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Cell Specialization · Paper 2 — Free Biology SL Practice Questions

1MasterySAQ-SStem cells and differentiation5 marksPaper 2~8 min
A research group investigates the potential of stem cells to treat spinal cord injuries. They obtain two types of cells from a patient: multipotent stem cells from the patient's bone marrow, and induced pluripotent stem cells (iPSCs) generated from the patient's skin fibroblasts.
(a)
State the difference in potency between multipotent stem cells and iPSCs. [1 mark]
(b)
The researchers culture iPSCs in a medium containing specific growth factors to direct differentiation into oligodendrocytes. After 14 days, the culture contains 5.0×1055.0 \times 10^{5} cells in total, of which 3.5×1053.5 \times 10^{5} have differentiated into oligodendrocytes. The culture dish has a surface area of 25 cm225\,\text{cm}^{2}. Calculate the percentage of cells that successfully differentiated into oligodendrocytes, and determine the density of differentiated oligodendrocytes per cm2\text{cm}^{2}. [2 marks]
(c)
The differentiated oligodendrocytes are transplanted into the injured spinal cord of the same patient. Evaluate one potential advantage and one potential risk of using the patient's own iPSCs rather than donor-derived neural stem cells for this treatment. [2 marks]
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Solutions

2MasterySAQ-SStem cells and differentiation5 marksPaper 2~8 min
A patient with type 1 diabetes has lost the function of insulin-producing beta cells in the pancreas. Scientists propose to generate new beta cells from stem cells for transplantation.
(a)
State one property of stem cells that makes them suitable for generating replacement beta cells. [1 mark]
(b)
The scientists compare two approaches: using embryonic stem cells (ESCs) from a donated embryo, and using induced pluripotent stem cells (iPSCs) derived from the patient's own skin cells. Explain one ethical advantage of using iPSCs over ESCs for this patient. [2 marks]
(c)
The scientists successfully differentiate iPSCs into insulin-producing cells and measure insulin release in response to glucose. The results are shown below. Glucose concentration — Insulin secretion 5 mM5\,\text{mM} — 2.1 ng insulin⋅10−6 cells⋅h−12.1\,\text{ng insulin} \cdot 10^{-6}\,\text{cells} \cdot \text{h}^{-1} 20 mM20\,\text{mM} — 9.8 ng insulin⋅10−6 cells⋅h−19.8\,\text{ng insulin} \cdot 10^{-6}\,\text{cells} \cdot \text{h}^{-1} Calculate the fold increase insulin secretion when glucose concentration is raised from 5 mM5\,\text{mM} to 20 mM20\,\text{mM}. [2 marks]
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Solutions

3ChallengeSAQ-LStem cells and differentiation7 marksPaper 2~11 min
A research team investigates the potential of induced pluripotent stem cells (iPSCs) to treat a patient with type 1 diabetes mellitus. The patient's own skin fibroblasts are reprogrammed into iPSCs using the Yamanaka factors (Oct4, Sox2, Klf4, c-Myc). These iPSCs are then differentiated into pancreatic beta cells. Data collected after 14 days of differentiation: - Untreated iPSCs: 15%15\% expressed the beta-cell marker PDX1 - Embryonic stem cells (ESCs) under the same protocol: 72%72\% expressed PDX1 - iPSCs pre-treated for 48 hours with a histone deacetylase inhibitor (HDACi): 68%68\% expressed PDX1 - Genome analysis of iPSCs before and after HDACi treatment: no change in DNA sequence; 40%40\% increase in acetylation of histone H3 at the PDX1 gene promoter
(a)
State the percentage-point increase in PDX1 expression when iPSCs are pre-treated with HDACi compared to untreated iPSCs. [1 mark]
(b)
Calculate the fold change in PDX1 expression between HDACi-treated iPSCs and ESCs. [2 marks]
(c)
Explain the molecular mechanism by which HDACi treatment increased PDX1 expression in the iPSCs. [2 marks]
(d)
Evaluate whether iPSCs or ESCs would be the more appropriate cell source for developing a patient-specific therapy for type 1 diabetes, using evidence from the data and your knowledge of stem cell biology. [2 marks]
diagram

Solutions

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