AeroLab Reading room

Biology / A2 level

Energy and respiration

ATP hydrolysis can be coupled to cellular work, while respiration regenerates ATP using energy transferred from substrates.

Learning objectives

The big idea

ATP hydrolysis can be coupled to cellular work, while respiration regenerates ATP using energy transferred from substrates. Glycolysis occurs in the cytoplasm; in eukaryotes, the link reaction, Krebs cycle and oxidative phosphorylation involve mitochondria.

Reduced carriers supply electrons to an electron-transport chain. Electron transfer supports proton movement across the inner membrane, and ATP synthase couples proton return to ATP production. Oxygen is the final electron acceptor in aerobic respiration; actual ATP yield depends on biological conditions rather than one universal fixed total.

Equations and relationships

RQ = carbon dioxide produced / oxygen consumed

Use comparable amounts or gas volumes under matching conditions.

Worked example

A sample releases 8 cm³ CO₂ while consuming 10 cm³ O₂. Find respiratory quotient.

Follow the solution

RQ=CO₂ produced/O₂ consumed=8/10=0.8, using volumes measured under comparable conditions.

Investigate and explain

Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.

No exact PhET model is claimed for this topic. Use diagrams and supplied-data reasoning instead.

Open the interactive investigation

Check your understanding

1. Where does glycolysis occur in a eukaryotic cell?

  1. Mitochondrial matrix only
  2. Cytoplasm
  3. Chloroplast thylakoid
Check the answer and reasoning

Cytoplasm

Glycolysis occurs in the cytoplasm and does not itself require a mitochondrion.

2. A sample releases 8 cm³ CO₂ while consuming 10 cm³ O₂. Find respiratory quotient.

  1. 1.25
  2. 18
  3. 0.8
Check the answer and reasoning

0.8

RQ=CO₂ produced/O₂ consumed=8/10=0.8, using volumes measured under comparable conditions.

3. Does oxygen directly power every reaction in glycolysis?

  1. No
  2. Yes
  3. Only in animals
Check the answer and reasoning

No

Oxygen accepts electrons at the end of the aerobic transport chain; glycolysis has a separate set of reactions.