what functioms might each of the three types of diffusion serve in a human (simple, facilated, active)?

Answer 1

Not sure what you mean...
An example of simple diffusion is that of steroid hormones which diffuse readily through the cell mebrane and reach their target molecules within the cell.

Facilitated diffusion you have for example for the uptake of many hydrophilic/charged nutrients from the blood. The concentration of the nutrient is higher on the outside of the cell, yet it cannot simply diffuse through the membrane; it needs the help of transport proteins.

Active transport means that the cell needs to import something uphill its gradient, using energy. The most profound example is the Na+/K+ ATPase which pumps Na+ out of the cell and K+ into the cell using ATP (both Na+ export and K+ import are uphill processes).

A beautiful combination of passive and active transport is seen in the intenstinal epithelial cells. The concentration of glucose in the gut is lower than inside the cell. So the human body needs to consume energy and actively import glucose. This happens via a symporter that imports Na+ together with glucose. The import of Na+ is downhill so it releases energy which is used for the uptake of glucose. Once the glucose is inside the epithelial cell it will be passively exported to go to to the bloodstream.

Answer 2

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