Transportation of Liquid and Food in Vascular Plants
Plant cells must receive water, nutrients, oxygen, and food and have wastes (such as carbon dioxide) removed. In vascular plants, xylem and phloem, miniature tube-like tissues, transport materials throughout the parts of the plants.
In this project, you will demonstrate how liquids move through vascular plants that have fibrovascular bundles consisting of xylem, phloem, and supportive fibers. You will also determine factors affecting the rate of translocation, such as the presence of leaves, light, and humidity.
Purpose: To demonstrate the transportation of liquid through a plant's vascular system.
- one clear drinking glass
- red food coloring
- 2 fresh stalks of celery with leaves (preferably the pale innermost stalks)
- Fill the glass about one-fourth full with water.
- Add enough food coloring to make the water in the glass a deep red color.
- Use the knife to cut across the bottom end of each celery stalk.
- Stand the cut end of the stalks in the glass of colored water.
- Observe and record the appearance of the stalks every hour for the first three hours. Make as many additional observations as often as possible during the first 12 hours. Be sure to record the time of each observation, starting with zero and indicating the amount of time that passes between each of the observations described. Include diagrams as part of the descriptions (see the sample data table in Figure 10.1).
- After 12 hours, remove one stalk of celery from the glass.
- Observe and record the appearance of the outside of this stalk.
- Use the knife to cut slices across the stalk. Remove sections 1 inch (2.5 cm) long from the bottom, middle, and top of the stalk. Observe and record the appearance of the slices.
- After 24 hours, observe the outside of the stalk still standing in the colored water.
- Cut three sections from this stalk as before (step 8). Observe and record their appearance.
During the first three hours, a faint red color can be seen rising up the stalks. After 12 hours, the leaves are reddish in color, and slices taken from the stalk reveal tiny red dots spaced around the outside edges. After 24 hours, the leaves show more of a red hue, but the stalk slices appear the same.
Vascular plants are plants that have special tissues for transporting food, minerals, and water (a system called translocation). These vascular tissues are made up of bundles of tubes. Phloem tubes transport food manufactured in the leaves to other parts of the plant The movement of water from the roots to the leaves is accomplished by xylem tubes. This upward movement of water against the downward pull of gravity is the result of capillary action and transpiration.
Capillary action is the rising of a liquid in small tubes because of adhesive and cohesive forces. Adhesion is the attraction between dissimilar molecules such as the attraction that water molecules have for the molecules that make up the sides of the xylem tubes. Cohesion is the attraction between similar molecules such as the attraction that water molecules have for one another. The adhesive attraction of the water molecules to the sides of the tubes moves the water up the sides of the tubes. The water molecules clinging to the tubes then pull the water below up the center of the tubes.
Transpiration is the evaporation of water through leaf pores called stomata. As the water evaporates from the plant, more water molecules are pulled in at the roots; thus, a continuous flow of water enters the roots and rises in the xylem, bringing necessary nutrients dissolved in the water to the plant This movement is evident by the intensifying of the red color in the leaves.