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.

The diagram shows the concentration of four cyclins during the cell cycle. Which curve represents the cyclin that promotes the assembly of the mitotic spindle?

The concentrations of cyclins rise and fall in cells at certain times.

What times are these?

The image is an electron micrograph.