18.5 Anaerobic Respiration

Question 1

When is anaerobic respiration used?

Answer 1

In the absence of O2

When O2 can’t be supplied fast enough to respiring cells

Question 2

When there’s lack of oxygen, what does anaerobic respiration act as?

Answer 2

An emergency measure to keep vital processes functioning

Question 3

What are the 3 categories of organisms based on their oxygen needs?

Answer 3

Obligate anaerobes
Facultative anaerobes
Obligate aerobes

Question 4

What is the O2 dependency of obligate anaerobes? What type of organism are most obligate anaerobes?

Answer 4

Can’t survive in presence of O2

• Almost all are prokaryotes, but there are some fungi

Question 5

What are facultative anaerobes? Give an example of this organism

Answer 5

Synthesise ATP by aerobic respiration if O2 is present, but can switch to anaerobic in absence of oxygen
e.g. yeast

Question 6

What are obligate aerobes? Give an example of this organism.

Answer 6

Only synthesise ATP in presence of oxygen

e.g. mammals

Question 7

Why can muscle cells of mammals be described as facultative anaerobes? Why aren’t they fully facultative anaerobes?

Answer 7

The cells can supplement ATP by anerobic respiration if O2 conc.s are low. However, eventually O2 is required.

Question 8

Why are mammals as a whole obligate anaerobes?

Answer 8

When anaerobic respiration is used during low oxygen periods, compounds are produced which have to be broken down when O2 is available again

Question 9

What is fermentation?

Answer 9

When complex organic compounds are broken down into simpler inorganic compounds w/o use of oxygen or ETC

Question 10

What type of respiration occurs in fermentation?

Answer 10

Anaerobic

Question 11

Why does fermentation produce less ATP than aerobic respiration?

Answer 11

Organic compounds (e.g. glucose) aren’t fully broken down

Question 12

Where does alcoholic fermentation occur?

Answer 12

In yeast and some plant roots

Question 13

What are the end products of fermentation?

Answer 13

Ethanol (alcohol) and CO2

Question 14

Where does lactate fermentation occur?

Answer 14

Animal cells

Question 15

What is the end product of lactate fermentation?

Answer 15

Lactate

Question 16

What happens when oxygen is no longer available to act as the final electron acceptor at the end of the ETC (in oxidative phosphorylation)?

Answer 16

1. Flow of electrons stops - so synthesis of ATP by chemiosmosis stops
2. Reduced NAD+FAD are no longer oxidised bc no flow of electrons
   • This means NAD + FAD no longer regenerated in Krebs cycle, so decarboxylation and oxidation of pyruvate + in Krebs cycle halts, as there are no coenzymes to accept the H removed

Question 17

How does lactate fermentation work?

Answer 17

1. Pyruvate acts as H acceptor, taking H from reduced NAD , catalysed by lactase dehydrogenase
2. Pyruvate is converted into lactate and NAD is regenerated
3. This regenerated NAD can be used prevent glycolysis stopping, so small amount of ATP are always synthesised

Question 18

What is the name of the enzyme which catalyses lactate fermentation?

Answer 18

Lactate dehydrogenase

Question 19

What is anaerobic respiration supported by?

Answer 19

ATP supplied by aerobic respiration

Question 20

What’s happening with aerobic respiration during exercise?

Answer 20

ATP from aerobic respiration is still being produced as fast as oxygen can be delivered into the body

Question 21

What happens to lactic acid once the body gets more O2?

Answer 21

The lactic acid is converted into glucose in the liver. O2 is needed for the conversion of lactate -> glucose

Question 22

What are the 2 reasons for why lactate fermentation can’t occur endlessly?

Answer 22

1. Reduced quantity of ATP produced wouldn’t be enough to maintain vital processes for extended periods of time
2. Accumulation of lactic acid decreases pH, leading to denaturing of proteins - respiratory enzymes and muscle filaments are made from proteins and won’t function at low pH

Question 23

What’s the difference between lactate fermentation and alcoholic fermentation in terms of reactions?

Answer 23

Lactate fermentation is reversible. Alcoholic fermentation is irreversible.

Question 24

What happens during alcoholic fermentation?

Answer 24

1. Pyruvate converted into ethanal, catalysed by pyruvate decarboxylase
2. Ethanal accepts a H from reduced NAD and becomes ethanol

Question 25

What’s the name of the enzyme that catalyses alcoholic fermentation?

Answer 25

Pyruvate decarboxylase

Question 26

What happens to the regenerated NAD in alcoholic fermentation?

Answer 26

It continues to act as coenzyme as glycolysis continues

Question 27

Why can alcoholic fermentation occur indefinitely in the absence of oxygen?

Answer 27

It can continue in the absence of oxygen

Question 28

What is ethanol for yeast?

Answer 28

Toxic waste product

Question 29

At what point does ethanol in yeast cells kill them?

Answer 29

When ethanol accumulates above 15%+