Involuntary weight loss exceeding 10 pounds or 5% of body weight over a period of a few months is cause for concern. Tests are done based on the person's symptoms and findings on physical examination.
Fluid Mosaic Model. A model of membrane structure; according to this model, membranes are composed of a double layer of phospholipids in which various proteins are embedded. The phospholipid bilayer is a somewhat fluid matrix that allows the movement of proteins within it.hospholipid Bilayer. A double layer of phospholipids that forms the basis of all cellular membranes. The phospholipids heads, which are hydrophilic, face the water of extracellular fluid or the cytoplasm; the tails, which are hydrophobic, are buried in the middle of the bilayer.
A major component ofevery membrane is a collection of proteins that floaton or in the lipid bilayer. These proteins provide pas-sageways that allow substances and information tocross the membrane. Many membrane proteins arenot fixed in position; they can move about, as thephospholipid molecules do.ell membranes are assembled from four com-ponents (table 6.1): 1. Lipid bilayer. Every cell membrane is composed ofa phospholipid bilayer. The other components of themembrane are enmeshed within the bilayer, whichprovides a flexible matrix and, at the same time, im-poses a barrier to permeability.