Respiration (Cambridge (CIE) A Level Biology): Flashcards
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Where do the link reaction and Krebs cycle occur in the mitochondrion?
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Where do the link reaction and Krebs cycle occur in the mitochondrion?
In the mitochondrial matrix.
Where does oxidative phosphorylation occur in the mitochondrion?
On the inner mitochondrial membrane (the cristae).
Define cristae.
Cristae are the folds of the inner mitochondrial membrane that increase surface area for the electron transport chain and ATP synthase.
How is the inner mitochondrial membrane adapted for oxidative phosphorylation?
Folded into cristae to increase surface area.
Holds the electron transport chain carriers and ATP synthase.
Define mitochondrial matrix.
The matrix is the fluid interior of the mitochondrion where the link reaction and Krebs cycle occur; it contains enzymes, NAD, FAD, DNA and ribosomes.
Why do mitochondria have two membranes?
The outer membrane encloses the organelle.
The inner membrane forms cristae and creates the intermembrane space needed to build a proton gradient for chemiosmosis.
The folds of the inner mitochondrial membrane are called .
The folds of the inner mitochondrial membrane are called cristae.
Name the four stages of aerobic respiration in order.
Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation
State where each of the four stages of aerobic respiration occurs.
Glycolysis — cytoplasm
Link reaction — mitochondrial matrix
Krebs cycle — mitochondrial matrix
Oxidative phosphorylation — inner mitochondrial membrane
Which two stages of aerobic respiration take place in the mitochondrial matrix?
The link reaction and the Krebs cycle.
Glycolysis takes place in the of the cell.
Glycolysis takes place in the cytoplasm of the cell.
Oxidative phosphorylation occurs on the inner mitochondrial .
Oxidative phosphorylation occurs on the inner mitochondrial membrane.
True or False?
Glycolysis requires oxygen and takes place inside the mitochondria.
False.
Glycolysis does not require oxygen and takes place in the cytoplasm, not the mitochondria.
Define glycolysis.
Glycolysis is the splitting of glucose (6C) into two molecules of pyruvate (3C) in the cytoplasm; it is the first stage of respiration.
What happens during the phosphorylation stage of glycolysis?
Glucose is phosphorylated using two ATP to form fructose 1,6-bisphosphate (6C).
What is fructose 1,6-bisphosphate split into?
Two molecules of triose phosphate (3C each).
What happens as triose phosphate is oxidised to pyruvate?
ATP is produced.
NAD is reduced to reduced NAD.
What is the net gain of ATP from glycolysis per glucose molecule?
A net gain of 2 ATP (4 produced − 2 used).
State the products of glycolysis from one glucose molecule.
2 pyruvate (3C)
2 net ATP
2 reduced NAD
Glucose is split during glycolysis into two molecules of .
Glucose is split during glycolysis into two molecules of pyruvate.
Fructose 1,6-bisphosphate is split into two molecules of phosphate.
Fructose 1,6-bisphosphate is split into two molecules of triose phosphate.
When oxygen is available, where does pyruvate go after glycolysis?
It is actively transported from the cytoplasm into the mitochondrial matrix.
When oxygen is present, pyruvate enters the mitochondrial to take part in the link reaction.
When oxygen is present, pyruvate enters the mitochondrial matrix to take part in the link reaction.
What happens to pyruvate in the link reaction?
It is decarboxylated (loses CO2) and dehydrogenated (loses hydrogen, reducing NAD) to form a 2C acetyl group.
What is the role of coenzyme A in the link reaction?
It accepts the 2C acetyl group to form acetyl coenzyme A, carrying it into the Krebs cycle.
Define decarboxylation.
Decarboxylation is the removal of a carboxyl group from a molecule, releasing carbon dioxide.
State the products when one pyruvate undergoes the link reaction.
Acetyl coenzyme A (2C)
One CO~2~
One reduced NAD
The 2C group formed in the link reaction combines with coenzyme A to form coenzyme A.
The 2C group formed in the link reaction combines with coenzyme A to form acetyl coenzyme A.
Where does the Krebs cycle take place?
In the mitochondrial matrix.
What happens when acetyl coenzyme A enters the Krebs cycle?
The 2C acetyl group combines with oxaloacetate (4C) to form citrate (6C).
What happens to citrate during the Krebs cycle?
It is converted back to oxaloacetate (4C) in a series of small steps, regenerating the acceptor.
The 2C acetyl group combines with oxaloacetate (4C) to form (6C).
The 2C acetyl group combines with oxaloacetate (4C) to form citrate (6C).
What is meant by decarboxylation in the Krebs cycle?
The removal of carbon as carbon dioxide from the intermediate molecules.
What is produced by dehydrogenation in the Krebs cycle?
Reduced NAD and reduced FAD, as hydrogen is removed from intermediates.
Define dehydrogenation.
Dehydrogenation is the removal of hydrogen from a substrate, which reduces a coenzyme such as NAD or FAD.
State the products of one turn of the Krebs cycle (per acetyl coenzyme A).
2 CO~2~
3 reduced NAD
1 reduced FAD
1 ATP
Define coenzyme.
A coenzyme is a non-protein molecule that helps an enzyme by carrying chemical groups or atoms between reactions (e.g. NAD and FAD carry hydrogen).
What is the role of NAD and FAD in respiration?
They accept hydrogen atoms (becoming reduced) during glycolysis, the link reaction and the Krebs cycle.
They transfer this hydrogen to carriers in the inner mitochondrial membrane.
What do reduced NAD and reduced FAD deliver to the electron transport chain?
Hydrogen atoms, which split into protons and electrons to drive oxidative phosphorylation.
What happens to NAD and FAD after they release their hydrogen at the inner membrane?
They are re-oxidised and can accept more hydrogen, so they are reused in the earlier stages of respiration.
At which stages of respiration is NAD reduced?
Glycolysis
Link reaction
Krebs cycle
At which stage is FAD reduced?
The Krebs cycle only.
NAD and FAD transfer to carriers in the inner mitochondrial membrane.
NAD and FAD transfer hydrogen to carriers in the inner mitochondrial membrane.
Define oxidative phosphorylation.
Oxidative phosphorylation is the synthesis of ATP using energy released as electrons pass along the electron transport chain on the inner mitochondrial membrane.
What happens to hydrogen atoms at the start of oxidative phosphorylation?
They split into protons (H^+^) and energetic electrons.
What happens as energetic electrons pass through the electron transport chain?
They release energy, which is used to transfer protons across the inner mitochondrial membrane.
How is the proton gradient used to make ATP?
Protons return to the matrix by facilitated diffusion through ATP synthase, and this provides the energy to synthesise ATP.
What is the role of oxygen in oxidative phosphorylation?
It acts as the final electron acceptor, combining with electrons and protons to form water.
Why is oxygen essential for the electron transport chain to keep working?
By accepting electrons at the end of the chain, it allows electrons to keep flowing.
Without it, the chain becomes blocked and ATP production stops.
In oxidative phosphorylation, acts as the final electron acceptor to form water.
In oxidative phosphorylation, oxygen acts as the final electron acceptor to form water.
Protons return to the matrix through the enzyme ATP .
Protons return to the matrix through the enzyme ATP synthase.
Define fermentation.
Fermentation is the production of ATP by glycolysis in the absence of oxygen, with pyruvate converted to lactate or ethanol to regenerate NAD.
Why must NAD be regenerated during anaerobic respiration?
So that glycolysis can continue to produce ATP.
The reduced NAD must be re-oxidised because the electron transport chain is not working.
What happens during lactate fermentation in mammals?
Pyruvate accepts hydrogen from reduced NAD to form lactate, regenerating NAD for glycolysis.
Describe ethanol fermentation in yeast.
Pyruvate is decarboxylated (loses CO2) to form ethanal.
Ethanal accepts hydrogen from reduced NAD to form ethanol, regenerating NAD.
Give one key difference between lactate and ethanol fermentation.
Lactate fermentation (mammals) produces no CO2 and is reversible.
Ethanol fermentation (yeast) releases CO2 and is irreversible.
In mammals, anaerobic respiration converts pyruvate into .
In mammals, anaerobic respiration converts pyruvate into lactate.
In yeast, anaerobic respiration produces ethanol and dioxide.
In yeast, anaerobic respiration produces ethanol and carbon dioxide.
Why is the energy yield from aerobic respiration much greater than from anaerobic respiration?
In aerobic respiration, reduced NAD and FAD are oxidised via the electron transport chain, and the Krebs cycle runs.
This produces large amounts of ATP by oxidative phosphorylation.
Why does anaerobic respiration yield so little ATP?
Only glycolysis occurs (net 2 ATP per glucose).
The link reaction, Krebs cycle and oxidative phosphorylation do not take place because there is no final electron acceptor.
How much ATP (net) is produced per glucose in anaerobic respiration?
2 ATP (from glycolysis).
Why can't the electron transport chain operate in anaerobic conditions?
There is no oxygen to act as the final electron acceptor, so the chain becomes blocked and oxidative phosphorylation stops.
In anaerobic respiration, the only stage producing ATP is .
In anaerobic respiration, the only stage producing ATP is glycolysis.
True or False?
Aerobic respiration releases much more energy per glucose molecule than anaerobic respiration.
True.
Aerobic respiration fully oxidises glucose using the Krebs cycle and oxidative phosphorylation, whereas anaerobic respiration only uses glycolysis.
Define aerenchyma.
Aerenchyma is plant tissue with large air spaces that allow oxygen to diffuse from the shoots down to the submerged roots.
How does aerenchyma help rice grow in waterlogged soil?
Its air spaces provide a low-resistance pathway for oxygen to reach the roots for aerobic respiration.
How do rice roots survive when oxygen is limited?
They carry out ethanol fermentation (anaerobic respiration) to keep producing ATP.
How does faster stem growth help rice in flooded conditions?
Rapid stem elongation keeps the leaves above the water surface, so photosynthesis and gas exchange can continue.
Rice roots contain air-filled tissue called that carries oxygen to submerged roots.
Rice roots contain air-filled tissue called aerenchyma that carries oxygen to submerged roots.
State the three adaptations that allow rice to grow with submerged roots.
Development of aerenchyma in the roots
Ethanol fermentation in the roots
Faster growth of stems
Define redox indicator.
A redox indicator is a dye that changes colour when it is reduced (gains hydrogen/electrons), used to indicate the rate of respiration.
What happens to DCPIP or methylene blue as yeast respires?
It becomes reduced and loses its colour (blue → colourless), because hydrogen is transferred to it during respiration.
How can the rate of respiration of yeast be measured using a redox indicator?
Time how long the dye (DCPIP or methylene blue) takes to change from blue to colourless.
A shorter time means a faster rate of respiration.
How would you investigate the effect of temperature on yeast respiration using methylene blue?
Set up yeast, glucose and methylene blue at different temperatures using water baths.
Record the time for the dye to decolourise at each temperature.
Why must a redox indicator experiment control the glucose concentration?
So that substrate concentration is kept constant when temperature is being investigated (and vice versa), making the results valid.
As yeast respires, methylene blue is reduced and turns from blue to .
As yeast respires, methylene blue is reduced and turns from blue to colourless.
How is a respirometer used to investigate the effect of temperature on respiration rate?
Measure the rate of oxygen uptake by an organism at different temperatures using water baths, keeping other variables constant.
In a respirometer investigating temperature, why is a control tube without organisms used?
To correct for changes in gas volume caused by temperature and pressure that are not due to respiration.
How would you investigate the effect of substrate concentration on yeast respiration using a redox indicator?
Set up tubes of yeast and methylene blue (or DCPIP) with a range of glucose concentrations, keeping temperature and yeast concentration constant.
Time how long the dye takes to decolourise at each concentration.
What is the expected effect of increasing glucose concentration on the rate of yeast respiration?
The rate increases, so the dye decolourises more quickly, because more substrate is available for respiration.
Above a certain concentration the rate levels off, as another factor becomes limiting.
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