College Board-Aligned Original Notes

AP Biology Unit 3 Topic 3: The processes of photosynthesis and cellular respiration

Photosynthesis captures energy into organic molecules, while cellular respiration transfers energy from organic molecules to ATP.

Unit 3: Cellular Energetics. College Board exam weighting listed for this unit: 12%-16% of exam score.

What to Know

Photosynthesis uses light reactions and the Calvin cycle to convert light energy into chemical energy stored in sugars.
Cellular respiration uses glycolysis, the Krebs cycle, and oxidative phosphorylation to harvest energy from organic molecules.
Electron carriers and proton gradients connect redox reactions to ATP production.
Always connect this topic back to the larger unit: Cellular Energetics.

Detailed Notes

The processes of photosynthesis and cellular respiration belongs to Unit 3: Cellular Energetics. Photosynthesis captures energy into organic molecules, while cellular respiration transfers energy from organic molecules to ATP. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Photosynthesis uses light reactions and the Calvin cycle to convert light energy into chemical energy stored in sugars. Cellular respiration uses glycolysis, the Krebs cycle, and oxidative phosphorylation to harvest energy from organic molecules. Electron carriers and proton gradients connect redox reactions to ATP production.

Model to use: Compare chloroplast and mitochondrial membranes by showing electron movement, proton pumping, and ATP synthase. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: For energy pathway questions, track matter and energy separately: carbon atoms, electrons, protons, ATP, and electron carriers. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Chemiosmosis

ATP production driven by proton movement through ATP synthase.

Electron transport chain

A series of membrane proteins that pass electrons and help build a proton gradient.

Calvin cycle

The photosynthetic pathway that fixes carbon dioxide into sugar-related molecules.

Glycolysis

The pathway that splits glucose into smaller molecules and produces some ATP and electron carriers.

Krebs cycle

A mitochondrial pathway that oxidizes carbon compounds and loads electron carriers.

Oxidative phosphorylation

ATP production powered by electron transport and a proton gradient during respiration.

Quick Practice

How would you explain The processes of photosynthesis and cellular respiration in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.