4.2.2.1 The human digestive system

What organs make up the digestive system?

Glands (salivary and pancreas), stomach, small intestine, liver, gall bladder, large intestine, rectum, anus

What do the glands do?

Produce digestive juices containing enzymes which break down food

What does the stomach do?

Produce hydrochloric acid to kill bacteria and to provide the optimum pH for the protease enzyme to work

What does the small intestine do?

Absorb soluble molecules into the blood

What does the liver do?

Produce bile which helps with the digestion of lipids and is stored in the gall bladder

What does the large intestine do?

Absorb water from undigested food to produce faeces which is passed out of the body through the rectum and anus

What are enzymes?

Biological catalysts as they increase the rate of reaction without being used up

What is the Lock and Key Hypothesis?

The shape of the substrate is complementary to the shape of the active site so when the bond, it forms an enzyme-substrate complex. Once bound, the reaction takes place and the products are released from the surface of the enzyme

What is the optimum temperature for enzymes?

37 degrees celsius

What happens if the temperature is too high for enzymes?

The bonds in the structure will break which changes the shape of the active site, so the substrate can no longer fit and the enzyme is said to be denatured

What is the optimum pH for enzymes?

7

What happens if the pH is too high or too low for enzymes?

The forces that hold the amino acid chains that make up the protein will be affected which will change the shape of the active site so the substrate can no longer fit in and the enzyme is said to be denatured

What are the three digestive enzymes?

Carbohydrases, proteases, lipases

What do carbohydrases do?

Convert carbohydrates into simple sugars

What do proteases do?

Convert proteins into amino acids

What do lipases do?

Convert lipids into fatty acids and glycerol

Where are carbohydrases produced?

Salivary glands, pancreas, small intestine

Where are proteases produced?

Pepsin which is produced in the stomach, other forms can be found in the pancreas and small intestine

Where are lipases produced?

Pancreas, small intestine

What is the test for sugars and the results if present?

Benedict’s, it turns brick red

What is the test for starch and the results if present?

Iodine, it turns blue-black

What is the test for protein and the results if present?

Biuret, it turns purple

What is the emulsion test for lipids and the results if present?

Add ethanol, results in a cloudy layer

Why is bile alkaline?

To neutralise the hydrochloric acid which comes from the stomach

Why does bile emulsify fats?

The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster

What is the method for investigating the rate of enzymatic reactions?

A drop of iodine is put in each well in a spotting tile. Using a water bath, warm a solution of amylase, starch and a buffer solution. At regular points in the experiment, take drops of the solution and place in the wells. The starch is no longer present and has been completely broken down when the iodine solution remains brown

What is the independent variable in the rate of enzymatic reactions investigation?

The buffer solution, pH values

What is the dependent variable in the rate of enzymatic reactions investigation?

The time taken for the iodine to be completely broken down and remain brown

What is the control variable in the rate of enzymatic reactions investigation?

Temperature