Respiration

Question 1

4 stages of aerobic respiration and an overview of each

Answer 1

1. Glycolysis - the 6C glucose is split into 2 x 3C pyruvate molecules
2. Link reaction - the 3C pyruvate enters a series of reactions which form acetyl coenzyme A (2C)
3. Krebs cycle - acetyl CoA enters a cycle of redox reactions that produce some ATP and a lot of reduced NAD and FAD.
4. Oxidative phosphorylation - electrons and reduced NAD and FAD from the Krebs cycle are used to synthesise ATP. Water is a by product.

Question 2

Aerobic vs anaerobic

Answer 2

Aerobic respiration requires oxygen and produces carbon dioxide, water and ATP.
Anaerobic respiration takes place in the absence of oxygen and produces lactate in animals, or ethanol and carbon dioxide in plants and fungi. Less ATP is produced.

Question 3

Link reaction - equation

Answer 3

Pyruvate + NAD + CoA ⇒ acetyl CoA + reduced NAD + CO2

Question 4

Stages of glycolysis

Answer 4

• phosphorylation of glucose to glucose phosphate using ATP
• splitting of glucose phosphate into 2x triose phosphate
• oxidation of triose phosphate to pyruvate.
  Net production of ATP and reduced NAD.

Question 5

What is the purpose of respiration?

Answer 5

Conserve energy from the breakdown of glucose in the production of ATP.

Question 6

Where does glycolysis occur?

Answer 6

in the cytoplasm

Question 7

How many molecules of ATP are produced in glycolysis?

Answer 7

2

Question 8

How many carbon atoms are there in a molecule of pyruvate?

Answer 8

3

Question 9

How is glycolysis indirect evidence for evolution?

Answer 9

it occurs in all living organisms

Question 10

Is glycolysis aerobic or anaerobic?

Answer 10

anaerobic.

Question 11

What happens to pyruvate from glycolysis in aerobic respiration?

Answer 11

it is actively transported into the mitochondrial matix, then used in the link reaction.

Question 12

What happens in the link reaction?

Answer 12

pyruvate is oxidised to acetate, producing reduced NAD and CO2 in the process. Acetate then combines with coenzyme A to produce acetylcoenzyme A.

Question 13

What happens in the Krebs cycle?

Answer 13

Acetyl CoA reacts with a 4C molecule, releasing CoA and prodcing a 6C molecule which enters the Krebs cycle.
There are a series of oxidation-reduction reactions, in which:
- reduced coenzymes are generated
- ATP is produced by substrate-level phosphorylation
- CO2 (x2) is lost.
the 4C molecule is regenerated.

Question 14

In which stages of aerobic respiation is ATP produced?

Answer 14

glycolysis, Krebs cycle, oxidative phosphorylation.

Question 15

Which stage of aerobic respiration produces the most ATP?

Answer 15

oxidative phosphorylation

Question 16

What respiratory substrates other than glucose are there? Which stage do the enter?

Answer 16

The breakdown products of lipids and amino acids - these enter the Krebs cycle.

Question 17

How is ATP synthesised using the electron transport chain in aerobic respiration?

Answer 17

by oxidative phosphorylation.

Question 18

How many times do the link reaction and Krebs cycle occur per molecule of glucose?

Answer 18

2

once per pyruvate and 2 pyruvates are produced per glucose

Question 19

What is the main purpose of the Krebs cycle?

Answer 19

To generate reduced coenzymes for use in oxidative phosphorylation and generate a small amount of ATP.

Question 20

Describe the stages of ATP production via oxidative phosphorylation. (aerobic respiration)

Answer 20

1. Reduced NAD and FAD from the Krebs cycle carry H+ and electrons to the electron transfer chain.
2. Electrons are transferred from NAD and FAD to the first molecule in the electron transfer chain.
3. The electrons pass between electron carriers in a series of redox reactions.
4. The electrons release energy as they are transferred from one electron carrier to the next. This energy is used to actively transport H+ ions (from coenzymes) from the matrix to the intermembrane space of the mitochondria.
5. H+ diffuse back into the matrix through ATP synthase channels. This allows the synthesis of ATP to occur: ADP + Pi ⇒ ATP + H2O
6. Electrons and H+ ions combine to form hydrogen atoms, which combine with oxygen to create water.

Question 21

What is the role of oxygen in aerobic respiration?

Answer 21

As the final electron acceptor - oxygen combines with electrons and protons from the electron transport chain to produce water.

Question 22

What are coenzymes? name some involved in respiration and photosynthesis.

Answer 22

molecules required for some enzymes to function, they are often involved in the transfer of chemical groups or electrons.
NAD, FAD, coenzyme A (respiration)
NADP (photosynthesis)

Question 23

What is the purpose of anaerobic respiration?

Answer 23

To regenerate oxidised NAD, which can be used to produce more ATP in glycolysis. This is needed as without oxygen, all coenzymes become reduced, and oxidative phosphorylation and the Krebs cycle become stop - no ATP would be produced.

Question 24

Equation for anaerobic respiration in plants and yeast

Answer 24

Pyruvate + reduced NAD ⇒ ethanol + carbon dioxide + oxidised NAD

Question 25

Equation for anaerobic respiration in animals and some bacteria

Answer 25

pyruvate + reduced NAD ⇒ lactate + oxidised NAD

Question 26

Which stages are common to both aerobic and anaerobic respiration?

Answer 26

glycolysis

Question 27

Where do the Krebs cycle and link reaction ocur?

Answer 27

the mitochondrial matrix

Question 28

Where does oxidative phosphorylation occur?

Answer 28

the inner mitochindrial membrane.

Question 29

What happens if oxygen is not present at the end of the electron transport chain in oxidative phosphorylation?

Answer 29

electrons and hydrogens would back up along the ETC and coenzymes would all become reduced. Aerobic respiration would stop.

Question 30

Which enzyme catalyses ATP synthesis in oxidative phosphorylation?
What is the equation for this reaction?
What type of reaction is this?

Answer 30

ATP synthase
ADP + Pi ⇒ ATP + H2O
Condensation

Question 31

Where is ATP synthase found in a mitochondrion?

Answer 31

embedded in the inner mitochondrial membrane.