Osmosis in Plant and Animal Cells

IGCSE Biology — Water movement across semi-permeable membranes

Solution Type
Isotonic
Water Potential
Equal
Net Water Movement
↔ No net movement
Osmotic Effect
Cells unchanged
Plant Cell State
Normal
Animal Cell State
Normal
In an isotonic solution the concentration of solutes outside the cell equals the concentration inside. There is no net movement of water, so cells remain at their normal size.

Key IGCSE Concepts

Osmosis
Net movement of water molecules from a region of higher water potential to lower water potential through a semi-permeable membrane.
Water Potential (Ψ)
The tendency of water to move. Pure water has the highest water potential (0 kPa). Adding solute lowers it.
Turgid
Plant cell swollen with water. Membrane pushes against cell wall, making the cell firm. Keeps plants upright.
Plasmolysed
Plant cell has lost water. Cell membrane pulls away from cell wall. Causes wilting in plants.
Lysis
Animal cell absorbs too much water in hypotonic solution and bursts. No cell wall to resist swelling.
Crenation
Animal cell loses water in hypertonic solution and shrivels, developing a spiky/wrinkled surface.
Semi-permeable Membrane
Allows small molecules (water) to pass through but blocks larger solute molecules (sugar, protein).
Turgor Pressure
Pressure of cell contents pushing outward against cell wall. Prevents further water uptake in plant cells.
IGCSE Science Simulations