8.2 (Cell Respiration HL)

Question 1

Compare oxidation and reduction.

Answer 1

Oxidation:

• Electrons lost
• Oxygen gained
• Hydrogen lost

Reduction:

• Electrons gained
• Oxygen lost
• Hydrogen gained

Question 2

What are the electron carriers in cell respiration?

Answer 2

Most common: Nicotinamide Adenine Dinucleotide (NAD)
NAD⁺ ——- NADH + H⁺

Less common: Flavin Adenine Dinucleotide (FAD)
FAD ——- FADH₂

Question 3

What is phosphorylation?

Answer 3

• A reaction where a phosphate group is added to an organic molecule
• The phosphorylated molecule is less stable and therefore reacts more easily in the metabolic pathway
• The phosphate group is usually transferred from ATP

Question 4

Outline the link reaction.

Answer 4

• Pyruvate (from glycolysis) enters the mitochondrion matrix
• Enzymes remove one carbon dioxide and hydrogen from the pyruvate
• Hydrogen is accepted by NAD to form NADH
• Removal of hydrogen is oxidation
• Removal of carbon dioxide is decarboxylation
• The link reaction is therefore oxidative decarboxylation
• The product is an acetyl group which reacts with coenzyme A
• Acetyl CoA enters Krebs cycle

Question 5

How are fatty acids used in cell respiration?

Answer 5

• Source of energy
• Have a long chain of carbon atoms
• CoA can oxidise (break down) the chain
• Makes Acetyl CoA with two carbons
• Carries them to Kreb’s cycle
• Glycolysis is not needed but reaction is slower

Question 6

Outline the Kreb’s cycle.

Answer 6

• Acetyl CoA enters the Krebs cycle
• Acetyl group (2C) joins a 4C sugar to form a 6C sugar
  oxidative decarboxylation of the 6C sugar to a 5C compound produces CO2
• Oxidative decarboxylation of the 5C compound to a 4C compound produces CO2
• The process is oxidative as NAD and FAD are reduced by the addition of hydrogen
• Two CO2 are produced per molecule of pyruvate / cycle
• Along with three NADH + H⁺ and one FADH₂ per molecule of pyruvate / cycle
• One ATP is produced by substrate level phosphorylation (from ADP + Pi) per molecule of pyruvate / cycle
• NADH and FADH₂ provide electrons to the electron transport chain

Question 7

Outline the electron transport chain.

Answer 7

• Electron carriers deposit their electrons and H⁺ ions
• A series of integral protein complexes act as electron carriers forming the electron transport chain
• H⁺ are passed through first channel, e⁻ moves along ETC and activates next channel
• H⁺ are passed through second channel, e⁻ move along, losing energy
• High concentration of H⁺

Question 8

What is chemiosmosis?

Answer 8

• The diffusion of ions across a semi-permeable membrane, through a carrier membrane
• In this case, the ions are hydrogen protons and the carrier is ATP synthase. The flow of the H⁺ through ATP synthase generates ATP

Question 9

Outline chemiosmosis.

Answer 9

• High concentration of H⁺, moves through ATP synthases
• Movement of H⁺ drives rotation of ATP synthase and ATP is made
• The yield of ATP from chemiosmosis is potentially 32 molecules, but in most conditions the yield is slightly lower.
• e⁻ need to be removed to allow ETC to continue
• Can ‘mop up’ excess H⁺ and e⁻ by using O2 to form water
• Oxygen is the terminal electron acceptor