effects of water potential

Question 1

what is water potential (ψ)?

Answer 1

• pressure created by water molecules measured in kPa
• ψ of pure water at 25℃ and 100kPa: 0
• more solute = ψ is more negative

Question 2

how does osmosis affect plant cells

Answer 2

• osmosis into cells / hypotonic solution: protoplast swells and pressure builds up = cell turgid
• osmosis out of cells / hypertonic solution: protoplast shrinks and pressure decreases, 0 pressure potential = incipient plasmolysis = cell flaccid / plasmolysed

Question 3

how does osmosis affect animal cells?

Answer 3

• osmosis into cells / hypotonic solution: cell membranes break as thin can’t extend and therefore release cells contents = haemolysis
• osmosis out of cells / hypertonic solution: cell shrinks and shrivels = crenation

Question 4

how do we prevent animal cells from bursting in haemolysis or shrivelling in crenation?

Answer 4

• cells are normally bathed in an isotonic liquid so no osmosis takes place