Page 7.5: Preserving Biodiversity
Preserving biodiversity is an extraordinary challenge that must be met by greater understanding of biodiversity itself, changes in human behavior and beliefs, and various preservation strategies.
Change in Biodiversity through Time
The number of species on the planet, or in any geographical area, is the result of an equilibrium of two evolutionary processes that are ongoing: speciation and extinction. When speciation rates begin to outstrip extinction rates, the number of species will increase. Likewise, the reverse is true when extinction rates begin to overtake speciation rates. Throughout the history of life on Earth, as reflected in the fossil record, these two processes have fluctuated to a greater or lesser extent, sometimes leading to dramatic changes in the number of species on the planet as reflected in the fossil record (Figure \(\PageIndex{1}\)).
Figure \(\PageIndex{1}\). Extinction intensity as reflected in the fossil record has fluctuated throughout Earth’s history. Sudden and dramatic losses of biodiversity, called mass extinctions, have occurred five times.Paleontologists have identified five layers in the fossil record that appear to show sudden and dramatic losses in biodiversity. These are called mass extinctions and are characterized by more than half of all species disappearing from the fossil record. There are many lesser, yet still dramatic, extinction events, but the five mass extinctions have attracted the most research into their causes. An argument can be made that the five mass extinctions are only the five most extreme events in a continuous series of large extinction events throughout the fossil record (since 542 million years ago). The most recent extinction in geological time, about 65 million years ago, saw the disappearance of most dinosaurs species (except birds) and many other species. Most scientists now agree the main cause of this extinction was the impact of a large asteroid in the present-day Yucatán Peninsula and the subsequent energy release and global climate changes caused by dust ejected into the atmosphere.
Recent and Current Extinction Rates
Many biologists say that we are currently experience a sixth mass extinction and it mostly has to do with the activities of humans. There are numerous recent extinctions of individual species that are recorded in human writings. Most of these are coincident with the expansion of the European colonies since the 1500s.
One of the earlier and popularly known examples is the dodo bird. The dodo bird lived in the forests of Mauritius, an island in the Indian Ocean. The dodo bird became extinct around 1662. It was hunted for its meat by sailors and was easy prey because the dodo, which did not evolve with humans, would approach people without fear. Introduced pigs, rats, and dogs brought to the island by European ships also killed dodo young and eggs (Figure \(\PageIndex{2}\)).
Figure \(\PageIndex{2}\). The dodo bird was hunted to extinction around 1662. (credit: Ed Uthman, taken in Natural History Museum, London, England)Steller’s sea cow became extinct in 1768; it was related to the manatee and probably once lived along the northwest coast of North America. Steller’s sea cow was discovered by Europeans in 1741, and it was hunted for meat and oil. A total of 27 years elapsed between the sea cow’s first contact with Europeans and extinction of the species. The last Steller’s sea cow was killed in 1768. In another example, the last living passenger pigeon died in a zoo in Cincinnati, Ohio, in 1914. This species had once migrated in the millions but declined in numbers because of overhunting and loss of habitat through the clearing of forests for farmland.
These are only a few of the recorded extinctions in the past 500 years. The International Union for Conservation of Nature (IUCN) keeps a list of extinct and endangered species called the Red List. The list is not complete, but it describes 380 vertebrates that became extinct after 1500 AD, 86 of which were driven extinct by overhunting or overfishing.
Estimates of Present-day Extinction Rates
Estimates of extinction rates are hampered by the fact that most extinctions are probably happening without being observed. The extinction of a bird or mammal is often noticed by humans, especially if it has been hunted or used in some other way. But there are many organisms that are less noticeable to humans (not necessarily of less value) and many that are undescribed.
The background extinction rate is estimated to be about 1 per million species years (E/MSY). One “species year” is one species in existence for one year. One million species years could be one species persisting for one million years, or a million species persisting for one year. If it is the latter, then one extinction per million species years would be one of those million species becoming extinct in that year. For example, if there are 10 million species in existence, then we would expect 10 of those species to become extinct in a year. This is the background rate.
One contemporary extinction-rate estimate uses the extinctions in the written record since the year 1500. For birds alone, this method yields an estimate of 26 E/MSY, almost three times the background rate. However, this value may be underestimated for three reasons. First, many existing species would not have been described until much later in the time period and so their loss would have gone unnoticed. Second, we know the number is higher than the written record suggests because now extinct species are being described from skeletal remains that were never mentioned in written history. And third, some species are probably already extinct even though conservationists are reluctant to name them as such. Taking these factors into account raises the estimated extinction rate to nearer 100 E/MSY. The predicted rate by the end of the century is 1500 E/MSY.
Figure \(\PageIndex{3}\). A typical species-area curve shows the cumulative number of species found as more and more area is sampled. The curve has also been interpreted to show the effect on species numbers of destroying habitat; a reduction in habitat of 90 percent from 100 km 2 to 10 km 2 reduces the number of species supported by about 50 percent.A second approach to estimating present-time extinction rates is to correlate species loss with habitat loss, and it is based on measuring forest-area loss and understanding species–area relationships. The species-area relationship is the rate at which new species are seen when the area surveyed is increased (Figure \(\PageIndex{3}\)). Likewise, if the habitat area is reduced, the number of species seen will also decline. This kind of relationship is also seen in the relationship between an island’s area and the number of species present on the island: as one increases, so does the other, though not in a straight line. Estimates of extinction rates based on habitat loss and species–area relationships have suggested that with about 90 percent of habitat loss an expected 50 percent of species would become extinct. Figure \(\PageIndex{3}\) shows that reducing forest area from 100 km 2 to 10 km 2 , a decline of 90 percent, reduces the number of species by about 50 percent. Species–area estimates have led to estimates of present-day species extinction rates of about 1000 E/MSY and higher.
Conservation of Biodiversity
The threats to biodiversity have been recognized for some time. Today, the main efforts to preserve biodiversity involve legislative approaches to regulate human and corporate behavior, setting aside protected areas, and habitat restoration.
Changing Human Behavior
Legislation has been enacted to protect species throughout the world. The legislation includes international treaties as well as national and state laws. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) treaty came into force in 1975. The treaty, and the national legislation that supports it, provides a legal framework for preventing “listed” species from being transported across nations’ borders, thus protecting them from being caught or killed when the purpose involves international trade. The listed species that are protected by the treaty number some 33,000. The treaty is limited in its reach because it only deals with international movement of organisms or their parts. It is also limited by various countries’ ability or willingness to enforce the treaty and supporting legislation. The illegal trade in organisms and their parts is probably a market in the hundreds of millions of dollars.
Within many countries there are laws that protect endangered species and that regulate hunting and fishing. In the United States, the Endangered Species Act (ESA) was enacted in 1973. When an at-risk species is listed by the Act, the U.S. Fish & Wildlife Service is required by law to develop a management plan to protect the species and bring it back to sustainable numbers. The ESA, and others like it in other countries, is a useful tool, but it suffers because it is often difficult to get a species listed or to get an effective management plan in place once a species is listed.
The Migratory Bird Treaty Act (MBTA) is an agreement between the United States and Canada that was signed into law in 1918 in response to declines in North American bird species caused by hunting. The Act now lists over 800 protected species. It makes it illegal to disturb or kill the protected species or distribute their parts (much of the hunting of birds in the past was for their feathers). Examples of protected species include northern cardinals, the red-tailed hawk, and the American black vulture.
Global warming is expected to be a major driver of biodiversity loss. Many governments are concerned about the effects of anthropogenic global warming, primarily on their economies and food resources. Because greenhouse gas emissions do not respect national boundaries, the effort to curb them is international. The international response to global warming has been mixed. The Kyoto Protocol , an international agreement that came out of the United Nations Framework Convention on Climate Change that committed countries to reducing greenhouse gas emissions by 2012, was ratified by some countries, but spurned by others. Two countries that were especially important in terms of their potential impact that did not ratify the Kyoto protocol were the United States and China. Some goals for reduction in greenhouse gasses were met and exceeded by individual countries, but, worldwide, the effort to limit greenhouse gas production is not succeeding. A renegotiated 2016 treaty, called the Paris Agreement , once again brought nations together to take meaningful action on climate change. But like before, some nations are reluctant to participate. The newly-elected President Trump has indicated that he will withdraw the United States’ support of the agreement.
Conservation in Preserves
Figure \(\PageIndex{4}\). National parks, such as Grand Teton National Park in Wyoming, help conserve biodiversity. (credit: Don DeBold)Establishment of wildlife and ecosystem preserves is one of the key tools in conservation efforts (Figure \(\PageIndex{4}\)). A preserve is an area of land set aside with varying degrees of protection for the organisms that exist within the boundaries of the preserve. In 2003, the IUCN World Parks Congress estimated that 11.5 percent of Earth’s land surface was covered by preserves of various kinds. This area is large but only represents 9 out of 14 recognized major biomes and research has shown that 12 percent of all species live outside preserves.
A biodiversity hotspot is a conservation concept developed by Norman Myers in 1988. Hotspots are geographical areas that contain high numbers of endemic species. The purpose of the concept was to identify important locations on the planet for conservation efforts, a kind of conservation triage. By protecting hotspots, governments are able to protect a larger number of species. The original criteria for a hotspot included the presence of 1500 or more species of endemic plants and 70 percent of the area disturbed by human activity. There are now 34 biodiversity hotspots (Figure \(\PageIndex{5}\)) that contain large numbers of endemic species, which include half of Earth’s endemic plants.
Figure \(\PageIndex{5}\). Conservation International has identified 34 biodiversity hotspots. Although these cover only 2.3 percent of the Earth’s surface, 42 percent of the terrestrial vertebrate species and 50 percent of the world’s plants are endemic to those hotspots.There has been extensive research into optimal preserve designs for maintaining biodiversity. The fundamental principles behind much of the research have come from the seminal theoretical work of Robert H. MacArthur and Edward O. Wilson published in 1967 on island biogeography. 1 This work sought to understand the factors affecting biodiversity on islands. Conservation preserves can be seen as “islands” of habitat within “an ocean” of non-habitat. In general, large preserves are better because they support more species, including species with large home ranges; they have more core area of optimal habitat for individual species; they have more niches to support more species; and they attract more species because they can be found and reached more easily. One large preserve is better than the same area of several smaller preserves because there is more core habitat unaffected by less hospitable ecosystems outside the preserve boundary. For this same reason, preserves in the shape of a square or circle will be better than a preserve with many thin “arms.” If preserves must be smaller, then providing wildlife corridors (narrow strips of protected land) between two preserves is important so that species and their genes can move between them. All of these factors are taken into consideration when planning the nature of a preserve before the land is set aside.
In addition to the physical specifications of a preserve, there are a variety of regulations related to the use of a preserve. These can include anything from timber extraction, mineral extraction, regulated hunting, human habitation, and nondestructive human recreation. Many of the decisions to include these other uses are made based on political pressures rather than conservation considerations. On the other hand, in some cases, wildlife protection policies have been so strict that subsistence-living indigenous populations have been forced from ancestral lands that fell within a preserve. In other cases, even if a preserve is designed to protect wildlife, if the protections are not or cannot be enforced, the preserve status will have little meaning in the face of illegal poaching and timber extraction. This is a widespread problem with preserves in the tropics.
Climate change will create inevitable problems with the location of preserves as the species within them migrate to higher latitudes as the habitat of the preserve becomes less favorable. Planning for the effects of global warming on future preserves, or adding new preserves to accommodate the changes expected from global warming is in progress, but will only be as effective as the accuracy of the predictions of the effects of global warming on future habitats.
Finally, an argument can be made that conservation preserves reinforce the cultural perception that humans are separate from nature, can exist outside of it, and can only operate in ways that do damage to biodiversity. Creating preserves reduces the pressure on human activities outside the preserves to be sustainable and non-damaging to biodiversity. Ultimately, the political, economic, and human demographic pressures will degrade and reduce the size of conservation preserves if the activities outside them are not altered to be less damaging to biodiversity.
Habitat Restoration
Habitat restoration is the process of bringing an area back to its natural state, before it was impacted through destructive human activities. It holds considerable promise as a mechanism for maintaining or restoring biodiversity. Reintroducing wolves, a top predator, to Yellowstone National Park in 1995 led to dramatic changes in the ecosystem that increased biodiversity. The wolves (Figure \(\PageIndex{6}\)) function to suppress elk and coyote populations and provide more abundant resources to the detritivores. Reducing elk populations has allowed revegetation of riparian (the areas along the banks of a stream or river) areas, which has increased the diversity of species in that habitat. Reduction of coyote populations by wolves has increased the prey species previously suppressed by coyotes. In this habitat, the wolf is a keystone species , meaning a species that is instrumental in maintaining diversity within an ecosystem. Removing a keystone species from an ecological community causes a collapse in diversity. The results from the Yellowstone experiment suggest that restoring a keystone species effectively can have the effect of restoring biodiversity in the community. Ecologists have argued for the identification of keystone species where possible and for focusing protection efforts on these species. It makes sense to return the keystone species to the ecosystems where they have been removed.
Figure \(\PageIndex{6}\). This photograph shows the Gibbon wolf pack in Yellowstone National Park, March 1, 2007. Wolves have been identified as a keystone species. (credit: Doug Smith, NPS)Other large-scale restoration experiments underway involve dam removal. In the United States, since the mid-1980s, many aging dams are being considered for removal rather than replacement because of shifting beliefs about the ecological value of free-flowing rivers. The measured benefits of dam removal include restoration of naturally fluctuating water levels (often the purpose of dams is to reduce variation in river flows), which leads to increased fish diversity and improved water quality. In the Pacific Northwest of the United States, dam removal projects are expected to increase populations of salmon, which is considered a keystone species because it transports nutrients to inland ecosystems during its annual spawning migrations. In other regions, such as the Atlantic coast, dam removal has allowed the return of other spawning anadromous fish species (species that are born in fresh water, live most of their lives in salt water, and return to fresh water to spawn). Some of the largest dam removal projects have yet to occur or have happened too recently for the consequences to be measured, such as Elwha Dam on the Olympic Peninsula of Washington State. The large-scale ecological experiments that these removal projects constitute will provide valuable data for other dam projects slated either for removal or construction.
The Role of Zoos and Captive Breeding
Zoos have sought to play a role in conservation efforts both through captive breeding programs and education (Figure \(\PageIndex{7}\)). The transformation of the missions of zoos from collection and exhibition facilities to organizations that are dedicated to conservation is ongoing. In general, it has been recognized that, except in some specific targeted cases, captive breeding programs for endangered species are inefficient and often prone to failure when the species are reintroduced to the wild. Zoo facilities are far too limited to contemplate captive breeding programs for the numbers of species that are now at risk. Education, on the other hand, is a potential positive impact of zoos on conservation efforts, particularly given the global trend to urbanization and the consequent reduction in contacts between people and wildlife. A number of studies have been performed to look at the effectiveness of zoos on people’s attitudes and actions regarding conservation and at present, the results tend to be mixed.
Figure \(\PageIndex{7}\). Zoos and captive breeding programs help preserve many endangered species, such as this golden lion tamarin. (credit: Garrett Ziegler)Suggested Supplemental Reading:
Paterniti. 2017.  National Geographic . October.
This article in National Geographic takes a closer look at whether or not sport hunting benefits wildlife conservation.
Contributors and Attributions
- Preserving Biodiversity by OpenStax is licensed under CC BY 4.0 . Modified from the original by Matthew R. Fisher.


44.2: Comparing Mean and Median
Lesson
Let's compare the mean and median of data sets.
Exercise \(\PageIndex{1}\): Heights of Presidents
Here are two dot plots. The first dot plot shows the heights of the first 22 U.S. presidents. The second dot plot shows the heights of the next 22 presidents.
Based on the two dot plots, decide if you agree or disagree with each of the following statements. Be prepared to explain your reasoning.
- The median height of the first 22 presidents is 178 centimeters.
- The mean height of the first 22 presidents is about 183 centimeters.
- A typical height for a president in the second group is about 182 centimeters.
- U.S. presidents have become taller over time.
- The heights of the first 22 presidents are more alike than the heights of the second 22 presidents.
- The MAD of the second data set is greater than the MAD of the first set.
Exercise \(\PageIndex{2}\): The Tallest and the Smallest in the World
Your teacher will provide the height data for your class. Use the data to complete the following questions.
- Find the mean height of your class in centimeters.
- Find the median height in centimeters. Show your reasoning.
-
Suppose that the world’s tallest adult, who is 251 centimeters tall, joined your class.
-
Discuss the following questions with your group and explain your reasoning.
- How would the mean height of the class change?
- How would the median height change?
- Find the new mean.
- Find the new median.
- Which measure of center—the mean or the median—changed more when this new person joined the class? Explain why the value of one measure changed more than the other.
-
Discuss the following questions with your group and explain your reasoning.
-
The world’s smallest adult is 63 centimeters tall. Suppose that the world’s tallest and smallest adults both joined your class.
-
Discuss the following questions with your group and explain your reasoning.
- How would the mean height of the class change from the original mean?
- How would the median height change from the original median?
- Find the new mean.
- Find the new median.
- How did the measures of center—the mean and the median—change when these two people joined the class? Explain why the values of the mean and median changed the way they did.
-
Discuss the following questions with your group and explain your reasoning.
Exercise \(\PageIndex{3}\): Mean or Median?
- Your teacher will give you six cards. Each has either a dot plot or a histogram. Sort the cards into two piles based on the distributions shown. Be prepared to explain your reasoning.
-
Discuss your sorting decisions with another group. Did you have the same cards in each pile? If so, did you use the same sorting categories? If not, how are your categories different?
Pause here for a class discussion. -
Use the information on the cards to answer the following questions.
- Card A: What is a typical age of the dogs being treated at the animal clinic?
- Card B: What is a typical number of people in the Irish households?
- Card C: What is a typical travel time for the New Zealand students?
- Card D: Would 15 years old be a good description of a typical age of the people who attended the birthday party?
- Card E: Is 15 minutes or 24 minutes a better description of a typical time it takes the students in South Africa to get to school?
- Card F: Would 21.3 years old be a good description of a typical age of the people who went on a field trip to Washington, D.C.?
- How did you decide which measure of center to use for the dot plots on Cards A–C? What about for those on Cards D–F?
Are you ready for more?
Most teachers use the mean to calculate a student’s final grade, based on that student’s scores on tests, quizzes, homework, projects, and other graded assignments.
Diego thinks that the median might be a better way to measure how well a student did in a course. Do you agree with Diego? Explain your reasoning.
Summary
Both the mean and the median are ways of measuring the center of a distribution. They tell us slightly different things, however.
The dot plot shows the weights of 30 cookies. The mean weight is 21 grams (marked with a triangle). The median weight is 20.5 grams (marked with a diamond).
The mean tells us that if the weights of all cookies were distributed so that each one weighed the same, that weight would be 21 grams. We could also think of 21 grams as a balance point for the weights of all of the cookies in the set.
The median tells us that half of the cookies weigh more than 20.5 grams and half weigh less than 20.5 grams. In this case, both the mean and the median could describe a typical cookie weight because they are fairly close to each other and to most of the data points.
Here is a different set of 30 cookies. It has the same mean weight as the first set, but the median weight is 23 grams.
In this case, the median is closer to where most of the data points are clustered and is therefore a better measure of center for this distribution. That is, it is a better description of a typical cookie weight. The mean weight is influenced (in this case, pulled down) by a handful of much smaller cookies, so it is farther away from most data points.
In general, when a distribution is symmetrical or approximately symmetrical, the mean and median values are close. But when a distribution is not roughly symmetrical, the two values tend to be farther apart.
Glossary Entries
Definition: Median
The median is one way to measure the center of a data set. It is the middle number when the data set is listed in order.
For the data set 7, 9, 12, 13, 14, the median is 12.
For the data set 3, 5, 6, 8, 11, 12, there are two numbers in the middle. The median is the average of these two numbers. \(6+8=14\) and \(14\div 2=7\).
Practice
Exercise \(\PageIndex{4}\)
Here is a dot plot that shows the ages of teachers at a school.
Which of these statements is true of the data set shown in the dot plot?
- The mean is less than the median.
- The mean is approximately equal to the median.
- The mean is greater than the median.
- The mean cannot be determined.
Exercise \(\PageIndex{5}\)
Priya asked each of five friends to attempt to throw a ball in a trash can until they succeeded. She recorded the number of unsuccessful attempts made by each friend as: 1, 8, 6, 2, 4. Priya made a mistake: The 8 in the data set should have been 18.
How would changing the 8 to 18 affect the mean and median of the data set?
- The mean would decrease and the median would not change.
- The mean would increase and the median would not change.
- The mean would decrease and the median would increase.
- The mean would increase and the median would increase.
Exercise \(\PageIndex{6}\)
In his history class, Han's homework scores are:
\(100\qquad 100\qquad 100\qquad 100\qquad 95\qquad 100\qquad 90\qquad 100\qquad 0\)
The history teacher uses the mean to calculate the grade for homework. Write an argument for Han to explain why median would be a better measure to use for his homework grades.
Exercise \(\PageIndex{7}\)
The dot plots show how much time, in minutes, students in a class took to complete each of five different tasks. Select all the dot plots of tasks for which the mean time is approximately equal to the median time.
Exercise \(\PageIndex{8}\)
Zookeepers recorded the ages, weights, genders, and heights of the 10 pandas at their zoo. Write two statistical questions that could be answered using these data sets.
(From Unit 8.1.2)
Exercise \(\PageIndex{9}\)
Here is a set of coordinates. Draw and label an appropriate pair of axes and plot the points. \(A=(1,0), B=(0,0.5), C=(4,3.5), D=(1.5, 0.5)\)
(From Unit 7.3.2)


1.17: Vocabulario. El clima y las estaciones
-
- Last updated
- Save as PDF
- Erica Brown, Alejandra Escudero, María Cristina Montoya, & Elizabeth Small
- SUNY Oneonta via OER SUNY
Objetivos
- Recognize the vocabulary of weather
Vocabulario: El clima y las estaciones
Weather expressions in Spanish are different from those in English, particularly in the way they are constructed.
A:
¿Qué tiempo hace hoy? (
What is the weather like today?
)
B:
Hoy hace frío y hace viento. (
Today it is cold and windy.
)
Most weather expressions in Spanish are built with hace , such as:
There are some weather expressions that are different and are not built with hace , such as:
Las estaciones del año ( The seasons of the year )
Text only
Most weather expressions in Spanish are built with hace:
- Hace mucho calor. (It’s hot)
- Hace fresco. (It’s cool)
- Hace frío. (It’s cold)
- Hace sol. (It’s sunny)
- Hace buen tiempo. (The weather is good)
- Hace mal tiempo. (The weather is bad)
- Hace viento. (It’s windy)
There are some weather expressions that are different and are not built with hace, such as:
- Hay niebla. (It’s foggy)
- Nieva / está nevando. (It’s snowing)
- Está despejado. (It’s clear)
- Está nublado. (It’s cloudy)
- Está húmedo. (It’s humid)
- Está soleado. (It’s sunny)
- Hay relámpagos. (There is lightning)
- Truena. (There is thunder)
- Llovizna. (It’s raining)
- Llueve mucho (It’s raining a lot)
- Está lloviendo. (It’s raining)
Las estaciones del año (The seasons of the year)
- El verano (summer)
- El otoño (fall)
- El invierno (winter)
- La primavera (spring)
Contributors and Attributions
- Late autumn in Wenquan<PHONE_NUMBER>4654). Authored by : N509FZ. Provided by : Wikimedia Commons. Located at : https://commons.wikimedia.org/wiki/File:Late_autumn_in_Wenquan_(20161107144654).jpg . License : CC BY-SA: Attribution-ShareAlike
- Snow Invierno Blanco Fru00edo. Authored by : StockSnap. Provided by : Pixabay. Located at : https://pixabay.com/es/photos/snow-invierno-blanco-fr%C3%ADo-clima-2595281/ . License : Other . License Terms : Pixabay License
- Sun. Authored by : gr33n3gg. Provided by : Flickr. Located at : https://www.flickr.com/photos/gr33n3gg/3445868159 . License : CC BY: Attribution
- Archivo:Lopud_10. Authored by : LBM1948. Provided by : Wikipedia. Located at : https://es.m.Wikipedia.org/wiki/Archivo:Lopud_10.jpg . License : CC BY-SA: Attribution-ShareAlike
- Mal Tiempo Tempestad de Trueno. Authored by : maralb56. Provided by : Pixabay. Located at : https://pixabay.com/es/photos/mal-tiempo-tempestad-de-truenos-2773034/ . License : Other . License Terms : Pixabay License
- Costa Turbina De Viento. Authored by : orange31. Provided by : Pixabay. Located at : https://pixabay.com/es/photos/costa-turbina-de-viento-mar-cielo-3970121/ . License : Other . License Terms : Pixabay License
- Llueve. Authored by : Maria del Mar. Provided by : Flickr. Located at : https://www.flickr.com/photos/mariauoc/15696770177 . License : CC BY: Attribution
- Nubes Cielo Naturaleza. Authored by : Konevi. Provided by : Pixabay. Located at : https://pixabay.com/es/photos/nubes-cielo-naturaleza-aire-nube-3788972/ . License : Other . License Terms : Pixabay License
- Rayo Truene. Authored by : WikimediaImages. Provided by : Pixabay. Located at : https://pixabay.com/es/photos/rayo-trueno-tormenta-de-rel%C3%A1mpagos-1056419/ . License : Other . License Terms : Pixabay License
- Thunder & Lightning. Authored by : MasterPhoto-DK. Provided by : Flickr. Located at : https://www.flickr.com/photos/euromagic/2804916709 . License : CC BY: Attribution
- Drizzles of Anticipation. Authored by : Ahmad Bagadood. Provided by : Flickr. Located at : https://www.flickr.com/photos/tawqee3/450361419/ . License : CC BY-SA: Attribution-ShareAlike
- Summer weather can be unpredictable in Alaska. Provided by : US Air Force. Located at : https://www.jber.jb.mil/News/Photos/igphoto/2001074881/ . License : Public Domain: No Known Copyright
- Project 365 #141: 210510 u00a1Hay Niebla!. Authored by : Pete. Provided by : Flickr. Located at : https://www.flickr.com/photos/comedynose/4628335377 . License : Public Domain: No Known Copyright
- Nevando en el Parque. Authored by : George Hodan. Located at : https://www.publicdomainpictures.net/es/view-image.php?image=34650&picture=nevando-en-el-parque . License : CC0: No Rights Reserved
- Sol de Fondo. Authored by : George Hodan. Located at : https://www.publicdomainpictures.net/es/view-image.php?image=190354&picture=sol-de-fondo . License : CC0: No Rights Reserved
- Archivo:Rain in Tena. Authored by : Lion Hirth. Located at : https://es.m.Wikipedia.org/wiki/Archivo:Rain_in_Tena.jpg . License : Public Domain: No Known Copyright
- Vocabulario: El clima. Authored by : SUNY Oneonta with Lumen Learning. Provided by : SUNY Oneonta. License : CC BY: Attribution
- Weather. Authored by : SUNY Oneonta with Lumen Learning. License : CC BY: Attribution


13.9: Challenges with Erections AKA when Penises Misbehave
Sometimes, people have trouble achieving and/or maintaining an erection. In the medical world, this is referred to as erectile dysfunction or ED for short. There can be many explanations for this. It is not always clear if the issue is psychological, physiological or both. In order to diagnose, a medical provider might ask if the problem has been lifelong or recently acquired. Does it happen all of the time or only with a partner? Does it happen with masturbation as well? Answering these questions can help a healthcare provider determine the reason. For example, if it doesn’t happen with masturbation but only with partners, then it is not physiological. It may be related to performance anxiety- when someone feels pressure to perform during sexual activity, and they get so nervous that they are unable to relax enough to let their natural body processes happen. Their brain instead gets fixated on managing the stress the person is experiencing. This can create a negative cycle. The more nervous someone is about performing and getting an erection, the less likely they are to achieve or maintain one.
A healthcare provider may also ask if the person has morning erections. If they have morning erections, even sometimes, that means the body can still achieve an erection on its own. There are some cases where a person is no longer capable of achieving an erection on their own. This could be because of removal of the prostate due to prostate cancer or other health issues. In this case, the medical options are penile pumps, implants or injections. These methods can be discussed with a urologist or primary care doctor.
If the person is able to achieve an erection, but not able to maintain it, then a medication such as Viagra or Cialis can be prescribed. These medications do not create erections, but they help maintain blood flow once an erection has been achieved.
If the issue is clearly psychological and more related to performance anxiety or other stressors, then looking at addressing the anxiety or stress is the key. For some people, working with a sexuality educator, counselor or therapist can help with this. There are a variety of exercises one can do to learn to relax during sexual activity and improve erections (see Metz and McCarthy book Coping with Erectile Dysfunction , for examples). If the person has a willing partner, they can involve their partner in the exercises as well. Sometimes, it is necessary to reassure a partner that the erection challenges are not their fault.
As a sexuality educator, I encourage people who are having erection challenges, to be kind and patient with their penises. Sometimes penises “misbehave” for good reasons. Rather than thinking of themselves as dysfunctional or as having a dysfunction, I encourage them to consider why their penis may not be cooperating with their plan for dependable erections. Sometimes, there are factors such as relationship issues, stress, exhaustion, or insecurity regarding sexual performance, or the influence of past negative experiences and other factors which could be at play.
It is also important to note that a soft penis can enjoy being touched and appreciated as much as an erect one.  This is not true.   Who knows, maybe then an erection will show up.
 If you are not using condoms, then the “stuff it” method could be an option, simply stuffing the soft penis inside the anus or vagina. Sometimes once inside, the penis may become erect, but this method does not work for everyone. One could consider taking intercourse off the menu temporarily, as this relieves the pressure that the person feels to achieve an erection.
If the partner feels that receiving an object in their vagina or anus is an important part of their sexual pleasure, then fingers or toys such as dildos (see Chapter 4 on Pleasure for more info on sex toys) can be used to achieve that.
Most importantly, I recommend that we take the stigma and shame out of erection challenges.


12.4.3: Big Data
selected template will load here
This action is not available.
A new buzzword that has been capturing the attention of businesses lately is big data . The term refers to such massively large data sets that conventional database tools do not have the processing power to analyze them. For example, Walmart must process over one million customer transactions every hour. Storing and analyzing that much data is beyond the power of traditional database-management tools. Understanding the best tools and techniques to manage and analyze these large data sets is a problem that governments and businesses alike are trying to solve.
Sidebar: What Is Metadata?
The term metadata can be understood as “data about data.” For example, when looking at one of the values of Year of Birth in the Students table, the data itself may be “1992″. The metadata about that value would be the field name Year of Birth, the time it was last updated, and the data type (integer). Another example of metadata could be for an MP3 music file, like the one shown in the image below; information such as the length of the song, the artist, the album, the file size, and even the album cover art, are classified as metadata. When a database is being designed, a “data dictionary” is created to hold the metadata, defining the fields and structure of the database.


Skip to main content
2: Foundations of Public/Community Health
-
-
Last updated
-
-
Save as PDF
-
-
-
2.0: Introduction
-
-
-
2.1: Defining Public Health
-
-
-
2.2: Historical Perspectives on Public/Community Health
-
-
-
2.3: The Importance of Public/Community Health
-
The section discusses the interconnected network of the U.S. public health system, highlighting collaboration between diverse organizations to improve health outcomes. It emphasizes the crucial role of public health in addressing population health needs through disease surveillance, emergency preparedness, and policy implementation. Concerns over inadequate funding and advocacy for public health programs are raised.
-
-
2.4: The Core Functions and Essential Services of Public Health
-
The section outlines learning objectives focused on understanding and applying the 10 Essential Public Health Services and their alignment with the three core functions of public health???assessment, policy development, and assurance. It emphasizes the role of these services and functions as a framework to address and reduce systemic and structural barriers contributing to health inequities.
-
-
2.5: Levels of Prevention
-
-
-
2.6: Chapter Summary
-
This page outlines key aspects of public health, emphasizing its role in preventing disease and promoting health through organized efforts. It differentiates public health from population health, highlighting a focus on collective action, policy, and governance. Historical events, like the Industrial Revolution, have shaped public health, underscoring the need for ongoing efforts. Collaboration among various entities is crucial for improving health.
-
-
2.7: Key Terms
-
This page provides definitions for various terms related to health practice and prevention. It covers concepts such as colonialism, community health, and public health systems, with a focus on different levels of prevention???primary, secondary, tertiary, and quaternary. It also discusses issues like public health emergencies and notifiable infectious diseases, explaining how public health efforts aim to support society's well-being through organized efforts and policy changes.
-
-
2.8: Review Questions
-


2.2: Introduction to Data Acquisition in Human Physiology
This week’s activity will teach you the basics of how to use the iWorx hardware and software that will help you acquire data for most of the physiology labs this semester. This activity uses a pulse plethysmograph or a pulse oximeter , sensors that record and measure pulse waves, to quantify the sensation you feel when physically taking a pulse with your two fingers over an artery.
The data acquisition hardware used in 256L is iWorx , and the software that interprets raw iWorx data is called LabScribe .
Turn off and put away phones before starting any experiment.
For the first lab, your research team should create a folder on the desktop of the lab computer to keep your group’s files in.
Sensors should be secured snugly, but not too tight to prevent blood flow or compress underlying tissues. Subjects should sit as quietly and motionless as possible while the device is recording.
Click Record to begin taking data. As soon as you start recording, type the subject’s name in the Mark Box to denote the subject’s data. Click Stop to quit recording data.
Save .iwxdata files to your folder with a descriptive name, so you can find the data later.
For all Biol 256L experiments, students will work in assigned lab groups (your 256L research team). During experiments, each student will record his or her own data by taking turns serving as the experimental subject. To fully participate, students should rotate through the following roles:
- Subject
- Student(s) helping the subject
- Reader of experimental methods
- Computer operator
PART I. Preparing for the iWorx lab
This lab is a basic introduction to how to use iWorx hardware and software, created by iWorx.
To Open Labscribe and begin an experiment, follow this Set-Up sequence each time you begin a Lab Experiment. Make sure each step is completed in order.
- Turn On iWorx Unit Box on Lab Table at the switch at the back of the box. Make sure Green Light is lit and all equipment is attached to the iWorx box.
- Log into the computer using your ISU ID.
- Click the folder icon in the lower left task bar.
- Click “this PC” in the left side task bar.
- Double click the Biol 256L Course Materials P-Drive under Network Locations.
- Double click the “Week 2 Pulse Oximeter” setup file.
- Click OK to the Hardware Found Box, if it appears.
After the experiment file is opened, the below screen will appear ( Figure 1 ) .
You will either use a pulse plethysmograph or pulse oximeter as the sensor for this activity. Both record the arterial pulse in a finger. The data on the Labscribe screen should look like smooth waves, representing the cardiac cycle. If you get a lot of inconsistent, messy waves, the sensor may not be appropriately attached, or the subject may be moving.
PART II. Placing the Pulse Plethysmograph or Pulse Oximeter
- Pick the experimental subject.
- Snugly velcro the plethysmograph with the white, flat side facing the finger pad on the middle finger or thumb. It should be snug!, but should not be so tight to compress arteries and diminish the signal.
- If a pulse oximeter is used , simply clamp the oximeter onto a finger as shown on picture on the sensor.
- Subject should sit away from the table, quietly, with palms up, in his or her lap. The subject (and attached wires) should not be touched or moving.
- Check to make sure personal electronic devices are off and put away.
PART III: Recording Data and Adding Marks
How to make Marks on a Recording for Noting Who the Data Belongs to in the Data File:
Large amounts of data can be recorded with LabScribe software, but, to be useful, the data that is interesting needs to be located and retrieved easily. Most often, data from multiple people (you and your lab team members) will all be recorded in the same file. Specific sections of data can be located or distinguished from other sections by placing marks and comments at those locations in the data file. Marks, with or without text comments attached, can be placed on the data during or after the recording.
To practice adding marks with comments during a recording, follow these instructions:
- Click Record ( Figure 3, above, Large Red Circle.)
- If necessary, adjust the height of the traces on the Pulse and Heart Rate channels by using the AutoScale buttons ( Figure 3 Small Red Circles) to help you see the data better.
- During data recording, an active text cursor appears in the Mark Box ( Figure 3 Blue box ). Type the subject’s name in the Mark Box using the keyboard.
- Press the Enter key on the keyboard to place the mark on the recording. The wording typed in the Mark box will appear in the lower right-hand corner of the data screen and move along with the subject’s data.
- Record for 60 seconds once the pulse wave pattern in the upper window looks like a regular (periodic) wave.
- After collecting normal data for 60 seconds, click on the Stop button to end the recording. Your recording should look similar to the example data screen in Figure 4.
PART IV: Saving your Data
Open the File menu and Select Save As in the File menu, type a name for the file. Choose a destination on the computer to which to save the file, like a lab group folder on the Desktop). Designate the file type as Your Lab section # and your Table # .iwxdata. Click on the Save button to save the data file (Ex. Section4Table2.iwxdata).
To save a file:
- Open the File menu and click “Save As.”
- Enter a descriptive file name.
- Save file to your group’s folder.
- Next, help others serve as the subject.
Go to the Week 2 Lab Report you downloaded or printed from Canvas and follow the instructions for completing your portion of the activity. Once your own data is gathered, another student will be the subject of this activity and others at the table will rotate duties.
Note: you may want to record all the subjects’ pulse data before helping each other do the data analysis on the lab report, but remember to correctly MARK EACH SUBJECT’S DATA , so you can find it later!
PART V. Data Analysis
Note: you may hover over LabScribe software icons to see the function of each button.
- Find a 20 second portion of your Pulse data. To do this click on Double Display Time .
- Click on the Two Cursors mode and move the cursors until you see that you have 20 seconds listed as T2-T1 on the top right tool bar ( Analysis Figure 1, below).
- Next, click on the Zoom Between Cursors icon. Now the segment of pulse waves on your screen is just 20 seconds of your recording on the Main Window (see display time in upper task bar) (Analysis Figure 2, below).
- Click the Analysis icon (magnifying glass over a graph) to switch to the data Analysis screen.
- Next, place the first cursor at the very peak of the first wave and the second cursor on the very peak of the second pulse wave (similar to what you see for the two waves in Analysis Figure 3 ). When the cursor is close to the peak, you may use the arrow keys on your computer keypad to move the cursor precisely to the top of the peaks.
- In your Lab Report Table record the Heart Rate in bpm (found in the gold square in the figure) on the lower Heart Rate Screen and the Time Between Beats found under T2-T1 (Red Circle) on the Pulse Screen ( Analysis Figure 3, above) .
- Now move the cursor from the first wave to the peak of the third wave, so now you have a cursor remaining on the second wave and a cursor on the third wave, record the same values for this set of data.
- Next, move the cursor from the second wave to the fourth wave, record the data. Continue moving the cursors in this manner until you have recorded data for ten waves.
- Calculate the mean for the 10 waves on your lab report and answer the questions. You’re all done with iWorx for this week!


25.9: Regulation of Fluid Volume and Composition
Learning Objectives
- Explain the mechanism of action of diuretics
- Explain why the differential permeability or impermeability of specific sections of the nephron tubules is necessary for urine formation
The major hormones influencing total body water are ADH, aldosterone, and ANH. Circumstances that lead to fluid depletion in the body include blood loss and dehydration. Homeostasis requires that volume and osmolarity be preserved. Blood volume is important in maintaining sufficient blood pressure, and there are nonrenal mechanisms involved in its preservation, including vasoconstriction, which can act within seconds of a drop in pressure. Thirst mechanisms are also activated to promote the consumption of water lost through respiration, evaporation, or urination. Hormonal mechanisms are activated to recover volume while maintaining a normal osmotic environment. These mechanisms act principally on the kidney.
Volume-sensing Mechanisms
The body cannot directly measure blood volume, but blood pressure can be measured. Blood pressure often reflects blood volume and is measured by baroreceptors in the aorta and carotid sinuses. When blood pressure increases, baroreceptors send more frequent action potentials to the central nervous system, leading to widespread vasodilation. Included in this vasodilation are the afferent arterioles supplying the glomerulus, resulting in increased GFR, and water loss by the kidneys. If pressure decreases, fewer action potentials travel to the central nervous system, resulting in more sympathetic stimulation-producing vasoconstriction, which will result in decreased filtration and GFR, and water loss.
Decreased blood pressure is also sensed by the granular cells in the afferent arteriole of the JGA. In response, the enzyme renin is released. You saw earlier in the chapter that renin activity leads to an almost immediate rise in blood pressure as activated angiotensin II produces vasoconstriction. The rise in pressure is sustained by the aldosterone effects initiated by angiotensin II; this includes an increase in Na + retention and water volume. As an aside, late in the menstrual cycle, progesterone has a modest influence on water retention. Due to its structural similarity to aldosterone, progesterone binds to the aldosterone receptor in the collecting duct of the kidney, causing the same, albeit weaker, effect on Na + and water retention.
Cardiomyocytes of the atria also respond to greater stretch (as blood pressure rises) by secreting ANH. ANH opposes the action of aldosterone by inhibiting the recovery of Na + by the DCT and collecting ducts. More Na + is lost, and as water follows, total blood volume and pressure decline. In low-pressure states, ANH does not seem to have much effect.
ADH is also called vasopressin. Early researchers found that in cases of unusually high secretion of ADH, the hormone caused vasoconstriction (vasopressor activity, hence the name). Only later were its antidiuretic properties identified. Synthetic ADH is still used occasionally to stem life-threatening esophagus bleeding in alcoholics.
When blood volume drops 5–10 percent, causing a decrease in blood pressure, there is a rapid and significant increase in ADH release from the posterior pituitary. Immediate vasoconstriction to increase blood pressure is the result. ADH also causes activation of aquaporin channels in the collecting ducts to affect the recovery of water to help restore vascular volume.
Diuretics and Fluid Volume
A diuretic is a compound that increases urine volume. Three familiar drinks contain diuretic compounds: coffee, tea, and alcohol. The caffeine in coffee and tea works by promoting vasodilation in the nephron, which increases GFR. Alcohol increases GFR by inhibiting ADH release from the posterior pituitary, resulting in less water recovery by the collecting duct. In cases of high blood pressure, diuretics may be prescribed to reduce blood volume and, thereby, reduce blood pressure. The most frequently prescribed anti-hypertensive diuretic is hydrochlorothiazide. It inhibits the Na + / Cl – symporter in the DCT and collecting duct. The result is a loss of Na + with water following passively by osmosis.
Osmotic diuretics promote water loss by osmosis. An example is the indigestible sugar mannitol, which is most often administered to reduce brain swelling after head injury. However, it is not the only sugar that can produce a diuretic effect. In cases of poorly controlled diabetes mellitus, glucose levels exceed the capacity of the tubular glucose symporters, resulting in glucose in the urine. The unrecovered glucose becomes a powerful osmotic diuretic. Classically, in the days before glucose could be detected in the blood and urine, clinicians identified diabetes mellitus by the three Ps: polyuria (diuresis), polydipsia (increased thirst), and polyphagia (increased hunger).
Regulation of Extracellular Na +
Sodium has a very strong osmotic effect and attracts water. It plays a larger role in the osmolarity of the plasma than any other circulating component of the blood. If there is too much Na + present, either due to poor control or excess dietary consumption, a series of metabolic problems ensue. There is an increase in total volume of water, which leads to hypertension (high blood pressure). Over a long period, this increases the risk of serious complications such as heart attacks, strokes, and aneurysms. It can also contribute to system-wide edema (swelling).
Mechanisms for regulating Na + concentration include the renin–angiotensin–aldosterone system and ADH (see [link]). Aldosterone stimulates the uptake of Na + on the apical cell membrane of cells in the DCT and collecting ducts, whereas ADH helps to regulate Na + concentration indirectly by regulating the reabsorption of water.
Regulation of Extracellular K +
Potassium is present in a 30-fold greater concentration inside the cell than outside the cell. A generalization can be made that K + and Na + concentrations will move in opposite directions. When more Na + is reabsorbed, more K + is secreted; when less Na + is reabsorbed (leading to excretion by the kidney), more K + is retained. When aldosterone causes a recovery of Na + in the nephron, a negative electrical gradient is created that promotes the secretion of K + and Cl – into the lumen.
Regulation of Cl –
Chloride is important in acid–base balance in the extracellular space and has other functions, such as in the stomach, where it combines with hydrogen ions in the stomach lumen to form hydrochloric acid, aiding digestion. Its close association with Na + in the extracellular environment makes it the dominant anion of this compartment, and its regulation closely mirrors that of Na + .
Regulation of Ca ++ and Phosphate
The parathyroid glands monitor and respond to circulating levels of Ca ++ in the blood. When levels drop too low, PTH is released to stimulate the DCT to reabsorb Ca ++ from the forming urine. When levels are adequate or high, less PTH is released and more Ca ++ remains in the forming urine to be lost. Phosphate levels move in the opposite direction. When Ca ++ levels are low, PTH inhibits reabsorption of \(\ce{HPO_4^2-}\) so that its blood level drops, allowing Ca ++ levels to rise. PTH also stimulates the renal conversion of calcidiol into calcitriol, the active form of vitamin D. Calcitriol then stimulates the intestines to absorb more Ca ++ from the diet.
Regulation of H + , Bicarbonate, and pH
The acid–base homeostasis of the body is a function of chemical buffers and physiologic buffering provided by the lungs and kidneys. Buffers, especially proteins, \[HCO_4^2-\], and ammonia have a very large capacity to absorb or release H + as needed to resist a change in pH. They can act within fractions of a second. The lungs can rid the body of excess acid very rapidly (seconds to minutes) through the conversion of HCO 3 – into CO 2 , which is then exhaled. It is rapid but has limited capacity in the face of a significant acid challenge. The kidneys can rid the body of both acid and base. The renal capacity is large but slow (minutes to hours). The cells of the PCT actively secrete H + into the forming urine as Na + is reabsorbed. The body rids itself of excess H + and raises blood pH. In the collecting ducts, the apical surfaces of intercalated cells have proton pumps that actively secrete H + into the luminal, forming urine to remove it from the body.
As hydrogen ions are pumped into the forming urine, it is buffered by bicarbonate (HCO 3 – ), H 2 PO 4 – (dihydrogen phosphate ion), or ammonia (forming NH 4 + , ammonium ion). Urine pH typically varies in a normal range from 4.5 to 8.0.
Regulation of Nitrogen Wastes
Nitrogen wastes are produced by the breakdown of proteins during normal metabolism. Proteins are broken down into amino acids, which in turn are deaminated by having their nitrogen groups removed. Deamination converts the amino (NH 2 ) groups into ammonia (NH 3 ), ammonium ion (NH 4 + ), urea, or uric acid (Figure \(\PageIndex{1}\)). Ammonia is extremely toxic, so most of it is very rapidly converted into urea in the liver. Human urinary wastes typically contain primarily urea with small amounts of ammonium and very little uric acid.
Elimination of Drugs and Hormones
Water-soluble drugs may be excreted in the urine and are influenced by one or all of the following processes: glomerular filtration, tubular secretion, or tubular reabsorption. Drugs that are structurally small can be filtered by the glomerulus with the filtrate. Large drug molecules such as heparin or those that are bound to plasma proteins cannot be filtered and are not readily eliminated. Some drugs can be eliminated by carrier proteins that enable secretion of the drug into the tubule lumen. There are specific carriers that eliminate basic (such as dopamine or histamine) or acidic drugs (such as penicillin or indomethacin). As is the case with other substances, drugs may be both filtered and reabsorbed passively along a concentration gradient.
Chapter Review
The major hormones regulating body fluids are ADH, aldosterone and ANH. Progesterone is similar in structure to aldosterone and can bind to and weakly stimulate aldosterone receptors, providing a similar but diminished response. Blood pressure is a reflection of blood volume and is monitored by baroreceptors in the aortic arch and carotid sinuses. When blood pressure increases, more action potentials are sent to the central nervous system, resulting in greater vasodilation, greater GFR, and more water lost in the urine. ANH is released by the cardiomyocytes when blood pressure increases, causing Na + and water loss. ADH at high levels causes vasoconstriction in addition to its action on the collecting ducts to recover more water. Diuretics increase urine volume. Mechanisms for controlling Na + concentration in the blood include the renin–angiotensin–aldosterone system and ADH. When Na + is retained, K + is excreted; when Na + is lost, K + is retained. When circulating Ca ++ decreases, PTH stimulates the reabsorption of Ca ++ and inhibits reabsorption of HPO 2 − 4 . pH is regulated through buffers, expiration of CO 2 , and excretion of acid or base by the kidneys. The breakdown of amino acids produces ammonia. Most ammonia is converted into less-toxic urea in the liver and excreted in the urine. Regulation of drugs is by glomerular filtration, tubular secretion, and tubular reabsorption.
Review Questions
Q. Which of these beverages does not have a diuretic effect?
A. tea
B. coffee
C. alcohol
D. milk
Answer: D
Q. Progesterone can bind to receptors for which hormone that, when released, activates water retention?
A. aldosterone
B. ADH
C. PTH
D. ANH
Answer: A
Q. Renin is released in response to ________.
A. increased blood pressure
B. decreased blood pressure
C. ACE
D. diuretics
Answer: B
Critical Thinking Questions
Q. Why is ADH also called vasopressin?
A. When first discovered, it was named for its known activity—vasoconstriction.
Q. How can glucose be a diuretic?
A. In cases of diabetes mellitus, there is more glucose present than the kidney can recover and the excess glucose is lost in the urine. It possesses osmotic character so that it attracts water to the forming urine.
Glossary
- diuretic
- compound that increases urine output, leading to decreased water conservation


9.3.3: Using a Trundle Wheel to Measure Distances
Lesson
Let's use our trundle wheels.
Exercise \(\PageIndex{1}\): Measuring Distances with the Trundle Wheel
Earlier you made trundle wheels so that you can measure long distances.
If you do not have a trundle wheel, you can use an applet to simulate measuring.
-
Measure the path with your trundle wheel three times and calculate the distance. Record your results in the table.
diameter number of rotations computation distance trial 1 trial 2 trial 3 Table \(\PageIndex{1}\) - Decide what distance you will report to the class. Be prepared to explain your reasoning.
- Compare this distance with the distance you measured the other day for this same path.
- Compare your results with the results of two other groups. Express the differences between the measurements in terms of percentages.
To use this applet:
- Choose a diameter for the wheel, and enter a number 1 -- 5 for the path you will measure.
- Watch carefully to keep track of the number of rotations that the wheel makes before it stops.
- Try three different diameters for the same path, and compare your results.
- Answer the questions.


13.8.4E: Exercises
-
- Last updated
- Save as PDF
Practice Makes Perfect
Multiply Square Roots
In the following exercises, simplify.
Example \(\PageIndex{48}\)
- \(\sqrt{2}·\sqrt{8}\)
- \((3\sqrt{3})(2\sqrt{18})\)
- Answer
-
- \(44\)
- \(18\sqrt{6}\)
Example \(\PageIndex{49}\)
- \(\sqrt{6}·\sqrt{6}\)
- \((3\sqrt{2})(2\sqrt{32})\)
Example \(\PageIndex{50}\)
- \(\sqrt{7}·\sqrt{14}\)
- \((4\sqrt{8})(5\sqrt{8})\)
- Answer
-
- \(7\sqrt{2}\)
- 160
Example \(\PageIndex{51}\)
- \(\sqrt{6}·\sqrt{12}\)
- \((2\sqrt{5})(2\sqrt{10})\)
Example \(\PageIndex{52}\)
\((5\sqrt{2})(3\sqrt{6})\)
- Answer
-
\(30\sqrt{3}\)
Example \(\PageIndex{53}\)
\((2\sqrt{3})(4\sqrt{6})\)
Example \(\PageIndex{54}\)
\((−2\sqrt{3})(3\sqrt{18})\)
- Answer
-
\(−18\sqrt{6}\)
Example \(\PageIndex{55}\)
\((−4\sqrt{5})(5\sqrt{10})\)
Example \(\PageIndex{56}\)
\((5\sqrt{6})(−\sqrt{12})\)
- Answer
-
\(−30\sqrt{2}\)
Example \(\PageIndex{57}\)
\((6\sqrt{2})(−\sqrt{10})\)
Example \(\PageIndex{58}\)
\((−2\sqrt{7})(−2\sqrt{14})\)
- Answer
-
\(28\sqrt{2}\)
Example \(\PageIndex{59}\)
\((−2\sqrt{11})(−4\sqrt{22})\)
Example \(\PageIndex{60}\)
- \((\sqrt{15y})(\sqrt{5y^3})\)
- \((\sqrt{2n^2})(\sqrt{18n^3})\)
- Answer
-
- \(5y^2\sqrt{3}\)
- \(6n^2\sqrt{n}\)
Example \(\PageIndex{61}\)
- \((\sqrt{14x^3})(\sqrt{7x^3})\)
- \((\sqrt{3q^2})(\sqrt{48q^3})\)
Example \(\PageIndex{62}\)
- \((\sqrt{16y^2})(\sqrt{8y^4})\)
- \((\sqrt{11s^6})(\sqrt{11s})\)
- Answer
-
- \(8y^3\sqrt{2}\)
- \(11s^3\sqrt{s}\)
Example \(\PageIndex{63}\)
ⓐ \((\sqrt{8x^3})(\sqrt{3x})\)
ⓑ \((\sqrt{7r})(\sqrt{7r^8})\)
Example \(\PageIndex{64}\)
\((2\sqrt{5b^3})(4\sqrt{15b})\)
- Answer
-
\(40b^2\sqrt{3}\)
Example \(\PageIndex{65}\)
\((\sqrt{38c^5})(\sqrt{26c^3})\)
Example \(\PageIndex{66}\)
\((6\sqrt{3d^3})(4\sqrt{12d^5})\)
- Answer
-
\(144d^4\)
Example \(\PageIndex{67}\)
\((2\sqrt{5b^3})(4\sqrt{15b})\)
Example \(\PageIndex{68}\)
\((2\sqrt{5d^6})(3\sqrt{20d^2})\)
- Answer
-
\(60d^4\)
Example \(\PageIndex{69}\)
\((−2\sqrt{7z^3})(3\sqrt{14z^8})\)
Example \(\PageIndex{70}\)
\((4\sqrt{2k^5})(−3\sqrt{32k^6})\)
- Answer
-
\(−96k^5\sqrt{k}\)
Example \(\PageIndex{71}\)
- \((\sqrt{7})^2\)
- \((−\sqrt{15})^2\)
Example \(\PageIndex{72}\)
- \((\sqrt{11})^2\)
- \((−\sqrt{21})^2\)
- Answer
-
- 11
- 21
Example \(\PageIndex{73}\)
- \((\sqrt{19})^2\)
- \((−\sqrt{5})^2\)
Exercise \(\PageIndex{74}\)
- \((\sqrt{23})^2\)
- \((−\sqrt{3})^2\)
- Answer
-
- 23
- 3
Example \(\PageIndex{75}\)
- \((4\sqrt{11})(−3\sqrt{11})\)
- \((5\sqrt{3})^2\)
Example \(\PageIndex{76}\)
- \((2\sqrt{13})(−9\sqrt{13})\)
- \((6\sqrt{5})^2\)
- Answer
-
- −234
- 180
Example \(\PageIndex{77}\)
- \((−3\sqrt{12})(−2\sqrt{6})\)
- \( (−4\sqrt{10})^2\)
Example \(\PageIndex{78}\)
- \((−7\sqrt{5})(−3\sqrt{10})\)
- \( (−2\sqrt{14})^2\)
- Answer
-
- \(105\sqrt{2}\)
- 56
Use Polynomial Multiplication to Multiply Square Roots
In the following exercises, simplify.
Example \(\PageIndex{79}\)
- \(3(4−\sqrt{3})\)
- \(\sqrt{2}(4−\sqrt{6})\)
Example \(\PageIndex{80}\)
- \(4(6−\sqrt{11})\)
- \(\sqrt{2}(5−\sqrt{12})\)
- Answer
-
- \(24−4\sqrt{11}\)
- \(5\sqrt{2}−2\sqrt{6}\)
Example \(\PageIndex{81}\)
- \(5(3−\sqrt{7})\)
- \(\sqrt{3}(4−\sqrt{15})\)
Example \(\PageIndex{82}\)
- \(7(−2−\sqrt{11})\)
- \(\sqrt{7}(6−\sqrt{14})\)
- Answer
-
- \(−14−7\sqrt{11}\)
- \(6\sqrt{7}−7\sqrt{2}\)
Example \(\PageIndex{83}\)
- \(\sqrt{7}(5+2\sqrt{7})\)
- \(\sqrt{5}(\sqrt{10}+\sqrt{18})\)
Example \(\PageIndex{84}\)
- \(\sqrt{11}(8+4\sqrt{11})\)
- \(\sqrt{3}(\sqrt{12}+\sqrt{27})\)
- Answer
-
- \(44+8\sqrt{11}\)
- 15
Example \(\PageIndex{85}\)
- \(\sqrt{11}(−3+4\sqrt{1})\)
- \(\sqrt{3}(\sqrt{15}−\sqrt{18})\)
Example \(\PageIndex{86}\)
- \(\sqrt{2}(−5+9\sqrt{2})\)
- \(\sqrt{7}(\sqrt{3}−\sqrt{21})\)
- Answer
-
- \(18−5\sqrt{2}\)
- \(\sqrt{21}−7\sqrt{3}\)
Example \(\PageIndex{87}\)
\((8+\sqrt{3})(2−\sqrt{3})\)
Example \(\PageIndex{88}\)
\((7+\sqrt{3})(9−\sqrt{3})\)
- Answer
-
\(60+2\sqrt{3}\)
Example \(\PageIndex{89}\)
\((8−\sqrt{2})(3+\sqrt{2})\)
Example \(\PageIndex{90}\)
\((9−\sqrt{2})(6+\sqrt{2})\)
- Answer
-
\(52+3\sqrt{2}\)
Example \(\PageIndex{91}\)
\((3−\sqrt{7})(5−\sqrt{7})\)
Example \(\PageIndex{92}\)
\((5−\sqrt{7})(4−\sqrt{7})\)
- Answer
-
\(27−9\sqrt{7}\)
Example \(\PageIndex{93}\)
\((1+3\sqrt{10})(5−2\sqrt{10})\)
Exercise \(\PageIndex{94}\)
\((7−2\sqrt{5})(4+9\sqrt{5})\)
- Answer
-
\(−62+55\sqrt{5}\)
Example \(\PageIndex{95}\)
\((\sqrt{3}+\sqrt{10})(\sqrt{3}+2\sqrt{10})\)
Example \(\PageIndex{96}\)
\((\sqrt{11}+\sqrt{5})(\sqrt{11}+6\sqrt{5})\)
- Answer
-
\(41+7\sqrt{55}\)
Example \(\PageIndex{97}\)
\((2\sqrt{7}−5\sqrt{11})(4\sqrt{7}+9\sqrt{11})\)
Example \(\PageIndex{98}\)
\((4\sqrt{6}+7\sqrt{13})(8\sqrt{6}−3\sqrt{13})\)
- Answer
-
\(−81+44\sqrt{78}\)
Example \(\PageIndex{99}\)
\((5−\sqrt{u})(3+\sqrt{u})\)
Example \(\PageIndex{100}\)
\((9−\sqrt{w})(2+\sqrt{w})\)
- Answer
-
\(18+7\sqrt{w}\)
Example \(\PageIndex{101}\)
\((7+2\sqrt{m})(4+9\sqrt{m})\)
Example \(\PageIndex{102}\)
\((6+5\sqrt{n})(11+3\sqrt{n})\)
- Answer
-
\(66+73\sqrt{n}+15n\)
Example \(\PageIndex{103}\)
- \((3+\sqrt{5})^2\)
- \((2−5\sqrt{3})^2\)
Example \(\PageIndex{104}\)
- \((4+\sqrt{11})^2\)
- \((3−2\sqrt{5})^2\)
- Answer
-
- \(27+8\sqrt{11}\)
- \(29−12\sqrt{5}\)
Example \(\PageIndex{105}\)
- \((9−\sqrt{6})^2\)
- \((10+3\sqrt{7})^2\)
Example \(\PageIndex{106}\)
- \((5−\sqrt{10})^2\)
- \((8+3\sqrt{2})^2\)
- Answer
-
- \(35−10\sqrt{10}\)
- \(82+48\sqrt{2}\)
Example \(\PageIndex{107}\)
\((3−\sqrt{5})(3+\sqrt{5})\)
Example \(\PageIndex{108}\)
\((10−\sqrt{3})(10+\sqrt{3})\)
- Answer
-
97
Example \(\PageIndex{109}\)
\((4+\sqrt{2})(4−\sqrt{2})\)
Example \(\PageIndex{110}\)
\((7+\sqrt{10})(7−\sqrt{10})\)
- Answer
-
39
Example \(\PageIndex{111}\)
\((4+9\sqrt{3})(4−9\sqrt{3})\)
Example \(\PageIndex{112}\)
\((1+8\sqrt{2})(1−8\sqrt{2})\)
- Answer
-
−127
Example \(\PageIndex{113}\)
\((12−5\sqrt{5})(12+5\sqrt{5})\)
Example \(\PageIndex{114}\)
\((9−4\sqrt{3})(9+4\sqrt{3})\)
- Answer
-
33
Mixed Practice
In the following exercises, simplify.
Example \(\PageIndex{115}\)
\(\sqrt{3}·\sqrt{21}\)
Example \(\PageIndex{116}\)
\((4\sqrt{6})(−\sqrt{18})\)
- Answer
-
\(−24\sqrt{3}\)
Example \(\PageIndex{117}\)
\((−5+\sqrt{7})(6+\sqrt{21})\)
Example \(\PageIndex{118}\)
\((−5\sqrt{7})(6\sqrt{21})\)
- Answer
-
\(−210\sqrt{3}\)
Example \(\PageIndex{119}\)
\((−4\sqrt{2})(2\sqrt{18})\)
Example \(\PageIndex{120}\)
\((\sqrt{35y^3})(\sqrt{7y^3})\)
- Answer
-
\(7y^3\sqrt{5}\)
Example \(\PageIndex{121}\)
\((4\sqrt{12x^5})(2\sqrt{6x^3})\)
Example \(\PageIndex{122}\)
\((\sqrt{29})^2\)
- Answer
-
29
Example \(\PageIndex{123}\)
\((−4\sqrt{17})(−3\sqrt{17})\)
Example \(\PageIndex{124}\)
\((−4+\sqrt{17})(−3+\sqrt{17})\)
- Answer
-
\(29−7\sqrt{17}\)
Everyday Math
Example \(\PageIndex{125}\)
A landscaper wants to put a square reflecting pool next to a triangular deck, as shown below. The triangular deck is a right triangle, with legs of length 9 feet and 11 feet, and the pool will be adjacent to the hypotenuse.
- Use the Pythagorean Theorem to find the length of a side of the pool. Round your answer to the nearest tenth of a foot.
- Find the exact area of the pool.
Example \(\PageIndex{126}\)
An artist wants to make a small monument in the shape of a square base topped by a right triangle, as shown below. The square base will be adjacent to one leg of the triangle. The other leg of the triangle will measure 2 feet and the hypotenuse will be 5 feet.
-
Use the Pythagorean Theorem to find the length of a side of the square base. Round your answer to the nearest tenth of a foot.
- Find the exact area of the face of the square base.
- Answer
-
- 4.6feet
- 21 sq. feet
Example \(\PageIndex{127}\)
A square garden will be made with a stone border on one edge. If only \(3+\sqrt{10}\) feet of stone are available, simplify \((3+\sqrt{10})^2\) to determine the area of the largest such garden.
Example \(\PageIndex{128}\)
A garden will be made so as to contain two square sections, one section with side length \(\sqrt{5}+\sqrt{6}\) yards and one section with side length \(\sqrt{2}+\sqrt{3}\) yards. Simplify \((\sqrt{5}+\sqrt{6})(\sqrt{2}+\sqrt{3})\) to determine the total area of the garden.
Example \(\PageIndex{129}\)
Suppose a third section will be added to the garden in the previous exercise. The third section is to have a width of \(\sqrt{432}\) feet. Write an expression that gives the total area of the garden.
Writing Exercises
Example \(\PageIndex{130}\)
- Explain why \((−\sqrt{n})^2\) is always positive, for \(n \ge 0\).
- Explain why \(−(\sqrt{n})^2\) is always negative, for \(n \ge 0\).
- Answer
-
- when squaring a negative, it becomes a positive
- since the negative is not included in the parenthesis, it is not squared, and remains negative
Example \(\PageIndex{131}\)
Use the binomial square pattern to simplify \((3+\sqrt{2})^2\). Explain all your steps.
Self Check
ⓐ After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.
ⓑ On a scale of 1–10, how would you rate your mastery of this section in light of your responses on the checklist? How can you improve this?


8.8: The Colon
You can use the colon several ways in MATLAB (see help :). Its basic meaning is a vector of sequential values. For example, type
≫ x = 3:9
to get
x = 3 4 5 6 7 8 9
For increments other than 1, use statements like
≫ x = 1:0.5:4 ≫ x = 6:-1:0
Most MATLAB functions will accept vector inputs and produce vector outputs. The statement
≫ y = sqrt(1:10)
builds a vector of integers from 1 to 10 and takes the square root of each of those numbers. Try it.
Now for another subtlety–what is the effect of each of the following statements and why?
≫ 1+1:5 ≫ 1+(1:5)
Appending to a Matrix or Vector
A matrix or vector can be enlarged in size by appending new values to the old values. Let
x=[1 3 5]
:
\[\mathrm{x}=[\mathrm{x} 6810] \Rightarrow \mathrm{x}= [1356810] \nonumber \]
\[y=[x ; 1: 6] \Rightarrow y=\left[\begin{array}{llllll}
1 & 3 & 5 & 6 & 8 & 10 \\
1 & 2 & 3 & 4 & 5 & 6
\end{array}\right] \nonumber \]


5.10: Why It Matters- Recruiting and Selecting New Employees
Why does recruiting matter?
Recruiting and selecting new employees can make or break a company. An employee represents, in the financial sense, a very high risk investment. A company’s personnel costs may be a business’ single largest expense.
According to the Society for Human Resource Management, salaries alone can account for 18 to 52 percent of your operating budget [1] . Add in payroll and unemployment insurance taxes, workers compensation, overtime, benefits, reimbursements, leave and holiday pay, and the full cost of salaries and benefits could be in the forty to eighty percent of gross revenue range [2] .
No wonder a famous saying in business reminds us that people are a company’s greatest asset.Choose well, and your employees can be a source of competitive advantage. On the other hand, a poor choice can represent a critical liability.
Let’s elaborate on the downside risk. The U.S. Department of Labor estimates that the average cost of a bad hiring decision is thirty percent of the employee’s first year projected earnings [3] . Note, however, that number represents only a fraction of the organizational impact. Chief financial officers surveyed by global staffing firm Robert Half ranked morale (39 percent) and productivity (34 percent) effects of a bad hire greater than the monetary (25 percent) cost.
In this module, we’ll learn how to choose well—from attraction phase through the selection phase—and how to avoid related legal liabilities.
- Deeb, Carol. " Percent of a Business Budget for Salary ." Chron . Web. 26 June 2018. ↵
- Ferguson, Grace. " What Percentage of the Budget Should Be Spent on Payroll? " Chron . Web. 26 June 2018. ↵
- Cardenas, Rebekah. " What's the Real Cost of a Bad Hire? " HR Exchange , 02 Apr 2014. Web. 26 June 2018. ↵
- Why It Matters: Recruiting and Selecting Employees. Authored by : Nina Burokas. Provided by : Lumen Learning. License : CC BY: Attribution


6.1.3: Anselm’s Ontological Argument and Gaunilo’s Lost Island
-
- Last updated
- Save as PDF
Anselm’s “Ontological Argument” 24
Therefore, Lord, you who give knowledge of the faith, give me as much knowledge as you know to be fitting for me, because you are as we believe and that which we believe. And indeed we believe you are something greater than which cannot be thought. Or is there no such kind of thing, for "the fool said in his heart, 'there is no God'" (Ps. 13:1, 52:1)? But certainly that same fool, having heard what I just said, "something greater than which cannot be thought," understands what he heard, and what he understands is in his thought, even if he does not think it exists. For it is one thing for something to exist in a person's thought and quite another for the person to think that thing exists. For when a painter thinks ahead to what he will paint, he has that picture in his thought, but he does not yet think it exists, because he has not done it yet. Once he has painted it he has it in his thought and thinks it exists because he has done it. Thus even the fool is compelled to grant that something greater than which cannot be thought exists in thought, because he understands what he hears, and whatever is understood exists in thought. And certainly that greater than which cannot be understood cannot exist only in thought, for if it exists only in thought it could also be thought of as existing in reality as well, which is greater. If, therefore, that than which greater cannot be thought exists in thought alone, then that than which greater cannot be thought turns out to be that than which something greater actually can be thought, but that is obviously impossible. Therefore something than which greater cannot be thought undoubtedly exists both in thought and in reality.
Gaunilo’s “Lost Island Objection”
For example, they say there is in the ocean somewhere an island which, due to the difficulty (or rather the impossibility) of finding what does not actually exist, is called "the lost island." And they say that this island has all manner of riches and delights, even more of them than the Isles of the Blest, and having no owner or inhabitant it is superior in the abundance of its riches to all other lands which are inhabited by men. If someone should tell me that such is the case, I will find it easy to understand what he says, since there is nothing difficult about it. But suppose he then adds, as if he were stating a logical consequence, "Well then, you can no longer doubt that this island more excellent than all other lands really exists somewhere, since you do not doubt that it is in your mind; and since it is more excellent to exist not only in the mind but in reality as well, this island must necessarily exist, because if it didn't, any other island really existing would be more excellent than it, and thus that island now thought of by you as more excellent will not be such." If, I say, someone tries to convince me though this argument that the island really exists and there should be no more doubt about it, I will either think he is joking or I will have a hard time deciding who is the bigger fool, me if I believe him or him if he thinks he has proved its existence without having first convinced me that this excellence is something undoubtedly existing in reality and not just something false or uncertain existing in my mind.


3: Factorization
In this chapter, we come to the heart of the text: a structural investigation of unique factorization in the familiar contexts of \(\mathbb{Z}\) and \(F[x]\). In Section 3.1 , we explore theorems that formalize much of our understanding of that quintessential high school algebra problem: factoring polynomials. As we saw in Theorem 1.2.4 and Theorem 2.4.9 , both \(\mathbb{Z}\) and \(F[x]\) have a division algorithm and, thus, are Euclidean domains. In Section 3.2 , we explore the implications for multiplication in Euclidean domains. That is: given that we have a well-behaved division algorithm in an integral domain, what can we say about the factorization properties of the domain?
Finally, in the optional Section 3.3 , we explore contexts in which unique factorization into products of irreducibles need not hold.
-
- 3.2: Factorization in Euclidean Domains
- In this section, our explorations of the structural arithmetic properties that guarantee unique factorization culminate in Theorem 3.2.7 . Specifically, we'll see that all Euclidean domains possess the unique factorization property. To prove this theorem, we will rely in part on an interesting property of chains of ideals in Euclidean domains.


1.2: The Difference Between Managers and Leaders
Managers and Leaders: What's the Difference?
There is a clear distinction between leadership and management and between managers and leaders . A manager’s behavior and activities focus on controlling, planning, coordinating, and organizing. This differs from a leader, whose behaviors and tasks focus on innovation, vision, motivation, trust, and change. e
Read the short article " The Difference between Managers and Leaders " to learn more about these important distinctions.
Source: 1.1 " The Difference Between Managers and Leaders. " Leading with Cultural Intelligence. Saylor Academy. 2012.
This text was adapted by Saylor Academy under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License without attribution as requested by the work's original creator or licensor.


3.4: Aquatic Biomes
Abiotic Factors Influencing Aquatic Biomes
Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water still absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach. While there are some abiotic and biotic factors in a terrestrial ecosystem that might obscure light (like fog, dust, or insect swarms), usually these are not permanent features of the environment. The importance of light in aquatic biomes is central to the communities of organisms found in both freshwater and marine ecosystems. In freshwater systems, stratification due to differences in density is perhaps the most critical abiotic factor and is related to the energy aspects of light. The thermal properties of water (rates of heating and cooling) are significant to the function of marine systems and have major impacts on global climate and weather patterns. Marine systems are also influenced by large-scale physical water movements, such as currents; these are less important in most freshwater lakes.
The ocean is categorized by several areas or zones (Figure \(\PageIndex{1}\)). All of the ocean’s open water is referred to as the pelagic zone . The benthic zone extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor. Within the pelagic realm is the photic zone , which is the portion of the ocean that light can penetrate (approximately 200 m or 650 ft). At depths greater than 200 m, light cannot penetrate; thus, this is referred to as the aphotic zone . The majority of the ocean is aphotic and lacks sufficient light for photosynthesis. The deepest part of the ocean, the Challenger Deep (in the Mariana Trench, located in the western Pacific Ocean), is about 11,000 m (about 6.8 mi) deep. To give some perspective on the depth of this trench, the ocean is, on average, 4267 m. These zones are relevant to freshwater lakes as well.
Marine Biomes
The ocean is the largest marine biome . It is a continuous body of salt water that is relatively uniform in chemical composition; it is a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second kind of marine biome. Estuaries, coastal areas where salt water and fresh water mix, form a third unique marine biome.
Ocean
The physical diversity of the ocean is a significant influence on plants, animals, and other organisms. The ocean is categorized into different zones based on how far light reaches into the water. Each zone has a distinct group of species adapted to the biotic and abiotic conditions particular to that zone.
The intertidal zone , which is the zone between high and low tide, is the oceanic region that is closest to land (Figure \(\PageIndex{2}\)). Generally, most people think of this portion of the ocean as a sandy beach. In some cases, the intertidal zone is indeed a sandy beach, but it can also be rocky or muddy. Organisms are exposed to air and sunlight at low tide and are underwater most of the time, especially during high tide. Therefore, living things that thrive in the intertidal zone are adapted to being dry for long periods of time. The shore of the intertidal zone is also repeatedly struck by waves, and the organisms found there are adapted to withstand damage from the pounding action of the waves (Figure \(\PageIndex{2}\)). The exoskeletons of shoreline crustaceans (such as the shore crab, Carcinus maenas ) are tough and protect them from desiccation (drying out) and wave damage. Another consequence of the pounding waves is that few algae and plants establish themselves in the constantly moving rocks, sand, or mud.
The neritic zone (Figure \(\PageIndex{1}\)) extends from the intertidal zone to depths of about 200 m (or 650 ft) at the edge of the continental shelf. Because light can penetrate this depth, photosynthesis can occur. The water here contains silt and is well-oxygenated, low in pressure, and stable in temperature. Phytoplankton and floating Sargassum (a type of free-floating marine seaweed) provide a habitat for some sea life found in the neritic zone. Zooplankton, protists, small fishes, and shrimp are found in the neritic zone and are the base of the food chain for most of the world’s fisheries.
Beyond the neritic zone is the open ocean area known as the oceanic zone (Figure \(\PageIndex{1}\)). Within the oceanic zone there is thermal stratification where warm and cold waters mix because of ocean currents. Abundant plankton serve as the base of the food chain for larger animals such as whales and dolphins. Nutrients are scarce and this is a relatively less productive part of the marine biome. When photosynthetic organisms and the protists and animals that feed on them die, their bodies fall to the bottom of the ocean where they remain. The majority of organisms in the aphotic zone include sea cucumbers (phylum Echinodermata) and other organisms that survive on the nutrients contained in the dead bodies of organisms in the photic zone.
The deepest part of the ocean is the abyssal zone , which is at depths of 4000 m or greater. The abyssal zone (Figure \(\PageIndex{1}\)) is very cold and has very high pressure, high oxygen content, and low nutrient content. There are a variety of invertebrates and fishes found in this zone, but the abyssal zone does not have plants because of the lack of light. Cracks in the Earth’s crust called hydrothermal vents are found primarily in the abyssal zone. Around these vents chemosynthetic bacteria utilize the hydrogen sulfide and other minerals emitted as an energy source and serve as the base of the food chain found in the abyssal zone.
Beneath the water is the benthic zone (Figure \(\PageIndex{1}\)), which is comprised of sand, silt, and dead organisms. This is a nutrient-rich portion of the ocean because of the dead organisms that fall from the upper layers of the ocean. Because of this high level of nutrients, a diversity of sponges, sea anemones, marine worms, sea stars, fishes, and bacteria exist.
Coral Reefs
Coral reefs are characterized by high biodiversity and the structures created by invertebrates that live in warm, shallow waters within the photic zone of the ocean. They are mostly found within 30 degrees north and south of the equator. The Great Barrier Reef is a well-known reef system located several miles off the northeastern coast of Australia. The coral organisms (members of phylum Cnidaria) are colonies of saltwater polyps that secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, forming the underwater reef (Figure \(\PageIndex{3}\)).
Corals found in shallower waters (at a depth of approximately 60 m or about 200 ft) have a mutualistic relationship with photosynthetic unicellular algae. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor and, without this mutualism, it would not be possible for large corals to grow. Some corals living in deeper and colder water do not have a mutualistic relationship with algae; these corals attain energy and nutrients using stinging cells on their tentacles to capture prey. It is estimated that more than 4,000 fish species inhabit coral reefs. These fishes can feed on coral, other invertebrates, or the seaweed and algae that are associated with the coral.
Link to Learning: Watch this National Oceanic and Atmospheric Administration (NOAA) video to see marine ecologist Dr. Peter Etnoyer discusses his research on coral organisms.
EVOLUTION CONNECTION: Global Decline of Coral Reefs
It takes a long time to build a coral reef. The animals that create coral reefs have evolved over millions of years, continuing to slowly deposit the calcium carbonate that forms their characteristic ocean homes. Bathed in warm tropical waters, the coral animals and their symbiotic algal partners evolved to survive at the upper limit of ocean water temperature.
Together, climate change and human activity pose dual threats to the long-term survival of the world’s coral reefs. As global warming due to fossil fuel emissions raises ocean temperatures, coral reefs are suffering. The excessive warmth causes the reefs to expel their symbiotic, food-producing algae, resulting in a phenomenon known as bleaching. When bleaching occurs, the reefs lose much of their characteristic color as the algae and the coral animals die if loss of the symbiotic zooxanthellae is prolonged.
Rising levels of atmospheric carbon dioxide further threaten the corals in other ways; as CO 2 dissolves in ocean waters, it lowers the pH and increases ocean acidity. As acidity increases, it interferes with the calcification that normally occurs as coral animals build their calcium carbonate homes.
When a coral reef begins to die, species diversity plummets as animals lose food and shelter. Coral reefs are also economically important tourist destinations, so the decline of coral reefs poses a serious threat to coastal economies.
Human population growth has damaged corals in other ways, too. As human coastal populations increase, the runoff of sediment and agricultural chemicals has increased, too, causing some of the once-clear tropical waters to become cloudy. At the same time, overfishing of popular fish species has allowed the predator species that eat corals to go unchecked.
Although a rise in global temperatures of 1–2˚C (a conservative scientific projection) in the coming decades may not seem large, it is very significant to this biome. When change occurs rapidly, species can become extinct before evolution leads to new adaptations. Many scientists believe that global warming, with its rapid (in terms of evolutionary time) and inexorable increases in temperature, is tipping the balance beyond the point at which many of the world’s coral reefs can recover.
Estuaries: Where the Ocean Meets Fresh Water
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity; mixing results in a diluted (brackish) saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives. Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies and is based on the rate of flow of its freshwater sources. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water.
The short-term and rapid variation in salinity due to the mixing of fresh water and salt water is a difficult physiological challenge for the plants and animals that inhabit estuaries. Many estuarine plant species are halophytes : plants that can tolerate salty conditions. Halophytic plants are adapted to deal with the salinity resulting from saltwater on their roots or from sea spray. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs. Other plants are able to pump oxygen into their roots. Animals, such as mussels and clams (phylum Mollusca), have developed behavioral adaptations that expend a lot of energy to function in this rapidly changing environment. When these animals are exposed to low salinity, they stop feeding, close their shells, and switch from aerobic respiration (in which they use gills) to anaerobic respiration (a process that does not require oxygen). When high tide returns to the estuary, the salinity and oxygen content of the water increases, and these animals open their shells, begin feeding, and return to aerobic respiration.
Freshwater Biomes
Freshwater biomes include lakes and ponds (standing water) as well as rivers and streams (flowing water). They also include wetlands, which will be discussed later. Humans rely on freshwater biomes to provide aquatic resources for drinking water, crop irrigation, sanitation, and industry. These various roles and human benefits are referred to as ecosystem services. Lakes and ponds are found in terrestrial landscapes and are, therefore, connected with abiotic and biotic factors influencing these terrestrial biomes.
Lakes and Ponds
Lakes and ponds can range in area from a few square meters to thousands of square kilometers. Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with deeper, cooler water. Light can penetrate within the photic zone of the lake or pond. Phytoplankton (small photosynthetic organisms such as algae and cyanobacteria that float in the water) are found here and carry out photosynthesis, providing the base of the food web of lakes and ponds. Zooplankton (very small animals that float in the water), such as rotifers and small crustaceans, consume these phytoplankton. At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom.
Nitrogen and phosphorus are important limiting nutrients in lakes and ponds. Because of this, they are determining factors in the amount of phytoplankton growth in lakes and ponds. When there is a large input of nitrogen and phosphorus (from sewage and runoff from fertilized lawns and farms, for example), the growth of algae skyrockets, resulting in a large accumulation of algae called an algal bloom . Algal blooms (Figure \(\PageIndex{4}\)) can become so extensive that they reduce light penetration in water. As a result, the lake or pond becomes aphotic and photosynthetic plants rooted in the lake bottom cannot survive. When the algae die and decompose, severe oxygen depletion of the water occurs. Fishes and other organisms that require oxygen are then more likely to die, and resulting dead zones are found across the globe. Lake Erie and the Gulf of Mexico represent freshwater and marine habitats where phosphorus control and storm water runoff pose significant environmental challenges.
Rivers and Streams
Rivers and streams are continuously moving bodies of water that carry large amounts of water from the source, or headwater, to a lake or ocean. The largest rivers include the Nile River in Africa, the Amazon River in South America, and the Mississippi River in North America.
Abiotic features of rivers and streams vary along the length of the river or stream. Streams begin at a point of origin referred to as source water. The source water is usually cold, low in nutrients, and clear. The channel (the width of the river or stream) is narrower than at any other place along the length of the river or stream. Because of this, the current is often faster here than at any other point of the river or stream.
The fast-moving water results in minimal silt accumulation at the bottom of the river or stream, therefore the water is clear. Photosynthesis here is mostly attributed to algae that are growing on rocks; the swift current inhibits the growth of phytoplankton. An additional input of energy can come from leaves or other organic material that falls into the river or stream from trees and other plants that border the water. When the leaves decompose, the organic material and nutrients in the leaves are returned to the water. Plants and animals have adapted to this fast-moving water. For instance, leeches (phylum Annelida) have elongated bodies and suckers on both ends. These suckers attach to the substrate, keeping the leech anchored in place. Freshwater trout species (phylum Chordata) are an important predator in these fast-moving rivers and streams.
As the river or stream flows away from the source, the width of the channel gradually widens and the current slows. This slow-moving water, caused by the gradient decrease and the volume increase as tributaries unite, has more sedimentation. Phytoplankton can also be suspended in slow-moving water. Therefore, the water will not be as clear as it is near the source. The water is also warmer. Worms (phylum Annelida) and insects (phylum Arthropoda) can be found burrowing into the mud. The higher order predator vertebrates (phylum Chordata) include waterfowl, frogs, and fishes. These predators must find food in these slow moving, sometimes murky, waters and, unlike the trout in the waters at the source, these vertebrates may not be able to use vision as their primary sense to find food. Instead, they are more likely to use taste or chemical cues to find prey.
Wetlands
Wetlands are environments in which the soil is either permanently or periodically saturated with water. Wetlands are different from lakes because wetlands are shallow bodies of water that may periodically dry out. Emergent vegetation consists of wetland plants that are rooted in the soil but have portions of leaves, stems, and flowers extending above the water’s surface. There are several types of wetlands including marshes, swamps, bogs, mudflats, and salt marshes (Figure \(\PageIndex{5}\)).
Contributors and Attributions
- Biology by OpenStax is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher.