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12.2.1112 · Energy and Respiration

Aerobic Respiration- Effect of Temperature and Substrate Concentration — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 9 parts Lesson 18 of 18 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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12.2.11 Aerobic Respiration: Effect of Temperature and Substrate Concentration — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe redox-indicator and respirometer methods for investigating the effect of temperature and substrate concentration on respiration.Re…

  • Redox indicator
  • Safe for cells
  • Process measured
  • Dehydrogenation
  • Hydrogen carriers
  • Dye reduction

Part 1 of 7Redox indicators in yeast

1Redox indicator
  • Redox indicator a substance that changes colour when it is reduced or oxidised.
2Examples
  • DCPIP and methylene blue.
3Safe for cells
  • Safe for cells the dyes can be added to living yeast suspensions without damaging the cells.
4Process measured
  • Process measured the rate of anaerobic respiration of yeast.

Part 2 of 7How the dye measures respiration

Dehydrogenation
  • Dehydrogenation hydrogens are removed from substrates throughout respiration.
Hydrogen carriers
  • NAD and FAD normally take up the hydrogens.
Dye reduction
  • DCPIP and methylene blue also take up hydrogens and are reduced.
Colour change
  • Colour change both dyes change from blue to colourless when reduced.
Rate link
  • Rate link faster respiration releases hydrogen faster, so the dye is decolourised sooner.
Calculation
  • Calculation rate of respiration is inversely proportional to the time taken for the colour to change.

Part 3 of 7Method for yeast

1
Prepare a yeast suspension with a substrate such as glucose.
2
To test temperature, place tubes in a water bath at a range of temperatures, such as 30, 35, 40 and 45 °C.
3
To test substrate concentration, use a range of concentrations, such as 0.1, 0.5 and 1.0 % glucose.
4
Add the dye and start timing.
5
Record the time taken for the colour change.
6
Repeat at each value and calculate a mean.

Part 4 of 7Variables to control

Variables to control
Volume of dye
  • Volume of dye more dye molecules take longer to decolourise.
Volume of yeast suspension
  • Volume of yeast suspension more yeast cells inflate the rate.
Type of substrate
  • Type of substrate yeast respires different substrates at different rates.
Concentration of substrate
  • Concentration of substrate limited substrate limits respiration.
    • (when testing temperature)
Temperature of added dye
  • Temperature of added dye it must match the temperature of the tube.
Colour check
  • Colour check use a control tube without dye because the yeast suspension itself is slightly yellow.

Part 5 of 7Respirometer at different temperatures

1
Place the respirometer tubes in a thermostatically controlled water bath.
2
Allow the apparatus to reach the temperature, close the screw clip and read the manometer movement over a fixed time.
3
Calculate the gas volume change in cm3 min-1.
4
Reset the manometer fluid, let air enter and change the bath temperature.
5
Allow the tubes to acclimatise and repeat at several temperatures.
Oxygen consumed
  • Oxygen consumed volume = π r2 h, with capillary radius r and fluid movement h in one minute.
Presentation
  • Presentation results are shown in a table or a graph of rate against temperature.

Part 6 of 7Explaining the temperature trend

1Low temperature
  • Low temperature molecules and enzymes have little kinetic energy and collide rarely, so the rate is low.
2Rising temperature
  • Rising temperature more frequent successful collisions raise the rate.
3High temperature
  • High temperature enzymes denature and the rate falls.
4Limit of the respirometer
  • Limit of the respirometer it measures aerobic respiration only, because anaerobic respiration uses no oxygen.

Part 7 of 7More from the specification

1
Respiratory dehydrogenase catalytic function
  • Respiratory dehydrogenase catalytic function optimal temperature preserves tertiary protein structure, maximizing substrate turnover rate and respiratory metabolic function.
2
Glycolysis to link reaction
  • Glycolysis occurs in the cytoplasm where glucose is broken down into pyruvate,
  • which is actively transported across the mitochondrial membrane into the matrix for the link reaction and Krebs cycle.
3
The Krebs cycle reactions
  • Within the mitochondrial matrix, acetyl-CoA enters a cyclic series of oxidation-reduction reactions, yielding carbon dioxide, reduced NAD, reduced FAD,
  • and ATP via substrate-level phosphorylation.
4
Oxidative phosphorylation and electron transport
  • The inner mitochondrial cristae membrane houses the electron transport chain,
  • where transfer of electrons drives proton pumping, generating a proton gradient that drives ATP synthase phosphorylation reactions.
5
Temperature and substrate concentration kinetics
  • The rate of aerobic respiration in mitochondria increases with rising temperature and substrate concentration until reaching an optimum, beyond which mitochondrial respiratory enzymes denature and reaction rates decline.
6
Glycolysis to link reaction
  • Glycolysis occurs in the cytoplasm where glucose is broken down into pyruvate,
  • which is actively transported across the mitochondrial membrane into the matrix for the link reaction and Krebs cycle.
7
The Krebs cycle reactions
  • Within the mitochondrial matrix, acetyl-CoA enters a cyclic series of oxidation-reduction reactions, yielding carbon dioxide, reduced NAD, reduced FAD,
  • and ATP via substrate-level phosphorylation.
8
Oxidative phosphorylation and electron transport
  • The inner mitochondrial cristae membrane houses the electron transport chain,
  • where transfer of electrons drives proton pumping, generating a proton gradient that drives ATP synthase phosphorylation reactions.
9
Temperature and substrate concentration kinetics
  • The rate of aerobic respiration in mitochondria increases with rising temperature and substrate concentration until reaching an optimum, beyond which mitochondrial respiratory enzymes denature and reaction rates decline.
10
Glycolysis to link reaction
  • Glycolysis occurs in the cytoplasm where glucose is broken down into pyruvate,
  • which is actively transported across the mitochondrial membrane into the matrix for the link reaction and Krebs cycle.
11
The Krebs cycle reactions
  • Within the mitochondrial matrix, acetyl-CoA enters a cyclic series of oxidation-reduction reactions, yielding carbon dioxide, reduced NAD, reduced FAD,
  • and ATP via substrate-level phosphorylation.
12
Oxidative phosphorylation and electron transport
  • The inner mitochondrial cristae membrane houses the electron transport chain,
  • where transfer of electrons drives proton pumping, generating a proton gradient that drives ATP synthase phosphorylation reactions.
13
Temperature and substrate concentration kinetics
  • The rate of aerobic respiration in mitochondria increases with rising temperature and substrate concentration until reaching an optimum, beyond which mitochondrial respiratory enzymes denature and reaction rates decline.
14
Glycolysis to link reaction
  • Glycolysis occurs in the cytoplasm where glucose is broken down into pyruvate,
  • which is actively transported across the mitochondrial membrane into the matrix for the link reaction and Krebs cycle.
15
The Krebs cycle reactions
  • Within the mitochondrial matrix, acetyl-CoA enters a cyclic series of oxidation-reduction reactions, yielding carbon dioxide, reduced NAD, reduced FAD,
  • and ATP via substrate-level phosphorylation.
16
Oxidative phosphorylation and electron transport
  • The inner mitochondrial cristae membrane houses the electron transport chain,
  • where transfer of electrons drives proton pumping, generating a proton gradient that drives ATP synthase phosphorylation reactions.
17
Temperature and substrate concentration kinetics
  • The rate of aerobic respiration in mitochondria increases with rising temperature and substrate concentration until reaching an optimum, beyond which mitochondrial respiratory enzymes denature and reaction rates decline.
18
Glycolysis to link reaction
  • Glycolysis occurs in the cytoplasm where glucose is broken down into pyruvate,
  • which is actively transported across the mitochondrial membrane into the matrix for the link reaction and Krebs cycle.
19
The Krebs cycle reactions
  • Within the mitochondrial matrix, acetyl-CoA enters a cyclic series of oxidation-reduction reactions, yielding carbon dioxide, reduced NAD, reduced FAD,
  • and ATP via substrate-level phosphorylation.
20
Oxidative phosphorylation and electron transport
  • The inner mitochondrial cristae membrane houses the electron transport chain,
  • where transfer of electrons drives proton pumping, generating a proton gradient that drives ATP synthase phosphorylation reactions.
21
Temperature and substrate concentration kinetics
  • The rate of aerobic respiration in mitochondria increases with rising temperature and substrate concentration until reaching an optimum, beyond which mitochondrial respiratory enzymes denature and reaction rates decline.
22
Oxidative phosphorylation
  • ATP production driven by the electron transport chain.
23
Intermembrane space
  • The gap between the two membranes where protons accumulate.
24
Mitochondria
  • Organelles where most aerobic respiration takes place.
25
Glycolysis
  • Splitting of glucose to pyruvate in the cytoplasm.
26
Pyruvate
  • A 3-carbon product of glycolysis.
27
Phosphorylation
  • Adding a phosphate group.
28
Ethanol
  • Alcohol produced by yeast in anaerobic respiration.
29
Matrix
  • The solution inside the inner membrane containing Krebs cycle enzymes.
30
Lactate
  • The product of anaerobic respiration in human cells.
31
Fermentation
  • Anaerobic respiration by yeast producing ethanol and carbon dioxide.

Key terms

TermMeaning
Redox indicatorDye that changes colour when reduced or oxidised.
DCPIPBlue redox dye that becomes colourless when reduced.
Methylene blueRedox dye that becomes colourless when reduced.
RespirometerApparatus measuring oxygen consumption of respiring organisms.
ManometerU-tube whose fluid moves as gas volume changes.
DehydrogenationRemoval of hydrogen atoms from a substrate.

Avoid these mistakes

1
Using a respirometer for anaerobic respiration — it measures oxygen uptake, which anaerobic respiration does not use.
2
Saying a faster colour change means slower respiration — shorter time means faster respiration.
3
Changing temperature and substrate together — only one variable may change at a time.
4
Using the volume πr squared h without the time — divide by minutes to get a rate.

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