Water and Osmosis

Describe water molecule

-polar molecule so has no overall charge

-hydrogen atoms have partial + charge, oxygen atoms have partial - charge

-water molecules form hydrogen bonds between each other as they are polar

How does sodium chloride dissolve in water?

-Cl ions attracted to H+ ions

-Na ions attracted to O- ions

-bonds between Cl and Na ions breaks

What are the properties of solid water?

-less dense than liquid water

-stable hydrogen bonds keep molecule further apart so ice floats

Describe properties of water

-has high specific heat capacity as it can absorb a lot of heat energy but not increase too much in temperature

-has high latent heat of vaporisation as it can absorb lots of heat energy before changing state (liquid to gas)

-surface tension occurs so supports mass of organisms = becomes habitat for them

-strong adhesive and cohesive properties as molecules stick together to other substances so can be placed under high tensile forces

Define Osmosis

passive movement of water from an area if less negative water potential to an area of more negative water potential across a partially permeable membrane

Define water potential

tendency of water to move and leave a system - measured in kPa

What happens when solute is added to pure water?

-water molecules pulled inwards and stick together

-water potential becomes more negative as water is bound to solute

Explain what happens to animal cell in water and salt solution

Water - cells have more negative water potential so water moves in by osmosis and cell bursts

Salt solution - cells have less negative water potential so water moves out by osmosis and cell shrivels

Explain what happens to plant cell in water and salt solution

Water - cells have more negative water potential so water moves in by osmosis so cell swells and becomes turgid (as vacuole expands and pushes against cell wall)

Salt solution - cells have less negative water potential so water moves out by osmosis so cell becomes flaccid and is plasmolysed

Define hypotonic solution

water moves into cell as external solution has a less negative water potential

Define hypertonic solution

water flows out of cell as external solution has a more negative water potential

How to calculate water potential of cell?

water potential of cell = pressure potential + solute potential

Define adhesion and cohesion

Adhesion - water hydrogen bonds to other stuff

Cohesion - water hydrogen bonds to itself