Cell Membranes and Transport

Osmosis is the [blank_start]diffusion[blank_end] of [blank_start]water molecules[blank_end] from a region of [blank_start]high water potential[blank_end] to a region of [blank_start]low water potential[blank_end], through a [blank_start]selectively permeable membrane[blank_end].

Water potential of an animal cell in pure water/dilute solution ([blank_start]hypotonic[blank_end] to the cell) causes [blank_start]haemolysis[blank_end]. Water potential of an animal cell in a concentrated solution ([blank_start]hypertonic[blank_end] to the cell) causes [blank_start]crenation[blank_end]. Water potential of an animal cell in a solution with the same concentration ([blank_start]isotonic[blank_end] to the cell) causes [blank_start]no change[blank_end].

The equation for water potential in a plant cell is: water potential = pressure potential - solute potential

[blank_start]Solute potential[blank_end] is the [blank_start]reduction[blank_end] in [blank_start]water potential[blank_end] due to the presence of [blank_start]solute[blank_end] molecules.

Label the diagram:

Which type of molecules needs to be 'assisted' in crossing membranes?

The equation for water potential in an animal cell is: water potential = solute potential

[blank_start]Intrinsic[blank_end] proteins exit across both [blank_start]phospholipid bilayers[blank_end]. Some are [blank_start]carriers[blank_end] and others allow [blank_start]active transport[blank_end] of [blank_start]ions[blank_end]. [blank_start]Extrinsic[blank_end] proteins are located in [blank_start]either surface[blank_end] of the [blank_start]phospholipid bilayer[blank_end]. These provide [blank_start]structural support[blank_end] and [blank_start]recognition sites[blank_end].

Which of these do NOT affect the rate of diffusion?

[blank_start]Water potential[blank_end] is the [blank_start]measure[blank_end] of the [blank_start]free energy[blank_end] of [blank_start]water molecules[blank_end] and is the [blank_start]tendency[blank_end] for [blank_start]water[blank_end] to [blank_start]move[blank_end].

Label the diagram of a plant cell:

Rate of diffusion equation: [blank_start]rate of diffusion[blank_end] = ([blank_start]surface area[blank_end] x [blank_start]difference in concentration[blank_end])/ [blank_start]length of diffusion pathway[blank_end]

What factors affect the permeability of water?

Passive diffusion is the [blank_start]passive movement[blank_end] of a [blank_start]molecule[blank_end]/[blank_start]ion[blank_end] down a [blank_start]concentration gradient[blank_end] from a region of [blank_start]high concentration[blank_end] to a region of [blank_start]low concentration[blank_end]. [blank_start]Facilitated[blank_end] diffusion is the [blank_start]movement[blank_end] of molecules/ions [blank_start]down[blank_end] a concentration gradient using protein [blank_start]carriers[blank_end]/[blank_start]channels[blank_end].

Where does active transport takes place?

Active transport is the [blank_start]movement[blank_end] of [blank_start]molecule[blank_end] or ion across a [blank_start]membrane[blank_end] [blank_start]against[blank_end] a [blank_start]concentration gradient[blank_end], using [blank_start]energy[blank_end] from the [blank_start]hydrolysis[blank_end] of [blank_start]ATP[blank_end] made by the cell in [blank_start]respiration[blank_end].

The process of Co-Transport: 1) Sodium ions are [blank_start]transported[blank_end] out of the cell into the blood, via active transport. 2) This creates a [blank_start]concentration gradient[blank_end] between the number of sodium ions [blank_start]inside and outside[blank_end] of the cell. 3) [blank_start]2[blank_end] sodium ions are attached to the binding sites on co-transport carrier proteins, along with [blank_start]1[blank_end] glucose molecule on the glucose binding site. 4) Protein [blank_start]carrier[blank_end] changed shape and moves the glucose molecule and sodium ions inside of the cell. 5) The glucose molecule and sodium ions move to opposite side of the cell, [blank_start]separately[blank_end]. 6) Glucose diffuse to the blood stream by [blank_start]facilitated diffusion[blank_end], along a concentration gradient. 7) Sodium ions goes into the blood stream through a [blank_start]sodium/potassium[blank_end] pump, by [blank_start]active transport[blank_end], against a concentration gradient.