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Summary questions from Kerboodle and CGP book
Terms in this set (25)
Glycolysis takes place in the ( 1 ) of cells and begins with the activation of the main respiratory substrate, namely the hexose sugar called ( 2 ).
( 1 ) Cytoplasm
( 2 ) Glucose
The activation of glucose involves the addition of two ( 3 ) molecules provided by two molecules of ( 4 ). The resultant activated molecule is known as ( 5 ).
( 3 ) Phosphate
( 4 ) ATP
( 5 ) Phosphorylated glucose
In the second stage of glycolysis the phosphorylated glucose is split into two molecules called ( 6 ). The third stage entails the oxidation of these molecules by the removal of ( 7 ), which is transferred to a carrier called ( 8 ).
( 6 ) Triose phosphate
( 7 ) Hydrogen
( 8 ) NAD
The final stage of glycolysis is the production of the 3-carbon molecule ( 9 ), which also results in the formation of two molecules of ( 10 ).
( 9 ) Pyruvate
( 10 ) ATP
State how many carbon molecules there are in a single molecule of pyruvate.
Name the 2-carbon molecule that pyruvate is converted to during the link reaction.
Acetyl coenzyme A.
The Krebs cycle involves a series of oxidation-reduction reactions. Where does the Krebs cycle take place?
The matrix of the mitochondria
The processes that occur in the electron transfer chain are also known as oxidative phosphorylation. Suggest why this term is used.
The movement of electrons along the chain is due to oxidation. The energy from the electrons combines inorganic phosphate and ADP to form ATP = phosphorylation.
The surface of the inner mitochondrial membrane is highly folded to form cristae. State one advantage of this arrangement to the electron transfer chain.
It provides a large surface area of membrane incorporating the coenzymes (NAD and FAD) and electron carriers that transfer the electrons along the chain.
The oxygen taken up by organisms has an important role in aerobic respiration. Explain this role.
Oxygen is the final electron (and proton) acceptor in the electron transfer chain. Without it the electrons would accumulate along the chain and respiration would cease.
As part of which molecule does the oxygen taken into an organism leave after being respired?
(Refer to Sequencing the chain) State the order of the electron transfer molecules in this chain and explain why.
1. Electron carriers become reduced by electrons from glycolysis and the Krebs cycle.
2. Enzymes catalyse the transfer of these electrons to the next carrier.
3. If an enzyme is inhibited all molecules prior to that enzyme will not be able to pass on their electrons and so will be reduced and those after it will be oxidized.
4. The first molecule in the chain will be reduced with all inhibitors; the second with 2 out of 3 inhibitor; the third with 1 out of 3; the last in the chain with none (i.e. it is always oxidised).
(Investigating where certain respiratory pathways take place in cells) Briefly describe how the different portions of the homogenate may have been separated out by centrifuging.
1. Homogenate is spun at slow speed.
2. Heavier particles (nuclei) form a sediment.
3. Supernatant is removed, transferred to another tube and spun at a greater speed.
4. Next heaviest particle is removed.
5. Process is repeated.
(Investigating where certain respiratory pathways take place in cells) Name two organelles that are not involved in respiration. Explain why.
Nuclei and ribosomes because neither carbon dioxide nor lactate (products of respiration) are formed in any of the samples.
(Refer to: Investigating where certain respiratory pathways take place in cells) In which cell organelle would you expect to find the enzymes of the Krebs cycle and why?
Krebs cycle produces carbon dioxide and results show that carbon dioxide is produced when mitochondria only are incubated with pyruvate.
(Investigating where certain respiratory pathways take place in cells) Suggest which portion of the homogenate contains the enzymes that convert pyruvate into lactate.
The remaining cytoplasm.
(Investigating where certain respiratory pathways take place in cells) Explain why lactate is produced in the presence of cyanide but carbon dioxide is not.
1. Cyanide prevents electrons passing down the transport chain.
2. Reduced NAD therefore accumulates and blocks the Krebs cycle where carbon dioxide is produced.
3. Glycolysis can still occur because the reduced NAD it produces is used to make lactate.
4. Glucose can therefore be converted to lactate, but not into carbon dioxide, in the presence of cyanide.
(Refer to: Investigating where certain respiratory pathways take place in cells) Explain why carbon dioxide can be produced by the complete homogenate when none of the separate portions can do so.
1. The conversion of glucose to carbon dioxide involves glycolysis (occurs in the cytoplasm) and Krebs cycle (occurs in mitochondria).
2. Only the complete homogenate contains both cytoplasm and mitochondria.
(Investigating where certain respiratory pathways take place in cells) Suggest which two products might be formed if glucose was incubated with cytoplasm from yeast cells.
Ethanol and carbon dioxide.
(Investigating where certain respiratory pathways take place in cells) Assess the relative number of mitochondria in the following: xylem vessel, liver cell, red blood cell, epithelial cell of intestine, myofibril (muscle fibre).
Xylem vessel: no mitochondria as mature xylem vessels are dead and the cell contents have been lost.
Liver cell: many mitochondria as it is metabolically very active and requires much ATP.
Epithelial cell of intestine: many mitochondria needed to provide the ATP required for the active transport of glucose, amino acids.
Myofibril: many mitochondria to provide ATP for contraction of fibre.
(Investigating where certain respiratory pathways take place in cells) Mature red blood cells do not possess mitochondria. Suggest two advantages of this to the functioning of these cells.
1. The absence of mitochondria leaves extra space for haemoglobin and so increases the oxygen carrying capacity of red blood cells.
2. As mitochondria carry out oxidative phosphorylation, they could use up some oxygen leaving less to be carried to the tissues by the red blood cell.
At the end of a 100m sprint, runners will have built up lactate in their muscle cells.
(a) Name the reduced coenzyme regenerated by lactate production.
(b) What is the advantage for the runner of producing lactate in anaerobic conditions?
(a) Reduced NAD.
(b) The regenerated NAD is needed for glycolysis to continue and ATP to be produced under anaerobic conditions, providing the energy to keep running.
Carbon monoxide inhibits the final electron carrier in the electron transport chain.
(a) Explain how this affects ATP production via the electron transport chain.
(b) Explain how this affects ATP production via the Krebs cycle.
(a) The transfer of electrons down the electron transport chain stops. So there's no energy released to phosphorylate ADP (produce ATP).
(b) The Krebs cycle stops because there's no oxidized NAD or FAD coming from the electron transport chain.
Describe how a 6-carbon molecule of glucose is converted to pyruvate.
1. Glucose is phosphorylated using a molecule of ATP.
2. This creates one molecule of glucose phosphate and one molecule of ADP.
3. ATP is used to add another phosphate to glucose phosphate forming hexose bisphosphate, which is then split into two molecules of triose phosphate.
4. Triose phosphate is oxidised (loses hydrogen) to form two molecule of pyruvate.
5. NAD collects the hydrogen ions, forming two molecules of reduced NAD.
A student was trying to find the optimum pH for yeast to produce ethanol. She set up three test tubes, each containing a solution of glucose buffered to a different pH. She then dissolved some dried Saccharomyces cerevisiae in the solution and trickled some liquid paraffin down the inside of the test tubes. Immediately after, she put a bung in the top of each test tube, with a tube attached to a gas syringe. Every 60 seconds, she recorded how much carbon dioxide had been released into the gas syringe.
(a) Why did the student trickle liquid paraffin down the inside of the test tubes?
(b) Why would measuring the rate of carbon dioxide production help her to find out how quickly ethanol was being produced?
(c) Give two variables that should have been controlled in this experiment and describe how each of these variables should have been controlled.
(d) What negative control should have been included in this experiment and why?
(a) To stop oxygen getting into the solution, which forces the yeast to respire anaerobically.
(b) Both ethanol and carbon dioxide are products of anaerobic respiration. Measuring how fast carbon dioxide is produced would indicate how fast ethanol is being produced.
(c) Temperature: put test tubes in a water bath at a set temperature. Mass of yeast: weigh out a set amount of yeast to use in each test tube. Volume/concentration of glucose solution: measure a known volume of glucose solution in each test tube.
(d) A control tube should be set up for each pH being investigated, which contains glucose solution but no yeast. No carbon dioxide should be produced. This will allow the student to check that any carbon dioxide being released in the other tubes is actually being produced by the yeast.
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