Aerobic/Anaerobic Respiration

Question 1

What are the 4 stages aerobic respiration can be divided into?

Answer 1

1) glycolysis
2) the link reaction
3) the Krebs cycle
4) oxidative phosphorylation

Question 2

Explain the stage of glycolysis

Answer 2

(Occurs in the cytoplasm)

Phosphorylation:
1) glucose is phosphorylated using a phosphate from ATP to form glucose phosphate and ADP
2) ATP is then used to add another phosphate to form hexose bisphosphate
3) hexose bisphosphate then splits into two molecules of triose phosphate

Oxidation:
4) Triose phosphate (3C) is oxidised (loses hydrogens) to form 2 molecules of pyruvate. NAD is a coenzyme that is used with dehydrogenase enzymes that accepts the hydrogens to become NADH

Question 3

What are the products of glycolysis?

Answer 3

2x ATP
2x pyruvate molecules
2x NADH

Question 4

Explain the Link Reaction

Answer 4

(Occurs in the mitochondrial matrix)

1) pyruvate is decarboxylated to produce carbon dioxide and oxidised to produce reduced NAD and acetate
2) the acetate then combines with co-enzyme A to form acetyl coenzyme A

Question 5

What are the products of the link reaction?

Answer 5

For every glucose molecule:

2x carbon dioxide
2x reduced NAD
2x acetyl coenzyme

No ATP is produced

Question 6

Explain the Krebs Cycle

Answer 6

(Occurs in the mitochondrial matrix)

1) acetyl Co enzyme A enters the Krebs cycle and combines with oxaloacetate(4C) to form a 6C intermediate called citrate and coenzyme A which can be reused
2) the 6C citrate is then decarboxylated and oxidised to from carbon dioxide and reduced NAD and a 5C intermediate
3) the 5C intermediate is then decarboxylated and oxidised to form reduced NAD and reduced FAD. ATP is also synthesised from ADP and Pi. This is known as substrate level phosphorylation. The intermediate is oxidised further to form more reduced NAD and the 4C oxaloacetate is then regenerated so the cycle can continue.

Question 7

What are the products produced from Krebs cycle?

Answer 7

Per molecule of glucose:
4x carbon dioxide
6x reduced NAD
2x reduced FAD
2x ATP

Question 8

Explain oxidative phosphorylation

Answer 8

(Occurs on cristae in the mitochondria)

1) hydrogen atoms are released from the reduced NAD and FAD. The hydrogen atoms split into protons (H+) and electrons (e^-)
2) the electrons pass through the electron carriers in the electron transfer chain in a series of redox reactions
3) as the electrons move along the chain they lose energy which is used to pump protons (H+) from the mitochondrial matrix into the inter membrane space between the inner and outer membranes of the mitochondria
4) this forms an electrochemical gradient (= concentration gradient of ions). There are one more protons in the inter membrane space than in the mitochondrial matrix
5) the protons then move down the electrochemical gradient from the inter membrane space back into the mitochondrial matrix through the ATP synthase which is embedded in the membrane
6) the flow of H+ through the ATP synthase dives the synthesis of ATP nfrom ADP and Pi. The process of ATP production linked to the flow of electrons and production of the H= gradient is known as chemiosmosis theory
7) at the end of the electron transport chain, the protons and electrons combine with oxygen, the final electron acceptor to form water

NAD and FAD are then recycled back to previous stages

Question 9

How many ATP can be synthesised per NADH and FADH?

Answer 9

1 NADH = 2.5 ATP
1 FADH = 1.5 ATP

Question 10

How many ATP are produced per molecule of glucose?

Answer 10

32

Question 11

How is anaerobic respiration different to aerobic?

Answer 11

• does not require presence of oxygen
• takes place in cytoplasm ONLY (doesn’t require presence of mitochondria)
• only includes glycolysis ( not link reaction/Krebs cycle/ oxidative phosphorylation)
• glucose is not complexity broken down which results in less ATP

2ATP being synthesised

Question 12

What are the 2 different types of anaerobic respiration?

Answer 12

1) alcoholic fermentation in plants and yeast
2) lactate fermentation in animals and some bacteria

Question 13

Describe alcoholic fermentation in plants and yeast

Answer 13

1) Pyruvate is decarboxylated to produce ethanal
2)hydrogens from NADH are then used to reduce ethanal and produce ethanol
3) NAD is regenerated so it can be used again so glycolysis can continue
4) the reduced NAD cannot enter oxidative phosphorylation, as there will be no oxygen as the final electron acceptor. This pathway is irreversible.

Question 14

Describe lactate fermentation in animals and some bacteria

Answer 14

1) hydrogens from NADH are used to reduce pyruvate to produce lactate.
2) NAD is regenerated so it can be used again in glycolysis
3) This pathway is reversible in the cori cycle

Question 15

What are respiratory substrates? What are alternative respiratory substrates?

Answer 15

A respiratory substrate is a substance able to be respired to produce ATP.

Alternative respiratory substrates:
- lipids (fatty acids)
- protein (amino acid)

Question 16

What respiratory substrate has the highest energy value and why?

Answer 16

Lipids have the highest energy value (39kJ/g) due to a higher proportion of H to C to O. The energy value of lipids is higher than carbohydrates and proteins because fatty acids have many hydrogens, which provide lots of NADH and FADH for oxidative phosphorylation. Carbohydrates and proteins are similar in their proportions of H to C and O, so have a similar energy value (17kJ/g)