- Students will learn about plant transportation systems by splitting the stem of a carnation and making observations.
- Students will dissect a piece of celery to examine the xylem and phloem of a plant system.
- Carnations (one per student or pair)
- Celery stalk (one per student or pair)
- Food coloring (2 colors)
- Beakers or clear jars
- One copy of handout per student
L.S. 2.a, 2.e
Vascular plants have a specialized system for transporting water and nutrients throughout their system. This works much like the human body’s veins and arteries. Vascular plants include ferns, horsetails, angiosperms (flowering plants) and gymnosperms (pine-like trees). Thallophytes (water type plants) and bryophytes (mosses) do not have true roots, stems, and leaves and possess no specialized system for the conduction of food and water from one part of the plant to another. Plants that have a vascular system are larger and able to cope with a "land situation." There are no plants with a vascular system in a total water environment because the water provides the nutrients the plants require, so they do not have to "conduct" these substances.
The stem of a plant has two main highways of transportation: xylem and phloem. Xylem is the woody tissue that transports water and minerals from the roots to the leaves. Xylem is made of vessels that are connected end to end for the maximum speed to move water around. They also have a secondary function of support. When someone cuts an old tree down, they reveal a set of rings. Those rings are the remains of old xylem tissue; one ring for every year the tree was alive.
Phloem cells transport food from the leaves to the rest of the plant. The phloem is located around the larger xylem cells. When sugars are made during photosynthesis in the leaves, they need to be given to every cell in the plant for energy. Enter phloem. The phloem cells are laid out end-to-end throughout the entire plant, transporting the sugars and other molecules created by the plant. Phloem is always alive. Xylem tissue dies after one year and then develops anew (rings in the tree trunk). What is the best way to think about phloem? Think about sap coming out of a tree. That dripping sap usually comes from the phloem.
In this picture, the far left is the xylem and the center red portion is the phloem.
Background Source: http://www.msnucleus.org/membership/html/k-6/lc/plants/3/lcp3_4a.html http://www.biology4kids.com/files/plants_xylemphloem.html
Plant celery seeds in greenhouse at the beginning of the fall. Move to garden beds once sturdy. Celery usually takes around 140-180 days until ready to harvest, although it can be harvested earlier for this activity.
Xylem: the plant cells that move water and nutrients from the roots to the leaves
Phloem: the plant cells that move food from the leaves to the rest of the plant
Vascular plant: the kind of plant that has a specialized transportation system.
Show students a tree ring or a stump. Ask them what they already know about tree rings. Explain to them that each ring represents a year of life for the tree. The rings with more spacing between them represent a year with more precipitation than those that are closer. They are looking at Xylem! This is not living tissue.
Show students a bottle of maple syrup. Ask them where they think syrup is made. Explain that sap is taken from maple trees, refined, and made into syrup. Phloem produces sap!
- Give each student (or pair) 2 stalks of celery
- Have the students put a drop of food coloring on the end of the stalk. The celery will show color in small dots. This is the xylem of the plant!
- One celery stalk should be placed whole in a cup of red-dyed water (or another color will work)
- With the second stalk, split the bottom of the celery. Half of the stem should be placed into a cup of red-dyed water; the other half should be placed in a cup of blue-dyed water.
- Discuss the xylem and phloem as the way plants transport food and water throughout their system. Have the students make a prediction (hypothesis) about what the celery will look like next class. (See Student Worksheet in Download Materials)
- Give each student (or pair) 2 white flowered carnations
- With the first carnation (or any plant with a white flower will work), students place the stem of their carnation in colored water
- With the second carnation, students will split the stem of a carnation. Half of the stem should be placed into a cup of blue-dyed water; the other half of the stem should be placed in a cup of red-dyed water. Allow the plants to sit at least 1 day.
- Next class, have the students record the results of the split celery, the non-split celery, the split carnation and the non-split carnation by making observations using words and drawings. Use Colored Celery & Flowers worksheet.
- Using a magnifying lens (or microscope if available), have students cut a cross-section of the celery. To learn the parts and functions of the xylem and phloem, students should draw or share orally what they discovered.
Wrap Up & Assessment
- Use the Colored Celery & Flowers worksheet to assess the students’ understanding of the xylem and phloem.
The students can write a song to help them remember the functions of xylem and phloem.
- Compare the experiment results as a class. Divide the board into four columns: Split Celery, Non-Split Celery, Split Carnation Stem, and Non-Split Carnation Stem. Tell the students to think of one observation they made. Give each student an opportunity to write their observation on the board in the correct column. Discuss as a class.
- Students can try the uptake of colored water on other plants. (Including non-vascular plants like moss to understand the differences between vascular and non-vascular)
Colored Celery & Flowers