4.5 water

water potential

the tendency of water to move from one area to another. kPa

isotonic solution

same concentration: no net movement / water goes in and out at the same time due to the same amount of water potential

hypotonic solution

solution has a higher water potential than cell

water moves into cell (hypO→inside) due to osmosis.

• plant cell : becomes turgid causes vacuole and cytoplasm push against the inelastic cell wall ~ pressure potential increases if more water moves in

• animal cell : lysis (burst) due to no cell wall

hypertonic solution

solution has a lower water potential than cell

water moves out the cell due to osmsosis

HYPER - mixes water to be LESS hyper

• plant cell: plasmolysed ~ vacuole & cytoplasm shrinks, cell membrane pulling away from the cell wall

• animal cell: shrivel

incipient plasmolysis

50% cells plasmolysed, 50% not. due to cell having varying water potential

equation for water potential

water potential = solute potential + pressure potential

osmosis

the net movement of water from an area of high water potential to an area of lower water potential, across a selectively permeable membrane.

Ice is less dense than water. Why is this useful for organisms?

Ice forms an insulating layer over aquatic habitats.

So animals in the water can still move/swim.

Explain what is meant by a high specific heat capacity of water.

A large amount of energy is required to increase 1kg of water by 1'C.

Water has cohesive properties.

What is meant by cohesion?

Water will form hydrogen bonds to other water molecules.

Water is a liquid at most temperatures on Earth. Why is this useful for organisms?

It can be used as a medium for chemical reactions and to help transport chemicals.

Water has a high specific heat capacity. Why is this useful for organisms?

Aquatic habitats and the

cytoplasm of cells remain a stable temperature.

Water has adhesive properties.

What is meant by adhesion?

Water will form hydrogen bonds with other polar or charged molecules.

Water has a high specific latent heat. Why is this useful for organisms?

It acts as a coolant (e.g. sweating) and aquatic habitats don't evaporate easily.

Explain what is meant by a high specific latent heat of water.

A large amount of energy is required to change the state of

1 kg of water.

Water is transparent. Why is this useful for organisms?

Light can pass through water to aquatic plants for photosynthesis.