5.2: Respiration

Question 1

Give a simple description of what respiration involves

Answer 1

involves the oxidation of organic molecules to release energy - this energy is used to synthesis ATP from ADP + Pi

Question 2

What are the two types of respiration and how do they differ

Answer 2

Aerobic - requires oxygen
Anaerobic - doesn’t require oxygen

Question 3

What is the equation for aerobic respiration

Answer 3

C6H12O6 + 6O2 -> 6CO2 + 6H2O

Question 4

What are the four stages of aerobic respiration and where do they each occur

Answer 4

1- Glycolysis - cytoplasm
2- Link reaction - mitochondrial matrix
3- Krebs cycle - mitochondrial matrix
4- The electron transport chain - inner mitochondrial membrane / cristae

Question 5

What is the significance of glycolysis, link reaction, and krebs cycle, taking place in the cytoplasm and mitochondrial matrix?

Answer 5

Location of the necessary enzymes - dehydrogenases being the most important as they catalyse the removal of hydrogen from molecules (oxidation)

Question 6

What is the role of the loop of DNA and the 70S ribosomes in the mitochondria for aerobic respiration

Answer 6

the loop of DNA contains the genes that code for enzyme whilst the 70S ribosomes they synthesise the enzymes involved in the link reaction and krebs cycle

Question 7

Explain fully the process of glycolysis in aerobic respiration

Answer 7

1- Glucose is phosphorylated to hexose bisphosphate using 2 ATP: makes glucose more reactive & overcomes the activation energy for the reaction
2- Hexose bisphosphate is split to form two triose phosphate
3- 2x Triose phosphate is oxidised to 2x pyruvate: 2x NAD is reduced to 2x NADH2 at the same time
Energy is released to synthesise 4 ATP from 4 ADP + (2) Pi by substrate level phosphorylation

Question 8

Give a summary of what is produced at the end of glycolysis in aerobic respiration

Answer 8

each molecule of glucose results in the production of:
2 x pyruvate
2 x NADH2
2 x ATP net (as 2 are used to get 4)

Question 9

Why does glycolysis have to occur for the link reaction and krebs cycle to be carried out

Answer 9

Glucose can’t enter the mitochondria as there are no glucose carrier proteins within these membranes.
Pyruvate, produced in glycolysis, passes into the mitochondria via carrier proteins in the mitochondrial membrane

Question 10

Explain fully the process of the link reaction in aerobic respiration

Answer 10

1- Pyruvate is oxidised to acetate, and NAD is reduced to NADH2. Acetate is a 2C molecule so a molecule of CO2 is also produced
2- Acetate combines with co-enzyme A to form acetyl co-enzyme A (Acetyl co-A)

Question 11

Give a summary of what is produced at the end of the link reaction in aerobic respiration

Answer 11

2 molecules of pyruvate leads to the production of:
2 x NADH2
2 x CO2
2 x Acetyl co-enzyme A

Question 12

Give a simple description of what the krebs cycle is in aerobic respiration

Answer 12

a series of oxidation and decarboxylation reactions

Question 13

Give a summary of what is produced at the end of the krebs cycle in aerobic respiration

Answer 13

1 molecule of Acetyl Co-A leads to the production of:
3 x NADH2
1 x FADH2
1 x ATP by substrate level phosphorylation
2 x CO2

Question 14

Explain fully the process of the krebs cycle in aerobic respiration

Answer 14

Acetyl Co-A (2C) reacts with Oxaloacetate (4C), releasing Co-enzyme A and producing Citrate - a 6C molecule
Citrate is oxidised to 𝝰-ketoglutarate -> one molecule of CO2 is released and NAD is reduced to NADH2
𝝰-ketoglutarate (5C) ix oxidised to Oxaloacetate (4C) -> 2 x NAD are reduced to 2 x NADH2, FAD is reduced to FADH2, 1 molecule of CO2 is released, ATP is synthesised from ADP + Pi

Question 15

What effect would having less enzymes be on the rate of ATP production in the Krebs cycle in aerobic respiration

Answer 15

less enzymes -> less NADH2 and FADH2 produced -> decreased rate of ATP production

Question 16

Give a brief description of how the electron transport chain in aerobic respiration works

Answer 16

The reduced co-enzymes NADH2 & FADH2 formed during glycolysis, link reaction and Krebs cycle, provide hydrogen (protons + electrons) for the E.T.C.
E.T.C. take place on the inner-mitochondrial membrane involving a series of electron carriers

Question 17

What theory is used to explain how the electron transport chain in aerobic respiration works

Answer 17

Chemiosmotic theory

Question 18

Fully explain the chemiosmotic theory in the electron transport chain in aerobic respiration

Answer 18

When NADH2 and FADH2 are oxidised, protons and high energy electrons are released. These electrons lose energy as they pass along a series of electron carriers
This energy is used to pump protons from the mitochondrial matrix into the intermembrane space, the protons accumulate forming a concentration gradient, the protons move back into the matrix by facilitated diffusion via ATP synthase providing the energy needed to synthesise ATP from ADP + Pi, by oxidative phosphorylation - 1x NADH2 results in 3x ATP, 1x FADH2 results in 2x ATP. The NAD and FAD is reused in the Krebs cycle. Oxygen is the terminal electron acceptor in the ETC, it accepts (2x) protons (from the oxidation of NADH2 and FADH2) and (2x) electrons and is reduced to water

Question 19

How many molecules of ATP are produced from NADH2 and FADH2 in the E.T.C. in aerobic respiration

Answer 19

Each NADH2 results in 3 x ATP
Each FADH2 results in 2 x ATP

Question 20

What is the role of oxygen in the E.T.C. in aerobic respiration

Answer 20

Oxygen is the terminal electron acceptor in the E.T.C. -> it accepts protons and electrons, and is reduced to water

Question 21

What stages in aerobic respiration are substrate level phosphorylation and as oxidative phosphorylation

Answer 21

Glycolysis, Link reaction, Krebs cycle are all substrate level phosphorylation
E.T.C. is oxidative phosphorylation

Question 22

What is the net number of ATP produced by substrate level phosphorylation in aerobic respiration

Answer 22

4
(2 from glycolysis
2 from 2 cycles of krebs cycle as there are 2x Acetyl Co-A)

Question 23

What is the net number of ATP produced by oxidative phosphorylation in aerobic respiration

Answer 23

34

Question 24

What is the total number of ATP produced by in aerobic respiration

Answer 24

38

Question 25

Without oxygen (anaerobic respiration), what effect does this have in the processes involved in the mitochondria

Answer 25

Without oxygen, the E.T.C. stops, no oxidative phosphorylation occurs, NADH2 can't be oxidised to NAD, therefore no more NAD can be produced and becomes a limiting factor, preventing the link reaction and Krebs cycle occurring

Question 26

Explain what happens during anaerobic respiration in animals

Answer 26

Glycolysis continues, as pyruvate is reduced to lactate -> caused by the oxidation of NADH2, and so NAD is available for glycolysis to continue, therefore ATP is still produced

Question 27

What is the difference in ATP molecules produced in aerobic and anaerobic respiration in animals

Answer 27

In aerobic respiration - 38 molecules of ATP are produced whereas in anaerobic respiration - 2 molecules of ATP are produced as only glycolysis can occur

Question 28

Explain what happens during anaerobic respiration in plants, fungi & some bacteria

Answer 28

pyruvate is decarboxylated (CO2 molecule is released) so pyruvate (3C) becomes ethanal (2C), ethanal is reduced to ethanol, at the same time NADH2 is oxidised to NAD

Question 29

What are 4 alternative respiratory substrates to glucose

Answer 29

1- other carbohydrates - glycogen in animals and starch in plants are stores of glucose, glycogen is hydrolysed to glucose, sucrose (hydrolysed to glucose + fructose) 2- Triglycerides 3- Proteins 4- Creatine

Question 30

Fully describe how triglycerides are used as an alternative respiratory substrate

Answer 30

Triglycerides are hydrolysed into glycerol and fatty acids. Glycerol is a 3C molecule that can be converted to triose phosphate and enter glycolysis. Fatty acids are further broken down into 2C fragments, which enter the link reaction/Krebs cycle. Gram for gram lipids provide about double the ATP than a carbohydrate, but require a large volume/conc of oxygen to respire them, lipids act as thermal insulation in the adipose tissue under the skin.

Question 31

Fully describe how proteins are used as an alternative respiratory substrate

Answer 31

Proteins are hydrolysed into amino acids, the amino acids are then deaminated in the liver. NH3 is converted into urea and most of the remaining organic acid is converted into acetyl coA -> used in the Krebs cycle

Question 32

Fully describe how creatine is used as an alternative respiratory substrate

Answer 32

creatine is stored in muscle fibres at rest creatine is phosphorylated to produce phosphocreatine (CP) ATP + C -> ADP + CP During exercise CP is used to quickly regenerate ATP ADP + CP -> ATP + C

Question 33

What 3 measurements would you need to take when calculating the rate of oxygen uptake using a pipette with a coloured liquid/bubble inside, boiling tube, and ruler scale

Answer 33

1- distance travelled by liquid/bubble 2- time taken for it to travel that distance 3- internal diameter of capillary tube

Question 34

What is the units for rate of oxygen consumption

Answer 34

cm3 per minute per gram