Biology  by Bradford
IB Biology 2025 · Theme B · Form and function

B2.3 Cell specialization. Practice questions with markscheme.

46 original IB-style questions on B2.3, written from the 2025 guide: 20 multiple-choice, 14 short-answer, 5 data-based, 5 extended-response part, 2 drawing. Below is a 20-mark standard-level practice paper built from them, ready to hand out as a class quiz or homework, or to sit yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

6 statements at SL and HL, 4 additional higher level.

  1. B2.3.1SL / HL Production of unspecialized cells following fertilization and their development into specialized cells by differentiation
  2. B2.3.2SL / HL Properties of stem cells
  3. B2.3.3SL / HL Location and function of stem cell niches in adult humans
  4. B2.3.4SL / HL Differences between totipotent, pluripotent and multipotent stem cells
  5. B2.3.5SL / HL Cell size as an aspect of specialization
  6. B2.3.6SL / HL Surface area-to-volume ratios and constraints on cell size
  7. B2.3.7HL Adaptations to increase surface area-to-volume ratios of cells
  8. B2.3.8HL Adaptations of type I and type II pneumocytes in alveoli
  9. B2.3.9HL Adaptations of cardiac muscle cells and striated muscle fibres
  10. B2.3.10HL Adaptations of sperm and egg cells

In the bank for B2.3

  • 20 multiple-choice
  • 14 short-answer
  • 5 data-based
  • 5 extended-response part
  • 2 drawing
  • 17 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

Make your own

The practice paper

Take it on screen → Build a fresh paper Paper code BbB-EAAAIAAAABQAOq8_
Biology · topic quiz
Standard level · topic practice, not an exam format
30 minutes20 marks

Paper code: this paper was generated, so the code is its recipe. Enter it at biologybybradford.com/exam-maker to rebuild this exact paper and its markscheme.

Covers B2.3 Cell specialization
Name:
1.

Cells in an embryo become different from one another even though they contain the same genome. What causes this differentiation?

[1]
  1. Different cells lose different genes
  2. The cytoplasm digests unused genes
  3. Mutations occur in each cell type
  4. Different cells express different genes
2.

Why does the surface area-to-volume ratio set an upper limit on cell size?

[1]
  1. Surface area increases faster than volume as a cell grows
  2. Volume increases faster than surface area as a cell grows
  3. The plasma membrane cannot expand beyond a fixed maximum area
  4. A single nucleus cannot supply mRNA to a large cytoplasm
3.

Which comparison of totipotent and pluripotent stem cells is correct?

[1]
  1. Only totipotent cells can give rise to the extra-embryonic tissues
  2. Only totipotent cells are found in the tissues of the adult body
  3. Only pluripotent cells can give rise to a complete organism
  4. Only pluripotent cells can differentiate into blood cell types
4.

Which two properties together define a stem cell?
I. The ability to divide repeatedly (self-renewal)
II. The ability to differentiate into specialized cell types
III. The absence of a nucleus

[1]
  1. I and III only
  2. II and III only
  3. I and II only
  4. I, II and III
5.

Discuss one benefit and one concern associated with the therapeutic use of stem cells.

[3]
6.

Outline the location and role of adult stem cells, using a named example.

[2]
7.

A motor neuron running from the spinal cord to a muscle in the foot can be more than 1 m long, and a striated muscle fibre in the thigh can be several centimetres long. Explain how the sizes of these two cells are related to their functions.

[3]
8.

Cells were taken from four sources in mice and cultured under conditions that encourage differentiation. After three weeks the percentage of colonies containing each of four cell types was recorded. The maximum number of times the cells could divide in culture was also recorded.

Source of cellsColonies with nerve cells / %Colonies with muscle cells / %Colonies with blood cells / %Colonies with placental cells / %Maximum divisions in culture
Embryo at 8-cell stage31282417unlimited
Inner cell mass of blastocyst3533300unlimited
Adult bone marrow0088055
Adult skin fibroblasts000028
(a)State which source produced the widest range of cell types.[1]
(b)Using the data, distinguish between totipotent, pluripotent and multipotent stem cells.[3]
(c)Explain why the skin fibroblasts did not form colonies of any of the four cell types.[2]
(d)Outline how the data show that bone marrow cells have the two defining properties of stem cells.[2]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
Rebuild or edit this exact paper (and its markscheme): biologybybradford.com/exam-maker?code=BbB-EAAAIAAAABQAOq8_

Show the markscheme

Markscheme BbB-EAAAIAAAABQAOq8_

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. B2.3.1 [1]
  • D: differentiation results from differential gene expression (switched on/off by signalling gradients/position in the embryo), not gene loss;
2. B2.3.6 [1]
  • B: as a cell grows, volume (demand) increases faster than surface area (supply); beyond a limit, exchange across the membrane cannot keep pace with metabolism;
3. B2.3.4 [1]
  • A: totipotent (zygote/early embryo) can form all cell types including placenta; pluripotent (embryonic stem cells) form body cell types; multipotent adult stem cells are more restricted;
4. B2.3.2 [1]
  • C: self-renewal plus differentiation potential; stem cells certainly have nuclei;
5. B2.3.3-B2.3.4 [3 max]
  • benefit: potential to replace damaged/lost tissues, e.g. treating leukaemia (bone-marrow transplant) / regenerating skin/retina cells;
  • (benefit developed) cells can be matched to the patient / reduce need for donor organs;
  • concern: ethical objections to using embryonic stem cells (destruction of embryos);
  • concern: medical risks, e.g. tumour formation / immune rejection / unproven commercial clinics, OWTTE;

At least one benefit AND one concern required for full marks.

6. B2.3.3 [2 max]
  • found in certain tissues (niches) of the adult body, e.g. bone marrow / base of intestinal crypts / skin;
  • they divide to replace lost/damaged specialized cells (of a limited range of types / multipotent);
  • named example correctly linked, e.g. bone-marrow (haematopoietic) stem cells producing blood cells;
7. B2.3.5 [3]
  • the neuron has a very long (thin) extension / axon so that a single cell carries the impulse the whole distance from the spinal cord to the muscle, OWTTE;
  • (so) no synapses are needed along the route, which would slow / could interrupt transmission of the impulse;
  • the muscle fibre is long so that its contraction acts along a large part of the length of the muscle / a single fibre can shorten by a useful distance, OWTTE;
  • the muscle fibre is wide / has a large volume to contain many contractile myofibrils, giving a large force;
  • very large cells need adaptations, e.g. many nuclei in a muscle fibre / a narrow axon, to keep the cell supplied and controlled despite its size;

Accept 'nerve fibre' for axon. Credit is for linking size to function; a description of size alone does not score.

8. B2.3.4, B2.3.2
  • (a) [1]
    • embryo at the 8-cell stage;
  • (b) [3]
    • totipotent (8-cell embryo): can form any cell type including placental (extra-embryonic) cells;
    • pluripotent (inner cell mass): can form all cell types of the body (nerve, muscle, blood) but not placental cells;
    • multipotent (bone marrow): can form only a limited range / closely related cell types (blood cells only), OWTTE;
  • (c) [2 max]
    • fibroblasts are (fully) differentiated cells, not stem cells;
    • during differentiation only some genes are expressed / other genes are switched off, so the cells cannot change into other cell types;
    • they have limited capacity to divide (28 divisions) rather than self-renewing indefinitely, OWTTE;
  • (d) [2]
    • they can divide repeatedly / self-renew (55 divisions, more than the differentiated fibroblasts);
    • they can differentiate into (specialised) blood cells (88 % of colonies), OWTTE;

More in Theme B · Form and function

All 40 IB Biology subtopics →  ·  AP Biology units →  ·  Open the exam maker →