Theme 6- THE RESEARCH OF THE DIFFUSION THROUGH A PERMEABLE MEMBRANE

Question 1

What is Fick’s 1st law

Answer 1

J = - D (dc/dx);
where J is the diffusion flux - the number of molecules diffused per unit time through a unit area,
D (m2/s) is the diffusion coefficient,
dc/dx is a very small change of the concentration dc at a very small distance dx

Question 2

What is Fick’s 2nd law

Answer 2

dc/dt = D(d2c/dx2), where dc/dt is the very small change in concentration
dc during a very short dt.
-The physical meaning of dc/dt is the rate of change of concentration as a function of time,
and d^2c/dx2 is the second derivative of concentration as a distance function.
-The transport of substances/molecules takes place only in the presence of a spatial gradient. -The direction of the gradient is taken to be positive from higher to lower concentration

Question 3

Types of passive transport

Answer 3

Diffusion
Filtration
Osmosis

Question 4

Functions of passive transport

Answer 4

Passive transport plays an important role in the normal functioning of cells, organs and tissues of organisms.

Question 5

Diffusion

Answer 5

-The transfer of molecules from a place of high to a place of low concentration due to the thermal movement of molecules.
-The driving force is the difference between the concentration of molecules on either side of the membrane or the region of various concentrations.

Question 6

Filtration

Answer 6

-The transfer of water molecules from a place of high to a place of low hydrostatic pressure.
-The driving force is the difference in hydrostatic pressures on the two sides of the membrane.
-The passage of water continues until the hydrostatic pressures equalize.
-The hydrostatic pressure P is created by a water column of height h and is measured in Pascals (Pa), atmospheres or mm of mercury: P=ρgh, where ρ is the density of water, g is the acceleration of free falling of the Earth.

Question 7

Osmosis

Answer 7

-The transfer of water from a place with a lower to a place with a higher osmotic pressure.
-The driving force in osmosis is the difference in osmotic pressures on the two sides of the membrane.
-The passage of water continues until the osmotic pressures equalize.
-The osmotic pressure π is created if the membrane does not allow a certain type of molecules through its pores

Question 8

What is a reflection coefficient

Answer 8

-To characterize the ability of the membranes to allow the passing of the molecules of the dissolved substance or of the solvent/water/, a “reflection coefficient” - σ is introduced.
-With a completely permeable membrane σ=0 i.e. the membrane allows all molecules to pass
through.
-Diffusion and filtration are possible