Question

In the early Spring, you can tap the trunk of a maple tree (or many other species), to collect sugary sap for the production of syrup. Since the phloem does not resume function until both day and night-time temperatures remain in the upper 30 F range (and the temperature during "syrup season" often drops below freezing at night), where does the sugar come from? Explain.

Think about where sugar is stored during the winter in a tree. (What part of the tree is protected from the environmental extremes which exist during the winter months?) Think about what molecule sugar is stored as during the winter. Think about what process must occur to convert the molecule that sugar is stored as, into sugar. Think about what would happen if you raise the sugar concentration in that tissue by conversion of the very large, osmotically inactive storage molecule, into sugar. What is osmosis? What is the difference in water concentration between the tissue and the surrounding soil? How would that concentration difference effect water movement, into or out of the tissue? If water moves into the tissue, would that generate pressure? How would that pressure be released?

Answer 1

During the fall, trees change color and then lose their leaves. This is in preparation for the winter season. Because it gets so cold, the trees have adapted to the winter by going into a period of dormancy or sleep. They also have thick bark to protect them from the cold weather.The sucrose in the sap of these trees is generally regarded as derived from the starch stored in the wood-parenchyma.  There is no need to infer a direct change of starch into sucrose.  The starch is broken down in the usual way, and either the maltose or the glucose. It is transformed into sugar on its way through to the xylem vessels.There is the role of carbohydrates in translocation in xylem sap, where sucrose levels apparently create positive pressure in the wood, or bleeding sap.