18.5 Anaerobic Respiration

Question 1

What is anaerobic respiration?

Answer 1

Respiration

in the absence of oxygen

Question 2

Anaerobic respiration results in the synthesis of [more/less] ATP molecules than aerobic respiration.

Answer 2

less

Question 3

Why do microorganisms carry out anaerobic respiration if it is not as efficient as aerobic respiration?

Answer 3

• O₂ may not be present/available
• O₂ sometimes cannot be supplied fast enough to meet demand for forming ATP. Anaerobic respiration helps meet ATP demand without O₂.

Question 4

What are the different categories which organisms can be classified into, based on their dependence on oxygen?

Answer 4

• OBLIGATE ANAEROBES
  
  • cannot survive in presence of O₂
    
    • almost all are prokaryotes
• FACULTATIVE ANAEROBES
  
  • primarily synthesise ATP by aerobic respiration, but can switch to anaerobic respiration if required
    
    • e.g yeast
• OBLIGATE AEROBES
  
  • can only synthesise ATP in presence of O₂
    
    • e.g mammals

Question 5

What are obligate anaerobes?

Answer 5

Organisms which can only synthesise ATP

in the absence of O₂ /

cannot survive in presence of O₂

Question 6

What are facultative anaerobes?

Answer 6

Organisms which primarily synthesise ATP

by aerobic respiration

but can switch to anaerobic respiration if required

e.g yeast

(facultative - occurring optionally in response to circumstances rather than by nature.)

Question 7

What are obligative aerobes?

Answer 7

Organisms which can only synthesise ATP

in the presence of O₂

_{e.g mammals}

Question 8

If an organisms has tissues which supplement their ATP supply by anaerobic respiration, but as a result produces products which require O₂ for breakdown, the organism as a whole is considered an [obligate aerobe/facultative anaerobe].

Answer 8

obligate aerobe

Question 9

What is fermentation?

Answer 9

anaerobic respiration

without the involvement of an electron transport chain

Question 10

Fermentation produces [less/more] ATP molecules than aerobic respiration.

Answer 10

less

(∵ organic products such as glucose are not fully broken down)

Question 11

The ATP produced from fermentation is produced by _____ phosphorylation alone.

Answer 11

substrate-level

Question 12

What is alcoholic fermentation?

Answer 12

Fermentation

which results in the formation of ethanol

Question 13

What is lactate fermentation?

Answer 13

Fermentation

which results in the formation of lactate

Question 14

What type of organisms carry out alcoholic fermentation?

Answer 14

yeast (& some plant root cells)

Question 15

What type of organisms carry out lactate fermentation?

Answer 15

animal cells

Question 16

When there is no final electron acceptor at the end of the electron transport chain in [substrate-level/oxidative] phosphorylation, electrons cannot flow through the electron transport chain, & therefore no chemiosmosis can occur to synthesise ATP.

Answer 16

oxidative

Question 17

What effect would a lack of O₂ have on the processes involved in respiration?

Answer 17

no final electron acceptor, so electrons cannot flow through electron transport chain, no ATP produced by chemiosmosis

NADH + FADH₂ cannot be oxidised to NAD + FAD by donating H atoms, so glycolysis, oxidative decarboxylation & Krebs cycle halt.

Question 18

Outline the process of lactate fermentation in mammals:

Answer 18

Lack of O2 causes buildup of NADH, so glycolysis cannot occur. anaerobic respiration begins:

1. Pyruvate accepts Hydrogen from NADH ⟶ Lactate + NAD
   
   1. Catalysed by lactate dehydrogenase
2. Regeneration of NAD allows glycolysis to continue, forming some ATP.
3. Lactic acid converted back to glucose in liver, using O₂ - gluconeogenesis
   
   1. O₂ required to convert lactic acid to pyruvate = O₂ debt

Question 19

Why can lactate fermentation not occur indefinitely?

Answer 19

• Reduced quantity of ATP produced cannot sustain metabolic processes for long period
• Accumulation of lactic acid decreases pH, denaturing proteins. Enzymes + muscle filaments no longer function.

Question 20

During lactate fermentation, lactic acid is removed from ____ cells & delivered to the ____ via the bloodstream to be converted into ____.

Answer 20

muscle

liver

pyruvate

Question 21

Outline the process of alcoholic fermentation in yeast:

Answer 21

1. Pyruvate ⟶ Ethanal + CO₂
   
   1. Catalysed by pyruvate decarboxylase
2. Ethanal accepts H atom from NADH ⟶ Ethanol + NAD
3. Regeneration of NAD allows glycolysis to continue, forming some ATP.

Question 22

What are the differences between lactate fermentation & alcoholic fermentation?

Answer 22

• Lactate fermentation is reversible by converting lactic acid to pyruvate in the liver. Alcoholic fermentation is irreversible, ∵ ethanol is not used to regenerate pyruvate.
• Alcoholic fermentation can occur indefinitely, lactate fermentation cannot due to accumulation of lactic acid.