Plant Biology: Photosynthesis Makes the World Go Round
Last semester I enrolled in a plant biology course because I have a thirst for knowledge about the world around me. Throughout the sixteen week affair, I learned about evolutionary theory, plant diversity, plant physiology, plant structure, ecology, and much more. I feel that learning is a cycle: one person teaches, the other learns, and the newly learned must turn around and teach anew.
I hope this information is useful for plant biology students and those with a genuine interest in the subject.
How much do you know about plant biology
Plant Physiology Pt 2
The key concepts of plant physiology and metabolism are complicated, thus a variety of resources were used to fully understand the material. Unlike previous essays, I found myself relying heavily on the textbook to understand the concepts of transpiration, water potential, and the negative pressure that aids tin the pull of water fro the roots to the leaves. For example, figure 36.12 of the textbook illustrated the nature of transpirational pull and its impact on the transportation of water within the xylem structures. Moreover, figure 36.9 on page 745 of the Campbell textbook explained the root structure as it meets with the vascular cylinder. It was here that gave reason as to why the water molecule must be in the cell via symplast in order to cross into the xylem structures. Additionally, two lectures aided in the understanding of the transportation of water through the xylem and its use in the phloem during sugar transportation. Andrew's lecture on xylem provided a substantial presentation on water potential, negative pressure, and the differences between the symplast and the apoplast. His thoroughness on the differences between the apoplast and symplast helped me understand which takes more effort to pass through. The second lecture that helped me understand the physiology of a plant was Dennis's lecture on phloem and sugar transport. Again, Dennis used several diagrams and slides that clarified the definitions of sources and sinks, and how positive pressure plays a direct role in the movement of sugar from one end of a sieve tube to the other end. Beside the physiology of plants, I used the textbook and an abstract to fully grasp the concepts of C3, C4, and CAM plants. The abstract on the article, "Photosynthetic Pathways in Freshwater Aquatic Plants" provided thoughtful information on the differences between C3, C4, and CAM plants, as well as the evolutionary processes that may have aided in the development of these adaptations(C4 and CAM) to the original Calvin Cycle.
The learning process isn't complete unless one can mentally and verbally express when the knowledge was obtained and how it changed their mental schema on the subject . As each week passes in this session of plant biology, I become more aware of plant life and less blind to the environment that surrounds me. This lat unit was not any different than the unit beforehand. Plant physiology is a critical component in plant biology and there are many concepts that can be related to the processes that occur elsewhere in the physical world. For example, I knew that understood the vascular system within a plant when I could explain the circulation of blood and nutrients in the human body and then relate it to the mechanisms that are found in the plant body. Although the two systems are different, there are crossovers in the basic functioning of each system. Now, when I picture the vascular system of the plant, I see blood flowing through the xylem and phloem, dropping off nutrients to tissues throughout the plant. Secondly, learning about the adaptations in the metabolic pathway of plants helped me to understand why certain plants have different physical morphologies than other plants. For example, I never knew why succulent plants were physically designed the way that they were, but now that I know that their stomata are open during the night and closed during the day, I understand the physical nature of these plants. Plus, prior to reading about the metabolic processes in the text and in the abstract, I have never been exposed to the variations of the Calvin Cycle.
Plant physiology and metabolism are intriguing, yet it is often overlooked by society. We are more concerned with medical advances and what we are having for dinner that night, but it is important to understand the concepts that keep that plants alive. Plant physiology, namely the vascular systems that conduct water and sugar throughout the plant body is regulated by solute concentration and pressure, known as water potential. The xylem transports water to the top of the plant for metabolizing or transpiration and is under negative pressure. On the other hand, the phloem transports sugars from sources to sinks and is regulated under positive pressure. In addition to physiology, the pathways of metabolism are specialized in plants, too. Plants metabolize carbon dioxide to be converted into sugars using photosynthesis. There are two adaptations to the C3 Calvin cycle, which fixes carbon into a three carbon compound. The C4 and the CAM adaptations evolved to provide adequate conversion of carbon dioxide into organic constituents that could be used for fuel. All three cycles play an important role in the homeostasis of the environment, as well as in the realm of agriculture. Lastly, plant physiology makes me happy because I love to know how things function!
Evolutionary Theory and Plants
Evolution, the change in gene frequency over time, has taken decades to fully understand and each day, bits of information come together to give it a stronger platform to stand upon. The theory of evolution, designed in part by Charles Darwin explores the adaptations of species, speciation, and the organization of the relationships between species. These components provide the heart of the theory of evolution. The evolution of species is witnessed through three methods- natural selection, genetic drift, and gene flow. All of the methods give rise to a varying gene pool with respect to the environment and frequency of certain alleles. Moreover, the gut of evolutionary theory revolves around speciation, which can arise in numerous ways. Two methods of speciation will discussed later on: allopatric and sympatric speciation. Finally, the organization of the relationships between species, phylogeny will be discussed in order to explain the importance of understanding who is related to who, and some species are not related to others, especially those that have similar characteristics(i.e. homologous vs. analogous). After completing the unit of evolution, I have gained a new found understanding on evolutionary theory through the use of lectures, text, and kinesthetic exercises, which have helped reinforce the information into my mind.
Evolution encompasses many notions, but there are three main components that comprise the theory: evolution of a species, speciation, and the representation of the relationships between species. The evolution of a species can occur through natural selection, genetic drift, and gene flow. According to Darwin, natural selection works to change a population over generations if individuals with heritable characteristics produce more offspring than other individuals (Campbell 443). For example, a population of red and white orchids inhabit a certain environment, but the white flowers are eaten more frequently than the red flowers. Over time, more red flowers will reproduce offspring(thus, more red flowers than white) as the white flowers are less populated in the environment. In addition to natural selection, genetic drift, the frequency of alleles in the gene pool each generation, can have a drastic impact of the evolution of species. Moreover, genetic drift can reduce the genetic variation in the gene pool of a population experience the founder or bottleneck effect. The bottleneck effect can be seen when a great disaster occurs and reduces the population size. For example, the recent oil leak in the Gulf of Mexico has significantly reduced the population of many species of fish- this decrease in numbers reduces the gene pool. A decrease in the variation of the gene pool allows for certain genes to be overrepresented(or vice versa). Beside the bottleneck effect, the founder effect reduces the genetic variation of a population, as well. The Campbell text cites that the founder effect is when a population is isolated from the original population and the new gene pool "is not reflective of the source population" (Campbell 462). An example is the early colonization of the Americas by Europeans; only a select group of men and women relocated, which significantly changed the gene pool. Both events can significantly evolve a species in a short amount of time because the gene pool was not changed due to natural selection, but by the change in allele frequency of the gene pool. Finally, evolution of species can occur by gene flow. A population experiences gene flow when it gains or loses alleles from its gene pool. Most commonly this happens when two populations are able to breed together, such as the seeds of a wildflower population blowing to another population of wildflowers, thus introducing a new allele. Over time, gene flow decreases the difference between populations as it spread the alleles throughout many populations.
The evolution of species is important to Darwin's theory, but it is the development of new species(speciation) that is a pivotal concept because it produces biological diversity. There are many definitions for species, but for the biological concept, Campbell describes a species as a "group or group of populations that have the potential to interbreed...produce viable, fertile offspring, and...cannot reproduce with members of other populations" (Campbell 473). Speciation can occur through two methods, allopatric speciation and sympatric speciation. Allopatric speciation refers to an interruption in gene flow caused by a geographical isolation. Islands (like Hawaii) are great examples of allopatric speciation; the isolated populations evolve over generations producing endemic species unique to that region(again natural selection plays a role here). Isolation creates a perfect environment for speciation, but the development of new species does not require geographical barriers. Sympatric speciation accounts for new species arising within the same geographical region. Oftentimes, the two species reside in the same region, but prefer different regions of the habitat and have opposing sexual selection factors. For example, Hawthorn flies used to feed on Hawthorn trees(and mate their too), but the introduction of the European Apple enticed many of the flies to feed on these apples because of their quick growth rate(Causes of Speciation). Over time, the original population of flies split into two species- the Hawthorn flies and the flies that chose the European apples.
Lastly, the evolutionary relationships between species, or phylogeny, allows biologists to examine the common ancestry of many species with respect to their morphology. Phylogeny is a visual picture of the relationships that many species share with each other, as it also depicts the distance between each other, as well. A phylogenic tree shows the common ancestor and the species that have adapted over time to create new species. Trees are relatively simple to read, once the vocabulary and its purpose are clearly understood. First, two terms can cause confusion for the reader of a phylogenic tree: analogous and homologous. An analogous characteristic, is one that is similar in nature between two species that are not related to each other by a common ancestor. For example, the dorsal fin of a dolphin and a shark are similar in structure and function, yet the two species are not related. They are said to be analogous to one another(these creatures would not be seen on a tree with a recent common ancestor). In other words, two species that are on the same tree, but do not share a most recent common ancestor, are said to be polyphyletic(Campbell 498). On the other hand, a homologous characteristic is one that is shared between two species that share a common ancestor. Species that are homologous to one another share similar characteristics at the anatomical and molecular levels. For example, all vertebrates have a tail during the embryonic stage.
The vast information on evolution can be confusing, but there are many tools that help the biology student understand the material. The first section on evolution involved learning the evolutionary process, particularly natural selection. After several thorough readings of these chapters, I understood the differences in the concepts of natural selection and genetic drift. For example, figure 22.14 in the Campbell text explained the homologous structures between four different species and that the adaptations over time allowed these same structures to perform very different functions. Speciation was very easy to understand, yet I found several tools on the Internet that aided in the
distinction between different forms of speciation. For example, I read "Evolutionary 101" developed by the evolutionary biology department at UC Berkeley. The web site provides clear images and explanations of allopatric and sympatric speciation. The last subject, phylogeny, required the most outside help in order to understand the difference between analogous and homologous, and monophyletic and polyphyletic characteristic with respect to the evolutionary tree. There were two items that I used to comprehend the structure and function of evolutionary trees. The first tool that explained the usefulness of phylogenic trees was the Mastering Biology quiz, "Trees/Evolution", particularly the exercise that involved arranging the aliens on the tree. Once I was able to arrange them in order and place the correct adaptations of traits in the correct locations, the ability to create or reconstruct a tree seemed like a simple task. In addition, "Understanding Evolutionary Trees" developed by University of California Museum of Paleontology, provided the qualitative information that explained how to read the trees regardless of its positioning of the different species.
Successful comprehension of the main concepts of evolutionary theory has allowed my mind to gain better understanding on former ideas that I had about evolution. Upon completion of the evolutionary unit in the course text, I gained a better understanding of the meaning of natural selection. Prior to class discussion, I have always been told that natural selection meant survival of the fittest, but the in-depth discussion clarified this loaded definition. I know recognize that natural selection is more about a selection of heritable traits that are passed on from one population to the next, which allows the more favorable traits to "survive". The second thing that changed my method of thinking about evolutionary theory was the ability to read phylogenic trees. Prior to the Mastering Biology exercise, my tree reading ability was minimal, but due to the clarification between monophyletic and polyphyletic, I now understand that two similar looking creatures do not have to be related to a recent common ancestor. Moreover,
Pop Quiz: Evolutionary Theory
What is the main theory that seeks to explain speciation?
Plant Diversity Part 1
The heart of the plant kingdom lies in the bed of diversity.Three main ideas were examined in the second unit of plant biology: autotrophic land plants,fungi, and the protist taxa, the main characteristics of these taxa, and how the groups are interrelated. Protists and fungi, while not considered land plants, must be discussed to grasp the evolutionary development of land plants. Plants can be divided into two sections: vascular and non-vascular plants. Additionally, vascular plants can be further subdivided into seedless vascular and seed vascular plants. The main groups studied under the plantae kingdom were bryophytes, lycophytes, pterophytes, gymnosperm, angiosperms, and charophytes. Each of these share certain characteristics and all taxons display novel characteristics that make them different from the other groups. As mentioned, the taxa share characteristics, thus demonstrating that there is an ancestral relationship between all of the groups discussed above. The diversity of plants can be seen in the variety of taxa which display common and novel characteristics among the groups, which illustrate the phylogenic relationships between all groups of land plants, fungi, and protists.
Before digging into the land plants, a discussion on lesser related organisms, protists, charophyceans, and fungi must be had. Protists are a complex kingdom of unicellular, colonial,and multicellular organisms that are autotrophic, heterotrophic, or mixotrophic. There are numerous clades of protists, yet there are several that provide a link to to the evolution of land plants. This can be explained by the endosymbiotic theory, which suggests that a heterotrophic protist ingested plastids and then later evolved into red and green algae(which we know land plants are closely related to green algae). Four clades demonstrate the diversity and evolutionary relationship of protists, plants, and fungi. First, the alveolata characteristically have sacs that regulate the cell's ion and water content. Moreover, the dinolagellates are armored with cellulose plated walls, which is a similar component in land plants(perhaps a relationship?) . The second clade, the stramenopila contain groups that are most similar to the red and green algae. In Sara's lecture on stramenopila, the clade exhibited many charactersitcs that can be found in plants and fungi. For example, the diatoms have hyphae to absorb nutrients much like fungi and the brown algae are multicellular with some alternation of generations much like land plants(5). There are interesting connections between the kingdoms and these similarities highlight the ancestral relationships(or convergent evolution) between the many clades. The last two clades, rhodophyta and chlorophyta are most closely related to the land plants. Rhodophyta, red algae, is known for its secondary pigment phycoerythrin and has no flagellated stages(5). Chlorophyta, green algae, is most similar to land plants and has chloroplasts similar to those found in plants. Most chlorophytes have complex life cycles with alternation of generations. According to the phylogenic tree, the charophyceans and land plants share the most recent common ancestor with chlorophyta.
Beside the protist kingdom, the Charophyceans are especially important to land plants because they are the closest living relative of land plants. Prior to the evolution of charophyceans, most plant life was aquatic. The charophyceans inhabit the shallow waters around lakes where they are exposed to the above water elements. Unlike its ancestors that were fully aquatic, the charophyceans are able to avoid drying out, which gives a clue to biologists how the development of land plants may have occurred. The plants have a layer of sporopollenin, which coats the outer plant tissue to prevent it from drying out. Scientists believe that the charophyceans developed derived traits that would enable the first land plants to survive without being submerged in water.
Fungi, a diverse and mysterious kingdom, that seem similar to land plants, but are remarkably different. Actually, fungi are closer related to animals, than they are to plants; for example, evidence shows that animals and fungi descended from a flagellated, unicellular organism(Campbell 612). There are five phyla of fungi: chytrids, zygomycetes, glomeromycetes, ascomycetes, and basidiomycetes. All phyla share similar characteristics such as being heterotrophic, are symbionts, and participate in asexual and sexual reproduction. Each phylum possesses a trait that discriminates it from the rest. The chytrids, the most primitive of the fungi illustrate a trait that supports the hypothesis that fungi evolved from a flagellated organism. All chytrids have motile sperm(4). The phyla zygomycetes and glomeromycetes are similar to one another, except few variations. The zygomycota, or molds, have a resistant zygosporangium that is multinucleate(Campbell 614). On the other hand, the glomeromycota exhibit similar traits, yet they are involved in a mutualistic relationship with trees and plants via the arbuscular mychorrizae. The arbuscular mychorrizae invade the living roots of plants and trees to absorb water and minerals(4,8). The remaining phyla, ascomycota and basidiomycota are sister groups that developed fruiting bodies, but differ in complexity and main function. The ascomycota range from microscopic yeasts to complex cup fungi and morels. Most ascomycota reproduce sexually by releasing conidospores that are dispersed by the wind, yet some do asexually reproduce(Campbell). Furthermore, the most common function that ascomycota participate in, is a mutualistic relationship with algae and cyanobacteria, known as lichen. Finally, the basidiomycota, the most commonly recognized fungi specialize in decomposition of wood and other plant materials. Basidiomycota are known for their elaborate "toadstool" bodies that are involved in sexual and asexual reproduction.
The main taxa of land plants, bryophytes, lycophytes, pterophytes, gymnosperms, angiosperms, and charophytes(and fungi will be included as well) comprise the taxa under the plantae kingdom. The groups are categorized as vascular(seed and seedless) and non-vascular, which highlight the common characteristics, as well as the differences between the land plants. Non-vascular land plants, bryophytes, lack a vascular tissue system, namely phloem and xylem. The bryophytes include the hornworts, liverworts, and mosses, but it is not clear if they form a clade or not(certain evidence illustrates that they are not monophyletic, as some mosses display a simple vascular system). The bryophytes are gametophyte dominant in the life cycle, unlike the vascular land plants(1). The gametophyte is comprised of protonemata and gametophore. The protonemata have large surface area for water and mineral absorption, plus it forms a bud with each apical meristem that will produce a gametophore. The gametophore produces the gamete which will turn into the mature gametophyte. The bryophytes "hug" the ground, often forming "carpets on the forest floor", which coincides with the idea that structurally, it cannot grow upwards(Campbell 580). The lack of vascular tissue prevents it from growing tall since it could not nourish itself without the use of vascular systems. Moreover, the bryophytes anchor themselves to the ground using rhizoids, rather than roots. Unlike the roots of vascular plants which help with absorption, rhizoids do not take part in absorption.
Pop Quiz: Plant Diversity
Which Species is most closely related to Land Plants?
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Plant Diversity, Part 2
As previously mentioned, the evolutionary relationship between the mosses, liverworts, and hornworts are under scrutiny. The hornworts and mosses are more complex than the liverworts; for example, the liverworts lack a stomata. Stomata are found in all vascular plants, meaning that the stomata evolved in the ancestor of the hornworts, mosses, and vascular plants, but not in the liverworts. There are several thought pools on the evolutionary relationship between these plant groups. For example, if the hornworts are the oldest of the plants, then perhaps it developed stomata, lost it in evolution, and then regained it, or the hornworts evolved separately from the mosses and vascular plants(Campbell 583). Again, the evolutionary relationship is partially understood with the respect to the remaining vascular plants.
The remaining plant groups, lycophytes, pterophytes, gymnosperms, and angiosperms are vascular land plants. The vascular land plants are divided into seedless and seed plants. Seedless vascular plants are lycophytes(club mosses, spike mosses, and quillworts) and pterophytes(ferns and fern allies), which have similar characteristics of nonvascular plants and novel characteristics that illustrate the process of evolution(2). All vascular seedless plants exhibit alternation of generations and reduced gametophytes. Most importantly, pterophytes and lycophytes have vascular systems. A vascular system contains xylem to conduct water and phloem to conduct sugars to the far stretches of the plant structures. This enables these groups to grow in height, unlike its bryophyte relatives. Furthermore, these groups have roots to anchor and absorb nutrients, as well as leaves to capture solar energy. Both of these traits are not seen in nonvascular plants. While the ferns and fern allies have bryophytic traits,they posses novel traits that connect them to the vascular seed plants. For example, pterophytes have flagellated sperm and require water to get to the eggs for fertilization, much like the bryophytes(3). On the other hand, the ferns and fern allies display reduced gametophytes and grow much larger than bryophytes. The lycophytes are the most primitive vascular plant, which are small, herbaceaous plants that look similar to true mosses. Plus, lycophytes tend to grow on tropical trees as epiphytes(3).
Lastly, the evolution of vascular seed plants paved the road for the evolution of animals. Seed plants developed 320 million years ago with remarkably different traits that would change the fate of the planet forever. Four main traits evolved to produce the vascular seed plants. For example, seed plants have microscopic gametophytes and are sporophyte dominant(Campbell 591). Furthermore, seed plants are heterosporous, meaning that there are bisexual gametophytes(unlike most seedless plants, which are homosporous). Thirdly, seed parents retain the megaspore within the mature sporophyte to protect it from damage. Lastly, microspores are contained in pollen grains, which can be dispersed via the wind or animals to fertilize a megaspore(Campbell 592). There are two clade of seed plants, the gymnosperms and the angiosperms. The gymnosperms have seeds that are not enclosed in ovaries. The four phyla are conferophyta, ginkgophyta, gnetophyta, and cycadophyta. Coniferophyta bear cones that release the seeds for fertilization. This is the largest phyla of gymnosperms. On the other hand, the cycadophyta, gingkophyta, and gnetophyta have a small number of species, which can be found in tropical regions and deserts. The second clade, the angiosperms are seed plants that produce flowers and fruits. The flower and fruit have key roles in the angiosperm life cycle. For example, the flower is the sexual reprodcuction structure, which for most angiosperms relies on fertilization by an insect or other animal(9). Secondly, the fruit is a mature ovary that encases the seed. Angiosperms are involved in double fertilization, meaning that one sperm fertilizes the egg to make a diploid zygote, while the other sperm fuses with the multinucleate female gametophyte cell. Only then, can the ovule mature into a seed.
The plant kingdom is vast, thus a variety of learning tools were used to turn the information into learned knowledge. Educational web sites, the Campbell text, student lectures, and lab activities provided the basis for understanding the plant, protist, and fungi taxa. First, the sexual cycles of all land plants are similar with slight variations, making it hard to differentiate between the differing cycles. However, two labs, the coniferophyta lab and the fern lab, taught me the structures of the megaspore, microspore, and the mechanisms for fertilization to occur. During the coniferophyta lab, the slides that I viewed gave a clear picture of what the megaspores and microspores looked like and how the seeds contain ovules and spores(6). After this I was able to explain to others what they look like, and how they are contained within the male and female cones. Moreover, the fern growing lab provided the platform to learn how the egg and sperm meet in fertilization. Fern sperm requires water to meet the egg, therefore we grew male and hermaphroditic (heterosporous) gametophytes in agar dishes and introduced them to one another in a water medium(7). Under the microscope, I was able to see the male release its sperm and migrate toward the hermaphroditic gametophyte. In addition to the lab slides, the student lectures, particularly, Tyler Waterman's on fungi and Sara Barnum's on protists provided a great toolbox to learn about taxa that seemed "all over the place" in my mind. For example, Tyler's presentation on fungi structure clarified the many structures of the fungus, such as differentiating between the fruiting body, hyphae, and mycelium(4). Another lecture that helped start the learning process of plants, was the protist lecture by Sara Barnum. Her lecture was so thorough that I have not needed to reference the text book to compare and contrast the differing groups of protists, i.e. stramenopiles, alveolates, red and green algae(5). It was this place when I fully comprehended the endosymbiotic hypothesis and the evolution of land plants.
Outside of the classroom, educational web sites and the Campbell text closed the gaps in my understanding of the information and provided clarification with the respect to the differing characteristics of the plant taxa. In the text book the most useful pages were, page 571, page 579, and page 624. Page 571, table 28.1 provided a table that categorized the groups of protists and their distinguishing characteristics. The straight-froward table made it easy to integrate the information in my mind. Secondly, the evolutionary tree on page 579 gave me a clear understanding of the relationships between all land plants. Lastly, page 624 provided the distinguishing characteristics of fungi phyla. Two websites gave me further understanding of the plant diversity unit. First, the bryophyte website clearly explained the key traits in bryophytes and how they are similar to some traits still maintained in the vascular plants. Second, the seedless vascular plant website from Ohio State gave a full discussion on the CO2 uptake by ferns and the possible connections that seedless vascular plants have to other plant life.
Learning about plants means nothing until one can say that it made a difference in their thinking about the diversity of plants. I have always valued plants and their contribution to my life, but it wasn't until we began discussing the seedless vascular plants and fungi did I gain a newfound perspective on plants. For example, I am vegan and have always paid my homage to the plants that provide nutrition to my life, but I never looked at the plants that were responsible for the evolution of many of the land plants that we see today. For example, the role of seedless vascular plants in harboring the carbon dioxide to provide a pristine environment for the development of seed plants went unnoticed until David discussed it in lecture. Furthermore, I was blind to the prevalence of symbiotic relationships between most plant life and fungi until I read the Campbell text and listened to Tyler Waterman's presentation. After I realized that plants work together in so many ways, I was able to put the evolutionary tree together in my mind without having to struggle with understanding why they are related in the ways that they are. Plant life is diverse. It covers the world in beautiful colors, it serves itself in economical and ecological ways, and it has evolved over the last 600 million years to produce an earth that animals can inhabit. The plantae kingdom continues to awe its followers as more relationships are being discovered between the phyla and as new species arise.
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Plant Structure and Function
Peering out the window in early springtime, one might see trees with little buds at the end of every branch. Look out the window within a few days and entire flowers or leaves have emerged from the spot where that tiny bud was only a few days ago. The shoots and roots of a plant appear to develop overnight and “out of nothing”, but these tissues are packaged in the apical meristem(that unconcerning bud). The apical meristem, the embryonic tissue at the root and shoot tips gives rise the three primary meristems, which, in turn give rise to three primary tissues, which are comprised of a variety of specialized cells. The three primary meristems, the protoderm, the procambium, and the ground meristem are the same in the development of the roots and shoots, but will differentiate into different primary tissues(some form of dermal, vascular, and ground). Moreover, these tissues will develop into differing tissues throughout root and stem development( many the same, but there is differentiation). All of the tissues found in the roots and shoots of the plant are made up of the same specialized cells found throughout the plant, or in distinct regions of the plant’s organs. The apical meristem produces all of the plants cells, which in turn make up the main plant tissues involved in the development of the roots and shoots.
Roots and stems develop from the differentiation of the apical meristem; the apical meristem gives rise to the protoderm, the procambium, and the ground meristem. The protoderm is the outermost layer of the root and the stem and develops into the epidermis. On leaves, the epidermis provides a protective barrier, much like the remainder of the plant. Moreover, there are specialized cells in the epidermis of leaves that play a role in gas exchange and transpiration. The guard cells are two epidermal cells that open and close to release water and exchange gases. The epidermis in roots and stems acts as a protective barrier, while regulating water loss and gas exchange(1). The protoderm does not differentiate into any other tissue(or cells), however the epidermis will be replaced by secondary tissues that make up the periderm, which will be discussed later.
The second meristematic tissue is the procambium. The procambium lies within the protoderm and will be responsible for developing much of the vascular tissue in the roots and shoots(2). Procambium in the stem and roots are very similar, yet the pathways are slightly different. For example, the procambium in the roots undergoes differentiation to produce the vascular cylinder. The vascular cylinder consists of the primary phloem and primary xylem, vascular cambium the pericycle, and the endodermis. Let’s go from the outside and work inward. The endodermis is a thick layer of cells that surround the vascular cylinder. Its main function is protection. After the endodermis lies the pericycle, which is a layer of parenchyma cells. Parenchyma cells are undifferentiated plant cells that can be found throughout the plant and are used for protection, secretion, and storage(2,5). The pericycle will give rise to the vascular cambium and in secondary growth it will produce the cork cambium, a secondary tissue that produces cork and phelloderm(all a part of the periderm). Taking one more step inward, we find the vascular cambium. It will produce the secondary xylem and phloem(2,3). However, the vascular cambium doesn’t disappear, rather it lies in between the secondary xylem and the secondary phloem, which are secondary tissues(6). In the roots, the vascular cambium is responsible for lateral growth.
On the other hand, the vascular development of a stem is slightly different. The procambium develops into the fascicular cambium, which is a connective tissue that will support further growth. It lies in between the primary phloem and xylem(2,3). Moreover, the fascicular cambium is connected into a ring via the interfascicular cambium which is in between the vascular cambium bundles(the xylem, cambium, and phloem) (4). As the cambium develops, it becomes the vascular cambium which follows the same pattern as the root development that can be seen on Figure 24-6(3).The vascular cambium is responsible for growth in stems, too. Understanding the functions of these structures is critical to understanding the nature of plant development. The vascular tissue within the stems and roots perform the same task: transportation. For example, primary xylem is responsible for the transportaion of water. Primary xylem utilizes tracheids, which are long, tapered cells to transport water throughout the plant(3). Moreover, vessels, which are barrel shaped take part in water movement, too. Primary phloem, the vascular tissue that moves sugars, relies on sieve tubes to conduct sugar throughout the plant tissues(8).
The final primary meristematic tissue is the ground tissue. Ground tissue can be viewed as the stuffing inside a blanket. It contains the collenchyma,sclerenchyma, and parenchyma cells. Since we already know the function of parenchyma, let’s evaluate the functions of sclerenchyma and collenchyma. Sclerenchyma are thick walled cells that are the “fiber” of the plant. They provide support for vertical growth. The best example of sclerenchyma is the stringy material in celery. Additionally, collenchyma cells provide plant support as well. The ground tissue has similar pathways for differentiation in the stem and the roots. In the roots, the ground tissue becomes the cortex, which is the layering of the aforementioned cells. The cortex lies between the protoderm and the procambium(2). In the stem of a plant, the ground tissue will develop into the pith, pith rays, and the cortex. The pith is in the center of the plant and is responsible for nutrient storage. The pith is made up of parenchyma cells. Furthermore, the pith rays are rows of parenchyma cells that lie between the vascular bundles(this can be seen in dicots).
The aforementioned information on plant structure and function, as well as development can be confusing, but many tools helped me fully understand the unique growth of plants. The first place tool that clarified the differences between the primary xylem and phloem and the secondary xylem and phloem was Matthew’s lecture on the vascular cambium(6). Matthew explained how the primary tissue was alive and transporting water and nutrients to the plant tissues, while the secondary tissues were supporting plant growth(laterally). It made sense that as the plant grew taller, it would need to increase its girth to withstand the extra mass. However, the real learning stemmed from the three handouts provided by professor Miller. The Handout that summarized root and stem development in a flow chart allowed me to divide and conquer the plant development. In addition, using this handout alongside the handout that visually expressed the growth of roots and stems, I was able to understand the development from apical meristem to primary meristems to primary tissues and finally, to secondary tissues(2,3). The handouts were clear, well-designed, and did not seek to confuse the student(myself) about where these tissues were developing from and how they produced vertical and lateral growth. After grasping the development of plants, the tissues were examined at the cellular level. The use of Table 19.2 that was provided in lab, explained the structure and function of each cell that made up tissues throughout the plant. Finally, I was able to make a connection between the tissues and cells that were responsible for these tissues. I understood that xylem had trachieds, while phloem and sieve tubes.
The development and function of plant tissues in the roots and shoots of a plant were never important to me, but now that I understand a plant(developmentally), I have gained an insight into the world. Prior to starting this unit, I knew that plants grew tall. I knew that they grew outwardly, too, but I didn’t know how. Taking on the task of learning about the major tissue systems, dermal, vascular, and ground, I am able to look at plants and know what they are made out of. Most importantly, I was able to relate plants to humans on a functional level, which prior to these lectures I had not been able to do. For example, I relate the pressure system of the vascular network to that of our own pulmonary/systemic circuit. Additionally, the epidermis of human skin and the epidermis of a plant do the same functions(protection, secretion). This unit has inspired me to consistently seek to make relationships between the plant world and the human world.
Plants are remarkable. They grow at all levels, ranging from centimeters to hundreds of feet tall. The development of a plant requires the differentiation of the apical meristem into three major tissues, that in turn will turn a small plant into a working machine. The dermal layer provides protection and serves as a regulator, while the vascular system transports water and sugar to all parts of the plant, and the ground tissue provides the bulk needed to stay alive. It is important to understand the structure and function of plants because it dictates the type of growth a plant is capable of and can provide a picture of what environmental factors a plant has endured over decades(even centuries).
Pop Quiz: Structure and Function
What tissue is predominantly made up of Parenchyma Cells?
Brief Abstract - "Will Plants Profit from High CO2”
The levels of carbon dioxide are the passionate topic for debate in the biology world, especially in the plant world. Science magazine published an article, “Will Plants Profit from High CO2” The article discusses the benefits and drawbacks of rising CO2 levels, as well as asking the question, “will plants gain an advantage from the high levels of CO2?”. Several points were made during the article: the effects on plants(both C3 and C4 plants), how the rise would effect an ecosystem as a whole, and the impact it would have on agriculture. First, the article cites that blowing CO2 into a section of plant life would increase the growth dramatically, but it would taper off over time in a natural ecosystem(so the effect wold not be long-lasting). Moreover, the article leads into a conversation on the CO2 sensitivities between C3 and C4 plants. C3 plants are more sensitive to carbon dioxide and would respond with a growth spurt, while C4 would not result in such a dramatic growth spurt. The main theme throughout the article was the advantages and disadvantages that pumping CO2 into regions would have on agriculture. Positively, the carbon dioxide levels would increase production and speed harvest times. Unfortunately, the increase in carbon dioxide levels would force farmers to provide super nutrient dense fertilizer to counteract any deficiencies that the high CO2 levels may produce. Moreover, scientists worry about other effects that this may have on the environment...i.e. the increase in growth may in turn inhibit plant growth if nutrients cannot be sufficiently provided. Unfortunately, the studies conflict in every which way- some show positive results and others demonstrate negative results. Overall, the article was intriguing. For example, I thought that it was fascinating that 1 billion metric tons of carbon dioxide is “missing” from the atmosphere and it is very likely that forests are harboring the gas. The information in the article was delivered in a clear, concise manner that made it easy to understand and enticed me to do further research on the subject. However, I would have liked to see better results(leaning one way or the other).
Personal journals are a great place to start a plant collection that you can pass down to future generations.
Plant Physiology Pt 1
Plant physiology and metabolism function similarly to that of animal physiology and metabolism. Animals and plants have vascular systems and must convert food into an organic product that can be used to produce energy. However, plants obtain nutrients and convert them into fuel using a different pathway than other organisms- photosynthesis. Plants use photosynthesis to convert carbon dioxide into organic compounds, primarily, sugars. Furthermore, plants use three pathways to convert carbon dioxide into sugar: C3, C4, and CAM. In addition the to metabolic pathways found within plants, the vascular system is important to understand since it is responsible for the transport of inorganic and organic compounds. The vascular system components, the xylem and the phloem, are responsible for transporting water and sugar throughout the body of the plants. Transportation is influenced in part by pressure. We will examine the pathway traveled by one water molecule from root to transpiration, further in the paper. The physiology and metabolism of a plant are intimately intertwined as the plant converts inorganic material into organic material which is then circulated throughout the plant.
Plants metabolize and convert carbon dioxide using photosynthesis, the Calvin Cycle. Photosynthesis has adapted to convert carbon dioxide into organic compounds using three methods: C3, C4, and CAM pathways. The different pathways differ in the temporal, spatial, product The Calvin Cycle, the pathway that C3 plants use is the most common plant pathway for all plants.C3 plants use the main pathway for photosynthesis with the first product from carbon fixation being a three carbon compound. Moreover, C3 plants, partially close their stomata on hot days and produce less sugar because of the declining levels of carbon dioxide. Although there are lower levels of carbon dioxide in the plant for fixation, rubisco can bind to oxygen instead, thereby maintaining proper energy requirements. This is known as photorespiration(Reference 1). The most common types of C3 plants are rice, wheat and soy. While C3 is the most common metabolic pathway, there are plants that have adapted to use other pathways. For example, the C4 plant introduces a prelude step to the Calvin Cycle that C3 plants use. The C4 plant fixes carbon dioxide into a four carbon compound catalyzed by PEP carboxylase in the mesophyll cell of the leaf(Reference 1). After the carbon is fixated into the four carbon compound, it is sent to the sheath cell where it is put into the Calvin cycle. Unlike the C3 pathway, the C4 pathway differs spatially by performing the functions in different cells on the leaf of the plant. The benefits of C4 plants is that it minimizes photorespiration by keeping its stomata partially open during hot, dry days (Reference 2). The carbon dioxide is concentrated in the cell and powered by ATP. The most common C4 plants are corn and sugar cane. Lastly, the CAM, crassulacean acid metabolism, is a unique pathway that evolved in plants that were subjected to exceptionally arid locations. CAM plants include succulent and pineapples, among other species differ temporally in comparison to C3 and C4 plants. CAM plants open their stomata during the nighttime, while taking up carbon dioxide and converting it to organic acids and storing them in the vacuoles(Reference 3). As morning arrives, the stomata close and the plant converts the organic acids into sugars. CAM is similar to C4 in that both pathways involve converting carbon dioxide into intermediates. On the other hand, they differ in the fact that CAM performs different functions within the same cell.
The vascular system of a plant, much like the human circulatory system, is responsible for transporting water, sugar, and solutes throughout the tissues of the plant. The xylem and phloem are the main components of the vascular system. Xylem conducts water throughout the plant, while the phloem transports sugar. There are other components that will be discussed, as well. To fully understand the physiology of a plant and how solutions go from ground to plant to air, let's consider a water molecule that travels throughout the plant. First, the water molecule that is in the soil solution near the roots is travels into the root hair and toward the vascular cylinder. The water molecule can travel to the vascular cylinder via two routes: apoplast or symplast. If the water chooses to travel through the apoplast, it does so by not entering the cells, rather it travels in the extracellular space(Reference 4). However, eventually it will have to cross into a cell to reach the vascular cylinder. On the other hand, the water can travel via symplast, which involves crossing in to the cell wall only once and then traveling from cell to cell using plasmadesmata. Why does the water move though? The concept is water potential, Y. Water potential is the potential energy of water to do work. Pressure and solute concentration have an impact on this value. Free water always moves from areas of high water potential to areas of low water potential. Oftentimes, an area of low water potential is highly concentrated with solute and is impacted by negative pressure. Let's move back to the water molecule: as the water molecule travels through the root hair, it must pass the endodermis, the dermal tissue surrounding the vascular cylinder(Reference 6). At this point, the molecule is able to pass from the root and into the vessels and tracheids of the xylem. Water does not travel through the xylem using passive transport; instead, the water is transported throughout the plant using bulk flow, which is the long distance method of water transport.Upon entering the xylem, the water molecule is pulled upward through the stem; this is caused by the transpiration-cohesion-tension mechanism. The transpirational pull exerts a negative pressure on the molecule encouraging it to ascend upward through the stem with the aid of cohesion. There is pull because water is leaving the plant through the stomata which in turn creates a negative water potential due to the increased negative pressure in the leaf-air interfaces(Reference 7). Moreover, the cohesion of water, its affinity to stick to itself, as well as the adhesion, the tension against the cell walls aid the water in its ascension to the top of the plant. The water molecule moves through the vein of a leaf and it approaches the mesophyll cell, where it would be transpired out of the stomata, however, a nearby cell is in the process of photosynthesis, thus the water molecule gets pulled back into the mesophyll leaf cell. From here, the cell is pulled back down through the mesophyll cell where it travels via symplast into a bundle sheath cell then into a companion cell and finally into a sieve tube member(Reference 8). A companion cell is the driving forced for all sieve tube members since they are dead at maturity. At this point, since the water molecule is near the top of the plant, the water is loaded into the sieve tube member where the pressure will build up (positive pressure)(Reference 9). A source is a location in the plant where there is organic production of sucrose. The water molecule waits in the phloem sap until the pressure builds up high enough and it is forced down toward the sugar sink. A sugar sink is a location on the plant that is a net consumer of sucrose (Reference 9). The pressure flow loads the sink with sugar and then relieved as the water molecule escapes through the sieve tube via diffusion and into the xylem. The water molecule travels up through the xylem being pulled by the negative pressure system(Reference 10). At the leaf, it is pulled through the air spaces between the mesophyll cells and transpires out of the stomata into the atmosphere.
Pop Quiz: Plant Physio
Where is the highest negative water potential in a plant?
Brief Abstract - Freshwater Aquatic Plants
Until recently, it was thought that aquatic plants were not carbon-limited, but Jon E. Keely’s article, “Photosynthetic Pathways in Freshwater Aquatic Plants,” highlights carbon-limiting as the driving force behind the pathways of such plants. Keely examines the three photosynthetic pathways that aquatic plants use: CAM, C3, and C4. In addition, he highlights the major reasons why certain aquatic plants select specific metabolic pathways in certain environmental conditions. First, he looks at th use of CAM in aquatic plants. Aquatic plants use CAM in temporary pools of water, but it cannot be used for long due to the speed of intake in comparison to the diffusion of CO2 into the water. Most often, CAM takes place in the nighttime when the plant turns the abundant CO2 into malic acid, which will be used throughout the next day when CO2 is scarce. Moreover, it is said that when the pools dry up, the plants revert to C3 photosynthesis. Keely further discusses C4 photosynthesis in aquatic plants, too. There are certain plants that perform C4 fixation above water and C3 fixation under water, demonstrating a plants ability to be involved in double fixation. Keely presents the evidence for these three pathways by citing a number of plant species (Hydrilla, Isoetes, Littorella Uniflora) that have been studied and demonstrate these photosynthetic pathways. While the information is interesting, visual aids would have been helpful(the visual pictures that are in the article are too dark to decipher). Moreover, Keely seeks to inform scientists and students alike about the evolution of photosynthetic pathways, as well as clarify the differences between each pathway, too. The results of this article successfully supported the evolutionary development of aquatic plants and the unique ability of plants to use different pathways of photosynthesis depending on the environmental stimuli. Lastly, this article fits into our lecture discussions well, as we are discussing plant structures, plant nutrition, and plant adaptation.
California Poppy Blooming!
Plant Biology Summative Essay - Part 1
As students, we step into biology classes with misconceptions or lack of understanding,as well as an immature platform of information on some major themes embedded in the curriculum. The goal of biology, especially plant biology, is to tear down common misconceptions of evolutionary theory and the significance of plant life to the homeostasis of the planet. Moreover, plant biology seeks to eliminate plant blindness through a wide variety of concepts including plant diversity, physiology, the human-plant relationship, ecology, and plant structure and function. Prior to completing a course in plant biology, I did not understand the physiology of plants, plant defenses against herbivores, or the extensive diversity of plant organisms. The ample amount of class activities, lab experiments, and field trips helped integrate the information in a manner that made it easier to understand(thereby learning it). Moreover, as the class progressed, the misconceptions or lack of understanding that I had on specific concepts within plant biology diminished and changed my thoughts on the green world around me. Plant biology has educated me in a wide variety of themes through the use of educational exercises that remedied former misconceptions and holes in my knowledge.
Walking into this course, I had little knowledge on plant physiology, plant defenses, and plant diversity; however, I can successfully acknowledge that I have changed that by learning these concepts to the best of my ability. The concepts that I did have knowledge on: plant nutrition, ecology, biotechnology, and plant structure were built upon and I am stronger in those regions. Originally, my awareness of plant physiology was little more than knowing that they used photosynthesis and had a vascular system. After the summation of this course, I can explain to another student the concepts of xylem and phloem, and the pressure systems that allow water and sugar to be transported up and down the body of a plant. Water potential was an intriguing concept and I can relate it to more than just plant biology, which tells me that I learned something. Another lesser known subject and one full of misconceptions, plant defenses and reactions to environmental stimuli became a subject that I am proud to claim some understanding in. Prior to this semester, I understood that plants either thrive or die in response to environmental factors, but I did not know that plants had the ability to defend themselves and react to such variables. For example, a plants innate defenses to predation shocked me. I did not know that plants had hormones that allowed them to fight off predators or communicate with other plants. The misconception lied in the deduction that if plants are immobile, then they cannot fight, nor converse. These ideas were exchanged for the correct ones in the last several weeks of class through discussions and lab experiments(discussed later). The final concept, plant diversity wasn't unknown to me, yet my mind was not aware of the hundreds of thousands of species that exist. I entered the class with the following plant species in my mind: trees, flowers, and vegetables. I am walking out of the class with angiosperms, gymnosperms, pterophytes, lycophytes, coniferphytes, algae, protists, fungi, and many, many more. This expansion makes me feel as though I have accomplished something this semester.
The three aforementioned concepts, plus the remaining themes discussed throughout the course were solidified through a number if class experiences. Plant physiology was the most difficult concept to understand, thus it took several learning activities to fully grasp the main objectives. For example, water potential and its relationship to transpiration was confusing until the group performed the experiment involving a tomato plant and a pressure gauge. In this experiment, we tested several variables such as heat, light, and humidity and their affect on the rate of transpiration. It was here that the negative pressure system that allows the water to move from root to leaf bore its ugly(yet smart) head. In addition to this lab experiment, the lectures done by Andrew and Dennis on xylem, phloem, sources and sinks, and water potential, were very useful in separating out the concepts and turning them into useful bits of information. It was here, in these intellectual class discussions that we, as a class could differentiate between negative and positive pressure systems and the roles that they play in the vascular system of a plant.
The second concept that I had very little knowledge on and a major misconception about was plants innate defenses against predation, as well as a plants reaction to environmental stimuli. The misconception was repaired and knowledge was gained through student lectures, the tomato torture lab, and a class activity. First, I learned about a plant's ability to defend itself in Megan's student lecture on hormones and communication. She explained how a plant releases volatile organic compounds in order to protect itself from further damage from herbivory. The lecture taught me about the mechanical adaptation of plants(i.e. the plant that recoiled when touched) when faced with tactile stimulation. Secondly, the tomato torture lab illustrated a plants reaction to environmental stimuli. The tomato plants were subjected to altering variables like shade, herbivory, and shaking. Each plant exhibited different amounts of growth due to these variables. Prior to this class, I would not have known that plants adapt to the environmental stimuli present. Lastly, the activity regarding phenotypic plasticity (after exam 2) taught me about a plants reaction to environmental differences, as well. For example, Toyon leaves became serrated to reduce surface area for light absorbance, while other leaves were not serrated.
The last subject, plant diversity, taught me about the wide variety of plants that exist on earth. The plant collection and the field trip were the most helpful in grasping the realm of plant diversity. The plant collection was an adventure in learning about the wide array of plant species in Tuolumne and Calaveras counties. This project opened my eyes to a newfound hobby. From this project, I can properly identify plants using keys. Furthermore, the Natural Bridges field trip broadened my understanding of the ridiculous amount of plant species that can live in an ecosystem. The field trip not only taught me about plant diversity, but it gave me an understanding of ecology and the importance of balance in an ecosystem. Of all of the activities that were done this semester, my favorite was the collaborative discussions between myself and the classmates. The open floor platform enriched my learning by providing a comfortable environment in which everyone contributed and learned and plant biology concepts.
Plant Biology Summative Essay - Part 2
Knowledge means nothing unless it modifies and improves ones existing thought processes. At the end of each semester, I reflect on how the material has affected my original ideas on the subject and if it has increased my knowledge. This semester is the perfect example of significantly increasing my knowledge and changing the way that I think about plant life. First, my mind has been opened to an array of biological concepts that have taught me about plants in all aspects. These concepts have made me aware of plants and their significance to our lives, thereby decreasing my plant blindness. Additionally, I learned several new skills that have made me more methodical and intrigued by plants. For example, the plant collection taught me about plant diversity and how to identify plants. I intend to continue my plant collection beyond the scope of this course and the project has brought the beauty of plant diversity into my direct view. Secondly, I learned how to test soil and plant tissue for nutrient deficiencies. As a seasonal gardener of many varieties of produce, I will use these skills to determine if the soil is in great condition for plant produce. Prior to learning this skill, I had never taken the opportunity to learn about the deficiencies of soil or how to test for them. Another skill that I learned over the course of them semester was how to prepare a presentation and present it to the class. While I have been in school for three years, I have only had to give one presentation to a class. The student lecture was a useful and exciting experience that gave me the confidence to speak in front of others, while helping them learn about a subject, as well. Moreover, I learned how to manipulate the growth of a plant by changing the environmental variables. For example, during the tomato torture experiment, we learned that the tomato plant thrived in semi-shaded areas. In the future I will use the skills that I learned on setting up a repeatable experiment that examine multiple variables, without getting overly complex. This lab skill will help me throughout my college career. Finally, a skill that I feel is most valuable, communication. The open platform of lecture, combined with a great group of students, made it easy to learn how to communicate ideas to the group without feeling “stupid”. Everybody as a whole allowed others to speak and this ability to communicate openly taught me how to speak up when I have a question or feel that I have th right answer. That is the highlight of the semester.
Looking back on the first day of class and reflecting on what I know now, growth has occurred. During the first few days in class, I was nervous that this would be a hard class(and it was), but as the weeks went by, I found a love for plant biology deep within my mind. The open attitude of the professor and the information that every student brought to class provided the perfect atmosphere for learning. As the semester kept moving, I felt myself developing a respect for the plants that didn’t feed me on a regular basis. As a vegetarian, I have always respected plants, but I never looked at the ones that stabilized the ecosystems that we live in. As my respect grew for the immobile environment around me, I got more interested in the chapters of the text regarding the world of plants. This intrigue taught me about vascular systems, plant responses, ecology, and plant nutrition. Moreover, after each exam, most of which I receive positive scores, I felt a sense of accomplishment for what I had learned about plants. As I am sitting here writing this paper, I can happily tell others that plant biology is a course that should be required for all college students because it provides an awareness that otherwise goes unnoticed. This semester opened my eyes to concepts within plant biology that I had yet to understand, namely, plant physiology, diversity and defense responses. The course taught me a variety of laboratory and field skills that will remain with me for years to come and the concepts have encouraged me to learn more about plant biology. The gain of knowledge is evident in the high scores that I receive, which can be seen in my portfolio. If I could improve on anything, it would be in my preparation of abstracts, which I often found myself doing at the last minute.
Ecology - Plant Biomes
In plant biology, a biome refers to communities of organisms, not limited to animals, plants and other organisms that are successful in the same climatic region. There are terrestrial and aquatic biomes, but for now, we will discuss terrestrial biomes.
Terrestrial biomes include:
Each of these biomes have characteristics that differentiate it from the others. Click on the links to learn more about these biomes!