Module 3/ Permeability and diffusion

Question 1

Permeability

Answer 1

Cell membranes are selective permeable; they only let specific substances go through. Substances show large differences in their diffusion rates.

Question 2

When is permeability higher

Answer 2

-Smaller molecules

-less polar (charged) molecules

-more hydrophobic molecules

-highly lipid-soluble substances

-Gas (ex:)2, CO2..)

Question 3

Transport proteins

Answer 3

They are transmembrane proteins that can modify temporarily the permeability of the membrane by allowing only specific molecules to cross (enter or leave the cell)

Question 4

Diffusion

Answer 4

The Fick’s law of diffusion: The flux of molecules go from regions of high concentration to a region of low concentration. This is because of the stochastic movement of each molecule in all direction.

-Net movement of a population of molecules towards lower concentration (chemical gradient).

-If the molecule is charges, its net movement will also depend on both the chemical gradient and the electric gradient across the plasma membrane

Question 5

Passive diffusion

Answer 5

Simple diffusion across the phospholipid double layer does not require energy (no ATP hydrolysis)

Question 6

Passive diffusion rates depends on

Answer 6

-Gradients of concentration

-Electrical gradients

-Mass of the molecules

-Temperature

-Solcent density

-Lipid solubility

-Membrane surface area

-Distance travelled by molecules

-Hydrostatic pressure or partial pressure

-Transport proteins

-Membrane fluidity