Facts for Kids

The tubes that move water from roots to leaves are called xylem. The liquid in these tubes is mostly water with tiny amounts of minerals and plant hormones. It travels upward because water molecules stick together and are pulled up from leaves when they lose water to the air, a bit like a chain being pulled from the top. This steady pull helps water reach the highest branches.

Sometimes the water flow can break if air gets into the tubes; this is called cavitation. Cavitation can happen during very dry times or when freezing and thawing occur, and it can stop water from moving until the plant repairs the break.

People collect some kinds of plant sap for food and drink. Maple syrup is made from the sap of sugar maple trees. Farmers tap the trees in early spring, collect the watery sap, and boil it down until the sugar becomes thick, sweet syrup. This turns a lot of watery sap into a small amount of syrup.

In northern countries people also harvest birch sap in spring to drink fresh or to turn into sweet drinks. Some palm trees give palm sap, which people collect and use to make sweet syrup or traditional sweet drinks in places such as the Canary Islands and parts of South America. These practices show how sap can be a gentle, seasonal treat.

The tubes that carry sugars and soluble things are called phloem. Phloem sap is rich in sugars (mainly sucrose), plus hormones and minerals dissolved in water. It moves from places that make or store sugar (sources), like leaves or roots, to places that use it (sinks), like growing shoots or fruit. One simple idea for how it moves is the pressure flow idea: sugar draws water into the phloem and that creates pressure that pushes the sap along.

Phloem also helps send messages because some proteins and bits of genetic material travel inside it. Tiny channels and special transport proteins help load and unload sugar. Some insects, such as aphids and other Hemiptera, feed directly on phloem sap and must rely on helpful microbes to get certain nutrients.

sap is the watery fluid that moves inside a plant to carry food, minerals, and messages. Plants have tiny tubes that act like roads: some tubes carry water and minerals up from the roots, and some move sugars and other stuff to places that need them. Because sap moves around, it helps a plant grow, make leaves and flowers, and heal small wounds.

Sap is different from things like latex or resin, which are thicker and used for other jobs. Sometimes you might hear about "honeydew" falling from trees — that is not pure sap but leftovers from insects that ate sap and plant parts.