Osmosis Flashcards
What is osmosis?
The diffusion of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane
What is water potential?
The ability of water molecules to move freely
Concentration of moles per dm3
Why does adding solutes decrease number of water molecules to move freely?
Due to ionic dipole interaction
What happens to water molecules in glucose solution?
Form hydrogen bonds with glucose, decreasing water potential
What are water potential values?
All solutions have negative value
More solute you add, lower the water potential
Pure water=highest water potential = 0KPa
What happens to an animal cell in a hypertonic solution?
Net movement out of cell
More concentrated than the cell (lower water potential).
Cell becomes crenated (shrivelled)
Less cytoplasm
What happens to an animal cell in an isotonic solution?
No net movement
Same water potential as cell
What happens to an animal cell in a hypotonic solution?
Net movement into cell
Less concentrated than the cell
Cell swells up, lysis
what is the equation for water potential?
water potential = osmotic (solute) potential + turgor (hydrostatic) pressure
What is turgor (hydrostatic) pressure?
pressure exerted by cell wall against the cells contents
What is the effect of a hypertonic solution on a plant cell?
water moves out of cell
cell becomes plasmolysed
potential pressure = 0
potential solute = water potential overall
What is the effect of an isotonic solution on a plant cell?
no net movement
cell is flaccid
potential pressure = 0
potential solute = water potential overall
What is the effect of a hypotonic solution on a plant cell?
water moves into cell
cell is turgid
cell contents presses on cell wall
water potential overall = potential solute + potential pressure
What condition do plant cells want to be in?
turgid -> provides structure and keeps plant upright
Why does glycogen have a much smaller influence on water potential than glucose?
glycogen is insoluble as very few OH groups are exposed on outside so form few H bonds
glucose is soluble as forms more H bonds with water as more OH groups are exposed
How do you perform a serial dilution?
changing conc. by factor of 10
e.g. start with 1 mole - 10ml water
dilute to 0.1M by 1ml + 9 ml water
dilute to 0.01M by 1mil + 9ml water
What are serial dilutions good for?
getting small conc.
e.g. drugs, hormones
What is a standard dilution?
C1V1 = C2V2
e.g. 20cm³ of 0.3M solution, with a 1M stock:
(0.3 x 20)/ 1 = 6cm³ of solution + 14cm³ water
