Welcome to this lesson from the Oak National Academy.

Today's lesson is called The effect temperature on cellular respiration in small organisms, and it is a practical lesson.

It's taken on the unit: Aerobic and Anaerobic Cellular Respiration.

Hiya, I'm Mrs. Wheate, and I'm gonna be your teacher for today's lesson.

By the end of today's lesson, you'll be able to use a simple respirometer to investigate the effect of temperature on cellular respiration in small living organisms. Let's have a look at our keywords.

We have five keywords for today's lesson and I'm gonna read them out now: Aerobic, a process that requires oxygen.

Cellular respiration, an exothermic chemical process that transfers energy for light processes using glucose as a fuel.

Respirometer, apparatus used to measure the rate of respiration in small organisms. Independent variable, the factor that we change in an experiment.

And dependent variable, the factor that we measure in an experiment.

So if you want some more time to read those through, and try and understand them, I'll be quiet for five seconds.

But if that's not quite enough time, you can click pause and click play when you're ready to move on with the lesson.

Today's lesson is in three parts.

In the first part of today's lesson, I will introduce the apparatus for measuring the rate of respiration called respirometer, and then we'll talk about how to use that apparatus to measure the rate of respiration, which is the practical.

And finally, we'll talk about the results.

We'll talk about evaluating validity and data processing.

So let's get started by talking about the apparatus for measuring rate of respiration.

So in order to understand this practical and understand how this apparatus works, the respirometer, you need to know the reactants and the products of cellular respiration.

So in aerobic cellular respiration, glucose is broken down in the presence of oxygen, producing carbon dioxide and water.

And we can summarise that in an equation, in a word equation or a balanced symbol equation.

So we have oxygen and glucose, those are our reactants, and they react to make water and carbon dioxide.

Those are our products.

So like I said, you need to know that part really, really well, what are the reactions to what are the products before we can understand the practical, before we can understand how the equipment works.

So we're gonna take a brief pause and we're gonna check to see if you can remember those before we move on with the rest of our lesson.

Which gas is used by aerobic cellular respiration? Is it A, oxygen, B, water, C, carbon oxide, or D, glucose.

Take five seconds or click pause.

Click play when you're ready to see the answer.

It is A, oxygen.

Let's try another one.

Which gas is produced by aerobic cell respiration? Is it A, oxygen, B, water, C, carbon oxide, or D, glucose? Again, take five seconds or click pause.

If you want some more time, click play when you're ready to see the answers.

It is C, carbon oxide.

Great job if you got those right.

There are many different factors which affect the rate of respiration.

For example, concentration of oxygen and glucose, those are both factors that can affect the rate of aerobic cellular respiration.

This is because oxygen and glucose are both reactants in aerobic cellular respiration.

And when there are more reactants, more products can be made.

And so that creates a faster rate.

Temperature is also a factor that affects the rate of aerobic cellular respiration, and this is because respiration is controlled by enzymes and the rate of enzyme activity is affected by changes in temperature.

Let's check to see if you understood that.

The rate of aerobic cellular respiration is affected by temperature.

Is that true or is that false? Take five seconds.

If you want more time, click pause.

Click play when you're ready to see the answer.

Okay, that is true.

Okay, why is it true? You've got five seconds to think about that.

Or if you want some more thinking time, click pause.

Click play when you're ready to see the answer.

It is true because cellular respiration is controlled by enzymes, and the rate of enzyme activity is affected by changes in temperature.

Great job if you got that right.

So in this practical, we will investigate the effect of temperature on the rate of respiration in small living organisms such as germinating peas.

A simple respirometer can be used to measure the rate of respiration at different temperatures.

And so this is the setup for the equipment that we're going to use today.

So we've got our germinating peas inside the boiling tube.

That's the organism that we've chosen to use for this practical.

And we've got a coloured liquid.

Now this coloured liquid will move up this tube when oxygen is used by the germinating peas for aerobic respiration, and we can measure the movement of that coloured liquid to help us to measure the rate of respiration.

So in our practical, the independent variable is the factor that we change.

And in this practical, that's the temperature.

We're gonna expose this setup to two different temperatures, and then we can compare the rate of respiration in each.

The dependent variable is the factor that we measure, and we're gonna measure the distance moved by the coloured liquid up the tube.

And now that we've got some variables, that should be controlled so that they don't affect our results.

So there's tonnes of things you could say for this, but just some of them are the various of glucose that the germinating peas have, because they use glucose for respiration.

The availability of oxygen.

Again, that's necessary for aerobic respiration.

So that affects the rate of aerobic respiration.

The number of organisms in the tube, that's important to keep constant.

And the length of time the organisms are allowed to respire.

Can you think of any others? I'll be quiet for a sec, so you can have a little discussion about that.

Which is a dependent variable? Is it A, availability of oxygen, B, distance moved by the coloured liquid at the tube, C, the length of time the organisms are allowed to respire, or D, the temperature? Take five seconds or if you want some more time to think about it, click pause.

Click play when you're ready to move on.

It is B, distance move by the coloured liquid up the tube.

Availability of oxygen and the length of time the organisms are allowed to respire, those are variables that should be controlled, and temperature, that was the independent variable.

Great job if you got that right.

In this part of the lesson, I'm gonna introduce you to the apparatus and materials that we need in order to carry out the practical.

So we start with a boiling tube.

In that boiling tube, we're gonna put some soda lime, some cotton wool and some small organisms. There're small organisms. I've chosen to use germinating peas with this practical, but you could use insects or invertebrates like mealworms or woodlice.

The cotton wool is there to prevent the organism from touching the soda lime, which is very corrosive.

So when you're handling this, please make sure that you don't touch the soda lime.

It should already be inside your pre-prepared boiling tube.

Make sure you don't get it in your skin or your eyes.

The soda lime is there to absorb the carbon dioxide produced by the organism.

Some other equipment we're gonna use.

So once we've set up our boiling tube, we're gonna put a bung and a capillary tube in the top of our boiling tube, and then we're gonna put the open end of the boiling tube into a beaker filled with coloured liquid.

So now, we're gonna set up the exact same apparatus, but it is not gonna have those small organisms in it.

And I'm gonna explain why that is at a later part in the lesson.

Right now, I just wanna talk about how to set up the equipment, okay, but it's okay if you don't understand like, okay, why do we have this almost exactly the same setup on the other side of the water bath? Don't worry about that now.

I promise I will explain it.

So as I've said already, actually, we then need to put both sets of our boiling tubes and our beakers into a water bath.

And the water bath is there 'cause it enables us to change the temperature of the organisms. So we're gonna conduct this experiment at two different temperatures, but whilst we've set it to the temperature we want, once it's in the water bath, it keeps those organisms at a constant temperature whilst they aspire.

You'll also need a timer or a stopwatch, and you'll need a permanent marker and you'll need a ruler.

Now that I've introduced you to the equipment, I'm gonna talk about how to set it up to make a respirometer.

So first step, collect a boiling tube containing soda lime.

Again, please remember soda lime is corrosive.

Make sure you wear safety glasses and avoid all contact with your skin and your eyes.

Number two, you're gonna add some cotton wool into the tube.

And number three, you're gonna add small living organisms, such as germinating peas on top of the cotton wool.

Step four, place a bung and a capillary tube into the top of the boiling tube.

And we're gonna call this tube tube A.

Repeat steps one, two and four to set up another boiling tube without organisms in it.

And that tube will be called tube B.

Step six, place both boiling tubes in a water bath at 25 degrees Celsius with the open end of the capillary tube outside the water bath.

Leave for five minutes to reach the temperature of the water bath.

Meanwhile, you can fill one or two large beakers with coloured liquid.

This video is gonna show you exactly how to set up your apparatus.

So it is possible to use other small living organisms and experiment instead of germinating peas.

One example is you could use mealworms, but it's really important to remember that whichever living organism we use, we must consider whether it's ethical to subject this organism to low and high temperatures that they're not used to, because it could cause them discomfort or it could kill them.

So keep that in mind when you're choosing which organism to use.

Okay, let's check to see if you understood that.

Label the apparatus.

Take five seconds or click pause if you need some more thinking time.

Click play when you're ready to move on.

Okay, let's look at the answers.

So A, that's the capillary tube.

B, that's the small organism.

For example, I'm choosing to use germinating peas.

C, that's the water bath, and D, that's the soda lime.

Well done if you got those right.

This is the first practise task for today's lesson.

Number one, why should you use safety glasses during this experiment? Number two, explain the purpose of the following parts of the apparatus.

A, soda lime, B, cotton wool, C, the water bath.

Number three, follow the method on the worksheet to set up the apparatus.

Okay.

You'll need to pause video now to give yourself enough time to carry out those tasks and click play when you're ready to move on with the lesson.

Let's look at the answers.

Why should you wear safety glasses during this experiment? Soda lime is corrosive.

So safety glasses reduce the risk of contact with your eyes.

Number two, explain the purpose of the following parts of the apparatus.

A, soda lime, to absorb the carbon dioxide produced by germinating pea, B, cotton wool, to stop the germinating peas from coming into contact with the soda lime, C, the water bath, to control the temperature the germinating peas are exposed to.

Great if you got those right.

Okay, we've completed the first part of today's lesson.

We've talked about the apparatus for measuring the rate of respiration, and now we're gonna talk about how to use the apparatus to measure the rate of respiration.

Step one, make sure the water bath is set to 25 degrees Celsius and that the boiling tubes have been left in for five minutes.

Step two, place the open end of each capillary tube into a beaker of coloured liquid.

Step three, mark the starting position of the coloured liquid on each capillary tube.

Step four, leave this for five minutes.

Step five, mark the end position of the coloured liquid on each capillary tube.

Step six, measure the distance the liquid in each capillary tube has travelled.

Step seven, using new capillary tubes, repeat the experiment two more times at 25 degrees Celsius.

And step eight, now do the experiment three times at 35 degrees Celsius using the same number of organisms. This video will show you exactly how to take the measurements you need in order to carry out the practical.

Which of these steps comes first? Is it A, after five minutes, measure the distance the liquid in each capillary tube has travelled, B, wait for the organisms to adjust to the temperature, C, mark the starting position of coloured liquid on the capillary tube, D, repeat at a different temperature.

Take five seconds.

If you want some more time, click, pause.

Click play when you're ready to see the answers.

Okay, the correct answer is B, wait for the organisms to adjust to the temperature.

That's really, really important to do before we start the practical properly.

Well done if you got that right.

Okay, this is the second practise task for today's lesson.

Step number one, follow the method on the worksheet to carry out the practical investigation.

And then the second thing I want you to do is to fill in tables one, this is what table one looks like, and table number two, this is what table two looks like, with your results.

Okay.

Pause video now to give yourself enough time to do that.

Good luck.

So you should have conducted your practical and you should have some results now, but in case something went a bit wrong, you didn't collect results, or if you just wanna see what typical results should look like, I provided some sample data here.

This is the final part of today's lesson.

We've talked about the apparatus for measuring the rate of respiration and how to set it up.

We've talked about the method for using the apparatus to measure the rate of respiration.

We've even got our results and now we're gonna talk about what to do with those results.

And we're gonna talk about evaluating the validity and data processing.

In order to collect valid results from an experiment, only the independent variable should affect the dependent variable.

A recap of what the variables are for this practical.

Our independent variable is temperature and the dependent variable is the distance moved by the coloured liquid at the top.

So what this first (indistinct) on the slide means is that for this, for the results of this practical to be valid, only the temperature should be affecting the distance moved by the coloured liquid at the tube.

There are some other factors that could affect the validity of the results, and we've taken some steps to ensure that doesn't happen.

So the availability of glucose, 'cause glucose is a reactant of respiration.

This is a good thing about using germinating peas.

Germinating peas have this, tonnes of glucose in them, so that's not something we need to worry about.

Availability of oxygen.

Again, this is present in excess in the boiling tube, so we don't need to worry about that.

That's taken care of.

The number of organisms. So for 25 degrees and for 35 degrees, we've chosen to use the same number of germinating peas each time 'cause otherwise, more germinating peas would be there's more organisms doing respiration, so that would increase the rate of respiration.

So we've taken care of that as well.

The length of time the organisms respire.

So we've chosen to use five minutes at each temperature.

So then we haven't talked about is the effect of atmospheric pressure on this practical, and that's why we have two tubes set up, tube A and tube B.

So now I'm gonna explain the purpose of tube B and what that's got to do with atmospheric pressure.

Pressure is important because the germinating peas use oxygen during aerobic cell respiration, and the soda lime that's in the boiling tube absorbs the carbon dioxide that's produced.

This decreases the number of gas molecules in the boiling tube, which decreases the pressure.

Let's have a look at that.

So my little square here is representing what's going on inside the boiling tube.

I've got a mixture of oxygen and molecules and a mixture of carbon monoxide molecules at the start of the practical.

After the practical, so after five minutes of the germinating peas respiring, we've got a different picture here.

So I want you to look at this second box, the end of the practical, and can you explain to me the difference between what the boiling tube looks like at the start of the practical in terms of gas molecules and why it has changed at the end of the practical? So I'll be quiet for five seconds.

If you need more time to think about it or to discuss with the people that are with you, click pause.

Click play when you're ready to see the answer.

So the number of carbon dioxide molecules has decreased, and this is because there was soda lime present in the boiling tube, and this has absorbed the carbon dioxide.

The number of oxygen molecules have also decreased.

This is because that oxygen has been used during aerobic cellular respiration.

So there are fewer gas molecules in the boiling tube at the end of the practical, and that decreases the pressure inside the boiling tube.

This means the pressure in the boiling tube is lower than in the capillary tube.

Air from the capillary tube moves into the boiling tube to equalise the pressure.

And this causes the liquid to be drawn up to move up the capillary tube towards the boiling tube.

This means the distance the liquid moves is related to the amount of oxygen that the germinating peas use for respiration and the distance measured by the coloured liquid, like the distance, how far the coloured liquid moves, we're gonna use that in our next lesson to calculate the rate of respiration.

Okay, let's check to see if you understood that.

Choose the correct option in each line to complete the explanation.

The coloured liquid moves away from or towards the boiling tube because oxygen or carbon dioxide gas is produced or used by aerobic respiration in the germinating peas.

Take five seconds.

If you want some more thinking time, click pause.

Click play when you're ready to see the answers.

Let's take a look at the correct answers.

The coloured liquid moves towards the boiling tube because oxygen gas is used by aerobic respiration in the germinating peas.

Great job if you got that right.

So there can be slight changes in air pressure all the time.

And changes in atmospheric pressure can affect the movement of liquid in the capillary tubes.

So boiling tube B, which is the boiling tube that we set up without the organism, enables us to measure the effects of slight changes in atmospheric pressure.

So we can subtract the distance moved by the liquid towards tube B from the distance moved towards tube A, which is the one with the organisms, and this enables to remove the effects of change in the atmospheric pressure from the results for tube A.

Let's see if you understood that.

True or false? Atmospheric pressure was controlled in the experiments.

Is that true or is that false? Take five seconds.

If you want some more thinking time, click pause.

Click play when you're ready to see the answer.

Okay, that is false.

Why is it false? Take another five seconds or pause the video again if you want some more time.

Click play when you're ready to move on.

It is false because atmospheric pressure was not controlled.

To increase the validity of the results, the effects of atmospheric pressure were measured in the tubes without organisms and then subtracted from the results for the tubes with organisms. Great job if you got that right.

This is the final practise task for today's lesson.

The first thing I want you to do is I want you to fill in table three.

So that will require you to calculate a mean, and just in case you forgot, here it is again.

So for the temperature for 25 degrees in tube A, let's say them are results were seven, eight, and six.

So I've got three results.

What I want you to do is to add them all together and then divide that answer by three and that will give you the mean.

So for my example here, the answer is seven.

You'll need to pause video now to give yourself enough time to fill in your table.

Click play when you're ready to move on with the lesson.

So you should have filled on your table now, but if you want some sample data to compare your results to, this is the kind of thing that you should have got.

Great work so far.

You've done really well.

This is the last question of the last practise task for the lesson.

So question number two.

A student is planning to investigate the effect of temperature on the rate of respiration in maggots.

This is a method.

Add the following to a boiling tube in this order: soda lime, cotton wool, 10 maggots.

Number two, step two.

Place a bung and capillary tube into the boiling tube.

Step three.

Place the end of the capillary tube into a beaker of coloured liquid.

Step four.

Mark the starting position of the coloured liquid on the capillary tube.

Step five.

After five minutes, mark the end position of the coloured liquid and measure the distance travelled by the liquid with a ruler.

Explain how they could improve their method to increase validity of their results.

You need to pause the video now to give yourself enough time to complete that answer and click play when you're ready to see what the correct answer is.

Good luck.

Okay, let's look at the answer.

So you should do the experiment at two or more different temperatures so you can see the effect of temperature on the rate of respiration.

Need to use a water bath to change the temperature of the maggots between experiments and to keep it constant during each experiment while the maggots expire.

Need to repeat the experiment three times at each temperature so that the mean distance moved by the liquid can be calculated.

And you need to include a tube without maggots so the effect of atmospheric pressure on the distance moved by the liquid can be measured and subtracted from the results from the tube with maggots.

Great job if you got that right.

Amazing work on today's lesson.

Let's summarise what we learned to help us remember it.

The effect of temperature on the rate of aerobic cellular respiration in small organisms can be investigated using a simple respirometer.

The independent variable is the temperature and the dependent variable is the distance moved by the coloured liquid up the capillary tube.

Controlling other variables releases their effects on the dependent variable, which increases the validity of the results.

When variables such as atmospheric pressure cannot be controlled, their effects can be measured and subtracted from the results.

The results will be used in the next lesson to calculate the rate of respiration.

Again, great job on today's lesson.

I hope to see you again soon for our next lesson.