Respiration (Edexcel A Level Biology (A) SNAB): Flashcards
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Define aerobic respiration.
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Define aerobic respiration.
Aerobic respiration is the breakdown of a respiratory substrate to produce ATP, using oxygen.
What is the word equation for aerobic respiration?
Glucose + oxygen → carbon dioxide + water (+ energy).
What is the main respiratory substrate used by cells?
Glucose.
Name the four stages of aerobic respiration.
Glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation.
Why is glucose broken down gradually in stages?
To release its energy gradually, not all at once.
A sudden release would raise body temperature enough to denature enzymes.
What is the role of the coenzymes NAD and FAD in respiration?
They transfer hydrogen between molecules.
They can reduce or oxidise a molecule depending on whether they give or take hydrogen.
What is the role of coenzyme A in respiration?
It transfers acetate (acetic acid) from one molecule to another.
Why is the inner mitochondrial membrane folded into cristae?
The folds give a large surface area.
This holds many electron transport chains and ATP synthase enzymes for oxidative phosphorylation.
What is found in the matrix of a mitochondrion?
Enzymes, ribosomes and circular mitochondrial DNA.
It is the site of the link reaction and Krebs cycle.
The energy released in respiration is used to phosphorylate ADP to form .
The energy released in respiration is used to phosphorylate ADP to form ATP.
True or False?
Only glucose can be used as a respiratory substrate.
False.
Other molecules such as fatty acids and amino acids can also be respired.
What determines the overall rate of aerobic respiration?
The enzyme that catalyses its reaction the slowest.
Where does glycolysis take place?
In the cytoplasm of the cell.
Where does the link reaction take place?
In the matrix of the mitochondria.
Where does the Krebs cycle take place?
In the matrix of the mitochondria.
Where does oxidative phosphorylation take place?
At the inner membrane of the mitochondria.
Which stage of respiration does not take place in the mitochondria?
Glycolysis, which occurs in the cytoplasm.
Why is it important that respiration occurs in many small steps?
So energy is released gradually and can be captured as ATP.
A single large release would be lost as heat and could denature enzymes.
What controls the reactions of each stage of respiration?
Intracellular enzymes — enzymes that catalyse reactions inside the cell.
The link reaction and the Krebs cycle both take place in the of the mitochondria.
The link reaction and the Krebs cycle both take place in the matrix of the mitochondria.
True or False?
Oxidative phosphorylation occurs in the matrix of the mitochondria.
False.
It occurs at the inner membrane of the mitochondria.
List the four stages of aerobic respiration in order.
Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation
Why is it not enough to say the Krebs cycle occurs 'in the mitochondria'?
You must specify the matrix.
Different stages happen in different parts of the mitochondrion.
Which stage of respiration can occur without oxygen?
Glycolysis — it is the shared first stage of both aerobic and anaerobic respiration.
Define glycolysis.
Glycolysis is the first stage of respiration, in which glucose is partially broken down to pyruvate in the cytoplasm.
Where does glycolysis take place and does it need oxygen?
In the cytoplasm.
It does not require oxygen, so it occurs in both aerobic and anaerobic respiration.
What happens during the phosphorylation stage of glycolysis?
Two ATP are used to phosphorylate glucose.
This produces two molecules of triose phosphate.
Why is glucose phosphorylated at the start of glycolysis?
To make the stable glucose molecule more reactive.
This lowers the activation energy for the reaction.
What is produced when triose phosphate is oxidised?
Two molecules of pyruvate.
The hydrogen removed reduces NAD to form two reduced NAD.
What is the net ATP yield of glycolysis, and why?
A net gain of 2 ATP.
Four are made but two are used to phosphorylate glucose.
List the products of glycolysis from one glucose molecule.
2 pyruvate, a net 2 ATP, and 2 reduced NAD.
Where does pyruvate go after glycolysis in aerobic conditions?
Into the matrix of the mitochondria.
There it is used in the link reaction.
Glycolysis produces a net gain of ATP per glucose molecule.
Glycolysis produces a net gain of two ATP per glucose molecule.
True or False?
Glucose is completely oxidised during glycolysis.
False.
Glucose is only partially oxidised in glycolysis; further oxidation happens in later stages.
How many carbon atoms are in a molecule of pyruvate?
Three (3C).
What is used to carry away the hydrogen removed during glycolysis?
The coenzyme NAD, which becomes reduced NAD.
Where does the link reaction take place?
In the matrix of the mitochondria.
Why is the link reaction called the 'link' reaction?
It links glycolysis to the Krebs cycle.
Describe what happens to pyruvate in the link reaction.
It is decarboxylated (loses CO₂) and oxidised (loses hydrogen, reducing NAD).
The resulting acetate joins coenzyme A to form acetyl CoA.
What are the products of the link reaction per pyruvate?
Acetyl CoA, carbon dioxide and reduced NAD.
No ATP is produced.
Why do the link reaction and Krebs cycle occur twice per glucose?
Glycolysis produces two pyruvate molecules per glucose.
Each pyruvate goes through the link reaction and Krebs cycle.
What combines with acetyl CoA at the start of the Krebs cycle?
The 4-carbon oxaloacetate.
This forms the 6-carbon citrate.
What is released as citrate is converted back to oxaloacetate?
Carbon dioxide (by decarboxylation).
Reduced NAD and FAD (by oxidation), plus ATP.
List the products of the Krebs cycle per glucose (two turns).
2 ATP, 6 reduced NAD, 2 reduced FAD and 4 CO₂.
Why is the Krebs cycle described as cyclical?
The acceptor molecule oxaloacetate is regenerated.
So it can combine with another acetyl CoA and start again.
In the link reaction, pyruvate is converted into CoA.
In the link reaction, pyruvate is converted into acetyl CoA.
True or False?
The link reaction produces ATP.
False.
No ATP is produced in the link reaction; it makes acetyl CoA, CO₂ and reduced NAD.
How is ATP produced directly within the Krebs cycle?
By substrate-level phosphorylation.
A phosphate is transferred from an intermediate to ADP.
Where does oxidative phosphorylation take place?
At the inner mitochondrial membrane.
What molecules donate hydrogen for oxidative phosphorylation?
Reduced NAD and reduced FAD from the earlier stages.
Define electron transport chain.
The electron transport chain is a series of membrane proteins that pass electrons along, releasing energy to pump protons across the membrane.
How is a proton concentration gradient established in oxidative phosphorylation?
Energy from electrons is used to pump protons from the matrix into the intermembrane space.
This builds up a high concentration of protons there.
How is ATP produced by chemiosmosis?
Protons flow back into the matrix by facilitated diffusion through ATP synthase.
The energy of this flow drives the phosphorylation of ADP to ATP.
What is the role of oxygen in oxidative phosphorylation?
It is the final electron acceptor.
It combines with electrons and protons to form water.
Why is oxygen essential for aerobic respiration?
Without oxygen to accept electrons, the electron transport chain stops.
Reduced NAD and FAD cannot be reoxidised, so hydrogen transport halts.
How many ATP are made per reduced NAD and per reduced FAD?
3 ATP per reduced NAD.
2 ATP per reduced FAD.
How many ATP molecules are produced per glucose in aerobic respiration?
A total of 38 ATP.
Protons flow back into the matrix through the channel enzyme , which makes ATP.
Protons flow back into the matrix through the channel enzyme ATP synthase, which makes ATP.
True or False?
Water is a product of oxidative phosphorylation.
True.
Oxygen combines with protons and electrons at the end of the chain to form water.
Why is the inner mitochondrial membrane impermeable to protons important?
It stops protons leaking back freely.
This maintains the concentration gradient needed to drive ATP synthase.
Define respirometer.
A respirometer is apparatus used to measure the rate of oxygen consumption during aerobic respiration.
What is the purpose of the soda lime (or potassium hydroxide) in a respirometer?
To absorb the carbon dioxide produced by respiration.
This means the volume change measured is due only to oxygen use.
Why does the manometer fluid move towards the organisms during the experiment?
As oxygen is consumed and CO₂ is absorbed, the volume and pressure of air falls.
The fluid moves towards the tube to equalise the pressure.
Why are germinating seeds often used in the respirometer practical?
They are actively respiring and consuming oxygen.
This produces a measurable volume change.
What does the control tube (with glass beads) show?
That any movement of the fluid is due to the organisms respiring.
It accounts for changes such as temperature or pressure not caused by respiration.
A manometer fluid moves distance h through a capillary tube of radius r. How is the volume of oxygen consumed calculated?
Volume = πr²h.
Why should the experiment be repeated and a mean calculated?
To improve reliability.
A mean reduces the effect of anomalous results.
Why is temperature kept constant in the respirometer practical?
Temperature affects the rate of respiration and the volume of gas.
Controlling it ensures a fair test.
In a respirometer, carbon dioxide is absorbed by so that only oxygen use changes the gas volume.
In a respirometer, carbon dioxide is absorbed by soda lime so that only oxygen use changes the gas volume.
True or False?
The respirometer measures oxygen consumption during respiration.
True.
It measures the fall in gas volume, which reflects oxygen consumed (CO₂ is absorbed).
What welfare consideration applies when using invertebrates in this practical?
They must be treated with respect and not harmed.
They should be returned safely afterwards.
How is the rate of oxygen consumption found from the practical?
By measuring the distance the fluid moves in a set time.
The volume change is then divided by the time.
Why does the electron transport chain stop without oxygen?
There is no final electron acceptor.
Electrons have nowhere to go, so the chain and oxidative phosphorylation stop.
Which stage of respiration still occurs during anaerobic respiration in muscle?
Glycolysis.
It continues, producing a small amount of ATP.
Describe lactate fermentation.
Reduced NAD transfers hydrogen to pyruvate, forming lactate.
This regenerates NAD so glycolysis can continue.
Why is regenerating NAD important in anaerobic respiration?
NAD is needed for glycolysis to continue.
Without it, glycolysis would stop and no ATP would be made.
Which enzyme converts pyruvate to lactate?
Lactate dehydrogenase.
What acts as the hydrogen acceptor in lactate fermentation?
Pyruvate, which is reduced to lactate.
What are the two fates of lactate after it is produced?
It can be oxidised back to pyruvate and used in the Krebs cycle.
Or it can be converted into glucose (or glycogen) by the liver.
Define oxygen debt.
The oxygen debt is the extra oxygen needed after exercise to oxidise the lactate that built up during anaerobic respiration.
Why do animals breathe deeper and faster after exercise?
To take in extra oxygen to repay the oxygen debt.
This oxygen is used to oxidise the accumulated lactate.
In anaerobic respiration in muscle, pyruvate is reduced to .
In anaerobic respiration in muscle, pyruvate is reduced to lactate.
True or False?
Anaerobic respiration produces more ATP than aerobic respiration.
False.
Anaerobic respiration produces only a small amount of ATP compared with aerobic respiration.
Which organ converts lactate back into glucose?
The liver.
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