Question

(a) List the chemical characteristics of molecules that are most likely to move by simple diffusion across the lipid bilayer of the plasma membrane and explain why.
(b) Explain the factors that Fick’s Law tells us to determine the rate of diffusion through the lipid bilayer.

Answer 1

Answer:

Explanation:a) low melting point

Poor conductivity

: Low solubility

Low solubility The mass is equal to the sum of the masses of all the individual atoms in the molecular structure.

b) The cross-sectional area of the fluid.

Therefore The diffusion coefficient is a physical constant dependent on molecule size and other properties of the diffusing substance as well as on temperature and pressure.

Answer 2

Answer:

1.Glycerol, alcohol and steroid hormones  diffuse easily; because they are  non-polar  and  soluble in the non-polar phospholipid tails of bilayer, (lipid solubility and composition  of the membrane)

2.Oxygen and Carbon dioxide, pass easily through  the lipid bilayer ; because they uncharged  and non-polar.(lack of polarity)

3. Water because of small molecular size pass through the membrane

Ficks stated that the rate of diffusion is proportional  to the surface area,concentration gradient and inversely proportional to the membrane thickness,

The larger the number of molecules  at  a point, the higher  the concentration of the molecules at  that  particular direction. These molecules have higher kinetic energy than other molecules of smaller number and concentrations in the same environment. Thus   move(diffuse) down their  concentration gradients to a less crowded environment .The higher the concentration gradient the faster the rate of diffusion.

The larger the surface area available  for molecules to get free  from their  intermolecular  forces  the faster the rate of diffusion. However, this varies with the size of organisms. For example small organism e.g Rat has large surface area to volume ratio, therefore the rate of diffusion of molecules is very high. Large organism like Elephant has low  surface-area to volume with lower rate of diffusion.

The thicker the membrane the longer the diffusion distant the  molecules need to pass  across to move down the concentration gradient and therefore the lower the rate of diffusion

Explanation: