Final answer:
Scientists struggle to grow specialized and unspecialized cells in the laboratory because the process of cell differentiation is not fully understood, and it's difficult to replicate the required conditions outside of the body.
Step-by-step explanation:
The main reason scientists face challenges in growing specialized and unspecialized cells in the lab is due to the poorly understood mechanisms that induce a non-differentiated cell to become a specialized cell. Cell differentiation is a complex process where stem cells transform into specific cell types with unique functions and structures. In the lab, inducing stem cells to differentiate requires manipulating the physical and chemical growth conditions.
However, this process is complicated because it's unclear how to precisely mimic the myriad of signals and environmental factors that in vivo conditions provide. Stem cells like embryonic stem cells (hESCs) are pluripotent and can become nearly any cell type, whereas adult stem cells are often multipotent, with a more limited range of differentiation.
In addition, ethical concerns, particularly surrounding the use of hESCs which involves the destruction of embryos, also restrict the ability to work with certain types of stem cells. While induced pluripotent stem cells (iPSCs) offer an alternative by reprogramming adult cells to a pluripotent state, the reprogramming process itself is not fully understood and can be inefficient. Challenges also include the potential immune rejection of transplanted cells and the risk of developing cancerous cells if the differentiation process isn't precisely controlled.