Question 1

What are the key differences between aerobic and anaerobic respiration in A Level Biology 9700?

Accepted Answer

Aerobic respiration requires oxygen, occurs in the cytoplasm and mitochondria, produces a high yield of ATP (around 30-32 per glucose), and results in carbon dioxide and water as end products. Anaerobic respiration occurs without oxygen, is confined to the cytoplasm, yields only 2 ATP per glucose (from glycolysis), and produces lactate (in animals) or ethanol and carbon dioxide (in yeast).

Question 2

How does chemiosmosis contribute to ATP production in respiration?

Accepted Answer

Chemiosmosis is the process where ATP is generated using energy from a proton (H⁺) gradient. In respiration, the electron transport chain pumps protons from the mitochondrial matrix into the intermembrane space. This creates a high concentration of protons, which then flow back into the matrix through the enzyme ATP synthase. This flow of protons provides the energy to drive the synthesis of ATP from ADP and inorganic phosphate.

Question 3

Why is oxygen essential for efficient ATP production during aerobic respiration?

Accepted Answer

Oxygen is crucial because it acts as the final electron acceptor at the end of the electron transport chain. It removes electrons and combines with protons to form water. Without oxygen, electrons would accumulate, halting the ETC. This would stop the pumping of protons and prevent the formation of the proton gradient needed for chemiosmosis, thereby stopping the majority of ATP synthesis.

Question 4

Why do lipids have a higher energy value than carbohydrates?

Accepted Answer

Lipids have a higher proportion of carbon-hydrogen bonds and a lower proportion of oxygen compared to carbohydrates. This means that for the same mass, lipids provide more hydrogen atoms to the electron transport chain via reduced NAD and FAD. This leads to a larger proton gradient and ultimately the production of more ATP molecules per gram, giving lipids a higher energy density.

Respiration

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Respiration