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So this practical is to demonstrate

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enzymes as a biological catalyst,

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so in our body we have chemical

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reactions going on all the time,

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but sometimes the products of those

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chemical reactions will require a little

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bit sooner than if we allow the reaction

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to take place naturally. So in order

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to speed up those chemical reactions,

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we produce enzymes and enzymes

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are biological catalysts.

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Catalysts speed up the rate of reaction.

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So what we're going to demonstrate with

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this one then is the complex structure

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of starch which we consume through

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our food products and amylase as

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our biological catalyst, the enzyme

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amylase. We produce this naturally

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in our salivary glands. So amylase then

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breaks down this complex starch

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into simple soluble molecules of sugars.

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We can then absorb those sugars

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for cellular respiration. We are not

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able to absorb the insoluble starch.

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So the way we're going to demonstrate

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we're going to use iodine as

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our indicator of starch. So when iodine

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comes into contact with starch, we get

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a color indicator that's a lovely,

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like dark purple colour. As the presence

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of starch reduces because starch has

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been broken down by our amylase, as

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we keep introducing iodine, then that

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colour is going to lighten in the purple

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and eventually turn to a brown kind

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of colour, until the point will become

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more yellow. Now, naturally, in this

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practical, you may experience

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where the iodine is been introduced

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every 30 seconds. But for the purpose

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of this demonstration, we are going

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to do it for 60 seconds. The reason

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we want to do this is so we've got

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a more pronounced gradient

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between the start of our demonstration

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to the end. So what we're going to do,

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starch and amylase, we're going

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to introduce together in our test tube.

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At their point of contact, the amylase

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will already be starting to break down

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our starch into those simple sugars.

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So at zero seconds, we will take

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a sample of the starch amylase mix

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into the first well labeled zero.

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Start the stopwatch, introduce iodine,

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and hopefully we'll get that lovely dark

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purple colour because the presence

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of starch. Over the course of time, as

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I say, normally this is 30 seconds,

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which is demonstrated in our well,

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but we're going to do it for 60 seconds,

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reintroduce the mix of amylase starch

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with some more iodine. And hopefully

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by the end of the time, we will have

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a nice gradient from that dark purple

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to hopefully a lighter brown yellow

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color, which then illustrates presence

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of starch is reduced over the course

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of time by our natural catalyst

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of amylase breaking it down into those

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simple sugars. So let's have a go.

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Over the course of time, we've been

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introducing iodine to each well over

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an interval of 60 seconds, and we're

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nicely demonstrating radiation

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from the start of the experiment

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where we had the presence of starch

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and as the amylase has been breaking

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it down, the amount of starch is reduced

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and it's demonstrated with the color

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change of the iodine. So we can see

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at the end of this demonstration that

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we have introduced our starch,

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which is representing our foodstuff,

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carbohydrates and our biological enzyme

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of amylase together. And then every 60

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seconds we've introduced our iodine,

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which is the indicator of presence

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of starch. And as we can see, as we've

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progressed along in time, that

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the indicator will be representing

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starch with this dark brown purple

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colour, which we can see. And as

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it progresses over time, this color has

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lightened, illustrating that

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the concentration of starch,

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which is present in our starch amylase

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mix, has reduced, and that reduction

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is from the success of our enzyme

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amylase breaking down the starch.

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Therefore, it's less present

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and producing those all important

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soluble sugars that then you need

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to absorb into your bloodstream via your

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small intestine to enable the cellular

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respiration to continue within your

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body, which is extremely important

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for survival.