Water as a delivery system
The roots are at the bottom. How does food reach the top leaf?
- A · net pot & seedling
- B · roots
- C · air stone
A plant has no heart to pump. So what moves the water?
Think of water as a delivery truck.
It picks up nutrients at the roots. It drops them off at every leaf.
First, the roots soak up water, with nutrients mixed in.
Tiny hairs on the roots help them take in more.
- A · roots
- B · tube in the stem
- C · leaf veins
- D · water vapor
Next, the water climbs tiny tubes inside the stem. They are called xylemTiny tubes in a plant's stem that carry water up from the roots.
See it in the glossary.
Put celery in colored water, and the color climbs to the leaves.
- A · colored water
- B · tubes in the stalk
- C · leaves
At the top, water drifts out through tiny holes in the leaves. You can’t see it go.
This is called transpirationWater leaving a plant's leaves as a gas you can't see.
See it in the glossary.
As water leaves the top, it tugs the water below it upward.
It works like sipping through a straw. The leaves do the sipping.
If the water runs out, the deliveries stop.
The leaves go soft and droop.
Your turn. Follow the water.
Put the steps in order, from root to leaf.
Which way does the water go?
Move the steps up or down. Then check.
- Water spreads into the leaves. Right spot Not quite
- Roots soak up water from the tub. Right spot Not quite
- Water climbs the tubes in the stem. Right spot Not quite
- Water drifts out of tiny holes in the leaves. Right spot Not quite
Which way does the water go?
The right order:
- Roots soak up water from the tub.
- Water climbs the tubes in the stem.
- Water spreads into the leaves.
- Water drifts out of tiny holes in the leaves.
Water goes in at the roots and out through the leaves.
Start at the bottom of the plant. Then work your way up.
Check 1 of 3
What does water carry from the roots up to the leaves?
Show the answer
Nutrients. Right. Water is the delivery truck for plant food.
Check 2 of 3
What are the tiny tubes inside a stem called?
Show the answer
Xylem. Right. Xylem tubes carry water up, a bit like straws.
Check 3 of 3
Water drifts out of the leaves. What does that do?
Show the answer
It pulls more water up the stem. Right. Like sipping a straw, it tugs the water below upward.
You just learned how water carries nutrients from root to leaf.
Next up: Growing without soil.
You finished Track 1. You can print a certificate for it.
Go deeper: tubes, holes, and a long pullOpenClose
Xylem carries water and dissolved minerals up from the roots. A second set of tubes, called phloem, carries sugar from the leaves to the rest of the plant.
The tiny holes in a leaf are called stomata. Each one has two guard cells that open and close it.
Most of the water a plant takes up leaves again through the stomata. Books give figures from about 90 to 99 percent. Only a small part stays in the plant.
Water molecules cling to each other. When water evaporates from a leaf, it pulls on the unbroken column of water below. This is the cohesion-tension theory.
Warm, dry, windy, or bright weather speeds up transpiration. That is why plants can wilt on a hot afternoon even when their roots have water.
Roots can also push water up a little on their own, which is called root pressure. At night it can squeeze drops out along leaf edges, seen the next morning.
Transpiration does a second job, too. Like sweat on your skin, the evaporating water helps keep leaves cool.
Sources
- Moore, K. A., and L. K. Bradley, eds. "3. Botany." North Carolina Extension Gardener Handbook, 2nd ed. NC State Extension, AG-831, 2022. Link
- Clark, M. A., M. Douglas, and J. Choi. "30.3 Roots." Biology 2e. OpenStax, 2018. Link
- Clark, M. A., M. Douglas, and J. Choi. "30.5 Transport of Water and Solutes in Plants." Biology 2e. OpenStax, 2018. Link
- Let's Experiment with Plant Plumbing. Washington State University and Master Gardener Foundation of King County. Link
- U.S. Geological Survey. Celery draws up water from the roots into the top of the stalks. USGS Water Science School image, credit K. Doyle. Link
- Transpiration - Water Movement through Plants: Introduction. Plant and Soil Sciences eLibrary (PASSel). Link
- Transpiration - Water Movement through Plants: Major Plant Highlights. Plant and Soil Sciences eLibrary (PASSel). Link
- U.S. Geological Survey. Evapotranspiration and the Water Cycle. USGS Water Science School, 2018. Link
- Starbuck, C. J. Guttation: A Pressure Relief for Plants. Missouri Environment & Garden, Integrated Pest Management, University of Missouri, 2009. Link
- Klepper, B., and M. R. Kaufmann. Removal of Salt from Xylem Sap by Leaves and Stems of Guttating Plants. Plant Physiology 41(10): 1743-1747, 1966. Link