Final answer:
A cellulose-based material that mimics plant capillaries is the best tool to help flowers retain water and nutrients while in a box; it absorbs and retains moisture for the flowers to uptake.
Step-by-step explanation:
To ensure that flowers retain water and nutrients while in a box, it is essential to understand the mechanisms of water and nutrient transport in plants. The structures responsible for this process include cellulose-based capillaries in plant tissues, which utilize capillary action. A useful tool to help flowers maintain moisture could be a cellulose-based material that mimics these natural capillaries. Such materials act like sponges, absorbing and retaining water that the flowers can then take up. This imitation of the plant's natural capillary action can be crucial in preserving the flowers' freshness during storage or transport.