IB Biology HL B2.3 Cell specialization Questions

Practise IB Biology HL B2.3 with evidence-led questions on stem-cell potency, differentiation, exchange surfaces and the structure–function adaptations of specialized cells.

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

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam analysis

HL · 2010–2025
Papers with this topic31 / 117in the analysed sample
Latest appearanceNovember 2025
Tagged question parts37
Paper types5

Most tested objectives

  1. B2.3.8 (HL)—Pneumocytes in alveoli8 papers
  2. B2.3.6—Surface area-to-volume ratios7 papers
  3. B2.3.9 (HL)—Cardiac and striated muscle7 papers
  4. B2.3.2—Properties of stem cells6 papers
  5. B2.3.7 (HL)—Adaptations to increase SA:V5 papers

Common question formats

  • Definition or recall
  • Graph interpretation
  • Process explanation
  • Diagram interpretation

Recent exam appearances

November 2025Paper 1A HL · TZ3Q14[ 1 ]
May 2025Paper 1A HL · TZ3Q15[ 1 ]
May 2025Paper 1A HL · TZ1Q15[ 1 ]

117 papers analysed · Tagging incomplete

Exam points

  • Use insulin-mRNA or signalling-gradient evidence to explain embryonic cell differentiation.
  • Explain how stem cells self-renew and use potency to produce specialized tissues.
  • Classify totipotent, pluripotent and multipotent stem cells by developmental potential.
  • Interpret cell-size graphs to explain falling SA:V ratios and their effect on exchange.
  • Relate microvilli, transport proteins and mitochondria to intestinal or renal absorption.
  • Distinguish thin type I gas-exchange cells from type II surfactant-secreting pneumocytes.
  • Explain how surfactant lowers alveolar surface tension and prevents collapse.
  • Compare cardiac and skeletal muscle; link cardiac branching and gap junctions to impulse conduction.
  • Relate the sperm mid-piece’s mitochondria to ATP production for movement.
  • Label mature human egg diagrams with the nucleus, cytoplasm and surrounding structures.

Covered syllabus points

B2.3.1—Differentiation after fertilizationB2.3.2—Properties of stem cellsB2.3.3—Stem cell niches in adult humansB2.3.4—Types of stem cellsB2.3.5—Cell size as specializationB2.3.6—Surface area-to-volume ratiosB2.3.7 (HL)—Adaptations to increase SA:VB2.3.8 (HL)—Pneumocytes in alveoliB2.3.9 (HL)—Cardiac and striated muscleB2.3.10 (HL)—Gamete adaptations

Exam points

  • Use insulin mRNA evidence to infer that differentiating embryonic cells are expressing the insulin gene.
  • Relate signalling-chemical gradients in unspecialized cells to cell differentiation.
  • Explain how selective gene expression and suppression differentiate embryonic cells.

Exam points

  • Explain how stem cells self-renew by dividing while remaining undifferentiated.
  • Explain potency as the ability to differentiate into mature specialized cell types.
  • Compare the broader differentiation potential of embryonic stem cells with that of most adult stem cells.

Question 1

[Maximum number: 1]

Stem cells can differentiate to produce a variety of cell types in the adult human body.

Figure for Question 1 — IB Biology HL

Which description corresponds to the stem cell in the diagram?

Type

Location

totipotent

bone marrow

multipotent

bone marrow

totipotent

blood

multipotent

blood

Exam points

  • Classify stem-cell potency from developmental stage or tissue source, including early embryonic totipotency and adult bone-marrow multipotency.

Exam points

  • Explain that surface-area-to-volume ratio decreases as a cell grows because volume increases faster than surface area.
  • Relate cell surface area to exchange rate and cell volume to metabolic demand or waste production.
  • Explain how a low surface area-to-volume ratio slows diffusion and limits cell size.

Question 1

[Maximum number: 1]

What happens to the cell surface area to volume ratio as a cell grows?

A

It decreases, so production of waste material is reduced.

B

It increases, so mineral ion absorption is increased.

C

It increases, so osmosis is reduced.

D

It decreases, so rate of gas exchange is too low.

Exam points

  • Explain how microvilli increase surface area for absorption in intestinal or proximal-tubule cells.
  • Relate mitochondria and transport proteins to active nutrient uptake and glucose reabsorption.

Question 1

[Maximum number: 2]

The diagram shows the emulsion and absorption of a fat globule in the gut.

Figure for Question 1 — IB Biology HL

Explain how epithelial cells in the gut are adapted for absorption.

Exam points

  • Interpret alveolar micrographs to link thin type I cells with gas exchange and type II cells with surfactant.
  • Explain how type II surfactant lowers surface tension and prevents alveolar walls from adhering.

Question 1

[Maximum number: 1]

The micrograph shows alveoli in a human lung.

Figure for Question 1 — IB Biology HL

How are the pneumocytes adapted to their function?

Type I pneumocytes

Type II pneumocytes

many secretory vesicles (lamellar bodies)

many secretory vesicles (lamellar bodies)

many secretory vesicles (lamellar bodies)

large number of mitochondria

large number of mitochondria

extreme thinness

extreme thinness

many secretory vesicles (lamellar bodies)

Exam points

  • Explain how branching and gap junctions at intercalated discs spread cardiac impulses and synchronize contraction.
  • Compare skeletal fibres and cardiac cells by nuclei, branching, sarcomeres and myofibril structure.
  • Explain how myogenic cardiac cells initiate impulses without nervous input.

Question 1

[Maximum number: 1]

What is contained in skeletal muscle?

A

Cross bridges between muscle fibres

B

Sarcomeres formed of contractile myofibrils

C

Myosin filaments forming cross bridges with troponin and tropomyosin

D

Multinucleate cells with numerous myofibrils made of contractile sarcomeres

Exam points

  • Relate the mitochondria-rich sperm mid-piece to ATP supply for flagellar motility.
  • Draw a mature egg with a haploid nucleus, cytoplasm, cortical granules, zona pellucida and follicle cells.

Question 1

[Maximum number: 1]

The micrograph shows part of a human sperm cell. Which region of the cell is responsible for the greatest production of ATP?

Figure for Question 1 — IB Biology HL