Topic 1: Introduction to Botany PDF

PBS 101.23 TOPIC 1: INTRODUCTION TO BOTANY Outline of Topics: a. Definition and Concept of plants b. Scientific method c. Origin and evolution of plants d. Sampung halamang gamot Definition and Concept of Plants Botany as a Science...

PBS 101.23 TOPIC 1: INTRODUCTION TO BOTANY Outline of Topics: a. Definition and Concept of plants b. Scientific method c. Origin and evolution of plants d. Sampung halamang gamot Definition and Concept of Plants Botany as a Science Botany is the scientific study of plants. This definition requires an understanding of the concepts “plants” and “scientific study.” It may surprise you to learn that it is difficult to define precisely what a plant is. Plants have so many types and variations that a simple definition has many exceptions, and a definition that includes all plants and excludes all nonplants may be too complicated to be useful. Also, biologists do not agree about whether certain organisms— particularly algae—are indeed plants. Rather than memorizing a terse definition, more is gained by understanding what plants are, what the exceptional or exotic cases are, and why botanists disagree about certain organisms. Your present concept of plants is probably quite accurate: Most plants have green leaves, stems, roots, and flowers (FIGURE 1-1), but you can think of exceptions immediately. Conifers such as pine, spruce, and fir have cones rather than flowers (FIGURE 1-2), and many cacti and succulents do not appear to have leaves. Both conifers and succulents, however, are obviously plants because they closely resemble organisms that unquestionably are plants. Similarly, ferns and mosses (FIGURES 1-3 and 1-4) are easily recognized as plants. Fungi, such as mushrooms (FIGURE 1-5) and puffballs, were included in the plant kingdom because they are immobile and produce spores, which function somewhat like seeds; however, biologists no longer consider fungi to be plants because recent observations show that fungi differ from plants in many basic biochemical and genetic respects. Algae are more problematical. One group, the green algae (FIGURE 1-6),  is similar to plants in biochemistry and cell structure, but it also has many significant differences. Some botanists conclude that it is more useful to include green algae with plants; others exclude them, pointing out that some green algae have more in common with the seaweeds known as red algae and brown algae (FIGURE 1-7). Arbitrarily declaring that green algae are or are not plants solves nothing; the important thing is to understand the concepts involved and why disagreement exists (TABLE 1-1). All plants have a scientific name. Each name consists of two words: a genus (pronounced GEE nus) name and a specific epithet. For example, the genus Prunus has several species with edible fruits, and they are distinguished by their species epithet: Cherries are Prunus avium, peaches are Prunus persica, and apricots are Prunus armeniaca. The name of cherries is not just “avium,” it is both words: Prunus avium. In the scientific names of plants, the genus name is always capitalized but the species epithet is not (it is not Prunus Avium). Both words are italicized or underlined. Closely related genera are grouped together into families; in botany, family names are always capitalized and always end in “-aceae” (pronounced as if you are spelling the word “ace”: AY see ee). Prunus is in the rose family Rosaceae (pronounced rose AY see ee), alone with roses (Rosa), apples (Malus), strawberries (Fragaria), and many others. A very few families have old, alternative endings, but those are rarely used. For example, the modern name for the mustard family is Brassicaceae (with the “-aceae” ending); the old family name, Cruciferae, is almost never encountered except in older publications. For animals, family names end in “-ae.” We humans are Homo sapiens in the family Hominidae; other members of our family are chimpanzees (Pan), gorillas (Gorilla), and orangutans (Pongo). In terms of etiology, the study of plants, called botany—from three Greek words, botanikos (botanical), botane (plant or herb), and boskein (to feed), and the French word botanique (botanical)— appears to have had its origins with Stone Age peoples who tried to modify their surroundings and feed themselves. Scientific Method The concept of a scientific study can be understood by examining earlier approaches to studying nature. Until the 15th century, several methods for analyzing and explaining the universe and its phenomena were used, with religion and speculative philosophy being especially important. In religious methods, the universe is assumed to either be created by or contain deities. The important feature is that the actions of gods cannot be studied: They are either hidden or capricious, changing from day to day and altering natural phenomena. Agricultural studies would be useless because some years crops might flourish or fail because of weather or disease, but in other years, crop failure might be due to a god’s intervention (a miracle) to reward or punish people. There would be no reason to expect consistent results from experiments. In a religious system, much of the knowledge of the world comes as a revelation from the deity rather than by observation and study of the world. A fundamental principle of all religions is faith: People must believe in the god without physical proof of its existence or actions. Speculative philosophy reached its greatest development with the ancient Greek philosophers. Basically, their method of analyzing the world involved thinking about it logically. They sought to develop logical explanations for simple observations and then followed the logic as far as possible. An example is the philosophical postulation of atoms by Democritus around 400 bce (before the common era). From the observation that all objects could be cut or broken into two smaller objects, it follows logically that the two pieces can each be subdivided again into two more, and so on. Finally, some size must be reached at which further subdivision is not possible; objects of that size are atoms. But there was no proof, no experiment to determine if that was actually valid. Democritus could have been wrong: For all anyone knew, it might have been possible to continue dividing pieces forever, infinitely. Speculative philosophy did not involve verification; philosophical predictions were made, but no actual experiment or observation was performed to see if they were correct. A speculation is a statement that cannot be proved or disproved (e.g., “If Elvis were still alive, he would still be performing in Las Vegas.”). A problem with this method is that often several alternative conclusions are equally plausible logically; only experimentation reveals which is actually true. Starting before the 1400s, a new method, called the scientific method, slowly began to develop. Several fundamental tenets were established: 1. Source of information. All accepted information can be derived only from carefully documented and controlled observations or experiments. Claims emanating from priests or prophets—or scientists—cannot be accepted automatically; they must be subjected to verification and proof. For example, for hundreds of years, medicine was taught using a text called Materia Medica written by Galen, a Roman physician who lived in the second century ce. (common era = ad). In the early 1500s, Andreas Vesalius began dissecting human corpses and noticed that in many cases Galen had been mistaken. Vesalius promoted the idea that observation of the world itself was more accurate than accepting undocumented claims, even if the claims had been made by an extremely famous, respected person. 2. Phenomena that can be studied. Only tangible phenomena and objects are studied, such as heat, plants, minerals, and weather. We cannot see or feel magnetism or neutrons, but we can construct instruments that detect them reliably. In contrast, we do not see or feel ghosts, and no instrument has ever detected ghosts reliably: If ghosts do exist, they must be intangible and cannot be studied by the scientific method. Anything that cannot be observed cannot be studied.  3. Constancy and universality. Physical forces that control the world are constant through time and are the same everywhere. Water has always been and always will be composed of hydrogen and oxygen; gravity is the same now as it has been in the past. The world itself changes—mountains erode, rivers change course, plants evolve—but the forces remain the same. Experiments done at one time and place should give the same results if they are carefully repeated at a different time and place. Constancy and universality allow us to plan future experiments and predict what the outcome should be: If we do the experiment and do not get the predicted outcome, it must be that our theory was incorrect, not that the fundamental forces of the world have suddenly changed. This prevents people from explaining things as miracles or the intervention of evil spirits. For example, if someone claims that a new drug cures a particular disease, we can check that by testing the same drug against that disease. If it does not work the first person may have (1) made an innocent mistake, (2) tested the drug on people who would have gotten better anyway, or (3) been committing fraud; however, we do not have to worry that the difference in the two experiments is due to the fundamental laws of chemistry and physics having changed or that the first experiment’s outcome was altered by benevolent spirits and the second by evil spirits. 4. Basis. The fundamental basis of the scientific method is skepticism, the principle of never being certain of a conclusion, of always being willing to consider new evidence. No matter how much evidence there is for or against a theory, it does no harm to keep a bit of doubt in our minds and to be willing to consider more evidence. For example, there is a tremendous amount of evidence supporting the theory that all plants are composed of cells, and there is no known evidence against it. All of our research, all of our teaching assumes that plants indeed are composed of cells, but the concept of skepticism requires that if new, contrary evidence is presented, we must be willing to change our minds. As a further example, consider people who have been convicted of crimes and then later—often years later—DNA-based evidence indicates that they are innocent: Skepticism is the willingness to consider new evidence. Scientific studies take many forms, but basically, they begin with a series of observations, followed by a period of experimentation mixed with further observation and analysis. At some point, a hypothesis, or model, is constructed to account for the observations: A hypothesis (unlike a speculation) must make predictions that can be tested. For example, scientists in the Middle Ages observed that plants never occur in dark caves and grow poorly indoors where light is dim. They hypothesized that plants need light to grow. This can be formally stated as a pair of simple alternative hypotheses: (1) Plants need light to grow, and (2) plants do not need light to grow. The experimental testing may involve the comparison of several plants outdoors, some in light and others heavily shaded, or it may involve several plants indoors, some in the normal gloom and others illuminated by a window or a skylight. Such experiments give results consistent with hypothesis 1; hypothesis 2 would be rejected. A hypothesis must be tested in various ways. It must be consistent with further observations and experiments, and it must be able to predict the results of future experiments: One of the greatest values of a hypothesis or theory is its power as a predictive model. If its predictions are accurate, they support the hypothesis; if its predictions are inaccurate, they prove that the hypothesis is incorrect. In this case, the hypothesis predicts that environments with little or no light will have few or no plants. Observations are consistent with these predictions. In a heavy forest, shade is dense at ground level, and few plants grow there (FIGURE 1-8). Similarly, as light penetrates the ocean, it is absorbed by water until at great depth all light has been absorbed; no plants or algae grow below that depth. If a hypothesis continues to match observations, we have greater confidence that it is correct, and it may come to be called a theory. Occasionally, a hypothesis does not match an observation; that may mean either that the hypothesis must be altered somewhat or that the entire hypothesis has been wrong. For instance, plants such as Indian pipe or Conopholis (FIGURE 1-9) grow the same with or without light; they do not need light for growth. These are parasitic plants that obtain their energy by drawing nutrients from host plants. Thus, our hypothesis needs only minor modification: All plants except parasitic ones need sunlight for growth. It remains a reasonably accurate predictive model. Note the four principles of the scientific method here. First, the hypothesis is based on observations and can be tested with experiments; we do not accept it simply because some famous scientist declared it to be true. Second, sunlight and plant growth are tangible phenomena that we can either see directly or measure with instruments. Third, if we repeat the experiment anytime or anywhere, we expect to get the same results. Fourth, we interpret the evidence as supporting the hypothesis, but we keep an open mind and are willing to consider new data or a new hypothesis. In former times, if a theory had sufficient support, it was referred to as a “law,” such as the laws of thermodynamics or the law that for every action there is an equal and opposite reaction. Physicists occasionally still do this but biologists never use the term “law.” Even though we have tens of thousands of observations that plants are composed of cells, there is no “law that all plants are composed of cells,” instead we just treat this as a well-supported theory. No biologist expects that there will be a discovery that shows that plants are not actually made up of cells, but we simply do not ever use the term “law.” Many people attempt to discredit the theory of evolution by natural selection by saying that it is merely a theory of evolution, not a law of evolution; these people do not realize that their argument is nonsensical. The concept of intelligent design has recently been proposed to explain many complex phenomena. Its fundamental concept is that many structures and metabolisms are too complicated to have resulted from evolution and natural selection. Instead, they must have been created by some sort of intelligent force or being. This may or may not be true, but this does not help us to analyze and understand the world; instead, it is used as an answer in itself that prevents further study. Photosynthesis is certainly complex, and it may have been designed by some intelligent being; however, believing that does not help us to understand photosynthesis at all, and it does not help us to plan future experiments. In contrast, the scientific method is a means through which we are discovering even the most subtle details of photosynthesis. Origin and Evolution of Plants Life on Earth began about 3.5 billion years ago. At first, living organisms were simple, like present- day bacteria, in both their metabolism and structure; however, over thousands of millions of years cells gradually increased in complexity through evolution by natural selection. The process is easy to understand: As organisms reproduce, their offspring differ slightly from each other in their features—they are not identical. Offspring with features that make them poorly adapted to the habitat probably do not grow well and reproduce poorly if they live long enough to become mature. Other offspring with features that cause them to be well-adapted grow well and reproduce abundantly, passing on the beneficial features to their own offspring. This is called natural selection. New features come about periodically by mutations, and natural selection determines which new features are eliminated and which are passed on to future generations. Evolution by natural selection is a model consistent with observations of natural organisms, experiments, and theoretical considerations. As early organisms became more complex, major advances occurred. One was the evolution of the type of photosynthesis that produces oxygen and carbohydrates. This photosynthesis is present in all green plants, but it first arose about 2.8 billion years ago in a bacterium-like organism called a cyanobacterium. Later, cell structure became more efficient as subcellular components evolved. These components, called organelles, each provide a unique structure and chemistry specialized to a specific function. Division of labor and specialization had come about. A particularly significant evolutionary step occurred when DNA, the molecule that stores hereditary information, became located in its own organelle—the cell nucleus. Because this step was so important and occurred with so many other fundamental changes in cell metabolism, we classify all cells as prokaryotes if they do not have nuclei (bacteria, cyanobacteria, and archaeans) or as eukaryotes if they do have nuclei (all plants, animals, fungi, and algae) (Table 1-1). By the time nuclei became established, evolution had produced thousands of species of prokaryotes. The newly evolved eukaryotes also diversified. Some acquired an energy-transforming organelle, the mitochondrion, and some acquired chloroplasts, which carry out photosynthesis and convert the energy in sunlight to the chemical energy of carbohydrates. Those with chloroplasts evolved into algae and plants; those without evolved into protozoans, fungi, and animals (FIGURE 1-13). All organisms are classified into three large groups called domains: domain Bacteria, domain Archaea, and domain Eukarya; within Eukarya are kingdom Plantae, kingdom Animalia, kingdom Myceteae (fungi), and protists (eukaryotes that do not fit easily into the other three eukaryotic kingdoms). Some protists are closely related to Plantae because some green algae became adapted to living on land and gradually evolved into true plants. As a consequence, early plants resembled those green algae, but as more mutations occurred and natural selection eliminated less adaptive ones, plants lost algal characteristics and gained more features suited to surviving on land. Thousands of species arose, but most became extinct, as those that were more fit grew more rapidly, survived longer, and produced more offspring. Species that did not become extinct evolved into more species and so on. The living plants that surround us are the current result of the continuous process of evolution. Not all organisms evolve at the same rate; some early species were actually so well adapted that they competed successfully against newer species. Algae are so well suited to life in oceans, lakes, and streams that they still thrive even though most features present in modern, living algae must be more or less identical to those present in the ancestral algae that lived more than 1 billion years ago. Features that seem relatively unchanged are relictual features (technically known as plesiomorphic features; formerly called primitive features). Like the algae, ferns are well-adapted to certain habitats and have not changed much in 250 million years; they too have many relictual features. Modern conifers are similar to early ones that arose about 320 million years ago. The most recently evolved group consists of the flowering plants, which originated about 100 to 120 million years ago with the evolution of several features: flowers; broad, flat, simple leaves; and wood that conducts water with little friction. The members of the aster family (sunflowers, daisies, and dandelions) (FIGURE 1-14) have many features that evolved recently from features present in ancestral flowering plants. These are derived features (technically known as apomorphic features; formerly called advanced features) (i.e., they have been derived evolutionarily from ancestral features). One recent (highly derived) feature in the asters is a group of chemical compounds that discourage herbivores from eating the plants. The terms “primitive” and “advanced” are avoided in that they imply inferior and superior. Sampung Halamang Gamot Please visit the link https://pitahc.gov.ph/directory-of-herbs/ This document is cited directly from: Names: Bidlack, James E., author. | Jansky, Shelley. Title: Introductory plant biology / James E. Bidlack, University of Central Oklahoma, Shelley H. Jansky, University of Wisconsin - Madison. Other titles: Stern’s introductory plant biology Description: 14th edition. | New York, NY : McGraw-Hill, 2017. | “Stern’s introductory plant biology, 14th edition”—T.p. verso. Identifiers: LCCN 2016044453 | ISBN 9781259682742 (alk. paper) Subjects: LCSH: Botany. Classification: LCC QK47.S836 2017 | DDC 580—dc23 LC record available at https://lccn.loc.gov/2016044453 Names: Mauseth, James D., author. Title: Botany : an introduction to plant biology / James D. Mauseth. Description: Sixth edition. | Burlington, Massachusetts : Jones & Bartlett Learning, Identifiers: LCCN 2016005564 | ISBN 9781284077537 Subjects: LCSH: Botany—Textbooks. Classification: LCC QK47.M38 2016 | DDC 580—dc23 LC record available at http://lccn.loc.gov/2016005564