In Unit 21 you have been learning how the circulatory and respiratory systems move nutrients and gases through the body of animals. In this unit you study the corresponding organ and tissues of plants. These systems are very different from those in animals in terms of their structure, but their functions are very similar; moving nutrients from one part of the organism to another and exchanging oxygen and carbon dioxide gases.
Learning Objectives: The successful student will be able to ...
- name and recognize the various tissue types of plants and describe their basic functions.
- describe in detail the cellular mechanisms of water uptake through root tissues, its transport up the plant, and transpiration out of the leaves.
- describe in detail the bulk transport of nutrients (mostly carbohydrates) from the source tissues to other tissues in the plant.
- compare these transport structures and processes in different taxonomic groups of plants and the adaptations of plants to aquatic, dessert, and other habitats.
Lesson One: Basic Plant Tissues.
At the cellular level plant cells are not too different from animal cells. However, at the tissue level differences become dramatic. Go to the Kimball pages and review the basic types of plant tissues. You should be able to name the major groups of tissues and describe their basic functions. Pay particular attention to the developmental role of meristematic tissue and the functions of xylem and phloem.
The Online Biology Book has a similar introduction to this material along with some good diagrams. This Plant Physiology website by Ross Koning has excellent diagrams and photographs of these tissues. You should know how the xylem and phloem tissues are organized in the leaf, stems, and roots of a typical plant.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- What is meristematic tissue? Where is it found in a growing plant and what is its relationship to xylem and phloem?
- Describe the general function of xylem and phloem. What do they transport and what are the origin and destinations of the materials they transport?
- Draw diagrams of cross sections through the root and stem of a plant showing the arrangement of xylem and phloem tissue. You can either hand these into me during class or, if you want to go to all the effort, you can scan you diagrams and email the image files to me.
Image from Ecoki.
Lesson Two: Water Uptake.
As with all organisms, water plays and import role as the solvent for nutrients, minerals, hormones, and gases. In plants, water also plays a critical role in maintaining cell shape, support, and pressure (turgor). In this lesson you will study how water is taken up the roots, transported by the xylem tissues, and ultimately released from the leaves by the process of transpiration.
Go to the Kimball pages and review the material on the physical properties of water. Be sure you understand why water is a polar molecule and the consequences this polarity has on the boiling point, cohesion, and capillary properties of water.
Now read the material in Kimball describing the general arrangement of tissues in the root. Pay attention to the location of the epidermis, endodermis, cambium, xylem, and phloem. Be sure you understand the different mechanisms used by the plant tissues to move water (osmosis) and minerals (active transport) into the root from the soil.
Read this section of Kimball; it outlines the alternative routes that water uses to pass into the central vascular tissues of the root. Here is an excellent animation of these processes from the University of Nebraska. Again, understand the various alternatives that water can take to move into the root. Pay close attention to the "casparian strip" which funnels water into the central vascular tissue bundle.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- Explain why the movement of water into the root from the soil requires both passive transport (osmosis) and energy using active transport. Hint: remember it is not just water that moves into the root.
- What are the different routes (no pun intended) used to move water from the soil into the central xylem tissues of the vascular bundle? How are they similar and how are they different?
- What is the role of the casparian strip in this process? What would happen to the transport of water to the xylem if the casparian strip failed?
Lesson Three: Transpiration.
Once water is moved into the xylem of the roots, it travels up the stem of the plant/tree and into the leaves. In the leaves, water is used to support the biochemical reactions of photosynthesis and cell respiration, maintain the shape and internal pressure of cell (turgor), and finally it moves out of the leaves back into the atmosphere (transpiration). The mechanism of transpiration depends heavily on the physical properties of water and the structure of xylem tissue.
This section of Kimball outlines the process of transpiration, this section briefly summarizes transpiration. Be sure you also read the section of gas exchange in leaves via the stomata.
Homework, Due . Go to this Pearson Lab Bench exercise. Read the material in the six concept sections for a review of transpiration, conduct the online experiment, and then complete the calculations in the final table for analysis of your results. Use an Excel spreadsheet to present your results and write a paragraph summarizing your conclusions. Be sure that your conclusions include reference to the specific data in your table that you use to support your arguments. Email your work using your Fontbonne account. You will need to send the spreadsheet as an attachment.
Lesson Four: Phloem, Translocation of Sucrose.
Go to the Online Biology text to review the structure of phloem tissue and Kimball to study the mechanisms of carbohydrate (usually the sugar sucrose). Appreciate the role of osmosis and active transport in this process as well as the close functional relationship between the phloem transporting the sucrose and the xylem that supplies the water to the phloem. Here is a simple animation that demonstrates these concepts. Here is another animation from Pearson. Understand what is meant by the "source" and the "sink" in the Pressure Flow theory (also called Bulk Flow).
Homework, Due . Draw a detailed diagram illustrating the Pressure Flow theory. Your diagram should include the various tissues and structures involved, where osmosis and active transport is used, and the direction of movement of water and sucrose between the source and sink structures. Unless you want to go to the bother of making an digital file, pass this assignment in during class.
Here is a nice summary of all this material from the University of Illinois. Be sure to view the animation; it ties all of our lessons together.
Xylem & Phloem as an art form by estherase.
