2.5.4Inquiry Process
Examples of Specialised Cells — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 62 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.
Section 1 of 4Why Cells Specialise
Every specialised cell is a case study in how structure suits function.
Differentiation
- Differentiation Cells in a multicellular organism express only some of their genes,
- so each cell type makes particular proteins and develops a distinctive shape and set of organelles.
Division of labour
- Division of labour Because each cell type performs one task very efficiently, the whole organism works better than if every cell tried to do everything.
Structure fits function
- Structure fits function The visible features of a cell,
- such as shape, organelle number and surface area, can almost always be linked directly to the job it does.
Same genome
- Same genome Specialised cells in one organism carry the same DNA;
- the differences come from which genes are switched on, not from different genetic information.
Section 2 of 4Transport and Signalling Cells
Red blood cell
- Red blood cell A flexible biconcave disc with no nucleus gives a large surface area to volume ratio and room for haemoglobin,
- so oxygen is carried efficiently.
Neuron
- Neuron A long axon carries electrical impulses over distance, while many short dendrites receive signals from other cells at synapses.
Sperm cell
- Sperm cell A flagellum drives the cell forward, mitochondria in the midpiece supply ATP,
- and the acrosome holds enzymes that digest the egg's outer layers.
Egg cell
- Egg cell A large cytoplasm store feeds the early embryo, and a protective outer layer plus cortical granules help block entry of more than one sperm.
| Cell | Key feature | Function it serves |
|---|---|---|
| Red blood cell | Biconcave, no nucleus | Maximises haemoglobin content and diffusion |
| Neuron | Long axon, dendrites | Rapid impulse conduction and receiving signals |
| Sperm | Flagellum, acrosome | Motility and egg penetration |
Section 3 of 4Plant and Epithelial Cells
Root hair cell
- Root hair cell A long thin extension greatly increases surface area for absorbing water and mineral ions from the soil by osmosis and active transport.
Palisade mesophyll cell
- Palisade mesophyll cell Many chloroplasts packed in a tall cell near the leaf surface capture light for photosynthesis.
Xylem vessel
- Xylem vessel Dead, hollow, lignified cells joined end to end form a continuous tube for water transport with strong walls that resist collapse.
Ciliated epithelial cell
- Ciliated epithelial cell Cilia beat in coordinated waves to move mucus and trapped particles along the airway towards the throat.
Section 4 of 4Exam Checklist & Tips
2.5.4 – Key Points for the Exam
- Specialised cell A cell whose structure has become adapted, through differentiation, to carry out a particular function.
- Differentiation The process in which an unspecialised cell develops into a specific cell type by gene expression changes.
- Surface area to volume ratio The relationship that determines how fast a cell can exchange materials with its surroundings.
- Acrosome A vesicle at the head of a sperm containing digestive enzymes used at fertilisation.
- Axon The long extension of a neuron that conducts an impulse away from the cell body.
Common Mistakes
- Writing that specialised cells have different DNA; they have the same genes but express different ones.
- Describing a feature without linking it to its function, such as saying 'it has cilia' without stating what cilia do.
- Forgetting that mature red blood cells in mammals lack a nucleus, which is why they cannot divide.
- Confusing the root hair cell's job (absorption) with the xylem's job (transport).
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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.