Plants like the stinging nettle seen here have sharp, needle-like hairs that inject a burning chemical into animals that touch the stems or leaves. these hairs are used for

protection against grazing animals

Physiological adaptation is the type of adaptation in which the plant metabolism releases certain biochemical products such as toxins which help plant to survive in it's environment. The needle hair of plants injects a burning chemical into animals which touch stems or leaves , it is an example of physiological adaptation. These hair are used for protection of plant against grazing by grazing or herbivorous animals.  

answer; both surfaces of the membrane are nonpermeable