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2.4.2Inquiry Process

Cell Compartmentalisation — IB Biology HL Revision Notes & Topical Questions

5 min read 6 parts Lesson 56 of 160

📚 IB Biology HL Hub / Topical Revision
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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.
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Part 1 of 6Benefits of Compartments

Compartmentalisation lets a large eukaryotic cell run many reactions efficiently.

Different conditions
  • Different conditions Each compartment can hold its own pH, enzymes and ion concentrations suited to the reactions inside it.
Concentration
  • Concentration Substrates and enzymes are gathered in a small volume, which raises the rate of reactions.
Isolation of harmful substances
  • Isolation of harmful substances Dangerous enzymes or toxic products are kept away from the rest of the cell.
Separation of pathways
  • Separation of pathways Opposing processes such as synthesis and breakdown can occur at the same time without interference.
AdvantageExample
Special pHLysosome interior is acidic
High concentrationEnzymes of Krebs cycle in the mitochondrial matrix
IsolationHydrolytic enzymes kept in lysosomes
GradientProton gradient across the inner mitochondrial membrane

Part 2 of 6Lysosomes

Lysosomes
Contents
  • Contents Hydrolytic enzymes that break down proteins, lipids, carbohydrates and nucleic acids.
Acidic interior
  • Acidic interior The enzymes work best at around pH 5, much lower than the cytoplasm, so leaked enzymes are less active.
Roles
  • Roles Digest material taken in by phagocytosis and recycle worn organelles.
Protection
  • Protection The membrane stops the enzymes from digesting the cell itself.

Part 3 of 6Membranes and Gradients

1
Mitochondria and chloroplasts have an inner membrane that separates two compartments.
2
Electron transport pumps hydrogen ions across the membrane into the smaller compartment.
3
A high concentration of protons builds up in the intermembrane space or thylakoid space.
4
Protons flow back through ATP synthase, driving ATP formation.
5
This process, chemiosmosis, depends on compartments being separated by a membrane that protons cannot cross freely.

Part 4 of 6Other Examples

Nucleus
  • Nucleus Separates transcription from translation, allowing time to process mRNA before translation.
Peroxisomes
  • Peroxisomes Contain enzymes that break down hydrogen peroxide, a harmful by-product of metabolism.
Vacuole
  • Vacuole Stores water, ions and pigments and maintains turgor in plant cells.
Golgi
  • Golgi Keeps protein modification separate from protein synthesis.

Part 5 of 6Worked Example

Question Explain why lysosomal enzymes would damage a cell if they were not separated from the cytoplasm, and how compartmentalisation protects it.

  1. Lysosomal enzymes are hydrolases that break down proteins, lipids, carbohydrates and nucleic acids.
  2. If they were free in the cytoplasm they would digest cell structures and macromolecules the cell needs.
  3. The lysosome membrane keeps them enclosed, and the acidic interior means any leaked enzymes work poorly at cytoplasmic pH.

Answer Compartmentalisation confines the digestive enzymes to the lysosome and so protects the rest of the cell.

Part 6 of 6Exam Checklist & Tips

2.4.2 – Key Points for the Exam

  • Compartmentalisation The division of a cell into membrane-bound regions with separate conditions and functions.
  • Lysosome An acidic organelle containing hydrolytic enzymes.
  • Proton gradient A difference in hydrogen ion concentration across a membrane that stores energy.
  • Chemiosmosis Production of ATP using energy of a proton gradient.

Common Mistakes

  • Saying compartments exist only to increase surface area.
  • Thinking lysosome enzymes work best at neutral pH.
  • Writing that prokaryotes have membrane-bound organelles.
  • Forgetting that separation allows different reactions to take place simultaneously.

Last updated:

Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.

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