SEC G3 Combined Science Biology component K327/K328
B1: Cell Structure and Organisation
Connect named plant and animal cell structures to their functions and to specialised-cell adaptations.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Cell structure is learned by linking each visible feature to its function, then using those links to compare cell types and explain specialised cells.
Plant and animal cell structures
The cell membrane controls movement into and out of the cell, cytoplasm is the site of many reactions, and the nucleus contains genetic material that controls cell activities. Vacuoles store water and dissolved substances: a plant cell typically has one large sap-filled vacuole that helps maintain turgor, while an animal cell may have small temporary vacuoles.
A cellulose cell wall supports a plant cell and helps it resist bursting. Chloroplasts contain chlorophyll and absorb light for photosynthesis. Compare only structures relevant to the given cell: not every plant cell is photosynthetic, and animal cells do not have cell walls or chloroplasts.
Microscopy, mitochondria, and ribosomes
Use prepared slides or temporarily stained fresh material under a light microscope, beginning at low power before centring and increasing magnification. Identify only structures that the image or specimen can resolve.
Mitochondria are sites of aerobic respiration, and ribosomes make proteins. They are identified from diagrams and electron micrographs because an ordinary school light microscope does not resolve their fine detail clearly.
Specialised cells
A muscle cell has many mitochondria to support energy transfer for contraction. A root hair cell has a long extension that increases membrane area for water and ion uptake.
A red blood cell lacks a nucleus, leaving more internal space for haemoglobin and oxygen transport. An adaptation answer must connect a named structure to the function it improves.
Formulae and relationships
This chapter is assessed mainly through models, field patterns and explanations. Build the causal chain before adding any calculation.
Worked examples
Example 1: A cell has a cell wall, large vacuole, and many chloroplasts. Identify it and explain two features.
- Cell wall and large vacuole indicate a plant cell.
- Many chloroplasts indicate a photosynthetic role.
- The wall supports the cell and chloroplasts absorb light energy.
Answer: It is a photosynthetic plant cell, such as a palisade cell.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Explain Plant and animal cell structures with the named terms, evidence, and causal links kept distinct.
- Use Microscopy, mitochondria, and ribosomes to interpret the evidence given and justify each conclusion.
- Apply Specialised cells to a new example, then check the conclusion against the information given.
Official outcome coverage
K327 B1: 4 mapped outcomes, references B1(a), B1(b), B1(c), B1(d). Check the official K327 syllabus.
K328 B1: 4 mapped outcomes, references B1(a), B1(b), B1(c), B1(d). Check the official K328 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Use a light microscope to observe cells, draw clear single lines, label familiar structures, state magnification, and measure to the nearest millimetre where required. Distinguish what is visible from functions inferred from the official cell model.
Exam traps and retrieval check
Avoid these traps
- Saying every plant cell has chloroplasts.
- Giving the cell wall as the selective boundary.
- Claiming ribosomes are clearly visible with a school light microscope.
Check from memory
Where are proteins made?
At ribosomes.
What is the cell membrane's role?
It controls movement of substances into and out of the cell.
Why does a root hair cell have an extension?
To increase surface area for absorption.
Official Combined Science scope
This shared Combined Biology owner serves both K327 and K328. Named plant and animal cell structures, mitochondria, ribosomes, microscopy, cell comparison, and prescribed specialised cells.