<span>Answer:The blood-brain
barrier (BHE)
BHE is a barrier that's highly permeability selective and protects
the central nervous system from potential dangers like viruses, bacteria and parasytes that may be circulating int he blood. <span>It is composed of endothelial cells, astrocytes, pericytes.</span></span>
Sunlight is the main change! sun light cannot penetrate into the deep layers of the ocean and availability of oxygen is also low there. this causes the considerable amount of organisms to live in the upper layers of the ocean and we can only observe decomposing organisms in the deeper layers!
Salt marshes are diverse ecosystems because there are resources from both