Practicals Flashcards
What is used to test for reduced sugars?
Benedict’s solution
How do you prepare a food sample?
(3)
- Grind the food sample with distilled water using a pestle and mortar
- Transfer this paste into a beaker and add more distilled water so that the chemilcals in the food dissolve in the water
- Filter the solution to remove any suspended food particles
Describe how you use Benedict’s solution to test for reduced sugars in a food sample
- Get 5cm cubed of the food sample and place it in a test tube
- Prepare a water bath at 75 degrees Celcius, when this is ready add a few drops (e.g. 10) of Benedict’s solution into the food sample and place it in the water bath
- Leave the sample for 5 minutes; if sugars are present in the food, the solution will turn from blue to brick red.
Desrcibe how you use iodine to test for starch in food
- Get 5cm cubed of the food sample and place in a test tube
- Add a few drops of iodine solution and give it a gentle stir
- If there is starch present, the solution should turn from a yellow brown colour to a blue-black colour.
Iodine is an irritant so be careful and ensure you wear goggles.
Describe how you use Biuret solution to test for proteins in food samples
- Get 2cm cubed of the food sample and place it in a test tube
- Add 2cm cubed ofBiuret solution to the food sample and give it a gentle stir
- If proteins are present, the solution will turn from blue to a pale purple colour.
Describe how you use ethanol to test for lipids in food
- Place your food sample into a test tube
- Add 2cm cubed of ethanol to the sample and shake it vigorously
- Add an equal 2cm cube of distilled water to the solution. If it turns cloudy white, then there are lipids present in the food.
Describe the practical to investigate the effect of pH on the rate of reaction of amylase enzyme
- Prepare a spotting tile by placing a drop of iodine solution into each of the wells in the spotting tile (iodine solution is orange-yellow)
- Now Prepare a water bath of 30 DEGREES CELCIUS
- Take three different test tubes; in the first, pour 2cm3 of starch solution. In the second test tube pour 2cm3 of amylase solution. Into the third, pour 2cm3 of pH 5 buffer solution (the buffer will control the pH)
- Now place the three test tubes into the water bath and leave them for 10 minutes to allow each solution to reach the same temperature of 30 DEGREES CELCIUS
- Then pour all of the solutions into a single test tube and combine using a stirring rod- then place the sample back into the water bath and start a stopwatch
- At 30 seconds use the striing rod to transfer a drop of the sample to a well in the spotting tile- the iodine solution will change colour from orange-yellow to blue-black because starch is present
- Now every 30 seconds repeat this, transferring the a drop of the sample to different wells on the spotting tile until the iodine solution stops changing colour to blue-black and remains orange-yellow, this means that starch is no longer present and the reaction is over. Now record the time on the stopwatch into a table
- Now repeat the entire experiment 5 times, this time increasing the pH of the buffer by 1 each time until you reach a pH of 10
What are the two problems with the practical of investigating the effect of pH on the amlase enzyme?
- We only take a sample every 30 seconds
- The colour change from blue-black to orange-yellow is gradual
Why is the fact that we only take samples every 30 seconds when investigating the effect of enzymes on pH a problem?
It means we only have an approximate time for the reaction to complete
Why is the fact that the colour change from blue-black to orange-yellow is graudal when investigating the effect of enzymes on pH a problem?
It makes it difficult to tell when the reaction is finished
How do we solve the problem when we only take samples every 30 seconds
Record every 10 seconds instead
How do we solve the problem of not knowing when the reaction is over due to the gradual colour change of iodine?
Ask several people to look and decide when the reaction is complete
What is the independant variable in the practical investigating the effect of pH on the amylase enzyme?
The pH conditions of the amylase enzyme
What is the dependant variable in the practical investigating the effect of pH on the amylase enzyme?
The time taken for the iodine solution to stop changing colour from orange-yellow to blue-black
What is the control variable in the practical investigating the effect of pH on the amylase enzyme?
The temperature conditions of the enzyme
(30 DEGREES CELCIUS)
Concentration of enzyme
Time intervals between taking each of the samples
