The scientist is relying on <span>reproductive isolation
Hope i helped you :)</span>
<span>Within eukaryotic cells, there is a network of organelles which have unique functions.
An organelle is termed as a specialized subunit within a cell which has specific functions and their functions are very vital for a cell to live. Organelles can be identified by microscopy and purified by cell fractionation.
In eukaryotic cells has many types of organelles. Larger organelles which are found in eukaryotic cells are visible with the light microscope, for example, vacuole and nucleus.
Some of the major eukaryotic organelles include plastid, endoplasmic reticulum, flagellum, mitochondrion, vacuole, nucleus and Golgi apparatus</span>
The correct answer is - D) covered by warm shallow seas.
The fact that the crinoids are have an abundance in the fossil records in Pennsylvania in the Mississippian Period, tells us that this area was covered with shallow and warm seas. The reason why we can get that conclusion is that the crinoids live only in that kind of environment, so it simply a logical conclusion.
The geological data is also confirming this, as it is easily noticeable in the layers that during this period of the geologic past, what is now Pennsylvania, was covered with shallow sea waters. Also, this waters were warm too, as the climate was warm and humid and that period, so it was a perfect environment for the crinoids to flourish.
A biological system is a complex network of biologically relevant entities. ... Examples of biological systems at the macro scale are populations of organisms. On the organ and tissue scale in mammals and other animals, examples include the circulatory system, the respiratory system, and the nervous system. source: google
