Line ventricles and produces CSF. : Maintain blood-brain-barrier and provides structural support. : Myelinate CNS axons. : Phagocytosis of cell debris and wastes. : Surrounds PNS neurons and provides support. : Myelinates the axons in PNS.

ash from a volcanic eruption kills new plant growth.

warm water from a nuclear power plant causes overgrowth of algae.

a river floods and deposits tree pollen along its banks.​

Explanation:

Ecosystem consist of biotic and abiotic elements. Biotic refers to all living organisms while abiotic refers to all non-living elements of the environment. Living organisms depends on abiotic factors such as light, temperature, water and soil etc for their growth and survival. In the above answer, Ash of volcano, warm water and rivers are abiotic elements while plant, algae and pollen are biotic elements.