NOS 18 Scientific Explanations

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1 Scientific Explanations Case Study Key Concepts How do independent and dependent variables differ? How is scientific inquiry used in a real-life scientific investigation? Identify the Main Ideas As you read, organize your notes in two columns. In the left column, write the main idea of each paragraph. In the right column, write details that support each main idea. Review your notes to help you remember the details of the lesson. Key Concept Check 1. Differentiate How do independent and dependent variables differ? Biodiesel from Microalgae For several centuries, fossil fuels have been the main sources of energy for industry and transportation. However, scientists have shown that burning fossil fuels negatively affects the environment. Also, some people are concerned about eventually using up the world s reserves of fossil fuels. During the past few decades, scientists have explored using protists to produce biodiesel. Biodiesel is a fuel made primarily from living organisms. Protists are a group of tiny organisms that usually live in water or moist environments. Some of these protists are plantlike because they make their own food using a process called photosynthesis. Microalgae are plantlike protists. Designing a Controlled Experiment Scientists use scientific inquiry to investigate the use of protists to make biodiesel. They designed controlled experiments to test their hypotheses. The tables in this lesson are examples of how scientists practiced inquiry and the skills you read about in Lesson 1. A controlled experiment is a scientific investigation that tests how one variable affects another variable. A variable is any factor in an experiment that can have more than one value. Controlled experiments have two types of variables. The dependent variable is the factor measured or observed during an experiment. The independent variable is the factor that you want to test. It is changed by the investigator to observe how it affects a dependent variable. Constants are the factors in an experiment that remain the same. A controlled experiment has an experimental group and a control group. The experimental group is used to study how a change in the independent variable changes the dependent variable. The control group contains the same factors as the experimental group, but the independent variable is not c hanged. Without a control, it is difficult to know whether your experimental observations result from the variable you are testing or from another factor. NOS 18 Scientific Explanations

2 Biodiesel The idea of running diesel engines on fuel made from plant or plantlike sources is not entirely new. Rudolph Diesel invented the diesel engine. He used peanut oil to demonstrate how the engine worked. However, once petroleum was introduced as a diesel fuel source, it was preferred over peanut oil because of it was cheaper. Oil-rich food crops such as soybeans can be used to produce biodiesel. However, some people are concerned that crops grown for fuel use will replace crops grown for food. If farmers grow more crops for fuel, then the amount of food available worldwide will be reduced. Because of food shortages in many parts of the world, replacing food crops with fuel crops is not a good solution. Aquatic Species Program In the late 1970s, the U.S. Department of Energy began funding its Aquatic Species Program (ASP) to investigate ways to remove air pollutants. Coal-fueled power plants produce carbon dioxide (CO 2 ), a pollutant, as a by-product. In the beginning, the study examined all aquatic organisms that use CO 2 during photosynthesis their food-making process. These included large plants, commonly known as seaweeds, plants that grow partially underwater, and microalgae. Scientists hoped that these organisms might remove excess CO 2 from the atmosphere. During the studies, however, the project leaders noticed that some microalgae produced large amounts of oil. The program s focus soon shifted to using microalgae to produce oils that could be processed into biodiesel. The scientists observations and prediction are summarized in the table below. When referring to the examples in tables in this lesson, recall that a hypothesis is a tentative explanation that can be tested by scientific investigation. A prediction is a statement of what someone expects to happen next in a sequence of events. Observation and Prediction Scientific investigations often begin when someone observes an event in nature and wonders why or how it occurs. Observation While testing microalgae to discover if they would absorb carbon pollutants, ASP project leaders saw that some species of microalgae had high oil content. Prediction If the right conditions are met, then plants and plantlike organisms can be used as a source of fuel. 2. Name What did Rudolph Diesel use as fuel? 3. Explain Why is there a concern that crops grown for fuel use will replace crops grown for food? Interpreting Tables 4. Relate How do scientific investigations often begin? Scientific Explanations NOS 19

3 5. Define What are microalgae? Interpreting Tables 6. State What was the goal of the screening test? Which Microalgae? Microalgae are microscopic organisms that live in marine (salty) or freshwater environments. Like many plants and plantlike organisms, they use photosynthesis and make sugar. The process requires light energy. Microalgae make more sugar than they can use. They convert excess sugar to oil. Scientists focused on these microalgae because their oil then could be processed into biodiesel. Scientists started by collecting and identify promising microalgae species. The search focused on microalgae in shallow, inland, saltwater ponds. Scientists predicted that these microalgae were more resistant to changes in temperature and salt content in the water. Design an Experiment and Collect Data One way to test a hypothesis is to design an experiment and collect data. The ASP scientists developed a rapid screening test to discover which microalgae species produced the most oil. Interpreting Tables 7. Identify What is the dependent variable in this example? By 1985, a test was in place for identifying microalgae with high oil content. Two years later, 3,000 microalgae species had been collected. Scientists checked these samples for tolerance to acidity, salt levels, and temperature. From the samples, 300 species were selected. Of these 300 species, green algae and diatoms showed the most promise. However, it was obvious that no one strain was going to be perfect for all climates and water types. Hypotheses and Predictions During a long investigation, scientists form many hypotheses and conduct many tests. Hypothesis: Microalgae species in shallow, saltwater ponds are most resistant to variations in temperature and salt content. Prediction: Microalgae species most resistant to variations in temperature and salt content will be the most useful species in producing biodiesel. Hypothesis: Microalgae grown with inadequate amounts of nitrogen alter their growth processes and produce more oil. Independent Variable: amount of nitrogen available Dependent Variable: amount of oil produced Constants: the growing conditions of algae (temperature, water quality, exposure to the Sun, etc.) NOS 20 Scientific Explanations

4 Oil Production in Microalgae Scientists also began researching how microalgae produce oil. Some studies suggested that starving microalgae of nutrients, such as nitrogen, could increase the amount of oil they produced. However, starving the microalgae also caused them to be smaller, resulting in no overall increase in oil production. Outdoor Testing v. Bioreactors By the 1980s, the ASP scientists were growing microalgae in outdoor ponds in New Mexico. However, outdoor conditions were very different from those in the laboratory. The cooler outdoor temperatures resulted in smaller microalgae. Native algae species also invaded the ponds, forcing out the high-oil-producing laboratory microalgae species. The scientists continued to focus on growing microalgae in open ponds. Many scientists still believe that these open ponds are better for producing large quantities of biodiesel from microalgae. But some researchers are now growing microalgae in closed glass containers called bioreactors. Inside these bioreactors, organisms live and grow under controlled conditions. This method avoids many of the problems associated with open ponds. However, bioreactors are more expensive than open ponds. A biofuel company in the western United States has been experimenting with a low-cost bioreactor. A scientist at the company explained that they examined the ASP program and hypothesized that they could use long plastic bags instead of closed glass containers. However, microalgae grown in plastic bags are more expensive to harvest. Why So Many Hypotheses? According to Dr. Richard Sayre, a biofuel researcher, all the ASP research was based on forming hypotheses. He says, It was hypothesis-driven. You just don t go in and say Well, I have a feeling this is the right way to do it. You propose a hypothesis. Then you test it. Dr. Sayre added, Biologists have been trained over and over again to develop research strategies based on hypotheses. It s sort of ingrained into our culture. You don t get research support by saying, I m going to put together a system, and it s going to be wonderful. You have to come up with a question. You propose some strategies for answering the question. What are your objectives? What outcomes do you expect for each objective? 8. Explain Why didn t starving microalgae of nutrients provide an overall benefit? 9. Relate What is a disadvantage of bioreactors? 10. Describe Why is it important for a scientific researcher to develop a good hypothesis? Scientific Explanations NOS 21

5 Interpreting Tables 11. State How did scientists think they could get microalgae to produce more oil? Increasing Oil Yield Scientists from a biofuel company in Washington State thought of another way to increase oil production. Researchers knew microalgae use light energy, water, and carbon dioxide and they make sugar. The microalgae eventually convert sugar into oil. The scientists wondered if they could increase microalgae oil production by distributing light to all microalgae, including those below the surface. Hypothesis and Prediction Scientists hypothesize that they can increase microalgae oil production by distributing light to greater depths. Hypothesis: If the top layer of microalgae blocks light from reaching microalgae beneath them, then they produce less oil because light is not distributed evenly to all the microalgae. Prediction: If light is distributed more evenly, then more microalgae will grow, and more biodiesel will be produced. 12. State Where do microalgae normally grow within a pond? 13. Identify In the experimental group, what variables are controlled in the bioreactor? Bringing Light to Microalgae Normally microalgae grow near the surface of a pond. Any microalgae about 5 cm below the pond s surface will grow less. Why is this? First, water blocks light from reaching deep into the pond. Second, microalgae at the top of a pond block light from reaching microalgae below them. Only the top part of a pond is productive. Experimental Group Researchers decided to assemble a team of engineers to design a light distribution system. Light rods distribute artificial light to microalgae in a bioreactor. The bioreactor controls the environmental conditions that affect how the microalgae grow. These conditions include temperature, nutrient levels, carbon dioxide level, airflow, and light. Data from their experiments showed scientists how their microalgae in well-lit environments grow compared to how microalgae grow in dimmer environments. Using solar data for various parts of the country, the scientists concluded that the light rod would significantly increase microalgae growth and oil production in outdoor ponds. These scientists next plan to use the light-rod growing method in outdoor ponds. NOS 22 Scientific Explanations

6 Field Testing Scientists plan to take light to the microalgae instead of moving microalgae to light. Dr. Jay Burns is chief microalgae scientist at a biofuel company. He said, What we are proposing to do is to take the light from the surface of a pond and distribute it throughout the depth of the pond. Instead of only the top 5 cm being productive, the whole pond becomes productive. Note that research scientists and scientists in the field rely on scientific methods and scientific inquiry to solve real-life problems. When a scientific investigation lasts for several years and involves many scientists, such as this study, many hypotheses can be tested. Some hypotheses are supported, and other hypotheses are not. Regardless of which hypotheses are supported, information is gathered and lessons are learned. Hypotheses are refined and tested many times. This process of scientific inquiry results in a better understanding of the problem and the possible solutions. 14. Summarize What is the benefit of the lightdistribution system? Analysis and Conclusion Scientists tested their hypothesis, collected data, analyzed the data, and drew conclusions. Analyze Results: The experimental results showed that microalgae would produce more oil using a light-rod system than by using just sunlight. Draw a Conclusion: The researchers concluded that the light-rod system greatly increased microalgae oil production. Another Way to Bring Light to Microalgae Light rods are not the only way to bring light to microalgae. Paddlewheels can be used to keep changing the location of the microalgae. Paddlewheels continuously rotate microalgae to the surface so the organisms are exposed to more light. Interpreting Tables 15. Express What did the researchers conclude would increase algae yield? Key Concept Check 16. Explain Describe three ways in which scientific inquiry was used in this case study. Scientific Explanations NOS 23

7 Why Grow Microalgae? Although the focus of this case study is microalgae growth for biodiesel production, growing microalgae has other benefits. Visual Check 17. Analyze What is used as a feedstock for microalgae? Some of the benefits of growing algae are shown in the figure below. Power plants that burn fossil fuels release carbon dioxide into the atmosphere. Evidence indicates that this contributes to global warming. During photosynthesis, microalgae use carbon dioxide and water, release oxygen, and produce sugar, which they convert to oil. Not only do microalgae produce a valuable fuel, they also remove pollutants from and add oxygen to the atmosphere. Cultivating Microalgae Scrubber removes from smokestack gases. The does not pollute the atmosphere, but it is used as a feedstock for microalgae. Sunlight Coal-burning electric power plant O2 O2 Pond with microalgae Microalgae use and water and make carbohydrates (sugars) and release oxygen. NOS 24 Scientific Explanations O2 Biodiesel Microalgae Carbohydrates and lipids extracted from microalgae Harvested microalgae are used to make several different products. Bioethanol Human and livestock food Pharmaceutical and cosmetic additives O2

8 Are microalgae the future? Scientists face many challenges in their quest to produce biodiesel from microalgae. For now, the costs of growing microalgae and extracting their oils are too high to compete with petroleum-based diesel. However, the combined efforts of government-funded programs and commercial biofuel companies might one day make microalgae-based biodiesel an affordable reality in the United States. New Plants One company in Israel has a successful test plant in operation. Plans are underway to build a large-scale industrial facility to convert carbon dioxide gases released from an Israeli coal-powered electrical plant into useful microalgae products. If this technology performs as expected, microalgae cultivation might occur near coal-fueled power plants in other parts of the world, too. Drawing Conclusions Currently, scientists have no final conclusions about using microalgae as a fuel source. As long as petroleum remains relatively inexpensive and available, it probably will remain the preferred source of diesel fuel. However, if petroleum prices increase or availability decreases, new sources of fuel will be needed. Biodiesel made from microalgae might be one of the alternative fuel sources used. 18. Assess What is preventing algae-based biodiesel from competing with petroleum-based diesel? 19. Predict If the technology is successful, what might happen to algae cultivation? 20. State What might cause a demand for biodiesel made from microalgae? Scientific Explanations NOS 25

9 Mini Glossary constant: a factor in an experiment that remains the same dependent variable: the factor measured or observed during an experiment independent variable: a factor that you want to test and that is changed by the investigator to observe how it affects a dependent variable variable: a ny factor in an experiment that can have more than one value 1. Review the terms and their definitions in the Mini Glossary. Write a sentence that describes the use of variables in controlled experiments. 2. Complete the following flowchart that shows the ASP s initial study of pollution control. a. power plants produce b., which is used by 3. Explain how identifying the main idea of each paragraph helped you understand this lesson. c. ConnectED to make sugar. Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. END OF LESSON NOS 26 Scientific Explanations