I think the deficiency of dedicated respiratory and circulatory systems in Planarians does not cause a problem because none of their cells are far removed from the gastrovascular cavity or from the external environment. Planarians are free-living flatworms and form the class Turbellarians in the Phylum Platyhelminthes. Flatworms have three tissue layers, that is the ectoderm, mesoderm, and endoderm.
Global and local climate change also makes marine ecosystems more vulnerable to lower oxygen levels (hypoxia). Aquatic organisms cannot survive without the presence of dissolved oxygen in the water.
When the climate is warmer, the surface water warms up more quickly and its density becomes lower than that of the underlying waters. However, it is the mixture of waters of different depths that helps to oxygenate the deeper waters. If the surface water is warmer and less dense, it mixes less well with the more dense bottom waters. As a result, the oxygen content will be lower in some places (deeper places for example).
At oxygen levels below 30%, species that do not tolerate hypoxic conditions must migrate to other geographic areas. If they can not migrate, their survival may be threatened.
D) all of the above are potential disadvantage for the use of adult stem cells.
I hope this helps you. ☺
