Lab #3: Diffusion, Osmosis, and Tonicity

Solution

a mixture of two substances with one dissolved in the other

Solute

molecules that dissolve in a solution

Solvent

the liquid into which solutes dissolve (water)

Media

substance through which diffusion occurs, such as water and air

Selectively Permeable Membrane

a property of cell membranes that allows some substances to pass through and blocks others based on size

Passive Transport

movement across a membrane along its concentration gradient that does not require the cell to expend energy

(high --> low concentration)

Active Transport

energy-requiring process that moves molecules across a membrane against its concentration gradient

(low --> high concentration)

Permeability

refers to the ease at which substances can pass through a membrane

Diffusion

the movement of solute molecules from an area of higher concentration to an area of lower concentration

Factors Affecting Rate of Diffusion

- concentration gradient

- molecular size

- density of media

- membrane permeability

- temperature

Diffusion is a _________ process

passive (no energy required)

Molecules move from _______ to _______ areas of concentration

higher / lower

There will be net movement until the concentration is _____ everywhere or when _______ is reached

equal / equilibrium

Diffusion is _____ over short distances, but much ______ over long distances.

rapid / slower

(1) Diffusion is _________ related to _________

directly / temperature

(2) Diffusion is ________ related to ___________

inversely / molecular size

Diffusion can take place in an ____________ or ____________

open system / across a partition that separates the two systems

Osmosis

the diffusion of water from an area of high water concentration to an area of low water concentration across a selectively permeable cell membrane

Tonicity

the ability of a solution to change the volume of a cell through osmosis

Tonicity is dependent on two factors

the osmolarity of the solution as well as the solutes ability to cross the membrane (nature of solutes)

Penetrating vs. Non-Penetrating Solutes

- a penetrating solute is one that can enter a cell by crossing the membrane

- a nonpenetrating solute is one that can't cross the cell membrane or enter the cell

Isotonic

- a solution that results in no net movement of water

- concentration of two solutions is equal

- cloudy/opaque appearence

Hypotonic

- a solution that causes a net movement of water into a cell

- cell swells/bursts (hemolysis)

- clear transparency

Hypertonic

- a solution that causes a net movement of water out of a cell

- cell shrinks/crenated

- cloudy/opaque appearence

Properties of Mature RBCs

- lack a nucleus

- float in isotonic blood plasma

- flattened biconcave disk shape

What is dialysis tubing made out of?

regenerated cellulose fibers

I2KI Test

- solution turns purple/black if starch is present

- solution remains a pale-yellow-amber color if no starch is present

Benedict's Test

- solution turns, green, yellow, and orange if glucose (a reducing sugar) is present

- solution remains blue if no glucose is present

High Glucose Concentration --> Low Glucose Concentration

brown, red, orange, yellow, green

Bag: Original Contents/Color

- glucose & starch

- clear

Bag: Final Color

- purple

- the purple color tells us that starch is still present in the bag and iodine from the beaker was able to diffuse into the bag and react with starch (iodine moved from high to low concentration)

Bag: Color After Benedict's Test

- yellow

- the yellow color tells us that glucose is still present in the bag but at a lower concentration

Beaker: Original Contents/Color

- water & iodine

- yellow amber

Beaker: Final Color

- amber

- the amber color tells us that no starch is present (due to its large molecular size)

Beaker: Color After Benedict's Test

- orange

- the orange color tells us that glucose is present in the beaker and at a higher concentration than the bag (glucose moved from a high to low concentration)

Control: Original Contents/Color

- distilled water

- clear

Control: Final Color

clear

Control: Color After Benedict's Test

- hint of blue

- no glucose present