Compare different transport mechanism studied by you based upon the uphill transport , requirement of energy , Requirement of special membrane proteins , Saturation of transport
Answers
Transport Across a Cell Membrane
The cell membrane is one of the great multi-taskers of biology. It provides structure for the cell, protects cytosolic contents from the environment, and allows cells to act as specialized units. A membrane is the cell’s interface with the rest of the world - it’s gatekeeper, if you will. This phospholipid bilayer determines what molecules can move into or out of the cell, and so is in large part responsible for maintaining the delicate homeostasis of each cell.
Semi-Permeability
Some cells function best at a pH of 5, while others are better at pH 7. The steroid hormone aldosterone is made in the adrenal gland, but affects mostly the kidney. Sodium is more than ten times more concentrated outside of cells rather than inside. If our cells couldn’t control what crossed their membranes, either no molecules would make it across, or they’d be traveling willy-nilly and the internal environment would always be in flux. It’d be like taking every item on a menu and blending it together before serving (not the tastiest idea).
So how do cells maintain different concentrations of proteins and molecules despite the pressures on them to be homogenous? Cell membranes are semipermeable, meaning they have control over what molecules can or cannot pass through. Some molecules can just drift in and out, others require special structures to get in and out of a cell, while some molecules even need an energy boost to get across a cell membrane. Each cell’s membrane contains the right mix of these structures to help that cell keep its internal environment just right.