---
title: 'Trees Are So Weird'
source: 'https://youtube.com/watch?v=ZSch_NgZpQs'
video_id: 'ZSch_NgZpQs'
date: 2026-07-20
duration_sec: 687
channel: 'Kurzgesagt – In a Nutshell'
---

# Trees Are So Weird

> Source: [Trees Are So Weird](https://youtube.com/watch?v=ZSch_NgZpQs)

## Summary

Trees are mostly dead, with only a thin layer of living cells. They evolved lignin to grow tall, use negative pressure to lift water over 100 meters, and have a unique transport system of xylem and phloem. This makes them potentially immortal.

### Key Points

- **Trees are mostly dead** [00:02] — The living part of a tree is just a paper-thin strip of cells; the vast majority of biomass is dead.
- **Lignin enabled height** [01:34] — Lignin, a rigid and waterproof macromolecule, gave plants the strength to grow tall and compete for sunlight.
- **Wood as biological concrete** [02:18] — Around 385 million years ago, plants developed wood, allowing the first trees to reach 20 meters high.
- **Cambium and xylem** [03:13] — The cambium is a thin layer of stem cells that produce xylem inward, which become hollow dead tubes for water transport.
- **Transpiration pull** [04:41] — Evaporation from leaves creates tension that pulls water up to 100 meters, generating negative pressure equivalent to dozens of atmospheres.
- **Phloem transport** [06:07] — Phloem cells sacrifice their nuclei to become living pipelines for sugar and signals, maintained by companion cells.
- **Bark protection** [08:00] — Outward-growing cells die to form bark, protecting the living layer from damage and invaders.
- **Potential immortality** [08:49] — Trees don't age like animals; they can grow nearly forever unless stopped by external factors.

### Conclusion

Trees are a remarkable evolutionary success, using dead structures and extreme physics to dominate land. Their unique biology allows them to grow tall, transport water efficiently, and potentially live indefinitely.

## Transcript

It turns out the alive part of a tree is  just a tiny, paper thin strip of cells, Trees are some of the most extreme beings on  earth with one of the most unique strategies in
nature – on top of being mostly dead stuff, they  forge their body out of thin air, they mercilessly crush rocks with acid, and they have an internal  negative pressure that would kill you instantly. Let’s go back…to the beginning.
For over a billion years the ancestors of plants only inhabited the sun  drenched surfaces of the oceans. Their bodies were thin and delicate  and absorbed water straight through
Forging sunlight, carbon  dioxide and water into sugar. But about 470 million years ago they decided  to conquer a hostile alien planet: the land.
Like green rugs with ambition these  plant ancestors began clinging to But now, with solid ground beneath  and no ability to float around a new dimension became a place of intense warfare: up.
The higher they grew, the more sun they would  get, while starving their competition below. Height became a deadly weapon.  The battle for the sky had begun. Until now, plants were built mostly from  cellulose, which was great for shape,
Over dozens of millions of  years of evolutionary warfare, a group of plants developed one of  life's greatest breakthroughs: lignin. Lignin is a macromolecule made  of ring-shaped structures.
It is rigid, tough, waterproof,  and incredibly hard to break down. It filled gaps between cellulose threads,  stiffening and locking everything into place. Lignin gave plants the strength to grow  taller and claim the sun for themselves.
which must have been really annoying for them. So as more millions of years passed,  some plants just went all in on lignin and produced more and more of it,  becoming stiffer, harder and stronger.
Until one day, around 385 million years ago they got the biological equivalent of  steel reinforced concrete: wood. More on it later, but with this magic  material the first trees emerged.
shooting up to 20 meters high into the  sky – and they only got bigger from here. But this enormous size created  extremely hard problems:
How do you get water from the ground up to the  green parts that do the actual photosynthesis? And how do you get the sugar they produce  down to the cells that keep you up there? On the scale of a cell a distance of  a few meters is like you’re working
in Britain while your lunch box is  in Egypt and your drink in New York. So trees came up with one of the  most amazing ways any organism grows, and became nearly immortal by accident.
Let us slice an ancient tree in half  and get to the heart running it all:   the cambium, a razor-thin, circular  zone, just a few stem cells wide.
These stem cells grow inward and outwards,  turning into two groups of specialists. The inward specialists are on a  conveyor belt of death, the xylem. making the tree thicker the older it gets.
As the xylem cells mature their  lignin production goes into overdrive, and they become hard and stuffy, like  a muscle slowly transforming into bone. They begin to hollow themselves out, shedding  everything that once made them alive.
What’s left is a corpse, a hard, empty tube. As the tree grows year after year, new  corpses are layered on old corpses, A graveyard of trillions of plant bones.
Stacked together they form a giant network of  pipes that stretches the whole length of the tree. and a few other tricks to move  it with incredible efficiency.
Water molecules are, for a lack of a  better word, sticky, like tiny magnets, When one moves, it pulls the next  along with it, like pulling on a rope. In trees this rope starts in the roots and ends in  the leaves that bathe in the warmth from the sun.
Here the heat from the sun evaporates 95% of releasing a constant invisible mist of water  molecules around the crown of the tree.
This process, called transpiration in plants,  creates tension on the rope of water molecules, stretching and lifting the entire column upwards,  all the way from the roots to the leaves. This pull is so insanely strong that  it can lift water over 100 meters,
dozens of atmospheres – as much as the crushing  pressure hundreds of meters deep in the ocean. Nothing humans have ever built  comes even close to this power.
Even our best machines can’t pull  water higher than about 10 meters, because the negative pressure required  to pull hard enough makes it boil. But the water pipes of trees are so tiny  and narrow, almost perfectly airtight that
despite the insane suction pressure inside a  tree, water stays liquid and reaches the top. As the tree ages old xylem cells  eventually stop working and fill Slowly they turn into heartwood, a dense,
chemically fortified core that  is extremely resistant to decay. But water is only one half of the story. The sugar produced in the sky needs to be  transported to nourish cells down below.
and exchange information about damage and growth. This is the job of the cambium stem  cells that grow outwards: the phloem.
As the Cells of the phloem  grow outwards they separate into three teams and make a brutal compromise. The first group are Sieve cells and their grim  fate is to become a living transport system.
As they mature they start to destroy themselves, digest their organelles and even their  nuclei that houses their genetic code. connecting to the sieve  cells above and below them.
This goes on until they are a  sad shadow of living beings. A drooling, living tool without a brain  or arms, unable to support themselves. Only the second group, their  companion cells, keeps them alive.
They connect with the crippled Sieve cells  via tiny channels and start maintaining them. Sending over energy, instructions  or repairing them if needed. Running along the entire tree, these  two teams form a tiny and very thin
layer of living sugar pipelines and signal  cables that stretch throughout the entire body. Providing food and information  wherever it is needed in the tree. workers of the tree that are carrying  out essential labor in the background.
sugars or water that the tree uses to survive  the winter, when it is unable to produce food. Others are like mini healers that can  repair damage, while some go onto the
offensive and create toxins and anti  fungal bio weapons to kill intruders. On top of the phloem sits  another layer of stem cells. They are producing a second conveyor  belt of death, moving outside.
Special cells grow from this layer and as they  mature, just like the xylem cells in the center, they kill themselves for the team,  turning into a hard guard wall – the bark. Just like your skin, it protects the tiny living  layer from damage, parasites and invaders.
The living part of the stem is really  just this extremely thin and tiny layer, a few millimeters thick, sitting on  a thick mountain of cell corpses, The vast majority of the  biomass of a tree is dead.
it seems you are only doing a little damage, you  are actually killing the living part of the tree. But unless a tree is stopped by droughts,  diseases, storms or a human axe,
this system of being mostly dead kind  of makes trees potentially immortal. They don’t age like we do, in principle  they could grow this way nearly forever. Egyptians started building their  first pyramid, 5000 years ago.
Trees are not a real biological category but one  of the most successful ideas life has ever had, These plants won the battle for the sky,  solved every challenge that had kept
plants small and fragile and they took  over the planet in a few million years. Even today three trillion of  them cast their majestic shadows. and the root system – one building  the tree from air, another mining
minerals with acid and involved in complex  communications with fungi and other trees. There’s so much more to talk about, so we’re  already working on the next part - stay tuned!
disappearing fast and we’re running  out of time to protect what’s left. Planet Wild is a community-based  nature protection organization
Every month, their community of over 15,000  members funds a new mission to restore nature. That’s why we love that Planet Wild  documents all their missions in video
reports right here on YouTube so you can  see what your contribution helped achieve. Take their underground forest mission in Tanzania:   While you think this desert is dead,  there’s actually life still here.
Beneath the surface, underground  forests are just waiting to grow. If you would like to help our planet’s  ecosystems, consider joining Planet Wild.
You can give any amount that feels  right to you – every dollar counts. KURZGESAGT11 will get their  first month paid for by us! Just scan the QR code or click  the link in the description.
Make a tree friend, and join the  Planet Wild community – today. If you want to see them in action first, check  out their underground forest mission here.