3.5.2 - RESPIRATION

Question 1

describe the process of glycolysis (4)

Answer 1

1. phosphorylation of glucose using ATP
2. oxidation of triose phosphate to pyruvate (removal of hydrogen for oxidation)
3. net gain of 2 ATP
4. NAD is reduced

Question 2

malonate inhibits a reaction in the Krebs cycle.

explain why malonate would decrease the uptake of oxygen in a respiring cell (2)

Answer 2

1. less/no reduced NAD/coenzymes OR fewer/no hydrogens/electronsremoved and passed to electron transfer chain
2. oxygen is the final/terminal electron acceptor

Question 3

in muscles, pyruvate is converted to lactate during prolonged exercise.

explain why converting pyruvate to lactate allows the continued production of ATP by anaeobic respiration (2)

Answer 3

1. regenerates/produced NAD OR oxidises reduced NAD
2. so glycolysis continues

Question 4

describe how acetylcoenzyme A is formed in the link reaction (2)

Answer 4

1. oxidation of pyruvate and CO2 released
2. addition of coenzyme A

Question 5

in the Krebs cycle, acetylcoenzyme A combines with 4-carbon oxaloacetate to form 6-carbon citrate. this reaction is catalysed by the enzyme citrate synthase.

oxaloaceate is the first substrate to bind with the enzyme citrate synthase.

this induces a change in the enzyme, which enables the acetylcoenzyme A to bind.

explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme (2)

Answer 5

1. change in the shape/tertiary structure of active site
2. substrate/active site are now complementary

Question 6

in the Krebs cycle, acetylcoenzyme A combines with four-cabon oxaloacetate to form x-carbon citrate. this reaction is catalysed by the enzyme citrate synthase.

another substance in the Krebs cycle is called succinyl coenzyme A. this substance has a very similar shape to acetylcoenzyme A.

suggest how production of succinylcoenzyme A could control the rate of the reaction catalysed by citrate synthase (2)

Answer 6

1. it is a competitive inhibitor/it attaches to the actie site
2. reduces/prevents enzyme substrate complex forming

Question 7

in muscles, pyruvate is converted to lactate during anaerobic respiration.

in muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen.

suggest one advantage of this (1)

Answer 7

1. pyruvate used in aerobic respiration/lactate (lactic acid) is toxic/harmful

Question 8

respiration produced more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent. explain why (2)

Answer 8

1.oxygen is final/terminal electon acceptor/oxygen combines with electrons and protons
2. oxidative phosphorlylation/electron transport chain provides most ATP/only glycolysis occurs without oxygen

Question 9

when investigating the rate of anaeobic respiration in yeast, explain why a layer of oil o top of the yeast n glucose solution is necessary (1)

Answer 9

to prevent entry of oxygen

Question 10

respiration produces more ATP per molecule of glucose in the prence of oxygen than it does when oxgen is absent.

explain why (2)

Answer 10

1. oxygen is final acceptor of electrons in ETC
2. oxidative phosphorylation provides ATP
3. only glycolysis occurs without oxygen / no krebs and link

Question 11

the following rection occurs in the Krebs cycle.

succinate ———> fumarate (enzyme on arrow)

a scientist investigated the effect of the enzyme inhibitor malonate on this reaction. the structure of malonate is very similar to the structure of succinate. the scientist added malonate and the respiratory substrate, pyruvate, to a suspension of isolated mitochondria. she also bubbled oxygenthroug the suspension.

explain why the scientist did not use glucose as the respiratory substancefor these isolated mitochondria (2)

Answer 11

1. glycose is used in glycolysis
2. glucose cannot cross the mitocjondrial membranes

Question 12

the following rection occurs in the Krebs cycle.

succinate ———> fumarate (enzyme on arrow)

a scientist investigated the effect of the enzyme inhibitor malonate on this reaction. the structure of malonate is very similar to the structure of succinate. the scientist added malonate and the respiratory substrate, pyruvate, to a suspension of isolated mitochondria. she also bubbled oxygenthroug the suspension.

explain how malonate inhibits the formation of fumarate from succinate (2)

Answer 12

1. it is a competitive inhibitor that attaches to the active site
2. prevents the formation of an enzyme-substrate complex

Question 13

the following rection occurs in the Krebs cycle.

succinate ———> fumarate (enzyme on arrow)

a scientist investigated the effect of the enzyme inhibitor malonate on this reaction. the structure of malonate is very similar to the structure of succinate. the scientist added malonate and the respiratory substrate, pyruvate, to a suspension of isolated mitochondria. she also bubbled oxygenthroug the suspension.

the scientist measured the uptake of oxygen by the mitochondria during the investigation. the uptake of oxygen decreased when malonate was added.

explain why (2)

Answer 13

1. Krebs cycle inhibited
2. NAD + FAD/coenzymes not reduced
3. hydrogn not passed to ETC
4. oxygen is used as final electron acceptor

Question 14

write a simple equation to show how ATP is synthesised from ADP (1)

Answer 14

ADP + Pi ——> ATP

Question 15

give two ways in which the properties of ATP make it a sutable source of energy in biological processes (2)

Answer 15

1. it is soluble
2. energy released in small amounts
3. involves a single/simple reaction

Question 16

humans synthesise more than their body mass of ATP each day. explain why this is necessary for them (2)

Answer 16

1. ATP cannot be stored/is an immediate source of energy
2. active transport/muscle contraction/glycolysis use ATP
3. ATP only releases a small amount of energy at a time

Question 17

describe the part played by the inner membrane of a mitocondrion in producing ATP (3)

Answer 17

1. electrons transferred down ETC
2. provide energy to transport protons into intermembrane space
3. protons transport back using ATP synthase
4. energy used to combine ADP and Pi to produce ATP

Question 18

why was the solution in which the mitochondria were suspended isotonic? (1)

Answer 18

1. to prevent damage (shrinking/bursting) to mtochondria caused by differencs in WP

Question 19

exain why the scientist did not use glucose as the respiratory substance when investigating ATP producion in mitochondia (2)

Answer 19

1. glucose is sued during glycolysis
2. glucose cannot cross mitochondrial membrane

Question 20

describe how ATP is made in mitochondria (6)

Answer 20

1. substrate level phosphorylation / ATP produced in Krebs cycle
2. Krebs cycle produces coenzymes - reduced NAD and reduced FAD
3. electrons released from the coenzymes
4. electrons pass through electron transport chain
5. which releases energy
6. which is used to combine ADP + Pi
7. protons move into intermembrane space
8. ATP synthase