Biological membranes GapFill

The  variable flexiblefluid mosaicmolten uniformdynamic lattice model of the plasma membrane describes how the  phospholipidstriglycerideshormonespolypeptides 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  fixedcostlessfreepassive, such as simple diffusion, facilitated diffusion and osmosis (for  waterinsulincarbon dioxideoxygen), meaning they do not require any energy inputs. These processes may be affected by a number of factors - for example, a greater  diffusion distancepHsurface areawater potential will generally decrease the rate of diffusion. In contrast, active transport moves substances  againstatdownwithin their concentration gradient using the energy from the hydrolysis of  glucoseATPinsulinglycogen.

Large substances travel into and out of cells via  nucleivesicleslysosomesribosomes. The movement of large substances out of a cell is referred to as  translocationfacilitated diffusionendocytosisexocytosis.

Other membranes exist within cells to separate  prosthetic groupscoenzymesorganellesantibodies from the cytoplasm, or to act as sites of chemical reactions; for example, photosynthetic reactions occur on the thylakoid membranes of  chloroplastsmitochondriaendoplasmic reticulumGolgi apparatus.