This module cites the implications of Biology being a field of Science. Life is explained by characterizing living things. Furthermore, the heterotroph hypothesis is discussed to explain the origin of life on earth. Then, a short discussion on evolution and the diversity of living things on earth is presented.
Introduction to the Living World Biology, The Science of Life Biology is defined as the science of life. This field of study deals with living things, their structure and functions, development, diversity and interactions with each other and the environment they live in. Biology as a Science Science is a systematized body of knowledge based on observations. All facts and truths in science have been acquired through the process of observation. Like any other fields of endeavor, the main objective of science is for man to understand himself and the universe he lives in. However, unlike other disciplines, the authority in science is observation because science relies on observations for proofs and explanations. The definition of Science clearly implies that it is limited in scope, wherein it can only prove or disprove things through observations. Whatever Concepts in Biology by C.C.Divina 2
cannot be proven by observation is not within the realms of science. Science is amoral and it does not make value judgment. It seeks the truth and does not tell men what is right o wrong, moral or immoral. Rather, man decides for himself how to use the facts and discoveries presented to him by Science. In Science, a standard procedure is followed in search of answers to scientific problems. This process is the scientific method. Its preliminary observation triggers a problem. The problem has to be formulated that it is limited and definite. A tentative answer, an intelligent guess, called the hypothesis is then formulated. The hypothesis has to be proven by experimentation and it guides the researcher on what to do during experimentation. In conducting an experiment, there are basic things to consider. There should be a control set-up and experimental set-ups. The control serves as a basis for comparison. There should be replication, to have more accurate data and observation and to show that the results were not just by chance. There should be randomization to prevent bias of results. As much as possible it is ideal to collect data that are quantitative so that they can Concepts in Biology by C.C.Divina 3
be easily subjected to statistical analysis. Data collected should be synthesized and analyzed to come up with the conclusion. The conclusion answers the problem and proves or disproves the hypothesis. The scientific method as a process takes a lot of time that in science there is no quick answers to problems. All inquiries are answered through the scientific method. Biology is a science, therefore; it follows the method of scientific inquiry. Facts and truth in Biology have been acquired through experimentation.it is not the objective of Biology to moralize but to present the facts related to living things so that man can have a broader understanding of himself and the world he lives in. Characteristics of Living Things Biology deals with living things. Life, per se is a phenomenon very difficult to define. To understand life, one has to understand the various characteristics of living thing. These unique sets of characteristics differentiate living things from nonliving things. The first characteristic of living thing is that they are highly organized. They are made up of atoms Concepts in Biology by C.C.Divina 4
that bind to form molecules. Distinct macromolecules in living systems perform specific functions and form structures like organelles and the cell. All living things are made up of cells. These cells group to form tissues, then organs and systems and eventually the organism. This organization is referred to as the hierarchy of levels of organization of living things. The second characteristic of living things is that they maintain a chemical composition different from that of their surroundings. Atoms found in living are likewise found in nonliving things but their arrangement differs. Organic compounds like proteins; carbohydrates, lipids and nucleic acids are exclusive macromolecules of living things. Moreover, living things keep a stable environment and characteristic chemical composition this property is called homeostasis or physiological equilibrium. The third characteristic of living things is that they are capable of taking in energy from the environment and transforming this into another form. For example, green plants absorb and convert light energy into chemical energy in the form of sugar in the presence of water and carbon dioxide. In turn, this sugar can be converted Concepts in Biology by C.C.Divina 5
into other macromolecules and be used as mechanical, electrical and heat energy as needed and utilized by the organism for its survival. Myriad of chemical reactions take place simultaneously in living systems so that life processes could be performed. Metabolism is the sum of all these chemical reactions. The fourth characteristic of living things is that they respond to stimuli. Stimuli are changes in the environment. Although, living things respond differently to stimuli, the ability to respond to each change in both external and internal environment is a basic function of living things. Responses are necessary to maintain homeostasis. The fifth characteristic of living things is that they are capable of reproduction. Species of the same kind are found in succeeding generations. Living things self-perpetuate ascertaining the continuity of species through generations. The sixth characteristic of living things is that they are capable of adapting to the environment. They adapt to survive in the environment they live in. For example, beaks of birds are shaped in ways to suit their feeding habits. Some animals have similar coloration as their habitats as Concepts in Biology by C.C.Divina 6
camouflage so that their enemies and predators cannot easily sight them. The seventh characteristic of living things is that they grow and develop. From zygote, an organism develops changes and grows into a mature individual through several differentiation processes. This may mean increase in size as in growth accompanied by differentiation of body parts. These characteristics are intimately related and each depends to a large extent on the presence of the others. At any given time of its life, an organism is organized maintaining a constant internal environment, transforming energy and adapting to its environment, the organism may or may not be responding to stimuli and reproducing at all times. One can therefore say that living things metabolize and self-perpetuate. Metabolism is the sum of the chemical reactions taking place in the organism. Self-perpetuating activities involve the assurance of continuity of species through generations. Thus, metabolism and self-perpetuation comprise all the functions of living things from steady state control to reproduction, growth and development and adaptation. Concepts in Biology by C.C.Divina 7
Branches of Biology Biology is broad field of science that it has different sub-sciences under it. The major fields of Biology are: Zoology- science that deals with animals Botany science that deals with plants Microbiology science that deals with microorganisms Yet under each of these fields of specialization, there are still other sub-branches of biology based on the concepts and principles they study. The following are some of the major fields of studies and their focus of study Cytology or Cell Biology - cells Histology - tissues Anatomy - internal parts Morphology - external parts and structures of organism Physiology - functions - Taxonomy and Systematics -- diversity of organisms, their classification, identification and naming Genetics - heredity and variation Ecology deals - interrelationship of organisms with each other and their environment Concepts in Biology by C.C.Divina 8
Questions and Tasks 1. Discuss the implications of science being the systematized body of knowledge based on observations. 2. Cite a scientific problem and design a simple experiment to answer the problem considering the necessary conditions of a good experiment. 3. Why do you consider yourself a living thing based on the different characteristics of living things mentioned above? 4. In a diagram, show the different levels of hierarchy of organization of living things. 5. If you were given an unidentified object, how would you prove that it is should be considered a living thing? Life Begins on Earth Many scientists believe that the earth developed form the condensation of hot gases into molten matter during the formation of the solar system. The matter cooled and solidified into rocks. Water accumulated in the rock basins and formed the sea. The soils were formed from the weathering action of heat, cold and chemicals that broke the rocks into smaller particles. Glaciers transported some of them and running water and deposited usually in bodies of quiet waters as sediments, layers of these sediments were compressed by the overlying layers above. Concepts in Biology by C.C.Divina 9
On the other hand, the most acceptable theory of the origin of life on earth is the HETEROTROPH HYPOTHESIS by A. I Oparin. This hypothesis considers that the original atmosphere consisted of a mixtures of the gases ammonia (NH 4 ) methane (CH4) hydrogen and water vapor with much higher temperature and more solar energy than today. In contrasts to the atmosphere today which has 79% nitrogen 20% oxygen and.4% carbon dioxide. With variable amount of water vapor. Water vapor condensed as the earth cooled and the water vapor condensed to fill the rock basin and form the ancient seas. The rain that fell on the land dissolved the mineral form the rocks and carried them to the sea. The electrical discharges from the solar and radiant energy caused the gas molecules to react and form organic substances such as amino acids, glucose, fatty acids, glycerol and nucleotides. These complex molecules together with rain formed an organic soup of the ancient seas. The soup became thicker as new organic compounds such as proteins including enzymes; nucleic acids and ATP were formed. This part of the theory has been proven possible in the laboratory by the work of S. Miller in 1953. Concepts in Biology by C.C.Divina 10
Somehow, the complex organic compounds interacted to form clusters of molecules called coacervates" or probionts. The coacervates consist both of organic and inorganic compounds. Glucose. enzymes and some energy from ATP were available to them and they performed anaerobic respiration. They were capable of reproduction since they have DNA and nucleotides. In effect, the coacervates are the first heterotrophs; the original form of life. As the heterotrophs respired anaerobically, they released carbon dioxide to the seas and atmosphere. These carbon dioxide in the atmosphere screened high-energy radiation that caused molecules to combine. Moreover, the food supply of the primitive life forms became scantier so that mutation in DNA led to the development of new enzymes and chlorophyll. In this manner, the first autotrophs evolved for some of the heterotrophs. These new autotrophic organisms not only provided food for themselves but also for the heterotrophs. Oxygen was released to the seas and the atmosphere and as oxygen accumulated in the atmosphere, the remaining methane reacted with oxygen to form carbon dioxide and water. The remaining ammonia and other compounds reacted with oxygen forming nitrogen carbon Concepts in Biology by C.C.Divina 11
dioxide and water which became part of the lower atmosphere. The presence of dissolved oxygen in the seawater enabled aerobic respiration to develop in aquatic organisms. Aerobic respiration made more energy available for the evolution of larger and more active organisms. Evolution of Organisms Most organisms today have evolved from simple forms that are now extinct and the study of fossils indicate this concept. Fossils are actual indicator remains of prehistoric plants and animals that had been naturally preserve. They provide means for man to understand the pattern of past changes. Fossils are found preserved naturally in ice, in hardened resin of extinct trees called amber, in pool of thick asphalt tar called tar pit and in coal. Fossils maybe imprint casts showing the external features of the organs. They maybe petrified when a slow decay took place and the organic matter was replaced with minerals to make a stone The fossil records show that many species became extinct while others remained unchanged and still others gave rise to our modern species. The major considerations for extinction of species is change in the earth s Concepts in Biology by C.C.Divina 12
surface, climate and destruction by other organisms. Some living organisms still resemble their prehistoric ancestors thus they are called living fossils. Examples of which are the lungfishes, the platypus, and the horseshoe crab and Ginko tree. The main idea in the theory of evolutions is that species descended form other species. This means that all living things share common ancestors in the distant past. Evolution is any change in the gene pool from one generation to the next. Evolution is a two-stage process. The first stage is the random occurrence of inherited genetic variations among individuals These variations have adaptive values that may more or less be useful to to organism as measured by its survival and reproduction. The second stage is natural selection which is the process of interactions between an organism and its environment. As a result of this interaction, some organisms leave more offspring than others with other inherited characteristics. Given enormous amounts of time, evolution leads to the accumulation of changes that differentiate one group of organisms from one another. The result Concepts in Biology by C.C.Divina 13
is that great diversity of living things that now inhabit this planet. Questions and Tasks 1. Why is the Heterotroph Hypothesis an acceptable theory on the origin of life. 2. How are fossils formed? What do they tell us about the past? Diversity of Living Things Organisms in this world maybe numerous and diverse, but some of them share similarities. The science of Taxonomy or Systematics put order among these organisms as this branch of Biology studies the classification, the ordering of organisms into a hierarchy that reflects the essential similarities and differences. Every individual organism is a member of a particular species, which in turn, belongs to a larger group, a genus (genera - plural.) so that when naming both genus and species names are included. This is the system of binomial nomenclature. In writing scientific names, only the first letter of the genus is capitalized and the rest in lower case. If possible they are italized, if not underlined separately. For example, the scientifie name of man is Homo sapiens (Homo Concepts in Biology by C.C.Divina 14
sapiens), rice Oryza sativa and corn Zea mays. Moreover, in the modern system of classification, related genera are grouped into families, related families into orders, related orders into classes, related classes into phyla (phylum singular) or divisions and related phyla or divisions into kingdoms. Each of this level of classification is called a taxon. Criteria such as structural features, details of biochemistry and patterns of reproductions and development are considered in classifying organisms. At present, the Whittaker fivekingdom scheme of classification of organisms is widely accepted. The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia. Kingdom Monera is composed of organisms with prokaryotic cells. Prokaryotic cells are those without nuclear organization. Examples of these are the bacteria and blue-green algae. Bacteria are the oldest and the most abundant group of organisms in the world. They can live in conditions that cannot support other organisms. Thy have been found in the icy wastes of Antarctica, in waters of natural hot springs and in the ocean beds. When conditions are unfavorable, some take forms of hard, resistant spores which Concepts in Biology by C.C.Divina 15
may lie dormant for years until conditions become more favorable for growth Most bacteria are heterotrophs and obtain their energy form the tissue or body fluid of other living organism like the disease-causing bacteria. Others live on dead organic matter serving as decomposer of the biosphere. Although there are some which can produce their own food. Blue green algae are capable of photosynthesis. They grow mostly in fresh water. They are sometimes found as isolated cells, but more often form clusters, threads and chains. Many species are able to incorporate atmospheric nitrogen into organic compounds. They are found in the surface of rice paddies and contributes nitrogen to rice plants. Protista is made up of the protozoans and the algae. These are eukaryotic organisms. The protozoans are unicellular heterotrophs, including the flagellates, amoeba-like organisms, ciliates and sporozans. The algae are autotrophic organisms and are classified the Euglenaphytes ( Euglena and related unicellular and mostly freshwater algae), diatoms, dinoflagellates and related algae, green algae, brown algae, red algae and slime olds. Concepts in Biology by C.C.Divina 16
Fungi are made up of organisms unlike any other. Except for some oncecelled forms, such as the yeast, fungi are basically composed of masses of filamentous hyphae collectively known as mycelia. All fungi are heterotophs. They obtain food by absorbing dissolved organic molecules, typically a fungus secrete digestive enzymes into food source and then absorb the smaller molecules released. Fungi live in soil, water, or in some other medium containing organic substances. Growth is their only form of mobility, except for spores. Together, with bacteria they are the decomposers of the world. Plants are multicellular photosynthetic organisms adapted for life on land. The two plant types are the bryophytes or the non-vascular plants and the tracheophytes or the vascular plants. Bryophytes include mosses, liverworts and hornworts. They do not develop elaborate conducting systems. They are comparatively simple in their structure and relatively small. Tracheophytes are vascular plants which dominant the modern world. They are characterized by their efficient system for the transport of water and sugar. Modern tracheophytes include club mosses, horsetails, fens, gymnosperms, and angiosperms. Concepts in Biology by C.C.Divina 17
Plants are the channels by which simple inorganic substances vital to life enter the biosphere. Carbon is taken from carbon dioxide and incorporated into organic compounds during photosynthesis. Nitrogen and sulfur are taken from the soil in the form of simple inorganic compound incorporated into proteins, vitamins and other essential organic compounds. Animals. Animals are many-celled heterotrophs. They depend directly of indirectly for their nourishment on plants or algae. Their cells do not have walls. Generally they move by means of contractile cells. Reproduction is usually sexual. The more recent the animals are the sponges, coelenterates, flatworms, roundworms annelids, mollusks, arthropods, echinoderms and the chordates. Concepts in Biology by C.C.Divina 18