Unit Overview
Energy and Respiration (AS Portion)
CIE A-Level BiologyΒ· 5 min read π n/a
1. Unit at a Glance
This unit follows a sequential learning arc: we start from the big picture of why organisms need energy, introduce the molecule that delivers usable energy to cells, then walk step-by-step through the first two stages of aerobic respiration that break down glucose to release energy.
Each sub-topic builds on the previous one: mastering these early stages is critical for understanding the later stages of aerobic respiration, anaerobic respiration and photosynthesis covered in subsequent units.
Core sub-topics in this unit:
Energy needs of living organisms
Introduces the types of work that require energy in living systems and the flow of energy through organisms.
β β± 3 min
ATP structure and role
Covers ATP's molecular structure and its function as the cell's immediate energy currency.
β β β± 4 min
Glycolysis
Breaks down the step-by-step process, location, inputs and net products of glycolysis.
β β β β± 6 min
Link reaction
Explains the conversion of pyruvate to acetyl CoA, its location, inputs and products.
β β β β± 5 min
2. Common Pitfalls
Wrong move:
Confusing ATP as a long-term energy store.
Why:
ATP is rapidly turned over in cells; it is not used for long-term energy storage.
Correct move:
Remember: ATP is an immediate energy currency, while fats/glycogen are the main long-term energy stores.
Wrong move:
Thinking glycolysis only occurs in aerobic respiration.
Why:
Glycolysis does not require oxygen, so it proceeds in all forms of respiration.
Correct move:
Note that glycolysis is the first step for both aerobic and anaerobic respiration pathways.
3. Quick Reference Cheatsheet
Concept | Key Summary |
|---|---|
Core energy needs | All organisms require energy for movement, active transport, synthesis, reproduction and homeostasis |
ATP hydrolysis reaction | |
Glycolysis location | Occurs in the cytoplasm of all prokaryotic and eukaryotic cells |
Glycolysis net yield (per glucose) | 2 ATP + 2 reduced NAD + 2 pyruvate |
Link reaction net yield (per glucose) | 2 acetyl CoA + 2 reduced NAD + 2 CO |
What's Next
Begin your study of this unit with the first sub-topic on energy needs of living organisms to build your foundational knowledge. Once you complete all four sub-topics in this unit, you will progress to the next unit covering the remaining stages of aerobic respiration and anaerobic respiration for CIE AS Biology.