Required Practical 5: Enzymes

Question 1

What is the aim of this practical?

Answer 1

To investigate the effect of different pHs on the rate of reaction on amylase

Question 2

What is amylase?

Answer 2

An enzyme that breaks down starch (a carbohydrate) into maltose.

Question 3

How do you test for starch?

Answer 3

With iodine solution

Question 4

Summarise what we will do in this experiment into three sentences.

Answer 4

We will use the enzyme amylase to break down starch at different pHs.
We will then use iodine solutions as an indication for the reaction occurring.
If there is starch present, then the iodine solution will turn blue-black, however if the reaction had successfully finished, the iodine would remain brown-orange-yellow

Question 5

Give me the definition of an independent variable and tell me what the independent variable is in the practical.

Answer 5

The independent variable is the variable that we change each time we repeat the experiment. The independent variable is unaffected by other variables. In this practical, the independent variable is the pH buffers we use.

Question 6

Give me the definition of a dependant variable and tell me what the dependant variable is in the practical.

Answer 6

The dependant variable is what we’re measuring throughout the course of this practical. It depends on all the other variables. For this practical, it’s the time taken for amylase to successfully break down starch

Question 7

List 5 control variables that we can include in this practical

Answer 7

The temperature (water bath at the start of the practical)
Use of pH buffers
Volume of all solutions used each time
Conc. of all solutions

Question 8

What is the first step to this practical?

Answer 8

We place one or two drops of iodine solution into every well of the spotting tile

Question 9

What is the second step to this practical?

Answer 9

Label a test tube with the name of pH to be tested in this turn

Question 10

What is the third step to this practical?

Answer 10

Using a syringe: add 1cm3 of pH buffer into the test tube that was labeled with the pH’s name.

Question 11

What is the fourth step to this practical?

Answer 11

Using another syringe, place 2 cm3 of amylase into the test tube labeled with the name of pH were using this round

Question 12

What is the fifth step to this practical?

Answer 12

Fill another test tube up with 2 cm3 of starch (there should be two test tubes now)

Question 13

What is the sixth step to this practical?

Answer 13

Using a syringe, or with just pouring, add the 2 cm3 of starch measured before into the test tube with amylase and the pH buffer in it. As soon as it’s placed in, start the stop watch up. Do this whilst simultaneously mixing the solution up with a pipette.

Question 14

What is the seventh step to this practical?

Answer 14

After ten seconds, use the pipette to place one drop of the mixture on the first well of the spotting tile with iodine solution in it. It should turn black-blue

Question 15

What is the eighth step to this practical?

Answer 15

Repeat the seventh step for every ten seconds until the iodine solution remains orange-brown instead of turning black-blue

Question 16

What is the ninth and final step to this practical?

Answer 16

Repeat the whole experiment again at a different pH value. The less time the iodine takes to remain orange-brown, the quicker all the starch has been broken down. This shows that the enzyme works better that at pH

Question 17

What is a pH buffer? Why do we use pH buffers?

Answer 17

A pH buffer solution is basically a solution that resists changes in pH, even if acids or alkalines were added to it. By adding it to the amylase, we ensure that the pH the amylase works in remains that that specific pH listed on the buffer. It’s a control variable

Question 18

Why do we repeat the experiment (repeat with diff. buffers and repeat with the same buffers)

Answer 18

We repeat the experiment to see how pH affects time taken for starch to break down. But if we repeat the experiment with the same pH used, we do it for the reliability. If our results are reliable, they are comparable. To make results more comparable, take all the values taken down for the same pH used and find the mean time taken instead of looking at all the individual values.

Question 19

How would we change this experiment to make temperature a control variable?

Answer 19

We could heat all of the test tubes in a water bath before we begin the practical. If we place all the test tubes in a water bath, we can keep all the test tubes at a constant temperature to make sure temperature change isn’t responsible for speeding or slowing down reactions. To make this work, we need to put all the solutions used in this practical (starch, amylase, pH buffers) into a water bath and keep them there for five minutes. They are kept in there for 5 minutes so all test tubes can reach the same temperature in the time given. The temperature of the water bath should be set to either 35 or 37 degrees Celsius

Question 20

If we were to add the water bath step into the practical, where would it go in the method?

Answer 20

In between the 5th and 6th steps