Enzyme action

Catalase is an enzyme found in many cells. This enzyme controls the breakdown of hydrogen peroxide into water and oxygen.

hydrogen water oxygen peroxide A teacher uses this method to investigate the effect of pH on catalase. Step 1 cut a cylinder of potato tissue into six equal sized discs Step 2 measure 10 cm3³ of hydrogen peroxide solution and place into a boiling tube Step 3 a dd a pH buffer solution to the tube to keep the pH at 7 Step 4 a dd the six potato discs to the boiling tube Step 5 c ollect the gas given off by the reaction in an inverted

Step 6 measure the total volume of gas collected after five minutes Repeat steps 1 to 6 using four different pH buffers (pH 4, pH 5, pH 6 and pH 8). The diagram shows the teacher’s apparatus.

State what is meant by the term enzyme.

Suggest why each potato cylinder was cut into six discs rather than left as one cylinder.

Give the dependent variable in this experiment.

The teacher controls the time for gas collection and also the volume of hydrogen peroxide used. State two other abiotic variables the teacher should control in this experiment.

The table shows the teacher’s results.

Calculate the percentage change in the mean rate of reaction as the pH is changed from pH 4 to pH 7.

percentage change =_........

The teacher calculated the mean rate of reaction by collecting the oxygen released for the first five minutes of the reaction. Explain why the mean rate of reaction changes beyond the first five minutes.

Explain the effect of changing pH on an enzyme-controlled reaction.

Pineapple juice contains a protease called bromelain.

A student uses this method to investigate the digestion of solid gelatine protein by bromelain.

• place solid gelatine protein into a test tube up to a height of 5 cm

• mix 5 cm³ pineapple juice with 1 cm³ of pH 4 buffer

• place 1 cm³ of the pineapple juice and buffer solution on top of the gelatine

• leave for one hour in a water bath set to 37 °C

• measure the height of the solid gelatine and use it to calculate the volume of gelatine that has been digested

Repeat the method three more times.

The diagram shows part of the student’s method.

The table shows the student’s results for the volumes of gelatine digested at pH 4.

Calculate the mean volume of gelatine digested in cm³.

Give your answer to two decimal places.

mean volume =_........ ³

State what substances are produced when the gelatine protein is digested.

The student repeats the investigation with different pH buffers.

The table shows their results.

Give two variables the student should control.

Explain the effect of changing the pH on the mean volume of gelatine digested.

Describe how to test for the presence of protein.

The diagram shows part of the gut of a rabbit. The rabbit is a primary consumer and eats mainly grass and other vegetable material.

Name the parts labelled A, B, C and D.

The gut of a rabbit has a large caecum and appendix. These contain bacteria that are able to produce the enzyme cellulase. Explain how these bacteria help the rabbits with their diet of plant material.

The human gut has a caecum and appendix but they are much smaller than those in the rabbit.

Suggest why the human gut only has a small caecum and appendix.

In humans the appendix also acts as a store of useful bacteria. Scientists have discovered that patients who have had their appendix removed are more likely to develop infections of the colon. Explain how having no appendix may increase the likelihood of bacterial infections of the colon.

Catalase is an enzyme found in many cells.

It speeds up the breakdown of hydrogen peroxide into water and oxygen.

The equation for the reaction is

A teacher demonstrates the effect of increasing catalase concentration on the initial rate of the reaction.

This is the teacher’s method.

• cut five equal size discs from a potato, each 0.2 mm thick

• place the discs in a boiling tube with 5 cm³ of buffer solution

• add 5 cm³ of hydrogen peroxide solution to the boiling tube

• place a bung and delivery tube firmly into the boiling tube

• position the other end of the delivery tube under an inverted measuring cylinder

• start a timer as soon as the first bubble of oxygen enters the measuring cylinder

• measure the volume of oxygen produced in one minute

Repeat this method three times.

The teacher uses this method with different numbers of potato discs, making sure that other conditions are unchanged.

Give the expected relationship between the named independent variable and the named dependent variable in this demonstration.

Give two variables that the teacher controls in this demonstration.

The table shows the teacher’s results.

Calculate the mean volume of oxygen produced in one minute using 5 potato discs.

Calculate the percentage increase in mean volume of oxygen produced in one minute as the concentration of enzyme changes from 15 to 20 discs.

Explain the relationship between the concentration of enzyme and mean volume of oxygen produced in one minute.

Suggest why the teacher measures the volume of oxygen after the first minute of the reaction rather than after 10 minutes.

Variation in a population can have different causes.

Which of these will not lead to an increase in genetic variation in a population of plants?

Explain how a change in the DNA of a microorganism can reduce its ability to digest a substance.

Explain why a change in DNA may not affect the phenotype of an organism.

Enzymes are biological molecules that act as catalysts in metabolic reactions.

State what is meant by the term catalyst.

State what is meant by the term metabolic.

A teacher investigates the effect of enzyme concentration on the rate of a reaction.

He uses the enzyme catalase, which is found in potato.

He changes the enzyme concentration by adding different numbers of potato discs.

Catalase breaks down hydrogen peroxide solution into water and oxygen.

This is his method.

● cut same-sized discs from a potato

● put 5 cm³ of hydrogen peroxide solution into each of five test tubes

● add a different number of potato discs to the hydrogen peroxide

● measure the volume of oxygen gas produced in three minutes

The teacher repeats each test four times for each concentration.

He then calculates the mean rate of oxygen production for each concentration.

The table shows his results.

Plot a line graph to show the effect of enzyme concentration on the mean rate of oxygen production.

Use a ruler to join the points with straight lines.

Explain the effect of increasing enzyme concentration on the rate of oxygen production.

Name a piece of apparatus suitable for measuring the volume of oxygen produced.

Explain why it is important for the teacher to keep the volume and concentration of the hydrogen peroxide constant.

Name another variable the teacher should keep constant in his investigation.