H2 Biology – Cellular Respiration Summary

These question-and-answer flashcards cover all major concepts in the lecture notes: mitochondrial structure recognition, glycolysis, link reaction, Krebs cycle, oxidative phosphorylation, chemiosmosis, respiratory quotient, anaerobic respiration, and factors influencing respiration rate.

What four sequential stages make up aerobic respiration in eukaryotic cells?

Glycolysis, Link reaction (pyruvate oxidation), Krebs cycle (citric-acid cycle) and Oxidative phosphorylation (electron transport chain + chemiosmosis).

Approximately how many ATP molecules are produced from one glucose molecule during complete aerobic respiration?

About 38 ATP.

In which cellular compartment does glycolysis take place?

The cytosol (cytoplasm).

Does glycolysis require oxygen to proceed?

No. Glycolysis occurs under both aerobic and anaerobic conditions.

List the direct products of glycolysis per glucose molecule.

2 pyruvate, 2 NADH and a net gain of 2 ATP (4 made − 2 used).

During glycolysis, what is the purpose of the two ‘priming’ phosphorylations of glucose?

They destabilise glucose, allowing it to be split (cleaved) into two triose-phosphate molecules.

Where in the mitochondrion does the link reaction occur?

In the mitochondrial matrix.

State the raw materials that enter the link reaction.

2 pyruvate, 2 NAD⁺ and 2 coenzyme A.

What three products are formed during the link reaction (per glucose)?

2 acetyl-CoA, 2 NADH and 2 CO₂.

Which enzyme removes CO₂ from pyruvate in the link reaction?

Pyruvate decarboxylase.

Which enzyme removes hydrogen from pyruvate to reduce NAD⁺ in the link reaction?

Pyruvate dehydrogenase.

What molecule combines with acetyl-CoA at the start of the Krebs cycle?

Oxaloacetate.

Name the mitochondrial compartment in which the Krebs (citric-acid) cycle occurs.

The mitochondrial matrix.

Enumerate the products of one turn of the Krebs cycle per acetyl-CoA.

3 NADH, 1 FADH₂, 2 CO₂, 1 ATP and regeneration of 1 oxaloacetate.

Where is the electron transport chain (ETC) located in mitochondria?

Embedded in the inner mitochondrial membrane.

What molecule acts as the final electron acceptor in the ETC?

Molecular oxygen (O₂).

Explain how proton pumping during oxidative phosphorylation leads to ATP synthesis.

Energy from electron transfer pumps H⁺ from the matrix to the inter-membrane space; the resulting proton gradient drives H⁺ back through ATP synthase, which phosphorylates ADP to ATP (chemiosmosis).

What compound is produced when electrons, protons and oxygen combine at the end of the ETC?

Water (H₂O).

Define ‘respiratory quotient’ (RQ).

RQ = (moles of CO₂ produced) ÷ (moles of O₂ consumed).

What is the RQ value for complete aerobic oxidation of glucose?

1 (6 CO₂ / 6 O₂).

Under anaerobic conditions in mammalian muscle, what product is formed from pyruvate?

Lactate (lactic acid).

Why is the formation of lactate or ethanol crucial during anaerobic respiration?

It regenerates NAD⁺, allowing glycolysis to continue and produce ATP when oxygen is unavailable.

State the ATP yield per glucose molecule during anaerobic glycolysis.

A net gain of 2 ATP.

How does substrate concentration affect the rate of respiration?

Rate increases with substrate concentration until enzymes become saturated, then plateaus.

Which type of carbohydrate leads to the fastest respiration rate: monosaccharide, disaccharide or polysaccharide?

Monosaccharide (e.g., glucose) because it can be used directly without prior hydrolysis.

Describe the effect of temperature on respiration rate.

Rate rises with temperature up to an optimum; above the optimum, enzyme denaturation causes a sharp decline.

How does pH deviation from optimum affect respiratory enzymes?

Alters ionic and hydrogen bonds, changing enzyme conformation and lowering activity; extreme pH causes denaturation.

Why does oxygen availability influence only aerobic respiration?

Oxygen is the final electron acceptor in the ETC; without it, oxidative phosphorylation, the Krebs cycle and link reaction cease.

What happens to water availability when respiration slows down?

Low water impairs enzyme function, reducing respiration rate. Less water for hydrolysis

Compare respiration rates between active and dormant cells.

Active (growing) cells respire faster due to higher ATP demand; dormant cells respire slowly.

What appearance can mitochondria have in micrographs depending on the section plane?

They may look rod-shaped or circular.