Other key concepts

Question 1

Oxidative Phosphorylation (where and when does it occur, what does it produce?) (6)

Answer 1

• In cellular respiration after the citric acid cycle (CAC)
• Uses NADH and FADH2 electrons that are transferred to a series of protein complexes
• As the electrons move down the chain, energy is released, which is then used to pump protons (H+) from the mitochondrial matrix across the inner membrane into the intermembrane space.
• This creates a concentration gradient of protons which drives protons back into the matrix through a protein complex called ATP synthase.
• As protons flow through ATP synthase, the enzyme uses the energy to convert ADP (adenosine diphosphate) and inorganic phosphate into ATP
• Oxygen acts as the final electron acceptor, combining with electrons and protons to form water.

Question 2

Photophosphorylation (where and when does it occur, what does it produce?)

Answer 2

• Occurs in photosynthesis in the electron transport chain (ETC) between PS2 and PS1
• Uses the splitting of water to provide electrons
• Energy is released as electrons move through the ETC creates a proton motive force.
• This is used to pump protons across the thylakoid membrane, creating a gradient.
• This gradient then drives ATP synthase, an enzyme that catalyses ATP production (ADP to ATP by addition of phosphate group)

Question 3

Compare and contrast oxidative phosphorylation and photophosphorylation

Answer 3

• Both processes that generate ATP
• Photophosphorylation uses light energy in chloroplasts during photosynthesis
• Oxidative phosphorylation uses the chemical energy of electron carriers (NADH and FADH2) within mitochondria during cellular respiration

Question 4

What is Chemiosmosis?

Answer 4

• Movement of ions across a semipermeable membrane, down their electrochemical gradient

Question 5

What is Complex 1 of the ETC in respiration, and what are the effects of blocking it?

Answer 5

• Oxidises NADH, transferring electrons and pumping protons
• Blocking would result in reduced ATP production, decreased oxygen consumption, and increased reactive oxygen species (ROS) production.

Question 6

What is Complex 2 of the ETC in respiration, and what are the effects of blocking it?

Answer 6

• Receives electrons from FADH2, transferring them
• Blocking would result in disruption of electron flow, leading to decreased ATP production and increased reactive oxygen species (ROS) generation

Question 7

What is Complex 3 of the ETC in respiration, and what are the effects of blocking it?

Answer 7

• Receives electrons from ubiquinone and passes them to cytochrome c, also pumping protons
• Blocking would result in disruption of the transfer of electrons and protons, leading to reduced ATP production, increased ROS generation, and potential mitochondrial damage

Question 8

What is Complex 4 of the ETC in respiration, and what are the effects of blocking it?

Answer 8

Oxygen receives final electrons, forming water. It also pumps protons across the inner mitochondrial membrane
- Blocking would prevent electrons from being transferred to oxygen, initially causing NADH and FADH2 accumulation and slowed ATP production
- Eventually this would halt the entire chain and consequently stop ATP production, leading to cellular asphyxiation.

Question 9

Equation for photosynthesis

Answer 9

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Question 10

Equation for respiration

Answer 10

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O energy (as ATP)