What can you remember about Osmosis from GCSE

What can you remember about Osmosis from GCSE? • Definition? • Passive/active? • Direction of movement • The difference between a solute, solvent & solution • The difference between concentrated & dilute solutions in terms of FREE water molecules

Osmosis q Explain what is meant by Osmosis, in terms of water potential q Recognise & explain the effects of solutions of different water potentials on plant & animal cells

At AS, you must call it water potential (not concentration!) Osmosis Water Potential • Diffusion of water molecules that are free to move from an area of high water potential to a low water potential through a partially permeable membrane • Measured in Kilopascals (k. Pa). • Pure-0 k. Pa. • Cell cytoplasm contains dissolved sugars, salts etc so water potential is more negative • A solution with a high water potential has a large number of water molecules that are free to move.

What happens?

Hypotonic vs. Hypertonic solutions Hypotonic • One of two solutions with MORE water and less solute (e. g. very watery) Hypertonic • One of two solutions with less water and MORE solute (e. g. very salty or very sugary) • Which solution will have the most negative water potential? • Write a definition for Isotonic • What will happen to animal and plants cells placed in a) Hypertonic solutions? b) Hypotonic solutions?

What happens in pure water? • Animal cell will eventually burst-HAEMOLYSED • Plant cells-swelling cytoplasm & vacuole will push against the cell wall which will stop the cell getting any larger-TURGID

What happens in conc. Sugar? • Animal cell: cell contents shrink & membrane wrinkles. FLACCID • Plant cell-cytoplasm & vacuole shrink and PM pulls away from cell wall-PLASMOLYSIS

Draw the table below & fill with annotated diagrams to explain what is happening… Hypotonic solution Animal cells Plant cells Hypertonic solution Keywords to include: q Turgid q. Flaccid q. Plasmolysis q. Water potential qk. Pa q. Solute q. Free water q Haemolysed

Hypotonic solution Animal cells Hypertonic solution Water potential lower outside cell than inside cell, water diffuses out of cell via osmosis down water potential gradient. Plant cells Draw the table above & fill with annotated diagrams to explain what is happening…

Hypotonic solution Hypertonic solution Animal cells Water potential higher outside cell than inside cell, water diffuses into cell via osmosis down water potential gradient Water potential lower outside animal cell than inside cell, water diffuses out of cell via osmosis down water potential gradient. Plant cells Water potential higher outside cell than inside cell, water diffuses into cell via osmosis down water potential gradient Water potential lower outside cell than inside cell, water diffuses out of cell via osmosis down water potential gradient Plant cell wall prevents cell wall from bursting. The cell is turgid. Plant cell membrane pulls away from cell wall. Cell is flaccid.

Osmosis Investigation • Laptops • G: Science Investigations 2 • Osmosis • Complete Worksheet