2.4.1Additional lessons
Cell Organelles — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 24 of 142
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 4Organelles and Compartments
Eukaryotic cell
- Eukaryotic cell Cells with a nucleus and membrane-bound organelles, which divide the cytoplasm into separate compartments.
Single membrane
- Single membrane Organelles such as the Golgi apparatus, lysosomes, vacuoles, vesicles and endoplasmic reticulum are bounded by one membrane.
Double membrane
- Double membrane The nucleus, mitochondria and chloroplasts are surrounded by two membranes.
Not membrane-bound
- Not membrane-bound Ribosomes have no membrane, and the cell wall, cytoskeleton and cytoplasm are not organelles.
Why it matters
- Why it matters Each compartment maintains its own conditions, so many reactions can occur at the same time without interfering.
Part 2 of 4Functions of Organelles
Functions of Organelles
Nucleus
- Nucleus Contains DNA and controls gene expression; transcription of DNA to mRNA takes place there.
Mitochondrion
- Mitochondrion Site of aerobic cell respiration, with a folded inner membrane that provides a large surface area.
Rough ER and ribosomes
- Rough ER and ribosomes Ribosomes on the rough endoplasmic reticulum make proteins for export or for membranes.
Golgi apparatus
- Golgi apparatus Modifies, sorts and packages proteins into vesicles for secretion or delivery.
Lysosome
- Lysosome Contains hydrolytic enzymes that digest worn-out organelles and material taken in by the cell.
Chloroplast
- Chloroplast Site of photosynthesis in plant cells, containing chlorophyll in thylakoid membranes.
| Organelle | Membranes | Main function |
|---|---|---|
| Nucleus | Double | Stores DNA, makes mRNA |
| Mitochondrion | Double | ATP production by aerobic respiration |
| Chloroplast | Double | Photosynthesis |
| Golgi apparatus | Single | Modifies and packages proteins |
| Lysosome | Single | Digests unwanted materials |
Part 3 of 4Advantages of Compartmentalisation
1
Enzymes and their substrates are held within one compartment, so their concentrations are high and reactions are faster.
2
Harmful substances are kept separate, for example digestive enzymes in lysosomes do not digest the rest of the cell.
3
Each compartment can maintain a suitable pH, such as the acidic interior of the lysosome.
4
Organelles can be increased or reduced in number and moved according to the needs of the cell.
5
Different pathways can proceed independently, such as protein synthesis on the rough ER while respiration occurs in mitochondria.
Part 4 of 4Exam Checklist & Tips
2.4.1 – Key Points for the Exam
- Organelle A specialised structure within a cell that carries out a particular function.
- Compartmentalisation Division of the cell into membrane-bound regions with different conditions and functions.
- Lysosome A membrane-bound sac containing digestive enzymes.
- Ultrastructure The fine detail of a cell visible with an electron microscope.
Common Mistakes
- Listing the cell wall and cytoplasm as membrane-bound organelles.
- Saying ribosomes have a membrane; they do not.
- Stating that mitochondria make energy; they release energy from food to make ATP.
- Describing the rough ER as the site of photosynthesis or respiration.
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.