Please help..Which of the following best explains why a cell's plasma membrane is composed of two layers of phospholipids rather than just a single layer? Having two oppositely oriented layers of phospholipids allows only the hydrophilic heads to interact with water inside and outside of the cell
B
Having two oppositely oriented layers of phospholipids allows the hydrophilic heads to repel water both inside and outside of the cells
Having two identically oriented layers of phospholipids gives cells more protection from the exterior environment than just a single layer would.
Having two identically oriented layers of phospholipids allows for the production of vacuoles while still maintaining a protective barrier.
No

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.

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