= Turgor pressure
{title2=$P_{\mathrm{in}}-P_{\mathrm{out}}$}
{wiki}
<Turgor pressure> is the internal <hydrostatic pressure> above the external <pressure> in a <biological cell>. When <water> enters a walled <biological cell> by <osmosis>, expansion loads the <cell wall>. Rising <pressure> can oppose further net entry while the <cell membrane> retains its <selective permeability>. Mechanical support therefore does not require the <cell wall> to block <water>.
As an original mechanical check, idealize a small flat patch of <cell wall> of <surface area> $A$ under uniform <turgor pressure> $\Delta P=P_{\mathrm{in}}-P_{\mathrm{out}}$. Its outward <force> is $F=\Delta P A$. Doubling $A$ at fixed <pressure> doubles the load; equal internal and external <pressures> give zero net pressure load. This is a force balance, not a measured wall strength or a complete model of a curved, growing <biological cell>. It says nothing about which <solutes> cross the <cell membrane>.
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