Respiration

Question 1

What is the equation of respiration?

Answer 1

Glucose + oxygen -> carbon dioxide + energy

Question 2

What is respiration?

Answer 2

The process by which organic molecules are broken down in a series of stages to synthesise ATP.

Question 3

What are the two methods of ATP generation in respiration?

Answer 3

Substrate phosphorylation- ATP generated directly through respiration.
Oxidative phosphorylation – ATP generated from the chemical energy released when a coenzyme has been reduced.

Question 4

What are the coenzymes found during respiration?

Answer 4

NAD and FAD are coenzymes which are molecules which acts as a hydrogen acceptor becoming reduced to NADH or FADH

NADH/FADH provides reducing power within reactions as it loses its hydrogen, becoming re oxidised to NAD/FAD.

Question 5

What is a redox reaction?

Answer 5

Redox reaction are the gain or loss of hydrogen or electrons ONLY!

Question 6

What are the stages of aerobic respiration?

Answer 6

1. Glycolysis
2. The Link Reaction
3. The Krebs Cycle
4. Oxidative Phosphorylation

Question 7

What are the steps of gycolysis?

Answer 7

1. Phosphorylation - Glucose is phosphorylated to Glucose phosphate using ATP (ADP is created)
2. Oxidation - GP is oxidised into two TP molecules
3. 4 phosphate from the TP joins 4 ADP to form ATP and 2 NAD is reduced to form pyruvate.

Question 8

Where does glycolysis occur?

Answer 8

In the cytoplasm

Question 9

What are the glycolysis yields per glucose?

Answer 9

· 2 ATP directly-substrate phosphorylation
· 2 reduced NAD (which will also be used to produce ATP by oxidative phosphorylation)
· 2 molecules of pyruvate

Question 10

What happens in the link reaction?

Answer 10

1. Two pyruvate are decarboxylated (2 CO₂ produced) and oxidated (2 NAD become 2 NADH) to form 2 acetate
2. Two coenzyme A is added to form 2 acetyl-coenzyme A

Question 11

Where does the link reaction take place?

Answer 11

The mitochondrial matrix

Question 12

Where does the Krebs cycle take place?

Answer 12

The mitochondrial matrix

Question 13

What are the steps in the Krebs cycle?

Answer 13

1. Acetyl-coenzyme A combines with a 4C compound to form 6C compound. The coenzyme A is released.
2. CO₂ and NADH₂ (NAD + 2H) are removed to form a 5C compound.
3. In a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate-level phosphorylation, and carbon dioxide is lost

Question 14

What are the yields of the Krebs cycle per glucose?

Answer 14

· 4 CO2 produced

· 2 ATP produced directly- substrate phosphorylation

· 6 Reduced NAD and 2 FAD produced to be used in

Question 15

Where does oxidative phosphorylation occur?

Answer 15

The mitochondrial membrane

Question 16

What are the steps of oxidative phosphorylation?

Answer 16

1. Electrons released from reduced / coenzymes / NAD / FAD;
2. (Electrons) pass along the electron transport chain through series of redox reactions;
3. Energy released, this energy is used to pump H+ into the intermembrane space. Some energy is released as heat
4. The H+ pass back through the inner membrane via ATP synthase enzymes
5. and as they pass through the enzymes, enough energy is released to form ATP from ADP + Pi
6. The electrons and H+ combine with oxygen to form water. The oxygen is the final electron acceptor.

Question 17

What are the yields of oxidative phosphorylation?

Answer 17

3 ATP are created per NADH2.
2ATP are created per FADH2

Question 18

What is the total yield of ATP in aerobic respiration?

Answer 18

38 ATP per glucose molecule

Question 19

What happens in aerobic respiration?

Answer 19

Only glycolysis takes place as it does not require oxygen and can continue in the absence of oxygen, but in order for glycolysis to continue NAD must be regenerated.

The H from the reduced NAD in glycolysis is now accepted by pyruvate rather than passing through the electron transport chain.

The pyruvate is reduced to lactate in animals and ethanol in plants and microorganisms

Question 20

What is the difference in energy produced during aerobic vs anaerobic respiration?

Answer 20

Aerobic respiration releases 38 molecules of ATP per molecule of glucose:

(4 via substrate phosphorylation. 34 via oxidative phosphorylation).

Anaerobic respiration yields 2 molecules of ATP per molecule of glucose.

Question 21

Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion. (3)

Answer 21

ATP formed as electrons pass along transport chain; oxygen is terminal electron acceptor / accepts electrons from electron transport chain / electrons cannot be passed along electron transport chain if no O2 to accept them; forms H2O / accepts H+ from reduced NAD / FAD / oxidises reduced NAD / FAD;

Question 22

Describe the part played by the inner membrane of a mitochondrion in producing ATP. (3)

Answer 22

1. Electrons transferred down electron transport chain;
2. Provide energy to take protons / H+ into space between membranes;
3. Protons / H+ pass back, through membrane / into matrix / through ATPase;
4. Energy used to combine ADP and phosphate / to produce ATP;
   Accept: alternatives for electron transport chain.

Question 23

DNP inhibits respiration by preventing a proton gradient being maintained across membranes. When DNP was added to isolated mitochondria the following changes were observed

• less ATP was produced
• more heat was produced
• the uptake of oxygen remained constant.

Explain how DNP caused these changes. (3)

Answer 23

1. Less / no proton / H+ movement so less / no ATP produced;
2. Heat released from electron transport / redox reactions / energy not used to produce ATP is released as heat;
3. Oxygen used as final electron acceptor / combines with electrons (and protons);

Question 24

Describe how ATP is made in mitochondria. (6)

Answer 24

ATP is produced in the Krebs cycle;
Krebs cycle/link reaction produces reduced coenzyme;
Electrons are released from reduced coenzymes;
And pass through electron transport chain;
Energy released is used to combine;
ADP + Pi to make ATP

Question 25

Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP during respiration. Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis. (5)

Answer 25

In the dark there is no ATP production by photosynthesis;
ATP cannot be stored so must be made continuously;
Plant uses more ATP than produced in photosynthesis;
ATP is needed for active transport;
ATP is needed for synthesis of essential enzymes

Question 26

Describe how this pyruvate is converted into a substance that enters the Krebs cycle. (2)

Answer 26

reacts with coenzyme A to give acetylcoenzyme A;
NAD is reduced

Question 27

In the presence of oxygen, respiration yields more ATP per molecule of glucose than it does in the absence of oxygen. Explain why. (5)

Answer 27

Oxygen is the final electron acceptor;
Process of electron transport chain;
Fate of pyruvate;
Krebs cycle;
Significance of ATP formed in glycolysis;

Question 28

Describe how NAD is regenerated in anaerobic respiration in yeast cells. (1)

Answer 28

Formed when reduced NAD is used to convert pyruvate to ethanol

Question 29

Give two ways in which anaerobic respiration of glucose in yeast is
(i) similar to anaerobic respiration of glucose in a muscle cell;
(ii) different from anaerobic respiration of glucose in a muscle cell. (4)

Answer 29

(i) ATP formed;
glycolysis involved;

(ii) ethanol formed by yeast, lactate by muscle cell;
CO2 released by yeast but not by muscle cell

Question 30

Explain the process of aerobic respiration. (6)

Answer 30

by glycolysis, glucose is broken down into pyruvate in the cytoplasm;
pyruvate converted to acetyl CoA;
by oxidative decarboxylation;
acetyl CoA enters the Krebs cycle;
Krebs cycle yields a small amount of ATP;
and FADH2 and NADH;
these molecules pass electrons to electron transport chain;
oxygen is final electron acceptor;