Chapter 4- Movement Of Molecules

Question 0

What is flux?

Answer 0

Flux is the amount of material crossing a surface in a unit of time.

Question 1

What is simple diffusion?

Answer 1

Simple diffusion is the movement of molecules from one location to another solely as a result of their random thermal motion.

Question 2

What is net flux?

Answer 2

Flux is the difference between the two one-way fluxes.

Question 3

What is diffusion equilibrium?

Answer 3

Diffusion equilibrium is when the two one-way fluxes are equal in magnitude but opposite in direction, and the net flux is zero.

Question 4

How does net flux proceed?

Answer 4

Net flux always proceeds from reregions of higher concentration to regions of lower concentration

Question 5

What are the factors that influence net flux?

Answer 5

1. Temperature–higher temp = greater net flux
2. Mass of molecule–smaller molecule = faster diffusion
3. Surface area–greater surface area = greater net flux
4. Medium in which molecules are moving–molecules diffuse more rapidly in gas than water
5. Distance–small distance = faster diffusion

Question 6

What is bulk flow?

Answer 6

Bulk flow is the movement of fluids or gases from a region of higher pressure to a region of lower pressure.

Question 7

What’s the major factor that limits diffusion across a membrane?

Answer 7

The major factor that limits diffusion across a membrane is the hydrophobic interactions of its membrane bilayer.

Question 8

Which molecules diffuse into cells faster? Polar or non-polar?

Answer 8

Polar molecules diffuse slowly if at all whereas nonpolar molecules diffuse much more rapidly because nonpolar molecules can dissolve in the nonpolar regions of the membrane.

Question 9

What is an ion channel?

Answer 9

An ion channel is an integral protein that allows ions to diffuse across the membrane.

Question 10

What is a special characteristic of ion channels?

Answer 10

They can show selectivity for the type of ion or ions that can diffuse through them. This selectivity is based upon the diameter of the channel, the charged and polar surfaces of the protein subunits that form the walls and electrically attract or repel the ions, and on the number of water molecules associated with the ions.

Question 11

What is a membrane potential?

Answer 11

A membrane potential is a separation of charge across plasma membranes of all cells which is measured in millivolts. The membrane provides an electrical force that influences the movement of ions across the membrane.

Question 12

What does the membrane potential do?

Answer 12

The membrane potential provides an electrical force that influences the movement of ions across the membrane.

Question 13

What is the electrochemical gradient?

Answer 13

The electrochemical gradient is both the concentration difference and the electrical difference (the membrane potential).

Question 14

Channel grating is the process of opening and closing of ion channels.

Answer 14

What is channel grating?

Question 15

What factors influence channel gating?

Answer 15

1. Binding of specific molecules to channel proteins may directly or indirectly cause an allosteric or covalent shape change in the channel protein. These channels are called Ligand-gated channels.
2. Changes in the membrane potential can cause movement of the charged regions on a channel protein, altering its shape. These channels are called voltage-gated channels.
3. Physically deforming (stretching) the membrane may affect the conformation of some of the channel proteins. These channels are called mechanically-gated channels.