Question

During fertilization in multicellular organisms, a sperm cell fuses with an egg cell to form a zygote. Then, the zygote begins to divide. First, one cell becomes two, then two cells become four, four cells become eight and so on and so forth until a large ball of identical cells is formed. At this point, the ball begins to change. A space forms in the middle, and the cells are pushed inward to form layers. If cell differentiation begins after this phase, what most likely triggers this process?

Answer 1

Cell differentiation is most likely triggered by signaling pathways influenced by the formation of a space within the cell mass, transforming a morula into a blastocyst, which leads to cells specializing into various organs and tissues.

Step-by-step explanation:

Triggers of Cell Differentiation After Blastulation

Cell differentiation in multicellular organisms begins after the formation of the blastula. The zygote undergoes a series of mitotic divisions called cleavage, forming a solid ball of cells known as a morula, which is still enclosed within the zona pellucida. This is later transformed into a fluid-filled structure called a blastocyst in mammals, characterized by an inner cell mass. When a space appears within the morula, transforming it into a blastocyst, cell differentiation is most likely triggered by signaling pathways influenced by cellular interactions and spatial changes within the structure, causing cells to specialize and form different organs and tissues.

Answer 2

Cell differentiation is triggered by a switch from one pattern of gene expression to another.
Each cell type is defined by its particular pattern of regulated gene expression, thus embryonic cells have their own pattern of gene expression. At some point, those embryonic patterns are turned off, and at the same time, tissue-specific genes are turned on. Cellular mechanisms that control these switches involve cell signalling, usually growth factors.