Chapter 4 - Cell Membranes & Transport

Question 1

Why are the terms fluid and mosaic used in the description of a cell membrane?

Answer 1

fluid - the phospholipids and proteins move

mosaic - the proteins are scattered (in a mosaic-like pattern) throughout the bilayer

Question 2

How thick is a phospholipid bilayer?

Answer 2

7 nm

Question 3

Why do signal molecules (ligands) bind only to specific target cells?

Answer 3

only target cells have complementary receptors for the ligands

Question 4

Cell signaling pathways consist of 3 steps: reception, transduction, & response. What is the main purpose of the transduction step?

Answer 4

this step generates secondary messengers that amplify the response

Question 5

Phospholipid bilayers are semi-permeable. What types of molecules are they permeable to? What types of molecules are they impermeable to?

Answer 5

permeable - nonpolar/hydrophobic/lipid-soluble

impermeable - polar/hydrophilic/water-soluble/charged (ions)

Question 6

What term is used to describe the movement of small, nonpolar molecules directly through the phospholipid bilayer from high to low concentration?

Answer 6

simple diffusion

Question 7

What term is used to describe the movement of polar or charged molecules, from high to low concentration, across a cell membrane via a channel or carrier proteins?

Answer 7

facilitated diffusion

Question 8

What type of cell transport involves using an ATP-powered membrane pump protein to move molecules against their gradient?

Answer 8

active transport

Question 9

What energy-requiring process is responsible for the secretion of ligands (e.g. hormones) from cells?

Answer 9

exocytosis

Question 10

What energy-requiring process is used by some types of white blood cells (e.g. macrophages and neutrophils) to engulf pathogens?

Answer 10

endocytosis/phagocytosis

Question 11

Describe osmosis in terms of water potential.

Answer 11

Water diffuses from regions of higher (less negative) water potential to regions of lower (more negative) water potential.

Question 12

What effect does adding solutes to a solution have on its water potential?

Answer 12

adding solution LOWERS the water potential

Question 13

What term is used to describe a swollen plant cell that has gained water by osmosis?

Answer 13

turgid

Question 14

What term is used to describe the process by which a plant cell loses water by osmosis causing its cell membrane to pull away from its cell wall?

Answer 14

plasmolysis

Question 15

The water potential of a solution is -700 kPa; the water potential a cell submerged in the solution is -300 kPa. Describe what will happen to the cell.

Answer 15

Water will diffuse OUT of the cell by osmosis down a water potential gradient causing the cell to shrink.