Cell Membrane Structure & Function

The best comparison for a cell membrane is __

• a brick wall that blocks anything from coming in and out

• a fence with gates for certain substances to enter

If the phosphate head is hydrophilic and polar, how will it interact with water and why?

• The phosphate will be attracted to water, since neither the phosphate group or water have any partial charges

• The phosphate will be attracted to water, since both the phosphate group and the water have any partial charges

• The phosphate will not be attracted to water, since neither the phosphate group or water have any partial charges

• The phosphate will not be attracted to water, since neither the phosphate group or water have any partial charges

Why do the lipid tails of the bilayer (2 layers) face inward toward each other.

• Since they are non-polar, they do not mix well with water, and instead clump together.

• There are hydrogen bonds between the end of one fatty acid tail and a tail from another lipid

Answer explanation

No.  There are not hydrogen bonds between lipid molecules.  Hydrogen bonds only due to attractions between polar molecules.  The fatty acid tails are NON-polar and do not have any charges. 

What is the affect of temperature on the cell membrane structure?

• At high temperatures, the membrane becomes more loose and fluid, while at low temperatures the membrane becomes more packed and rigid.

• At high temperatures, the membrane becomes becomes more packed and rigid, while at low temperatures the membrane becomes more loose and fluid.

Why is cholesterol an important molecule for animal cells? 

• It helps keep the membrane stable, even though the temperature may change.

• It helps keep the phospholipids from forming covalent bonds with each other.

• It serves a channel that lets certain molecules in and out of the cell. 

Which type of molecules would have to pass through a channel protein in order to get across the membrane?

• small, non-polar (non-charged) molecules

• 
  

  large or charged molecules

Carrier proteins help with __

• passive transport that does not require energy

• active transport that requires energy

In the example of the sodium-potassium pump, if sodium is being pumped through a carrier protein OUT of the cell, it must mean...

• there was a high concentration of sodium in the cell and a low concentration outside of the cell

• 
  

  there was a low concentration of sodium in the cell and a high concentration outside of the cell

Answer explanation

Yes, since it is being pumped, it must be moving from a low concentration to a high concentration ("uphill" against the gradient)