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>
Red Blood Cells would take up 41% of the blood's overall volume.
Cellular respiration provides the ATP necessary for muscle contractions
A) A mixture because they can be taken apart without changing the physical form
Great question!
Before genetic engineering, people who needed insulin to survive (diabetics) had to obtain their insulin from pancreases of pigs! When pigs were slaughtered, they removed the pancreas to take out the insulin. Expensive, time consuming - and for jews, not kosher!
Genetic engineering changed all this - they have cloned the gene for human insulin into a plasmid which they then express in the bacterium Escherichia coli (E. coli). The E. coli makes A LOT of insulin this way - it's made in a stainless steel fermentor (think of how they brew beer) - and it is easily purified. So, now there is human insulin (not pig - so kosher!) and is made fast and cheap!!! No need to slaughter an animal for this anymore!
