Cell Bio Lab #7 - Phospholipid and Membrane Transport - Review

Diffusion

This is the net passive movement of molecules down their concentration gradient; molecules are in constant motion and tend to move from regions where they are in higher concentration to regions where they are less concentrated

Facilitated Diffusion

This is the passive movement of molecules along their concentration gradient, guided by the presence of another molecule that is usually an integral membrane protein forming a pore or channel

Osmosis

This is the diffusion/passive transport of water as it moves through a selectively permeable membrane from a region of its higher concentration to a region of its lower concentration

Water potential

- Water potential is the potential energy of water in a system compared to pure water, when both temperature and pressure are kept the same

- Water always moves from an area of higher water potential to an area of lower water potential

This is the tendency of water to leave one place in favor of another. It is the ability of any biological cell to take in water, creating pressure exerted on the cell wall.

Pressure and amount of solute

What are the factors affecting water potential?

Water potential (Ψ) = pressure potential (Ψp) + solute potential (Ψs)

What is the equation used to calculate water potential?

Into the cell

Where does water move if it has a negative water potential?

Solute potential

In lab, pressure potential is equal to zero, so what is water potential equal to?

(final weight - initial weight) / (Initial weight) x 100

What is the formula for percent weight change?

Ψs = -iCRT

What is the formula used to calculate solute potential?

The ionization constant which depends on what solute is provided

- e.g. sucrose: i = 1 ; NaCl: i = 2 ; MgCl2: i = 3

For the solute potential equation, what does "i" stand for?

The concentration fo solute as determined

For the solute potential equation, what does "C" stand for?

The pressure/gas constant which is equal to 0.0831 (L)(bar)/(mol)(K)

For the solute potential equation, what does "R" stand for?

Temperature in degrees Kelvin which is 273 + °C of the solution

For the solute potential equation, what does "T" stand for?

The cell is hypertonic, so it takes up water from the solution. Negative water potential draws water up into the plant stem

If the water potential of a plant cell is negative, is the cell hypertonic or hypotonic compared to its surrounding solution? Will this cause water to rise through the plant stem?