Transport across cell membranes GapFill

The  variable flexiblefluid mosaicdynamic latticemolten uniform model of the cell-surface membrane describes how the  phospholipidstriglyceridespolypeptideshormones which make up its bilayer are flexible in their relative positions to one another, and how the bilayer is studded with proteins and other molecules of different shapes and sizes. These molecules include:

Substances can be transported across membranes by several different methods. Some of these methods are  costlessfixedpassivefree, such as simple diffusion, facilitated diffusion and osmosis (for  oxygencarbon dioxideinsulinwater), meaning they do not require any energy inputs. In contrast, active transport moves substances  atagainstdownwithin their concentration gradient using the energy from the hydrolysis of  glycogenATPinsulinglucose, and  facilitated diffusionco-transportneutral transportcyclo-diffusion is a cyclic process involving both passive and active transport.

The rate of transport of a substance can be increased by providing a larger  concentration gradientsurface areavolumepermeability through stretching or folding, or by adding  morewiderrougherlonger protein channels and carrier molecules in the membrane if these are required.