Welcome to this lesson from the Oak National Academy.

Today's lesson is a practical lesson, and we're gonna look at "The Effect of Different Substrates on Cellular Respiration in Yeast," and it's taken from the unit Aerobic and Anaerobic Cellular Respiration.

Hi, 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 investigate the effect of different substrates on cellular respiration in yeast by using a measuring cylinder to collect the gas produced.

Let's have a look at our keywords.

Today's lesson has five keywords.

I'm gonna read them out now.

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

Independent variable, the factor that we change in an experiment.

Dependent variable, the factor that we measure in an experiment.

Random error causes results to differ by different amounts due to a factor other than the independent variable, which is the factor we change.

Systematic error causes measurements to differ from the true value by the same amount each time they're taken.

Okay, if you want some more time to read through those, I'll be quiet for five seconds, but if that's not enough time for you, you can pause the video and then click play when you're ready to move on.

Today's lesson is in three parts.

In the first part of today's lesson, we'll talk about the context of the practical and how to set up the apparatus for measuring the rate of respiration.

In the second part of today's lesson, we'll talk about how to use the apparatus to measure the rate of respiration, which is the proper part of the practical.

And then finally, we'll talk about what to do with the results and how we ensure validity.

But first, let's talk about the apparatus for measuring rate of respiration.

The organism we're measuring the rate of respiration in this practical is yeast.

So let's give you a little context for yeast, what they are, and why we're gonna use them.

So here we have a yeast cell, and yeast are a unicellular, so made of one cell, microorganism, and they're classified as a fungi.

Anaerobic cellular respiration in yeast helps us make useful products, including bread and alcoholic drinks.

So you might have made bread at home or in a food tech lesson, and you add yeast to it in order to produce carbon dioxide, and that causes the bread to rise.

Yeast also make ethanol, what's used to make drinks alcoholic like beer and like wine.

Anaerobic cellular respiration is a form of respiration that occurs when oxygen isn't available.

In microorganisms such as yeast, anaerobic cellular respiration can be summarised using the following equations.

Before I introduce the equations, I just wanna point out that anaerobic cellular respiration is many different chemical reactions, and these equations are a summary of all of those chemical reactions.

I'm not telling you the whole story, but they're a useful summary.

It's really important that we know this equation because it's gonna help us to put in context what's happening in the lesson.

And we're collecting a gas, well, what gas is that? Why are we collecting it? Why is it being produced? So this is gonna help us contextualise some of that.

So, I'm gonna show you the word equation and the balanced symbol equation.

So our only reactant in anaerobic cellular respiration is glucose.

So that's what it looks like as a balanced symbol formula.

So yeah, like I said, that's our only reactant glucose reacts to make, and then we have two products, we have ethanol, that's what it looks like in chemical formula.

And then we also have carbon dioxide.

And as I said, those are our products.

So, it's important to remember the reactants and the products of anaerobic respiration 'cause that's gonna help us to understand the practical.

So before we do anything else, I'm gonna check to see if you can remember that word equation and that balanced symbol equation.

Which gas is produced by yeast in anaerobic cellular respiration? Is it a, oxygen, b, water, c, carbon dioxide, or d, lactic acid? Take five seconds or if you want some more time to think about it, click pause, and click play when you're ready to see the answer.

Okay, let's have a look at the answer, it is c, carbon dioxide.

Great job if you got that right! So this practical is looking at the rate of respiration in yeast and it's looking at the effect of different substrates on the rate of respiration.

So let's talk about enzymes and substrates.

Anaerobic cellular respiration is controlled by enzymes.

So here I've got a simple diagram of an enzyme.

And this part that I've labelled here is the active site.

At the start of the process of anaerobic cellular respiration, glucose is the substrate that fits into the act of site of the enzyme.

So here I've got here my little purple hive skin that represents glucose, and that's a substrate.

A substrate is something that fits into the active site of an enzyme.

So in this context, glucose is the substrate for this enzyme.

And this can be likened to a key fitting into a lock.

Well, you have a key to your front door, only one key opens your front door, your front door key, and that's it.

You can't use a key that opens a window on your house to open the front door of your house.

And enzymes are specific to specific substrates just like keys are specific to certain locks.

So different substrates will not fit into the active site of an enzyme.

And this is because the active site of each enzyme is specific to its substrate, like a lock and its key.

Yeast can break down some other carbohydrates to produce glucose to use in cellular respiration.

So here we've got a polysaccharide called starch.

So it's made up of lots of different glucose molecules chemically joined together.

So the yeast can break down starch and turn that into glucose, and then that glucose can fit into the active site.

But you probably guessed that takes extra time.

It takes extra time to break down the carbohydrates to produce glucose.

And so that has an effect on the rate of cellular respiration, which is what we're gonna look at today.

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

True or false.

Many different substrates can fit into an enzyme's active site.

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 false.

But why is it false? Take another five seconds or pause if you want some more thinking time, and click play when you're ready to answer.

It is false, because each enzyme is specific to just one substrate, other substrates will not fit into an enzymes active site.

Great job if you got that right! We will investigate the effect of different substrates on the rate of cellular respiration in yeast.

This can be done by collecting the carbon dioxide gas produced by the yeast during anaerobic cellular respiration.

So I'm gonna show you the apparatus we're gonna use.

So let's label it.

We've got a conical flask.

In the top of that conical flask is a bung that's connected to a delivery tube, which is connected to a measuring cylinder that's been turned upside down, and that's to collect the gas.

The measuring cylinder is inside a water tank, which is filled with water.

And inside that conical flask, we've got our yeast, and this is the organism that's doing the respiring and then producing the carbon dioxide gas, and the yeast have been immobilised inside alginate beads.

We also have a water bath, and this controls the temperature.

Okay, let's see if you understood that.

Label the apparatus.

Take five seconds or click pause if you want some more time to think about your answer, and click play when you're ready to see the answers.

Okay, let's look at the answers.

a is the delivery tube, b is a measuring cylinder, c is the yeast, which is immobilised in sodium alginate, and d is the water bath.

Great job if you got that right! Let's look at the variables in our practical.

The independent variable, the factor we change, is the type of substrate we're gonna use.

The dependent variable, which is the factor that we measure, is the volume of gas collected in the measuring cylinder.

Variables that should be controlled so that they don't affect our results are the mass of substrate, volume of water, mass of yeast of alginate beads, the temperature, the length of time the organism are allowed to aspire.

Can you think of any others? I'll be quiet for five seconds and if you want some more time to think about it or discuss, click pause, and click play when you're ready to move on with the lesson.

Let's check to see if you understood that.

Which is the dependent variable? Is it a, the mass of the yeast in alginate beads, b, the substrate, c, the temperature, d, the volume of gas collected in measuring cylinder.

Take five seconds or click pause if you want more time, click play when you're ready to see the correct answer.

The answer is d.

Volume of gas collected in the measuring cylinder.

Great job if you got that right! Now that we're familiar with the equipment we're gonna use, let's talk about how to set up the apparatus.

Step one, add the substrate to a conical flask.

Step two, add water to the conical flask and swirl carefully.

Step three, add the alginate beads containing immobilised living yeast cells to the conical flask.

Step four, place a bung and delivery tube into the conical flask.

Step five, place a conical flask in a 40 degree water bath.

And step six, wait five minutes for the yeast to start respiring at constant rate.

So that five minutes whilst you're waiting for the yeast to respire at constant rate, you can also set up the following.

Fill up your measuring cylinder with water.

Cover the end of your measuring cylinder and carefully turn it upside down.

So we're inverting it.

Place the measuring cylinder in a tank of water and clamp it into position.

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

Let's see if you understood that.

Which of the following is not a step in setting up the apparatus? Is it a, add the alginate beads containing immobilised living yeast cells to the conical flask? b, wait five minutes for the yeast to start respiring at constant rate.

c, place the conical in a hundred degree water bath and clamp it in place.

d, fill the measuring cylinder with water.

Take five seconds, and if you want some more time to think about it, click pause, and click play when you're ready to see the answers.

It is c.

We should not be placing a clinical mask in a hundred degree water bath.

It should be 40 degrees.

Well done if you got that right! This is the first practise task of today's lesson.

Step number one, follow the method on the worksheet to set up the apparatus.

Number two, label the apparatus on the diagram.

Number three, explain why using a different substrate will affect the rate of cellular respiration in yeast.

You'll need to pause the video now to give yourself enough time to think about your answers, to write 'em down, and click play.

And we'll need to move on with the lesson.

Good luck.

Let's check your answers.

So here's the apparatus, and let's label it correctly.

Got conical flask, bund, delivery tube, measuring cylinder, water tank filled with water, yeast immobilise in alginate beads, and the water bath.

Question three, explain why using a different substrate will affect the rate of cellular respiration in yeast.

Cellular respiration's controlled by enzymes.

Each enzyme has an active site that is specific for its substrate, like a lock and its key.

A different substrate will not fit into the active site.

Yeast can break down some other carbohydrates to produce glucose to use in cellular respiration, but takes extra time to break down these carbohydrates.

So this affects the rate of cellular respiration.

Great job if you got that right! We completed the first part of today's lesson.

We've talked about yeast and the apparatus needed for the measuring rate of respiration.

Now, I'm gonna talk about how to use the apparatus to measure the rate of respiration.

This is a method for the practical.

Step one, at the start of the experiment, record the volume of gas that is already present at the top of the measuring cylinder.

So in order to do that, you need to make sure that you read the volume from the bottom of the meniscus.

I've magnified here on what the meniscus is.

So you can see, in the measuring cylinder, the surface of the water isn't flat, it's curved, and that curve in the surface of the water is the meniscus.

So you read the volume of liquid from looking at the bottom of the meniscus, moving along and seeing what volume of water that corresponds to.

Okay, once you've done that, you then place the end of the delivery tube into the measuring cylinder.

You leave it for five minutes, and after five minutes, remove the end of delivery tube from the measuring cylinder.

Then you record the volume of gas in the measuring cylinder.

Repeat steps one to two, one to five, sorry, two more times.

Remember to record the volume of gas at the start and at the end each time.

Then repeat the experiment to collect data for the other two substrates you're gonna use.

So maybe you start with glucose and then you'll use starch next, and then sucrose, for example.

Okay, let's see if you understood that.

This video will show you exactly how to take the measurements you need in order to carry out the practical.

Which measuring cylinder contains 20 centimetres cubed of gas? Take five seconds.

If you want some more time to think about it, click pause, and click play when you're ready to see the answer.

Okay.

The answer is a.

And that's because if we look at the surfaces of the water, there is the meniscus, which is that curved layer at the top of the water.

And the bottom of the meniscus, that's on the same mark as the 20.

Well done if you got that right! This is the second practise task for today's lesson.

The first thing you need to do is to follow the method on the worksheet to carry out the practical investigation.

And then you need to fill in Table 1 with your results.

Okay, you'll need to pause the video now to give yourself enough time to do that and click play when you're ready to move on with the lesson.

So you should have completed the practical by now and you should have some results.

In case something went wrong with your practical or if you just wanna compare your results against some sample data, here's some sample data.

We're onto the final part of today's lesson.

We've talked about how to set up the apparatus for measuring the rate of respiration, we then measured the rate of respiration with the apparatus, and now we're gonna talk about results and ensuring validity.

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

A reminder that independent variable for this experiment was the type of substrate and the dependent variable was the volume of gas collected in the measuring cylinder.

So validity in the context of this experiment means that only the type of substrate should be affecting the volume of gas that's been collected in the measuring cylinder.

Some other things that could affect the volume of gas include the mass of the substrate, the volume of water, the mass of yeast in alginate beads, the length of time the organisms respire, and the temperature.

And we try to keep these the same for each substrate.

So measuring the results, when we're using glucose, kept all these things the same, when we carried out the practical using starch, try to keep all those things the same.

And for every substrate, try to make sure these are as constant as possible.

So it's important to control the temperature using the water bath because temperature affects the rate of cellular respiration.

As temperature increases, enzyme and substrate molecules move faster.

So in my diagram here, there's little orange shapes, those are our enzymes, and the little purple shapes, those are the substrate.

So they're moving faster when they've got more temperature, they've got increased kinetic energy.

And so there are more successful collisions, and that means that the rate of reaction increases.

Above the optimum temperature however, the enzyme is denatured and the substrate no longer fits.

So denaturing is when that special part of the enzyme, the active site, the bonds break down in the active site and it's no longer the right shape, the substrate no longer fits into it.

And when this happens, the rate of reaction decreases.

Let's check to see if you understood that.

True or false.

Increasing the temperature allows enzyme reaction to keep increasing forever.

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

If you want some more time, click pause, click play when you're ready to move on.

Okay, it is false.

But why is it false? Take another five seconds or click pause if you want some more time, click play when you ready to see the answer.

It is false because high temperatures above the optimum cause enzyme molecules to change shape, so the enzyme works less well and reaction rate drops.

At very high temperatures, the enzyme is denatured and stops working.

So the rate equals zero.

Great job if you got that right! Another thing to consider in a practical is how you take measurements.

The way we measure and record the volume of gas in the measuring cylinder also affects the results.

As we talked about before, the surface of the water in the measuring cylinder is curved, and this is called the meniscus.

We always read the volume from the bottom of the meniscus.

If we read it a different way each time, this could cause a random error in the data.

So maybe one time you read the volume of water from the top of meniscus, but all the other times, you read it from the bottom of meniscus, that would be an example of a random error because that one time that you measured it from the different part of the meniscus, your result is gonna be out by the difference between the top and the bottom of the meniscus.

So that's an example of a random error.

Because we read it the same way each time, any difference between the reading and then the true value is the same for each reading.

And this is a systematic error, and it affects all the results equally, reflect them all in the same way.

And so we can still make valid comparisons between each of the results because they're all affected equally.

So the volume of gas in the measuring cylinder at the end of the experiment is not actually a direct measurement of the rate of cellular respiration.

In the next lesson, we will process our data, use the processed data to calculate the rate of respiration in yeast, and then explain the effect of different substrates on the rate of cellular respiration.

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

The volume should always be read from the bottom, middle, or top of the meniscus.

This removes meniscus, random, or systematic error from the data.

Any difference between the reading and the true value is the same for each reading.

It affects all the rules the same way, so we can make a valid comparison between them.

This is a meniscus, a random, or a systematic error.

You can take five seconds and think out your answers, or if you want some more time, click pause, and click play when you're ready to move on.

Let's look at the answers.

The volume should always be read from the bottom of the meniscus.

This removes random error from the data.

Any difference between the reading and the true value is the same for each reading.

It affects all the results the same way, so we can make bad comparisons between them.

This is a systematic error.

Great job if you got that right! This is the final practise task for today's lesson.

For this practical investigation, identify the independent variable, dependent variable, describe how temperature was controlled, what is a meniscus? Describe how to use a meniscus to measure the volume of gas in the measuring cylinder.

And number five, Izzy noticed that after 30 minutes, the yeast stop producing carbon dioxide.

Explain why? You need to pause the video now to give yourself enough time to write down your answers and click play when you ready through the answers.

Good luck.

Let's look at the answers.

For this practical, the independent variable was the type of substrate the yeast used to respire.

The dependent variable was the volume of gas in the measuring cylinder.

Number two, describe how temperature was controlled.

The conical flask containing the yeast was placed in a water bath.

Number three was a meniscus, the curved surface of water in a container, for example, a measuring cylinder.

Number four, describe how to use the meniscus to measure the volume of gas in the measuring cylinder.

You read the volume from the bottom of the meniscus each time.

And finally, number five, Izzy noticed that after 30 minutes, the yeast stopped producing carbon dioxide.

Explain why? The yeast may have used up all the substrate they had available for cellular respiration.

If they can no longer respire, they won't produce carbon dioxide gas as this is a product of cellular respiration.

Great job if you got those right! Great job on today's lesson.

I hope you really enjoyed the practical, and let's summarise it now so we can help remember it.

The effect of different substrates on the rate of cellular respiration yeast can be investigated using simple apparatus.

As the yeast respire, they produce carbon dioxide, which will displace water in a measuring cylinder.

The independent variable is the substrate and the dependent variable is the volume of gas collected.

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

Reading the volume from the bottom of the meniscus each time removes random error from the results, leaving only systematic error.

So valid comparisons between the results can be made.

Again, amazing work.

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