Why do you think that a thick cuticle on the outer wall of epidermis is advantageous for a plant living in the desert but disadvantageous for a plant living underwater?
A thick cuticle on the epidermis is advantageous for a desert plant because it helps to reduce water loss during transpiration. Since desert habitats are very dry, this waxy layer is crucial for the plant's survival by preventing excessive evaporation.
Conversely, it is disadvantageous for an underwater plant because these plants are already submerged in water and do not need to prevent water loss. A thick cuticle would act as an unnecessary barrier, hindering essential gaseous exchange and the direct absorption of water and minerals from the surrounding aquatic environment.
Explanation
The textbook states that in very dry habitats, a thick cuticle reduces water loss via transpiration, which is a survival advantage for desert plants. However, for underwater plants, preventing water loss is irrelevant as they are submerged. A thick waxy cuticle becomes disadvantageous as it blocks direct contact with the water, impeding gaseous exchange and the absorption of water and minerals, which are vital functions for aquatic plants.