Bio Lab Midterm - Permeability

Diffusion

movement of molecules from a region of high concentration to a region of low concentration (move down the gradient)

Passive movement

diffusion of molecules or ions through a selectively permeable membrane (move down the gradient)

Dialysis

passive movement where one solute is separated from another solute due to a selectively permeable membrane allowing one solute to pass but not another

Osmosis

special case of passive movement in which solvent molecules (water) whose movement through the membrane is of interest.

hypotonic vs hypertonic

• hypotonic - low solute concentration

• hypertonic - high solute concentration

how does water move in comparison to hyper and hypotonic solutions

water moves from hypotonic solutions to hypertonic solutions (down water gradient)

solute

minor component in solution that is dissolved in solvent

solvent

major component in solution that dissolves solute (usually water)

solution

mixture where solute is dissolved in solvent

what is agar solution

• agar is a polysaccharides. (it is heated then cooled to be gel like)

• 1% agar and 99% water

agar plate procedure

agar plate has two holes 1.5cm apart and when blue dye and HCl are put in both you will observe them diffuse through agar.

why use the dye

it is a pH indicator that changes from blue to yellow when pH drops below 4.0. We observed that there was yellow meaning H+ ions from HCl diffused towards the dye

molecular weight effect on diffusion

higher molecular weight results in a slower diffusion rate

Was the yellow closer to where the HCl started or the bromophenol blue dye?

It was closer to the bromophenol blue because HCl is lighter and diffuses faster.

Based on what you've seen here, do you think diffusion is an effective way to move substances from place to place in multicellular organisms? For example, would diffusion serve for moving inhaled oxygen from your lungs to your brain? Why/why not?  

Diffusion is not an effective way to move substances from place to place in multicellular organisms because it is effective over short distances but due to the long time it takes to occur it would not be plausible.

dialysis tubing

membrane with tiny pores that we cannot see

Cut off value and what can pass through

The size biggest size of molecules that can pass through. In this lab it’s 12,000 Daltons so proteins and polysaccharides cannot pass through but carbohydrates and amino acids can.

Water gradient

Water concentration between two areas

osmotic pressure

Pressure that would have to applied to solution in the bag to prevent water on other side of membrane from diffusing into bag

How does osmotic pressure increase

Osmotic pressure increases with solute concentration

• water has O.P. value of 0

• solution with 10% salt has greater O.P. than solution with 5% salt

Colligative Property

properties of solution that depend on ratio of solute particles to solvent particles. Osmotic pressure depends on this

Colligative property with molecules that dissociate in water

0.1M glucose and 0.1M sucrose have the same O.P. but 0.1M NaCl has a higher O.P. because it has 0.1 Na+ and 0.1 Cl-

rate of diffusion/osmosis

how fast water diffuses into bag

Does osmosis happen indefinitely?

rate of osmosis would eventually level off due to reverse pressure from bag or the bag would burst

Measure the weight of bags with what?

Balance not a scale

tare weight

Weight of paper that we do not want to account for.

raw data and how to adjust

Data in tables that accounts for membrane weight, tie weight, and solution weight. We only want solution weight so subtract 0.4g for the membrane and tie.

How do we express the weight change of solutions?

express them as a percentage of the starting weight.

When making the table what is the control and variable?

• Control: Bag #1

• Variable: Solute concentration or molecular weight

There should be no significant change in the weight of bag #1.  Why?  If you do find slight changes with time, how do you explain that?

There is no weight change because there is no water gradient as the concentration of water in the bag and out is the same. If any changes did occur it would be do to error as contaminants could have entered the water.

The bags with sucrose still gained weight even though both sucrose and water can diffuse freely, what does this tell us?

Water diffuses faster than sucrose as more water entered the bag than sucrose left meaning that water is smaller lighter than sucrose.