Respiration (A Level only) (AQA A Level Biology): Flashcards
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Define respiration.
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Define respiration.
Respiration is a chemical process that occurs inside living cells; it releases energy from organic molecules.
Where does respiration take place?
Inside living cells.
During respiration, what happens to the chemical energy stored in nutrient molecules such as carbohydrates?
It is transferred to ATP.
How is energy released from ATP inside cells?
By the hydrolysis of ATP.
Why should you never say that respiration "produces energy"?
Because, according to the laws of thermodynamics, energy cannot be created or destroyed.
Respiration releases or transfers energy; it does not create it.
Give three cellular processes that use energy from ATP.
Any three of:
Active transport across membranes
DNA synthesis
Protein synthesis
Muscle contraction
True or False?
Respiration produces energy.
False.
Respiration releases (transfers) energy; it does not produce energy. It is correct to say that respiration produces ATP.
True or False?
It is acceptable to say that ATP is produced during respiration.
True.
While you should never say energy is produced, it is correct to say that ATP is produced.
During respiration the chemical energy stored in nutrient molecules is transferred to .
During respiration the chemical energy stored in nutrient molecules is transferred to ATP.
Energy is released from ATP inside cells by ATP .
Energy is released from ATP inside cells by ATP hydrolysis.
What is the main respiratory substrate used by cells?
Glucose.
In one sentence, what is aerobic respiration?
The process that uses oxygen to produce ATP from a respiratory substrate such as glucose.
Name the four stages of aerobic respiration in order.
Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation
Where does glycolysis take place?
In the cell cytoplasm.
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.
True or False?
It is enough to say that the Krebs cycle takes place in the mitochondria.
False.
You must state that it takes place in the matrix of the mitochondria.
Glycolysis takes place in the of the cell.
Glycolysis takes place in the cytoplasm of 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.
Oxidative phosphorylation occurs at the membrane of the mitochondria.
Oxidative phosphorylation occurs at the inner membrane of the mitochondria.
Where in the cell does glycolysis take place?
In the cell cytoplasm.
Is oxygen required for glycolysis?
No.
Glycolysis is an anaerobic process and occurs in both aerobic and anaerobic respiration.
Describe the stages of glycolysis.
Glucose (6C) is phosphorylated to glucose phosphate, using 2 x ATP.
Glucose phosphate (6C) is split into two molecules of triose phosphate (3C).
Triose phosphate is oxidised to pyruvate (3C), reducing NAD and producing ATP by substrate-level phosphorylation.
Why is glucose phosphorylated at the start of glycolysis?
To make it more reactive, as glucose is usually a very stable molecule.
How many ATP are used and how many produced during glycolysis, and what is the net gain?
2 ATP are used and 4 ATP are produced.
This gives a net gain of 2 ATP per glucose molecule.
What are the products of glycolysis per molecule of glucose?
2 x pyruvate (3C)
A net gain of 2 x ATP
2 x reduced NAD
Which coenzyme is reduced during glycolysis, and how many molecules per glucose?
NAD is reduced; 2 x reduced NAD are produced per glucose molecule.
True or False?
Glycolysis requires oxygen.
False.
Glycolysis is anaerobic and does not require oxygen; it occurs in both aerobic and anaerobic respiration.
Glucose phosphate (6C) is split into two molecules of phosphate.
Glucose phosphate (6C) is split into two molecules of triose phosphate.
During glycolysis glucose is converted into two molecules of .
During glycolysis glucose is converted into two molecules of pyruvate.
Glycolysis produces a net gain of ATP per glucose molecule.
Glycolysis produces a net gain of two ATP per glucose molecule.
How does pyruvate enter the mitochondrial matrix?
By active transport.
It moves against a concentration gradient, so ATP and a membrane transport protein are required.
Why is ATP required for pyruvate to enter the mitochondrial matrix?
Because pyruvate moves against a concentration gradient, which is active transport.
Pyruvate enters the mitochondrial matrix from the cytoplasm by transport.
Pyruvate enters the mitochondrial matrix from the cytoplasm by active transport.
Where does the link reaction occur?
In the mitochondrial matrix.
Between which two stages of respiration does the link reaction occur?
Between glycolysis and the Krebs cycle.
Describe the link reaction.
Pyruvate is oxidised to acetate, producing reduced NAD and CO~2~.
Acetate combines with coenzyme A to produce acetyl coenzyme A (acetyl CoA).
What are the products of the link reaction?
Acetyl CoA
Carbon dioxide
Reduced NAD
How many times does the link reaction occur per molecule of glucose, and why?
Twice.
This is because two pyruvate molecules are produced per glucose molecule during glycolysis.
True or False?
The link reaction produces ATP.
False.
The products of the link reaction are acetyl CoA, carbon dioxide and reduced NAD; no ATP is produced.
In the link reaction, acetate combines with coenzyme A to form CoA.
In the link reaction, acetate combines with coenzyme A to form acetyl CoA.
During the link reaction pyruvate is decarboxylated, releasing dioxide.
During the link reaction pyruvate is decarboxylated, releasing carbon dioxide.
Where does the Krebs cycle take place?
In the matrix of the mitochondria.
By what other name is the Krebs cycle known?
The citric acid cycle.
Describe the Krebs cycle.
Acetyl CoA releases a 2C molecule (acetate), which reacts with a 4C molecule (oxaloacetate) to produce a 6C molecule (citrate); coenzyme A is freed to return to the link reaction.
A series of oxidation-reduction reactions converts the 6C molecule back into the 4C molecule, during which NAD and FAD are reduced, ATP is produced by substrate-level phosphorylation and carbon dioxide is lost.
What are the products of one turn of the Krebs cycle?
Reduced NAD
Reduced FAD
ATP
Carbon dioxide
(and regenerated oxaloacetate)
How is ATP produced in the Krebs cycle?
By substrate-level phosphorylation.
What happens to coenzyme A after it delivers acetate into the Krebs cycle?
It is freed and returns to the link reaction, where it can combine with more acetate.
Where do the reduced coenzymes produced by the Krebs cycle go next, and what do they carry?
They enter oxidative phosphorylation, carrying hydrogen ions and electrons.
True or False?
The Krebs cycle turns once for each molecule of glucose.
False.
The Krebs cycle turns twice for each molecule of glucose that enters aerobic respiration.
The reduced coenzymes produced during the Krebs cycle are reduced NAD and reduced .
The reduced coenzymes produced during the Krebs cycle are reduced NAD and reduced FAD.
The Krebs cycle turns times for each molecule of glucose.
The Krebs cycle turns twice for each molecule of glucose.
The 4C molecule that combines with acetate at the start of the Krebs cycle is .
The 4C molecule that combines with acetate at the start of the Krebs cycle is oxaloacetate.
Where does oxidative phosphorylation take place?
On the cristae of the inner mitochondrial membrane.
How does the folding of the cristae aid oxidative phosphorylation?
The large surface area of the folded cristae provides many locations for oxidative phosphorylation to occur.
Describe oxidative phosphorylation.
Hydrogen atoms are donated by reduced NAD and reduced FAD and split into protons and electrons.
The electrons enter the electron transport chain, releasing energy as they pass between electron carriers.
The released energy is used to actively transport protons from the matrix into the intermembrane space.
The protons move back to the matrix down their concentration gradient through ATP synthase, a process called chemiosmosis.
ATP synthase catalyses the formation of ATP from ADP and Pi.
The electrons and protons combine with oxygen, the final electron acceptor, to form water.
What is the role of oxygen in oxidative phosphorylation?
It acts as the final electron acceptor, combining with protons and electrons to form water and allowing the electron transport chain to continue functioning.
Define chemiosmosis.
Chemiosmosis is the movement of protons down their concentration gradient, from the intermembrane space back into the matrix, through ATP synthase.
Which enzyme catalyses the formation of ATP, and from what?
ATP synthase, from ADP and inorganic phosphate (Pi).
Which molecules donate hydrogen atoms to oxidative phosphorylation, and where do they come from?
Reduced NAD (from glycolysis, the link reaction and the Krebs cycle) and reduced FAD (from the Krebs cycle).
What is the waste product of oxidative phosphorylation?
Water.
True or False?
Oxidative phosphorylation produces energy.
False.
Oxidative phosphorylation produces ATP; you should never say that energy is produced.
In oxidative phosphorylation, oxygen acts as the final acceptor.
In oxidative phosphorylation, oxygen acts as the final electron acceptor.
The movement of protons through ATP synthase down their concentration gradient is called .
The movement of protons through ATP synthase down their concentration gradient is called chemiosmosis.
Protons are actively transported from the matrix into the space.
Protons are actively transported from the matrix into the intermembrane space.
When do cells switch to anaerobic respiration?
When oxygen is absent or in short supply.
Why does the electron transport chain stop when oxygen is unavailable?
There is no final electron acceptor, so the electron transport chain stops and oxidative phosphorylation stops producing ATP.
Name the two anaerobic respiration pathways and give an example organism or cell for each.
Ethanol fermentation, e.g. in yeast cells
Lactate fermentation, e.g. in mammalian cells
What is the purpose of fermentation?
To regenerate NAD so that glycolysis can continue producing ATP.
Why can glycolysis not continue indefinitely without fermentation?
Because cells would run out of NAD.
Describe ethanol fermentation.
Pyruvate is decarboxylated to ethanal, giving off CO~2~ as a waste product.
Ethanal is reduced to ethanol; the hydrogen comes from NADH, so NADH is oxidised to regenerate NAD.
What are the products of ethanol fermentation?
Ethanol
Carbon dioxide
NAD
Describe lactate fermentation.
Pyruvate accepts hydrogen from NADH and is reduced to lactate.
NADH is oxidised to regenerate NAD.
What are the products of lactate fermentation?
Lactate
NAD
True or False?
Ethanol and lactate fermentation produce ATP.
False.
Fermentation does not produce ATP; its purpose is to regenerate NAD, which allows glycolysis to continue producing ATP.
The purpose of fermentation is to regenerate so that glycolysis can continue.
The purpose of fermentation is to regenerate NAD so that glycolysis can continue.
In yeast, pyruvate is decarboxylated to ethanal and then reduced to .
In yeast, pyruvate is decarboxylated to ethanal and then reduced to ethanol.
How can a redox indicator be used to investigate respiration rate in yeast?
A redox indicator (e.g. DCPIP or methylene blue) changes from blue (oxidised) to colourless (reduced); the rate of colour change represents the respiration rate.
Why does a redox indicator change colour in the presence of respiring cells?
Many respiration reactions involve oxidation and reduction; the indicator becomes reduced instead of NAD or FAD, changing colour.
How does respiration rate affect the colour change of the indicator?
The faster the respiration rate, the faster hydrogen is released, so the dye is reduced faster and changes colour more quickly.
Why is a buffer solution added to each test tube in the yeast practical?
To maintain a constant pH.
Why are the tubes left in the water bath for at least ten minutes before adding DCPIP?
To allow the tube contents to reach the desired temperature before testing.
The stopwatch is started when the DCPIP is added and stopped when the solution its blue .
The stopwatch is started when the DCPIP is added and stopped when the solution loses its blue colour.
Why should the same person judge the end-point colour change in every repeat?
Judging the colour change is subjective, so using the same person improves consistency between repeats.
What is the purpose of a control tube containing only yeast and glucose?
It provides a reference for colour comparison when judging the end-point.
Why are three repeats carried out at each temperature?
To allow anomalies to be identified and to improve the reliability of the results.
How could the colour change be measured more objectively?
A colorimeter could be used to measure the colour intensity of the redox indicator in a less subjective, more quantitative way.
Describe an alternative method of measuring respiration rate in yeast.
Measure the volume of carbon dioxide produced by the yeast suspension.
Adding a layer of oil on top allows the anaerobic respiration rate to be measured.
True or False?
As temperature increases, the time taken for the DCPIP solution to become colourless decreases.
True.
As temperature increases, the rate of respiration increases (up to the optimum), so the solution loses its colour more quickly.
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