5.2Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Respiration — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 10 parts Lesson 3 of 36 1 quiz
Curriculum Equation Key Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP)
Lesson summary
5.2 Respiration — IAL EDEXCEL LINEAR notes: Describe the stages of aerobic and anaerobic respiration, calculate the respiratory quotient, and describe the yeast and respirometer practicals.Aerobic respiration = breaking down a respiratory substrate, mainly glucose, using oxygen t…
- Mitochondrion
- Glycolysis
- Net products per glucose
- Fate of pyruvate
- Link reaction
- Krebs cycle
Section 1 of 10Overview of aerobic respiration
Aerobic respiration
Aerobic respiration breaking down a respiratory substrate, mainly glucose, using oxygen to make ATP: C6H12O6 + 6O2 → 6CO2 + 6H2O + 2870 kJ.
- The energy released phosphorylates ADP to ATP, which powers other cell processes.
- Other substrates, such as fatty acids and amino acids, can also be respired.
Control
- Control enzymes release the energy gradually, as a sudden release would raise temperature enough to denature enzymes.
- The slowest enzyme sets the overall rate.
Coenzymes
- NAD and FAD transfer hydrogen, and coenzyme A transfers acetate.
| Stage | Location |
|---|---|
| Glycolysis | Cytoplasm |
| Link reaction | Mitochondrial matrix |
| Krebs cycle | Mitochondrial matrix |
| Oxidative phosphorylation | Inner mitochondrial membrane |
- Mitochondrion
- two phospholipid membranes enclose the organelle.
- The outer membrane is smooth and permeable to small molecules.
- The inner membrane is folded into cristae, is less permeable and holds the electron transport chain and ATP synthase.
- The intermembrane space has a low pH because protons accumulate there.
- The matrix contains enzymes, ribosomes and circular DNA.
Section 2 of 10Glycolysis
- Glycolysis the first stage of respiration, in the cytoplasm, which needs no oxygen and only partially oxidises glucose.
Glycolysis
Two ATP phosphorylate glucose, trapping it in the cell and making it more reactive, and give two molecules of triose phosphate.
Triose phosphate is oxidised by losing hydrogen, which reduces NAD to reduced NAD.
Each triose phosphate forms pyruvate, and four ATP are made in total.
Net products per glucose
- 2 pyruvate (3C), a net gain of 2 ATP (4 made, 2 used) and 2 reduced NAD.
Fate of pyruvate
- Fate of pyruvate it enters the mitochondrial matrix when oxygen is available.
- Under anaerobic conditions, glycolysis ends in lactate or ethanol.
Section 3 of 10Link reaction and Krebs cycle
1Link reaction
- Link reaction pyruvate enters the matrix by active transport using a transport protein and a little ATP.
- Pyruvate is oxidised (dehydrogenated) and decarboxylated, producing acetate that joins coenzyme A to form acetyl CoA.
- pyruvate + NAD + CoA → acetyl CoA + CO2 + reduced NAD, and no ATP is made.
2Krebs cycle
- Krebs cycle it is a cycle of enzyme-controlled reactions in the matrix.
1
Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C), and coenzyme A is released for reuse.
2
Citrate is decarboxylated, releasing 2 CO2.
3
Citrate is dehydrogenated, reducing 3 NAD and 1 FAD.
4
Substrate-level phosphorylation transfers a phosphate to ADP to form 1 ATP.
5
Oxaloacetate is regenerated.
1
Acetyl CoA from fatty acids and amino acids can also enter the cycle.
2Per glucose
- Per glucose each glucose gives two acetyl CoA, so the link reaction and Krebs cycle occur twice.
- The link reaction gives 2 CO2 and 2 reduced NAD.
- The Krebs cycle gives 2 ATP, 6 reduced NAD, 2 reduced FAD and 4 CO2.
Section 4 of 10Oxidative phosphorylation
- Chemiosmosis
- energy from electrons passed along the electron transport chain pumps protons across the inner membrane to produce ATP.
1
Reduced NAD and reduced FAD from the Krebs cycle donate hydrogen, which splits into protons and high-energy electrons.
2
The electrons pass along carriers in the inner membrane, releasing energy.
3
The energy pumps protons from the matrix into the intermembrane space, creating a proton gradient (the inner membrane is impermeable to protons).
4
Protons return to the matrix by facilitated diffusion through the channel enzyme ATP synthase, which phosphorylates ADP to ATP.
5
Oxygen is the final electron acceptor and combines with protons and electrons to form water.
Yield
- Yield about 3 ATP per reduced NAD and 2 per reduced FAD, giving up to 38 ATP per glucose in total.
Role of oxygen
- Role of oxygen without it the chain stops, reduced NAD and FAD cannot be reoxidised, and the Krebs cycle and link reaction stop.
Section 5 of 10Anaerobic respiration
1
Consequence of no oxygen
- Consequence of no oxygen the electron transport chain stops, no ATP comes from oxidative phosphorylation, and the Krebs cycle and link reaction stop.
2
Anaerobic pathways
- Anaerobic pathways reduced NAD from glycolysis is reoxidised so glycolysis continues and a small amount of ATP is still made.
3
Lactate fermentation
- Lactate fermentation it occurs in mammalian muscle and some microorganisms.
- Reduced NAD transfers hydrogen to pyruvate, forming lactate by lactate dehydrogenase, a one-step pathway.
- Lactate is oxidised back to pyruvate, which needs extra oxygen (oxygen debt), or the liver converts it to glucose and glycogen.
- Oxygen debt explains deeper, faster breathing after exercise.
4
Ethanol fermentation
- Ethanol fermentation it occurs in yeast and plant cells.
- Pyruvate is decarboxylated to ethanal, releasing CO2, then reduced NAD reduces ethanal to ethanol using alcohol dehydrogenase, a two-step pathway.
- Ethanol is a waste product that cannot be metabolised further.
Section 6 of 10Respiratory quotient (RQ)
RQ
RQ volume (or moles) of CO2 produced ÷ volume (or moles) of O2 taken in.
- Equal numbers of gas molecules occupy equal volumes, so the ratio of coefficients in a balanced equation gives the RQ.
Typical values
- Typical values carbohydrate 1.0, protein about 0.9 and lipid about 0.7.
- Lipids have more C–H bonds, so more oxygen is needed to form water.
Mixed substrates
- Mixed substrates an RQ of 0.85 suggests carbohydrate and lipid are both being used,
- and substrates are normally used in the order carbohydrate, lipid, protein.
Interpretation
- Interpretation an RQ above 1 may indicate anaerobic respiration, since little oxygen is used, or excess carbohydrate intake.
- An RQ below 0.7 suggests underfeeding.
Calculation
- Calculation write and balance the equation first, then divide CO2 by O2.
Section 7 of 10Practical: respiration in yeast
- Principle
- DCPIP or methylene blue are redox indicators that take up hydrogen released by dehydrogenase, changing from blue to colourless.
- The faster the respiration, the faster the colour change, so rate = 1 ÷ time (s−1).
1
Add a set volume of yeast suspension to tubes containing glucose solution.
2
Hold each tube in a water bath at a set temperature for 5 minutes.
3
Add a set volume of DCPIP and start the stopwatch at once.
4
Stop timing when the blue colour is lost, using the same person each time.
5
Repeat across temperatures such as 30, 35, 40 and 45 °C, or use glucose concentrations such as 0.1%, 0.5% and 1.0%.
Controlled variables
- Controlled variables volume of dye, volume of yeast, type and concentration of substrate, temperature and pH (using a buffer).
Result
- Result the time for colour loss falls as temperature rises, and at extreme temperatures the enzyme denatures and no colour change occurs.
Control tube
- Control tube yeast without dye helps show when the blue has fully gone because the suspension may be yellow.
Section 8 of 10Practical: respirometer and RQ
- Principle
- germinating seeds or small invertebrates consume oxygen in a sealed tube, and soda lime absorbs carbon dioxide.
1
Run the respirometer with soda lime for a set time, such as 30 minutes.
2
As oxygen is used, pressure falls and manometer fluid moves towards the organisms.
3
Measure the distance moved and calculate the gas volume change x (cm³ min−1) using πr²h.
4
Reset the apparatus, remove the soda lime and repeat to find the volume change y.
Calculation
- Calculation x is the volume of oxygen consumed, and y is the oxygen consumed minus carbon dioxide produced.
- RQ (x + y) ÷ x, where y is negative when the fluid moves towards the organisms.
Reliability
- Reliability use a water bath to keep temperature constant, a control tube with inert material of equal volume to correct for pressure changes,
- and repeat to find a mean.
Variations
- Variations temperature can be changed with several water baths, and a changing RQ shows the substrate has changed.
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Glycolysis | Breakdown of glucose to pyruvate in the cytoplasm with a net gain of 2 ATP. |
| Link reaction | Conversion of pyruvate to acetyl CoA in the mitochondrial matrix. |
| Krebs cycle | Cycle in the matrix that produces reduced NAD, reduced FAD, ATP and carbon dioxide. |
| Oxidative phosphorylation | ATP production by chemiosmosis on the inner mitochondrial membrane. |
| Oxygen debt | Extra oxygen needed after exercise to deal with lactate. |
| Respiratory quotient | Carbon dioxide produced divided by oxygen consumed. |
| Redox indicator | A dye that changes colour when it is reduced or oxidised. |
Section 10 of 10Exam technique
1
Saying the Krebs cycle takes place in the mitochondria generally — it takes place in the matrix.
2
Saying oxygen is used in glycolysis or the Krebs cycle — oxygen is the final electron acceptor in oxidative phosphorylation.
3
Forgetting that glycolysis nets 2 ATP — 2 ATP are used and 4 are made.
4
Treating lactate fermentation as two steps — it is one step, whereas ethanol fermentation takes two.
Marked practiceQuizzes for this lesson
Last updated:
\n