Topic 3.7 Cell Respiration

Question 1

3.7.1 Define cell respiration.

Answer 1

Cell respiration: the controlled release of energy from organic compounds in cells to form ATP.

Question 2

3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into ________, with a small yield of ____.

Answer 2

In cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP.

Question 3

3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.

Answer 3

• anaerobic organisms derive ATP completely without the use of oxygen.
  
  • (breakdown of organic molecules for ATP production in an anaerobic way is also called fementation)
• to generate small amounts of energy provided by glycolysis, pyruvate must be converted into another substance before more glucose can be used (because conversion of pyruvate replenishes the levels of H⁺ acceptor (NAD⁺) needed for glycolysis to occur)
• In anaerobic cell respiration, pyruvate stays in cytoplasm
• In animal cells, excess pyruvate molecules are convered into lactic acid molecules (also 3-carbon like pyruvate) (lactic acid fermentation)
  
  • allows glycolysis to continue
• In plants, yeast & bacteria, pyruvate is converted into ethanol & CO_2​
  
  • also allows glycolysis to continue
• No ATP produced in either case

Question 4

3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.

Answer 4

Cells with mitochondria use aerobic pathway for cell respiration

1. pathway begins with glycolysis - net gain of 2 ATP + 2 pyruvate molecules
2. 2 pyruvate molecules are absorbed by a mitochondrion to be metabolized
3. each pyruvate loses a CO₂ molecule → becomes acetyl-CoA
4. each acetyl-CoA enters Krebs cycle → 2 more CO₂ produced from each pyruvate that entered
   
   • cycle because each time it returns to the molecule that reacts with an incoming acetyl-CoA
   • Some ATP are directly generated during Krebs cycle, some are indirectly generated through a later series of reactions involving oxygen
5. Aerobic cell respiration completely oxidizes a glucose molecule & produces CO₂ and H₂O
   
   • more efficient than anaerobic cell respiration because anaerobic pathways don’t completely oxidize glucose molecule
   • thus, aerobic pathways result in greater yield of ATP per glucose than anaerobic pathways