How come we can have maple syrup?

Question

The roots of maple suck in water from underground, and pump it into the trunk. If we cut the bark, we can collect the syrup at significatly higher level of altitude. Does not it violate conservation of energy, and if not, what is the mechanism behind this phenomenum?

Answer 1

You can't make a perpetual motion machine using capillarity alone. It's cell osmosis that provides the extra pressure needed to be able to tap and collect the syrup.
The sugar maple tree acts as a pump with a diurnal cycle during the sap season (ref.). In the relatively warm daytime half-cycle, the combined effects of CO2 dissolution/expansion and cell osmosis pressurize the tree and the sap flows. In the cooler nighttime half-cycle, the CO2 contracts and redissolves and the increased "suction" causes the roots to increase the rate of water absorption from the soil. There is, of course, chemistry at work, especially in daytime, to maintain the solute concentration gradients across the osmotic membranes.

Answer 2

What you think would be true if there were long hollow tubes leading from underground to the branches several feet above the ground, but they aren't long hollow tubes that carry water up (and sap down) the tree.

Even if it was single long hollow tubes, there is a phenom. called capillary action that works on very narrow hollow tubes. The action of surface tension (a force) against the sides of the narrow tubes can force water upward.

Capillary action is only a small part of the 'story'. The 'tubes' that carry water upward are composed of individual cells. Cells have membranes, and by chemical action water is transported from where it is in high concentration (roots) to where it is in lower concentration (higher up).

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Answer 3

Capillary action in the leaves draws up the sap. This is a form of molecular potential energy (water has lower potential in a capillary). Photosynthesis provides the energy for capillary growth. What keeps the sap flowing after it's metabolized or tapped, however, is evaporation (an endothermic process). This extracts heat from the air, thereby cooling it.