GCSE Biology: Cell Structure and Organisation Revision Guide

Cell structure and organisation is a fundamental topic in GCSE Biology, appearing across AQA, Edexcel, and OCR specifications. Understanding cells properly sets you up for success in other topics like disease, respiration, and photosynthesis. Let’s break down everything you need to know.

The Two Types of Cells

All living organisms are made of one of two cell types: prokaryotic (bacteria) or eukaryotic (animals, plants, fungi, protists). Know the difference—it comes up regularly in exams.

Eukaryotic Cells

These have a true nucleus containing genetic material and are generally larger and more complex. Both animal and plant cells are eukaryotic, but they have key differences.

Prokaryotic Cells

Bacteria are prokaryotic. They’re smaller, simpler, and lack a true nucleus. Their DNA floats freely in the cytoplasm in a region called the nucleoid.

Animal Cell Organelles (What You Must Know)

Nucleus:

Contains genetic material (DNA) organised into chromosomes
Controls cellular activities
Surrounded by a double membrane called the nuclear envelope

Cytoplasm:

Jelly-like substance where chemical reactions occur
Contains dissolved nutrients and salts

Cell membrane:

Controls what enters and leaves the cell
Selectively permeable

Mitochondria:

Site of aerobic respiration
Release energy from glucose
Cells that need lots of energy (like muscle cells) have more mitochondria

Ribosomes:

Site of protein synthesis
Found in the cytoplasm or attached to rough endoplasmic reticulum
Read the genetic code and assemble amino acids into proteins

Additional Plant Cell Structures

Plant cells have everything animal cells have, plus three extra structures:

Cell wall:

Made of cellulose
Provides structural support
Fully permeable (unlike the cell membrane)

Permanent vacuole:

Contains cell sap (a solution of sugars and salts)
Maintains internal pressure to keep the cell rigid
Helps support the plant

Chloroplasts:

Site of photosynthesis
Contain chlorophyll, which absorbs light energy
Only in green parts of plants (not roots)
More in upper leaf cells where light reaches

Bacterial Cell Structure

Bacteria (prokaryotic cells) have:

Chromosomal DNA: Single circular chromosome floating in cytoplasm
Plasmids: Small rings of extra DNA (can be transferred between bacteria)
Cell wall: Different structure to plant cell walls
Cell membrane
Ribosomes: Smaller than eukaryotic ribosomes
Sometimes: Flagella (tail for movement) or Capsule (protective slime layer)

Exam tip: Questions love asking what bacteria lack compared to eukaryotic cells. Answer: mitochondria, chloroplasts, and a true nucleus.

Specialised Cells

Cells become specialised through a process called differentiation. They develop specific features that help them perform particular functions.

Animal Specialised Cells

Sperm cells:

Long tail (flagellum) for swimming
Lots of mitochondria for energy
Acrosome contains enzymes to digest egg membrane
Haploid nucleus (half the genetic information)

Nerve cells (neurons):

Long axon to transmit electrical impulses over distance
Branched endings (dendrites) to connect with other neurons
Myelin sheath insulates and speeds up impulse transmission

Muscle cells:

Contain protein fibres that can contract
Lots of mitochondria for energy during contraction
Can store glycogen as an energy reserve

Red blood cells:

Biconcave disc shape increases surface area for oxygen absorption
No nucleus to maximise space for haemoglobin
Haemoglobin binds to oxygen

Plant Specialised Cells

Root hair cells:

Long extension increases surface area for water absorption
Thin cell wall for easy diffusion
Lots of mitochondria for active transport of minerals

Xylem cells:

Transport water and minerals up the plant
Hollow tubes (dead cells) with no end walls
Walls strengthened with lignin

Phloem cells:

Transport sugars (dissolved food) around plant
Sieve plates with small holes between cells
Companion cells alongside provide energy

Cell Organisation (The Hierarchy)

Living things are organised in levels of increasing complexity. Learn this order:

Organelles (e.g., nucleus, mitochondria)
Cells (e.g., muscle cell, root hair cell)
Tissues (groups of similar cells, e.g., muscle tissue, epithelial tissue)
Organs (groups of tissues working together, e.g., heart, stomach, leaf)
Organ systems (groups of organs, e.g., digestive system, circulatory system)
Organism (the whole plant or animal)

Exam questions often ask you to put these in order or explain the difference between a tissue and an organ.

Common Exam Questions

“Explain how [specialised cell] is adapted to its function” Pick 2-3 features and explain how each helps the cell do its job. Use this structure:

Feature → Function → Benefit

Example: “Root hair cells have a long extension which increases surface area, allowing more water to be absorbed from the soil.”

“Compare animal and plant cells” Give similarities and differences:

Both have: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
Only plant cells have: cell wall, chloroplasts, permanent vacuole

“Describe the function of [organelle]” Keep it simple and specific. For mitochondria: “The site of aerobic respiration, which releases energy from glucose.”

Microscopy Basics

You need to know how to use a light microscope and calculate magnification.

Magnification formula: Magnification = Image size ÷ Real size

Or rearranged:

Image size = Magnification × Real size
Real size = Image size ÷ Magnification

Units matter! Convert everything to the same unit (usually micrometres, μm) before calculating.

1 mm = 1000 μm 1 cm = 10,000 μm

Revision Strategy

Draw and label diagrams: Animal cell, plant cell, bacterial cell from memory
Create comparison tables: What’s in each cell type?
Make flashcards: One organelle per card with structure and function
Practice calculations: Magnification questions appear frequently
Learn the hierarchy: Organelles → Cells → Tissues → Organs → Systems → Organism
Understand, don’t just memorise: Why does a muscle cell need lots of mitochondria?

This topic connects to almost everything else in GCSE Biology, so getting it solid now pays off throughout your course. UpGrades can help you test your understanding with targeted questions on cell structure and specialised cells, ensuring you’re exam-ready.