Biology practical 9

Question 1

Redox indicator

Answer 1

Changes colour when reduced and oxidised so indicates when NAD is reduced (glycolysis, link reaction, Krebs)
And NAD is oxidised (Oxidative phosphorylation)

Question 2

Aim

Answer 2

Investigate effect of variable on dehydrogenase enzyme in respiration so rate of respiration

Question 3

Dehydrogenase

Answer 3

Catalyses the reeduction and oxdiation (transfer of H+) from co enzymes

Question 4

Set up

Answer 4

5 test tubes at different temperatures (thermostatically controlled)
Contains solutions of yeast + glucose
And solutions of redox indicator (left in water baths for each condition to equilibrate to correct temp)

Question 5

Mixing indicator with yeast and substrate

Answer 5

Start of experiment: start stop watch

Question 6

Standardised colour change

Answer 6

Have a set colour that all test tubes must reach before stopping the experiment

Question 7

Maintain temp

Answer 7

Leave in water bath with thermometer to monitor temp at correct condition

Question 8

Why is glucose needed?

Answer 8

Substrate for respiration to occur

Question 9

Why do we stir frequently?

Answer 9

So yeast and glucose and indicator dont separate

Question 10

End point

Answer 10

Once colour reaches end point so indicates reduction/Oxidation has occured thus measures rate of reaction

Question 11

Variables effect on enzyme catalysed reaction

Answer 11

Increase temp= increase rate
Increase substrate conc = increase rate
Increase enzymes = increase rate
Addition of inhibitors = decrease rate

Question 12

Limitations of method

Answer 12

Colour change is subjective to indicate end point despite standardisation
Removing test tubes from water bath to check colour change decreases temp

Question 13

How to prevent subjectivity of colour change

Answer 13

Use colorimeter to detect the end point