Use this information to explain why the phenolphthalein changes colour.
What is the effect of temperature on the time taken for lipase to break down the fat in milk?
Why does the temperature affect the action of lipase in this way?
What is the difference between a ‘time taken’ and a ‘rate of reaction’ curve for this investigation?
Why is it necessary to break down fat in the digestive system?
Use other sources of information to find out about:
bile salts and their effects on digestion of fats
what happens to the fatty acids and glycerol once they have been absorbed from the digestive tract.
When fat breaks down, fatty acids and glycerol are produced.
The fatty acids lower the pH of the mixture which changes the colour of the phenolphthalein from pink to colourless.
Increasing temperatures from 0 ºC to around 45 ºC will reduce the time taken for the lipase to break down the fat in milk. Over this temperature, the time taken will increase, or perhaps the lipase will not work at all.
Temperature affects the action of lipase this way because increasing temperatures (up to around 40 ºC) increase the rate of reaction, by increasing the collision rate between the enzyme and substrate molecules (as in any chemical reaction). The highest rate of reaction is at the optimum temperature for the enzyme. The rate of reaction then reduces as temperature increases until, at some point, the reaction stops altogether. This is because at high temperatures (usually over 45 ºC), the protein structure of the enzyme is denatured by heat. The molecule loses its shape and the enzyme is de-activated.
A ‘time taken’ curve and a ‘rate of reaction’ curve show similar patterns, but one is an upside-down version of the other.
It is necessary to break down fat in the digestive system to make it easier to absorb through the membranes of the gut and also to make it soluble enough to transport in the blood.
Bile salts emulsify fats, which means they make it easier to form an emulsion of tiny droplets of fat suspended in water. A fatty emulsion will not separate quickly. This increases the surface area of fat exposed to enzymes in solution and increases the rate of digestion.
When fatty acids and glycerol have been absorbed from the digestive tract, they are transported through the lymphatic system and enter the bloodstream at the sub-clavian vein (underneath the collar bone).