2016年5月IB生物SL真题下载-Paper2
1. During the development of multicellular organisms, cells differentiate into specific cell lines. A study was carried out on the early stages of differentiation in cells from mouse embryos that were grown in cultures. Two differentiated cell lines were studied, one of inner embryonic tissue (endodermal cells) and the other of external embryonic tissue (nerve cells) after 48 and 96 hours of incubation in cell cultures. A culture of undifferentiated cells was used as a control group. Cell population growth was measured by changes in cell density in all three cell lines.
(a) Distinguish between the changes in cell numbers in the three cell lines that occur during the 96 hour period.
(b) Using the data in the graph, deduce the relationship between cell differentiation and population growth.
There are three phases of interphase in the cell cycle:
- • the growth phase with the synthesis of RNA and proteins (G1)
- • the phase of DNA replication (S)
- • and the pre-mitotic phase of rapid growth (G2).
The graph shows the percentage distribution of the three cell lines in the different stages of interphase after 96 hours of incubation.
(c) Compare and contrast the percentage of control and nerve cells in each of the three phases after 96 hours of incubation.
(d) Using the data of both graphs, deduce the relationship between the percentage of cells in each cell cycle phase and the population growth.
(e) Interphase is followed by mitosis. State the final product of the mitotic cell cycle.
The role of regulators in the different stages of differentiation was also studied. After 96 hours of incubation a sample was taken of each cell line and the cyclins separated by gel electrophoresis. The presence of different cyclins D1, D2 and D3 was analysed in the three cell lines. The image shows the results. The size and the intensity of the band is an indicator of the quantity of cyclins.
(f) Compare and contrast the amounts of the different cyclins in nerve cells and control cells.
(g) Using the data, discuss the possible roles of the three cyclins in the differentiation of nerve and endodermal cell lines.
2016年5月IB生物SL真题余下省略！
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