Cell Membrane and Membrane Transport

Question 1

The substances in cell membranes that form a barrier to the movement of materials across the membrane are

Answer 1

lipids

Question 2

The _____ portion of the cell membrane is responsible for the isolating function of the membrane, whereas the _____ portion regulates exchange and communication with the environment.

Answer 2

lipid; protein

Question 3

Plasma membranes are best described as a

Answer 3

double layer of phospholipids with hydrophobic tails oriented toward one another.

Question 4

The hydrophobic tails of a phospholipid bilayer are oriented toward the

Answer 4

interior of the plasma membrane (i.e. toward one another)

Question 5

Which of the following would NOT be found in a membrane?

Answer 5

Cellulose

Question 6

The net movement of molecules from a high concentration to a low concentration is best described by which of the following?

Answer 6

simple diffusion

Question 7

For diffusion to occur, there must be

Answer 7

a gradient

Question 8

The bacterium Vibrio cholera releases a toxin that blocks a channel protein in the membranes of cells that line the intestine. This toxin prevents the movement of sodium ions from the inside of the intestine into cells. If the sodium ions could not move into the cells, how would this affect the movement of water between the inside of the intestine and the cells?

Answer 8

Water would leave the cells and enter the intestines by osmosis.

Question 9

Which of the following is an energy-requiring mode of transport that brings substances into a cell?

Answer 9

Receptor-mediated endocytosis

Question 10

In reference to diffusion, “passive” really means

Answer 10

no energy required

Question 11

Carbon dioxide crosses the plasma membrane by simple diffusion. The rate at which carbon dioxide enters the cell is determined by the

Answer 11

concentration of carbon dioxide on each side of the membrane

Question 12

What is active transport

Answer 12

movement of molecules into or out of a cell against a concentration gradient

Question 13

When substances move through a plasma membrane and down gradients of concentration, this is called

Answer 13

passive transport

Question 14

To say that a cell is “selectively permeable” means

Answer 14

only certain molecules can pass through.

Question 15

Molecules that permeate a plasma membrane by facilitated diffusion

Answer 15

require the aid of transport proteins

Question 16

Which of the following occurs as an enzyme produced by a cell is secreted from the cell?

Answer 16

exocytosis

Question 17

molecules assisted by carrier proteins may cross a selectively permeable membrane by

Answer 17

facilitated diffusion

Question 18

If red blood cells are taken from the body and placed in a hypertonic solution, what happens to the cells?

Answer 18

The cells shrivel up because water leaves them.

Question 19

Osmosis moves water from a region of

Answer 19

low solute concentration off to a region of high solute concentration.

Question 20

The cytoplasm of a certain cell, such as a neuron, already has a high concentration of K+ ions. How can K+ ions continue to enter the cell?

Answer 20

active transport

Question 21

The process in which white blood cells engulf bacteria is termed

Answer 21

phagocytosis

Question 22

Cells use exocytosis to

Answer 22

release substances from the cell.

Question 23

T/F Carrier molecules in the plasma membrane are required only for active transport

Answer 23

False