Respiration

Question 1

What is respiration?

Answer 1

• A set of metabolic reactions that take place in organisms and break down respiratory substances, such as glucose, into smaller inorganic molecules, like water and carbon dioxide.
• Linked to the synthesis of ATP.

Question 2

Why is respiration described as a catabolic process?

Answer 2

Complex molecules (respiratory substrates) are broken down into smaller, simpler molecules.

Question 3

Why do organisms need to respire?

Answer 3

• Produces chemical energy in ATP for a variety of processes including active transport, metabolic reactions and muscle contraction.
• Releases heat energy for thermoregulation.

Question 4

Define aerobic respiration.

Answer 4

A form of cellular respiration that takes place in the presence of oxygen and produces carbon dioxide, water and ATP.

Question 5

Name the four main stages of aerobic respiration and state where they occur.

Answer 5

• Glycolysis (cytoplasm).
• Link reaction (mitochondrial matrix).
• Krebs cycle (mitochondrial matrix).
• ETC (inner mitochondrial membrane).

Question 6

Outline the stages of glycolysis.

Answer 6

1. Glucose (hexose sugar) phosphorylated to hexose bisphosphate by 2x ATP.
2. Hexose bisphosphate splits into 2x triose phosphate (TP).
3. 2 molecules of TP oxidised to 2x pyruvate.
   Net gain of 2x reduced NAD (NADH) and 2x ATP per glucose.

Question 7

Write an equation to summarise glycolysis.

Answer 7

Glucose + 2NAD + 2ADP + 2Pi = 2 pyruvate + 2NADH + 2ATP + heat.

Question 8

How does pyruvate from glycolysis enter the mitochondria.

Answer 8

Via active transport.

Question 9

Outline the link reaction.

Answer 9

1. Oxidative decarboxylation and dehydrogenation of pyruvate to form acetate.
   Net gain of carbon dioxide and 2x reduced NAD.
2. Acetate combines with coenzyme A (CoA) to form acetyl coenzyme A.

Question 10

Write an equation to summarise the link reaction.

Answer 10

Pyruvate + NAD + CoA = acetyl CoA + reduced NAD + CO2.

Question 11

What is the Krebs cycle?

Answer 11

A series of oxidation-reduction reactions in the matrix of the mitochondria in which acetyl coenzyme A is oxidised generating reduced NAD, reduced FAD, ATP and carbon dioxide.

Question 12

What is the function of the Krebs cycle?

Answer 12

It is a means of releasing energy from carbon bonds to provide ATP, reduced NAD and reduced FAD (with the release of carbon dioxide) for the ETC

Question 13

How many reduced NAD and reduced FAD does the complete oxidation of one glucose molecule yield?

Answer 13

• 10 reduced NAD

- 2 reduced FAD

Question 14

What is the electron transport chain?

Answer 14

A series of electron carrier proteins that transfer electrons in a chain of oxidation-reduction reactions, releasing energy.

Question 15

What happens in the ETC?

Answer 15

• Electrons released from reduced NAD and FAD undergo successive redox reactions.
• The energy released is coupled to maintaining the proton gradient or is released as heat.
• Oxygen acts as the final electron acceptor.

Question 16

Describe the role of reduced NAD and reduced FAD in the ETC.

Answer 16

They are a source of electrons and protons.

Question 17

How does chemiosmosis produce ATP during aerobic respiration?

Answer 17

• Protons flow down their concentration gradient from the intermembrane space into the mitochondrial matrix via ATP synthase.
• ATP synthase phosphorylates ADP to form ATP as protons flow through it.

Question 18

State the role of oxygen in the ETC.

Answer 18

Final electron acceptor.

Question 19

How many ATP are produced per oxidised NAD in aerobic respiration?

Answer 19

3 ATP

Question 20

How many ATP are produced per oxidised FAD in aerobic respiration?

Answer 20

2 ATP

Question 21

Define anaerobic respiration.

Answer 21

A form of cellular respiration that takes place in the absence of oxygen. Less ATP is formed than in aerobic respiration.

Question 22

State the product of anaerobic respiration in animals.

Answer 22

Lactic acid.

Question 23

Outline anaerobic respiration in animals.

Answer 23

• Only glycolysis continues.
• Reduced NAD (product of glycolysis) transfers the H to pyruvate, forming lactic acid and regenerating NAD.
• Catalysed by enzyme lactate dehydrogenase.

Question 24

State the products of anaerobic respiration in plants and microorganisms,

Answer 24

Ethanol and carbon dioxide.

Question 25

Outline anaerobic respiration in plants and microorganisms.

Answer 25

• Only glycolysis continues.
• Pyruvate is decarboxylated to form ethanal.
• Ethanal accepts a H from reduced NAD making ethanol. NAD regenerated for glycolysis.

Question 26

Compare the yield of ATP in aerobic and anaerobic respiration.

Answer 26

Aerobic - 30 to 32 ATP.

Anaerobic - 2 ATP.

Question 27

Why is the maximum yield of ATP in aerobic respiration never achieved?

Answer 27

• ATP lost due to leaky membranes.

- Energy required to move pyruvate and ADP into the mitochondrial matrix.

Question 28

Name two types of molecule that can be used as alternative respiratory substrates.

Answer 28

• (amino acids from) proteins.

- (glycerol and fatty acids from) lipids.

Question 29

Explain how lipids are used in respiration.

Answer 29

• Hydrolysed to glycerol or fatty acids.
• Glycerol converted to a 3C sugar and enters glycolysis.
• Fatty acids broken down into 2C acetate fragments which enter the Krebs cycle as acetyl coenzyme A.

Question 30

Explain how proteins are used in respiration.

Answer 30

• Hydrolysed to amino acids.
• Amino acids deaminated in the liver forming keto acids and ammonia.
• Keto acids enter glycolysis and the Krebs cycle.