Mitochondria are often called the powerhouses of the cell, and for good reason. They are the site of aerobic respiration, where most of a cell’s ATP—its usable chemical energy—is produced. In IB Biology, mitochondria appear repeatedly across topics such as cell structure, metabolism, genetics, and bioenergetics. Having a strong understanding of their function helps students answer a wide range of exam questions, which is why many students begin their cell biology revision with organelles. This approach is recommended in How to Pass IB Biology SL Exams (https://www.revisiondojo.com/blog/how-to-pass-ib-biology-sl-exams-proven-study-strategy) , where building foundational knowledge is key to exam confidence.
Mitochondria as the Site of ATP Production
The primary function of mitochondria is ATP generation through aerobic respiration. ATP (adenosine triphosphate) is the energy currency of the cell and fuels nearly all biological processes, including:
- Active transport
- Muscle contraction
- Protein synthesis
- DNA replication
- Cell division
Mitochondria produce ATP mainly during the final stages of cellular respiration: the Krebs cycle and oxidative phosphorylation. Understanding this process is essential for metabolic pathways, and many students find that mastering the respiration equation makes the entire topic easier. This equation is clearly explained in the earlier article based on your list and also aligns with the content depth described in IB Biology HL vs SL: 7 Key Differences (https://www.revisiondojo.com/blog/ib-biology-hl-vs-sl-difficulty-7-key-differences-every-ib-student-must-know) .
Structure Supporting Function
Mitochondria have several key structural features that enable efficient ATP production:
- Outer membrane: protects the organelle and controls entry/exit of substances.
- Inner membrane: folded into cristae to increase surface area for electron transport chains.
- Matrix: contains enzymes for the Krebs cycle.
- Own DNA and ribosomes: support self-replication and protein synthesis.
This high surface area-to-volume ratio allows many electron transport chains to function simultaneously, maximizing ATP output. The relationship between structure and function is a common feature in Paper 2 extended-response questions, and building these kinds of explanations is easier when students understand how IB exam command terms work. Resources like How to Understand IB Biology Command Terms (https://www.revisiondojo.com/blog/how-to-understand-ib-biology-command-terms-for-exam-success) help students write clearer, more accurate responses.
Mitochondria and Aerobic Respiration
Mitochondria host the final stages of aerobic respiration:
- Link reaction
- Krebs cycle
- Electron transport chain (ETC)
- Oxidative phosphorylation
These stages together produce far more ATP than anaerobic respiration. This efficiency is why mitochondria are abundant in energy-demanding cells such as muscle cells, neurons, and sperm.
When interpreting respiration-related graphs, such as oxygen consumption or CO₂ production, students benefit from techniques taught in IB Biology Paper 1B: Data-Based Questions Explained (https://www.revisiondojo.com/blog/ib-biology-paper-1b-data-based-questions-explained-for-beginners) .
Mitochondria’s Role Beyond ATP
Although ATP production is their primary function, mitochondria also:
- Regulate the cell cycle
- Assist in heat production (thermogenesis)
- Help initiate apoptosis (programmed cell death)
- Manage calcium storage
- Contribute to steroid synthesis
These additional roles make mitochondria essential for maintaining overall cellular homeostasis.
Mitochondria in Evolution
Mitochondria originated through endosymbiosis—the idea that an ancestral prokaryote was engulfed by another cell and became a permanent resident. This explains why mitochondria have:
- Their own circular DNA
- 70S ribosomes
- Double membranes
- The ability to replicate independently
This concept often appears in Paper 2 and Paper 3 questions, especially those involving cell biology and evolution.
Mitochondria in the IB Biology IA
Experiments involving respiration and mitochondria are popular IA topics, including:
- Measuring the rate of respiration in yeast
- Investigating temperature effects on respiration
- Studying oxygen consumption in plants or organisms
- Analyzing CO₂ production under different conditions
For support designing IA methods, students often use IB Biology IA: 8 Essential Tips to Score a 7 (https://www.revisiondojo.com/blog/ib-biology-ia-8-essential-tips-to-score-a-7-expert-guide) and the Sample IB Biology IA Example (https://www.revisiondojo.com/blog/sample-ib-biology-ia-a-step-by-step-example-to-guide-your-own-investigation) .
FAQ
Why do mitochondria have their own DNA?
Because they evolved from free-living bacteria through endosymbiosis.
Do all cells have mitochondria?
No. Some cells like mature red blood cells lack them.
Why do muscle cells contain many mitochondria?
They require large amounts of ATP for contraction.
RevisionDojo Call to Action
If you want to master cell biology, metabolism, and every major IB Biology topic, RevisionDojo gives you the structure, clarity, and strategies you need to succeed—whether preparing for exams or designing your IA.
