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Chapter 3: Enzymes

A-Level Biology Teacher Pack | | ©HarperCollinsPublishers Limited 2015

Scheme of work

Chapter 3: Enzymes

CHAPTER PLANNING

Nine hours

This chapter explores the application of some proteins as enzymes.

Lessons 3.1 and 3.2 explore how enzymes work. These should be delivered first.

Lessons 3.3 to 3.7 focus on the factors affecting enzyme activity and should be taught as a block. Lessons 3.3 and 3.4 should be delivered sequentially as students will analyse data from lesson 3.3 during lesson 3.4. However, lessons 3.5, 3.6 and 3.7 could be delivered in any order and before or after 3.3 and 3.4. Lessons 3.3 to 3.7 provide opportunities to carry out Required practical 1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction.

Lessons 3.8 and 3.9 focus on the applications of enzymes and their versatile nature.

ONE HOUR LESSONS SPECIFICATION CONTENT

3.1 Enzymes as biological catalysts

3.1.4.2 Many proteins are enzymes

Each enzyme lowers the activation energy of the reaction it catalyses

MS 0.5 Use calculators to find and use power, exponential and logarithmic functions

3.2 How enzymes work 3.1.4.2 Many proteins are enzymes

The induced-fit model of enzyme action

The properties of an enzyme relate to the tertiary structure of its active site and its ability to combine with complementary substrate(s) to form an enzyme-substrate complex

Students should be able to:

• appreciate how models of enzyme action have changed over time

3.3 Factors affecting enzyme activity (temperature)

3.1.4.2 Many proteins are enzymes

• The specificity of enzymes • The effects of the following factors on the rate of enzyme-controlled

reactions – enzyme concentration, substrate concentration, concentration of competitive and of non-competitive inhibitors, pH and temperature

Required practical 1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction.

MS 1.2 Find arithmetic means

M 1.3 Construct and interpret frequency tables and diagrams, bar charts and histograms

MS 3.1 Translate information between graphical, numerical and algebraic forms

MS 3.2 Plot two variables from experimental or other data

MS 3.6 Draw and use the slope of a tangent to a curve as a measure of rate of change

PS 2.1 Comment on experimental design and evaluate scientific methods

PS 2.2 Present data in appropriate ways

PS 2.4 Identify variables including those that may be controlled

PS 3.1 Plot and interpret graphs

PS 3.3 Consider margins of error, accuracy and precision of data

3.4 Factors affecting enzyme activity (analysing data)

3.5 Factors affecting enzyme activity (pH)

3.6 Factors affecting enzyme activity (enzyme and substrate concentration)

3.7 Factors affecting enzyme activity (competitive and non-competitive inhibition)

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Chapter 3: Enzymes


AT a use appropriate apparatus to record a range of quantitative measurements (to include mass, time, volume, temperature, length and pH)

AT b Use appropriate instrumentation to record qualitative measurements, such as a colorimeter or potometer

AT c Use laboratory glassware apparatus for a variety of experimental techniques to include serial dilutions

3.8 Applications of enzymes 3.1.4.2 Many proteins are enzymes

The effects of the following factors on the rate of enzyme- controlled reactions enzyme concentration, substrate concentration, concentration of competitive and of non- competitive inhibitors, pH and temperature

3.9 Extreme enzymes 3.1.4.2 Many proteins are enzymes

The effects of the following factors on the rate of enzyme-controlled reactions – enzyme concentration, substrate concentration, concentration of competitive and of non-competitive inhibitors, pH and temperature

PRIOR KNOWLEDGE

Students were taught about proteins in Chapters 1 and 2 and are likely to know that some proteins are enzymes. They may remember that protein molecules are made up of amino acid monomers and that the protein chains are folded to produce a specific shape. They are most probably aware that the shape of an enzyme molecule is vital to its function.

During KS3 and KS4, students are likely to have learned that enzymes are involved in digestion. Using this context, they are likely to have learned that each enzyme is involved in a specific type of reaction. They may remember some enzyme examples and their roles, for example, protease enzymes involved in breaking down protein molecules, lipase enzymes involved in breaking down lipid molecules and carbohydrase enzymes involved in breaking down carbohydrates. Some students may have come across the term ‘amylase’ for the carbohydrase that breaks down starch to glucose.

Students are likely to be aware that enzymes are catalysts and that these speed up reactions. Some students may be aware that enzymes can be involved in building up molecules, but the majority of their experience is likely to be of the role of enzymes in breaking down molecules.

At KS4, students may have learned about the importance of enzymes in industry, for example proteases and lipases in washing powders, proteases in producing baby foods, and carbohydrases in the manufacture of glucose syrup. They are likely to be aware that enzymes work best within a certain temperature and pH range. They are likely to be aware of the term ‘denaturation’, linked with high temperatures.

Students are likely to have been taught that the reactions involved in respiration are controlled by enzymes. Students are, therefore, likely to be aware that the temperature of the human body must be maintained within a range that allows enzymes to work best.

During KS3 and KS4, students are likely to have had experience of carrying out practical work to investigate enzyme action. Students may have carried out practical work to demonstrate that carbohydrase enzyme breaks down starch molecules but not protein or lipid molecules, for example. They may also have experience of investigating the temperature at which an enzyme works most effectively, for example, in the context of washing powders.

WHERE IT LEADS

Students will learn more about the role of enzymes in digestion during Chapter 8, and about the many roles of enzymes in DNA replication and protein synthesis in Chapter 10.

If students continue to study A-Level, they will learn more about DNA technology and the ways that enzymes are utilised, and about the roles of enzymes in photosynthesis and respiration.

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Chapter 3: Enzymes


Lesson plan 3.1

Lesson 3.1 Enzymes as biological catalysts

LEARNING OUTCOMES

• Define enzymes as biological catalysts that remain unchanged by a reaction and recall examples of enzymes • Describe what activation energy is and explain how enzymes affect activation energy of a reaction

THE JOURNEY SO FAR

Students were taught about proteins in Chapters 1 and 2 and are likely to know that some proteins are enzymes. They are likely to recall the term ‘catalyst’ and know that catalysts speed up reactions.

POSSIBLE BARRIERS TO PROGRESS

Some students may assume that all proteins are enzymes, rather than appreciating that all enzymes are proteins but not all proteins are enzymes. Some students will neglect the details that the enzyme remains unchanged after it has catalysed a reaction.

LESSON OUTLINE

Engage and remind

Show a conical flask containing hydrogen peroxide (35% with a small amount of water added). Explain that hydrogen peroxide is produced as a by-product of many metabolic reactions and that it is damaging to cells. Ask students to look carefully for any signs of a reaction. Students should observe some bubbling (although this will only be gentle). Encourage students to look for other signs of a reaction, such as feeling the flask to detect any heat produced. Explain that the hydrogen peroxide is slowly decomposing and that the bubbles are oxygen. Ask students to reflect on why it is important that hydrogen peroxide is broken down in the body.

Ask students to suggest how we could increase the reaction to breakdown the hydrogen peroxide. Students are likely to suggest heating up the conical flask. Show a video clip of hydrogen peroxide being heated (there are some good examples on YouTube). Note: it is not safe to heat the hydrogen peroxide in the school/college laboratory. Ask students to reflect on whether it is possible to use this strategy to speed up the breakdown of hydrogen peroxide in our cells.

Core activities

Display the word ‘enzyme’. Ask students to work in pairs to write down as many points as they can about enzymes. Sticky notes or large sheets of paper could be used for this activity.

Take some feedback from pairs and elicit from students that enzymes are protein molecules (but not all proteins are enzymes), enzymes catalyse reactions, and enzymes remain unchanged by the reactions that they catalyse. Use this discussion as an opportunity to identify and address misconceptions about enzymes.

Use Activity sheet 3.1.1 Decomposition of hydrogen peroxide to demonstrate the effect of an enzyme. Add a spatula of catalase enzyme powder (or manganese dioxide) to the hydrogen peroxide in the conical flask. Ask students to observe and then describe their observations. Ask them to suggest what type of molecule catalase is. Next add a piece of raw liver to a second conical flask containing hydrogen peroxide. Ask students to suggest what the observations tell us about liver.

Explain to students that, when hydrogen peroxide is broken down, bonds are being broken and that energy is needed to do this. Ask students to read Biology Student Book 1, Section 3.2. Then ask them to explain to a partner what is meant by activation energy and how enzymes affect activation energy.

Students complete Activity sheet 3.1.2 Enzymes catalysing reactions. Check answers as a class.

Consolidate and look ahead

Students summarise, using notes and diagrams, what each of the demonstrations during the lesson showed.

BUILDING ON THE OUTLINE

A demonstration of ‘the genie in the bottle’ could be carried out using potassium permanganate as the catalyst suspended over hydrogen peroxide in a bottle.

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Activity sheet 3.1.1

Decomposition of hydrogen peroxide This is a teacher demonstration of the decomposition of hydrogen peroxide.

Always wear suitable protective gloves when handling hydrogen peroxide. Wear eye protection and a laboratory coat and avoid contact with the face. Ensure the lid is replaced on the bottle immediately after use.

EQUIPMENT AND MATERIALS

• hydrogen peroxide, 35% w/v • water in a squeezy bottle • 2 x 500 cm3 conical flask • catalase enzyme powder (or manganese dioxide powder) • piece of raw liver to fit into the 500 cm3 conical flask • spatula

PROCEDURE

01. Pour hydrogen peroxide (35% w/v) into one of the measuring cylinders to a depth of approximately 3 cm. Add an approximately-equal volume of water.

02. Add a spatula of catalase enzyme powder (alternatively, use manganese dioxide powder).

03. Pour hydrogen peroxide (35% w/v) into the second measuring cylinder to a depth of approximately 3 cm. Add an approximately-equal volume of water.

04. Add a piece of liver to the measuring cylinder.

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Chapter 3: Enzymes


Technician notes for Activity sheet 3.1.1

Decomposition of hydrogen peroxide Always wear suitable protective gloves when handling hydrogen peroxide. Wear eye protection and avoid contact with the face. Ensure the lid is replaced on the bottle immediately after use.

A risk assessment must be made before students start work.


• hydrogen peroxide, 35% w/v • water in a squeezy bottle • 2 x 500 cm3 conical flask • catalase enzyme powder (or manganese dioxide powder) • piece of raw liver to fit into the 500 cm3 conical flask • spatula

NOTES

The liver used in this demonstration must be raw (in cooked liver, catalase has been denatured and will not catalyse the breakdown of the hydrogen peroxide).

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Enzymes catalysing reactions

TASK 1: ACTIVATION ENERGY

Hydrogen peroxide is a by-product of many metabolic reactions. The molecule causes damage to cells and so it must be broken down in our cells. The enzyme that can break down hydrogen peroxide is called catalase.

01. Write a word equation for the decomposition of hydrogen peroxide.

02. Explain why energy is needed for a chemical reaction such as the decomposition of hydrogen peroxide.

Changes in energy level during a reaction

03. Identify which label on the graph represents

a. energy level of reactants

b. energy level of products

c. activation energy

04. Define activation energy.

05. Explain the difference between the energy level of product molecules and the energy level of reactant molecules.

06. Make a large, labelled copy of the graph and add a curve to show the effect of adding an enzyme specific to that reaction.

07. Indicate on your graph the difference between the activation energy of the reaction without the enzyme and with the enzyme.

TASK 2: ENZYMES AND MISCONCEPTIONS

A student has written the following piece about enzymes:

All protein molecules are enzymes. This means that they are formed from amino acids as monomers. A carbohydrase enzyme breaks down starch to glucose in our mouths. This enzyme must be constantly made in the body as it gets used up quickly at the start of digestion. Enzymes increase the rate of reactions by breaking the bonds within molecules.

01. There are three misconceptions in the understanding of this student. Identify each of the misconceptions and explain the correct science to the student.

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Chapter 3: Enzymes


Lesson plan 3.2

Lesson 3.2 How enzymes work

LEARNING OUTCOMES

• Describe and explain how enzymes work by the induced fit model • Compare and contrast the lock and key and induced fit models of enzyme action

THE JOURNEY SO FAR

Students may remember that protein molecules are made up of amino acid monomers and that the protein chains are folded to produce a specific shape. They are most probably aware that the shape of an enzyme molecule is vital to its function. Students may have come across the ‘lock and key’ theory of enzyme action at KS4.


Some students may find it difficult to differentiate between the lock and key model and the induced fit theory of enzyme action. Some students may believe that the substrate has an active site, rather than the enzyme.

LESSON OUTLINE

Engage and remind

Ask students to work in pairs to discuss how enzymes work. Provide pairs with large sheets of paper and pens and ask them to represent their discussions in images. They could use the specific example from Lesson 3.1 of the enzyme catalase catalysing the decomposition of hydrogen peroxide. Ask each group to describe, briefly, what their images show to assess understanding of how enzymes work.

Core activities

Use verbal questioning to recap the definitions of primary, secondary and tertiary structure of proteins. Show computer generated images of enzymes and substrates. Use these images to demonstrate the globular nature of enzymes and the active site of enzymes as an indent in the structure. Use Biology Student Book 1, Section 3.3, Figure 5 to discuss how enzymes catalyse reactions using the induced fit model. (Students are likely to be familiar with the lock and key model of enzyme action from KS4 so it is important that they understand that the shape of the active site is changed, induced by the enzyme.)

Students complete Activity sheet 3.2.1 Models of enzyme action, Tasks 1 and 2. Display annotated diagrams produced (Task 2, question 01) and allow students time to compare each. Students should then add to or amend their own annotations.

Reflect on the discussions that took place during Engage and remind about students original perceptions of enzyme action. Point out those models that were based on the lock and key model and ask students to comment on the similarities and differences between the lock and key and induced theories. Students complete Activity sheet 3.2.1 Models of enzyme action, Task 3.


Ask students to complete questions 1 and 2 from Biology Student Book 1, Section 3.3.


Students could search computer-generated images to show induced fit theory.

Students could research how theories about enzyme action developed and changed over time.

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Chapter 3: Enzymes



Models of enzyme action

TASK 1: ENZYME SHAPE

01. Match the following aspects of the structure of a protein molecule (on the left) with the correct description (on the right): Primary structure The coiling of an amino acid chain into a spiral structure

Secondary structure The association of several polypeptide chains

Tertiary structure The sequence of amino acids in a polypeptide chain

Quaternary structure The irregular folding of a polypeptide chain into a globular shape

02. Enzymes are globular proteins. Describe what this means.

TASK 2: INDUCED FIT MODEL OF ENZYME ACTION

Enzymes are thought to work by an induced fit model.

01. Draw a large annotated diagram to show how enzymes work to catalyse the breakdown of a larger molecule to two smaller molecules according to the induced fit model. Use the checklist below to ensure that you include key terminology.

R groups | Active site | Substrate | Enzyme-substrate complex | Collisions | Product | Specific

02. Explain why this model is called the induced fit model.

03. Describe how this model can also be used to explain how enzymes can catalyse anabolic reactions.

TASK 3: HOW THEORIES HAVE CHANGED

Theories describe ideas that we have about how things work. These theories can change over time, as we discover facts that support or disprove original ideas.

Lock and key model of enzyme action

01. Amylase is a carbohydrase enzyme that catalyses the breakdown of starch to glucose. Using this reaction as an example, together with the diagram, describe how it was originally thought that enzymes worked by the lock and key mechanism.

02. Compare and contrast the induced fit model and lock and key model of enzyme action.

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Chapter 3: Enzymes


Lesson plan 3.3

Lesson 3.3 Factors affecting enzyme activity (temperature)

LEARNING OUTCOMES

• Design an investigation to study the effect of temperature on enzyme action • Carry out an accurate investigation into the effect of temperature on enzyme action and record results

THE JOURNEY SO FAR

Students may have experience of investigating the temperature at which an enzyme works most effectively, for example, in the context of washing powders. During these investigations, students may have been provided with a method to follow and may have investigated only one or two temperatures.


Some students may describe enzymes as being ‘killed’ at high temperatures, rather than denatured.

LESSON OUTLINE

Engage and remind

Arrange students in small groups. Ask groups to brainstorm factors that affect enzyme activity. Groups should record their ideas in a mind map or spider diagram. Encourage students to explain any of the effects, if possible. Lead a discussion eliciting the factors that will be considered across Lessons 3.3 to 3.7 (temperature, pH, enzyme and substrate concentration, inhibitors) but do not go into any more detail at this stage. Retain the mind maps and/or spider diagrams for use in Lesson 3.7.

Core activities

Show students the reagents that are to be used in the investigation (full-fat milk and lipase) and ask them to identify which is the enzyme and which is the substrate in the reaction that they will investigate. Lead a discussion to describe the context of the reaction and the investigation, for example asking why we need lipase enzyme in the body and what it will break the lipids down to in the milk (fatty acids and glycerol). Demonstrate the colour of phenolphthalein indicator in alkali (pink) and then in acid (colourless).

Carry out a demonstration by adding five drops of phenolphthalein indicator to a test tube. Then add approximately 5 cm3 of milk and then approximately 7 cm3 of sodium carbonate solution, 0.05 mol dm–3. Do not appear to measure the volumes accurately as students should trial different volumes prior to carrying out the investigation. Ask students to observe the colour of the solution (pink) and to predict the colour change following the breakdown of lipids in the milk to form fatty acids (colourless). Ask students to reflect on how they could compare the rate of the reaction at different temperatures based on what they have seen.

Ask students to discuss the first two headings (The investigation and Hypothesis) on Activity sheet 3.3.1 Planning an investigation of enzyme activity. Students should then complete these sections in writing. Students may need access to Biology Student Book 1, Section 3.4 to support a hypothesis.

Explain to students that their investigation will involve carrying out a Required practical activity; written examinations will assess knowledge and understanding of Required practical activities. Students work in pairs to plan an investigation using Activity sheet 3.3.1 Planning an investigation of enzyme activity. Students should carry out trial experiments as they plan, for example, to decide an appropriate range and volumes of reagents to use. It is most likely that electric water baths will need to be set up in advance at a range of temperatures; this means that the temperature range to be investigated is provided for students.

Check the plan of each pair before they carry out their investigation.

Students carry out the investigation in pairs and record their results in pre-prepared results tables.


Students work individually to complete Activity sheet 3.3.2 Enzyme action. This work could be done during incubation periods during the investigation, if time allows.

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Chapter 3: Enzymes



Planning an investigation of enzyme activity

THE INVESTIGATION

Describe your investigation using the sentence stem below:

We are investigating the effect of …

HYPOTHESIS

Make a prediction about your investigation.

Use scientific knowledge to support your prediction.


You will be provided with reagents to use in the investigation.

List these and any other equipment that you will use.

VARIABLES

Identify the variables in the investigation:

• Independent variables • Dependent variables • Control variables

TRIAL EXPERIMENTS

Carry out some trial experiments to test the range of values that you will use for your independent variable and the volumes of reagents that you will use.

Keep a rough record of your findings and use these to help you to decide on the procedure for the investigation.

PROCEDURE

Write a method for the investigation as a numbered list of instructions.

Ensure that these instructions could be followed by a peer to carry out the investigation in exactly the same way as you will.

HEALTH AND SAFETY

Use the health and safety information provided with each reagent to identify any health and safety guidance that should be given to anyone carrying out this investigation.

Consider any other guidance that would be useful to ensure that the procedure is carried out safely.

RESULTS

Plan how you will record your results and design a table (or similar) prior to the investigation.

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Technician notes for Activity sheet 3.3.1

Planning an investigation of enzyme activity There are two sets of equipment and materials required for this lesson.

The first is for a short teacher demonstration, as described in the lesson plan.

The second is for a student practical. The materials listed are for a standard practical – pairs of students will plan an investigation independently, so there will be variations on the equipment required.

Students are required to carry out their own health and safety assessment and should be provided with information to do this. This must be checked before they proceed.

EQUIPMENT AND MATERIALS: TEACHER DEMONSTRATION

• one test tube • 10 cm3 measuring cylinder • five drops of phenolphthalein indicator • approximately 5 cm3 of full-fat milk • approximately 7 cm3 of sodium carbonate solution, 0.05 mol dm–3

EQUIPMENT AND MATERIALS: STUDENT PRACTICAL

• milk, full-fat, 5 cm3 per student per temperature assessed • phenolphthalein in a dropper bottle [Ethanol (IDA) in the phenolphthalein indicator is HIGHLY FLAMMABLE

and HARMFUL, because of the presence of methanol] • 5% lipase solution, 1 cm3 per student per temperature assessed • sodium carbonate solution, 0.05 mol dm–3, 7 cm3 per student per temperature assessed [Sodium carbonate

solution is an IRRITANT at concentrations over 1.8 M] • electric hot water baths set to a range of temperatures (for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C)

each containing a thermometer, a test-tube rack and a beaker of lipase solution • ice (to allow a low temperature to be investigated) • marker pen, one per group • test tube rack, one per group • measuring cylinder (or syringe), 10 cm3, two per group • beaker, 100 cm3, two per group (for milk and sodium carbonate solution) • beaker, 250 cm3, two per group (to act as water baths for temperatures below room temperature) • thermometer, one per group per temperature tested • test tube, one per group per temperature tested • glass rod, one per group per temperature tested • syringe, 2 cm3, one per group per temperature tested • stop clock, one per group per temperature tested

NOTES

Lipase solution is best freshly made, but it will keep for two days in a refrigerator. Students shouldn’t try to study different temperatures on different days for the same investigation; the activity of the enzyme will change and it will not be a fair test.

To make phenolphthalein indicator, dissolve 1 g in 600 cm3 of IDA then make up to one litre with water. Label the bottle HIGHLY FLAMMABLE.

Electric water baths should be used during this investigation, rather than naked flames.

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Chapter 3: Enzymes



Enzyme action

TASK 1

01. The diagram shows how an enzyme is involved in the breakdown of a substrate molecule to give two product molecules.

a. Give the name of the part of the enzyme molecule into which the substrate molecule fits.

b. Give two explanations for the fact that only certain substrate molecules will fit into this part of the enzyme molecule.

c. Explain why an increase in temperature from 20 °C to 30 °C will result in a faster rate of reaction.

d. Explain why, at a temperature of 70 °C, the reaction involving the enzyme no longer takes place.

The enzyme catalase is found in nearly all living cells. It catalyses the conversion of hydrogen peroxide to oxygen and water. The faster the rate of reaction, the more vigorous the bubbling.

02. The table shows the rate of reaction when equal masses of a number of different substances were each added to 5 cm3 of hydrogen peroxide. The rate of reaction goes from 0, where no bubbles were observed, to 5, which was the most vigorous bubbling.

Tube Substance added Rate of reaction

A Liver 3

B Ground liver and sand 5

C Sand 0

D Cold, boiled water 0

E Manganese dioxide 4

F Cold, boiled manganese dioxide 4

a. Explain the difference in the rate of reaction for

i. tube A and tube B

ii. tube A and tube D

b. Explain how tube C acts as a control.

c. Use the results of this investigation to describe one important difference between an enzyme such as catalase and a chemical catalyst such as manganese dioxide.

03. A cylinder of potato is placed in a container with 100 cm3 of hydrogen peroxide. The graph shows the percentage loss in mass of the container over the following 15 minutes.

a. Explain why there was a loss in mass over this period.

b. Describe how the curve would have differed if the potato cylinder had been cut into discs before being added to the hydrogen peroxide.

c. Explain your answer to part b., in terms of enzyme–substrate complexes.

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Chapter 3: Enzymes


Lesson plan 3.4

Lesson 3.4 Factors affecting enzyme activity (analysing data)

LEARNING OUTCOMES

• Analyse data to explain the relationship between temperature and enzyme activity in a named reaction • Apply knowledge and understanding about the effect of temperature on enzymes to washing powders • Evaluate an investigation and suggest improvements to a method

THE JOURNEY SO FAR

At KS4, students may have learned about the importance of enzymes in industry, for example proteases and lipases in washing powders, proteases in producing baby foods, and carbohydrases in the manufacture of glucose syrup. During KS3 and KS4, students are likely to have had experience of making conclusions from practical work to investigate enzyme action. Students are likely to have presented data graphically and to have analysed results and evaluated experimental methods, but they may not have carried out all of those processes within the same investigation. They are likely to be aware that enzymes work best within a certain temperature range. They may be aware of the term ‘denaturation’, linked with high temperatures.


Some students may assume that all enzymes work best within the same temperature range. (Lesson 3.8 considers enzymes that work under unusual conditions.)

LESSON OUTLINE

Engage and remind

Ask students to suggest why scientists use graphs to display data. Facilitate a discussion of the ideas (such as: graphs allow scientists to visualise relationships, infer relationships in addition to specific readings, and extrapolate from results).

In the same working groups as in Lesson 3.3, students discuss how the data in results tables should be best displayed graphically.

Core activities

Students work individually to present their own data graphically. Encourage students to compare graphs with others in their group and to make amendments as necessary. Students then analyse and evaluate their investigation by completing Activity sheet 3.4.1 Analysing and evaluating. It may be useful to revisit key terminology linked with practical work, such as accuracy, precision, repeatability, anomalous results, random errors, systematic errors and range prior to students completing Activity sheet 3.4.1 Analysing and evaluating Task 3.

It would be useful for students to receive feedback on Activity sheet 3.4.1 Analysing and evaluating before carrying out another investigation in Lesson 3.5.

Ask students to reflect on the relevance of this data to real life. Students complete Biology Student Book 1, Chapter 3, Assignment 1: Investigating biological washing powders.


Assess students’ understanding by asking them to work individually to complete questions 3-8 from Biology Student Book 1, Section 4. Students could then work in pairs to mark answers using a mark scheme, or they could mark their own work as part of a class discussion.


Students could use other sources of information to find out about bile salts and their effects on digestion of fats, or what happens to the fatty acids and glycerol once they have been absorbed from the digestive tract.

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Chapter 3: Enzymes



Analysing and evaluating Use the results that you obtained during Lesson 3.3 to analyse and evaluate the investigation into the effect of temperature on lipase enzyme.

TASK 1: ANALYSING DATA

01. Display your data graphically.

02. Describe what your graph shows about the effect of temperature on the time taken for lipase to break down the fat in milk. Try to use numerical evidence to support your description.

TASK 2: EXPLAINING RESULTS

Use these questions as prompts to help you explain what your results show. Provide as much detail as you can.

01. Describe what is produced when fat breaks down.

02. Use this information to explain why the phenolphthalein changes colour.

03. Explain why the temperature affects the action of lipase in this way.

04. Describe and explain the difference between a ‘time taken’ and a ‘rate of reaction’ curve for this investigation.

05. Explain why it is necessary to break down fat in the digestive system.

06. State whether a graph drawn of different enzyme reactions would appear as the one produced from this investigation. Explain your answer.

TASK 3: EVALUATING THE INVESTIGATION

01. Identify any anomalous results in your data.

02. Suggest reasons for any anomalous results.

03. Consider these definitions, then comment on the accuracy, precision and repeatability of your investigation:

• Accuracy: a measurement result is accurate if it is judged to be close to the true value. • Precision: a measurement is precise if values cluster closely. • Repeatability: a measurement is repeatable when repetition under the same conditions gives the same or

similar results (for example: when comparing results from the same group, using the same method and equipment).

04. Suggest improvements to your method for future investigations, explaining how each suggestion could improve the quality of evidence.

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