10 Chapter 10
LAB 10
Plant Diversity & Flowering Plant Organization
Prepared by Jason R. Jones, University of North Alabama
OBJECTIVES
After completing these laboratory activities, you should understand/be able to:
- Define the terms angiosperm, autotroph, bryophyte, consumer, eudicot, gametophyte, gymnosperm, heterotroph, meristem, monocot, producer, pteridophyte, secondary growth, sporophyte, vegetative propagation
- The basic anatomy of plant roots, stems, and leaves.
- The three basic types of tissues in vascular plants: dermal tissue, ground tissue, and vascular tissue
- The two types of vascular tissue in plants, and what they transport: xylem (water & ions), and phloem (transports sugars)
- Identify each of the following structures on a plant: leaf, blade, petiole, node, internode, axillary bud, apical bud, taproot, lateral roots.
- The major anatomical differences between monocots and eudicots.
- The botanical distinction between vegetables and fruits.
- Give examples of vegetables and recognize whether the eaten portions are roots, stems, or leaves.
- Examine secondary (woody) growth in angiosperms, and learn how to determine the age of trees.
INTRODUCTION
Plants are a crucial part of every ecosystem on Earth. Through the process of photosynthesis, plants combine carbon dioxide, water, and light energy harvested from the sun, and store that energy in the form of the chemical bonds in glucose and other carbohydrates. Since plants make their own food, they are referred to as producers (or autotrophs, literally “self feeders”). This energy is then available to other organisms (consumers, aka heterotrophs) that utilize this stored energy.
Plants are an extremely diverse group of organisms, with an estimated 300,000 species globally. Of this diversity, plants can be further broken down into several sub-groups:
- Bryophytes (non-vascular plants, including mosses, liverworts, and hornworts – approximately 22,750 species
- Pteridophytes (vascular seedless plants, including ferns, horsetails, and their relatives) – approximately 15,000 species
- Gymnosperms (vascular non-flowering seed plants including conifers and their relatives) – approximately 1,050 species
- Angiosperms (vascular flowering seed plants): plants with specialized tissues for transport of water and nutrients; produce seeds housed inside fruits which are derived from flowers – about 250,000 species
In this lab, you will examine the diversity and anatomy of angiosperms, or flowering plants., particularly the three main organs in flowering plants: roots, stems, and leaves. The lab is set up with several different stations at each lab table, you must visit each lab table, and observe the various materials at each. The stations can be completed in any order you like.
*Answer all questions in the worksheet at the end of this lab exercise.*
STATION I: Plant Diversity
At this station, there are several examples of angiosperms (flowering plants). angiosperms, are vascular plants that produce flowers, fruits, and seeds. Angiosperms are divided into two major groups, the monocots and the eudicots, based on several different characteristics, some of which are shown in Figure 4 below.
Figure 4. Several differences between monocots and eudicots. Credit: Flowerpower207 on Wikipedia (modified). (https://en.wikipedia.org/wiki/Monocotyledon#/media/File:Monocot_vs_Dicot.svg)
Using the characteristics of leaves and flowers as shown in Figure 4, determine whether each Angiosperm at this station is either a Monocot or a Eudicot, and fill in the table on the worksheet at the end of this lab exercise.
Basic Angiosperm Anatomy
All angiosperms consist of two major organ systems: the subterranean (below ground) root system, and the above ground shoot system. The shoot system also includes other important plant organs: leaves, and in angiosperms only, flowers. Overall, however, the major non-reproductive organs of angiosperms are roots, stems, and leaves.
The root system of monocots and eudicots are different. Monocots have a root system that is referred to as a fibrous root system, composed of many roots all about the same size. Eudicots, on the other hand, typically have one large central root, called the taproot, which may have many smaller lateral roots extending from it. The root systems of plants serve several functions: (1) anchor a plant into place, (2) absorb water and minerals from the soil in which they grow. Examine the modified roots that serve other purposes in some plants.
The shoot system of angiosperms includes both the stem and leaves. The primary function of most stems is to provide support to the leaves, which are the primary site of glucose (food) production during photosynthesis. The stems of angiosperms can be divided into several regions. The points at which leaves emerge from the stem are referred to as nodes, and the lengths of stem in between the nodes are called internodes. The leaves themselves can be divided into two main regions. The blade of the leaf is the large, expanded portion of the leaf where the majority of chloroplasts (the site of photosynthesis) can be found, and the petiole is the stem-like portion of the leaf that attaches it to the stem. Occasionally buds, which can produce either new leaves or flowers can be found on the stem. Buds that are found at the tips of stems are referred to as apical buds, while buds found along the axis of the stem are called axillary buds. Familiarize yourself with the previously described angiosperm anatomy, using Figure 5 to assist you.
Figure 5. Basic eudicot anatomy. Credit: Kelvinsong on Wikipedia (https://en.wikipedia.org/wiki/Botany#/media/File:Plant.svg)
STATION II: Root Anatomy & Diversity
Examine the basic anatomy of roots, compare the root systems of monocots and eudicots, examine a few adaptations of roots for different purposes, examine relationships between plant roots and other organisms, and also observe several roots used as food.
First, examine the model of a monocot root. Make sure you are able to locate and identify the following structures, and their functions. Notice the three main types of tissues found in vascular plants: dermal tissue, which forms the “skin” of plants, and protects, ground tissue which mostly serves as support tissue, and a site for storage/secretion of materials, and vascular tissue, which transports water and nutrients throughout plants.
Locate the root epidermis. The epidermis is the outer layer of cells covering the root’s surface, and mostly provides protection to the root. Next, look at the cross sectional view from the top of the model, and locate the cortex, which is composed of parenchyma cells (ground tissue), and forms the majority of the interior of the root. Next, locate the two types of vascular tissue in the root. Xylem, which transports water throughout vascular plants, is composed of two different types of cells (tracheids and vessel members), both of which are actually dead at functional maturity. Phloem, which transports sugars in vascular plants, consists of several types of cells, including sieve elements, companion cells, fibers, and parenchyma cells, which are alive at functional maturity.
Also locate the root apical meristem on the root model. In plants, meristems are areas of plant tissue where active cell division takes place. The word “apical” means “near the tip”, so this is the region of active cell division near the root’s tip where root elongation occurs. Incidentally, the tips of plant shoots also have apical meristems, which lengthen the shoots. Some plants also have lateral meristems that increase root/shoot girth instead of length.
Also notice that the tips of roots are protected by a root cap. The root cap is produced by cells formed during cell division at the apical meristem. Initially, these cells differentiate into a type of cell called columella cells, which contain structures that allow for gravity detection, and thus directs the root to grow downward. If the root cap is removed from a root, the root would grow in random directions instead of downward. The root cap also serves to protect the delicate, newly-produced cells generated during cell division at the apical meristem, as well as to lubricate the root, allowing it to more easily penetrate the soil. Additionally, notice that the exterior of the root has multiple projecting root hairs. Using the model, answer the questions on the worksheet at the end of this lab exercise.
Comparing monocot and eudicot roots
The root systems of monocots and eudicots are different. Firstly, the root systems of monocots consist of numerous small roots that are all about the same size in diameter. This is what is referred to as a fibrous root system. Eudicots, on the other hand, typically have one large central root called a taproot, which may have numerous smaller lateral roots that extend from it. Grass would be a good example of a monocot showing a fibrous root system, and a carrot (a eudicot) would be a good example of a taproot. The roots of monocots and eudicots also differ in terms of the arrangement of their vascular tissue, which you will examine later at another station.
Figure 6. Fibrous and tap root systems.
Look at the provided sedge (grass) and dandelion plants. Compare their roots and answer the questions on the worksheet at the end of this lab exercise.
Normally, roots typically develop from other root tissues. However, occasionally, plants will develop new roots from other plant organs, such as stems or leaves. These types of roots are known as adventitious roots, and they may play additional or different roles beyond those performed by “normal” roots. Two examples of plants displaying adventitious roots are provided: English ivy and corn, both of which develop adventitious roots that arise from stem tissue. Examine these adventitious roots, and answer the questions about them on the worksheet at the end of this lab exercise.
Finally, observe the examples of root vegetables provided at this station. If you are curious about the technical botanical difference between vegetables and fruits, that distinction is made based on which plant part is being eaten. Vegetables, botanically speaking, are edible plant parts that are derived from either the roots, stems, or leaves of plants, while fruits are edible plant parts that are derived from the ovary/ovaries of flowers, and contain seeds. At this station, you may notice that there are some vegetables you’d expect to see here, as you might think of them as roots, but you may be surprised to actually correctly find them placed at another station.
*Answer the questions on the worksheet related to the root model.*
STATION III: Stem Anatomy & Diversity
The main functions of plant stems are to support the organs of photosynthesis, the leaves, but also to carry water and minerals to the leaves (through xylem), and to carry sugars made during photosynthesis to other parts of the plant (through phloem). At this station, you will be observing the major differences between the stems of monocots and eudicots, observing several examples of modified stems, learning a few vegetables that are composed of stem tissue, and examining secondary growth (also known as woody growth) in eudicots, and learning how to determine the age of trees by examining this secondary growth.
The stems of both monocots and eudicots contain all three major types of plant tissue: dermal tissue, ground tissue, and vascular tissue. Observe the models of both monocot and eudicot stems, and locate the following structures on each: epidermis (composed of dermal tissue), cortex (composed of ground tissue), and the xylem and phloem (vascular tissue). Also notice that in stems, the vascular tissue is arranged in vascular bundles, which are surrounded by vascular bundle girdles. Notice that the way that these vascular bundles are arranged differs in monocots and eudicots. Use these models to answer the questions about stem anatomy on the worksheet at the end of this lab exercise.
Now you will examine some examples of modified stems that do not look like “typical” stems. These include specialized stems called stolons, rhizomes, bulbs, and tubers.
First, look at the herbarium sheet showing a grass plant exhibiting a stolon, which is a horizontal plant stem that takes roots at points along its length to form new plants, or, in other words, is a means for plants that have them to engage in vegetative propagation, which is a form of asexual reproduction that produces new plants that are clones of the original parent plant. For another example of vegetative propagation, you can also examine the mother of thousands plant at Station 1. Another example of a stolon can be seen in Figure 7.
Figure 7. Vegetative propagation in a grass through the use of stolons.
Another type of modified stem is a rhizome, which is similar to a stolon. A rhizome is a a horizontal underground stem that puts out lateral shoots and adventitious roots. This type of modified stem can be seen in plants such as irises, and also ginger. Examine the provided iris and ginger rhizomes, and note the lateral shoots and adventitious roots on the iris rhizome. An example of a rhizome can also be seen in Figure 8.
Figure 8. A rhizome.
Another type of modified stem is a bulb. A bulb is an underground stem that consists of one or more buds enclosed in overlapping fleshy or membranous leaves. Bulbs primarily serve as food storage organs as a source of stored carbohydrates that are used during periods when the rest of the plant is dormant. Some examples of bulbs that are used as food include onions, garlic, and shallots. Even though you might think of these as “root vegetables”, they truly are not, as the part that is eaten is actually stem tissue. Examine the provided onions and garlic, and observe the small roots at the base of the bulb.
A final type of modified stem that you will examine this week is the tuber. A tuber is a much thickened underground part of a stem, serving as a food reserve, and producing buds from which new plants arise. A classic example of a tuber used as food is the white potato. Potatoes are very rich in starch, which is a polymer of glucose molecules. In this way, tubers are similar to bulbs, in that both serve as underground food storage organs for the plants that produce them. Incidentally, the “eyes” of potatoes are buds that can produce new potato plants.
Finally, at this station, you will observe secondary growth, also known as woody growth, which produces (unsurprisingly) wood. True woody growth is only seen in eudicots, and not monocots. In secondary growth, woody eudicots produce additional vascular tissue (xylem and phloem) as they grow, as well as bark, consisting of new ground and dermal tissue. These additional tissues are actually produced by two lateral meristematic regions (remember, meristems are areas of active cell division in plants). Also, since these meristematic regions are lateral tissues, cell division in each of these meristems results in an increased girth in woody plants as they grow.
In eudicots that exhibit secondary (woody) growth, the meristematic region that produces new vascular tissue is a layer called the vascular cambium, which is a layer found between the primary xylem and primary phloem. As woody eudicots grow, new layers of secondary xylem and secondary phloem are formed, increasing the diameter of the eudicot, forming the characteristic growth rings that can be observed in woody eudicots. The actual tissue that is referred to as wood is actually the secondary xylem tissue. The darker wood towards the center of woody eudicots is often referred to as heartwood, and consists of dry dead cells that no longer transport water, and primarily serves to support the woody eudicot. The lighter wood surrounding the heartwood is known as the sapwood, which contains xylem that is actually transporting water and nutrients through the plant.
Additionally, as woody eudicots grow, another layer of lateral meristematic tissue called the cork cambium, produces cork, a protective substance consisting of dead cells, and new epidermal tissue, as well as new living parenchyma tissue, all of which constitute the bark. See Fig. 9 on the following page for an illustration of secondary growth.
Figure 9. Differences between primary and secondary growth in eudicots.
Examine the model of secondary growth in woody eudicots, which is essentially a model illustrating a cross section through a tree. Using Figure 9 on the previous page, try to identify the primary xylem, primary phloem, vascular cambium, secondary xylem, secondary phloem, cork cambium, cork, and epidermis. Also, notice the ring-like pattern of growth in the wood, which displays wider, lighter colored rings called early wood, and thinner, darker rings called late wood. The early wood, per its name, is produced during periods of rapid growth in the spring and early summer, and late wood is produced in late summer and fall. The rings of late wood are thinner because growth is slower during that time of year. Together, a single ring of early wood and the following single ring of late wood represent a single year’s worth of growth, and are referred to as annual rings. See Figure 10 below for an example of these.
Examine the provided “tree cookies” (yes, they’re actually called that!) of various woody eudicot species, and see if you can determine how old they were when they were cut. Pick at least 2 of the available species, and record your estimates of their age when cut on the worksheet at the end of this lab exercise.
Figure 10. Annual growth rings in trees.
STATION IV: Leaf Anatomy & Diversity
Leaves are the primary photosynthetic organs in plants. At this station, familiarize yourself with basic leaf anatomy, examine the major difference between the leaves of monocots and eudicots, learn about various characteristics of leaves, examine the differences between simple and compound leaves, as well as observe several examples of leaves used in food, and for other culinary purposes.
The basic structure of angiosperm includes all three types of plant tissues (dermal, ground, and vascular tissues). The upper and lower surfaces of leaves consist of single layers of dermal cells arranged to form the epidermis of the leaf. In many species, these epidermal cells produce a waxy secretion deposited on top of the epidermal cells, and formsia protective called the cuticle, which primarily serves to reduce water loss. On the lower epidermis, pore-like openings called stomata (singular = stoma)primarily function in gas exchange. During photosyntheis, plants use carbon dioxide as a carbon source for producing glucose, and CO2, enters the leaf through the stomata. Plant cells also produce oxygen as a waste product during photosynthesis; O2, is also released from leaf tissue through the stomata. The drawback of having stomata openfor gas exchange, is that water is lost from the leaf. Fortunately, plants regulate when stomata are open, in the form of two bean-shaped guard cells on either side of each stoma. When conditions are hot and dry, the guard cells change shape to close the stomata to reduce water loss in this way.
Just beneath the upper epidermis is a layer of ground tissue called the palisade mesophyll, whose cells contain numerous chloroplasts, the site of photosynthesis. The cells of the palisade mesophyll are arranged in a very regular fashion, making this layer easy to distinguish. Below the palisade mesophyll, is another layer of mesophyll tissue (also containing numerous chloroplasts) called the spongy mesophyll. Spongy mesophyll cells are arranged much more haphazardly than the palisade mesophyll, and have lots of air spaces between them, which allow for more efficient air circulation and gas exchange.
Additionally, leaves of vascular plants such as angiosperms also possess vascular tissue in the form of xylem and phloem, which, in the leaves, take the form of vascular bundles that form veins. The xylem in leaf veins brings water from the roots (through the stem) to the leaf tissue, and the phloem in leaf veins carries sugars manufactured in the leaves during photosynthesis to other parts of the plant. Examine Figure 11 on the following page and the provided leaf tissue model, and try to identify each of the structures shown below on the leaf model. Answer the questions on the worksheet at the end of this lab exercise.
Figure 11. Basic leaf anatomy. Credit: H McKenna on Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Leaf_anatomy.svg)
One of the major differences between the leaves of monocots and eudicots is the pattern in which their leaf veins are arranged. You may have noted this difference back at Station 1 when you were identifying each of the provided angiosperms as either a monocot or eudicot. To refresh your memory, examine the laminated figure showing the difference in the venation (vein arrangement pattern) in monocot and eudicot leaves, and answer the questions on the worksheet at the end of this lab exercise.
Leaves can be described based on a number of their characteristics, including such things as the shape of the leaf, the shape of the leaf’s margin, the pattern of veining in the leaf, and whether it is a simple leaf or a compound leaf. Remember, a leaf’s petiole joins the stem of a plant at a node. A simple leaf is a leaf whose petiole has a single blade. However, a compound leaf is a leaf whose blade tissue is subdivided to form several leaflets, all of which are connected to a single petiole. Compound leaves can be pinnately compound, where several leaflets emerge along the sides (and tip) of the petiole, much in the way that the barbs of a feather are all joined to the feather’s central shaft. Alternatively, compound leaves can be palmately compound, in which all leaflets emerge from a single point on the tip of the petiole, similar to how all of your fingers emerge from your hand. Look at Figure 12, the laminated sheet of leaf characteristics, and the provided leaf examples to familiarize yourself with the differences between leaf types. Answer the question on the worksheet at the end of this lab.
Figure 12. Simple and compound leaves.
Similar to modifications seen in roots and stems, many plants have modified leaves that serve different and/or additional functions besides photosynthesis. For example, the leaves of the Venus flytrap are photosynthetic, but they are also modified to capture insect prey. Venus flytraps grow in areas where the soil is very poor in nitrogen, an important element for plant growth. Insects, are a very rich source of nitrogen, and their modified “trap jaw” leaves are adaptations that allow Venus flytraps to obtain sufficient nitrogen.
Figure 13. Venus flytraps showing leaves modified for prey capture. Credit: Юкатан on Wikimedia Commons
(http://commons.wikimedia.org/wiki/File:Venus_flytrap_in_Utopia_park_Israel_-_01.jpg)
Another great example of a group of plants with leaves modified for another purpose are the cacti. Look at the provided cactus, and identify the spines all over its surface. The spines of cacti are actually modified leaves that protect cacti from herbivores. Using this information, answer the question on the worksheet at the end of this lab exercise.
Examine some examples of leaves used as food, as well as for other culinary purposes. First, examine the stalk of celery in the beaker of colored water. You might be tempted to think that a celery stalk is actually stem tissue, but celery is technically a leaf vegetable, because the celery stalk is actually a modified petiole, or the leaf stalk from which the blades of the celery leaves emerge. Notice that in the celery, certain tissue is stained the same color as the water in which the stalk is sitting. Using what you have learned about plant tissues so far, answer the question on the worksheet at the end of this lab exercise.
Finally, examine the other examples of leaves used as food and other culinary purposes. This includes several different leaf vegetables, tea, which is brewed from leaves of the tea plant, and several different herbs. Incidentally, the difference between herbs and spices, botanically speaking, is that herbs are food seasonings derived from the leaves of plants, and spices are food seasonings that are derived from other plant parts (bark, seeds, roots, etc.). Answer the question on the worksheet at the end of this lab exercise.
STATIONS V-VI: Microscopic Examination of Plant Tissues
These last two stations are located on the back two tables in the lab, and consist of several microscopes set up for you to make microscopic examinations of various plant tissues, including root tissue, stem tissue, and leaf tissue. Essentially, all you will do for these stations is to make sure you visit each microscope and view the slide set up on each one, and use those to answer question on the worksheet at the end of this lab exercise.
BI 102 Lab Worksheet: Plants I Name _________________________________ Section _______
STATION I: Plant Diversity
- List each of the angiosperms at Station 1 in the table below, and identify each of those plants as either a monocot or a eudicot. Also list the characteristic(s) you used to determine whether each is a monocot or a eudicot.
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Monocot or Eudicot? |
Characteristic(s) used to determine monocot or eudicot |
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STATION II: Root Anatomy & Diversity
2. Write the number(s) on the structures on the root model next to the correct names of the structures below:
_____ Apical meristem
_____ Cortex
_____ Epidermis
_____ Phloem
_____ Root cap
_____ Xylem
3. Based on its roots, is the grass a monocot or a eudicot? What about the dandelion?
4. What is the function of adventitious roots in ivy or Virginia creeper?
5. What are the functions of prop roots in corn?
STATION III: Stem Anatomy & Diversity
6. Write the number(s) on the structures on the monocot stem model next to the correct names of the structures below:
_____ Cortex
_____ Epidermis
_____ Phloem
_____ Vascular bundle girdle
_____ Xylem
7. Write the number(s) on the structures on the eudicot stem model next to the correct names of the structures below:
_____ Cortex
_____ Epidermis
_____ Phloem
_____ Vascular bundle girdle
_____ Xylem
8. What is the major difference between the arrangement of vascular bundles in monocot and eudicot stems?
9. Onions and potatoes grow underground. However, they are not considered root vegetables. Why not?
10. Pick at least two of the provided “tree cookies”, and list the species you chose, and your estimates of their ages below:
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Estimated age (years) |
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STATION IV: Leaf Anatomy & Diversity
11. Write the number(s) from the leaf model next to the correct names of the structures below:
_____ Chloroplast
_____ Cuticle
_____ Lower epidermis
_____ Palisade mesophyll
_____ Phloem
_____ Spongy mesophyll
_____ Stoma
_____ Upper epidermis
_____ Vascular bundle sheath
_____ Xylem
12. In the space below, sketch a monocot leaf and a eudicot leaf, making sure to illustrate the differences in the arrangement of their veins. Label each picture as either a monocot or a eudicot, and also give a description of the arrangement of their leaf veins.
13. Knowing that the spines on the provided cactus are actually modified leaves, what is the green portion of the cactus at this station, and where (in what structure) would photosynthesis occur in this cactus?
14. What specific tissue in the celery stalk is stained the same color as the colored water? How did you come to this conclusion?
15. What is the botanical difference between herbs and spices?
STATIONS V-VI: Microscopic Examination of Plant Tissues
16. Look at the slide showing a longitudinal section of a root with root hairs on its surface. What do you think might be the function of root hairs?