5.2.2 Respiration

Question 1

What is ATP and what is its role in cells?

Answer 1

ATP or adenesine triphosphate in the universal energy currency for cells.
It provides energy for various cellular processes.

Question 2

How ATP synthesised in respiration?

Answer 2

Pi and ADP combines to form ATP, using energy released in respiration.

Question 3

Why is ATP synthesis considered an anabolic reaction?

Answer 3

Small molecules (ADP and Pi) are built up into larger ones (ATP)

Question 4

What are the two main ways cells regenerate ATP during respiration?

Answer 4

Substrate-level phosphorylation - direct transfer of phosphate group, without involvement of an ETC (occurs in glycolysis & krebs)
Chemiosomsis - using movement of protons across a membrane to generate energy for ATP synthesis via ATP synthase (occurs in oxidative phosphorylation).

Question 5

Name the two types of cellular respiration.

Answer 5

Aerobic respiration
Anaerobic respiration

Question 6

What are the four stages of aerobic respiration in order?

Answer 6

1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidatve phosphorylation

Question 7

Where does glycolysis occur and what does it produce?

Answer 7

Location: cytoplasm
Main products: 2 ATP, 2 reduced NAD & 2 pyruvate.

Question 8

Where does the link reaction occur and what does it produce?

Answer 8

Location: Mitochondrial matrix
Main products: (per pyruvate) 1 acteyl coA, 1 reduced NAD and 1 CO₂.

Question 9

Where does the Krebs cycle occur and what does it produce?

Answer 9

Location: Mitochondrial matrix
Main products: (per acetyl coA) 1 ATP, 3 reduced NAD,
1 reduced FAD and 2 CO₂.

Question 10

Where does oxidative phosphorylation occur and what does it produce?

Answer 10

Location: Inner mitochondrial membrane of the cristae
Main products: 30-32 ATP and water

Question 11

Is glycolysis an aerobic or anaerobic process?

Answer 11

Glycolysis is anaerobic - it does not require oxygen.

Question 12

Describe the main steps of glycolysis.
(four stages)

Answer 12

1. Phosphorylation of glucose - 2 ATP donate phosphate groups to glucose, forming hexose biphosphate (6C)
2. Lysis - Hexose biphosphate molecule is split into 2 molecules of triose phosphate (TP)
3. Phosphorylation of TP - A second phosphate is added to TP, converting them into 2 molecules of triose biphosphate.
4. Dehydrogenation - A hydrogen is removed from each triose biphosphate (oxisised) = forming 2 red NAD , 2 pyruvate molecules and 4 ATP (substrate-level phosphorylation)

Question 13

How does pyruvate reach the mitochondrial matrix for the link reaction?

Answer 13

By active transport via specific carrier proteins.

Question 14

Describe the main steps of the link reaction.
(five stages)

Answer 14

1. Decarboxylation - In mitochondrial matrix, each pyruvate is decarboxylated, removing 1 CO₂.
2. Removal of CO₂ - CO₂ diffuses out of mitochondria as waste
3. Oxidation of pyruvate - Two hydrogen atoms are removed from pyruvate to form 2C molecule acetate.
4. Reduction of NAD - The hydrogen aroms removed are used to reduce NAD, forming NADH (an electron carrier).
5. Formation of acetyl CoA - Acetate binds to coenzyme A, forming acetyl coenzyme A.

Question 15

What is the role of acetyl CoA?

Answer 15

It delivers the acetyl group to the Krebs cycle.

Question 16

Describe the main steps of the Krebs cycle.
(five stages)

Answer 16

1. Acetly CoA (2C) merges with oxaloacetate (4C) to form a molecule of citrate (6C)
2. Citrate is decarboxylated, releasing two molecules of CO₂.
3. Citrate is also dehydrogenated (oxidised), releasing hydrogens that reduce 3 NAD and 1 FAD.
4. One ATP is synthesised directly by substrate-level phosphorylation - per acetyl CoA.
5. Oxaloacetate is regenerated from citrate to repeat cycle.

Question 17

What is the role of NAD and FAD in the Krebs cycle?

Answer 17

Act as oxidsing agents
They are reduced - accept electrons & protons
The reduced coenzymes later donate these electrons & protons to the ETC for oxidative phosphorylation

Question 18

What is the electron transport chain (ETC)?

Answer 18

A series of electron carrier molecules in the inner mitochondrial membrane, releasing energy in stages

Question 18

What are the differences between NAD and FAD?

Answer 18

• NAD accepts 1 electron and 1 proton but FAD accepts 2 protons and 2 electrons.
• NAD participates in all three stages, but FAD only accepts in the Krebs cycle.

Question 19

What are the reactants in oxidative phosphorylation?

Answer 19

Reduced NAD, Reduced FAD, Oxygen
ADP and inorganic phosphate (Pi)

Question 20

Describe the main steps of oxidative phosphorylation.
(seven stages)

Answer 20

1. NADH and FADH₂ release hydrogen, transfering H⁺ and high energy electrons (e⁻) into the mitochondrial matrix.
2. The e⁻ are passed along a series of electron carrier molecules in the ETC embedded in inner mitochondrial membrane, releasing energy as transferred.
3. The energy is used to actively transport H⁺ across inner mitochondrial membrane from matrix into intermembrane space.
4. Accumulation of H⁺ in intermembrabe space sets up steep electrochemical gradient of H⁺ across inner membrane.
5. H⁺ diffuses back into matrix down electrochemical gradient through ATP synthase.
6. This releases energy and catalyses the synthesis of ATP from ADP and Pi.
7. Oxygen is final electron acceptor & combines with H⁺ and e⁻ to form water - help maintain proton gradient.

Question 21

What is chemiosmosis in oxidative phosphorylation?

Answer 21

The diffusion of protons across partially permeable inner mitochondrial membrane.
Down their electrochemical gradient through ATP synthase, catalysing ATP synthesis.

Question 22

How much ATP is produced in oxidative phosphorylation per glucose molecule?

Answer 22

Between 30-32 ATP

Question 23

What is the total ATP yield from one glucose molecule in aerobic respiration?

Answer 23

2 ATP produced in glycolysis
0 ATP in link reaction
2 ATP in Krebs cycle
30-32 in Oxidative phosphorylation
So, 34-36 ATP molecules in total.

Question 24

What is the function of the intermembrane space in mitochondria?

Answer 24

Protons are pumped during oxidative phosphorylation.

Question 25

Describe some adaptations of mitochondria.

Answer 25

* Matrix contains all the enzymes needed for the link reaction and the Krebs cycle. * Mitochondrial DNA and ribosomes allow it to produce **proteins rapidly**. * The **cristae** significantly increase the inner membrane's **SA**, so it can contain more proteins, e.g. in the electron transport chain and enzymes (ATP synthase). * The intermembrane space is **small**, so the proton concentration **gradient** between the intermembrane space and the mitochondrial matrix **builds up quickly**.

Question 26

What is the main difference between aerobic and anaerobic respiration?

Answer 26

Aerobic respiration - Requires oxygen and occurs mainly in mitochondria Anaerobic respiration - No oxygen required and only occurs in cytoplasm

Question 27

What stage of respiration is only present in anaerobic respiration?

Answer 27

Glycolysis

Question 28

Why is anaerobic respiration considered an emergency measure?

Answer 28

It provides **ATP** without oxygen but in much **lower quantities**.

Question 29

What is the purpose of fermentation in anaerobic respiration?

Answer 29

To regenerate NAD - glycolysis can continue in the absence of oxygen.

Question 30

Why can’t the link reaction or Krebs cycle occur during anaerobic respiration?

Answer 30

NAD and FAD remain reduced, so they can’t accept more electrons or protons.

Question 31

Describe the steps in alcohol fermentation.

Answer 31

1. Gltcolysis: Glucose → 2 Pyruvate + 2 ATP + 2 NADH 2. Step 1 – Decarboxylation: Pyruvate → Ethan**al** + CO₂ (This is catalysed by pyruvate **decarboxylase**) 3. Step 2 – Reduction of ethanal: Ethanal + NADH → Ethan**ol** + NAD⁺ (This is catalysed by ethanol **dehydrogenase**)

Question 32

Where does alcohol fermentation occur?

Answer 32

Yeast and some plants

Question 33

Describe the steps in lactic acid fermentation.

Answer 33

1. Pyruvate **accepts** a hydrogen from reduced NAD, catalysed by **lactate dehydrogenase**. 2. This forms **lactic acid**, and regenerates NAD.

Question 34

Where does lactic acid fermentation occur?

Answer 34

In some animals and bacteria

Question 35

What happens to lactic acid after anaerobic respiration?

Answer 35

It can be oxidised in the liver back to pyruvate or stored as glycogen. Gluconeogenesis

Question 36

What are the effects of prolonged anaerobic respiration in muscles?

Answer 36

Lactic acid accumulates/builds up Causing cramps and muscle fatigue It also reduces the pH affecting enzymes.

Question 37

What are alternative respiratory substrates to glucose?

Answer 37

Lipids and amino acids

Question 38

Which respiratory substrate yields the most ATP per gram?

Answer 38

Lipids

Question 39

Which substrate yields intermediate energy and is only used when others are limited?

Answer 39

Proteins

Question 40

Why are carbohydrates the primary respiratory substrate?

Answer 40

Easily accessible Quickly metabolised, (even though they release less energy per gram)

Question 41

What is the formula for calculating RQ?

Answer 41

RQ = volume of CO₂ produced ÷ volume of O₂ consumed

Question 42

What does an RQ > 1 indicate?

Answer 42

Anaerobic respiration is occurring. more CO₂ is being produced than O₂ is being used