Respiration (A Level Only)

Lerne es beim Spielen

Beantworte diese Fragen für Energie, dann angle und erkunde. Kein Konto nötig.

Für Lehrkräfte: sofort einsetzbare Lektionsfolien, Lernnotizen für Respiration (A Level Only) (Biology, AQA) — nutze sie in deiner Lektion oder starte das Thema als interaktive Klassenaktivität, die deine Lernenden als Live-Spiel spielen.

Lektionsnotizen

Respiration & Energy

Respiration is a chemical process inside living cells that releases energy from organic molecules.
The chemical energy stored in nutrient molecules, e.g. carbohydrates, is transferred to ATP.
Energy is released easily inside cells by ATP hydrolysis.
Energy from ATP is used for active transport across membranes, e.g. via sodium-potassium pumps.
ATP also provides energy for DNA synthesis, protein synthesis and muscle contraction.
Energy cannot be created or destroyed; say energy is transferred or released, never 'created' or 'produced'.
It is acceptable to say that ATP is produced.

The Stages of Aerobic Respiration

Glucose is the main respiratory substrate used by cells.
Aerobic respiration is the breakdown of a respiratory substrate to produce ATP using oxygen.
Using glucose, aerobic respiration has four stages: glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation.
Glycolysis takes place in the cell cytoplasm.
The link reaction takes place in the matrix of the mitochondria.
The Krebs cycle takes place in the matrix of the mitochondria.
Oxidative phosphorylation occurs at the inner membrane of the mitochondria.
You must state the exact location, e.g. the Krebs cycle occurs in the matrix of the mitochondria, not just in the mitochondria.

Glycolysis

Glycolysis is the first stage of respiration and takes place in the cell cytoplasm.
Oxygen is not required for glycolysis, so it is an anaerobic process; it occurs in both aerobic and anaerobic respiration.
Phosphorylation of glucose (6C) to glucose phosphate requires 2 x ATP; the added phosphate makes glucose more reactive.
Glucose phosphate (6C) is split to produce two molecules of triose phosphate (3C).
Oxidation of triose phosphate to pyruvate (3C) transfers electrons and hydrogen to NAD, so 1 x NAD is reduced per triose phosphate.
Phosphate groups are transferred to ADP in substrate-level phosphorylation, producing 2 x ATP per triose phosphate; a total of 4 x ATP.
The products of glycolysis are 2 x pyruvate, a net gain of 2 x ATP and 2 x reduced NAD.
As 2 ATP are used and 4 are produced, there is a net gain of 2 ATP per glucose molecule.

The Link Reaction

When oxygen is available, pyruvate produced during glycolysis enters the mitochondria.
Pyruvate moves across the double membrane into the mitochondrial matrix by active transport, against a concentration gradient.
Active transport requires ATP and involves a membrane transport protein.
In the link reaction, pyruvate is oxidised to acetate, producing reduced NAD and CO₂.
Acetate combines with coenzyme A to produce acetyl coenzyme A (acetyl CoA).
Products of the link reaction are acetyl CoA, carbon dioxide and reduced NAD.
Acetyl CoA and NADH enter the Krebs cycle, while carbon dioxide is released as a waste product.
Two pyruvate molecules are produced per glucose, so the link reaction happens twice per glucose molecule.

The Krebs Cycle

The Krebs cycle (citric acid cycle) is a series of enzyme-controlled reactions in the mitochondrial matrix.
Acetyl coenzyme A releases a two-carbon molecule, which reacts with a four-carbon molecule (oxaloacetate) to produce a six-carbon molecule (citrate).
Coenzyme A is freed up to return to the link reaction and combine with more acetate.
A series of oxidation-reduction reactions convert the 6C molecule back into a 4C molecule.
During these reactions, coenzymes NAD and FAD are reduced, ATP is produced by substrate-level phosphorylation, and carbon dioxide is lost.
Reduced NAD and reduced FAD carry hydrogen ions and electrons to oxidative phosphorylation.
Other respiratory substrates may enter the Krebs cycle, e.g. breakdown products of lipids and amino acids.
The Krebs cycle turns twice for each molecule of glucose entering aerobic respiration.

Oxidative Phosphorylation

Oxidative phosphorylation is the final stage of aerobic respiration and takes place on the cristae of the inner mitochondrial membrane.
It relies on proteins embedded in the membrane, e.g. ATP synthase enzymes; the folded cristae provide a large surface area.
Hydrogen atoms are donated by reduced NAD and reduced FAD from the Krebs cycle.
Hydrogen atoms split into protons (H⁺ ions) and electrons; electrons enter the electron transport chain and energy is released as they pass between carriers.
The released energy is used to actively transport protons from the matrix into the intermembrane space.
Protons move down their concentration gradient back to the matrix by facilitated diffusion via proton channels associated with ATP synthase; this is chemiosmosis.
ATP synthase catalyses the formation of ATP from ADP and π.
At the end of the electron transport chain, electrons pass to oxygen, the final electron acceptor; oxygen combines with protons and electrons to form water as a waste product.

Anaerobic Respiration

When oxygen is absent or in short supply, cells may switch to anaerobic respiration.
Without oxygen there is no final electron acceptor, so the electron transport chain stops and oxidative phosphorylation stops producing ATP.
Examples of anaerobic pathways are ethanol fermentation (e.g. in yeast) and lactate fermentation (e.g. in mammalian cells).
Fermentation allows cells to produce ATP continuously via glycolysis.
Without fermentation, glycolysis cannot continue indefinitely because cells would run out of NAD.
Fermentation regenerates NAD so that glycolysis can continue.
In ethanol fermentation, pyruvate is decarboxylated to ethanal (CO₂ given off), then ethanal is reduced to ethanol by alcohol dehydrogenase; NADH is oxidised to regenerate NAD.
In lactate fermentation, pyruvate accepts hydrogen from NADH and is reduced to lactate; NADH is oxidised to regenerate NAD.
Fermentation does not produce ATP; its purpose is to regenerate NAD so glycolysis can continue producing ATP.

Required Practical: Investigating Respiration Rate

Respiration in yeast can be investigated using a redox indicator, a substance that changes colour depending on whether it is reduced or oxidised.
Examples of redox indicators are DCPIP and methylene blue; blue = oxidised, colourless = reduced.
Redox indicators change colour in the presence of respiring cells because respiration involves oxidation and reduction, e.g. during glycolysis triose phosphate is oxidised and NAD is reduced, and during the Krebs cycle NAD and FAD are reduced.
When a redox indicator is added to living cells, the rate of colour change represents the rate of respiration; faster respiration means faster hydrogen release and faster colour change.
Method: place set volumes of glucose solution and buffer solution (to maintain constant pH) into test tubes, place in water baths at different temperatures for at least ten minutes, then add yeast suspension and DCPIP and start the stopwatch.
Stop the stopwatch when the solution loses its blue colour; this is subjective, so the same person should judge all repeats, and a control tube of yeast and glucose should be used for colour comparison.
Repeat at each temperature to give three repeats, allowing anomalies to be identified.
Results: as temperature increases, the rate of respiration should increase, so the time taken for the solution to become colourless decreases.
Alternatives include investigating substrate concentration, substrate type or pH; a colorimeter can measure colour intensity more quantitatively, or the volume of carbon dioxide produced can be measured.
Yeast can respire anaerobically, so a layer of oil can be added on top of the yeast suspension to measure anaerobic respiration rate.
When investigating one variable, it is essential to control all other variables that might affect the results.

Folien

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

REGISTRIEREN — GRATIS ANMELDEN

Übungsfragen

Gratis-Vorschau — 8 von 64 Fragen. Registriere dich, um alle zu sehen.

1.Where in a eukaryotic cell does glycolysis take place?
Easy
- ACell cytoplasm
- BMitochondrial matrix
- CInner mitochondrial membrane
- DIntermembrane space
2.Which of the following is the correct balanced chemical equation for aerobic respiration?
Easy
- AC6H12O6 + 6O2 → 6CO2 + 6H2O
- BC6H12O6 + 6O2 → 6CO2 + 6H2O + energy
- CC6H12O6 + O2 → CO2 + H2O
- DC6H12O6 → 2C3H6O3 + energy
3.During the link reaction, pyruvate is converted into which product?
Medium
- AAcetyl coenzyme A
- BCitrate
- CLactate
- DEthanol
4.Which of the following is a product of the Krebs cycle?
Medium
- AReduced NAD
- BPyruvate
- CGlucose
- DEthanol
5.In oxidative phosphorylation, what is the role of oxygen?
Medium
- AIt acts as the final electron acceptor
- BIt is the final product of the electron transport chain
- CIt donates electrons to the electron transport chain
- DIt is used to phosphorylate ADP directly
6.Which of the following statements about anaerobic respiration is correct?
Medium
- AIt produces ATP by substrate-level phosphorylation during glycolysis
- BIt produces large amounts of ATP via the electron transport chain
- CIt requires oxygen as a final electron acceptor
- DIt occurs in the mitochondria of eukaryotic cells
7.In the required practical investigating respiration rate in yeast using DCPIP, what does the rate of colour change indicate?
Medium
- AThe rate of respiration
- BThe rate of photosynthesis
- CThe rate of fermentation only
- DThe rate of ATP hydrolysis
8.Which of the following are products of glycolysis? (select all that apply)
Medium
- APyruvate
- BATP (net gain of 2)
- CReduced NAD
- DCarbon dioxide
- EAcetyl coenzyme A

Mehr Fragen

9.Which of the following statements about the Krebs cycle are correct? (select all that apply)
Medium
- AIt occurs in the mitochondrial matrix
- BIt produces reduced NAD and reduced FAD
- CIt produces ATP by substrate-level phosphorylation
- DIt requires oxygen directly as a reactant
- EIt produces pyruvate
10.Glycolysis requires oxygen to occur.
Easy
True or false?
11.ATP is produced during the Krebs cycle by substrate-level phosphorylation.
Easy
True or false?
12.The link reaction occurs in the cytoplasm of the cell.
Medium
True or false?
13.Match each stage of aerobic respiration with its correct location in a eukaryotic cell.
Medium
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
- Cell cytoplasm
- Mitochondrial matrix
- Inner mitochondrial membrane
14.Place the stages of aerobic respiration in the correct chronological order.
Medium
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
15.Match each stage of aerobic respiration with the correct description of what happens during that stage.
Medium
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
- Phosphorylation and splitting of glucose
- Decarboxylation and dehydrogenation of pyruvate
- Cyclical pathway of enzyme-controlled reactions
- Production of ATP through oxidation of hydrogen atoms
16.Which of the following are products of the link reaction? (select all that apply)
Medium
- AAcetyl coenzyme A
- BCarbon dioxide
- CReduced NAD
- DPyruvate
- EATP
17.Which molecule is the final electron acceptor at the end of the electron transport chain?
Easy
- ANAD
- BOxygen
- CATP synthase
- DPyruvate
18.Which of the following statements about glycolysis are correct? (select all that apply)
Medium
- AIt occurs in the cell cytoplasm.
- BIt requires oxygen to occur.
- CIt produces a net gain of 2 ATP per glucose molecule.
- DIt produces 2 molecules of reduced NAD per glucose molecule.
- EIt produces carbon dioxide.
19.In the Krebs cycle, which molecule reacts with acetyl coenzyme A to produce citrate?
Medium
- AOxaloacetate
- BPyruvate
- CAcetate
- DNAD
20.The Krebs cycle occurs in the matrix of the mitochondria.
Easy
True or false?
21.Which of the following are products of the Krebs cycle? (select all that apply)
Medium
- AReduced NAD
- BReduced FAD
- CATP
- DCarbon dioxide
- EPyruvate
22.Match each molecule with its role in the link reaction.
Medium
- Pyruvate
- Coenzyme A
- NAD
- Carbon dioxide
- Oxidised to acetate
- Combines with acetate to form acetyl CoA
- Reduced during the reaction
- Released as a waste product
23.Which of the following is a product of glycolysis?
Medium
- APyruvate
- BCitrate
- CAcetyl coenzyme A
- DEthanol
24.During oxidative phosphorylation, what is the role of ATP synthase?
Medium
- AIt catalyses the formation of ATP from ADP and π.
- BIt transports pyruvate into the mitochondrial matrix.
- CIt reduces NAD to NADH.
- DIt decarboxylates pyruvate to acetate.
25.Which of the following statements about anaerobic respiration are correct? (select all that apply)
Hard
- AEthanol fermentation produces ethanol and carbon dioxide.
- BLactate fermentation produces lactate.
- CBoth ethanol and lactate fermentation regenerate NAD.
- DAnaerobic respiration produces large amounts of ATP.
- EEthanol fermentation occurs in yeast cells.
26.Which of the following are adaptations of the inner mitochondrial membrane for oxidative phosphorylation? (select all that apply)
Medium
- AFolded into cristae to provide a large surface area.
- BContains ATP synthase enzymes.
- CContains electron carrier proteins.
- DIs impermeable to protons.
- EContains enzymes for glycolysis.
27.A lack of fully formed cristae in mitochondria would most directly reduce ATP production because:
Hard
- AThere is a reduced surface area for the electron transport chain and ATP synthase.
- BGlycolysis cannot occur.
- CThe Krebs cycle cannot occur.
- DPyruvate cannot be transported into the mitochondria.
28.In the investigation of respiration rate in yeast using DCPIP, why is a buffer solution added?
Medium
- ATo maintain a constant pH.
- BTo provide a respiratory substrate.
- CTo denature enzymes.
- DTo act as a redox indicator.
29.Which of the following statements about the regeneration of NAD in fermentation are correct? (select all that apply)
Hard
- AIn ethanol fermentation, NAD is regenerated when ethanal is reduced to ethanol.
- BIn lactate fermentation, NAD is regenerated when pyruvate is reduced to lactate.
- CNAD regeneration allows glycolysis to continue.
- DFermentation produces ATP directly.
- ENAD is regenerated by the electron transport chain in fermentation.
30.A respirometer containing 1.8 g of germinating seeds recorded a syringe reading of 0.86 cm³ at 0 minutes and 0.54 cm³ at 12 minutes. What is the rate of oxygen consumption per gram of seeds per hour?
Medium
- A0.89 cm³ g⁻¹ hour⁻¹
- B0.027 cm³ g⁻¹ hour⁻¹
- C0.16 cm³ g⁻¹ hour⁻¹
- D0.53 cm³ g⁻¹ hour⁻¹
31.Insects of the same species were kept at 15 °C, 25 °C and 35 °C. Their rates of CO₂ release per gram were 2.94, 7.80 and 11.7 μdm³ g⁻¹ min⁻¹ respectively. Which statement best describes the effect of temperature on respiration rate?
Medium
- ARate increases as temperature rises because enzyme and diffusion rates increase
- BRate decreases as temperature rises because enzymes denature
- CRate stays constant because insects are ectotherms
- DRate increases then decreases because enzymes denature above 25 °C
32.Figure 1 shows the rate of CO₂ excretion by an insect over time, with regular sharp peaks. Using knowledge of insect gas exchange, why do these peaks occur?
Hard
- ASpiracles open periodically to allow gas exchange, then close to reduce water loss
- BThe insect respires only when it moves, causing bursts of CO₂ release
- CCO₂ is stored in the tracheoles and released all at once
- DThe insect switches between aerobic and anaerobic respiration
33.In a respirometer, the tap on tube 1 was left open and the syringe removed from tube 2 for the first 12 minutes. Why was this done?
Medium
- ATo allow the apparatus to equilibrate with the external air pressure and temperature
- BTo allow the seeds to use up all the oxygen before readings began
- CTo prevent the coloured liquid from moving
- DTo allow carbon dioxide to escape from the apparatus
34.A student suggested raising the respirometer temperature from 25 °C to 30 °C, but the teacher refused. What is the most likely reason?
Medium
- AHigher temperature would increase water evaporation and pressure changes, giving inaccurate readings
- BEnzymes would be denatured at 30 °C
- CThe seeds would stop respiring at 30 °C
- DOxygen would dissolve less readily in the seeds
35.Guinea pig muscle fibres were stained for succinic acid dehydrogenase (SDH) activity; exercised guinea pigs stained darker than non-exercised ones. Which statements explain this difference? (select all that apply)
Hard
- AExercised muscle fibres have more mitochondria
- BExercised muscle fibres have higher SDH activity, so more Krebs cycles occur
- CDarker staining shows greater dehydrogenase activity
- DNon-exercised fibres have more SDH enzyme
- EDarker staining shows less respiration
36.In an investigation of respiration in yeast, a colorimeter can be used to measure the colour intensity of DCPIP, making the result less subjective than judging colour change by eye.
Easy
True or false?
37.A suspension of yeast was layered with oil before measuring CO₂ production. What does this allow the investigator to measure?
Medium
- AThe rate of anaerobic respiration
- BThe rate of aerobic respiration
- CThe rate of photosynthesis
- DThe rate of fermentation only in plant cells
38.A respirometer's coloured liquid moved towards tube 1, which contained germinating seeds. What does this indicate?
Hard
- AOxygen is being taken up by the seeds, reducing the volume of gas in tube 1
- BCarbon dioxide is being produced, increasing the volume in tube 1
- CThe seeds are releasing oxygen during respiration
- DThe temperature of tube 1 has fallen, reducing pressure
39.A respirometer reading dropped from 0.86 cm³ to 0.54 cm³ over 12 minutes using 1.8 g of seeds. A student calculated the rate as 0.32 cm³ g⁻¹ hour⁻¹. What error did the student make?
Medium
- AThey did not convert the 12-minute period into an hourly rate
- BThey divided by the wrong mass
- CThey added instead of subtracting the readings
- DThey used the final reading rather than the initial reading
40.In the required practical investigating respiration rate in yeast using DCPIP, why is a control tube containing only yeast and glucose set up?
Medium
- ATo provide a colour comparison so the endpoint of the colour change can be judged consistently
- BTo measure the rate of anaerobic respiration in the absence of DCPIP
- CTo ensure that the yeast cells remain at a constant temperature throughout the investigation
- DTo act as a source of additional NAD so that glycolysis can continue
41.During glycolysis, 2 ATP are used and 4 ATP are produced per glucose molecule. What is the net gain of ATP per glucose molecule?
Medium
42.Complete the sentence about the link reaction.
Medium
In the link reaction, pyruvate is oxidised and decarboxylated to form ____, which then combines with coenzyme A to produce ____.
43.Complete the sentence about the Krebs cycle.
Medium
The Krebs cycle is a series of ____ controlled reactions which occur in the ____ of the mitochondria. Products include ____, NADH, ATP and CO2.
44.Name the process by which protons (H+ ions) move down their concentration gradient through ATP synthase during oxidative phosphorylation.
Easy
45.In a respirometer experiment, the volume of oxygen consumed by 1.8 g of seeds over 12 minutes was 0.32 cm3. Calculate the rate of oxygen consumption in cm3 g−1 hour−1. Give your answer to 2 significant figures.
Medium
46.In an experiment measuring the rate of CO2 release by insects, a group of insects with a mean mass of 0.050 g released CO2 at a rate of 0.39 μdm3 min−1. Calculate the rate of CO2 release per gram in μdm3 g−1 min−1. Give your answer to 3 significant figures.
Medium
47.Complete the sentence about the electron transport chain.
Medium
The electron transport chain is made up of ____ proteins embedded in the inner mitochondrial membrane. The energy released as electrons pass between carriers is used to actively transport ____ from the matrix into the intermembrane space.
48.Name the enzyme that catalyses the formation of ATP from ADP and π in oxidative phosphorylation.
Easy
49.In an experiment, a group of insects with a mean mass of 0.050 g released CO₂ at a rate of 0.39 μdm³ min⁻¹. Calculate the rate of CO₂ release per gram of insect in μdm³ g⁻¹ min⁻¹. Give your answer to 3 significant figures.
Medium
50.In an experiment, a yeast suspension reduced DCPIP in 45 seconds at 20 °C. Calculate the rate of respiration in seconds per colour change per minute (i.e. how many colour changes would occur per minute at this rate). Give your answer to 2 decimal places.
Medium
51.A respirometer measured oxygen consumption of 1.8 g of germinating seeds. The volume of oxygen consumed over 12 minutes was 0.32 cm³. Calculate the rate of oxygen consumption in cm³ g⁻¹ hour⁻¹. Give your answer to 2 decimal places.
Medium
52.In an investigation of respiration in insects, a group with a mean mass of 0.050 g released CO₂ at a rate of 0.39 μdm³ min⁻¹. Calculate the rate of CO₂ release per gram of insect in μdm³ g⁻¹ min⁻¹. Give your answer to 3 significant figures.
Medium
53.Describe the mechanism by which ATP is formed in the mitochondria.
Hard
54.Explain why the solution used in the investigation of isolated mitochondria was isotonic.
Medium
55.Explain why glucose would not be a good choice for the respiratory substrate in an investigation using isolated mitochondria.
Hard
56.Describe and explain how temperature influences the rate of ATP production in respiration.
Hard
57.Explain why individuals with mitochondrial disease are only able to endure intense exercise for a short period of time.
Hard
58.During glycolysis, 2 ATP are used and 4 ATP are produced per glucose molecule. What is the net gain of ATP per glucose molecule?
Medium
- A3 ATP
- B1 ATP
- C2 ATP
- D4 ATP
59.In a respirometer experiment, the volume of oxygen consumed by 1.8 g of seeds over 12 minutes was 0.32 cm3. Calculate the rate of oxygen consumption in cm3 g−1 hour−1. Give your answer to 2 significant figures.
Medium
- A-0.11 cm3 g−1 hour−1
- B2.89 cm3 g−1 hour−1
- C0.89 cm3 g−1 hour−1
- D1.89 cm3 g−1 hour−1
60.In an experiment measuring the rate of CO2 release by insects, a group of insects with a mean mass of 0.050 g released CO2 at a rate of 0.39 μdm3 min−1. Calculate the rate of CO2 release per gram in μdm3 g−1 min−1. Give your answer to 3 significant figures.
Medium
- A6.8 μdm3 g−1 min−1
- B7.8 μdm3 g−1 min−1
- C8.8 μdm3 g−1 min−1
- D9.8 μdm3 g−1 min−1
61.In an experiment, a group of insects with a mean mass of 0.050 g released CO₂ at a rate of 0.39 μdm³ min⁻¹. Calculate the rate of CO₂ release per gram of insect in μdm³ g⁻¹ min⁻¹. Give your answer to 3 significant figures.
Medium
- A7.8 μdm³ g⁻¹ min⁻¹
- B6.8 μdm³ g⁻¹ min⁻¹
- C9.8 μdm³ g⁻¹ min⁻¹
- D8.8 μdm³ g⁻¹ min⁻¹
62.In an experiment, a yeast suspension reduced DCPIP in 45 seconds at 20 °C. Calculate the rate of respiration in seconds per colour change per minute (i.e. how many colour changes would occur per minute at this rate). Give your answer to 2 decimal places.
Medium
- A1.33 colour changes per minute
- B2.33 colour changes per minute
- C3.33 colour changes per minute
- D0.33 colour changes per minute
63.A respirometer measured oxygen consumption of 1.8 g of germinating seeds. The volume of oxygen consumed over 12 minutes was 0.32 cm³. Calculate the rate of oxygen consumption in cm³ g⁻¹ hour⁻¹. Give your answer to 2 decimal places.
Medium
- A-0.11 cm³ g⁻¹ hour⁻¹
- B0.89 cm³ g⁻¹ hour⁻¹
- C1.89 cm³ g⁻¹ hour⁻¹
- D2.89 cm³ g⁻¹ hour⁻¹
64.In an investigation of respiration in insects, a group with a mean mass of 0.050 g released CO₂ at a rate of 0.39 μdm³ min⁻¹. Calculate the rate of CO₂ release per gram of insect in μdm³ g⁻¹ min⁻¹. Give your answer to 3 significant figures.
Medium
- A9.8 μdm³ g⁻¹ min⁻¹
- B7.8 μdm³ g⁻¹ min⁻¹
- C8.8 μdm³ g⁻¹ min⁻¹
- D6.8 μdm³ g⁻¹ min⁻¹

Lernnotizen

## Respiration & Energy - Respiration is a chemical process inside living cells; it **releases energy** from organic molecules. - Chemical energy in nutrient molecules (e.g. carbohydrates) is **transferred to ATP**. - Energy is released easily inside cells by **ATP hydrolysis**. - ATP is used for: **active transport** across membranes (e.g. sodium–potassium pumps), **DNA synthesis**, **protein synthesis**, **muscle contraction**. - Never say energy is "created" or "produced" — say **transferred** or **released**. Saying ATP is produced is fine. ## The Stages of Aerobic Respiration Aerobic respiration = breaking down a respiratory substrate to produce ATP **using oxygen**. Glucose is the main substrate. Four stages: | Stage | Description | Location | |---|---|---| | 1. Glycolysis | Phosphorylation and splitting of glucose | Cell cytoplasm | | 2. Link reaction | Decarboxylation and dehydrogenation of pyruvate | Matrix of mitochondria | | 3. Krebs cycle | Cyclical pathway with enzyme-controlled reactions | Matrix of mitochondria | | 4. Oxidative phosphorylation | Production of ATP through oxidation of hydrogen atoms | Inner membrane of mitochondria | Learn exact locations — "matrix of the mitochondria", not just "mitochondria". ## Glycolysis - First stage; in the **cell cytoplasm**; **oxygen not required** (anaerobic process); occurs in both aerobic and anaerobic respiration. 1. **Phosphorylation** of glucose (6C) to glucose phosphate — requires **2 x ATP**; phosphate makes glucose more reactive. 2. Splitting of glucose phosphate (6C) into **two molecules of triose phosphate (3C)**. 3. **Oxidation** of triose phosphate to **pyruvate (3C)**. Electrons and hydrogen transferred to NAD (**1 x NAD reduced per triose phosphate**). Phosphate groups transferred to ADP in **substrate-level phosphorylation** — 2 x ATP per triose phosphate (total 4 x ATP). - Products: **2 x pyruvate (3C)**, **net gain of 2 x ATP**, **2 x reduced NAD**. ## The Link Reaction - Pyruvate enters the mitochondrial matrix from the cytosol by **active transport** (against a concentration gradient; requires ATP; membrane transport protein involved). - Pyruvate is **oxidised to acetate**, producing **reduced NAD and CO₂**. - Acetate combines with **coenzyme A** to produce **acetyl coenzyme A (acetyl CoA)**. - Products: **acetyl CoA, carbon dioxide, reduced NAD**. CO₂ is released as waste. - Happens **twice per glucose** (two pyruvate molecules). ## The Krebs Cycle - Series of **enzyme-controlled reactions** in the matrix. 1. Acetyl CoA releases a **two-carbon molecule**, which reacts with a **four-carbon molecule (oxaloacetate)** to produce a **six-carbon molecule (citrate)**. Coenzyme A is freed to return to the link reaction. 2. Oxidation–reduction reactions convert the 6C molecule back to 4C; **NAD and FAD are reduced**, **ATP produced by substrate-level phosphorylation**, **carbon dioxide lost**. - Reduced NAD and reduced FAD carry hydrogen ions and electrons to oxidative phosphorylation. - Other substrates (breakdown products of **lipids, amino acids**) may enter the cycle. Turns **twice per glucose**. ## Oxidative Phosphorylation - Final stage; on the **cristae of the inner mitochondrial membrane**; relies on membrane proteins e.g. **ATP synthase**. Folded cristae give a **large surface area**. 1. Hydrogen atoms donated by reduced NAD and reduced FAD. 2. Hydrogen atoms split into **protons (H⁺) and electrons**. 3. Electrons enter the **electron transport chain**; energy released as they pass between electron carriers. 4. Energy used to **actively transport protons** from the matrix into the intermembrane space. 5. Protons move down their concentration gradient back to the matrix by **facilitated diffusion** via proton channels associated with ATP synthase — this is **chemiosmosis**. 6. **ATP synthase** catalyses formation of ATP from ADP and Pi. - **Oxygen is the final electron acceptor**; it combines with protons and electrons to form **water** as waste. ## Anaerobic Respiration - When oxygen is absent/short: no final electron acceptor → ETC stops → oxidative phosphorylation stops producing ATP. - Pathways: **ethanol fermentation** (yeast), **lactate fermentation** (mammalian cells). - Purpose: **regenerate NAD** so glycolysis can continue producing ATP. Fermentation does **not** produce ATP. - **Ethanol fermentation**: pyruvate decarboxylated to **ethanal** (CO₂ given off); ethanal reduced to **ethanol** by hydrogen from NADH, regenerating NAD; enzyme **alcohol dehydrogenase**. Products: ethanol, CO₂, NAD. - **Lactate fermentation**: pyruvate accepts hydrogen from NADH and is reduced to **lactate**; NADH oxidised to regenerate NAD. Products: lactate, NAD. ## Required Practical: Investigating Respiration Rate - Use a **redox indicator** (e.g. DCPIP, methylene blue): **blue = oxidised**, **colourless = reduced**. - Respiration involves oxidation/reduction; the indicator can be reduced instead of NAD/FAD. Faster respiration → faster hydrogen release → faster colour change. - Method: glucose solution + **buffer** (constant pH) in tubes; equilibrate in water baths ~10 min; add yeast, then DCPIP, start stopwatch; stop when blue colour lost; control tube of yeast + glucose for comparison; three repeats per temperature. - Plot temperature against time for colour change; as temperature rises, respiration rate rises and time to decolourise falls. - Alternatives: substrate concentration, substrate type, pH; **colorimeter** for quantitative measurement; measure CO₂ volume; oil layer to measure anaerobic rate. - Control all other variables.

Respiration: A chemical process that occurs inside living cells; it releases energy from organic molecules.
ATP: The molecule to which chemical energy from nutrient molecules is transferred; energy is released easily inside cells by its hydrolysis.
Aerobic respiration: The process of breaking down a respiratory substrate in order to produce ATP using oxygen.
Glycolysis: The first stage of respiration: phosphorylation and splitting of glucose; takes place in the cell cytoplasm and does not require oxygen.
Link reaction: Decarboxylation and dehydrogenation of pyruvate; takes place in the matrix of the mitochondria.
Krebs cycle: A cyclical pathway of enzyme-controlled reactions in the matrix of the mitochondria.
Oxidative phosphorylation: The production of ATP through oxidation of hydrogen atoms; occurs at the inner membrane of the mitochondria.
Substrate-level phosphorylation: The transfer of phosphate groups to ADP to produce ATP, as occurs in glycolysis and the Krebs cycle.
Acetyl coenzyme A (acetyl CoA): The product formed when acetate (from oxidised pyruvate) combines with coenzyme A in the link reaction.
Oxaloacetate: The four-carbon molecule in the Krebs cycle that reacts with the two-carbon molecule from acetyl CoA to produce citrate.
Citrate: The six-carbon molecule produced in the Krebs cycle when the two-carbon molecule from acetyl CoA reacts with oxaloacetate.
Chemiosmosis: The movement of protons down their concentration gradient back into the matrix by facilitated diffusion via proton channels associated with ATP synthase.
Electron transport chain: Electron carrier proteins embedded in the inner mitochondrial membrane; energy is released as electrons pass between them.
ATP synthase: The enzyme on the cristae of the mitochondria that catalyses the formation of ATP from ADP and Pi.
Oxygen: The final electron acceptor at the end of the electron transport chain; it combines with protons and electrons to form water.
Anaerobic respiration: Respiration that occurs when oxygen is absent or in short supply; includes ethanol fermentation and lactate fermentation.
Ethanol fermentation: Regeneration of NAD in yeast: pyruvate is decarboxylated to ethanal, which is reduced to ethanol by hydrogen from NADH (enzyme: alcohol dehydrogenase).
Lactate fermentation: Regeneration of NAD in mammalian cells: pyruvate accepts hydrogen from NADH and is reduced to lactate.
Redox indicator: A substance that changes colour depending on whether it is reduced or oxidised, e.g. DCPIP and methylene blue; blue = oxidised, colourless = reduced.

Unlock all 64 questions & more

Erstelle ein Gratis-Konto, um alle Fragen, Folien, Karteikarten und Lernnotizen zu diesem Thema zu sehen.

REGISTRIEREN — GRATIS ANMELDEN

Altklausuren

Altklausuren-Übungen für dieses Thema kommen bald.

Bald verfügbar