Lesson video

Welcome to this lesson from the Oak National Academy.

The title of today's lesson is explaining the effect of different substrates on the rate of cellular respiration, and it is taken from 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 analyse data collected from measuring cylinder, calculate the rate of cellular respiration, and explain the effect of different substrates on the rate.

Let's have a look at our keywords.

Today's lesson has got five keywords, and I'll read them out now.

Rate, a measure of how much change occurs per unit of time.

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

Substrate, the substance that fits into an enzyme's active site.

Enzyme, a biological catalyst.

And active site, the parts of an enzyme where a substrate binds.

So if you wanna go through this again, I'll be quiet for about five seconds, but if you want even more time maybe to copy those down and to read through them a couple of times, I suggest pausing in the video and then clicking play When you're ready to move on with the lesson.

Today's lesson is in two parts.

In the first part of the lesson, we'll talk about the data that you can process when you measure the rate of respiration by collecting the carbon dioxide produced by yeast in a measuring cylinder.

And in the second part of today's lesson, we'll talk about the effect of different substrates on respiration.

But first, data processing and the rate of respiration.

The rates of anaerobic cellular respiration in yeast can be measured using simple apparatus, shown in this diagram here.

So we have our yeast, which is immobilised and alginate beads.

The yeast are also submerged in water, so yeast can't respire the oxygen using the oxygen that's dissolved in water, so they're carrying around an aerobic cell respiration, cell respiration that's occurring without oxygen present.

So the yeast are inside this conical flask, which is connected to a delivery tube, and that delivery tube is connected to a measuring cylinder that is full of water, which has been turned upside down and it's also submerged inside a tank of water.

So as the yeast respire anaerobically, they produce carbon dioxide gas.

This carbon dioxide gas is represented in the bubbles you can see in the diagram, and that moves up the delivery tube and is then collected in the upturned measuring cylinder in the water.

So as the carbon dioxide gas moves through the delivery tube and into the measuring cylinder, it displaces the waters in the measuring cylinder, pushes it out, and then measuring the volume of carbon dioxide gas inside the measuring cylinder produced enables us to calculate the rate of respiration.

When setting up the measuring cylinder, it is usual to find some gas, which is air, trapped in the top.

And this is because you fill up the measuring cylinder with water, you place your hand on the open end of the tube and then you flip it round, you invert it as fast as possible.

So it's really, really easy to not fill up the measuring cylinder completely or for a small amount of water to escape, and that leads to this air pocket at the top of the measuring cylinder.

So this means the volume of gas recorded at the end of the experiment is not the true volume of carbon dioxide produced because of that air pocket that was there as a result of how you set up that apparatus.

The volume of gas in measuring cylinder at the start is likely to be different each time we set up the apparatus.

It was not controlled.

Again, because of this filling out the measuring cylinder and flipping it over, which is gonna have a little bit of water escaping or very easy not to fill out the measuring cylinder the whole way, you've got that air pocket, not a variable that's controlled.

So what do we do about it then? Because if we don't do something about it, this will cause random errors in the data because the amount of difference between the recorded volume of gas at the end and at the true volume of carbon dioxide produced will be different each time.

So as I said, this isn't something in experiment that's controlled, but we need to do something about it to negate the effects, otherwise, we're gonna have these random errors in our data.

The volume of gas in the measuring sensor at the start of the experiment was recorded.

To ensure the results are valid, we must subtract the volume of gas at the start from the volume of gas recorded at the end of the experiment.

This will tell us how much carbon oxide gas was produced by the yeast due to cellular respiration and not just because of that weird little air pocket that you have before you start recording the rate of respiration.

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

Calculate the amount of carbon oxide gas produced by yeast with sucrose and starch as substrates.

So the first line has been done for you for the substrate glucose.

So at the start of the practical, the volume of gas inside the measuring cylinder was four centimetres cubed.

At the end of the practical, it was 34 centimetres cubed.

So the total volume of carbon dioxide gas produced was 34, takeaway 4, which is 30.

I'll give you five seconds to complete the table, or if you want more time, you can get pause and click play when you're ready to see the answer.

Okay, let's go through the answers.

So for the substrate sucrose, there were 23 centimetres cubed of gas at the end of the practical, and eight centimetres cubes of gas at the beginning.

So we do 23, takeaway 8, that gives us 15 centimetres of cubed of carbon dioxide gas produced.

For the substrate starch, there were 10 centimetres cubes of gas at the end of the practical, and seven centimetres cubed of gas at the beginning of the practical.

So we do 10, takeaway 7, that gives us 3 centimetres cubed of carbon dioxide gas produced during this practical.

Well done if you got those right.

So in this practical, we measured the volume of carbon dioxide gas produced by the yeast in order to help us to understand the rate of respiration.

But the volume of carbon dioxide gas collected is not the rate of cellular respiration.

And I'll explain what I mean by that.

A rate is a measure of how much change occurs per unit of time.

So in this experiment, we calculate the rate of respiration using the volume of carbon dioxide gas produced in five minutes.

So our rate, the units we have for our rate, are centimetres cubed divided by minutes, so centimetres cubed per minute, and that we get that from the fact that we measured the volume of carbon dioxide produced in centimetres cubed, and then we divide that by the amount of time we took our measurement, which was five minutes.

So let's have a look at this table.

So this is for the substrate glucose.

The volume of carbon dioxide gas produced was 30 centimetres cubed.

So the rate of respiration is gonna be 30 centimetres cubed divided by the amount of time we measured that.

So that's five minutes, five.

so 30 divided by 5, so six centimetres cube a minute is our rate of respiration for the substrate glucose.

Let's check to see if you understood that.

Calculate the rate of respiration for each substrate.

The first one has been done for you.

So if the substrate glucose, the volume of carbon dioxide gas produced was 30, in order to figure out the rate of respiration, we do 30, the volume of carbon dioxide gas, divided by five, the number of minutes the measurement was taken, and that equals six.

Take five seconds to finish the rest of the table, but if that's not enough time, click pause and click play when you're ready to move on.

Okay, let's have a look at the answers.

So for sucrose, we need to do 15 centimetres cubed divided by five, and that gives us 3.

0 centimetres cube per minute.

For start, we need to do three divided by five, and that gives us 0.

6 centimetres cube per minute.

Well done if you've got those right.

We can use the data from the practical to compare the rate of respiration for different substrates.

A comparison points out similarities and differences, and it does this by using words such as more or less or using words that end in E-R such as bigger or E-S-T such as biggest.

So let's have a look at the table here.

What I want you to do now is to compare the rate of respiration for the different substrates in the table.

You can have five seconds, or if that's not enough time, you can hit pause and you can hit play when you're ready to move on.

How did you do? Let's have a look at the kind of thing you could have written.

So what I've written is the table shows that the rate of respiration is greatest, E-S-T, when the substrate is glucose and lower for sucrose and lowest for starch.

Well done if you got that right.

Let's keep practising that.

Whose statement best compares the rate of respiration for different substrates? Is it Aisha? "The rate of respiration is highest when glucose is used and lower when other substrates are used." Is it Lucas? "When glucose is used, the rate of respiration is high." Or is it Sofia? "The rate of respiration changes depending on the substrate used." Take five seconds, or if that's not enough time, click pause and click play when you're ready to see the answers.

Let's have a look at the answers.

So Aisha is correct.

Let's have a look at all of them to figure out why Aisha is correct.

Let's start with Sofia.

"The rate of respiration changes depending on the substrate used." That's a correct statement, but it's not a comparison.

It's too vague to compare anything.

It's not really saying much at all.

Let's have a look at Lucas' statement one.

"Glucose is used, the rate of respiration is high." That's another correct statement, and it is slightly more detailed, but again, it's not comparing the rates of respiration.

It's only mentioned glucose, for example, it's not mentioned any of the other substrates, and it's not used words that end in E-R or E-S-T.

So that's another giveaway that might not be a comparison.

Let's look at Aisha's.

"The rate of respiration is highest when glucose is used and lower when other substrates are used." So she's mentioned more than one substrate.

She's used the word that ends in E-S-T and the word that ends in E-R.

So these are all good indicators that it's a comparative statement.

Well done, if you've got that right.

When describing data, it's also useful to make a general comment and describe a specific example from the data.

A general comment might be, as the temperature increases, the rate of respiration increases, and a specific example might be, at 40 degrees, the rate is double than the rate of 20 degrees.

So a specific example is about looking at a pattern in the data and saying something like double or triple or half looking for a numerical relationship between the data points.

So let's have a look at this table now.

So I want you to look at that table and describe the data.

First, make a general comment about the trend of the data and then try and give a specific example from the data.

So you can have five seconds or if that's not enough time, click pause and click play when you're ready to move on with the lesson.

How was that? Let's have a look at the kind of thing that you could have written.

So the general comment could be, the table shows that the rate of respiration changes as the substrate changes.

A specific example could be, the rate of respiration measured for glucose is double the rate of sucrose, and it is 10 times the rate for starch.

So that's looking at a numerical relationship between the data in the table.

Well done if you got that right.

Let's keep practising that.

Which of the statements about the table is correct? Is it A, the rate of respiration for glucose is double the rate for sucrose.

B, the rate of respiration for glucose is 10 times the rate for starch.

C, the rate of respiration for sucrose is five times the rate for starch.

Or D, the rate of respiration for sucrose is faster than the rate for glucose.

Take five seconds, or if that's not enough time, Click pause and click play when you're ready to see the answers.

Okay, let's look at the answers.

C is correct.

The rate of respiration for sucrose, so let's have a look, 2.

5 is 5 times the rate for starch, 0.

5.

Yep, that makes sense.

Let's have a look at the other ones.

A, the rate of respiration for glucose is double the rate for sucrose.

Rate of respiration for glucose is 5.

4.

Rate of respiration for sucrose is 2.

5, no, double 2.

5 would be 5.

0.

B, the rate of respiration for glucose is 10 times the rate of starch.

Let's have a look.

Rate of respiration for glucose 5.

4, rate of respiration for starch is 0.

5.

No, again, 10 times 0.

5 would be 5.

0.

And D, the rate of respiration for sucrose is faster than the rate for glucose.

The rate of respiration when sucrose is used is 2.

5 centimetres cube per minute.

But the rate of respiration when glucose is used is 5.

4 centimetres cube per minute, which is much higher than when sucrose is used, so D can't be correct either.

Well done if you got that right.

This is the first practise task of today's lesson, and you're doing really well so far.

Answer the following questions about the experiment.

Number one, use the sample data on the worksheet to complete table two.

Number two, explain why the units for rate of respiration in this experiment are centimetres cubed per minute.

And number three, use table two to describe the effect of the different substrates on the rate of respiration.

You'll need to pause a video now to give yourself enough time to do your answers, and then click play when you're ready to check your answers.

Good luck.

Let's have a look at the answers.

So our sample data for sucrose is this.

Our mean would be 15 plus 21 plus 12.

All of that added together, and then divided by by three, so that would be 16.

And then our rate of respiration would be 16 divided by 5 'cause that's the length of time that the measurement was taken, so that's 3.

2.

Again for starch, three plus one plus five all added together and then all divided by three, that would be three.

And then 3 divided by 5, 0.

6.

Question two, explain when the units for rate of respiration in this experiment are centimetres cubed per minute.

A rate is a measure of how much change occurs per unit of time.

The rate was calculated by measuring the volume of carbon dioxide produced, measured in centimetres cubed, over five minutes.

Number three, use table two to describe the effect of the different substrates on the rate of respiration.

The table shows that the rate of respiration is greatest when the substrate is glucose, lower for sucrose, and lowest for starch.

Great job of you got that right.

We completed the first part of today's lesson.

We looked at data processing and the rate of respiration.

Now we're gonna talk about the effect of different substrates on respiration.

The type of substrate you used affects the rate of respiration because cellular respiration is controlled by enzymes.

So here, we've got a diagram of an enzyme.

An enzyme is a biological catalyst.

It speeds up the rate of reaction.

Every enzyme has an active site.

And the substrate fits into the active site.

So that purple hexagon there, that's a substrate fitting into the active site of the enzyme.

We can use a lock and key as a model of an enzyme and its substrate.

In this model, the lock is the enzyme, the keyhole is the active site, and the key is the substrate.

Locks are specific for their key.

Keys come in many different shapes, but only one key has the correct shape to fit into the lock's keyhole.

Enzymes are specific for their substrate.

Substrate molecules can also have many different shapes, just like keys, but only one substrate has the correct shape to fit into the enzyme's active site.

Let's check to see if you understood that.

Each enzyme can act on many different substrates.

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

If you want more thinking time, Click pause and click play when you're ready to see the answer.

That is false, but why is it false? Take another five seconds to think about it, or click pause if you want some more time.

Click play when you're ready to move on.

It is false because each enzyme is specific to just one substrate.

Other substrates will not fit into an enzyme's active site.

Well done if you got that right.

Let's take what we just learned about enzymes, active sites, and substrates and put it into the context of this practical.

For this practical, the rate of cellular respiration was highest when glucose was used as substrate.

This is because the enzyme that initiates cellular respiration has an active site that's specific to glucose molecules.

For yeast to use starch or sucrose respiration, the starch and sucrose must be first broken down into glucose.

So here we've got a starch molecule, which is made up of lots of different glucose molecules bonded together.

So the yeast needs to break down the starch into all these individual glucose molecules before cellular respiration can begin.

So this takes time, and this causes the rate of respiration to be lower.

In the sample data, the rate of respiration was: fastest with glucose, slower with sucrose, and slowest with starch.

How can we explain these observations? Take five seconds, or if that's not enough time, click pause and click play when you're ready to move on.

Let's have a look.

starch is a larger molecule in sucrose, so it takes longer to break down starch into glucose respiration, and not as long to break down sucrose.

Glucose is the correct shape to fit into the active site, and so that's why glucose is the fastest.

Let's check to see if you understood that.

The enzyme that initiates cell respiration is A, specific to starch, B, specific to sucrose, C, specific to glucose, D, can use any substrate.

Take five seconds, or if that's not enough time, click pause and click play when you're ready to see the answer.

Okay, let's look at the answer.

The answer is C, the enzyme that initiates cell respiration is specific to glucose.

Well done if you got that right.

This is the final practise to ask for today's lesson.

Number one, define the following key terms: enzyme, active site, substrate.

Number two, use the lock and key model to explain why the rate of respiration is faster when glucose is provided as a substrate, and slower when starch is provided.

You'll need to pause the video now to give yourself enough time to do that, and then click play when you're ready to see the answers.

Good luck.

Let's look at the answers.

Define the following keywords.

A, enzyme, a biological catalyst.

B, active site, the part of an enzyme where the substrate binds.

C, substrate, the substance that fits into an enzyme's active site.

Number two, use the lock and key model to explain why the rate of respiration is highest when glucose is used as a substrate.

Enzymes are specific to only one type of substrate.

In the lock and key model, the enzyme is the lock and the substrate is the key.

Only one type of substrate key will fit into the enzyme's active site, lock.

The enzyme that initiates cellular respiration is specific to glucose.

This means that other carbohydrate substrates, such as starch, must be broken down into glucose first before respiration can take place.

This is why when yeast are given glucose, the rate of respiration is much faster than if they're given starch.

Well done if you've got that right.

Well done on today's lesson.

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

The rate of cellular respiration yeast can be measured by collecting the carbon dioxide produced in an upturned measuring cylinder.

The rate of respiration is calculated by measuring the volume of carbon dioxide gas produced and dividing this by the period of time the experiment lasted.

The units are centimetres cubed per minute.

The enzyme that initiates cellular respiration has an active site that is specific for glucose molecules.

No other substrate will fit.

For yeast to use starch for sucrose respiration, they must be broken down into glucose first.

This takes time, so the rate of respiration is slower.

Well done on all your hard work today, and I hope to see you again really soon for our next lesson.