Experiment 14: Osmotic Pressure and Growth

what is osmosis?

movement of water from one side of the semipermeable cell membrane to the other side

what is osmotic pressure?

soln takes in water across the semipermeable cell membrane affects the ability of the water entering and leaving the cell

impacts survivability and growth

movement of water?

from lower solute to higher solute

so high water conc to low water conc

what are solutes in cells?

dissolved salts, sugars, and amino acids

what are the 3 ways of characterizing osmosis enviros?

1. Hypotonic

2. Hypertonic

3. Isotonic

what is a hypotonic environment?

enviro has low solute

water flows into cell from enviro

cell SWELLS

what is a hypertonic environemnt?

enviro has higher solute

water flows out of cell

cytoplasm dehydrates and shrinks through plasmolysis

back to normal when placed in isotonic

what is a isotonic?

solute conc same in and out of cell

What are osmophilic organisms?

thrive in hypertonic enviros with high solute concs

what are osmotolerant?

can survive in range of osmotic pressures

what happens when bact are placed in hypertonic solns?

their metabolism and growth is inhibited

what are halotolerant specieis?

can grow at low to moderate salt concs

what are halophiliic species?

require high salt concs (3-5x ocean)

find in marine, salt lakes, skin

exp 14 learning objectives

1. observe bact growth under varying salt concs

2. analyze tolerance in hypo/hypertonic solns

exp 14 materials (in pairs)

1. E.coli

2. Staphylococcus aureus lvl 2

3. Halobacterium salinarium

4. Nutrient agar 0.5% NaCl

5. Salt agar 5% NaCl

6. Salt agar 10% NaCl

7. Salt agar 25%

8. Swabs

Exp 14 method

1. label, inoculate ea bact on each plate (start w/ 0.5% - 25%)

2. incubate inverted for 48hr at 37deg

3. 25% plate may need additional 48hr incubation so 72 total. (placed in plastic bags to avoid drying

Results - E.coli

0.5% = (+++)

5% = (+)

10% = (-)

25% = (-)

Best = low NaCl

Results - S. aureus

0.5% = (+++)

5% = (++)

10% = (+)

25% = (-)

Best = low NaCl

Results - Halobacterium salinarium

0.5% = (- - - )

5% = (- - -)

10% = (- -)

25% = (++) reddish

Best = high NaCl = HALOPHILE