Cell Structure, Specialised Cells and Magnification

CIE IGCSE Biology· 2.1, 2.2· 20 min read

1. Core: Eukaryotic Cell Structure★★☆☆☆⏱ 6 min

Eukaryotic cells (animal, plant, fungal) are complex cells with a nucleus and membrane-bound organelles. You must be able to identify and state the function of 8 key organelles for Core exams.

📘 Definition

Organelle

A specialised subcellular structure that performs a specific function inside a cell

Organelle	Found in animal cells?	Found in plant cells?	Function
Nucleus	Yes	Yes	Controls cell activities, stores genetic material
Cytoplasm	Yes	Yes	Gel-like substance where most chemical reactions occur
Cell membrane	Yes	Yes	Partially permeable, controls movement of substances in/out of cell
Mitochondria	Yes	Yes	Site of aerobic respiration, releases energy for the cell
Ribosomes	Yes	Yes	Site of protein synthesis
Cell wall	No	Yes (cellulose)	Provides rigid structural support for the cell
Chloroplasts	No	Yes (green plant parts only)	Site of photosynthesis, contains light-absorbing chlorophyll
Permanent vacuole	No	Yes	Filled with cell sap, maintains cell turgidity

📐 Worked Example

Name three organelles found only in plant cells, and state the function of each.

1
1. Identify plant-exclusive organelles from the table: cell wall, chloroplasts, permanent vacuole.
2
1. State each function: Cell wall provides rigid structural support made of cellulose. Chloroplasts carry out photosynthesis to make glucose for the plant. Permanent vacuole stores cell sap and keeps the cell turgid.

Exam tip:

You will be asked to label organelles on unannotated cell diagrams in exams, so practice drawing and labelling animal and plant cells regularly.

2. Core: Prokaryotic vs Eukaryotic Cells★★☆☆☆⏱ 4 min

Prokaryotic cells (bacteria) are smaller and simpler than eukaryotic cells, with no nucleus or membrane-bound organelles. You must know 3 key differences between the two cell types for Core exams.

📘 Definition

Prokaryotic cell

A simple, single-celled organism with no nucleus or membrane-bound organelles

Feature	Eukaryotic cell	Prokaryotic cell
Size	10-100 μm	0.1-5 μm
Genetic material	Stored inside a nucleus	Found as a single chromosomal loop in cytoplasm, plus small plasmids
Membrane-bound organelles	Present (e.g. mitochondria, chloroplasts)	Absent
Cell wall	Only in plant/fungal cells	Always present (not made of cellulose)

📐 Worked Example

A student observes a cell that is 2 μm wide, has no nucleus, and contains plasmids. State if this cell is prokaryotic or eukaryotic, and give two reasons for your answer.

1
1. Match observed features to cell type characteristics: 2 μm size falls in the prokaryotic size range, no nucleus and plasmids are unique to prokaryotes.
2
1. Final answer: Prokaryotic. Reason 1: No nucleus is present. Reason 2: It contains plasmids, which are not found in eukaryotic cells.

3. Core: Specialised Cells★★★☆☆⏱ 7 min

Specialised cells have unique structural adaptations that allow them to perform one specific role in an organism. For Core exams, you must know adaptations and function links for 4 cell types: ciliated epithelial cell, sperm cell, root hair cell, and palisade mesophyll cell.

📘 Definition

Specialised cell

A cell with structural modifications adapted to carry out a specific function in an organism

Ciliated epithelial cell: Hair-like cilia move mucus and trapped particles out of the respiratory tract
Sperm cell: Long tail for swimming, many mitochondria for energy, acrosome with enzymes to digest egg membrane
Root hair cell: Long hair projection increases surface area, thin cell wall reduces absorption distance, many mitochondria for active transport of mineral ions
Palisade mesophyll cell: Many chloroplasts for photosynthesis, packed closely at the top of leaves to absorb maximum light

📐 Worked Example

Explain how a palisade mesophyll cell is adapted for its function in a leaf.

1
1. State the cell's core function: Palisade mesophyll cells carry out photosynthesis to make glucose for the plant.
2
1. Name key adaptations: Packed with many chloroplasts, located at the top surface of the leaf, regular shape allows close packing.
3
1. Link adaptations to function: Many chloroplasts contain chlorophyll to absorb light energy. Position at the top of the leaf maximises light exposure. Close packing allows more cells to fit in the photosynthetic layer.

Exam tip:

Always link adaptations to function in exam answers: just naming an adaptation only gets 1 mark, explaining how it helps the cell do its job gets the second mark.

4. Core: Magnification Calculations★★★☆☆⏱ 6 min

You will be asked to calculate magnification, image size, or actual size of cells in every exam series. Always convert all units to micrometres (μm) before calculating, as this avoids unit errors. The formula is:

M = \frac{I}{A}

Where $M$ = magnification (no units), $I$ = image size, $A$ = actual size of the specimen. You can rearrange the formula to find $I = M \times A$ or $A = \frac{I}{M}$ .

📐 Worked Example

An image of a red blood cell is 5 mm wide. The actual width of the red blood cell is 7 μm. Calculate the magnification of the image.

1
1. Convert units to match: Image size $I$ = 5 mm = $5 \times 1000$ = 5000 μm. Actual size $A$ = 7 μm.
2
$2. Substitute into formula: M = \frac{5000}{7}$
3
1. Calculate and round to a reasonable whole number: $M \approx 714$ (no units required, you may add an x before the number if requested)

Exam tip:

You will always get 1 mark for correct unit conversion even if your final calculation is wrong, so always write down your conversion step clearly for the examiner.

5. Extended Only: Additional Content★★★★☆Extended only⏱ 5 min

Extended learners must master two additional skills: describing prokaryotic plasmid function, and calculating actual size from scale bars on cell diagrams. Plasmids are small loops of extra DNA in bacteria that carry accessory genes (e.g. antibiotic resistance) separate from the main chromosomal loop.

📐 Worked Example

A scale bar on a cell diagram is 1 cm long and labelled 10 μm. The image of a bacterial cell on the diagram is 3 cm wide. Calculate the actual size of the bacterial cell.

1
1. Calculate magnification from the scale bar first: 1 cm image = 10 μm actual. Convert 1 cm to μm: 1 cm = 10000 μm. Magnification $M = \frac{10000}{10} = 1000$ .
2
1. Convert image size of the cell to μm: 3 cm = 30000 μm.
3
$3. Rearrange formula to find actual size: A = \frac{I}{M} = \frac{30000}{1000} = 30 \mu m$

6. Common Pitfalls

Wrong move:

Stating animal cells have a cell wall

Why:

Animal cells only have a cell membrane, only plant cells have a rigid cellulose cell wall.

Correct move:

Memorise the three plant-exclusive organelles: cell wall, chloroplasts, permanent vacuole.

Wrong move:

Mixing units in magnification calculations (using mm and μm together)

Why:

Units must be identical to get an accurate ratio for magnification.

Correct move:

Always convert all values to micrometres (μm) first, and write down your conversion step explicitly.

Wrong move:

Naming specialised cell adaptations without linking to function

Why:

Exam questions ask for explanations, which require a clear link between structure and role.

Correct move:

Use the structure: [Adaptation] → this allows [function], e.g. 'Long tail allows sperm to swim to the egg'.

Wrong move:

Stating prokaryotic cells have a nucleus or mitochondria

Why:

Prokaryotic cells have no membrane-bound organelles, their genetic material is free in the cytoplasm.

Correct move:

Use the mnemonic: Pro = before, karyon = nucleus, so prokaryotes evolved before cells had nuclei.

Wrong move:

Giving units for magnification (e.g. writing 700 μm instead of x700)

Why:

Magnification is a ratio of two lengths, so it has no units.

Correct move:

Omit units for magnification answers, add an x only if explicitly requested in the question.

Wrong move:

Confusing chromosomal DNA and plasmids in prokaryotes (Extended only)

Why:

Chromosomal DNA is the main genetic material, plasmids are small extra loops carrying accessory genes like antibiotic resistance.

Correct move:

Name both types of DNA when asked to describe prokaryotic genetic material for Extended questions.

7. Quick Reference Cheatsheet

Topic	Core Key Points	Extended Extra Points
Cell Organelles	Memorise 8 organelles, their location and function	No extra content, same as Core
Prokaryotes vs Eukaryotes	Know 3 key differences between cell types	Describe plasmid function in bacterial cells
Specialised Cells	Know 4 cell types and adaptation-function links	Know 2 extra cells (red blood cell, nerve cell) adaptations
Magnification	Use $M = I / A$ , convert all units to μm first	Calculate actual size from diagram scale bars

8. Frequently Asked

Do Core learners need to memorise all organelle functions?

Yes, Core exams regularly ask 1-2 mark questions to label organelles and state their functions, so you must memorise all 8 listed in this guide.

What units should I use for magnification calculations?

Always convert all values to micrometres (μm) before calculating: 1 mm = 1000 μm. Magnification itself has no units, you can add an 'x' before the number if requested.

How many marks do I get for adaptation questions?

You get 1 mark for naming an adaptation, and 1 extra mark for linking it to the cell's function, so always include both parts in your answer.

Going deeper

Official SyllabusCIE IGCSE Biology 0610 SpecificationRefer to section 2 for full Unit 2 outcomes

What's Next

Now you have mastered cell structure, specialised cells and magnification, you are ready to move on to the next topics in Unit 2: movement of substances into and out of cells, including diffusion, osmosis and active transport. This foundational cell knowledge is required for all later syllabus topics, including plant nutrition, animal transport, and inheritance. Practice magnification calculations regularly, as they appear in almost every exam paper across both Core and Extended tiers. Extended learners should spend extra time practicing scale bar questions, which are common in Paper 4 structured exams.