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What do plants use to grow? (self.askscience)
submitted 1d ago by randomhuman1816
I understand that plants need nutrients to grow, but if I plant an apple seed in a pot, the dirt levels dont fall as the sapling grows bigger, so my question is: where the plants gets their Mass, because it has to come from somewhere right?
My only real guess is that their mass comes from air, but i cant find anywhere that explains the process beyond "photosynthesis"
This question has been messing with my brain for a while so any suggestion is appreciated :))
My only real guess is that their mass comes from air, but i cant find anywhere that explains the process beyond "photosynthesis"
This question has been messing with my brain for a while so any suggestion is appreciated :))
m4gpi 10 points 14h ago
The green parts of plants, especially the leaves, contain microscopic structures called chloroplasts that uses some pretty complicated (and impressive) chemical reactions that convert carbon dioxide and water into sugar (glucose) and oxygen in the presence of sunlight. The carbon dioxide comes from the air, and the water comes from (usually) the soil (sometimes from ambient humidity but this is a very small amount). The sugar gets transported down to the roots, which perform other chemical reactions to convert that sugar into other chemical structures that the plant can use for all the other functions, and build new components from. The roots also absorb other nutrients and elements, like nitrogen, phosphorous, etc. from the soil.
When a plant is just a seed, it has everything spring-loaded inside to start a baby plant, all it needs is water to unlock these first transformations to put out its first baby roots and baby stem, and as soon as the seedling grows up above the soil line, the sunlight “turns on” the chloroplasts, which then turn on the rest of the factory.
You do technically lose mass from soil, but it’s at a very slow rate, almost too slow to observe in a pot, and in nature, soil is constantly being replenished and added to from other organisms. In truth, soil is mostly a physical structure that holds the plant in place; it’s the nutrient-rich water that percolates between soil particles that feeds the plant.
When a plant is just a seed, it has everything spring-loaded inside to start a baby plant, all it needs is water to unlock these first transformations to put out its first baby roots and baby stem, and as soon as the seedling grows up above the soil line, the sunlight “turns on” the chloroplasts, which then turn on the rest of the factory.
You do technically lose mass from soil, but it’s at a very slow rate, almost too slow to observe in a pot, and in nature, soil is constantly being replenished and added to from other organisms. In truth, soil is mostly a physical structure that holds the plant in place; it’s the nutrient-rich water that percolates between soil particles that feeds the plant.
atomicsnarl 4 points 13h ago
The main take here is answering where the mass of the plant comes from as it grows.
Air (CO2) + Water + Sunlight = Wood, leaves, and roots.
The nutrients from the soil are a fraction of the Carbon to Wood transformation amounts.
Air (CO2) + Water + Sunlight = Wood, leaves, and roots.
The nutrients from the soil are a fraction of the Carbon to Wood transformation amounts.
ellipsis31 1 points 4h ago
But where do lichens and mosses growing on rocks with no soil get their micronutrients? Obviously they also photosynthesize, but I have a hard time believing that they are somehow eating the rock to get their heavier elements.
e-chem-nerd 4 points 14h ago
Plants use photosynthesis to create sugar molecules from water and carbon dioxide, using sunlight as an energy source. They do also draw minerals from the soil, but those are in very small amounts compared to the much greater mass of water and carbon dioxide they require.
The same happens for humans, but in reverse. If you weight everything you eat and drink and also all your solid and liquid wastes (perhaps indirectly by recording your weight before and after excretion, also sweat might be a little hard to weigh) you will notice there is a missing amount of mass in the balance: your total consumption minus excretion will be larger than your new weight minus original weight. This is because there is a missing excretion: gaseous excretion via carbon dioxide you breath out.
The same happens for humans, but in reverse. If you weight everything you eat and drink and also all your solid and liquid wastes (perhaps indirectly by recording your weight before and after excretion, also sweat might be a little hard to weigh) you will notice there is a missing amount of mass in the balance: your total consumption minus excretion will be larger than your new weight minus original weight. This is because there is a missing excretion: gaseous excretion via carbon dioxide you breath out.
Tampflor 4 points 12h ago
The mass gain as a plant grows comes mainly from carbon dioxide in the atmosphere and water.
This is also the answer to where a person's mass goes when they lose weight--for every oxygen molecule you breathe in, you breath out one carbon dioxide molecule, which weighs just a bit more.
This is also the answer to where a person's mass goes when they lose weight--for every oxygen molecule you breathe in, you breath out one carbon dioxide molecule, which weighs just a bit more.
SwissFennel 1 points 5h ago
Great answer! The only thing I need to get clarification on is where you say "for every oxygen molecule you breathe in, you breath out one carbon dioxide molecule."
A nurse told me once that "the air you breathe in is 20 percent oxygen; the air you breathe out is 18 percent oxygen, 2 percent carbon dioxide." Did you mean something like the following? "Every oxygen molecule that gets used in your cells to provide energy ends up as carbon dioxide. CO2 weighs just a bit more than O2 because of that extra carbon atom."
A nurse told me once that "the air you breathe in is 20 percent oxygen; the air you breathe out is 18 percent oxygen, 2 percent carbon dioxide." Did you mean something like the following? "Every oxygen molecule that gets used in your cells to provide energy ends up as carbon dioxide. CO2 weighs just a bit more than O2 because of that extra carbon atom."
Tampflor 1 points 1h ago
>Every oxygen molecule that gets used in your cells to provide energy ends up as carbon dioxide.
It's not *quite* this simple--we don't make the carbon dioxide by attaching one carbon atom to the O2 molecules you breathe in. The oxygen you breathe in winds up as part of water molecules, while the oxygen in the carbon dioxide you breathe out comes from the organic molecules you've eaten and the oxygen from other water molecules.
However it is true that there is a 1:1 ratio between oxygen breathed in and carbon dioxide breathed out, which is the main thing to consider when we're just interested in asking "why did biomass change?"
It's not *quite* this simple--we don't make the carbon dioxide by attaching one carbon atom to the O2 molecules you breathe in. The oxygen you breathe in winds up as part of water molecules, while the oxygen in the carbon dioxide you breathe out comes from the organic molecules you've eaten and the oxygen from other water molecules.
However it is true that there is a 1:1 ratio between oxygen breathed in and carbon dioxide breathed out, which is the main thing to consider when we're just interested in asking "why did biomass change?"
organiker 5 points 15h ago
Seems like you have the answer already. What kind of detail/explanation are you looking for?
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