INRS State Scientific Surveys
GRADE LEVEL: K-5
SUBJECTS: Science, Language Arts, Math
SKILLS: observing, critical thinking, counting
OBJECTIVE: Students will learn how trees produce their own food by combining water,
carbon dioxide, nutrients from the soil, and sunlight, and how every part of the tree
contributes to the process of making and distributing food.
BACKGROUND:
Trees require food, just like animals and people. They produce and distribute their own
food in a special way.
Little Green Food Factories. The food that trees need is made in the leaves. Each leaf contains millions of chlorophyll cells. Chlorophyll cells are green, which is why leaves are green in the spring and summer. These cells actually make food through a process called photosynthesis. Chlorophyll cells take in carbon dioxide - people and animals breathe out carbon dioxide. Chlorophyll cells combine this carbon dioxide with water sent up from the roots of the tree. In the chlorophyll cell, sunlight passes through this mixture and turns it into sugar and oxygen. The sugar is the food that trees need to grow.
Pipelines inside Pipelines. Inside the trunk of the tree is a two-way pipeline.
Just inside the bark there is a pipeline that the leaves use to send food down to the
roots. This pipeline is called phloem (flo-em). Next to the phloem towards the middle
of the tree is another pipeline - this one is called xylem (zi-lem) - that sends water
up from the roots to the leaves. Between the phloem and the xylem there is an area of
wood called the cambium. The phloem, cambium and xylem are the living portions of the
trunk of a tree. Every year the tree trunk becomes wider as new layers of phloem and
xylem grow from the sides of the cambium. When you look at a cut section of a log you
can see the rings of new wood that are added each year the tree lives. In the center of
the trunk of a tree is the heartwood. This portion of the tree is old phloem, cambium
and xylem layers that are non living. The heartwood is very hard and gives a tree the
strength to stand straight and tall.
At the Root of the System. Underground, under every tree, there is a root system that extends two to four times further than the branches of the tree. In some trees the room system spread may be twice the height of the tree. Attached to every root are tiny root hairs. They act like miniature straws to draw up water and nutrients. That mixture is sent up the pipeline to the leaves. Roots also receive food from the pipeline so they can grow. Every part of the tree is involved in this system. The roots gather water. Water flows up the trunk to the leaves where it is combined with carbon dioxide and sunlight to make food. This food flows back down through the trunk to help all parts of the tree grow.
PROJECTS AND ACTIVITIES:
If there is a microscope or magnifying glass available, show students a slide from a leaf
so that they can actually see chlorophyll cells. Take the class to a nearby tree stump,
take a cross section of a log to class or purchase slices of tree branches at a craft
store. Show them the layers that make a tree's food transportation system. Explain
that there is a layer of new wood for every year that the tree lived and discuss why
they think this happens. Have them count the rings to see how old the tree was when it
was cut. Have them try to count rings to see how big around the tree was the year they
were born. As a class project, make several jugs of sun tea. This will show students
how water, other ingredients, and sunlight can combine to make something new. Take the
class outside under a large tree. Explain that the root system of the tree extends well
beyond the branches of the tree. Measure the distance from the end of the branches to
the trunk of the tree. Have the class form a circle around the tree at a distance twice
as long as the branch measurement. The area encompassed contains the roots that support
and feed the tree.
EVALUATION:
Divide the class into three sections. The students should develop a three-act
play with one group being the leaves, one group being the trunk and one group being the
root system. Each group should create its own description of the function of its part
of the tree. An elected spokesperson should present the description while the others
act it out.
EXTENSIONS:
Take a class trip to an area where maple syrup is produced. Explain that
sometimes people eat the very same food that trees do - in this case maple syrup from
sugar maple trees. If a sugar maple tree is available near the school, it is easy for
the class to make real maple syrup. Detailed instructions can be found in Project
Learning Tree from the National Forest Council, 1993.
VOCABULARY:
chlorophyll, photosynthesis, phloem, xylem, carbon dioxide
Next lesson - Bugs, Beavers, Birch Trees, and Bluebirds