principals of organisation and the human digestive system (includes RP4 & 5)

biology aqa gcse

What are the levels of organisation?

Cell, tissue, organ, organ system

What is a cell?

Basic building blocks and units of an organism (e.g. muscle cells)

What are tissues?

Groups of cells with a similar structure and function (e.g. muscle tissue)

What is an organ?

Groups of tissues working together to perform a specific function (e.g. stomach)

What is an organ system?

A group of organs performing specific functions (e.g. digestive system)

What are all the organs in the digestive system?

Mouth, salivary glands, oesophagus, liver, stomach, gallbladder, pancreas, small intestine, large intestine

Through which of the organs in the digestive system does food actually pass through?

Mouth, oesophagus, stomach, small intestine, large intestine

What is digestion?

Breaking down large, insoluble molecules of food into smaller, soluble molecules that can be absorbed into the blood

How does the stomach help with digestion?

The stomach contracts its muscular walls to churn and mix the food

What is an enzyme?

A biological catalyst which speeds up the rate of reaction without being used up or changed

How do enzymes work? Explain using the lock and key theory. (4)

The active site of an enzyme is complementary to a specific substrate (like a key to a lock), which binds to the enzyme’s active site, causing a chemical reaction (e.g. substrate breaks into two smaller molecules) after which the products are released from the unchanged enzyme

Why can each enzyme only catalyse a specific reaction?

Each enzyme’s active site is complementary to a specific individual substrate, so can only bind to that substrate

How are enzymes related to metabolism?

Different enzymes catalyse different metabolic reactions (e.g. respiration) which may join together smaller molecules to form larger ones or break down larger molecules to form smaller ones

What is lipase and what does it do?

An enzyme which breaks down lipids into fatty acids + glycerol

Where is lipase produced?

Pancreas and small intestine

Where does lipase act?

Small intestine

What is carbohydrase (e.g. amylase) and what does it do?

An enzyme that breaks down carbohydrates into simple sugars (e.g. starch into glucose)

Where is carbohydrase produced?

Salivary glands, pancreas and small intestine

Where does carbohydrase act?

Mouth and small intestine

What is protease and what does it do?

An enzyme which breaks down proteins into amino acids

Where is protease produced?

Stomach, pancreas and small intestine

Where does protease act?

Stomach and small intestine

What are fatty acids and glycerol used for?

To build new lipids

What are simple sugars used for?

To build new carbohydrates, some glucose used in respiration to release energy

What are amino acids used for?

To build new proteins

Where is bile produced, stored and released into?

Produced in the liver, stored in the gall bladder, released into the small intestine

What does bile do?

Neutralises stomach acid to create optimum pH for enzymes in small intestine and emulsifies lipids by converting large droplets into smaller droplets to increase surface area for enzymes to break down lipids faster

What does it mean when an enzyme denatures?

The structure of the enzyme’s active site has changed and so is no longer complementary to the substrate and cannot bind to it

How does temperature affect enzyme activity?

As temperature increases and eventually reaches an optimum, enzymes gain kinetic energy so there are more frequent enzyme-substrate collisions, however after passing the optimum temperature enzymes begin to denature and rate of reaction reaches 0

How does pH affect enzyme activity?

Enzyme activity is at a maximum at the optimum pH but if pH reaches above or below this, enzymes denature and activity decreases, so rate of reaction reaches 0

How do you calculate rate of reaction?

change in quantity (e.g. product used or produced)/change in time

What is metabolism?

All the chemical reactions that occur within a living organism

How do you test for the effect of pH on amylase (enzyme) activity, RP5? (17 points)

On a spotting tile, label each well with a number starting from 0 (each number represents a 30s interval), add a drop of iodine solution to each well, label 5 test tubes 3-7 (noting the pH), using a pipette add 2cm³ of correct pH buffer solution to each test tube, place test tube 3 along with the 2cm³ amylase and starch solutions in a 20^oC water bath, leave for a few minutes, remove from water bath and place in test tube rack, add amylase and starch solutions to buffer solution test tube, return to water bath, stir with stirring rod, start timer, add drop of solution from test tube to first tile using stirring rod, repeat every 30 seconds until iodine stays orange/doesn’t turn blue black, stop timer, record time taken for reaction to be completed/starch no longer present, repeat whole solution using pH/test tubes 4-7

What is the independent variable in the effect of pH on enzyme activity practical/RP5?

The pH level of the buffer solution

What is the dependent variable in the effect of pH on enzyme activity practical/RP5?

The time taken for the starch to be fully broken down/iodine to remain orange

What are some control variables in the effect of pH on enzyme activity practical/RP5?

Temperature of water bath, length of intervals between adding solution to tiles, how long you stir for after removing solution from water bath, volume of starch and amylase

What are two problems with required practical 5 (effect of pH on enzyme activity)?

Taking samples every 30s means only have approximate time taken, waiting for iodine to not change colour, colour change is gradual so can be difficult to see when reaction fully finished

How do you prepare a food sample?

Take a food sample and grind it with distilled water using a pestle and mortar to form a paste, add to a beaker and add more water, stir so chemicals in food dissolve into water, filter solution to remove solid food particles

How do you test for starch?

Add 2cm³ of food sample to test tube, add a few drops of iodine solution, if it turns to a blue/black colour starch is present, if it remains/becomes a yellow-orange colour starch is not present

How do you test for reducing sugars?

Add 2cm³ of food sample to test tube, add 10 drops of Benedict’s solution which is light blue, place the test tube into a hot water bath, if sugar is present will change to green (small amount of sugar), yellow (medium amount of sugar) or brick red (lots of sugar present)

What are reducing sugars?

Sugars that act as reducing agents, e.g. glucose

How do you test for proteins?

Add 2cm³ of food sample to test tube, add 2cm³ of Biuret reagent which is a blue colour, will turn purple if proteins are present

How do you test for lipids?

Add 2cm³ of food sample to test tube, when making food sample do not filter it, leave food particles in it, add few drops of ethanol, place bung over top of test tube and shake gently, if lipids are present a cloudy, white emulsion appears