2.2Structures and Functions in Living Organisms

Cell structure — Edexcel Modular - OL Revision Notes & Topical Questions

10 min read 13 parts Lesson 2 of 12 1 quiz

📚 Edexcel Modular - OL Hub / Topical Revision

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Lesson summary

Cell structure Edexcel O Level Modular Biology notes: describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole1 mm = 1000 µm; 1 µm = 1000 nm.Prokaryotes have 70S ribosomes, eukaryotes 80S in cytoplasm.…

Viruses are acellular
Cell structure Edexcel O Level Modular Biology: what to do next
Magnification
Resolution
Cell fractionation
Eyepiece graticule

Section 1 of 13Process & sequence

Name the cell part shown.

State whether it is in plant cells, animal cells or both.

Give its structure in one line.

Give its function in one line.

Link structure to function with "so that".

Name the part
Where found
Structure
Function

Section 2 of 13Keep going

Cell structure Edexcel O Level Modular Biology: what to do next

These Cell structure Edexcel O Level Modular Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Cell structure Edexcel O Level Modular Biology understanding with the practice questions below, then reread any Cell structure Edexcel O Level Modular Biology point you were unsure about before moving on.

Practice: Cell structure Edexcel O Level Modular Biology practice questions

Previous lesson: 2.1 Level of organisation — Notes

Next lesson: 2.3 Biological molecules — Notes

Course: Edexcel Modular - OL — all units

Official syllabus: Pearson Edexcel International GCSEs

Section 3 of 13Specialised cells and differentiation

Cells in multicellular organisms become specialised for particular jobs by differentiation, which means they develop a shape and organelles suited to their function.

Specialised cells and differentiation

Examples: a red blood cell (no nucleus, haemoglobin), a root hair cell (extension for absorption), a palisade cell (chloroplasts), a nerve cell (long axon), a sperm (tail, many mitochondria).

Specialised cells are organised into tissues, organs and organ systems.

Section 4 of 13Stem cells

A stem cell is an undifferentiated cell that can divide by mitosis an unlimited number of times. When a stem cell divides, the new cells may remain undifferentiated (and divide again) or differentiate into specialised cells. Undifferentiated cells have not specialised for a particular function.

	Embryonic stem cells	Adult stem cells
Source	Early embryo	Bone marrow and other tissues
Can become	Almost any cell type	Limited range of cell types
Main issue	Ethical objection, since embryos are a potential human life	Limited range; if donor cells are used they may be rejected

Rejection happens because antigens on donor-derived cells differ from the patient's own, which is why using stem cells from the patient is better.

Section 5 of 13Uses in medicine

Many blood conditions can be treated using stem cells from bone marrow: red blood cells for anaemia (blood unable to carry enough oxygen), white blood cells (phagocytes and lymphocytes) in patients with reduced immunity, and platelets for clotting problems.

Uses in medicine

Research aims to grow replacement tissue for damaged organs, nerve injuries and diabetes.

Advantages: they could repair damaged tissue, reduce transplant waiting lists, and enable testing of drugs.

Disadvantages: ethical objections, risk of tumours, risk of rejection or transfer of viruses from donors, and cost.

Section 6 of 13Specialised cells, tissues and organs

Cell	Specialised feature	Function
Red blood cell	Biconcave, no nucleus, haemoglobin	Carry oxygen
Root hair cell	Long thin extension	Absorb water and ions
Palisade cell	Many chloroplasts	Photosynthesis
Neurone	Long axon, branched ends	Carry electrical impulses
Sperm	Tail, many mitochondria, enzyme in head	Swim to and enter the egg
Egg cell	Large, food store	Nourish the early embryo

A tissue is a group of similar cells working together (muscle tissue), an organ is a group of tissues forming a structure with a function (the stomach contains muscle, glandular and epithelial tissue), and an organ system is a group of organs (the digestive system).

Specialised cells, tissues and organs

A multicellular organism is made up of organ systems working together.

Stem cells in plants are found in meristems at the tips of roots and shoots,

where they divide to allow growth and can differentiate into xylem, phloem and other tissues,
which is why cuttings can regrow whole plants.

Therapeutic cloning is the creation of embryonic stem cells genetically identical to a patient to avoid rejection,

which raises further ethical questions.

Section 7 of 13Why cells differentiate: link to exam questions

In an exam you may be given an unfamiliar cell and asked to explain how its structure suits its function.

Use the formula: structure, effect, function.

For example, a ciliated epithelial cell has hair-like cilia that beat to move mucus, so dust and bacteria are swept out of the airway.

A muscle cell has many mitochondria to release energy for contraction.

A white blood cell is flexible with a large lobed nucleus, so that it can squeeze through capillary walls.

Each feature must be linked to a function for full marks.

Section 8 of 13Compare

Organelles – structure and function
Organelle	Membrane	Structure	Function	Found in	Seen with
Nucleus	Double (envelope with pores)	Chromatin, nucleolus	Contains DNA; controls cell; makes rRNA	Eukaryotes	Light microscope
Rough ER	Single	Cisternae with 80S ribosomes	Protein synthesis and transport	Eukaryotes	Electron microscope
Smooth ER	Single	Cisternae, no ribosomes	Lipid and steroid synthesis	Eukaryotes	Electron microscope
Golgi body	Single	Stack of flattened sacs + vesicles	Modifies, packages proteins; makes lysosomes	Eukaryotes	Electron microscope
Mitochondrion	Double; inner folded (cristae)	Matrix, 70S ribosomes, circular DNA	Aerobic respiration – ATP	Eukaryotes	EM (just visible LM)
Chloroplast	Double + thylakoids	Grana, stroma, starch, 70S ribosomes	Photosynthesis	Plants, algae	Light microscope
Ribosome	None	Two subunits; 80S (cytoplasm) or 70S	Translation	All cells	Electron microscope
Lysosome	Single	Vesicle of hydrolytic enzymes	Digests old organelles, pathogens	Animal cells	Electron microscope
Centriole	None	Microtubules in 9 triplets	Spindle formation	Animal cells	Electron microscope

Section 9 of 13Worked examples

Define a stem cell. [2]2 marks
Give one advantage and one disadvantage of adult stem cells. [2]2 marks
Why do embryonic stem cells raise ethical issues? [1]1 mark

Section 10 of 13Key terms

Term	Meaning
Differentiation	Development of a cell into a specialised type.
Stem cell	Undifferentiated cell that can divide repeatedly.
Undifferentiated	Not specialised for any particular function.
Mitosis	Cell division producing identical cells.
Antigen	Molecule on a cell surface that the immune system recognises.

Section 11 of 13Syllabus checklist

Syllabus points

describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole

describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole

know the similarities and differences in the structure of plant and animal cells 2.5B explain the importance of cell differentiation in the development of specialised cells 2.6B understand the advantages and disadvantages of using stem cells in medicine

Section 12 of 13Command terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Section 13 of 13Exam technique

Saying stem cells are specialised.

Saying embryonic cells cannot differentiate.

Saying rejection occurs with a patient's own cells.

Saying adult stem cells can form any cell type.

Last updated: 18 October 2026