This lesson is called the effect of pH on the rate of an enzyme reaction: plan and is from the unit biological molecules and enzymes.

Hi there.

My name's Mrs. McCready, and I'm here to guide you through today's lesson today.

So thank you very much for joining me.

In our lesson today, we're going to write a testable prediction and plan an investigation into the effect of changing the pH on the rate of an enzyme reaction.

So in order to do that, we're going to look at a good number of keywords in our lesson today, and they're shown up on the screen now.

Now, you might wish to pause the video to make a note of them, but I will introduce these words as we come across 'em throughout the lesson.

In our lesson today, we are going to plan the aim, then we're going to plan the method, and then we're going to plan for risk.

So I hope you're ready to go.

I am, let's get started.

So we know that enzymes are biological catalysts, which speed up the rate of a chemical reaction, and we can measure how quickly substrates are turned from substrates into products by the enzyme to see how quickly that chemical reaction is happening, to see what the rate is.

So by measuring the amount of substrate and how little there is left or how much product there is and how quickly that is being produced, over time we can measure the rate of the reaction, and therefore the rate of the reaction is simply a measure of how much change is happening per unit of time.

So how many substrates are being broken down or how many products are being created over a unit of time, such as a second or a minute.

So let's quickly check that.

Which of these is a measurement of the rate of a reaction? Is it A, how much substrate has been used up in grammes? Is it B, how much product was formed when the reaction finished in grammes? Or is it C, how much product was formed every second in grammes per second? I'll give you five seconds to think about it.

Okay, so hopefully from this you've spotted that the rate is grammes per second.

So there are two parts to the rate.

Remember that rate is a bit like speed.

And we're measuring the speed of a car, we're talking about things like miles per hour.

So we're talking about two units of measurement there.

And in this case it's grammes per second.

Well done.

So pH is a measure of the acidity of a solution.

Now, the lower the pH, so the nearer one, the pH is the more acidic that solution is, whereas the higher the value, the nearer number 14 it is, the more alkaline the solution is.

And I'm sure you're very familiar with this through a number of chemistry experiments that you've done in recent years.

Now, biologically enzymes that operate in the stomach, for instance, in the stomach acid, have the highest rate of reaction at between pHs of 1.

5 and 2.

So a pH of between 1.

5 and 2 would be considered the optimum pH for enzymes that operate within the stomach acid.

And if we took those enzymes outta the stomach and placed them somewhere where the pH was significantly different, such as in the intestines with a pH of 7.

5 to 8.

5, we would find that they wouldn't work anymore because the pH is radically different.

Now, if we compare the enzymes that are operating within the stomach acid to those which are operating within a cell, we'll see that enzymes that operate within cells have the highest rate of reaction within a pH of 7.

1 to 7.

2.

So a very narrow range of optimum enzyme activity for this pH.

So these enzymes work best at a pH of 7.

1 to 7.

2.

So if we took the enzymes that are working within a cell outta the cell and put them within the stomach acid, they wouldn't work anymore.

They would stop working because the pH is too extreme.

So we can see that enzymes have what we would call an optimum pH to work within, and that will be different depending on what the enzyme is and what its function is.

So enzymes designed to work in the stomach have a very different optimum pH from those designed to work within cells.

So let's quickly check our understanding.

So the enzyme amylase works in the mouth, which pH is likely to be the optimum pH for amylase.

So think about what the pH of your mouth might be.

So is it going to be pH 3.

0, pH 7.

0, or pH 10.

0? What do you think? I'll give you five seconds to think about it.

Okay, so hopefully you thought, well, the mouth isn't particularly acidic.

It doesn't burn my fingers when I put my fingers in my mouth, for instance.

So therefore a pH of 7.

0 is likely to be the optimum pH for the enzyme amylase, well done.

Now we're looking at planning a practical in today's lesson.

And when we're planning a practical, the first thing we need to decide is what we're aiming to investigate.

Because unless we've decided what we want to find out, we can't do any of the other planning that goes with planning a practical either.

Now, an aim of the investigation should be specific, concise and accurate.

It should really succinctly summarise what we're planning on finding out about within that practical.

So for instance, an investigation into the effect of temperature on the rate of reaction might have an aim along the lines of to measure the effect of changing temperature on the rate of enzyme activity.

So we can see within this aim that it's very specific, it is concise, that means it's short and is accurate, it very clearly states exactly what it is that we're looking for.

So we're measuring the effect of changing temperature on the rate of enzyme activity.

So let's check our understanding.

So the three students here are investigating how changes of pressure affect the boiling point of water.

So whose aim is most specific, accurate and concise? So Aisha says, "Whether the water will boil or not at different temperatures and pressures." Jacob thinks his aim should be "How a change in boiling point will affect the pressure of water." And Sophia is stating her aim as "To measure the effect of changing pressure on the boiling point of water." So whose aim is most specific, accurate and concise? I'll give you five seconds more to think about it.

Okay, so hopefully on review, you've said that Sophia's aim to measure the effect of changing pressure on the boiling point of water is most specific, accurate and concise of the three of them.

Well done if that's who you chose.

Now, once we've stated our aim, scientists usually then state what they think will happen in an experiment, and we call this a prediction.

So a prediction sets out the expected results using scientific understanding.

So in the experiment to investigate the effective temperature on the rate of reaction, a prediction might be that as the temperature increases, the rate of reaction should increase.

And above the optimum temperature, the enzyme becomes denatured, so the rate of reactions should decrease to zero.

So we can see within this prediction we are stating what we think is going to happen and a little bit about why we think that's going to happen happen, but most particularly we are stating what we think will happen.

So when we're writing a prediction, it's really important that we write a prediction that can be tested.

A testable prediction is really important.

Now the prediction doesn't have to be right and usually scientists write a prediction that they can then prove to be wrong.

But regardless of whether your prediction is right or wrong, it has to be testable.

And you can see that within this prediction that as the temperature increases, the reaction rate increases.

So we can test to see that as we increase temperature, whether the reaction rate does increase and then over the optimum past the optimum, the enzyme should denature and the rate of reaction should decrease to zero.

And again, that's another set of predictions that can be tested.

We can measure those, we can continue to increase the temperature and continue to measure what is happening to rate.

So let's check our understanding again.

So these students are still continuing their investigation interchanging pressure on water boiling point.

So who has stated a testable prediction? So Aisha says, "As pressure increases, the temperature at which water will boil will increase." Jacob says, "Pressure and temperature of boiling are related." And Sophia says, "Changing the temperature will alter the pressure and change the boiling point." But whose prediction is testable? I'll give you five seconds to think about it.

Okay, well hopefully you've said that Aisha this time has the testable prediction because you can see that she says, "As pressure increases the temperature at which water will boil will increase.

"So we can increase the pressure and measure the boiling point and see whether her prediction is correct.

So what I'd like you to do is to plan the aim and a prediction for the following investigation.

So the investigation that you will be doing is investigating the effect of changing the pH on the rate of enzyme reaction.

So using that, I would like you to firstly write an aim for the practical, and then I would like you to write a prediction please.

Now remember with a prediction, you don't need to prove yourself right in the experiments.

So, it doesn't matter whether it's right or wrong, but it must be testable.

So take your time over these, make sure you've got a really good aim and prediction and come back to me when you are ready.

Okay, so let's see what you might have written for your aim and prediction.

So for the aim, your aim should be along the lines of to measure the effect of changing pH on the rate of enzyme activity.

And it should be fairly close to that.

Your prediction might be something like at the optimum pH rate should be highest, and at other pHs the rate will be less.

But you might have worded it slightly differently or organised it in a different way, or you might have predicted the other way round for the rate, for instance.

But hopefully you've said something about the optimum pH and then other pHs that the enzyme will be subjected to within this experiment.

So check your work over, make any corrections if you need to, and then let's move on, well done.

So the next part of our experiment preparation is to plan the method.

So let's look at what we're going to be using in our experiment.

Well starch, as you hopefully will know, is a carbohydrate polymer of a sugar.

And because it's a polymer, it can be broken down into many, many smaller units.

Now these smaller units are called maltose, and that digestion happens by the enzyme amylase.

So amylase is the enzyme and it's taking the polymer, starch, and it's breaking it down into smaller molecules called maltose, which is a form of sugar.

And we're going to investigate the effect of pH on this chemical reaction.

Now we can use the chemical substance iodine to test for the presence of starch.

Now iodine usually has an orange brown colour to it, but in the presence of starch, iodine turns blue/black, and that's a very specific colour.

It's not blue, it's not black, it is blue/black.

So make sure you call it that.

So when starch is present, iodine is blue/black, and when there isn't any starch present, then iodine remains an orange brown colour.

So what colour does iodine turn in the presence of starch? Is it orange/brown, blue/black, or is there no change? I'll give you five seconds to think about it.

So hopefully you've remembered that starch turns iodine, blue/black, well done.

Now we're going to use a type of sampling method called continuous sampling.

And what that means is taking measurements frequently and regularly.

For instance, taking the temperature every minute would be continuous sampling or recording the volume of gas which has been produced every minute.

Again, that's an example of continuous sampling.

Now, continuous sampling can be done manually or it can be done using a data logger.

And a data logger is a piece of equipment that takes the measurement regularly and frequently and records it onto a computer.

So which of these methods is an example of continuous sampling, measuring the cloudiness every minute, measuring the mass, or taking the start and end pH, what do you think? I'll give you a few seconds to think about it.

So hopefully you've said that an example of continuous sampling is measuring the cloudiness every minute because this is frequent and regular.

So we are going to investigate the effect of change in the pH on the rate of the enzyme amylase at turning starch into maltose.

So we're going to have starch present to start off with, with amylase and a particular pH that we're investigating.

And that amylase will hopefully turn starch into maltose by digesting it.

Now we're going to use a continuous sampling method to see how quickly this chemical reaction takes place, if indeed it happens at all at the different pHs that we're going to investigate.

Now, when we're continuously sampling this practical, we are going to take a sample every minute of the chemical solution.

So that's the solution involving the amylase and the starch and the pH buffer.

And we're gonna take that sample every minute for 10 minutes and see how quickly that chemical reaction takes place, how quickly this starch is digested.

Now, every minute we're going to mix a sample with a spot of iodine solution within a spotting tile, and we're gonna do that every minute for 10 minutes.

So you can see on the spotting tile in the picture there, we've got 10 dots of iodine solution ready to go.

And into that are 10 samples of starch and the amylase.

So at the start, iodine will turn blue/black because there's plenty of starch present.

However, as the experiment continues, amylase will be able to digest the starch into maltose, and therefore the amount of which is present will reduce.

So eventually there will be no starch present and the iodine will stay orange/brown.

Now the rate at which this happens will depend on how quickly the amylase is able to work, and we're gonna see whether this is impacted by the pH that amylase is operating at or not.

So let's just quickly check our understanding using the following words, fill in the gaps to complete the sentences.

We will test for the presence of starch every so on.

This methodology is called something.

I'll give you a few seconds to think about it.

Okay, so hopefully you've said that we will test this presence of starch every minute, and this methodology is called continuous sampling.

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

So when we're planning a method, it's really important that we identify the variables within that method.

So the independent variable is the one that we're choosing to change.

The dependent variable is the one that we are measuring, and the control variables are the ones we are keeping the same across the entire experiment.

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

If we are measuring the rate of an enzyme reaction at three different temperatures, our independent variable would be the temperature because that is the one that we are choosing to change.

The dependent variable, the variable that we are measuring will be whether starch is present or absent.

In other words, the colour of the iodine solution and the control variables are all of the variables that we're keeping the same, such as the time interval between taking samples, how much so the volume that we're testing and the method that we're using to test and so on.

All of the things that we're keeping the same between the different experiments, they are our control variables.

So what I'd like you to do is match the variable with the example.

I'll give you a few seconds to think about it.

Okay, so hopefully you've identified that the independent variable will be the temperature.

That's the one we are choosing to change.

The dependent variable is the one that we are measuring, and that's going to be the presence of starch.

And the control variable might be the volume of sample that we're taking.

Well done if you've got all of those right.

Once we've decided our variables, we then need to write our methods so we know precisely what it is we're going to be doing step by step.

So a method is simply a list of instructions that we need to follow.

And because it is a list of instructions, like a recipe, it needs to be written very, very clearly and succinctly.

And the best way to do that is to firstly write it as a numbered list.

So you can see here in this method, each step is numbered 1, 2, 3, and so on.

We also need to make it very clear what it is that we want the person who's following this method to do.

So in each step, we're starting with a verb.

We're starting with a with a word which means that we have to do something.

And the words such as measure, place, combine, and use, continue and repeat are all good examples of verbs that we're starting our sentence with.

So we don't need to be fluffy with what we're saying, like firstly, you need to then go and do such and such and blah, blah, blah.

We just need to get on with what it is that we want them to do.

Because the person who is following the method won't want to have to wade through all our waffle to get through to exactly what it is that we are wanting them to do.

They want to just read what they've got to do and get on with it without having all that extra superfluous bumf around it.

So make sure that unlike my description just then, your method is short and succinct, following those two points, numbered list and starting with a verb.

So what did I just say then? How should a method be written? Should it be listed starting with a verb, numbered, starting with a verb, or numbered starting with then or next? What do you think? I'll give you a few seconds to think about it.

Okay, so hopefully you've identified the fact that our method should be written, numbered, and starting with a verb, well done.

So what I'd like you to do now is spend some time planning your investigation.

Now, the investigation that we're going to be planning is to investigate the effect of three different pHs on the rate of amylase digestion of starch using a continuous sampling method.

So the first thing you need to plan are the independent, dependent and control variables.

Remember that the independent variable is the one that you change.

The dependent variable is the one that you measure, and the control variables are the ones you keep the same.

Once you've planned your variables, then write your method.

And remember, the method needs to be written as a numbered list, starting each instruction with a verb and using short, succinct sentences.

And finally, I would like you to list the apparatus that you will use.

So take your time over this, follow the instructions really carefully and come back to me when you are ready.

Okay, so let's see what our method and variables might be.

So the independent, dependent and control variables.

Well, the independent variables should be the pH because that is the thing we are choosing to change.

The dependent variable is the presence or the absence of starch over time.

So that's the one which we are measuring.

And the control variables are all the variables that we're keeping the same.

So these might include the starting volumes, the starting concentrations, the temperature of the solutions, the volume, which is mixed with the iodine, the time between samples.

These are all example control variables, and hopefully you've listed at least some of those.

So just check your work over before we move on.

Then I asked you to write a method for this experiment using a numbered list and starting with a verb for each step.

So your method should be something along the lines of measure five millilitres of starch solution into a test tube.

Measure five millilitres of amylase solution into a different test tube.

Add five millilitres of pH7 buffer solution to this test tube.

Place both test tubes in a water bath at 21 degrees centigrade for five minutes.

Combine the starch and amylase plus buffer solutions and mix gently, then return to the water bath.

Using a pipette, remove a sample of solution and test in a spotting tile with iodine solution.

Continue testing every minute until the iodine solution stays orange/brown or 10 minutes has passed.

Repeat steps one to five using buffers at pH2 and pH12.

Now that's a long method, so check your work over and see if there's anything that you need to amend or add.

And finally, I asked you to list the apparatus that you will use.

So what will you ask your technician to provide for you? Well, hopefully you've included that you'll need two test tubes.

You'll need a water bath at 21 degrees centigrade.

You'll need a pH buffer solutions of pH2, 7 and 12.

You'll need iodine solution.

You'll three spotting tiles, one for each of the pHs.

You'll need a pipette.

You'll need a measuring cylinder, and you'll need a stop clock.

Maybe you call that a stopwatch or a timer.

So again, just check what you're going to be requesting from your technician in order to run this experiment.

And well done, that was quite an intense piece of planning to do.

So the final part of our planning involves planning for risk.

So we need to make sure that we are aware of the hazards that are present within our practical, what the risks are that they pose, and how we might then go on to limit them.

So a hazard is something that might cause harm.

A risk is the harm that it might cause.

And a limitation is something that you might do or an action that you might take that is going to reduce the risk of the hazard.

So for instance, a hazard might be glassware, a risk might be if it's broken, then it will be sharp and could cut.

And a limitation that you take might be to sweep up any broken glass as quickly as possible.

Now, it's really important that you identify the risks of these hazards in an experiment and then put safety measures in place to reduce those risks so that you keep yourself and other people within the lab nice and safe.

Now, if we did the experiment to measure the rate of an enzyme reaction at three specific temperatures, what might our risks be? So we're looking at enzyme rate at different temperatures.

So the hazards which we might identify in this practical might include hot water.

Now, hot water is likely to result in burns and scalds.

So our limitation would be to handle the equipment in water baths above 37 degrees with tongs and gloves.

Glassware might be another hazard, and the risk here would be breakages causing cuts, and our limitations would be worn others if breakages occur and to clear up broken glassware immediately.

And another hazard might be spilled liquids.

So if we drop some liquid as say on the floor for instance, it might cause a slip or a fall, and therefore our limitations would be to warn others if spillages occur and to clear up those spilt liquids immediately.

So that's an example of the hazards, the risks that they pose, and the limitations that we can put in place to limit the risks for an experiment to do with temperature.

So let's just check ourselves on this.

It is important to minimise the hazards of risks, true or false? I'll give you a few seconds to think about that.

Well, you should have said that that is false, but why is that false? So have a think using those two justifications, which justification correctly says why that is false? So you should have said that a hazard is what can cause harm, and a limitation is what reduces the likelihood of risks occurring.

In other words, the statement should say it is important to minimise the risks of hazards, well done.

So what I'd like you to do now is consider the risks involved or the hazards with this experiment.

So the experiment that you are planning is to investigate the effect of three different pHs on the rate of amylase digestion of starch using the continuous sampling method.

Now remember, the pHs that you are using include pH2, 7 and 12.

So a very acidic solution, a very alkaline solution, and a neutral solution.

So have a think about the whole of the experiment and I identify the hazards and their risks and then plan some appropriate limitations to manage and reduce the risk.

And I suggest you set it out in a neat table in order to do so.

Now pause the video and come back to me when you are ready.

Okay, so what sort of risks might you have identified with the hazards in this experiment? Well, you might have said that the pH buffers and the iodine solution are both hazards, and the risks are that they might produce acid or alkali burns or irritations.

So the limitations would be to avoid contact with skin and eyes, to wear eye goggles, and to wash solutions off skin immediately.

Another hazard might be glassware because the risk would be breakages causing cuts.

And so the limitations would be to warn others if breakages occur and to clear up broken glassware immediately.

And you might have also said that spilt liquids would become a hazard because the risks would be slips and falls, and so appropriate limitations would include warning others if S spillages occur and clearing up spilt liquids immediately.

Now, you might well have identified other hazards and their risks and limitations, but just review my work against yours and see if there's anything that you need to add or amend with your own limitations.

Now, well done.

That again, takes quite a lot of analysis and a lot of prediction as well, both in terms of the practical equipment we are using and how humans behave with that practical equipment, and that's quite a tricky thing to do.

So well done indeed.

So in our lesson today, we have planned an experiment to investigate the effective pH on the rate of enzyme activity.

And we've seen that when we're planning an experiment, we must consider the scientific context because this will allow us to develop an appropriate aim and a testable prediction.

Once we've written both of those, we then need to identify the independent and dependent variables and decide which variables we are going to control.

And that will then allow us to write an appropriate, concise and structured method that can be followed and also decide what apparatus we're going to require.

Once we've done all of that, we can then identify the hazards and their risks and consider how we might limit those risks, what limitations we can put in place.

And once we've done all of that, we are ready with our plan for the experiment investigating the effect of changing pH on the rate of reaction of the enzyme amylase on starch using a continuous sampling method.

So I hope you've enjoyed our lesson today and are feeling ready for this practical.

Thank you very much for joining me, and I hope to see you again soon, bye.