bio 1.7 assignment carbon cycle

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High school biology

Course: high school biology   >   unit 9.

• Biogeochemical cycles overview
• The water cycle

The carbon cycle

• The nitrogen cycle
• Biogeochemical cycles review
• Biogeochemical cycles

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Video transcript

• Instructors
• Getting Help
• Orientation

Lab 5: Carbon Cycle Modeling (Introduction)

The goals of this lab are to:

• Simulate the fate of CO 2 added to the atmosphere;
• Interpret what happens when we increase the rate of fossil fuel burning;
• Evaluate how the rate of carbon addition affects the maximum temperature and minimum pH attained under fossil fuel burning;
• Simulate the impact of the different emission scenarios on global temperature;
• Evaluate how permafrost melting amplifies warming under the different emission scenarios.

Please make sure that you read the Introduction to the lab. Skipping it will result in a lot of confusion and a lower score on the assignment.

Introduction

In the lab activity for this module, we will be working with a STELLA model of the global carbon cycle that is attached to the climate model we used in Module 3. This model incorporates the processes of carbon transfer in the terrestrial and oceanic realms discussed in the previous sections; it also includes the history (from 1880 to 2010) of human impacts on the carbon cycle in the form of emissions from burning fossil fuels, burning forests, and disrupting the soil. The model is initially set up to represent the carbon cycle in a steady state just before the industrial revolution, at which point human alterations to the carbon cycle began in earnest. We will use this model to explore different carbon emissions scenarios for the future, to see how the climate and carbon cycle might respond.

Here is what the model looks like, in a very simple, stripped-down form:

In this figure, you can see the initial amounts of carbon in each reservoir in GT and the annual flows of carbon between reservoirs in GT C/yr. A couple of things should be pointed out about this model. In some cases, flows have been combined into things called bi-flows that have arrows on each end; this means that carbon can flow either way. There is a bi-flow connecting the atmosphere and surface ocean that represents the two-way transfer of ocean-atmosphere exchange. There is another bi-flow connecting the surface and deep ocean that represents upwelling and downwelling combined into one.

The real model is quite a bit more complex-looking, as can be seen below:

The complications here arise from the fact that most of the flows are expressed by rather complicated equations. Most of the flows have small red arrows attached to them; these show you what things affect the flow rate. Think of the circle in the middle of the flow pipe as being a valve on a water pipe that controls how much water moves through the pipe. In many cases, the red arrows come from the reservoir that is being drained by the flow; this means that the outflow is dependent on how much is in the reservoir — when you have more in a reservoir, the outflow is often greater, and in essence, the outflow is a percentage of how much is in the reservoir.

Note that the atmosphere reservoir is connected to a converter called pCO 2   atm — this is the concentration of CO 2 in the atmosphere and the units are in parts per million or ppm, the same units that CO 2 concentrations are typically given in. In this model, the initial amount of carbon in the atmosphere gives a pCO 2 value of 280 ppm (and by now, it is just over 400 ppm). The  pCO 2   atm  converter is in turn connected to the same climate model we used in Module 3, where it determines the strength of the greenhouse effect. The climate model calculates the temperature at each moment in time and then passes that information back to the carbon cycle model in the form of a converter called  global temp change , which is the change in global temperature relative to the starting temperature — this is like a temperature anomaly. 

The global temp change converter is then attached to a couple of other converters that attach to the photosynthesis flow and the soil respiration flow. Both of these flows are sensitive to temperature and the temperature combines with something called a temperature sensitivity. You can see something above called the Tsens sr — this is the temperature sensitivity for soil respiration. Both photosynthesis and soil respiration are sensitive to the temperature; they increase with temperature. Global temp change is also connected to the surface temperature of the oceans ( T surf ) via a "ghosted" version of the converter — a dashed line version that helps eliminate so many long connecting arrows running all over the diagram.

The photosynthesis flow has lots of converters associated with it since it is dependent on numerous factors, but the main things are temperature and the atmospheric CO 2 concentration.

The model also includes a whole set of connected converters in the upper right that do all of the calculations related to the carbon chemistry in the oceans; this is where the pH or acidity of the surface ocean is calculated.

At the very top right of the model, there is a converter called Observed Atm CO 2 that contains the observed history of atmospheric CO 2 concentration since 1880. This is in the model so that we can test how good the model is. If our carbon cycle model is good, then it should calculate a pCO 2 that closely matches the observed record.

The model includes the history of carbon emissions from burning fossils fuels shown in the previous section; it also includes a history of land use changes that impact the carbon cycle. These land use changes are broken up into tree burning (that accompanies deforestation) and soil disruption (related to farming); they are then additions to the flow of carbon from the land biota and soil back into the atmosphere. These human alterations to the carbon cycle are shown in the model by clicking on the pink graph icons labeled ffb and land use changes on the right side of the model, as shown below.

As before, the model we will work runs on a browser; here is a link to the model . When you follow the link, you should see a screen like this (note the model has changed but the functions are similar):

You can think of this as the control panel for the model, where you can run it, stop it, make changes, and look at the results in the form of different graphs. You can access the different graphs by clicking on the triangular tab at the lower left of the graph window. The controls here consist of a set of switches you can turn on or off — these will determine which of 3 different emissions scenarios are applied to the model. The three buttons on the right-hand side show what the 3 emissions scenarios look like. The video below explains how to work the switches. There is also a switch that can be used to either include or exclude the carbon emissions to the atmosphere from human-related land-use changes such as deforestation and soil disruption, but we will not mess around with this switch — just leave it in the "on" or up position as it is in the diagram above.

This initial model is set up to run from 1880 to 2100. Later, we will work with a model that runs farther into the future.

This is the interface to the carbon cycle model that we will be working with in this module. If we click on this button here, we would see a view of what the carbon cycle looks like that's implemented in this model. It's a complicated thing, but it's a very realistic carbon cycle model that's going to allow us to explore, in a pretty realistic way, what will happen to atmospheric CO 2 and to other aspects of the carbon cycle as we change the burning of fossil fuels and the human effect on this particular system. This carbon cycle model here is attached to a little climate model, that you can see the edge of it over here, that's the same one that we worked with in Module 3. And so, the carbon cycle model will control the atmospheric CO 2 concentration here, and then that will feed into the climate model here and control the greenhouse effect. And then the temperature, determined by the climate model, will then come back and affect different parts of the carbon cycle model here.

So, let me show you how to work this model. If you run it just the way you first open it, you'll see it calculates the global temperature change over time. So, zero is the temperature at 1880, but this is temperature relative to that time. And then, the temperature rises as we go to the year 2000 and 2100. Now, these switches down in here control different histories or scenarios of fossil fuel burnings. The business-as-usual emission scenario is what we ran first. So, when this switch is on, it uses that business-as-usual scenario, and it looks like this, where the carbon emissions just go up and up and up with no change all the way to 2100.

If we click this off, and leave this switch off, it's going to implement a scenario in which the fossil fuel burning just levels off. So, after the year 2010, it just levels off like this. So, we hold emissions constant, and we can see what happens to the temperature in the rest of the system in that case. If we turn this switch on, like that, it will implement this scenario here. It's a very unrealistic one, where after 2010, we drop quickly down to zero fossil fuel burning for the rest of time. So, this is a really dramatic case, just to see how the system will respond to that change.

Now, you can graph different parts of the system. Here, we can look at the atmospheric CO 2 concentration. Here, we can look at the ocean pH. Here, we can look at where the carbon goes, what fraction of it stays in the atmosphere, what fraction goes into the biosphere, and what fraction goes into the oceans. This shows us the details of the fossil fuel burning history that we applied in that case. This plots both the atmospheric CO 2 concentration and the fossil fuel burning history together, so you can see how they compare. This shows the values of carbon and all the different reservoirs in the carbon cycle model. This is the cumulative amount of carbon that we've released over time, so it just gets bigger and bigger and bigger. This is not the annual amount, but the cumulative.

Now, this is an interesting one to look at because it goes from 1880 to 2010, so the period of time that we know something about. And it plots in red the actual observed atmospheric CO 2 level and in blue the CO 2 level that the model calculates. And so, you can see that those two are very close throughout this whole time. And so, that means that our carbon cycle model, coupled with the climate model, is giving us a result that matches a historical record. And so, we say we have a good model, and we can essentially trust what it tells us in terms of projections off into the future.

This activity has been extensively reviewed for inclusion in the Climate Literacy and Energy Awareness Network's collection of educational resources. For information the process and the collection, see http://cleanet.org/clean/about/selected_by_CLEAN .

Carbon on the Move!

Introduction.

After completing this Lab, you should be able to:

• Describe how the primary carbon cycle processes of photosynthesis, respiration, decomposition, ingestion and combustion transport and transform carbon compounds as they move throughout Earth's Geosphere and Biosphere.
• Identify the four major carbon reservoirs and explain how carbon can move from one reservoir to another.
• Provide examples of the various time scales at which carbon moves through Earth's Geosphere and Biosphere.
• Describe the effects of negative and positive feedbacks on the carbon cycle system.

Keeping Track of What You Learn

• Checking In questions are intended to keep you engaged and focused on key concepts and to allow you to periodically check if the material is making sense. These questions are often accompanied by hints or answers to let you know if you are on the right track.
• Stop and Think questions are intended to help your teacher assess your understanding of the key concepts and skills you should be learning from the lab activities and readings.
• Discuss questions are intended to get you talking with your neighbor. These questions require you to pull some concepts together or apply your knowledge in a new situation.

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Effects of Changing the Carbon Cycle

All of this extra carbon needs to go somewhere. So far, land plants and the ocean have taken up about 55 percent of the extra carbon people have put into the atmosphere while about 45 percent has stayed in the atmosphere. Eventually, the land and oceans will take up most of the extra carbon dioxide, but as much as 20 percent may remain in the atmosphere for many thousands of years.

The changes in the carbon cycle impact each reservoir. Excess carbon in the atmosphere warms the planet and helps plants on land grow more. Excess carbon in the ocean makes the water more acidic, putting marine life in danger.

It is significant that so much carbon dioxide stays in the atmosphere because CO 2 is the most important gas for controlling Earth’s temperature. Carbon dioxide, methane, and halocarbons are greenhouse gases that absorb a wide range of energy—including infrared energy (heat) emitted by the Earth—and then re-emit it. The re-emitted energy travels out in all directions, but some returns to Earth, where it heats the surface. Without greenhouse gases, Earth would be a frozen -18 degrees Celsius (0 degrees Fahrenheit). With too many greenhouse gases, Earth would be like Venus, where the greenhouse atmosphere keeps temperatures around 400 degrees Celsius (750 Fahrenheit).

Rising concentrations of carbon dioxide are warming the atmosphere. The increased temperature results in higher evaporation rates and a wetter atmosphere, which leads to a vicious cycle of further warming. ( Photograph ©2011 Patrick Wilken. )

Because scientists know which wavelengths of energy each greenhouse gas absorbs, and the concentration of the gases in the atmosphere, they can calculate how much each gas contributes to warming the planet. Carbon dioxide causes about 20 percent of Earth’s greenhouse effect; water vapor accounts for about 50 percent; and clouds account for 25 percent. The rest is caused by small particles (aerosols) and minor greenhouse gases like methane.

Water vapor concentrations in the air are controlled by Earth’s temperature. Warmer temperatures evaporate more water from the oceans, expand air masses, and lead to higher humidity. Cooling causes water vapor to condense and fall out as rain, sleet, or snow.

Carbon dioxide, on the other hand, remains a gas at a wider range of atmospheric temperatures than water. Carbon dioxide molecules provide the initial greenhouse heating needed to maintain water vapor concentrations. When carbon dioxide concentrations drop, Earth cools, some water vapor falls out of the atmosphere, and the greenhouse warming caused by water vapor drops. Likewise, when carbon dioxide concentrations rise, air temperatures go up, and more water vapor evaporates into the atmosphere—which then amplifies greenhouse heating.

So while carbon dioxide contributes less to the overall greenhouse effect than water vapor, scientists have found that carbon dioxide is the gas that sets the temperature. Carbon dioxide controls the amount of water vapor in the atmosphere and thus the size of the greenhouse effect.

Rising carbon dioxide concentrations are already causing the planet to heat up. At the same time that greenhouse gases have been increasing, average global temperatures have risen 0.8 degrees Celsius (1.4 degrees Fahrenheit) since 1880.

With the seasonal cycle removed, the atmospheric carbon dioxide concentration measured at Mauna Loa Volcano, Hawaii, shows a steady increase since 1957. At the same time global average temperatures are rising as a result of heat trapped by the additional CO 2 and increased water vapor concentration. (Graphs by Robert Simmon, using CO 2 data from the NOAA Earth System Research Laboratory and temperature data from the Goddard Institute for Space Studies. )

This rise in temperature isn’t all the warming we will see based on current carbon dioxide concentrations. Greenhouse warming doesn’t happen right away because the ocean soaks up heat. This means that Earth’s temperature will increase at least another 0.6 degrees Celsius (1 degree Fahrenheit) because of carbon dioxide already in the atmosphere. The degree to which temperatures go up beyond that depends in part on how much more carbon humans release into the atmosphere in the future.

About 30 percent of the carbon dioxide that people have put into the atmosphere has diffused into the ocean through the direct chemical exchange. Dissolving carbon dioxide in the ocean creates carbonic acid, which increases the acidity of the water. Or rather, a slightly alkaline ocean becomes a little less alkaline. Since 1750, the pH of the ocean’s surface has dropped by 0.1, a 30 percent change in acidity.

Some of the excess CO 2 emitted by human activity dissolves in the ocean, becoming carbonic acid. Increases in carbon dioxide are not only leading to warmer oceans, but also to more acidic oceans. ( Photograph ©2010 Way Out West News. )

Ocean acidification affects marine organisms in two ways. First, carbonic acid reacts with carbonate ions in the water to form bicarbonate. However, those same carbonate ions are what shell-building animals like coral need to create calcium carbonate shells. With less carbonate available, the animals need to expend more energy to build their shells. As a result, the shells end up being thinner and more fragile.

Second, the more acidic water is, the better it dissolves calcium carbonate. In the long run, this reaction will allow the ocean to soak up excess carbon dioxide because more acidic water will dissolve more rock, release more carbonate ions, and increase the ocean’s capacity to absorb carbon dioxide. In the meantime, though, more acidic water will dissolve the carbonate shells of marine organisms, making them pitted and weak.

Warmer oceans—a product of the greenhouse effect—could also decrease the abundance of phytoplankton, which grow better in cool, nutrient-rich waters. This could limit the ocean’s ability to take carbon from the atmosphere through the fast carbon cycle.

On the other hand, carbon dioxide is essential for plant and phytoplankton growth. An increase in carbon dioxide could increase growth by fertilizing those few species of phytoplankton and ocean plants (like sea grasses) that take carbon dioxide directly from the water. However, most species are not helped by the increased availability of carbon dioxide.

Plants on land have taken up approximately 25 percent of the carbon dioxide that humans have put into the atmosphere. The amount of carbon that plants take up varies greatly from year to year, but in general, the world’s plants have increased the amount of carbon dioxide they absorb since 1960. Only some of this increase occurred as a direct result of fossil fuel emissions.

With more atmospheric carbon dioxide available to convert to plant matter in photosynthesis, plants were able to grow more. This increased growth is referred to as carbon fertilization. Models predict that plants might grow anywhere from 12 to 76 percent more if atmospheric carbon dioxide is doubled, as long as nothing else, like water shortages, limits their growth. However, scientists don’t know how much carbon dioxide is increasing plant growth in the real world, because plants need more than carbon dioxide to grow.

Plants also need water, sunlight, and nutrients, especially nitrogen. If a plant doesn’t have one of these things, it won’t grow regardless of how abundant the other necessities are. There is a limit to how much carbon plants can take out of the atmosphere, and that limit varies from region to region. So far, it appears that carbon dioxide fertilization increases plant growth until the plant reaches a limit in the amount of water or nitrogen available.

Some of the changes in carbon absorption are the result of land use decisions. Agriculture has become much more intensive, so we can grow more food on less land. In high and mid-latitudes, abandoned farmland is reverting to forest, and these forests store much more carbon, both in wood and soil, than crops would. In many places, we prevent plant carbon from entering the atmosphere by extinguishing wildfires. This allows woody material (which stores carbon) to build up. All of these land use decisions are helping plants absorb human-released carbon in the Northern Hemisphere.

Changes in land cover—forests converted to fields and fields converted to forests—have a corresponding effect on the carbon cycle. In some Northern Hemisphere countries, many farms were abandoned in the early 20th century and the land reverted to forest. As a result, carbon was drawn out of the atmosphere and stored in trees on land. ( Photograph ©2007 Husein Kadribegic. )

In the tropics, however, forests are being removed, often through fire, and this releases carbon dioxide. As of 2008, deforestation accounted for about 12 percent of all human carbon dioxide emissions.

The biggest changes in the land carbon cycle are likely to come because of climate change. Carbon dioxide increases temperatures, extending the growing season and increasing humidity. Both factors have led to some additional plant growth. However, warmer temperatures also stress plants. With a longer, warmer growing season, plants need more water to survive. Scientists are already seeing evidence that plants in the Northern Hemisphere slow their growth in the summer because of warm temperatures and water shortages.

Dry, water-stressed plants are also more susceptible to fire and insects when growing seasons become longer. In the far north, where an increase in temperature has the greatest impact, the forests have already started to burn more, releasing carbon from the plants and the soil into the atmosphere. Tropical forests may also be extremely susceptible to drying. With less water, tropical trees slow their growth and take up less carbon, or die and release their stored carbon to the atmosphere.

The warming caused by rising greenhouse gases may also “bake” the soil, accelerating the rate at which carbon seeps out in some places. This is of particular concern in the far north, where frozen soil—permafrost—is thawing. Permafrost contains rich deposits of carbon from plant matter that has accumulated for thousands of years because the cold slows decay. When the soil warms, the organic matter decays and carbon—in the form of methane and carbon dioxide—seeps into the atmosphere.

Current research estimates that permafrost in the Northern Hemisphere holds 1,672 billion tons (Petagrams) of organic carbon. If just 10 percent of this permafrost were to thaw, it could release enough extra carbon dioxide to the atmosphere to raise temperatures an additional 0.7 degrees Celsius (1.3 degrees Fahrenheit) by 2100.

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1.8: Respiration and Fermentation

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• Page ID 75793

• Brad Basehore, Michelle A. Bucks, & Christine M. Mummert
• Harrisburg Area Community College

Introduction

All organisms must break down organic molecules to release chemical energy to synthesize adenosine triphosphate (ATP). The energy stored in ATP can be released to perform cellular work. Organisms break down organic molecules, such as glucose, through the common processes of cellular respiration and fermentation (Figure 1). Cellular respiration is generally described as an aerobic process, requiring oxygen, which yields the most possible ATP generated from one molecule of glucose. But, technically, cellular respiration can occur in an anaerobic environment in some microorganisms. Anaerobic cellular respiration yields variable amounts of ATP, but much less than is generated in aerobic cellular respiration. In this laboratory, our discussion of cellular respiration will focus on aerobic cellular respiration .

Both aerobic cellular respiration and fermentation involve many chemical reactions that release high energy electrons from organic molecules and transfer the electrons to other molecules, often referred to as electron carriers (or coenzymes). These chemical reactions involving the transfer of electrons are called reduction-oxidation reactions, or redox reactions . In a redox reaction, one of the molecules gains electrons and becomes reduced (rig, r eduction i s g ain of electrons) and one of the molecules loses electrons and becomes oxidized (oil, o xidation i s l oss of electrons). In cellular respiration, electrons are often transferred to the electron carrier nicotinamide adenine dinucleotide (NAD+). When this redox reaction occurs, the organic molecule that loses the electrons has been oxidized. When NAD+ gains the electrons it forms NADH. NADH is the reduced form of NAD.

\[\ce{NAD^{+} + 2e^{-} + H^{+} ->[\text{Redox Reaction}] NADH}\]

Aerobic cellular respiration involves a series of three processes of enzymatic chemical reactions: glycolysis , the citric acid cycle (also known as the Kreb’s cycle), and the electron transport chain . Aerobic cellular respiration begins in the cytoplasm with glycolysis and ends in the mitochondria with the citric acid cycle and the electron transport chain. Aerobic cellular respiration results in fully oxidizing glucose, and can yield a maximum of 32 ATP per glucose molecule. At the culmination of the electron transport chain, the electrons are passed to oxygen, a highly electronegative element, to form water. Therefore, at the end of this process, the high energy electrons that were previously a part of glucose are now at a lower energy state, as they are held very closely by the electronegative oxygen.

Fermentation is an anaerobic process of breaking down organic molecules. It occurs in the absence of oxygen. Fermentation breaks down organic molecules, such as glucose, into smaller organic molecule end products. Fermentation begins with the process of glycolysis to produce pyruvic acid and 2 net ATP. Enzymes then carry out chemical reactions to convert pyruvic acid into various fermentation end products. Two common types of fermentation are named for their end products, alcoholic fermentation and lactic acid fermentation . Fermentation produces organic end products that still contain high-energy electrons. Fermentation does not fully oxidize glucose, and yields only 2 net molecules of ATP, along with organic end products.

PART 1: CELLULAR RESPIRATION

Exercise 1 : Investigating Cellular Respiration in Plants

This part of the lab investigates cellular respiration in pea seeds. Seeds of plants are stuffed full of sugars like starch. Cellular respiration involves breaking down sugars to generate ATP. Therefore, this process allows plants to harvest energy necessary to produce roots, shoots, and leaves. The process of cellular respiration also results in the release of carbon dioxide gas. Carbon dioxide will react with water to form carbonic acid. The formation of carbonic acid will affect the pH of an aqueous solution. Since carbon dioxide is colorless, odorless, and very hard to detect, we are going to use a pH indicator to detect the presence of carbonic acid and thus carbon dioxide. pH indicators, like red cabbage juice, bromothymol blue, and phenol red are chemicals that change color when pH is altered. In this experiment, we will observe cellular respiration in germinating pea seeds by detecting the production of carbon dioxide and monitoring the changes in the pH of the solution.

• Pea seeds (20 germinating/ lab group and 20 dormant / lab group)
• Large sealable bag
• Test tube rack (that can accommodate wide mouth test tubes)
• Wide mouth test tubes with rubber stoppers (3/ lab group)
• Distilled water or spring water (non-chlorinated water)
• Paper towels
• Nonabsorbent cotton plugs
• Glass beads (20 / group)
• Gloves and safety goggles
• Sharpie or red wax pencil
• Indicator reagent [Choose 1: red cabbage juice, or bromothymol blue (0.04% solution), or phenol red (0.04% solution)] (need 15 ml of indicator solution / lab group)

Overall Timeline:

Employing Steps in the Scientific Method:

• Record the Question that is being investigated in this experiment. ________________________________________________________________
• Record a Hypothesis for the question stated above. ________________________________________________________________
• Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
• Perform the experiment below and collect your data.
• Two days before beginning the experiment, pour half of the peas into a glass container and cover with several inches of non-chlorinated water to compensate for the expansion of the seeds as they swell. Allow the seeds to soak overnight.
• The next day, pour the water off of the seeds. Place the seeds onto a wet paper towel, place in a plastic sealable bag, seal the bag, and store the seeds overnight in the dark.
• On the day of the experiment carefully remove the rehydrated (germinating) seeds from the paper towel.
• Label 3 wide mouth tubes #1 - #3.
• Wear gloves when handling the indicator solution. Place 5 ml of the indicator solution into each test tube.
• Using the glass rod, push a plug of nonabsrobent cotton into each test tube until it sits right above the indicator solution.
• Tube 1: add 20 glass beads
• Tube 2: add 20 germinating peas
• Tube 3: add 20 dry dormant peas
• Tightly cap the tubes with rubber stoppers. ( If the rubber stoppers have a hole, cover the stoppers with cling wrap, and then place each stopper into a tube.)
• Observe the color of the indicator reagent at the beginning of the experiment and record your results in Table 1.
• Observe the color of the indicator reagent after the 2-hr incubation and record your results in Table 1.
• Observe the color of the indicator reagent after the 24-hr incubation and record your results in Table 1.
• Once the experiment has been completed, carefully pour the indicator reagent into the appropriate location as indicated by your instructor, being sure to collect the glass beads by pouring through a wire mesh filter.
• Rinse and wash the test tubes thoroughly.

Questions for Review

• What is the color of the indicator at at
• Neutral pH?
• What was the purpose of Tube #1 ?
• What specifically was produced as a result of cellular respiration that changed the color of the indicator?
• How is carbon dioxide an indicator that cellular respiration is taking place in these peas?
• Germination is the process by which a dormant seed begins to sprout and grow into a seedling. What are some possible metabolic processes that are required for seed germination?
• During respiration, a seed metabolizes sugars. What is the source of the sugar metabolized by the seed?
• What variables do you think may affect the respiration rate of the seeds?
• The equation for cellular respiration is:

\[\ce{C6H12O6 + 6O2 → 6CO2 + 6H2O + 32 ATP}\]

The energy released from the complete oxidation of glucose under standard conditions is 686 kcal/mol. The energy released from the hydrolysis of ATP to ADP and inorganic phosphate under standard conditions is 7.3 kcal/mol. Using the equation for cellular respiration above, calculate the efficiency of respiration (i.e. the percentage of chemical energy in glucose that is transferred to ATP). *For help with answering this question, refer to Concept 9.4 (Campbell Textbook).

• How might the process of photosynthesis affect pH? Form a hypothesis.

PART 2: AEROBIC RESPIRATION IN YEAST

Optional Activity or Demonstration

This part of the lab investigates aerobic cellular respiration by Saccharomyces cerevisiae , also referred to as “baker’s yeast” and “brewer’s yeast.” Yeast is a unicellular fungus that can convert glucose into carbon dioxide and ATP when oxygen is present. Methylene blue dye can be used as an indicator for aerobic respiration in yeast. Aerobic respiration releases hydrogen ions and electrons that are picked up by the methylene blue dye, gradually turning the dye colorless. This redox reaction can be observed when viewing a wet mount of yeast and methylene blue under the compound light microscope. The mitochondria of yeast cells undergoing aerobic respiration will appear as a clear area surrounded by a ring of light blue cytoplasm. If cellular respiration is not taking place, the mitochondria will absorb the blue dye and will not turn colorless.

• Yeast (not quick rise)
• Distilled water
• Transfer pipette
• Methylene blue dye (in dropper bottle)
• Compound light microscope
• Microscope slide and cover slip
• Electronic balance, spatula, and weigh paper
• Prepare yeast suspension: Add 7 grams yeast to 50 ml warm tap water. Stir to mix. Save the yeast suspension for Part 3.
• Place a drop of yeast suspension on a clean microscope slide with a transfer pipette.
• Add one drop of methylene blue dye and place a cover slip on the microscope slide over the yeast suspension.
• Observe the yeast using the scanning objective lens. Use the coarse adjustment knob to focus on the yeast cells. Switch to the low power objective lens and then to the high power objective lens.
• In the circle below, draw several yeast cells undergoing aerobic respiration and several yeast cells not undergoing aerobic respiration. Label the cytoplasm and nucleus if visible.

PART 3: ALCOHOLIC FERMENTATION IN YEAST

This part of the lab investigates alcoholic fermentation by Saccharomyces cerevisiae , also referred to as “baker’s yeast” and “brewer’s yeast.” Yeast converts pyruvate from glycolysis into acetaldehyde, releasing carbon dioxide gas. Acetaldehyde is then enzymatically converted by the enzyme alcohol dehydrogenase into ethanol (Figure 2). In this lab, we will measure the accumulation of carbon dioxide released in the first enzymatic reaction as an indicator of the progression of fermentation.

Exercise 1: Investigating Different Concentrations of Yeast

• 4 identical saccharometers (glass fermentation hydrometer with either a 10-cm or a 15-cm vertical tube, Figure 3) / lab group
• Wax pencil or Sharpie
• 10% glucose solution
• Transfer pipettes
• Test tube rack
• 4 large (20 ml) test tubes or small Erlenmeyer flasks for larger volumes
• Large plastic tray
• Masking tape or lab tape
• Large weigh boat (4/group)
• Metric ruler
• Electronic balance
• Weigh paper
• Red food coloring (optional)

*Double these amounts if using saccharometers that have a 15-cm vertical tube. See table below

• Prepare yeast suspension: Add 7 grams yeast to 50 ml warm tap water. Stir to mix. Alternatively, you can use the yeast suspension from Part 2. Optional: Add a few drops of red food coloring to the yeast to increase contrast, allowing easier measuring of the height of yeast in saccharometers.
• Label 4 test tubes and 4 saccharometers # 1- 4. Use a transfer pipette to add the appropriate amount of glucose and distilled water listed in Table 2 to the corresponding labeled test tubes.
• Use a transfer pipette to add the appropriate amount of yeast solution listed in Table 1 to the corresponding labeled test tubes. It is important to work carefully and quickly after adding the yeast solution to the glucose and water.
• Carefully pour the contents of the test tubes into the correspondingly labeled saccharometer, ensuring that the solutions are well mixed.
• Carefully tilt the saccharometers to allow any air bubbles that are trapped in the arms of the vertical tube to escape.
• Begin the timer for the experiment and measure the size of any bubbles (in mm) that are trapped in the vertical arms of the saccharometers. Record this measurement as the 0 time point.
• Position the saccharometers on the large plastic tray, positioning them around a plastic weigh boat to catch any fermentation overflow that may occur.
• Carefully tape the saccharometers to the large plastic tray to prevent them from falling and breaking.
• Every 2 minutes measure and record the total amount of bubbles that accumulate in the top of the vertical arm of the saccharometer. Record the mm of carbon dioxide (bubble) measurements in Table 3.
• Continue recording the total amount of carbon dioxide released every 2 minutes for 20 minutes.
• After completing the experiment carefully carry the saccharometers to a sink for washing. Carry only one saccharometer at a time . Spill the yeast mixture into the sink and wash the saccharometer carefully and thoroughly. Return the saccharometer to the plastic tray, laying it down on its side when not in use.

Extension Activity: (Optional)

The results of this experiment can be presented graphically. The presentation of your data in a graph will assist you in interpreting your results. Based on your results, you can complete the final step of scientific investigation, in which you must be able to propose a logical argument that either allows you to support or reject your initial hypothesis.

• Graph your results using the data from Table 3.
• What is the dependent variable? Which axis is used to graph this data? ___________________________________________________________________
• What is your independent variable? Which axis is used to graph this data? ___________________________________________________________________

Exercise 2: Investigating the fermentation of different carbohydrates

• 4 identical saccharometers (glass fermentation hydrometer with either a 10-cm or a 15-cm vertical tube) / lab group
• 1% starch solution
• 10% sucrose solution
• Masking or lab tape
• Large weigh boat
• Prepare yeast suspension: Add 7 grams yeast to 50 ml warm tap water. Stir to mix. Optional: Add a few drops of red food coloring to the yeast to increase contrast, allowing easier measuring of the height of yeast in saccharometers.
• Label 3 test tubes and 3 saccharometers # 1- 3. Use a transfer pipette to add the appropriate amounts of carbohydrates and distilled water listed in Table 4 to the corresponding labeled test tubes.
• Use a transfer pipette to add 6 ml yeast solution to each of the test tubes. It is important to work carefully and quickly after adding the yeast solution to the carbohydrate.
• Every 2 minutes measure and record the total amount of bubbles that accumulate in the top of the vertical arm of the saccharometer. Record the mm of carbon dioxide (bubble) measurements in Table 5.
• Graph your results using the data from Table 5.
• Fermentation involves redox reactions . Explain what happens to electrons during a redox reaction and how this changes a molecule’s potential energy.
• Why did we add the Saccharomyces cerevisiae (baker's yeast) to the fermentation tubes? Specifically, what did the yeast provide to the fermentation mixture?
• What is the purpose of Saccharomyces cerevisiae (“baker’s yeast) in the bread-making process?
• We measured the formation of what end product to determine the fermentation rate? Name the end product that we measured.
• List two specific factors (as they relate to the experiment performed in our lab) that affect the rate of fermentation.

Practical Challenge Questions:

• What other variables could be investigated that might affect the rate of alcoholic fermentation by yeast?

1.1 The Science of Biology

Learning objectives.

By the end of this section, you will be able to do the following:

• Identify the shared characteristics of the natural sciences
• Summarize the steps of the scientific method
• Compare inductive reasoning with deductive reasoning
• Describe the goals of basic science and applied science

What is biology? In simple terms, biology is the study of life. This is a very broad definition because the scope of biology is vast. Biologists may study anything from the microscopic or submicroscopic view of a cell to ecosystems and the whole living planet ( Figure 1.2 ). Listening to the daily news, you will quickly realize how many aspects of biology we discuss every day. For example, recent news topics include Escherichia coli ( Figure 1.3 ) outbreaks in spinach and Salmonella contamination in peanut butter. Other subjects include efforts toward finding a cure for AIDS, Alzheimer’s disease, and cancer. On a global scale, many researchers are committed to finding ways to protect the planet, solve environmental issues, and reduce the effects of climate change. All of these diverse endeavors are related to different facets of the discipline of biology.

The Process of Science

Biology is a science, but what exactly is science? What does the study of biology share with other scientific disciplines? We can define science (from the Latin scientia , meaning “knowledge”) as knowledge that covers general truths or the operation of general laws, especially when acquired and tested by the scientific method. It becomes clear from this definition that applying scientific method plays a major role in science. The scientific method is a method of research with defined steps that include experiments and careful observation.

We will examine scientific method steps in detail later, but one of the most important aspects of this method is the testing of hypotheses by means of repeatable experiments. A hypothesis is a suggested explanation for an event, which one can test. Although using the scientific method is inherent to science, it is inadequate in determining what science is. This is because it is relatively easy to apply the scientific method to disciplines such as physics and chemistry, but when it comes to disciplines like archaeology, psychology, and geology, the scientific method becomes less applicable as repeating experiments becomes more difficult.

These areas of study are still sciences, however. Consider archaeology—even though one cannot perform repeatable experiments, hypotheses may still be supported. For instance, archaeologists can hypothesize that an ancient culture existed based on finding a piece of pottery. They could make further hypotheses about various characteristics of this culture, which could be correct or false through continued support or contradictions from other findings. A hypothesis may become a verified theory. A theory is a tested and confirmed explanation for observations or phenomena. Therefore, we may be better off to define science as fields of study that attempt to comprehend the nature of the universe.

Natural Sciences

What would you expect to see in a museum of natural sciences? Frogs? Plants? Dinosaur skeletons? Exhibits about how the brain functions? A planetarium? Gems and minerals? Maybe all of the above? Science includes such diverse fields as astronomy, biology, computer sciences, geology, logic, physics, chemistry, and mathematics ( Figure 1.4 ). However, scientists consider those fields of science related to the physical world and its phenomena and processes natural sciences . Thus, a museum of natural sciences might contain any of the items listed above.

There is no complete agreement when it comes to defining what the natural sciences include, however. For some experts, the natural sciences are astronomy, biology, chemistry, earth science, and physics. Other scholars choose to divide natural sciences into life sciences , which study living things and include biology, and physical sciences , which study nonliving matter and include astronomy, geology, physics, and chemistry. Some disciplines such as biophysics and biochemistry build on both life and physical sciences and are interdisciplinary. Some refer to natural sciences as “hard science” because they rely on the use of quantitative data. Social sciences that study society and human behavior are more likely to use qualitative assessments to drive investigations and findings.

Not surprisingly, the natural science of biology has many branches or subdisciplines. Cell biologists study cell structure and function, while biologists who study anatomy investigate the structure of an entire organism. Those biologists studying physiology, however, focus on the internal functioning of an organism. Some areas of biology focus on only particular types of living things. For example, botanists explore plants, while zoologists specialize in animals.

Scientific Reasoning

One thing is common to all forms of science: an ultimate goal “to know.” Curiosity and inquiry are the driving forces for the development of science. Scientists seek to understand the world and the way it operates. To do this, they use two methods of logical thinking: inductive reasoning and deductive reasoning.

Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. This type of reasoning is common in descriptive science. A life scientist such as a biologist makes observations and records them. These data can be qualitative or quantitative, and one can supplement the raw data with drawings, pictures, photos, or videos. From many observations, the scientist can infer conclusions (inductions) based on evidence. Inductive reasoning involves formulating generalizations inferred from careful observation and analyzing a large amount of data. Brain studies provide an example. In this type of research, scientists observe many live brains while people are engaged in a specific activity, such as viewing images of food. The scientist then predicts the part of the brain that “lights up” during this activity to be the part controlling the response to the selected stimulus, in this case, images of food. Excess absorption of radioactive sugar derivatives by active areas of the brain causes the various areas to "light up". Scientists use a scanner to observe the resultant increase in radioactivity. Then, researchers can stimulate that part of the brain to see if similar responses result.

Deductive reasoning or deduction is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the opposite direction as compared to inductive reasoning. Deductive reasoning is a form of logical thinking that uses a general principle or law to predict specific results. From those general principles, a scientist can deduce and predict the specific results that would be valid as long as the general principles are valid. Studies in climate change can illustrate this type of reasoning. For example, scientists may predict that if the climate becomes warmer in a particular region, then the distribution of plants and animals should change.

Both types of logical thinking are related to the two main pathways of scientific study: descriptive science and hypothesis-based science. Descriptive (or discovery) science , which is usually inductive, aims to observe, explore, and discover, while hypothesis-based science , which is usually deductive, begins with a specific question or problem and a potential answer or solution that one can test. The boundary between these two forms of study is often blurred, and most scientific endeavors combine both approaches. The fuzzy boundary becomes apparent when thinking about how easily observation can lead to specific questions. For example, a gentleman in the 1940s observed that the burr seeds that stuck to his clothes and his dog’s fur had a tiny hook structure. On closer inspection, he discovered that the burrs’ gripping device was more reliable than a zipper. He eventually experimented to find the best material that acted similarly, and produced the hook-and-loop fastener popularly known today as Velcro. Descriptive science and hypothesis-based science are in continuous dialogue.

The Scientific Method

Biologists study the living world by posing questions about it and seeking science-based responses. Known as scientific method, this approach is common to other sciences as well. The scientific method was used even in ancient times, but England’s Sir Francis Bacon (1561–1626) first documented it ( Figure 1.5 ). He set up inductive methods for scientific inquiry. The scientific method is not used only by biologists; researchers from almost all fields of study can apply it as a logical, rational problem-solving method.

The scientific process typically starts with an observation (often a problem to solve) that leads to a question. Let’s think about a simple problem that starts with an observation and apply the scientific method to solve the problem. One Monday morning, a student arrives at class and quickly discovers that the classroom is too warm. That is an observation that also describes a problem: the classroom is too warm. The student then asks a question: “Why is the classroom so warm?”

Proposing a Hypothesis

Recall that a hypothesis is a suggested explanation that one can test. To solve a problem, one can propose several hypotheses. For example, one hypothesis might be, “The classroom is warm because no one turned on the air conditioning.” However, there could be other responses to the question, and therefore one may propose other hypotheses. A second hypothesis might be, “The classroom is warm because there is a power failure, and so the air conditioning doesn’t work.”

Once one has selected a hypothesis, the student can make a prediction. A prediction is similar to a hypothesis but it typically has the format “If . . . then . . . .” For example, the prediction for the first hypothesis might be, “ If the student turns on the air conditioning, then the classroom will no longer be too warm.”

Testing a Hypothesis

A valid hypothesis must be testable. It should also be falsifiable , meaning that experimental results can disprove it. Importantly, science does not claim to “prove” anything because scientific understandings are always subject to modification with further information. This step—openness to disproving ideas—is what distinguishes sciences from non-sciences. The presence of the supernatural, for instance, is neither testable nor falsifiable. To test a hypothesis, a researcher will conduct one or more experiments designed to eliminate one or more of the hypotheses. Each experiment will have one or more variables and one or more controls. A variable is any part of the experiment that can vary or change during the experiment. The control group contains every feature of the experimental group except it is not given the manipulation that the researcher hypothesizes. Therefore, if the experimental group's results differ from the control group, the difference must be due to the hypothesized manipulation, rather than some outside factor. Look for the variables and controls in the examples that follow. To test the first hypothesis, the student would find out if the air conditioning is on. If the air conditioning is turned on but does not work, there should be another reason, and the student should reject this hypothesis. To test the second hypothesis, the student could check if the lights in the classroom are functional. If so, there is no power failure and the student should reject this hypothesis. The students should test each hypothesis by carrying out appropriate experiments. Be aware that rejecting one hypothesis does not determine whether or not one can accept the other hypotheses. It simply eliminates one hypothesis that is not valid ( Figure 1.6 ). Using the scientific method, the student rejects the hypotheses that are inconsistent with experimental data.

While this “warm classroom” example is based on observational results, other hypotheses and experiments might have clearer controls. For instance, a student might attend class on Monday and realize she had difficulty concentrating on the lecture. One observation to explain this occurrence might be, “When I eat breakfast before class, I am better able to pay attention.” The student could then design an experiment with a control to test this hypothesis.

In hypothesis-based science, researchers predict specific results from a general premise. We call this type of reasoning deductive reasoning: deduction proceeds from the general to the particular. However, the reverse of the process is also possible: sometimes, scientists reach a general conclusion from a number of specific observations. We call this type of reasoning inductive reasoning, and it proceeds from the particular to the general. Researchers often use inductive and deductive reasoning in tandem to advance scientific knowledge ( Figure 1.7 ). In recent years a new approach of testing hypotheses has developed as a result of an exponential growth of data deposited in various databases. Using computer algorithms and statistical analyses of data in databases, a new field of so-called "data research" (also referred to as "in silico" research) provides new methods of data analyses and their interpretation. This will increase the demand for specialists in both biology and computer science, a promising career opportunity.

Visual Connection

In the example below, the scientific method is used to solve an everyday problem. Match the scientific method steps (numbered items) with the process of solving the everyday problem (lettered items). Based on the results of the experiment, is the hypothesis correct? If it is incorrect, propose some alternative hypotheses.

Decide if each of the following is an example of inductive or deductive reasoning.

• All flying birds and insects have wings. Birds and insects flap their wings as they move through the air. Therefore, wings enable flight.
• Insects generally survive mild winters better than harsh ones. Therefore, insect pests will become more problematic if global temperatures increase.
• Chromosomes, the carriers of DNA, are distributed evenly between the daughter cells during cell division. Therefore, each daughter cell will have the same chromosome set as the mother cell.
• Animals as diverse as humans, insects, and wolves all exhibit social behavior. Therefore, social behavior must have an evolutionary advantage.

The scientific method may seem too rigid and structured. It is important to keep in mind that, although scientists often follow this sequence, there is flexibility. Sometimes an experiment leads to conclusions that favor a change in approach. Often, an experiment brings entirely new scientific questions to the puzzle. Many times, science does not operate in a linear fashion. Instead, scientists continually draw inferences and make generalizations, finding patterns as their research proceeds. Scientific reasoning is more complex than the scientific method alone suggests. Notice, too, that we can apply the scientific method to solving problems that aren’t necessarily scientific in nature.

Two Types of Science: Basic Science and Applied Science

The scientific community has been debating for the last few decades about the value of different types of science. Is it valuable to pursue science for the sake of simply gaining knowledge, or does scientific knowledge only have worth if we can apply it to solving a specific problem or to bettering our lives? This question focuses on the differences between two types of science: basic science and applied science.

Basic science or “pure” science seeks to expand knowledge regardless of the short-term application of that knowledge. It is not focused on developing a product or a service of immediate public or commercial value. The immediate goal of basic science is knowledge for knowledge’s sake, although this does not mean that, in the end, it may not result in a practical application.

In contrast, applied science or “technology,” aims to use science to solve real-world problems, making it possible, for example, to improve a crop yield, find a cure for a particular disease, or save animals threatened by a natural disaster ( Figure 1.8 ). In applied science, the problem is usually defined for the researcher.

Some individuals may perceive applied science as “useful” and basic science as “useless.” A question these people might pose to a scientist advocating knowledge acquisition would be, “What for?” However, a careful look at the history of science reveals that basic knowledge has resulted in many remarkable applications of great value. Many scientists think that a basic understanding of science is necessary before researchers develop an application, therefore, applied science relies on the results that researchers generate through basic science. Other scientists think that it is time to move on from basic science in order to find solutions to actual problems. Both approaches are valid. It is true that there are problems that demand immediate attention; however, scientists would find few solutions without the help of the wide knowledge foundation that basic science generates.

One example of how basic and applied science can work together to solve practical problems occurred after the discovery of DNA structure led to an understanding of the molecular mechanisms governing DNA replication. DNA strands, unique in every human, are in our cells, where they provide the instructions necessary for life. When DNA replicates, it produces new copies of itself, shortly before a cell divides. Understanding DNA replication mechanisms enabled scientists to develop laboratory techniques that researchers now use to identify genetic diseases, pinpoint individuals who were at a crime scene, and determine paternity. Without basic science, it is unlikely that applied science could exist.

Another example of the link between basic and applied research is the Human Genome Project, a study in which researchers analyzed and mapped each human chromosome to determine the precise sequence of DNA subunits and each gene's exact location. (The gene is the basic unit of heredity represented by a specific DNA segment that codes for a functional molecule. An individual’s complete collection of genes is their genome.) Researchers have studied other less complex organisms as part of this project in order to gain a better understanding of human chromosomes. The Human Genome Project ( Figure 1.9 ) relied on basic research with simple organisms and, later, with the human genome. An important end goal eventually became using the data for applied research, seeking cures and early diagnoses for genetically related diseases.

While scientists usually carefully plan research efforts in both basic science and applied science, note that some discoveries are made by serendipity , that is, by means of a fortunate accident or a lucky surprise. Scottish biologist Alexander Fleming discovered penicillin when he accidentally left a petri dish of Staphylococcus bacteria open. An unwanted mold grew on the dish, killing the bacteria. Fleming's curiosity to investigate the reason behind the bacterial death, followed by his experiments, led to the discovery of the antibiotic penicillin, which is produced by the fungus Penicillium . Even in the highly organized world of science, luck—when combined with an observant, curious mind—can lead to unexpected breakthroughs.

Reporting Scientific Work

Whether scientific research is basic science or applied science, scientists must share their findings in order for other researchers to expand and build upon their discoveries. Collaboration with other scientists—when planning, conducting, and analyzing results—is important for scientific research. For this reason, important aspects of a scientist’s work are communicating with peers and disseminating results to peers. Scientists can share results by presenting them at a scientific meeting or conference, but this approach can reach only the select few who are present. Instead, most scientists present their results in peer-reviewed manuscripts that are published in scientific journals. Peer-reviewed manuscripts are scientific papers that a scientist’s colleagues or peers review. These colleagues are qualified individuals, often experts in the same research area, who judge whether or not the scientist’s work is suitable for publication. The process of peer review helps to ensure that the research in a scientific paper or grant proposal is original, significant, logical, and thorough. Grant proposals, which are requests for research funding, are also subject to peer review. Scientists publish their work so other scientists can reproduce their experiments under similar or different conditions to expand on the findings.

A scientific paper is very different from creative writing. Although creativity is required to design experiments, there are fixed guidelines when it comes to presenting scientific results. First, scientific writing must be brief, concise, and accurate. A scientific paper needs to be succinct but detailed enough to allow peers to reproduce the experiments.

The scientific paper consists of several specific sections—introduction, materials and methods, results, and discussion. This structure is sometimes called the “IMRaD” format. There are usually acknowledgment and reference sections as well as an abstract (a concise summary) at the beginning of the paper. There might be additional sections depending on the type of paper and the journal where it will be published. For example, some review papers require an outline.

The introduction starts with brief, but broad, background information about what is known in the field. A good introduction also gives the rationale of the work. It justifies the work carried out and also briefly mentions the end of the paper, where the researcher will present the hypothesis or research question driving the research. The introduction refers to the published scientific work of others and therefore requires citations following the style of the journal. Using the work or ideas of others without proper citation is plagiarism .

The materials and methods section includes a complete and accurate description of the substances the researchers use, and the method and techniques they use to gather data. The description should be thorough enough to allow another researcher to repeat the experiment and obtain similar results, but it does not have to be verbose. This section will also include information on how the researchers made measurements and the types of calculations and statistical analyses they used to examine raw data. Although the materials and methods section gives an accurate description of the experiments, it does not discuss them.

Some journals require a results section followed by a discussion section, but it is more common to combine both. If the journal does not allow combining both sections, the results section simply narrates the findings without any further interpretation. The researchers present results with tables or graphs, but they do not present duplicate information. In the discussion section, the researchers will interpret the results, describe how variables may be related, and attempt to explain the observations. It is indispensable to conduct an extensive literature search to put the results in the context of previously published scientific research. Therefore, researchers include proper citations in this section as well.

Finally, the conclusion section summarizes the importance of the experimental findings. While the scientific paper almost certainly answers one or more scientific questions that the researchers stated, any good research should lead to more questions. Therefore, a well-done scientific paper allows the researchers and others to continue and expand on the findings.

Review articles do not follow the IMRAD format because they do not present original scientific findings, or primary literature. Instead, they summarize and comment on findings that were published as primary literature and typically include extensive reference sections.

Scientific Ethics

Scientists must ensure that their efforts do not cause undue damage to humans, animals, or the environment. They also must ensure that their research and communications are free of bias and that they properly balance financial, legal, safety, replicability, and other considerations. All scientists -- and many people in other fields -- have these ethical obligations, but those in the life sciences have a particular obligation because their research may involve people or other living things. Bioethics is thus an important and continually evolving field, in which researchers collaborate with other thinkers and organizations. They work to define guidelines for current practice, and also continually consider new developments and emerging technologies in order to form answers for the years and decades to come.

For example, bioethicists may examine the implications of gene editing technologies, including the ability to create organisms that may displace others in the environment, as well as the ability to “design” human beings. In that effort, ethicists will likely seek to balance the positive outcomes -- such as improved therapies or prevention of certain illnesses -- with negative outcomes.

Unfortunately, the emergence of bioethics as a field came after a number of clearly unethical practices, where biologists did not treat research subjects with dignity and in some cases did them harm. In the 1932 Tuskegee syphilis study, 399 African American men were diagnosed with syphilis but were never informed that they had the disease, leaving them to live with and pass on the illness to others. Doctors even withheld proven medications because the goal of the study was to understand the impact of untreated syphilis on Black men.

While the decisions made in the Tuskegee study are unjustifiable, some decisions are genuinely difficult to make. Bioethicists work to establish moral and dignifying approaches before such decisions come to pass. For example, doctors rely on artificial intelligence and robotics for medical diagnosis and treatment; in the near future, even more responsibility will lie with machines. Who will be responsible for medical decisions? Who will explain to families if a procedure doesn’t go as planned? And, since such treatments will likely be expensive, who will decide who has access to them and who does not? These are all questions bioethicists seek to answer, and are the types of considerations that all scientific researchers take into account when designing and conducting studies.

Bioethics are not simple, and often leave scientists balancing benefits with harm. In this text and course, you will discuss medical discoveries, vaccines, and research that, at their core, have an ethical complexity or, in the view of many, an ethical lapse. In 1951, Henrietta Lacks , a 30-year-old African American woman, was diagnosed with cervical cancer at Johns Hopkins Hospital. Unique characteristics of her illnesses gave her cells the ability to divide continuously, essentially making them “immortal.” Without her knowledge or permission, researchers took samples of her cells and with them created the immortal HeLa cell line. These cells have contributed to major medical discoveries, including the polio vaccine. Many researchers mentioned in subsequent sections of the text relied on HeLa cell research as at least a component of their work related to cancer, AIDS, cell aging, and even very recently in COVID-19 research.

Today, harvesting tissue or organs from a dying patient without consent is not only considered unethical but illegal, regardless of whether such an act could save other patients’ lives. Is it ethical, then, for scientists to continue to use Lacks’s tissues for research, even though they were obtained illegally by today’s standards? Should Lacks be mentioned as a contributor to the research based on her cells, and should she be cited in the several Nobel Prizes that have been awarded through such work? Finally, should medical companies be obligated to pay Lacks’ family (which had financial difficulties) a portion of the billions of dollars in revenue earned through medicines that benefited from HeLa cell research? How would Henrietta Lacks feel about this? Because she was never asked, we will never know.

To avoid such situations, the role of ethics in scientific research is to ask such questions before, during, and after research or practice takes place, as well as to adhere to established professional principles and consider the dignity and safety of all organisms involved or affected by the work.

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• Authors: Mary Ann Clark, Matthew Douglas, Jung Choi
• Publisher/website: OpenStax
• Book title: Biology 2e
• Publication date: Mar 28, 2018
• Location: Houston, Texas
• Book URL: https://openstax.org/books/biology-2e/pages/1-introduction
• Section URL: https://openstax.org/books/biology-2e/pages/1-1-the-science-of-biology

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