AS Biology - AQA - Digestion help please!

Hi,

Today I started my AS biology course and the entire lesson just stumped me. I didn't really understand much of what the teacher was on about at the time, but now that I've come home and done a little bit of the homework set, I've understood most of what she said.

But two of the homework questions have stumped me and I don't think we've even been taught about it yet - I can't even remember doing it at GCSE.

The questions are:

How would you practically measure the action of the enzyme lipase? Explain.

How would you practically measure the action of the enzyme amylase? Explain.

If anyone could help me out and just explain in a bit more detail about digestion that would help me answer these questions I'd be highly grateful. I'm not asking for the direct answers to the questions as I don't really want to just be told about it - I want to try and actually improve my knowledge.

So if anyone could help, thank you in advance!

Reply 1

gravedanger96

Okay so you digest big, complex molecules into smaller more simple ones. This is because the body can't absorb large molecules. Breaking down these molecules is catabolic and once the molecules have been absorbed they can be joined together again to make new large molecules that the body can use. This is an anabolic process. The process of catabolism then anabolism forms your metabolism.

Since you're looking at enzymes I shall go into a little more detail about them. They are biological catalysts (molecules that speed up the rate of reaction without being used up) and are made from protein. They are often depicted as a little pac man that 'eat' molecules. They can both join molecules and break molecules. In the case of your questions you have lipase and amylase. The difference between them is what they break down. Looking at the prefix you can work out what the large molecule is that they're breaking down. In LIPase they break down LIPids/fats/oils into glycerol and fatty acids. Amylase breaks down starch (a polysaccharide- meaning many repeating units of sugar joined together) into the simple sugar glucose (a monosaccharide).

Hope this helps and let me know if anything more needs explaining or you want more anatomical detail :smile:

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Reply 2

blue1211823

starch - mono/disacharides produced so use benedicts sol.?
lipase - use a pH test for the product

Reply 3

Dubois98

Original post by gravedanger96

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Thanks! You definitely helped me understand a bit more of it, but how would I then test the action of these enzymes? Is there a specific test or is it just 'You'll know by X and Y'?

Reply 4

blue1211823

Original post by Dubois98

Thanks! You definitely helped me understand a bit more of it, but how would I then test the action of these enzymes? Is there a specific test or is it just 'You'll know by X and Y'?

Use the tests I listed, in the presence of an inhibitor

Reply 5

Dubois98

What is involved in these tests? I've never heard of the benedict's solution test? :s

This is stressful and I've only just started AS biology. Regretting taking it now :/

Reply 6

blue1211823

Original post by Dubois98

What is involved in these tests? I've never heard of the benedict's solution test? :s

This is stressful and I've only just started AS biology. Regretting taking it now :/

no no don’t regret it! :smile:

Its also called a reducing sugars test, so basically it tests whether a sugar contains an aldehyde group or not.

Starch is broken down to maltose I’m pretty sure, and this test can detect its presence because its a reducing sugar (there will be a colour change)

My biology is a tiny bit rusty because I did A levels 3 years ago now, but I study medicinal Physiology at uni, so its still one of my stronger points if you need help with any thing else biological/chemical :smile:

Reply 7

gravedanger96

Original post by Dubois98

Thanks! You definitely helped me understand a bit more of it, but how would I then test the action of these enzymes? Is there a specific test or is it just 'You'll know by X and Y'?

To test the action of an enzyme you can look at two things. One is the rate at which the substrate molecule (the molecule the enzyme is breaking down) concentration falls and the second is the rate at which the products are formed. As mentioned about for the amylase you can measure how much reducing sugar (the product) is made. This will involve the Benedicts test which is something you may have learnt at GCSE but if not just google it! But since you will want to look at the rate you should take measurements at regular intervals to see how the concentration of the reducing sugar changes over time. For the lipase I would again agree to test for pH. This is because when the fat is broken up it will form glycerol and fatty acids. These fatty acids will lower the pH (more acidic). So again to measure rate you will want to take pH readings at regular intervals. You may also want to compare your results to a control (exam boards like that) so you can see the difference the enzyme makes!

Hope this helps :smile:

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