions are absorbed via the root hair cells and are combined with carbohydrates, with glucose, rearranged to form amino acids.

And amino acids are then used to build proteins.

So if there are insufficient quantities of nitrate irons within the soil, then less protein can be made by the plant, and that will restrict biomass growth in the plant because the plant won't be able to make as many proteins and therefore won't be able to continue growing as quickly.

So a restriction on the number of nitrates in the soil will significantly impede plant growth and crop yield.

Now, we could circumvent that by adding nitrate fertilisers to the soil.

However, this will worsen climate change because it will add more greenhouse gases into the atmosphere, because quite a lot of energy is required in order to make the fertiliser in the first place, and therefore, more greenhouse gas emissions will be produced and released into the atmosphere, worsening climate change further.

So why is nitrogen availability in the soil a limiting factor for plant growth? Is it because it is needed to make carbohydrates, it is needed to make fats, or it is needed to make proteins? I'll give you five seconds to decide.

Okay, so you should have said that it is needed to make proteins.

Well done if you did.

So although carbon dioxide is a limiting factor for plants, and increasing carbon dioxide levels around plants is likely to lead to an increase in photosynthesis, actually, the long-term implications of increasing the amount of carbon dioxide within the atmosphere are much more serious.

Because atmospheric carbon dioxide concentrations drive global warming and therefore drive climate change.

And the negative impacts of climate change far outweigh any benefits from an increase in the rate of photosynthesis.

Because increasing global temperatures and increasing climate change and the weather uncertainty that comes with that means that some areas will be much hotter than they would normally be, and because they are hotter and drier, then the drought will kill crops.

So any increase in the rate of photosynthesis will be nullified by the fact that the crops are dead.

Also, and elsewhere, other places will be deluged by storms and high wind and rain leading to flooding.

And flooding will ruin crops which are not adapted to survive in waterlogged soils.

And again, the negative impact of this far outweighs any benefit from an increase in the rate of photosynthesis by increased concentration of carbon dioxide in the atmosphere and an increase availability of water because the crops will be dead, and therefore they won't be able to grow.

And then coastal areas in particular will be impacted by rising sea levels.

So rising sea levels are occurring because global temperatures are increasing and this is causing land-based ice to melt and run off into the sea, and also for the oceans to expand because the water is getting warmer and therefore taking up more volume.

And those two things are causing sea levels to rise, which impacts coastal areas most significantly because of an increase in coastal flooding.

Now, where coastal flooding occurs, any plants which are growing in areas which have not previously been flooded but now become flooded, are likely to not be salt tolerant.

And sea water, as I'm sure you are aware, is very salty.

And the increase in salt concentration of water around these crops means that unless they are adapted to survive high salt concentrations in the water, they also will die, and therefore the positive impact of increasing carbon dioxide levels on photosynthesis rate will be far outweighed by the death of crops, either because they've been killed by drought, or because they've been killed by flooding, or because they've been killed by high salt concentration because of coastal flooding.

Now, all plants are adapted through the process of natural selection to survive best in the environmental conditions in which they live.

But if those environmental conditions are changing, then their adaptations may no longer be best suited to the new conditions.

Now, enzymes are one of the things that are highly adapted in plants, because enzymes are essential to catalyse chemical reactions for the processes that are required within plants to enable them to survive and grow and thrive.

And they work best within a narrow temperature range.

And if the temperature increases beyond that narrow temperature range, that optimal temperature range, then the enzymes will start to denature and therefore the rate of reactions being catalysed by the enzymes will decrease, because the enzymes are now no longer able to catalyse the chemical reactions at the optimum rate.

Now, as climate change continues and global temperatures increase, this is going to have an ongoing and significantly deleterious effect also on the ability for plants to survive.

Now, different areas and the people who live in those areas across the globe, will be affected differently.

In wealthy countries, people will be able to survive, because countries which have wealth will be able to invest in building flood defences.

They will be able to artificially irrigate and fertilise farmland to offset drought or to increase nitrate concentrations within soil.

Or they'll be able to import food from other parts of the world to supplement the food supply chain within their own country.

However, people who are living in developing countries, countries which are not wealthy, will suffer the greatest by climate change, because floods or droughts could equally devastate their communities because they are entirely dependent on the crops that they are growing.

And if those crops fail, then their food chain collapses and can lead to starvation, malnutrition, and to death.

And unfortunately, it's the people living in the developing countries, who are less able to respond to climate change, who are also the ones who are least impacting on climate change in the first place, they aren't the ones who are causing climate change by releasing vast quantities of greenhouse gases through their human activities, but they are the ones who are feeling the effects of those greenhouse gas emissions and the impact that it's having on climate change.

So who is correct? Andeep says, "To make sure we have food security, we have to reduce emissions of carbon dioxide to reduce climate change." Izzy says, "We should increase emissions to add more carbon dioxide to the atmosphere to increase the amount of photosynthesis." And Sofia says, "The risks of increasing carbon dioxide massively outweigh the benefits of more photosynthesis." But who is correct? I'll give you five seconds to decide.

Okay, so you should have said that both Andeep and Sofia are correct, but Izzy is absolutely not correct.

So what I'd like you to do now is to summarise what we've learned from this part of the lesson.

I would firstly like you to use the graph of annual carbon dioxide emissions from burning fossil fuels and industry to estimate how many billion tonnes of carbon dioxide were emitted in 2022.

So study the graph carefully and see how accurate you can be.

And then I would like you to calculate the increase in atmospheric carbon dioxide between 1965 and 2015, using the second graph.

Once you've done that, I would then like you to predict what will happen to the atmospheric carbon dioxide levels if the trending carbon dioxide emissions continues, before finally explaining in your own words why increasing atmospheric carbon dioxide levels will not increase food security.

So pause the video and come back to me when you're ready.

Okay, let's review your work.

So from the first graph, you should have estimated that more than 35 billion tonnes or approximately 38 billion tonnes of carbon dioxide were emitted in 2022.

From the second graph, you should have seen that there were 400 parts per million of carbon dioxide in the atmosphere in 2015, and 320 parts per million carbon dioxide in the atmosphere in 1965.

So taken 320 parts per million away from 400, to say that there was an increase in atmospheric carbon dioxide of 80 parts per million between 1965 and 2015.

Then I asked you to predict what will happen to atmospheric carbon dioxide levels if the trending carbon dioxide emissions continues.

And you should have said that if the trend of CO2 emissions continues, then atmospheric CO2 levels will continue to increase also.

Then finally, I asked you to explain why increasing atmospheric carbon dioxide levels will not increase food security.

And you might have said that by increasing carbon dioxide levels, whilst this will increase the rate of photosynthesis in some crop species, plant growth will be limited by limiting factors such as the availability of water, nitrogen, and the temperature.

And temperatures which are higher than the optimum could denature photosynthesis enzymes causing the rate to decrease.

And climate change will make it harder to grow crops in some areas due to drought and flooding.

So review your work, check if you've got all of those correct, add anything that you've missed, and well done indeed.

Okay, we've come to the end of our lesson today.

So thank you for joining me, and I hope you found that interesting.

We've seen how we can make a prediction about how the rate of photosynthesis will be affected by the temperature and the availability of water and carbon dioxide, and how these factors can also be limiting factors on the rate.

We've seen how temperature affects photosynthesis due to its effects on enzymes.

And we've also seen how photosynthesis in producers creates the biomass in food chains, which all consumers, including humans, depend upon, and this is crucial for our food security.

Now, climate change and global warming affect the temperature and the availability of water.

And in some places there will be droughts, and in other places there will be floods.

And both of these will reduce the yield of crop plants that feed farm animals and humans.

However, different parts of the world will be able to respond differently according to how climate change is affecting them and also how wealthy those countries are, and therefore how able they are to respond.

So there's plenty of content to think about in this lesson and lots of complex links to be made between photosynthesis, climate change, and limiting factors.

So thank you very much for joining me today, and I hope to see you again soon.

Bye.