The workers are trailer, closely related sister ants. Because of their genetic relationship, we can view the members of a colony as a supererogation. The queen serves as the reproductive system, while the workers serve as the digestive and urinary systems, as well as all the other systems that keep the supererogation functioning. What fosters cooperation between the members of the supererogation? The answer is chemicals, pheromones secreted externally that influence the behavior and even the development of the ants. Fire ants, like other ants, produce several different pheromones that send messages when released into the air.
The message could be “food is available” or “be alert for possible danger. ” The queen even releases pheromones that cause workers to attend her. Why does it work, in a biological sense, for these sisters to spend their lives slavishly working away, raising more sterile sisters and defending the colony with little regard for their own safety? It works because the few sexual females that survive their temporary existence on the outside pass the colony Joint genes on to future generations in new and different places. Any social system that allows an organism to pass on its genes is a successful one from an evolutionary point of view.
In this chapter, we will FL rest learn how the scientific understanding of life progresses by making observations and doing experiments. Then we will examine the five scientific theories around which this book is organized. The theory of evolution is examined in particular detail because it is the unifying theory of biology. Queen larvae workers eggs A fire ant colony (Solenoids invoice). Pustules caused by fire ants. 3 Science Helps Us Understand the Natural World Learning Outcomes Divide the scientific method into four steps and discuss each one. (1 . 1) Describe an experimental design that contains a control group. . 2) Biology is the scientific study of life, and therefore it is appropriate for us to first consider what we mean by science. Science is a way of making sense of the natural world around us. Religion, aesthetics, and ethics are all ways that human beings can find order in the natural world. Science, unlike these other ways of knowing is testable. It also leads to improved technology and is responsible for the modern ways in which we travel, communicate, farm, build our houses, and even how we conduct science. 1. 1 Scientists use a preferred method Despite the wide diversity of scientists and what they study (Fig. AAA), the usual four steps of the scientific method are: (1) making observations, (2) formulating a hypothesis, (3) performing experiments and making observations, and (4) coming to a conclusion (Fig. 1. 1 B). Cohesive whole. Chance alone can help a scientist arrive at an idea. The most famous case pertains to the antibiotic penicillin, which was discovered in 1928. While examining a Petri dish of bacteria that had accidentally become contaminated with the mold Penicillin, Alexander Fleming observed an area around the mold that was free of bacteria.
Fleming had long been interested in ending cures for human diseases caused by bacteria, and was very knowledgeable about antibacterial substances. So when he saw the dramatic effect of Penicillin mold on bacteria, he reasoned that the mold might be producing an antibacterial substance. We call such a possible explanation for a natural event a hypothesis. A hypothesis is based on existing knowledge, so it is much more informed than a mere guess. Flemings hypothesis was supported by further observations. Sometimes a hypothesis is not supported, and must be either modified and subjected to additional study, or rejected.
All of a scientist’s past experiences, no matter what they might be, may influence the formation of a hypothesis. But a scientist only considers hypotheses that can be tested by experiments or further observations. Moral and religious beliefs, while very important to our lives, differ between cultures and through time, and are not always testable. Making Observations The scientific method begins with observation. We can observe Witt our noses that dinner is almost ready, observe Witt our fingertips that a surface is smooth and cold, and observe with our ears that a piano needs tuning.
Scientists also extend the ability of their senses by using instruments; for example, the microscope enables them to see objects they could never see with the naked eye. Finally, scientists may expand their understanding even further by taking advantage of the knowledge and experiences of other scientists. For instance, they may look up past studies on the Internet or at the library, or they may write or speak to others who are researching similar topics. Formulating a Hypothesis After making observations and gathering knowledge about a phenomenon, a scientist uses inductive reasoning.
Inductive reasoning occurs whenever a person uses creative thinking to combine isolated facts into a FIGURE 1 . IA Biologists work in a variety of settings. Scientist in an agricultural field Biochemist in a laboratory Ecologist examining an artificial reef 4 CHAPTER 1 Performing Experiments and Making Observations Scientists often perform an experiment, a series of procedures to test a hypothesis. The manner in which a scientist intends to conduct an experiment is called its design. A good experimental design ensures that scientists are testing what they want to test and that their results will be meaningful.
When an experiment is done in a laboratory, all conditions can be kept constant except for an experimental variable, which is deliberately changed. One or more test groups are exposed to the experimental variable, but one other group, called the control group, is not. If, by chance, the control group shows the same results as the test group, the experimenter knows the results are invalid. Scientists often use a model, a representation of an actual object. For example, modeling occurs when scientists use software to decide how human activities will affect climate, or when they use mice instead of humans or, say, testing a new drug.
Ideally, a medicine that is effective in mice should still be tested in humans. And whenever it is impossible to study the actual phenomenon, a model remains a hypothesis in need of testing. Someday, a scientist might devise a way to test it. The results of an experiment or further observations are referred to as the data. Mathematical data are often displayed in the form of a graph or table. Sometimes studies rely on statistical data. Let’s say an investigator wants to know if eating onions can prevent women from getting osteoporosis (weak bones).
The scientist conducts a survey asking women about their intonating habits correlates these data with the condition of their bones. Other scientists critiquing this study would want to know: How many women were surveyed? How old were the women? What were their exercise habits? What criteria were used to determine the condition of their bones? And what is the probability that the data are in error? Even if the data do suggest a correlation, scientists would want to know if there is a specific ingredient in onions that has a direct biochemical or physiological effect on bones.
After all, correlation does not necessarily mean causation. It could be that women who eat onions eat lots of vegetables, and have healthier diets overall than women who do not eat onions. In this way scientists are skeptics who always pressure one another to keep investigating. Observation New observations are made, and previous data are studied. Hypothesis Input from various sources is used to formulate a testable statement. Experiment/Observations The hypothesis is tested by experiment or further observations.
Conclusion The results are analyzed, and the hypothesis is supported or rejected. Scientific Theory Many experiments and observations support a theory. FIGURE 1 . B Flow diagram for the scientific method. Are accepted explanations (concepts) for how the world works. The results of innumerable observations and experiments support a scientific theory. This text is organized around the following five basic theories of biology: Theory Cell Gene Evolution Homeostasis Concept All organisms are composed of cells, and new cells only come from preexisting cells.
All organisms contain coded information that dictates their form, function, and behavior. All organisms have a common ancestor, UT each is adapted to a particular way of life. All organisms have an internal environment that must stay relatively constant within a range protective of life. All organisms are members of populations that interact with each other and with the physical environment within a particular locale. Coming to a Conclusion Scientists must analyze the data in order to reach a conclusion about whether a hypothesis is supported or not.
The data can support a hypothesis, but they do not prove it “true” because a conclusion is always subject to revision. On the other hand, it is possible to prove a hypothesis false. Because science progresses, the conclusion of one experiment can lead to the hypothesis for another experiment as represented by the return arrow in Figure 1. 18. In other words, results that do not support one hypothesis can often help a scientist formulate another hypothesis to be tested. Scientists report their findings in scientific journals so that their methodology and data are available to other scientists.
Experiments and observations must be repeatable-?that is, the reporting scientist and any scientist who repeats the experiment must get the same results, or else the data are suspect. Scientific Theory The ultimate goal of science is to understand the natural world in terms of scientific theories, which Ecosystem We will discuss these theories in detail later in the chapter, but right now let’s turn our attention to an example of a scientific experiment. 1. 1 Check Your Progress You hypothesize that only the queen fire ant produces eggs. What type of data would allow you to come to a conclusion?
What data would prove it false? 5 1. 2 Control groups allow scientists to compare experimental results Now that you are familiar with the common steps in the scientific method, let’s consider an actual tidy that utilizes these steps. Because the use of synthetic nitrogen fertilizer is harmful to the environment (as described in “Organic Farming” on this page), researchers decided to study the yield of winter wheat utilizing a winter wheat/ pigeon pea rotation. The pigeon pea is a legume, a plant that has root nodules where bacteria convert atmospheric nitrogen to a form plants such as winter wheat can use.
The scientists formulated this hypothesis: Hypothesis A winter wheat/pigeon pea rotation will cause winter wheat production to increase as well as or better than the application of synthetic nitrogen fertilizer. This study had a good design because it included test groups and a control group. Having a control group allows researchers to compare the results of the test groups. All environmental conditions for all groups is kept constant, but the test groups are exposed to an experimental variable, the factor being tested.
The use of a control group also ensures that the data from the test groups are due to the experimental variable and not to some unknown outside influence. Test groups should be as large as possible to eliminate the influence of undetected differences in the test subjects. The investigators decided to grow the winter wheat in pots and to have three sets of pots: Control Pots Winter wheat was planted in clay pots of soil that received no fertilization treatment-?that is, no nitrogen fertilizer and no preprinting of pigeon peas.
Test Pots I Winter wheat was grown in clay pots in soil treated with synthetic nitrogen fertilizer. Test Pots II Winter wheat was grown in clay pots following pigeon pea plants grown in the summertime. The pigeon pea plants were then turned over in the soil. Results Figure 1. 2 includes a color-coded bar graph that allows you to see at a glance he comparative amount of wheat obtained from each group of pots. After the first year, winter wheat yield was higher in test pots treated with nitrogen fertilizer than in the control pots.
To the surprise of investigators, test Application IA Organic Farming Besides being health conscious, people who buy organic may also be socially conscious. Organic farming is part of a movement to make agriculture sustainable by using farming methods that protect the health of people and ecosystems and preserve the land so that it can be productive for our generation and all future generations. Modern agricultural methods have been dramatically successful at increasing yield, but at what price?
We now know that modern farming practices lead to topsoil depletion and groundwater contamination. Without topsoil, the nutrient- rich layer that nourishes plants, agriculture is impossible, and yet modern farming practices such as tilling the land and allowing it to lie fallow (bare) allow topsoil to erode and disappear. One solution is to use a legume as a ground cover because it both protects and nourishes the soil (Fig. IA). The researchers who did the study described in Section 1. Used pigeon peas as a way to enrich the soil between winter wheat plantings.
Instead of growing legumes, farmers in recent years are accustomed to making plants bountiful by applying more and more synthetic nitrogen fertilizer. Unfortunately, nitrogen fertilizers pollute wells used for drinking water and also huge bodies of water, such as the Chesapeake Bay, the Gulf of Mexico, and the Great Lakes. Nitrates in the drinking water of infants leads to the “blue-baby’ syndrome and possible death due to lack of oxygen in the blood. In adults, nitrates are implicated in causing digestive tract cancers.
Certainly they can cause an algal bloom, recognized as a green scum on the water’s surface. In response to these problems, organic farmers severely limit the use of nitrogen fertilizers and instead rely on crop rotation, alternately planting a nitrogen-providing legume and a nitrogen-requiring crop such as wheat. Organic farmers also cut way back on the use of herbicides and pesticides, and this may be the primary reason you and others buy organic. The long-term consumption of these chemicals has been associated with such health problems as birth defects, nerve damage, and cancer.
Children may be especially sensitive to health risks posed by pesticides; this is the FIGURE IA chief reason lawns sprayed with pesticides Legume plants have carry warning signs. We should all be nodules. Aware that we too can contribute to an organic lifestyle by limiting the use of synthetic chemicals on our lawns and gardens. In doing so, we improve our health and help preserve the environment for ourselves and future generations. FORM YOU ROPING 1 . The United States exports its current farming technology, with all its long-range problems, to other countries. Should this be continued? 2.
What circumstances might discourage a farmer from growing food organically, and how might these obstacles be overcome? 6 Control pots no treatment Test pots fertilization treatment 20 Control Pots = no treatment 1 5 Wheat Yield (grams/pot) Test Pots = fertilization treatment 10 O year 1 The results year 2 year 3 = pigeon pea/winter wheat rotation Control pots and test pots of the experiment Test pots Pigeon pea/winter wheat rotation FIGURE 1. 2 Design and results of the pigeon pea/winter wheat rotation study. Pots preplanned with pigeon peas did not produce as high a yield as the control pots.
Conclusion The hypothesis was not supported. Wheat yield following the growth of pigeon peas was not as great as that obtained with nitrogen fertilizer treatments. Follow-Up Experiment and Results The researchers decided to continue the experiment, using the same design and the same pots as before, to see whether the buildup of residual soil nitrogen from pigeon peas would eventually increase wheat yield to a greater extent than the use of nitrogen fertilizer. This was their new hypothesis: Hypothesis A sustained pigeon pea/winter wheat rotation will eventually cause an increase in winter wheat production.
They predicted that wheat yield following three years of pigeon pea/winter wheat rotation would surpass wheat yield following nitrogen fertilizer treatment. Analysis of Results After two years, the yield from pots treated with nitrogen fertilizer was less than it had been the first year. Indeed, wheat yield in pots following a summer planting of pigeon peas was the highest of all the treatments. After three years, wheat yield in pots treated with nitrogen fertilizer was greater than in the control pots but not nearly as great as the yield in pots following summer planting of pigeon peas.
Compared to the first year, wheat yield increased almost outdoor in pots having a pigeon pea/winter wheat rotation. Conclusion The hypothesis was supported. At the end of three years, the yield of winter wheat following a pigeon pea/winter wheat rotation was much better than for the other types of test pots. To explain their results, the researchers suggested that the soil was improved by the buildup of the organic matter in the pots as well as by the addition of nitrogen from the pigeon peas. They published their results in a scientific Journal,l where their experimental method and results would be available to the scientific community. 2 Check Your Progress What would your control group and test groups be composed of if you were testing whether a parasite could reduce the size of a fire ant colony? CHAPTER 1 Biology, the study of Life Biddable,J. E. , Raw, S. C. , and Demeans, D. H. 2001. Undulation, nitrogenous activity, and dry weight of chickpea and pigeon pea cultivar using different Praseodymium strains. Journal of Plant Nutrition 24:549-60. 7 FIGURE 1. AAA Levels of biological organization. Biosphere Regions of the Earth’s crust, waters, and atmosphere inhabited by living things Ecosystem A community plus the physical environment
Community Interacting populations in a particular area Population Organisms of the same species in a particular area Organism An individual; complex individuals contain organ systems Organ System Composed of several organs working together Organ Composed of tissues functioning together for a specific task Tissue A group of cells with a common structure and function Cell The structural and functional unit of all living things Molecule Union of two or more atoms of the same or different elements Atom Smallest unit of an element composed of electrons, protons, and neutrons
THE CELL THEORY Organisms Are Composed of Cells Explain the unique place of cells in biological organization. (1. 3) Relate the reproduction of cells and organisms and also their need for materials and energy to the cell theory. (1. 3) From huge menacing sharks to miniscule exotic orchids, life is very diverse. Despite this diversity, biologists have concluded that life can be understood in terms of the five theories that are emphasized in this text. The first theory we will discuss is the cell theory. 1. 3 Cells are the fundamental unit of living things Figure 1.
A illustrates very well why we will first discuss the cell theory which says that cells are the fundamental unit of living things. In a cell, atoms, the smallest portions of an element, combine with themselves or other atoms to form molecules. Although cells are composed of molecules, cells, and not molecules, are alive. Some cells, such as unicellular paramecia, live independently. Other cells, such as those of the alga Volvo, cluster together in microscopic colonies. An elephant is a multicultural organism in which similar cells combine to form a tissue; one common tissue in animals is nerve tissue.
Tissues make up organs, as when various tissues combine to form the brain. Organs work together in organ systems; for example, the brain works with the spinal cord and a network of nerves to form the nervous system. Organ systems are Joined together to form a complete living thing, or organism. Only a microscope can reveal that organisms are composed of cells (Fig. 1. 38). Later in this chapter, we will consider the higher levels of biological organization shown in Figure 1 . AAA. Is more complex. It begins with the pairing of a two cells-?a sperm from one partner and an egg from the other partner.
The union of sperm and egg, followed by many cell divisions, results in an immature stage that grows and develops through various stages to become an adult. Cells Come from Other Cells Cells come only from a previous cell, and organisms come only from other organisms. In other words, cells and organisms reproduce. Every type of living thing can reproduce, or make another organism like itself. Bacteria, protests, and other unicellular organisms simply split in two. In most multicultural organisms, the reproductive process Cells Use Materials and Energy Cells and organisms cannot maintain their