Lesson 1
Pipes made of cells
Xylem (ZY-lum) cells are long tube-shaped cells that stack end to end, like pieces of a drinking straw.
- When a xylem cell finishes growing, it dies and its insides disappear, leaving a hollow tube.
- The ends open up, so the tubes join into long pipes running from the roots to the leaves.
- Their walls are made extra stiff by a tough stuff called lignin (LIG-nin), often in rings or spirals, so the pipes don't collapse.
- Tiny holes in the sides let water move sideways between pipes.
Wow!
Wood is made mostly of old xylem pipes! A wooden table is really a giant bundle of dead plant pipe cells.
Lesson 2
How water climbs up
Plants don't have a heart to pump water. So how does water climb up a tall tree? The leaves do the pulling!
- Water escapes from leaves through tiny doors called stomata.
- Water likes to stick together, so it forms a long, unbroken chain inside the pipes.
- As water leaves the top, it pulls the whole chain up, like sipping through a straw.
- The roots give it a little push from below too.
Try this
Scroll up to the 3D pipes and press Pump water up.
Wow!
The tallest trees are over 100 meters tall, and water still makes it all the way to the top!
Lesson 3
Tree rings and partner pipes
Xylem has a partner pipe called phloem (FLOH-em). Xylem carries water up. Phloem carries sugar food made in the leaves to every part of the plant.
Every year, a tree grows a new layer of xylem. These make the rings you see in a tree stump. Count the rings and you'll know how old the tree is!
Try this: the colorful celery experiment
Put a few drops of food coloring in a glass of water. Stand a stalk of celery (with leaves) in it overnight. The next day, the leaves will be tinted, and if a grown-up cuts the stalk, you'll see colored dots. Those dots are the xylem pipes!