Deck 4: Diffusion

Question 1

Fic k's se co nd law of d iffu sio n fo llow s f ro m the firs t law if you ap ply

A) The continuity equation
B) Poiseuille's equation
C) LaPlace's Law
D) The conservation of mom entum
E) T he ran do m wa lk

Answer 1

A

Question 2

The Stokes -Einstein equation is valid only if the diffusing particles are

A) At equilibrium (there is no co ncentration gradient)
B) W arm
C) C old
D) Spheres
E) Newtonian

Answer 2

D

Question 3

Which of the followin g are app ropr iate un its for a diffus ion co efficie nt?

A) cm s-1
B) Joules s-1
C) N s-1
D) cm 2 s-1
E) cm 3 s-1

Answer 3

D

Question 4

If the gradient of the flux is negative, it means that

A) The con cen tration at the p oint w here the gra dien t is nega tive m ust be inc reasing w ith time.
B) The concentration is at steady state.
C) The flux is positive.
D) The concentration at any point is decreasing with distance.
E) The co nce ntration is con stan t.

Question 5

The major reason that the apparent diffusion coefficient of Ca₂+ in muscle cell cytosol is much lower than in water is that

A) The cytosol is more viscous than water
B) The re are obstacles to the free movement of Ca₂+ in the cytosol that aren't present in water
C) Cytosol contains fixed proteins that bind Ca₂+, slowing its movement
D) The cytosol moves most electrolytes, but not Ca₂+, around by convection
E) Ca₂+ causes solidification or gelling of the cytosol

Question 6

According to the Stokes-Einstein equation, if the radius of one particle is twice the radius of a second particle ( r1 = 2 r2) , then the relative value of their diffusion coefficients should be

A) D 1 = 2 D2
B) D 1 = D2 / 2
C) D 2 = D2 / 4
D) D 1 = D2 / 8
E) D 1 = D2 / 16

Question 7

In the rand om walk deriva tion of Fick 's Se con d La w, the diffus ion co efficie nt wa s eq uate d to

A) H₂ / 2 t
B) kt /þ
C) h / t
D) H₂ / h
E) tc /

Question 8

Consider two spherical cells that are identical in all respects except that cell one has a rad ius tha t is 20% greater than the radius of cell 2 (r1 = 1.2 r2). One substance is transported into the ce ll pa ss ive ly. The relative flux of the material across the mem branes of the two cells is given as

A) J1 = 1.2 J2
B) J1 = 1.44 J2
C) J1 = J2
D) J1 = 1.728 J2
E) Cannot be determined from the information given.

Question 9

Diffusion of a small non-electrolyte (D = 0.5 x 10-5 cm 2s-1) across a 50 µm cell tak es a bou t

A) 2.5 milliseconds
B) 25 milliseconds
C) 2.5 seconds
D) 25 seconds
E) 250 seconds

Question 10

If Ca > Cb and a > b, where a and b are x-coordinates, then

A) The gradient of C is negative and diffusive flux is positive, going from a to b
B) The gradient of C is positive and diffusive flux is negative, going from a to b
C) The gradient of C is negative and diffusive flux is negative, going from b to a
D) The gradient of C is positive and diffusive flux is negative, going from a to b
E) The gradient of C is negative and diffusive flux is positive, going from b to a

Question 11

The diffusion coefficient of Na+, K+ and many more solutes is slower in cytosol than in water because

A) The cytosol is more viscous than water
B) The re are obstacles to the free movem ent of ions in the cyto so l tha t ar en 't present in water
C) Cytosol contains fixed proteins that bind ions, slowing their movem ent
D) The cytosol moves most electrolytes around by convection
E) Ca₂+ causes solidification or gelling of the cytosol

Question 12

Consider two spherical cells th at are identic al in all resp ects ex ce pt th at c ell o ne ha s a rad ius tha t is 20% greater than the radius of cell 2 (r1 = 1.2 r2). O ne su bs tan ce is tr an sp or ted into the ce ll pa ss ive ly. The relative flow of the material across the mem branes of the two cells is given as

A) Q 1 = 1.2 Q 2
B) Q 1 = 1.44 Q 2
C) Q 1 = Q2
D) Q 1 = 1.728 Q 2
E) Cannot be determined from the information given