BRAINCAKELenticels
Woody stems and roots are covered by bark, whose outer layer is made of cork. Cork cells are dead and their walls contain suberin, a waxy substance that is impermeable to water and gases. This protects the stem and reduces water loss, but it creates a problem: the living tissues underneath, such as the phloem and cambium, still respire and need oxygen.
The solution is lenticels. A lenticel is a small area of the bark where the cork cells are loosely packed, with many air spaces between them. Gases can diffuse through these spaces:
• oxygen diffuses in to the living cells beneath the bark
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All 23 lessons in Gas Exchange · All Edexcel AS-level Biology topics