IB Biology SL B2.3 Cell specialization questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type
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Question 1

Multiple choiceMedium1 mark

A signal forms a gradient across four adjacent regions of an early embryo. Gene G is expressed only where the signal concentration exceeds 6 arbitrary units. Cells expressing gene G differentiate into specialized cell type P; cells not expressing it differentiate into another type. Which outcome is predicted? [1 mark]

Embryo regionSignal concentration / arbitrary units
W8
X7
Y5
Z3
Show answer and explanation

Answer: C. Gene G is expressed only where the signal concentration exceeds 6 arbitrary units. Regions W and X have concentrations of 8 and 7, so their cells express gene G and differentiate into type P. Regions Y and Z are below the threshold and differentiate into another type.

A: considers only the region with the highest concentration, overlooking that X also exceeds the threshold.
B: reverses the effect of the signal by assigning type P to regions below the threshold.
D: assumes all regions have the same gene expression and fate despite their different signal concentrations.

Remember: a gradient can lead to different gene-expression patterns and cell fates in an early embryo.

Question 2

Paper 2Medium16 marks

Adult human bone-marrow stem cells were divided into equal groups of 100 cells. Each group was exposed for seven days to a different set of signals, M or N, from bone-marrow niche cells. Assume that no cells died, differentiated cells did not divide, and all cells present at day 7 were either stem cells or newly differentiated blood cells.

Signal conditionStem cells at day 7Newly differentiated blood cells at day 7
M24060
N60240
(a)

State two properties of stem cells.

[2]
(b)

Name two adult human locations that contain stem-cell niches, and state one role of a niche.

[3]
(c)

Calculate the percentage of counted cells that were stem cells in condition M and condition N.

[3]
(d)

Compare the outcomes for M and N and infer which set of signals favoured maintenance or proliferation of the stem-cell population and which favoured differentiation.

[4]
(e)

A researcher concludes that these results prove that the stem cells can divide endlessly and differentiate along different pathways. Evaluate this conclusion using the data.

[4]

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