D. Polarity and size.
<span>The size, polarity, and charge of a substance will determine whether or not the substance can cross the cell membrane by diffusion. The cholesterol was an example of a lipid, and is highly soluble in the nonpolar environment of the lipid bilayer. You saw, in the animation above, the cholesterol freely passing into the hydrophobic environment of the membrane. Cholesterol distributes freely in the membrane and then some fraction will dissolve in the aqueous environment of the cytoplasm. Water, on the other hand, while polar, is small enough to cross the membrane at a slow rate. Note that specialized transport proteins in certain cell membranes can provide a channel for the water, greatly increasing its rate of crossing the membrane. The lipid bilayer is much less permeable to the ion, because of its charge and larger size. As a general rule, charged molecules are much less permeable to the lipid bilayer.</span>
<span>The two basic molds are: Expendable
mold and permanent mold. </span>
Molding is a
process where a rigid frame (mold) is being used to manufacture by shaping liquid
or pliable raw materials. However, molding is synonymous to casting; casting is
a process where a liquid metal is delivered into a mold which contains a hollow
cavity of the intended shape.
Expendable mold casting can be classify as
sand, plastics, plaster which make use of non-reusable or temporary molds while Permanent mold casting is a metal
casting process that use reusable molds.
<span>a. the cell uses information from messenger rna to produce proteins.</span>
