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Maris Stella High School Name: ___________________ GCE O Level Science Biology Class (Index No.): _____ ( ) 2011 GEP Lesson 3 Date: ________________

Enzymes

SUMMARY

Factors affecting rate of enzyme reactions:

1. Temperature 2. pH 3. Enzyme Concentration 4. Substrate Concentration

How temperature affects rate of enzyme activity:

•Rate of enzyme activity depends on kinetic energy (K.E.) of molecules: 1. Rise in temperature 2. Rise in kinetic energy of molecules 3. Rise in collisions between enzymes and substrate molecules 4. Increase chance of formation of enzyme substrate complex 5. Increase in rate of reaction

Denaturation

•Occurs when 3D protein structure changes its shape •Results in the loss/changing of active sites •No longer acts as a catalyst •Caused by acids, alkalis and extreme heat (boiling) •Irreversible

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Revision Questions

1)

Catalase, an enzyme, is present in all living cells including those of potato and liver. It speeds up the breakdown of hydrogen peroxide as shown by the equation:

catalase

hydrogen peroxide oxygen + water

The oxygen is given off as a gas which can be collected over water, as shown in Fig. 1.

Fig. 1

Two different tissues, potato and liver, were used for this investigation. Samples, each of one gram, were prepared from both tissues. Some of the samples were left raw and others were boiled. Some samples were left as one cube and others were chopped into small pieces as shown in Table 1.1.

2 cm3 hydrogen peroxide was added to each sample. The volume of oxygen produced in five minutes was collected in the measuring cylinders, as shown in the table below

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Table 1.1

(a) (i) Complete Table 1.2, by reading the values for oxygen collected in the measuring cylinders in Table 1.1. [2]

Table 1.2

volume of oxygen collected from each sample / cm3

tissue

A B C D

potato

liver

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(ii)

Plot the volumes of oxygen collected from the samples as a bar chart on a graph paper. [4]

(iii) Describe the difference in results between sample A for potato and sample A for liver.

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………………………………………………………….…………………………...[2]

(iv) There is a difference between the samples for A and B for liver.

Suggest an explanation for this difference.

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……………………………………………….……………………………………...[2]

(b) State the importance of samples C and D in this investigation.

………………………………………………………………………….…………………...[1]

(c) Suggest how you could test that the gas given off was oxygen.

………………………………………………………………………….…………………...[1]

2. An experiment investigating the effect of temperature on the activity of catalase was carried out at two temperatures, 400C and 700C. The graph below (Figure 2.1) was plotted based on the results obtained during the experiment.

 

 

 

 

 

 

 

 

 

 

Total volume of gas produced /cm3

Time /min 6

Temperature: ___

Temperature: ___

Figure 2.1

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(i) Name the gas that was produced during the reaction. ______________ [1] (ii) Complete Figure 2.1 by filling in the respective temperatures that each curve represents. [2] (iii) Explain the difference in the shape of the two curves before the 6 minute point. [3]

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(iv) Explain the difference in the shape of the two curves after the 6 minute point. [4]

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(v) This experiment is repeated at 200C, using the same substrate and enzyme concentrations. Sketch and label on Figure 2.1, the curve you would expect to obtain for the experiment. [1] (vi) Explain your answer for part (v). [3]

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