Practice question

Cuticle comprises cutin polyester matrix impregnated and covered by epicuticular waxes deposited on outer epidermal wall of aerial organs of embryophytes. Ultrastructurally it forms continuous hydrophobic barrier dramatically reducing non-stomatal water loss rate by orders of magnitude, preventing tissue desiccation under fluctuating humidity and allowing survival away from water films. Additional functions include UV screening, mechanical defense, prevention of pathogen entry and self-cleaning, but primary selective pressure during terrestrialization was water retention. CO2 absorption occurs via stomata whose opening regulated; cuticle actually impedes gas exchange.