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A level practicals - Biology > Practical 8 - Investigation into the effect of temperature or pH on enzyme activity > Flashcards

Practical 8 - Investigation into the effect of temperature or pH on enzyme activity Flashcards

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1
Q

Why do we use milk in this practical?

A

Contains fats/lipids that lipase will break down

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2
Q

What contains fats/lipids in this practical and what happens to this?

A

Milk, which is broken down by lipase

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3
Q

What does lipase break down in this practical?

A

The milk

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4
Q

What does phenolphthalein do at different pH levels?

A

Pink in alkaline (pH of about 10)
Colourless in a pH less than 8.3

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5
Q

What’s our indicator that we’re using and the colour change we’re expected to see as we stir?

A

Phenolphthalein
Pink (alkali) to colourless (acidic)

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6
Q

What makes the phenolphthalein turn pink at the start of the reaction and why?

A

Sodium carbonate - is an alkali

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7
Q

What is sodium carbonate?

A

An alkali

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8
Q

How much lipase do we need in total for this practical?

A

5g/100cm^3

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9
Q

What does lipase do in this practical?

A

Catalyses the hydrolysis of triglycerides into fatty acids and glycerol

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10
Q

What catalyses the hydrolysis of triglycerides into fatty acids and glycerol in this practical?

A

Lipase

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11
Q

What is lipase?

A

An enzyme

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12
Q

What is our enzyme in this practical?

A

Lipase

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13
Q

What causes the pH of the solution to change and how?

A

Fatty acids from the hydrolysis of the triglycerides in the milk, which contribute H+ ions to the solution, making it more acidic

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14
Q

Which ions make a solution more acidic?

A

H+

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15
Q

What do H+ ions do to a solution?

A

Make it more acidic

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16
Q

What do fatty acids do to the solution here and where have they come from?

A

Turn it colourless
From the hydrolysis of triglycerides by lipase to the milk

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17
Q

Concentration of sodium carbonate used

A

0.05moldm^-3

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18
Q

What are the temperatures of the water baths used in this practical?

A

15, 25, 35, 45, 55 (degrees Celsius)

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19
Q

Which one of the temperatures used in the practical is different and why?

A

15 degrees Celsius - is below room temperature, so we need ice

20
Q

What do we need to do to the 15 degrees Celsius water bath and why?

A

Add ice as it’s below room temperature

21
Q

What’s the first thing we do during this practical?

A

Place a breaker of lipase solution in the 25 degrees Celsius (will be at different temperatures to match the other ones) water bath

22
Q

Why do we place the beaker of lipase solution in the water bath that’s to be used?

A

To equilibrate the enzyme to the right temperature

23
Q

How do we equilibrate the enzyme to the correct temperature?

A

Place a breaker of lipase solution in the water bath at the correct temperature

24
Q

How much milk do we use in the test tube?

A

5cm^3

25
Q

How much phenolphthalein do we use in the test tube?

A

5 drops

26
Q

How much sodium carbonate solution do we add to the test tube?

A

7cm^3

27
Q

What do we do with the test tube once we’ve added all of the solutions?

A

Place in the water bath for 10 minutes to equilibrate

28
Q

Why do we place the test tube in the water bath for 10 minutes?

A

To equilibrate

29
Q

How much of the lipase from the beaker do we add to the test tube?

A

1cm^3

30
Q

What do we do once we’ve added the lipase from the beaker into the test tube?

A

Start the stop clock - stir the contents of the test tube until the solution loses its pink colour and record the time taken

31
Q

What are we recording the time taken for?

A

The solution to turn from pink to colourless by stirring it

32
Q

What do we repeat this whole practical for?

A

All of the different temperatures (remember that the lipase solution temperatures is to be kept the same too)

33
Q

What’s the result of this practical?

A

The higher the temperature, the less time taken for the colour change

34
Q

Why did we receive the result we did - the higher the temperature, the less time taken for the colour change - ?

A

Increased temperature = more kinetic energy = probability of successful collisions to form enzyme-substrate complexes increases = less time to change colour as milk is catalysed faster to release fatty acids which lower the pH, causing the colour of the phenolphthalein to change

35
Q

Under which conditions is milk catalysed faster to release fatty acids that lower the pH and why?

A

Higher temperatures, as there’s more kinetic energy, meaning that the probability of successful collisions to form enzyme-substrate complexes increases

36
Q

Why does milk being catalysed faster cause the colour of the phenolphthalein to change quicker?

A

Releases fatty acids faster, which lower the pH, causing the colour change

37
Q

Does the rate of the reaction continue to increase? Why?

A

No - the enzyme starts becoming denatured

38
Q

Why does having some denatured enzymes decrease the rate of a reaction?

A

Less available active sites for the substrate to collide with to catalyse the reaction

39
Q

Does denaturing happen immediately?

A

No - it’s a process

40
Q

How do we actually get the lipase in the first place for this practical?

A

Extract it from a living cell and purify it for laboratory use

41
Q

What must lipase be after being extracted from a cell before laboratory use?

A

Purified

42
Q

What type of range bars on a graph show more reliable data?

A

-smaller
-no overlap with next set of results

43
Q

Which other variables which were not controlled SHOULD have been controlled?

A

Enzyme concentration
Milk concentration
pH of milk
Type of milk used

44
Q

What are the sources of inaccuracy in this practical?

A

Maintaining a constant temperature
Difficulty determining when the milk has changed colour

45
Q

How do we maintain a constant temperature in this practical?

A

Use a thermostatically controlled water bath

46
Q

How do we solve the problem of having difficulty determining when the milk has changed colour?

A

Use a colourimeter

47
Q

Why should we have used a colourimeter in this practical?

A

As we had some difficulty determining when the milk had changed colour

A level practicals - Biology (20 decks)

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