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 include 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. Overall:
6H20C6H12O6 +602→ 6CO2+ 6H2O

Question 5

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

Answer 5

Glycolysis - cytosol
Link reaction - mitochondrial matrix
Krebs cycle - mitochondrial matrix
Electron transport chain - 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 2× ATP per glucose.

Question 7

Write an equation to summarise glycolysis.

Answer 7

Glucose + 2NAD + 2ADP + 2P =
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 CO2 and 2× 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

Outline the stages of the Krebs cycle.

Answer 12

Look at image bruv
https://www.google.com/url?sa=i&url=http%3A%2F%2Fib.bioninja.com.au%2Fhigher-level%2Ftopic-8-metabolism-cell%2Funtitled%2Fkrebs-cycle.html&psig=AOvVaw33lujUmQUjC2jKUTWO0U–&ust=1700683911894000&source=images&cd=vfe&opi=89978449&ved=0CBIQjRxqFwoTCJCE57Xz1YIDFQAAAAAdAAAAABAZ

Question 13

What is the function of the Krebs cycle?

Answer 13

It is a means of releasing energy from carbon bonds to provide ATP, reduced NAD and reduced FAD (with the release of CO2).

Question 14

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

Answer 14

10 reduced NAD
2 reduced FAD

Question 15

What is the electron transport chain?

Answer 15

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

Question 16

What happens in the electron transport chain?

Answer 16

• 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 17

Describe the role of reduced NAD and reduced FAD in the electron transport chain.

Answer 17

They are a source of electrons and protons.

Question 18

How does chemiosmosis produce ATP during aerobic respiration?

Answer 18

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 19

State the role of oxygen in the electron transport chain.

Answer 19

Final electron acceptor:
O2 + 4H+ + 4e → 2H2O

Question 20

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

Answer 20

3 ATP

Question 21

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

Answer 21

2 ATP

Question 22

Define anaerobic respiration.

Answer 22

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

Question 23

State the product of anaerobic respiration in animals.

Answer 23

Lactic Acid

Question 24

Outline anaerobic respiration in animals.

Answer 24

• Only glycolysis continues
• Reduced NAD (product of glycolysis) transfers the H to pyruvate, forming lactic acid

Question 25

State the products of anaerobic respiration in plants and microorganisms.

Answer 25

Ethanol and carbon dioxide.

Question 26

Outline anaerobic respiration in plants and microorganisms.

Answer 26

Only glycolysis continues
* Pyruvate is decarboxylated to form ethanal
* Ethanal is reduced to ethanol using reduced NAD, producing oxidised NAD for further glycolysis

Question 27

Compare the yield of ATP in aerobic and
anaerobic respiration.

Answer 27

Aerobic - 30 to 32 ATP
Anaerobic - 2 ATP

Question 28

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

Answer 28

• ATP lost due to leaky membranes
• Energy required to move pyruvate and ADP into the mitochondrial matrix

Question 29

Name two types of molecules that can be used as alternative respiratory substrate

Answer 29

(amino acids from) proteins
(glycerol and fatty acids from) lipids

Question 30

Explain how lipids are used in respiration.

Answer 30

*Hydrolysed to glycerol and 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 31

Explain how proteins are used in
respiration.

Answer 31

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