OFFICIAL72 The professor makes the point that cells in maple trees are mostly filled with gas. What does this point explain (CIick on 2 answers)

[00:00.00]Listen to part of a lecture in a botany class.
[00:04.76]Professor: Ok. During the break, some of you have some questions. [00:07.14]And while we were talking, I mentioned that my family owns a maple syrup business in the Massachusetts. [00:11.99]And some of you asked, if I talk a little bit about how that works, give you a brief lesson in applied button as David put it. [00:18.74]So, yes, ok.
[00:21.54]Well, maple sap is collected from several species of maple trees that grow primarily in the northeastern United States and southeastern Canada. [00:30.38]You know you don’t actually get syrup from a maple tree ready to put on your pancakes. [00:35.21]What you get is sap that can be made into syrup. [00:38.35]So first, sugar is created through photosynthesis, then it's converted into starch, and it's set for storage, usually in the roots of the tree. [00:46.98]Then as springtime approaches, the starch is converted back into sugar. [00:51.97]The sugar and starch is dissolved in this watery liquid that we call sap. [00:56.41]They're moved around to various places in the tree, in vessels that are referred to as phloem. [01:02.96]So phloem can either move sugar down toward the roots or up toward the leaves, or horizontally from one side of the tree to another. [01:12.55]During the spring in proper weather conditions, the sap in the tree begins to rise.
[01:20.35]And for this sap to move throughout the tree, the weather conditions have to be just right, when the days become mild above freezing and the nights are still freezing. [01:31.36]So there needs to be an alternate, warm day and below freezing night. [01:37.22]We're still not totally sure exactly how this promotes sap movement. [01:43.15]The most popular theory involves the unique structures found in maple trees. [01:48.36]These flowing vessels are surrounded by other cells, which in most species of trees are filled with fluid. [01:55.94]But in the maple trees, these are mostly filled with gas. [02:00.17]During the night, when it's cold the gas in these cells contracts, causing the cells to shrink. [02:06.44]This creates a low pressure in the tree. [02:09.32]So the higher pressure in the roots pushes the sap up. [02:13.26]So during the night, the sap moves up into the trunk and the leaves, ok? [02:18.49]The pressure is lower in the tree than it is in the roots. [02:22.35]Then during the day, as the temperature rises, the gases in these cells expand, the cells heat up, so they expand creating greater pressure in the tree.
[02:33.29]Now, the pressure is higher in the tree, moving this out in in various directions. [02:39.77]The important thing for collecting the sap is, since there's this pressure in the tree. [02:44.85]If you put a hole into the tree, it's called tapping. [02:48.60]The sap will flow out of the tree due to this pressure. [02:53.06]We're often asked, you know, doesn't that hurt the trees when you drill holes in them? [02:59.15]Well, the sap you extract is only a small portion of the trees’ total production, and the hole, it heals over by the next year. [03:07.44]So a maple tree does need to be about 40 years old before it can be tapped. [03:13.36]But a good tree, if taking care of properly, can produce that year after year for well over 100 years.
[03:20.69]So anyway, there are several species of maples. [03:24.19]The most common species that's used is the sugar maple, followed by the black maple, are the most common types tapped. [03:33.48]There are other maples that can be used. [03:36.30]But they don't produce the same quality or quantity of sap. [03:40.19]And there are other trees other than maples that may when drilled produce a sap. [03:45.77]But due to a combination of dissolved minerals, the taste of the syrup derived from their sap is not that pleasant.
[03:53.58]Now in order to make maple syrup, it takes a lot of sap about 125 to 250 liters of sap. [04:02.78]It has to be reduced and concentrated down to about 4 liters of syrup. [04:07.96]The color and flavor of the syrup is determined by the minerals in the sap. [04:13.18]During the early part of the season, the sap usually runs much clearer. [04:18.00]But as we get later into the season, more and more dissolved minerals are found in the south and it tends to be darker. [04:25.55]No, the harvester can't really control either the quality or the amount of syrup produced in any given year. [04:32.44]It's all dependent on weather conditions. [04:34.64]Once the weather warms up, once you don't have the freezing temps at night anymore, and or the buds start opening into leaves. [04:44.73]At that point, the sap is no longer running and the harvest is over. [04:49.42]And then of course you've got to convert that sap into syrup.