AP Bio Chp 5: Membrane Transport and Cell Signaling

In what ways do the membranes of a eukaryotic cell vary?

• Phospholipids are found only in certain membranes

• Certain proteins are unique to each type of membrane

• Only certain membranes of the cell are selectively permeable

• Only certain membranes are constructed from amphipathic molecules

Which of the following factors would tend to increase membrane fluidity?

• A greater proportion of unsaturated phospholipids

• A greater proportion of saturated phospholipids

• A lower temperature

• A relatively high protein content in the membrane

Phosphorylation cascades involving a series of protein kinases are useful for cellular transduction because

• They are species specific

• They always lead to the same cellular response

• They amplify the original signal many fold

• They counter the harmful effect of phosphatases

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because:

• Only target cells retain the appropriate DNA segments

• Intracellular receptors are present only in target cells

• Only target cells have enzymes that break down aldosterone

• Only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on

Which of the following processes includes all the others?

• Osmosis

• Diffusion of a solute across a membrane

• Passive transport

• Transport of an ion down its electrochemical gradient

Under what conditions will a substance be likely to enter a cell through diffusion?

• When a molecule of the substance is very large

• When the substance is a particle of food

• When the concentration of the substance is greater outside the cell than inside

• When the concentration of the substance is greater inside the cell than outside