Module 5: Respiration

Question 1

State the function of mitochondria

Answer 1

Site of aerobic respiration

Question 2

What is structure and function of different parts of the mitochondria

Answer 2

Outer membrane: compartmentalisation
Inner membrane: contains proteins for electron transport chain
Cristae: folded to increase surface area for oxidative phosphorylation
Inter membrane Space: helps with storing protons for ATP synthesis
Matrix: contains enzymes for link and Krebs reactions and mitochondrial DNA

Question 3

1. What is an co enzyme

2. What are the co enzymes used in respiration

Answer 3

Co enzyme: molecule that aids the function of an enzyme by transferring chemical group from one molecule to another

2. NAD, FAD, coenzyme A

Question 4

State the 4 stages of aerobic respiration

Answer 4

1. Glycosis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation

Question 5

Describe the first stage of aerobic respiration (glycolysis)

Answer 5

-Happens in cytoplasm

1. Glucose has two phosphate groups added to it from 2 ATP molecules which males hexose bisphosphate
2. Splits into two so it becomes triosr phosphate
3. Another phosphate group is added to make triose bisphophate
4. Then triose bisphosphate is oxidised and is converted into pyruvate, NAD becomes reduced NAD
   And ADP is phosphorylated and becomes ATP

Question 6

What is substrate level phosphorylation

Answer 6

When ATP is produced without use of electron transport chain and ATP synthase. ADP is is phosphorylated by an unstable intermediate to form ATP

Question 7

What happens to the products of glycosis

Answer 7

Products
2x pyruvate-> link and Krebs reaction
2 reduced NAD -> to oxidative phosphorylation
2 ATP (net gain) because we use to at the start (used for energy)

Question 8

Describe what happens in the link reaction

Answer 8

1. Pyruvate transported into matrix of mitochondria
2. Pyruvate is decarboyliated (one Carbon atom is removed in the form of CO2
3. NAD is reduced to reduced NAD as it gains a hydrogen from pyruvate
4. This changes pyruvate into acetate
5. Acetate is combined with co enzyme A to form acetyl co enzyme A

Question 9

What happens to the products of the link reaction

Answer 9

2x Acetyl CoA- Krebs cycle
2x Carbon dioxide - released as waste product
2 reduced NAD- to oxidative phosphorylation

Question 10

Describe what happens in the Krebs cycle

Answer 10

• acetyl CoA (2 carbon) from link reaction combines with oxaloacetate (4 carbon) to form citrate (6 carbon) this is catalysed by citrate synthese
• Citrate (6) is converted into a 5c by the removal of Carbon dioxide through carbon dioxide decarboxylation
• Dehyrodegination also occurs and hydrogen produced reduced NAD
• This converts the 5c molecule into a 4c molecule
• which creates reduced FAD, 2x reduced NAD, and ATP which is produced by substrate level phosphorylation

Question 11

What happens to the products in the Krebs cycle

Answer 11

Co enzyme A- reused in next link reaction
Oxaloacetate: regenerated for next Krebs cycle
4 Carbon dioxide: released as waste
6 reduced NAD: to oxidative phosphorylation
2 reduced FAD to oxidative phosphorylation

This is for both Krebs cycles because we have how acetyl CoA, for one it would be half

Question 12

Describe what happens in oxidative phosphorylation

Answer 12

1. Hydrogen atoms are realesed from reduced NAD and reduced FAD
2. Hydrogen then splits into hydrogen ions and electrons
3. Electrons move along electron transport chain- losing energy
4. Energy lost Is used so proton pumps can pump H+ ions into inter membrane space, so conc of H+ ions is higher in inter membrane space than in mitochondrial matrix
5. Hydrogen ions move down electrochemical gradient through ATP synthase (chemosomis) back into mitochondrial matrix which increases ATP production,
6. In matrix the electrons join onto their final acceptor oxygen to make water

Question 13

When does anaerobic respiration occur

Answer 13

Happens when there is an absence of oxygen

Less ATP is produced through anaerobic respiration so it’s is a temporary measure

Question 14

What are obligate anaerobes

Answer 14

Organism that cannot survive in presence of oxygen

Question 15

What are facultative anaerobes

Answer 15

Organism that mostly use aerobic respiration but can switch to anaerobic if conditions dictate this should happen

Question 16

What are obligate aerobes

Answer 16

Can only synthasise ATP in presence of oxygen

Question 17

What is fermentation

Answer 17

Process by which complex organic compounds like glucose are broken down into simpler inorganic compounds without using oxygen as final electron acceptor

Question 18

Describe how lactate fermentation

Answer 18

1. reduced NAD donates hydrogen (and electrons) to pyruvate, producing lactate and NAD.
2. This uses lactate dehydrogenase
3. Lactate reacts with oxygen in liver to make glucose through gluconeogenesis

(More NAD being regenerated means more for glycolysis. This enables anaerobic respiration to continue and ensures that small amounts of energy can still be made in the absence of oxygen)

Question 19

Describe how alcoholic fermentation happens

Answer 19

1. Pyruvate turns into ethanal by Pyruvate decarboxylate, which realises carbon dioxide
2. Which then turns into ethanol ad reduced NAD from glycolysis transfers hydrogen to ethanol to form ethanol and NAD

Question 20

Why is a small amount of ATP produced during anaerobic respiration

Answer 20

In a mark scheme
1. Anaerobic respiration only goes through glycolysis, which produces 2ATP molecules per glucose molecule
2. Both Krebs and oxidative phosphorylation need oxygen, so if there is no oxygen there is no final electron acceptors
3. Only substrate level phosphorylation occurs
4. pyruvate / ethanol , used
5. Krebs cycle and)
electron transport chain / chemiosmosis /
oxidative phosphorylation , do not occur ;

Extra in book
to regenerate NAD for glycolysis (to continue)
3. This means electrons are still in electron transport chain and reduced NAD and FAD cannot be oxidised as there is no where for electrons to go
4. So no NAD or FAD is recycled
5. So decarboxylation and dehydrogenation cannot occur in Krebs
6. Glycolysis would come to a halt due to lack of NAD

Question 21

What are examples of respiratory substrates

Answer 21

1. Lipids: which can be broken down to
   - glycerol which is converted into Pyruvate(enters link reaction)
   - fatty acids go onto make 50 acetyl CoA which goes into make 500 ATP
2. Proteins: breaks down into amino acids
   - remove amino group in liver through deamination which makes Pyruvate

Question 22

Why do we avoid proteins as a respiratory substrate

Answer 22

Deamination uses ATP which decreases net ATP production

Also proteins comes from muscles which is broken down

Question 23

What is the equation for the respiratory quittent

Answer 23

CO2 produced/ o2 absorbed

Question 24

Why does lipids have a lower respiratory quotient compared to carbohydrates

Answer 24

More oxygen is needed to break lipids down

Question 25

How much ATP is produced in aerobic respiration

Answer 25

Glycolysis: make 2 ATP and 2 Red NAD
Link: 1 red NAD x2 because there are two Pyruvate
Krebs: make 1 ATP, 3 red NAD and 1 FAD

So we made 8ATP from stage 1, 6 ATP from link reaction and 24 from Krebs

1 glucose makes- 38 ATP

But other sources say 32 because FAD makes 1.5 ATP and and NAD makes 2.5 ATP

Question 26

How much ATP is produced from

1 reduced NAD
1 reduced FAD

Answer 26

1 Red NAD: 3 ATP

1 Red FAD: 2ATP

Question 27

Compare NAD and FAD

Answer 27

1- NAD takes part in all stages but FAD only involved in Krebs
2- NAD accepts 1 proton but FAD accepts 2 protons
3- Reduced NAD oxidised at start of, whereas reduced FAD oxidised further along cycle
4- 1 reduced NAD makes 3 ATP whereas 1 reduced FAD makes 2 ATP