It’s easy conceptually to understand when animals eat physical food matter, it adds to their own body mass as they grow.
But potted plants grow 2x, 3x, etc their mass while the only (seemingly) inputs are Sun, water and occasional plant food. The soil level doesn’t seem to change much either, so where is the “material” coming from to make the plant bigger? Is it just from what I mentioned, and is there an easy way to understand how those things transforms to plant mass?
Edit: Thanks for all the answers! It unexpectedly helped me understand how plants capture carbon from the air and “store” it physically. I have a new appreciation for my houseplants 🪴
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You may have heard the term ‘carbon based lifeform’ which refers to the fact that the majority of living tissue is made from carbon. When you see those chemical chain drawings in movies all of those lines represent carbon, to give you an idea of just how much of every molecule is made of carbon.
Plants are no different and are also mostly made from carbon, something that is abundant in the air. Plant leaves have microscopic holes all over them called stomata, and these organs are responsible for gas exchange in the plant, just like how humans breathe.
These stomata create a kind of vacuum to suck CO2 in from the air and that CO2 is used as the backbone or building block for all of the plants tissue.
In the 1600s Jon Von Helmont had the same question about potted plants so he ran an experiment. He weighed out soil in a massive pot and then planted a willow tree in it. A few years of growth later he weighed the soil and found it weighed pretty much the same as before, proving that most of a plants mass came from the air.
Lots of great explanations here. I’d like to point out that anyone that takes basic biology or life science in school learns about photosynthesis, and how plants convert CO2 into oxygen, etc. but the focus is/was always on the oxygen part of the cycle.
Its been almost 40 years since I first learned about that and I only came to understand the carbon part of that cycle in the past 5 years. I was literally shocked to learn that most of the mass of a tree comes from the air. I was taught “plants grow by getting energy from sunlight through photosynthesis, and drawing nutrients and water from the ground.” which totally failed to mention carbon capture. I never connected that if they are releasing oxygen, the carbon must be kept in the plant.
In 1640s van Helmont discovered that plants DO NOT eat soil and that the weight of the plant must come from water. He had no idea about gasses playing a role in plant growth.
In 1772 Priestley discovered that plants replenish oxygen in an low-oxygen chamber.
In 1778 Ingen-Housz discovered that the effect Priestly discovered only when the plant was illuminated and ONLY in the green parts of the plant.
Senebier made the connection with CO2, albeit incorrect.
Greater clarity about photosynthesis would follow in the following years!
If it was common knowledge that plants are mainly made from carbon from the atmosphere, I think more people would understand climate change..
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