Anaerobic Respiration

Question 1

what happens without oxygen

Answer 1

-oxygen cannot act as the final electron acceptor in electron transport chain= stops oxidative phosphorylation
-the reduced NAD and FAD cannot unload their hydrogen atoms and reoxidised =stops Krebs and link reaction

Question 2

what is the only stage of respiration to take place in anaerobic respiration

Answer 2

glycolysis and NAD is regenerated by 2 pathways

Question 3

what are the two anaerobic pathways in mammals and yeast

Answer 3

yeast = ethanol fermentation
mammals= lactate fermentation

Question 4

what is the energy yield for both anaerobic reactions

Answer 4

neither produce any ATP but they enable glycolysis to continue to produce 2 ATP per glucose

Question 5

explain lactate fermentation in mammalian

Answer 5

-occurs during vigorous activity when demand for ATP for muscle contraction is high and there is an oxygen deficit

1. pyruvate (from glycolysis) acts as a hydrogen acceptor taking hydrogen ions from reduced NAD and forming lactate (NADH is reoxidised)
2. the reaction is catalysed by the enzyme lactate dehydrogenase
3. once the NAD is reoxidised it can accept more hydrogen ions from glucose and glycolysis can continue to generate enough ATP to sustain muscle contraction

Question 6

what is the fate of lactate

Answer 6

lactate is carried by blood from the muscles (reduces pH inhibiting the enzyme activity of muscles) to the muscles to the liver

when oxygen is available it is either:
-converted back into pyruvate and can enter the link and krebs cycle
-recycled to glucose or glycogen

Question 7

explain anaerobic respiration (ethanol fermentation) in yeast

Answer 7

glucose -> ethanol + carbon dioxide + energy

1. Pyruvate is decarboxylated forming ethanal, catalysed by the enzyme pyruvate decarboxylase which has a coenzyme bound to it (CO2 is released)
2. ethanal accepts hydrogen atoms from reduced NAD which becomes reoxidised at the same time as ethanal is reduced to ethanol (catalysed by ethanol dehydrogenase)
3. reoxidised NAD is then able to accept more hydrogen atoms from glucose and glycolysis can continue

-when concentration of ethanol produced by the yeast reaches 15% the yeast die

Question 8

what are facultative anaerobes and obligate anaerobe

Answer 8

-facultative anaerobes = some organisms carry out aerobic respiration if oxygen is available but can switch to anaerobic respiration in the absence of oxygen e.g yeast

obligate anaerobe= live permanently in oxygen-deficient conditions and have no need for oxygen e.g clostridium welchii

Question 9

suggest one benefit of anaerobic respiration to an organism

Answer 9

ATP produced/ energy released still

Question 10

explain why the incomplete breakdown of glucose in anaerobic respiration produces less ATP than aerobic respiration

Answer 10

-glycolysis is broken into pyruvate
-produces 2 molecules of ATP net
-only substrate level phosphorylation occurs
-oxygen not available as final electron acceptor
-pyruvate/ ethanal used to regenerate NAD for glycolysis to continue
-krebs cycle and electron transport chain/ oxidative phosphorylation do not occur

Question 11

what can be used to count cells e.g yeast cells

Answer 11

Haemocytometer