When a tree grows, where does the mass for its trunk and branches come from? How does the mass and stuff get to the top to make new tree parts?


Physics has the conservation of mass right? … And … Things like trees sit in the ground. Where do they get the mass to grow tall? How do they move it up their trunk? How do really old trees get more dirt when they make it into trunks?

In: Biology

They actually get all the stuff from the air.

They can turn, using photosynthesis water and co2 into sugar, and then turn the sugar into other stuff like wood and leaves

Trees pull water up their roots, and that water carries all the vital nutrients they need to grow and thrive. Combining that with photosynthesis bringing in all the energy they need, plants and trees have it pretty good. All that root action brings up nutrients and chemicals that have been deposited by dead and decaying animals and plants.

All that mass is kind of like our human skin. All the outer layers are dead, and the new/forming layers gently push them out from the core.

> Where do they get the mass to grow tall?

Not from the dirt! The vast majority of the mass which makes up plants including trees comes from the air and water.

Cellulose, the main structure of the tree, is composed of carbon, hydrogen, and oxygen. The carbon and oxygen can come from the air, while water of course contains the hydrogen and more oxygen.

> How do they move it up their trunk?

Water moves up the trunk of the tree via capillary action, water’s surface tension, and something called “transpiration”. Basically water evaporates from the bottom of leaves and this acts to pull water into the leaves from the trunk, and by extension all the way from the roots.

Trees are mostly made out of air and water.

6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O

Trees take in CO2, water and light. The use photosynthesis to create glucose and oxygen. The oxygen is released into the air. The sugar is used for the tree to grow.

They don’t use the dirt much to grow. They only take small amount of minerals from the dirt.

Trees are made of carbon and they get essentially all of this carbon (C) from the air they breathe in and then they breathe out oxygen (O) which is how we breathe.
This might seem odd, but we actually do the essentially the same but in reverse. If you have ever heard that you breathe in O and breathe out carbon dioxide (CO2). This is a mix of C and O and actually comes from the food you break down and the fats that you burn. So trees gain mass from breathing in C in the same way that we lose it as we breathe out C, humans have almost the same reactions as plants but in reverse.

As to how they move their mass around, trees mostly breath through their green leaves and then the carbon is transported around the tree through different cells. This is why trees don’t grow in winter when they lose their leaves, but spark up again in spring.