IB Biology SL A2.2 Cell structure Questions

Practise IB Biology SL A2.2 with questions on cell theory, prokaryotic and eukaryotic cells, organelles, microscopy and structure–function links.

117 questions in this syllabus scope, with question parts counted together.

Exam analysis

SL · 2010–2025

Papers with this topic87 / 141in the analysed sample

Latest appearanceNovember 2025

Tagged question parts133

Paper types5

Most tested objectives

A2.2.5—Prokaryote cell structure35 papers
A2.2.2—Microscopy skills30 papers
A2.2.10—Cell identification in micrographs12 papers
A2.2.1—Cells as basic structural unit8 papers
A2.2.6—Eukaryote cell structure8 papers

Common question formats

Definition or recall
Graph interpretation
Process explanation
Calculation
Evaluation
Structured response

Recent exam appearances

November 2025Paper 2 SL · TZ1Q3(b), 3(c), 3(d)[ 3 ]

November 2025Paper 1B SL · TZ3Q1(a), 1(b)(i), 1(b)(ii), 1(c)[ 5 ]

November 2025Paper 1A SL · TZ1Q8[ 1 ]

141 papers analysed · Tagging incomplete

Exam points

State cell theory and identify evidence that living cells are basic units arising from pre-existing cells.
Calculate magnification or actual cell size, calibrate eyepiece graticules and report microscope measurements with correct units.
Compare light and electron microscopy using resolution, preparation and the ultrastructure visible in each.
Identify structures common to cells, compare prokaryotic and eukaryotic organization, and link prokaryotic structures such as plasmids, pili, flagella or ribosomes to function.
Relate eukaryotic organelle compartmentalization and plant, animal or fungal cell features to structure and function.
Explain how unicellular organisms carry out nutrition, response, homeostasis, growth and reproduction in one cell.
Explain atypical cells, identify cells or organelles in micrographs, and draw or label unshaded cell diagrams with proportions and scale.

Covered syllabus points

A2.2.1—Cells as basic structural unit A2.2.2—Microscopy skills A2.2.3—Developments in microscopy A2.2.4—Structures common to all cells A2.2.5—Prokaryote cell structure A2.2.6—Eukaryote cell structure A2.2.7—Processes of life in unicellular organisms A2.2.8—Differences in eukaryotic cells A2.2.9—Atypical cell structure A2.2.10—Cell identification in micrographs A2.2.11—Drawing and annotation

Exam points

State that organisms are composed of cells and that cells are the basic units of life
Explain how a unicellular organism carries out all its life functions within one cell

[Maximum number: 3]

Pictured below are Louis Pasteur's original drawings of swan-necked flasks.

Fig. 25 D.

Describe how Pasteur's experiments provided convincing evidence to falsify the concept of spontaneous generation.

Exam points

Describe how to prepare and stain cell mounts for observation with a light microscope.
Measure cells using an eyepiece graticule and a stage micrometer.
Calculate magnification and actual size, and use or construct scale bars.

[Maximum number: 5]

The micrograph is an image of human cheek cells viewed with a light microscope.

(a)

Identify the piece of equipment that is used together with the microscope to measure the size of the cells.

[ 1 ]

(b)

Each small division of the scale in the micrograph is equivalent to $2.5 \mu \mathrm{~m}$ .

[ 2 ]

(i)

Calculate the diameter of the cell labelled X .

[ 1 ]

$42.5 \mu \mathrm{~m}$

OR

$45 \mu \mathrm{~m}$ ;

Marking guidance:

Accept any value within the range:

42 to $45 \mu \mathrm{~m}$ ;

Unit required.

(ii)

Calculate the magnification of the image.

[ 1 ]

(c)

Compare and contrast the cell components of eukaryotic and prokaryotic cells.

[ 2 ]

Eukaryotic cells	Prokaryotic cells
have 80s/bigger ribosomes	have 70s/smaller ribosomes
have (DNA in) a nucleus / nuclear membrane	have nucleoid/DNA free in the cytoplasm / lack a nucleus
are compartmentalized / have membrane-bound organelles/a named membrane-bound organelle	are not compartmentalized / do not have membrane-bound organelles/a named membrane-bound organelle
have proteins/histones associated with DNA	have no proteins/histones / have naked DNA
have linear chromosomes/DNA	have circular chromosomes/(loops of) DNA;

Exam points

Explain why resolution, not magnification alone, determines the detail visible in a microscope image.
Distinguish TEM imaging of internal ultrastructure from SEM imaging of surface detail.
Describe how cryogenic electron microscopy, fluorescence and immunofluorescence reveal molecules or specific structures.

[Maximum number: 1]

In 2020, Peplow and co-workers obtained an image showing a GABA cell membrane protein receptor. The technique they used allowed them to take the image at a particular moment in time by treating the sample so that the protein molecules were firmer and more stable.

What technique did they use to obtain this image?

Electrophoresis

Immunofluorescence

Cryogenic electron microscopy

Fluorescent dyes

Exam points

Identify the plasma membrane, cytoplasm, DNA and ribosomes as structures shared by all cells.
Explain how these structures support exchange, metabolism, information storage and protein synthesis.

[Maximum number: 1]

Which cell organelle is common to all prokaryotic and eukaryotic cells?

Nucleus

Cell wall

Vesicle

Ribosome

Exam points

Explain that prokaryotes lack a nucleus and membrane-bound organelles.
Identify the cell wall, plasma membrane, cytoplasm, 70S ribosomes, naked circular DNA and plasmids in prokaryotic cells.
Recognise E. coli, Bacillus and Staphylococcus as bacterial examples.

[Maximum number: 1]

Eukaryotic cells have certain characteristics in common.

Outline one difference between the structure of prokaryotic and eukaryotic cells.

a. prokaryotes have no membrane bound organelles/nucleus/other named organelle whereas eukaryotes do

OR

prokaryotes are not compartmentalized whereas eukaryotes are;

b. prokaryotes have a single loop of DNA (in the cytoplasm) whereas eukaryotes have (linear) chromosomes (in a nucleus);

c. prokaryotes have naked DNA/not bound to histones whereas eukaryotes have DNA bound to histones;

d. prokaryotes have 70 s ribosomes whereas eukaryotes have $80 \mathrm{~s} /$ both 70 s and 80 s ;

e. prokaryote cell walls have a different structure and composition to eukaryote cell walls;

Both comparative statements about the aspect are required to gain the 1 mark.

Marking guidance:

Accept answers presented as a table.

Exam points

Describe the nucleus, 80S ribosomes, cytoskeleton and compartmentalised cytoplasm as features of eukaryotic cells.
Identify mitochondria, endoplasmic reticulum, Golgi apparatus, vesicles, lysosomes and vacuoles as eukaryotic organelles.
Identify chloroplasts, large vacuoles and cellulose cell walls as possible features of plant cells.

[Maximum number: 1]

What is a difference between eukaryotic and prokaryotic cells?

Cell walls are found only in prokaryotes.

Naked DNA with histones is found only in prokaryotes.

Compartmentalization is found only in eukaryotes.

Cilia and flagella are found only in prokaryotes.

Exam points

State that unicellular organisms carry out all life processes within one cell.
Identify Amoeba, Chlamydomonas and Escherichia coli as examples of unicellular organisms.
Identify nutrition, metabolism, response, excretion, homeostasis, growth and reproduction as life processes carried out by unicellular organisms.

[Maximum number: 1]

What life function is illustrated?

Nutrition

Homeostasis

Endocytosis

Response

Exam points

Compare plant, animal and fungal cells by their cell walls, vacuoles and storage structures.
Identify cellulose cell walls, chloroplasts and large permanent vacuoles as features of plant cells.
Identify centrioles, cilia, flagella, lysosomes and temporary vacuoles as structures that may occur in animal cells.

[Maximum number: 2]

The micrograph shows a human cheek cell magnified with a light microscope.

Explain what causes the irregular shape of the cheek cells rather than the uniform shape of plant cells.

Exam points

Describe multinucleate fungal hyphae and striated muscle fibres as atypical cells with multiple nuclei.
State that mature red blood cells and phloem sieve tubes lack nuclei.
Explain how these examples show limits to simple cell theory.

[Maximum number: 1]

The micrographs show two examples of atypical cells.

Aseptate fungal hyphae

Striated muscle fibres

Which feature shared by both types of cells makes them atypical?

Both have cell walls.

Both have several nuclei.

Both lack membrane-bound organelles.

Both are divided into compartments.

Exam points

Identify prokaryotic, plant and animal cells in light and electron micrographs using visible structures and tissue context.
Recognise the nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, vacuoles and ribosomes in micrographs.
Use visible structures and scale as evidence when identifying a cell or organelle in a micrograph.

[Maximum number: 1]

The electron micrograph shows part of a eukaryotic cell.

What is the organelle labelled X ?

Mitochondrion

Smooth endoplasmic reticulum

Lysosome

Nucleus

Exam points

Draw clear biological diagrams from electron micrographs without shading.
Label visible organelles and include magnification or scale information.
Annotate structures with their functions where required.

[Maximum number: 3]

(a) Draw a labelled diagram of the structure of a mitochondrion as seen under the electron microscope.
(b) Explain how the structure of a mitochondrion is related to its function.

(a)
Award [1] for two correct labels.
Structures must be drawn correctly for mark to be awarded.
Outer membrane;
drawn as a continuous line.
Inner membrane;
showing folding to create cristae.
Cristae;
shown as distinct infoldings of inner membrane.
Matrix.
Intermembrane space;
shown as continuous space between outer and inner membranes.
(70S) ribosomes;
shown as small dots in proportion with organelle, not too large.
(Naked) loop of DNA.

(b)
Matrix is site of reactions of Krebs cycle.
Thin intermembrane space to build up high proton concentration/ $[\mathrm{H}^{+}]$ .
ATP synthase/respiratory complex on inner membrane to produce ATP as protons pass back to matrix.
Folded inner membrane/cristae to increase surface area for electron transport chain.
Ribosomes to make enzymes/proteins required for Krebs cycle.

Exam analysis

Most tested objectives

Common question formats

Recent exam appearances

Covered syllabus points

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