AP Biology Cell Membranes Tuff!

Biological membranes are composed primarily of 

• nucleotides and nucleosides
• enzymes, electron acceptors, and electron donors
• monosaccharides and diasaccharides
• lipids

The compounds in biological membranes that form a barrier to the movement of hydrophilic materials across the membrane are 

• integral membrane proteins
• carbohydrates
• lipids
• peripheral membrane proteins

In biological membranes, the phospholipids are arranged in a _______, with the_______.

• bilayer; fatty acids pointing toward each other
• bilayer; fatty acids facing outward
• single layer; fatty acids facing the interior of the cell
• single layer; phosphorus-containing region facing the interior of the cell

A characteristic of plasma membranes that helps them fuse during vesicle formation and phagocytosis is the

• ratio of one protein molecule for every 25 phospholipid molecules
• capacity of lipids to associate and maintain a bilayer organization
• constant length of the fatty acid chain and the degree of saturation
• ability of phospholipid molecules to flip over and trade places with other phospholipid molecules

Which statement about cholesterol molecules is true?

• They help hold a membrane together.
• They alter the fluidity of the membrane.
• They attach to carbohydrates.
• They disrupt membrane function.

House plants adapted to indoor temperatures may die if they are left outdoors, because in a cold environment their

•  DNA cannot function.
• membranes lack adequate fluidity.
• photosynthesis is impaired.
• membranes contain too many unsaturated fatty acids.

In hibernating animals during the winter

• signal transduction pathways cease.
• membrane lipid composition changes: saturated fatty acids are replaced withunsaturated fatty acids.
• membranes toughen as more saturated fatty acids accumulate in them.
• there are no changes in lipid composition.

The plasma membranes of winter wheat are able to remain fluid when it is extremely cold by

• synthesizing new forms of cholesterol
• closing protein channels
• decreasing the number of hydrophobic proteins present
• replacing saturated fatty acids with unsaturated fatty acids

Which type of membrane protein would likely be most easily removed in a laboratory experiment?

• Integral membrane proteins
• Channel proteins
• Peripheral membrane proteins
• Transmembrane proteins

A protein that forms an ion channel through a membrane is most likely 

• a peripheral membrane protein
• a phospholipid
• an enzyme.
• a transmembrane protein