2.4.3Inquiry Process
Adaptations of Mitochondria and Chloroplasts — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 57 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 6Mitochondrial Structure
Mitochondria carry out the aerobic stages of cell respiration.
Double membrane
- Double membrane The outer membrane is smooth and the inner membrane is folded, which separates the intermembrane space from the matrix.
Cristae
- Cristae Folds of the inner membrane greatly increase the surface area available for electron transport chains and ATP synthase.
Small intermembrane space
- Small intermembrane space A small volume allows a steep proton gradient to build up quickly.
Matrix
- Matrix A fluid containing enzymes for the Krebs cycle and link reaction, plus DNA and 70S ribosomes.
| Feature | Adaptation for |
|---|---|
| Cristae | Large surface for ATP synthesis |
| Small intermembrane space | Rapid proton gradient |
| Matrix enzymes | Krebs cycle |
| Own ribosomes and DNA | Making some of own proteins |
Part 2 of 6Chloroplast Structure
Chloroplasts are the sites of photosynthesis.
Chloroplast Structure
Thylakoids
- Thylakoids Flattened sacs with a membrane carrying photosystems, electron carriers and ATP synthase for the light-dependent reactions.
Grana
- Grana Stacks of thylakoids that give a large surface area for light capture.
Thylakoid space
- Thylakoid space A small internal space where protons accumulate, creating a gradient.
Stroma
- Stroma A fluid containing Calvin cycle enzymes, DNA, 70S ribosomes and starch grains.
Part 3 of 6Comparing the Two
Proton pumping
- Proton pumping In mitochondria protons enter the intermembrane space, whereas in chloroplasts they accumulate inside the thylakoid space.
Energy source
- Energy source Mitochondria use energy from oxidising food molecules, while chloroplasts use light energy.
Shared features
- Shared features Both have double membranes, circular DNA, 70S ribosomes and ATP synthase.
Products
- Products Mitochondria produce ATP, carbon dioxide and water, while chloroplasts produce organic molecules and oxygen.
| Feature | Mitochondrion | Chloroplast |
|---|---|---|
| Inner structure | Cristae | Thylakoids and grana |
| Fluid | Matrix | Stroma |
| Process | Aerobic respiration | Photosynthesis |
Part 4 of 6Evidence of Shared Ancestry
1
Both organelles contain their own circular DNA, like prokaryotes.
2
They have 70S ribosomes that resemble those of bacteria.
3
They reproduce by dividing in a way that resembles binary fission.
4
The theory of endosymbiosis proposes that they derive from engulfed prokaryotes.
5
This explains why they have two membranes.
Part 5 of 6Worked Example
Question Explain how the folding of the inner mitochondrial membrane increases the rate of ATP production.
- Folding forms cristae, which increase the area of the inner membrane.
- Electron carriers and ATP synthase are embedded in this membrane, so a larger area holds more of them.
- More carriers and ATP synthase molecules mean more protons pumped and more ATP made per unit time.
Answer Cristae raise the surface area, so more ATP synthesis can happen at once.
Part 6 of 6Exam Checklist & Tips
2.4.3 – Key Points for the Exam
- Cristae Folds of the inner mitochondrial membrane.
- Matrix The fluid inside the inner membrane of a mitochondrion.
- Granum A stack of thylakoids in a chloroplast.
- Stroma The fluid surrounding thylakoids in a chloroplast.
- ATP synthase An enzyme that makes ATP using the flow of protons.
Common Mistakes
- Mixing up matrix and stroma.
- Saying grana are in mitochondria.
- Stating that protons accumulate in the stroma in chloroplasts.
- Saying mitochondria produce energy; they convert it into ATP.
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