Lesson video

Hello and welcome to today's lesson.

I'm Mr. Jarvis and I'm gonna be taking you through today's lesson.

Today we are looking at material cycles and in particular the carbon cycle.

And this lesson forms part of the unit on living organisms and their environments.

By the end of today's lesson, you should be able to describe the processes that take place in the carbon cycle.

There are four key words to today's lesson.

They are atmosphere, photosynthesis, cellular respiration, and combustion.

Here are the definitions of those terms. You can pause the video at this point if you want to read through them, but don't worry because we will be talking about the definitions and what those terms mean as we go through the lesson.

Today's lesson is broken down into two parts.

First of all, we're going to be looking at carbon in the atmosphere, and then in the second part of the lesson we're going to look at the carbon cycle itself and understand the processes that are taking place.

So if you're ready, let's get started with our first section, which is all about carbon in the atmosphere.

So the atmosphere is a layer of gas that surrounds a planet.

It may contain a small amount of solid and liquid particles.

The earth's atmosphere has a number of different layers.

The layer immediately around the earth up to about 12 kilometres in height is called the troposphere.

That's where all our weather occurs.

The layer above that, up to 50 kilometres high is the stratosphere and that contains the ozone layer.

The whole layer isn't the ozone layer, but the ozone layer sits within the stratosphere.

The mesosphere is the next layer that's 80 kilometres up, and that's where meteors burn up.

The thermosphere is up to 700 kilometres high, and that's where we see the northern lights, the aurora borealis.

And finally, the top of the atmosphere is the exosphere, and that's up to 10,000 kilometres and that's what we call the edge of space.

The atmosphere comprises around 78% of nitrogen, 21% of oxygen 0.

9% argon and trace gases, which include nor point 0.

04% carbon dioxide.

Here's a graph, a pie chart showing the composition of the Earth's atmosphere, and you can see that carbon dioxide makes up a really small part of it.

Here's a quick check.

What's the percentage of carbon dioxide in the Earth's atmosphere? Is it A, 79%, B, 20%, C, 0.

9%, or D 0.

04%? I'll pause for a few seconds and then we'll check your answer.

The correct answer is D 0.

04%.

Well done if you remembered that.

So even though carbon dioxide makes up a small part of the atmosphere that 0.

04%, it is absolutely vital for living things.

Carbon dioxide helps to insulate the earth so that it has a temperature at which life can exist.

Carbon dioxide is a molecule.

It's made up of one carbon atom and two oxygen atoms. It has the chemical formula, CO2.

And the carbon from the carbon dioxide is used to make carbohydrates, proteins, fats, and other important molecules which make up living organisms. Here's another check.

Carbon is found as carbon dioxide in the atmosphere.

It's a gas.

What's the chemical formula of carbon dioxide? Is it A, CO, B, C2O or C, CO2? Again, I'll pause for a few seconds and then we'll check your answer.

And the correct answer is C, CO2.

CO2 is the formula of carbon dioxide.

Well done if you got that right.

Let's move to our first task of the lesson.

First of all, I'd like you to tell me what is the atmosphere? Then I'd like you to complete the table to show the percentage composition of some of the gases that are found in the Earth's atmosphere.

We have nitrogen, oxygen, and carbon dioxide.

And then thirdly, I'd like you to explain why carbon dioxide is important for living things.

You'll need to pause the video, write down your answers, and then when you're ready, press play and we'll check your answers, good luck.

How did you find that? I hope that you didn't find it too tricky.

First of all, I asked you what is the atmosphere? You should have said that the atmosphere is a layer of gas that surrounds a planet.

The second question was to complete the table to show the composition of some of the gases found in the earth's atmosphere.

Nitrogen, you should have been about 78%.

Oxygen is about 21%, and carbon dioxide is 0.

04%.

Well done if you got those.

And thirdly, I asked you to explain why carbon dioxide is important for living things.

You should have said that carbon dioxide is used by plants to make carbohydrates, proteins, fats, and other molecules which make up living things.

Atmospheric carbon dioxide helps to insulate the earth so that it has a temperature at which life can exist.

Well done if you've got those answers correct.

Now, we're gonna move into the second part of the lesson today, and that's all about understanding the carbon cycle.

So if you're ready, let's move on.

All living things need carbon.

Carbon is made into molecules such as carbohydrates, fats, and proteins that are used by living things.

And the small amount of carbon dioxide in the atmosphere is cycled between living things and the environment.

The cycling of carbon we know as the carbon cycle.

Let's look at the carbon cycle.

We're going to start with that 0.

044% of carbon dioxide that makes up the atmosphere.

That's going to be our starting point.

That 0.

04% is used by plants.

They take some of that carbon dioxide in from the air and they use it for the process called photosynthesis, and that's the process that's used by plants to make their own food.

Remember, plants are producers.

They make their own food.

Photosynthesis is a process that needs light.

The equation for photosynthesis is water plus carbon dioxide gives us glucose and oxygen.

One of the reactants of photosynthesis, that's one of the things that goes into the reaction, is carbon dioxide.

The other is water.

That carbon dioxide is taken in through the underside of the leaves through pores or holes in the leaf called stomata.

The water is taken up by the roots.

The plants turn the water and carbon dioxide into products, and the products are glucose and oxygen.

Glucose is a type of sugar, it's a carbohydrate, and that's the plant's food.

And carbohydrates contain lots of carbon atoms. Let's do a check.

Carbon moves from the atmosphere into plants by the process of photosynthesis.

This makes the food for the plant.

What's the name of the food that plants make which contains carbon? Is it A, carbon, B, carbohydrates, C, water, or D, carbon dioxide? I'll pause for a few seconds and then we'll check your answer.

The correct answer is B, carbohydrates is the food that plants make that contains carbon.

Well done if you got that.

So having made the food by photosynthesis, some of the food has to pass on to other organisms. Some animals eat plants for their food.

When they do that, they consume the plants and they consume the carbon.

Sometimes the animals will eat other animals and the carbon that's contained within the animal's body is passed on.

Not all of the carbon in the food is used by animals.

Some carbon is contained within the waste that's excreted from the animal.

The excretion of material is either through urine or faeces, and that goes into the soil.

All organisms die.

When this happens, decomposers use the dead animals and dead plants as food.

And decomposers also break down the faeces and urine, and they use that for food too.

The decomposers take the carbon into their bodies, and as the organisms decay, minerals are released into the soil.

Those minerals are taken up by plants to help them for healthy growth.

Here's another check.

How to decomposers get carbon into their bodies? Is it A, by breaking down animal faeces and urine? Is it B, by breaking down dead animals and plants? Or C, by eating the soil as food? I'll pause and then we'll check your answer.

The correct answer is A and B.

Decomposers get carbon into their bodies by breaking down animal faeces and urine and by breaking down dead animals and plants.

Well done if you've got both of those answers.

So plants and animals use some of their food for cellular respiration.

And respiration provides the energy for life processes.

Respiration also releases carbon dioxide back into the air.

Cellular respiration is not just one chemical reaction.

It's a series of chemical reactions that happen inside the cells, but it's useful to remember a word summary of reactants and products.

So we have the reaction overall, which is oxygen plus glucose gives us water and carbon dioxide.

Oxygen and glucose are our reactants, the things that go into the reaction.

And the water and carbon dioxide are the products, the things that come out of the reaction.

The important thing is that respiration provides energy that's needed for life processes.

Let's do another check.

Which of the following is the correct word summary of cellular respiration.

Is it A, carbon dioxide plus water gives glucose and oxygen, B, glucose and oxygen give carbon dioxide and water or C, glucose and carbon give us oxygen and water? I'll pause for a few seconds and then we'll check to see whether you got the right answer.

The correct answer is B, glucose and oxygen give us carbon dioxide and water, and that reaction gives the energy that's needed for life processes.

Well done if you got that.

When some organisms die, they turn into fossil fuels.

Examples of fossil fuels are coal, oil, and natural gas.

Fossil fuels contain the carbon from the organisms that they're made from and it takes many millions of years for fossil fuels to form.

And so the carbon is locked inside the fossil fuels over many millions of years.

Humans take fossil fuels from the ground and then they burn them in a process called combustion, and that combustion releases the carbon dioxide back into the atmosphere.

Fossil fuels contain carbon and that carbon comes from the dead organisms which made the fuel millions of years ago.

Combustion can be summarised by the following chemical equation, which shows the reactants and the products.

Oxygen plus fuel gives us water and carbon dioxide.

We can see that the fuel, the fossil fuel is one of the reactants, one of the substances that goes into the reaction and carbon dioxide is one of the products that's given out by the reaction.

Combustion is what we call an oxidation reaction, and that provides energy to make things work.

For example, a car moving, petrol is a fossil fuel, it's burned inside an engine and that gives the energy that's needed to make the car work, to actually make the car move forward.

But it also releases carbon dioxide into the atmosphere.

The carbon cycle provides organisms with the carbon that they need to make carbohydrates, proteins, and fats.

And this process continues over and over and over again.

The carbon cycle needs to stay balanced.

If we take the carbon dioxide in the atmosphere, some of that is taken in and it's used by plants for photosynthesis.

Respiration from animals and plants give out CO2 and combustion also gives out CO2.

The carbon cycle keeps a healthy balance.

It keeps the carbon dioxide stable.

However, in recent times, humans have been putting more carbon dioxide into the atmosphere by deforestation and through burning fossil fuels.

And that means that there's more carbon dioxide going into the atmosphere and less carbon dioxide being taken out.

And this is causing climate change, which is causing the increase in temperature of the planet.

Here's a quick check.

Which of the following statements about the amount of carbon dioxide in the atmosphere is correct? A, the carbon dioxide levels are decreasing because plants are taking in more carbon dioxide during photosynthesis.

B, the carbon dioxide levels are increasing because of man's combustion of fossil fuels.

Or C, the carbon dioxide levels are decreasing because all organisms are respiring more.

I'll pause for a few seconds and then we'll check your answer.

The correct answer is B.

The carbon dioxide levels are increasing because of man's combustion of fossil fuels.

Well done if you got that right.

Let's move to our task.

The diagram shows a summary of part of the carbon cycle.

You can see I've labelled some of the arrows A, B, C, and D.

I'd like you to state the processes that are represented by A to D and then explain how each process is involved in the cycling of carbon.

You'll need to pause the video at this point, write down your answer, and then when you're ready, press play and we'll see how well you've done, good luck.

How did you get on with that? Let's check to see how well you did.

I asked you first of all to state the processes represented by A to D.

So let's check those first.

Process A is converting carbon dioxide in the atmosphere into plants, so A is photosynthesis.

The carbon moves from plants into animals by process B, which is eating or feeding.

You might have even said consuming.

Process C is going from animals and from plants back into the atmosphere.

Process C is therefore respiration or cellular respiration.

Well done if you got that.

And finally, fossil fuels going into the atmosphere, that's combustion.

Well done if you got that.

The second part of the question was to explain how each process is involved in the cycling of carbon.

While plants take in carbon dioxide from the air to make their food from photosynthesis, animals eat plants and other animals that contain carbon that was made as food, so things like carbohydrates, proteins or fats.

Plants and animals release CO2, that's carbon dioxide, into the air as they carry out cellular respiration.

And when combustion of fossil fuels takes place, carbon dioxide is released back into the atmosphere.

There's a balance between processes taking in carbon dioxide and processes that are releasing carbon dioxide.

Well done if you got all of those answers correct.

That brings us to the summary of today's lesson and what we've done today is seen that carbon is an element that's found in very small amounts in the earth's atmosphere, just 0.

04%.

And the carbon cycle shows how carbon is cycled between living things and the environment.

We've looked at how carbon dioxide is removed from the atmosphere by plants as they make food by the process of photosynthesis.

And we've seen that carbon dioxide is returned to the atmosphere by the combustion of fossil fuels, and when plants and animals including decomposers undergo cellular respiration.

We've also seen that increased combustion is causing an imbalance of carbon in the atmosphere.

It's that the balance of carbon in the atmosphere is changing and that is resulting in climate change.

It's been great as always learning with you today, and I look forward to hopefully seeing you again soon.

Take care for now.