This presentation is going to review the starch and amylase experiment that you did in class. So in this experiment we used the enzyme amylase and that was salivary amylase. So we used our spit to break down starch into simple sugars and those sugars were glucose molecules.
The presentation is going to explain how iodine is used as a test for starch. We can use this test to track the digestion of starch by amylase. We know that starch is a type of carbohydrate, find it in potatoes, rice and pasta. Iodine is a chemical and one of its uses can be to test for the presence of starch. So it's known as the starch test and as you can see here, iodine normally is this sort of orangey yellow colour.
Typically we say that it's yellow. And when iodine is dropped onto something which is starchy, we get this blue-black colour. A very dark blue-black colour.
So this is known as a positive test for starch. Now starch is known as a polymer. Polymers are very long molecules.
So this is only part of a starch molecule. This molecule would be stretching on and on and on and on and on. Very long polymers. The enzyme amylase has an active site which perfectly fits this particular substrate. So here's the enzyme fitting into this substrate.
So starch is the site. substrate. Amylase is the enzyme and the amylase can break down the starch molecule into these smaller glucose molecules and these small molecules are known as monomers. So as you can see we can go from a very long polymer to much smaller monomers. So let's have a look and see what's happening in this experiment.
You can pause the slides, of course, to read the information. So let's get over this idea of a water bath. So simply, what we've got here is a beaker containing water. And we're going to keep this water at a particular temperature.
So we'll use a thermometer just to gauge that temperature. Inside the water bath, we've got a couple of test tubes or boiling tubes. Now, one of these boiling tubes contains the enzyme amylase, our spit.
And the other... test tube or boiling tube contains the starch solution and we're going to keep them in this water bath for 15 minutes. So here's a question why do the solutions need to start at the same temperature? Pause the video and see if you can think of the answer to that.
So the answer is temperature can affect the enzyme activity. So this variable must be controlled. So obviously we're controlling temperature because temperature affects the rate of reaction.
OK, so what we've got here is a spotting tile. and the spotting tile is used in experiments like this and we can place in each one of these dimples of the spotting tile some iodine and you can see the iodine is a yellowy colour in this tile Okay, so after 15 minutes we're going to mix the starch and the enzyme together. So we're hoping that this enzyme will start digesting the starch. You can see the level in the boiling tube is a little higher here. So another question here, why is the starch stroke amylase solution, why is this mixture kept in the water bath?
Again, think of the answer to that question, typical GCSE question. The answer is pretty much the same as the last one. It's all about controlling variables, it's about controlling the temperature so it doesn't affect our results.
So every few minutes what we're going to do is take a drop out of the starch amylase solution that's sitting in the water bath. You're going to take that from the tube and you're going to add it to one of these dimples in the tile. So here you can see the first one carried out and it's a blue So now we can see the results of this experiment.
This was at the very start of the experiment, so time zero. Then at two minutes, a little drop of the starch amylase mixture was taken out and placed in the iodine. And you can see this was done every two minutes.
So another GCSE question. When was the digestion of starch by MLAs complete? Explain your answer. So the answer should be between 12 and 14 minutes. It would be quite easy just to say 14 minutes, but in reality that complete digestion of starch could have happened somewhere between 12 and 14 minutes.
To explain the answer, of course, we can see the colour change taking place. Thank you. So there are two parts to this question really. When was the digestion of starch complete? Well, between 12 and 14 minutes, that'll get you a mark.
And explain your answer. What you need to do there is explain the colour change. So we've got a slight change in colour, and that would be the explanation there. So when we see yellow, that means we know all the starch has been broken down.
So there's the explanation. So that's the starch enamelase experiment explained and I know that our year 9 students got some good results here.