They are metals. Metals are the most common.
Coal mining produces not only air pollution but solid waste; ash and flue - gas desulferization sludge ( look it up ), which contains toxic arsenic and radioactive uranium among other heavy metals. Water becomes polluted with these harmful substances through mountain top removal mining and so underwater creatures are poisoned and plants absorb deadly substances and die, which also contributes to the aquatic organisms death as the plants may have been a food source.
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Eons: Hadean, Archean, Proterozoic
Answer
Complex barrier to the flow of substances out of the cells,and restrictions to inflow of unwanted substances into the cells. The hydrophobic and hydrophilic nature of the cell membrane controls the entry of substances from the extracellular medium into the intracellualr. In addition the polarity restricts certain substance movement across the walls.
Serve as the selective channels for the influx of certain substances into the cells, and the out flux of wastes.This is through ion channels for the movements of ions across.
Provide insulation to the cells,to maintain the constant internal temperature,this is through the presence of lipids as( Phospholipids and cholesterol).The latter prevent the clogging of the lipids in the cell membrane therefore preventing frozen up of the cell membrane,providing insulation.
Separation of metabolic process in the cell.
Explanation:
Cell membrane-This is present in all cells.But the variation of its constituents makes it unique to each cell. Although it performs the same role, the location and role the cells it bounded, reflects its constituents, it is made up of lipids, carbohydrate, protein and cholesterol
