7.3: Stress in Earth's Crust
INTRODUCTION
Enormous slabs of lithosphere move unevenly over the planet’s spherical surface, resulting in earthquakes. This chapter deals with two types of geological activity that occur because of plate tectonics: mountain building and earthquakes. First, we will consider what can happen to rocks when they are exposed to stress.
CAUSES AND TYPES OF STRESS
Stress is the force applied to an object. In geology, stress is the force per unit area that is placed on a rock. Four types of stresses act on materials.
Figure 1. Stress caused these rocks to fracture.
- A deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform. This is called confining stress.
- Compression squeezes rocks together, causing rocks to fold or fracture (break) (figure 1). Compression is the most common stress at convergent plate boundaries.
- Rocks that are pulled apart are under tension . Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries.
- When forces are parallel but moving in opposite directions, the stress is called shear (figure 2). Shear stress is the most common stress at transform plate boundaries.
When stress causes a material to change shape, it has undergone strain or deformation . Deformed rocks are common in geologically active areas.
Figure 2. Shearing in rocks. The white quartz vein has been elongated by shear.
A rock’s response to stress depends on the rock type, the surrounding temperature, and pressure conditions the rock is under, the length of time the rock is under stress, and the type of stress.
Rocks have three possible responses to increasing stress (illustrated in figure 3):
- elastic deformation : the rock returns to its original shape when the stress is removed.
- plastic deformation : the rock does not return to its original shape when the stress is removed.
- fracture : the rock breaks.
Figure 3. With increasing stress, the rock undergoes: (1) elastic deformation, (2) plastic deformation, and (3) fracture.
Under what conditions do you think a rock is more likely to fracture? Is it more likely to break deep within Earth’s crust or at the surface? What if the stress applied is sharp rather than gradual?
- At the Earth’s surface, rocks usually break quite quickly, but deeper in the crust, where temperatures and pressures are higher, rocks are more likely to deform plastically.
- Sudden stress, such as a hit with a hammer, is more likely to make a rock break. Stress applied over time often leads to plastic deformation.
GEOLOGIC STRUCTURES
Sedimentary rocks are important for deciphering the geologic history of a region because they follow certain rules.
- Sedimentary rocks are formed with the oldest layers on the bottom and the youngest on top.
- Sediments are deposited horizontally, so sedimentary rock layers are originally horizontal, as are some volcanic rocks, such as ash falls.
- Sedimentary rock layers that are not horizontal are deformed.
You can trace the deformation a rock has experienced by seeing how it differs from its original horizontal, oldest-on-bottom position (figure 4a). This deformation produces geologic structures such as folds, joints, and faults that are caused by stresses (figure 4b). Using the rules listed above, try to figure out the geologic history of the geologic column below.
Figure 4. (a) In the Grand Canyon, the rock layers are exposed like a layer cake. Each layer is made of sediments that were deposited in a particular environment – perhaps a lake bed, shallow offshore region, or a sand dune. (b) In this geologic column of the Grand Canyon, the sedimentary rocks of the “Layered Paleozoic Rocks” column (layers 1 through 11) are still horizontal. Grand Canyon Supergroup rocks (layers 12 through 15) have been tilted. Vishnu Basement Rocks are not sedimentary (rocks 16 through 18). The oldest layers are on the bottom and youngest are on the top.
Folds
Rocks deforming plastically under compressive stresses crumple into folds (figure 5). They do not return to their original shape. If the rocks experience more stress, they may undergo more folding or even fracture.
Figure 5. Snow accentuates the fold exposed in these rocks in Provo Canyon, Utah.
Three types of folds are seen.
-
Mononcline: A
monocline
is a simple bend in the rock layers so that they are no longer horizontal (see figure 6 for an example).
Figure 6. At Colorado National Monument, the rocks in a monocline plunge toward the ground. -
Anticline: An
anticline
is a fold that arches upward. The rocks dip away from the center of the fold (figure 7). The oldest rocks are at the center of an anticline and the youngest are draped over them.
Figure 7. (a) Schematic of an anticline. (b) An anticline exposed in a road cut in New Jersey.
When rocks arch upward to form a circular structure, that structure is called a dome. If the top of the dome is sliced off, where are the oldest rocks located?
-
Syncline: A
syncline
is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (figure 8).
When rocks bend downward in a circular structure, that structure is called a basin (figure 9). If the rocks are exposed at the surface, where are the oldest rocks located?
Figure 9. Basins can be enormous. This is a geologic map of the Michigan Basin, which is centered in the state of Michigan but extends into four other states and a Canadian province.
Faults
A rock under enough stress will fracture. If there is no movement on either side of a fracture, the fracture is called a joint , as shown in (figure 10).
Figure 10. Granite rocks in Joshua Tree National Park showing horizontal and vertical jointing. These joints formed when the confining stress was removed from the granite.
If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault (figure 11). Sudden motions along faults cause rocks to break and move suddenly. The energy released is an earthquake.
Figure 11. Faults are easy to recognize as they cut across bedded rocks.
Slip is the distance rocks move along a fault. Slip can be up or down the fault plane. Slip is relative, because there is usually no way to know whether both sides moved or only one. Faults lie at an angle to the horizontal surface of the Earth. That angle is called the fault’s dip. The dip defines which of two basic types a fault is. If the fault’s dip is inclined relative to the horizontal, the fault is a dip-slip fault (figure 12). There are two types of dip-slip faults. In normal faults , the hanging wall drops down relative to the footwall. In reverse faults , the footwall drops down relative to the hanging wall.
Figure 12. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a resource along a fault. The hanging wall is where miners would have hung their lanterns. The footwall is where they would have walked.
Here is an animation of a normal fault.
A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults ( Figure 13).
Figure 13. At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks. How could this happen?
Here is an animation of a thrust fault.
Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress (figure 14).
Figure 14. The Teton Range in Wyoming rose up along a normal fault.
A strike-slip fault is a dip-slip fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses (figure 15).
Figure 15. Imagine placing one foot on either side of a strike-slip fault. One block moves toward you. If that block moves toward your right foot, the fault is a right-lateral strike-slip fault; if that block moves toward your left foot, the fault is a left-lateral strike-slip fault.
California’s San Andreas Fault is the world’s most famous strike-slip fault. It is a right-lateral strike slip fault (figure 16).
Figure 16. The San Andreas is a massive transform fault.
Here is a strike-slip fault animation.
People sometimes say that California will fall into the ocean someday, which is not true. This animation shows movement on the San Andreas into the future.
STRESS AND MOUNTAIN BUILDING
Two converging continental plates smash upwards to create mountain ranges (figure 17). Stresses from this uplift cause folds, reverse faults, and thrust faults, which allow the crust to rise upwards.
Figure 17. (a) The world’s highest mountain range, the Himalayas, is growing from the collision between the Indian and the Eurasian plates. (b) The crumpling of the Indian and Eurasian plates of continental crust creates the Himalayas.
Subduction of oceanic lithosphere at convergent plate boundaries also builds mountain ranges (figure 18).
Figure 18. The Andes Mountains are a chain of continental arc volcanoes that build up as the Nazca Plate subducts beneath the South American Plate.
When tensional stresses pull crust apart, it breaks into blocks that slide up and drop down along normal faults. The result is alternating mountains and valleys, known as a basin-and-range (figure 19).
Figure 19. (a) In basin-and-range, some blocks are uplifted to form ranges, known as horsts, and some are down-dropped to form basins, known as grabens. (b) Mountains in Nevada are of classic basin-and-range form.
This is a very quick animation of movement of blocks in a basin-and-range setting.
LESSON SUMMARY
- Stress is the force applied to a rock and may cause deformation. The three main types of stress are typical of the three types of plate boundaries: compression at convergent boundaries, tension at divergent boundaries, and shear at transform boundaries.
- Where rocks deform plastically, they tend to fold. Brittle deformation brings about fractures and faults.
- The two main types of faults are dip-slip (the fault plane is inclined to the horizontal) and strike-slip (the fault plane is perpendicular to the horizontal).
- The world’s largest mountains grow at convergent plate boundaries, primarily by thrust faulting and folding.
REFLECTION QUESTIONS
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Contributors and Attributions
-
Original content from Kimberly Schulte (Columbia Basin College) and supplemented by Lumen Learning . The content on this page is copyrighted under a Creative Commons Attribution 4.0 International license.


36.4: Appendix E - Edge Runners program
To recognize the work, leadership, determination, and contributions of nurses who are at the forefront of innovations in population health, the American Academy of Nursing (AAN, 2023) created the Edge Runners program. The AAN annually recognizes nurse-designed models of care that reduce cost, improve care quality, promote health equity, and increase client satisfaction. Table E1 lists population health programs across care areas that were invented by nurses. Please note, the table is a comprehensive listing as of June 2023.
| Program Name | Nurse Innovators |
|---|---|
| 10 Steps to Promote and Protect Human Milk and Breastfeeding in Vulnerable Infants | Diane L. Spatz PhD, RN-BC, FAAN |
| 11th Street Family Health Services | Patricia Gerrity PhD, RN, FAAN |
| A Caring Science Model of Specialized Dementia Care for Transforming Practice and Advancing Health Equity | María de los Ángeles Ortega (formerly Ordóñez), DNP, APRN, GNP-BC, PMHNP-BC, CDP, FAANP, FAAN |
| Accountable Community of Health | Billie Lynn Allard, MS, RN |
| The Aging in Place Project | Marilyn Rantz, PhD, RN, FAAN |
| The American Association of Critical Care Nurses (AACN) Clinical Scene Investigator (CSI) Academy | Karen Cox, PhD, RN, FAAN; Susan R. Lacey, PhD, RN, FAAN |
| Angel Eye Web-Camera System | Sarah Rhoads, PhD, DNP, WHNP-BC |
| Arkansas Aging Initiative | Claudia J. Beverly, PhD, RN, FAAN |
| Canines Providing Assistance to Wounded Warriors (C-P.A.W.W.) | Cheryl Krause-Parello, PhD, RN, FAAN |
| Caregiver Skill Building Intervention (CSBI) | Carol J. Farran, DNSc, RN, FAAN |
| Center for Midwifery – CU College of Nursing | Jessica Anderson, DNP, CNM, WHNP, FACNM |
| Centering Healthcare Institute | Sharon Schindler Rising, CNM, MSN |
| The Chicago Parent Program | Deborah Gross, DNSc, RN, FAAN; Susan Breitenstein, PhD, RN, FAAN; Christine Garvey, PhD, RN; Wrenetha Julion, PhD, MPH, RN, FAAN |
| Collaborative Alliance for Nursing Outcomes | Nancy Donaldson, DNS, RN, FAAN; Diane Storer Brown, PhD, RN, FNAHQ, FAAN |
| Collaborative KMC Care Model | John N. Cranmer, DNP, MPH, MSN, BSN, ANP, CPH, EBP(CH); Lynn M. Sibley, CNM, RN, PhD, FACNM, FAAN; Abebe Gebremariam Gobezayehu, MD; Lamesgin Alamnih, BSc, MPH; Mulusew Lijalem Belew, MHS, BS, AD |
| Community Aging in Place: Advancing Better Living for Elders (CAPABLE) | Sarah Szanton, PhD, ANP, FAAN |
| Community-Based Smoking Cessation Program (CSCP) | Man Ping Wang, PhD, MPH, MPhil, BNurs, RN, FAAN |
| Community Health Education, Advocacy, and Empowerment: Promotores de la Salud | Connie Vance, EdD, RN, FAAN; Mary Healey-Sedutto, MPA, PhD |
| Complex Care Center | Lauran Hardin, MSN, RN-BC, CNL |
| Coping Skills Training | Margaret Grey, DrPH, RN, FAAN |
| Creating Opportunities for Parent Empowerment (COPE) | Bernadette Mazurek Melnyk, PhD, RN, CPNP/PMHNP, FAAN, FNAP |
| Creating Opportunities for Personal Empowerment (COPE) for Children, Teens, and College-Age Students | Bernadette Mazurek Melnyk, PhD, RN, CPNP/PMHNP, FAAN, FNAP |
| ¡Cuídate! | Antonia M. Villaruel, PhD, FAAN; Loretta Sweet Jemmott, PhD, RN, FAAN |
| Danger Assessment: An Instrument to Help Abused Women Assess Their Risk of Homicide | Jacquelyn Campbell, PhD, RN, FAAN |
| Durham Homeless Care Transitions | Julia Gamble, MPH, NP, RN; Donna Biederman, DrPH, MN, RN, CPH, FAAN; Sally Wilson, MDiv |
| Fall Tailoring Interventions for Patient Safety (TIPS) | Patricia C. Dykes PhD, MA, RN, FAAN, FACMI; Ann Hurley, DNSc FAAN, FGSA; Diane Carroll, PhD, RN, FAAN, FAHA, FESC |
| Family Health and Birth Center in the Developing Families Center | Ruth Watson Lubic, EdD, RN, CNM, FAAN |
| Family Practice and Counseling Network | Donna Torrisi, MSN, CRNP |
| Family Presence During Invasive Procedures and Cardiopulmonary Resuscitation | Cathie Guzzetta, PhD, RN, FAAN; Angela Clark, PhD, RN, FAAN, FAHA |
| Families Talking Together | Vincent Guilamo-Ramos, PhD, MPH, LCSW, RN, ANP-BC, PMHNP-BC, FAAN |
| Farm Dinner Theatre | Deborah B. Reed, PhD, MSPH, RN, FAAOHN, FAAN |
| The Harambee Nursing Center | Kay T. Roberts, EdD, MSN, ARNP, FAAN |
| The Harriet Lane Compassionate Care Program | Cynda Hylton Rushton, PhD, RN, FAAN |
| Immersion Model for Diversifying Nurse Anesthesia Programs | Wallena Gould, EdD, CRNA, FAANA, FAAN |
| Improving the Accuracy of Linear Growth Assessment in Children | Terri Lipman, PhD, CRNP, FAAN; Karen D. Hench, MS, RN |
| INSIGHTS into Children's Temperament | Sandee McClowry, PhD, RN, FAAN |
| Integrated Health Care (IHC) | Judith Storfjell, PhD, RN, FAAN |
| Interprofessional Practice at the Vine School Health Center: A School-Based Nurse-Managed Clinic | Nan M. Gaylord, PhD, RN, CPNP- PC, PMHS, FAANP, FAAN |
| Kentucky Racing Health Services Center | Whitney Nash, PhD, APRN; Sara Robertson, DNP, APRN, FNP |
| Living Independently for Elders Center (LIFE) | Eileen M. Sullivan-Marx, PhD, RN, FAAN |
| Los trastornos del sueño y la promoción del sueño saludable [Sleep disorders and the promotion of healthy sleep] | Carol M. Baldwin, PhD, RN, CHTP, CT, AHN-BC, FAAN; Cipriana Caudillo Cisneros, MS, RN; Luxana Reynaga Ornelas, PhD, MSN, RN |
| Making Transitional Care More Effective & Efficient | Mary D. Naylor, PhD, RN, FAAN |
| Mantram Repetition Program: Mind-Body-Spiritual Approach to Symptom and Stress Management | Jill E. Bormann, PhD, RN, FAAN |
| Marquette Model of Natural Family Planning and Fertility Awareness Based Method | Richard J. Fehring, PhD, RN, FAAN; Mary Schneider, PhD, APRN, FNP-BC; Susana Crespo, BSN, RN, NFPI; MaryLee (Kiene) Barron, PhD, APRN, FNP-BC; Qiyan Mu, PhD, RN; Thomas Bouchard, MD, Family Medicine; Kathleen Raviele, MD, Ob/Gyn |
| Mental Health Integration at Intermountain Healthcare, UT | Brenda Reiss-Brennan, PhD, APRN |
| The Mount Sinai Primary Care Hepatitis C Clinical and Research Program | Donald Gardenier, DNP, FNP-BC, FAANP, FAAN; Jeffrey J. Weiss, PhD, MS |
| National University Nurse Managed Clinic | Gloria J. McNeal, PhD, MSN, ACNS-BC, FAAN; Arneta Finney, PhD, APRN, FNP-C, APWHc, CNL; Angela Williams, PhD, FNP-C, APRN, CNL; Patricia L. Humbles, PhD, RN (Ret.) |
| Nurse Managed Health Centers | Tine Hansen-Turton, FAAN; Joanne M. Pohl, PhD, ANP-BC, FAAN |
| Nurse-Family Partnerships Helping First-Time Parents Succeed | Harriet Kitzman, PhD, RN, FAAN |
| Nurses Improving Care for Healthsystems Elders (NICHE) | Mattia J. Gilmartin PhD, RN, FAAN; Jennifer L. Pettis, MSN, RN, CNE; Eugenia Bachaleda, MA; Louise Simon, BS, LLM, ICBB; Joanna Melendez, BS; Eileen Sullivan-Marx, PhD, RN, FAAN; Terry Fulmer, PhD, RN, FAAN |
| On Lok Senior Health Services | Jennie Chin Hansen, MS, RN, FAAN |
| One Year Post-Baccalaureate Nurse Residency | Colleen J. Goode, PhD, RN, FAAN, NEA-BC; Cathleen Krsek, MSN, MBA, RN, FAAN |
| Oral Care in Mechanically Ventilated Adults | Cindy Munro, PhD, RN, ANP-BC, FAANP, FAAN, FAAAS |
| Oral Health Nursing Education and Practice Program | Judith Haber, PhD, APRN, FAAN; Erin Hartnett, DNP, PNPPC-BC, CPNP |
| PATHways Prenatal Program and Beyond Birth Comprehensive Treatment and Recovery Program | Kristin Ashford, PhD, WHNP-BC, FAAN; John O’Brien, MD, MFM; Seth Himelhoch, MD, MPH |
| Perioperative Pressure Ulcer Prevention Program | Susan M. Scott, MSN, RN, WOCN |
| Quality Improvement Program for Missouri (QIPMO) | Marilyn J. Rantz, PhD, RN, FAAN |
| Quiet4Healthy Farm | Marjorie McCullagh, PhD, RN, APHN-BC, COHN-S, FAAOHN, FAAN |
| Reducing Depressive Symptoms & Enhancing Parenting in Low-Income & Newly-Immigrated Mothers of Infants & Toddlers | Linda S. Beeber, PhD, PMHCNS-BC, FAAN |
| RightCare Solutions | Kathryn H. Bowles, PhD, RN, FAAN, FACMI |
| Senior ASSIST | Diane McGee, MSN, RN |
| SeniorWISE | Graham J. McDougall, Jr., PhD, RN, FAAN, FGSA |
| Special Care Unit for the Critically Ill | Barbara Daly, PhD, RN, FAAN |
| Suicide Prevention in Nursing: Breaking the Silence | Judy E. Davidson, DNP, RN, MCCM, FAAN |
| Talking Circle Intervention | John Lowe, PhD, RN, FAAN |
| TelEmergency: Distance Emergency Care Using Nurse Practitioners | Kristi Henderson, MSN, FAEN |
| Tobacco Free Nurses | Linda Sarna, PhD, RN, FAAN; Stella Aguinaga Bialous, DrPH, RN, FAAN |
| Training in the Assessment of Depression | Ellen L. Brown, EdD, RN |
| Transforming Care at the Bedside | Susan B. Hassmiller, PhD, RN, FAAN; Patricia Rutherford, MS, RN |
| Transforming the Alzheimer's Experience with an App: Dementia Guide Expert | Valerie Gruss, PD, APRN, GNP-BC, FAAN |
| Transforming Post-Hospitalization, Newborn Circumcision Care Through a Nurse Practitioner-Led Care Delivery Model | Vivian W. Williams, MSN, RN, CPN |
| UCLA Alzheimer’s and Dementia Care (ADC) Program | Leslie Chang Evertson, GNP-BC; Mihae Kim, AGPCNP-BC; Michelle Panlilio, GNP-BC; Kelsey Stander, AGNP-BC |
| Wise Health Decisions | Nancy E. Dayhoff, EdD, RN, CNS; Patricia S. Moore, MSN, RN, CNS, CDE |


7.4: Verismo
Verismo, which in this context means “realism,” is the name for a movement that arose in opera near the end of the 19th century. Composers of versimo operas chose realisting settings, often depicting the struggles and drama of common people. In this they were reacting against the grandiosity and mythological focus of Romanticism. Verismo, like Impressionism, is part of the transition from the Romantic to the Modern era and could justifiably be studied as part of either period. Just as we studied Beethoven in the Classical era and Schubert in the Romantic era, we will examine verismo opera (and one of its greatest practitioners, Giacomo Puccini) in our study of the Romantic period and Impressionism in our study of the 20th century.
Introduction
In opera, verismo (meaning “realism,” from Italian vero , meaning “true”) was a post-Romantic operatic tradition associated with Italian composers such as Pietro Mascagni, Ruggero Leoncavallo, Umberto Giordano and Giacomo Puccini.
Verismo as an operatic genre had its origins in an Italian literary movement also called ‘verismo’ (see Verismo (literature)). The Italian literary movement of verismo , in turn, was related to the international literary movement of Naturalism as practiced by Émile Zola and others. Like naturalism, the verismo literary movement sought to portray the world with greater realism. In so doing, Italian verismo authors such as Giovanni Verga wrote about subject matter, such as the lives of the poor, that had not generally been seen as a fit subject for literature. A short story by Verga called Cavalleria rusticana (“Rustic Chivalry”), then developed into a play by the same author, became the source for what is usually considered to be the first verismo opera: Cavalleria rusticana by Mascagni, which premiered on 17 May 1890 at the Teatro Costanzi in Rome. Thus begun, the operatic genre of verismo produced a handful of notable works such as Pagliacci , which premiered at Teatro Dal Verme in Milan on 21 May 1892, and Puccini’s Tosca (premiering at the Teatro Costanzi in Rome on 14 January 1900.) The genre peaked in the early 1900s, and lingered into the 1920s.
In terms of subject matter, generally “[v]erismo operas focused not on gods, mythological figures, or kings and queens, but on the average contemporary man and woman and their problems, generally of a sexual romantic, or violent nature.” However, two of the small handful of verismo operas still performed today take historical subjects: Puccini’s Tosca and Giordano’s Andrea Chénier. “Musically, verismo composers consciously strove for the integration of the opera’s underlying drama with its music.” These composers abandoned the “recitative and set-piece structure” of earlier Italian opera. Instead, the operas were “through-composed,” with few breaks in a seamlessly integrated sung text. While verismo operas may contain arias that can be sung as stand-alone pieces, they are generally written to arise naturally from their dramatic surroundings, and their structure is variable, being based on text that usually does not follow a regular strophic format.
The most famous composers who created works in the verismo style were Giacomo Puccini, Pietro Mascagni, Ruggero Leoncavallo, Umberto Giordano and Francesco Cilea. There were, however, many other veristi : Franco Alfano, Alfredo Catalani, Gustave Charpentier ( Louise ), Eugen d’Albert ( Tiefland ), Ignatz Waghalter ( Der Teufelsweg and Jugend ), Alberto Franchetti, Franco Leoni, Jules Massenet ( La Navarraise ), Licinio Refice, Ermanno Wolf-Ferrari ( I gioielli della Madonna ), and Riccardo Zandonai.
The term verismo can cause confusion. In addition to referring to operas written in a realistic style, the term may also be used more broadly to refer to the entire output of the composers of the giovane scuola (“young school”), the generation of composers who were active in Italy during the period that the verismo style was created. One author (Alan Mallach) has proposed the term “plebian opera” to refer to operas that adhere to the contemporary and realistic subject matter for which the term verismo was originally coined. At the same time, Mallach questions the value of using a term such as verismo , which is supposedly descriptive of the subject and style of works, simply to identify an entire generation’s music-dramatic output. For most of the composers associated with verismo , traditionally veristic subjects accounted for only some of their operas. For instance, Mascagni wrote a pastoral comedy ( L’amico Fritz ), a symbolist work set in Japan ( Iris ), and a couple of medieval romances ( Isabeau and Parisina ). These works are far from typical verismo subject matter, yet they are written in the same general musical style as his more quintessential veristic subjects. In addition, there is disagreement among musicologists as to which operas are “verismo” operas, and which are not. (Non-Italian operas are generally excluded). Giordano’s Andrea Chénier , Mascagni’s Cavalleria rusticana , Leoncavallo’s Pagliacci , and Puccini’s Tosca and Il tabarro are operas to which the term verismo is applied with little or no dispute. The term is sometimes also applied to Puccini’s Madama Butterfly and La fanciulla del West . Because only three verismo works not by Puccini continue to appear regularly on stage (the aforementioned Cavalleria rusticana , Pagliacci , and Andrea Chénier ), Puccini’s contribution has had lasting significance to the genre.
Some authors have attempted to trace the origins of verismo opera to works that preceded Cavalleria rusticana, such as Georges Bizet’s Carmen , or Giuseppe Verdi’s La traviata .
Verismo Singers
The verismo opera style featured music that required singers to more declamatory singing, in contrast to the traditional tenets of elegant, 19th century bel canto singing that had preceded the movement. Opera singers adapted to the demands of the new style. The most extreme exponents of verismo vocalism sang habitually in a vociferous fashion, often forfeiting legato to focus on the passionate aspect of the music. They would ‘beef up’ the timbre of their voices, use excessive amounts of vocal fold mass on their top notes, and often employ a conspicuous vibrato in order to accentuate the emotionalism of their ardent interpretations. The results could be exciting in the theatre but such a strenuous mode of singing was not a recipe for vocal longevity. Some prominent practitioners of full-throttle verismo singing during the movement’s Italian lifespan (circa 1890 to circa 1930) include the sopranos Eugenia Burzio, Rosina Storchio and Adelaide Saraceni, the tenors Aureliano Pertile, Cesar Vezzani and Amadeo Bassi, and the baritones Mario Sammarco and Eugenio Giraldoni. Their method of singing can be sampled on numerous 78-rpm gramophone recordings. See Michael Scott’s two-volume survey The Record of Singing , published in London by Duckworth in 1977/79, for an evaluation of most of these singers, and others of their Ilk, and a discussion of the adverse impact that verismo music had on singing standards in Italy.
Such great early-20th century international operatic stars as Enrico Caruso, Rosa Ponselle and Titta Ruffo developed vocal techniques which harmoniously managed to combine fundamental bel canto precepts with a more ‘modern,’ straightforward mode of ripe-toned singing when delivering verismo music, and their example has influenced operatic performers down to this day (see Scott).
Contributors and Attributions
- Authored by : Elliott Jones. Provided by : Santa Ana College. Located at : http://www.sac.edu . License : CC BY: Attribution
- Verismo (music). Provided by : Wikipedia. Located at : http://en.Wikipedia.org/wiki/Verismo_(music) . License : CC BY-SA: Attribution-ShareAlike


14.4D: Plasmids and Lysogeny
- Distinguish between plasmids and lysogeny in regards to pathogenecity
Plasmids
Plasmids are DNA molecules that are capable of replicating independently from the chromosomal DNA. Plasmids are often characterized by their circular appearance and double-strands; they also vary in size and number. Plasmids are present in the three major domains (Archaea, Bacteria and Eukarya) and are considered to be ‘naked DNA’. ‘Naked DNA’ refers to a specific type of DNA which does not encode for genes promoting the transfer of genetic material to a new host. The plasmids are present within the cells as extra chromosomal genomes and are a common tool used in molecular biology to integrate new DNA into a host. In the field of molecular biology, plasmid DNA is often referred to as ‘ vectors ‘ due to their ability to transfer DNA between organisms. The use of plasmid DNA in molecular biology is considered to be recombinant DNA technology. In addition, plasmid DNA provides a mechanism by which horizontal gene transfer can occur, contributing to antibiotic resistance.
Horizontal gene transfer is a major mechanism promoting bacterial antibiotic resistance, as the plasmid DNA can transfer genes from one species of bacteria to another. The plasmid DNA which is transferred often has developed genes that encode for resistance against antibiotics. The ability to transfer this resistance from one species to another is increasingly becoming an issue in clinics for treatment of bacterial infections. The process of horizontal gene transfer can occur via three mechanisms: transformation, transduction and conjugation. Plasmid DNA transfer is associated with conjugation as the host-to-host transfer requires direct mechanical transfer. The advantages of plasmid DNA transfer allow for survival advantages.
Lysogeny
Lysogeny is the process by which a bacteriophageintegrates its nucleic acids into a host bacterium’s genome. Lysogeny is utilized by viruses to ensure the maintenance of viral nucleic acids within the genome of the bacterium host. The virus displays the ability to infect the bacterium host and integrate its own genetic materials into the host bacterium genome. The bacteriophages newly integrated genetic material, called a prophage, is transferred to new bacterial daughter cells upon cell division. The prophage is integrated into the bacterium genome at this point. The lysogenic cycle is key to ensure the transmittance of bacteriophage nucleic acids to host bacterium’s genome. Lysogeny is one of two major methods of viral reproduction utilized by viruses.
Lysogenic cycles are utilized by specific types of viruses to ensure viral reproduction, but they also need the second major method of viral reproduction, the lytic cycle, as well. The lytic cycle, considered the primary method of viral replication, results in the actual destruction of the infected cell. Upon destruction of the infected cell, the new viruses, which have developed after undergoing biosynthesis and maturation, are free to infect other cells. The lytic cycle is characterized by the breakdown of the bacteria cell wall intracellularly. The viruses cause disruption of the bacterial cell by producing enzymes which facilitate this process. An example of a virus which can promote the transformation of bacterium from a nontoxic to toxic strain via lysogeny is the CTXφ virus. Specifically, the bacterium, Vibrio cholerae , is transformed into a toxic strain upon infection with the bacteriophage. This bacterium is then able to produce a cholera toxin, the cause of the disease cholera.
Key Points
- Plasmids are double-stranded circular forms of ‘naked DNA ‘.
- Plasmids are responsible for horizontal gene transfer which promotes the development of antibiotic resistance in bacterium.
- Lysogeny is a major method of viral reproduction characterized by the integration of viral nucleic acids in the bacterium genome.
Key Terms
- bacteriophage : A virus that specifically infects bacteria.
- lysogeny : the process by which a bacteriophage incorporates its nucleic acids into a host bacterium


Ancient History
Skills to Develop
- Distinguish physical changes from chemical changes
- Identify the three states of matter and their respective properties
- Understand some of the history behind identifying the three states of matter
- Define matter and its components (i.e. mass, weight, volume)
Humanity's first chemical knowledge was mostly technology , like metal working, ceramics, cooking, etc. Early civilizations learned to control fire, to cast metals and make alloys, to make glass and ceramics, and so forth. The first chemical thinking, as opposed to chemical applications, asked: What is matter ? Matter is stuff. It's what we are made of, what the earth and the air are made of. Matter is anything that has mass... what is mass ? It's the amount of stuff. Not how much space it occupies (that's volume ) but how much stuff is there. We measure mass using weight , which is how strongly the stuff in question is attracted to the earth by gravity.
What is matter made of? Well, one philosopher of ancient Greece proposed that all matter is made of water . He observed that water can "become air" by evaporation , or become solid by freezing into ice. He reasoned therefore that water can convert into everything, and matter is made of water. Now, we call those changes physical changes . The water is still water when it boils and turns into steam. The water is still water when it freezes into ice. We changed its temperature , not its nature.
Another Greek philosopher said that everything was made of air : when air becomes less compressed, it becomes fire, and when more compressed, it turns into water, stones, and so forth. He offered the proof that when you breathe through open lips, the air is warm, and when you compress it by breathing through puckered lips, it's cold, and condenses into liquid or solid. Air turning into stone would be a chemical change , in modern terms. In terms of Dalton's Atomic Theory, a chemical change means that the atoms form new combinations, like one atom of A combining with an atom of B. Before A and B were separate, but now they are attached. That's a chemical change.
Others proposed 5 elements, with distinct shapes: octahedra , tetrahedra , cubes , etc. For a long while, the four element model (earth, air, fire, water) was popular. (In Greece it was proposed by a man who was asked to become king of his city, but created a democracy instead. Then he declared himself a god and jumped into a volcano. It's said that the volcano tossed back his sandals to prove he wasn't a god.) This model, which Plato and Aristotle also used, suggested that all matter was composed of these four elements in different ratios. For instance, when wood is burned, you get smoke (air), ash (earth), pitch (a viscous liquid, here identified with water), and fire, so wood is made of all these things. Wood burning is a great example of a chemical change.
From a modern perspective, in all these theories an important element was lacking: experimentation. The Greeks preferred thinking to trying things, and you might say that it shows in their theories. For them, the fundamental difference was what we now call the state of matter or the phase of matter . Solid , liquid and gas are the three main states of matter.
- Ice, wood and stone are all solids
- Water is a liquid, like oil
- Air is a gas, like steam, and like the gas that you use in a stove
The three states are fundamentally different in nature. Gases take up as much space as they can, in whatever shape they can: the molecules are far apart, and try to spread out. Liquids change shape but have a constant volume. Solids have a constant shape and volume. Now we know that you can change the state of matter just by changing the temperature and pressure, and the molecules stay the same. So the wrong theories of the Greeks were based on not recognizing the difference between physical changes, which are changes in the state of matter, and chemical changes, changes in the combination of atoms.
Summary
Matter is anything that has volume and mass. Mass is the amount of matter in a substance. Physical changes involve processes that change the form of a substance but not its chemical composition. Chemical changes involves processes in which a new substances are formed with new chemical compositions. Weight is the force resulting from a mass being pulled towards a particular location as a result of gravity. The three states of matter are: solid, liquid, and gas. A solid is an object with a fixed shape and volume. Liquids are fluids have a constant volume but are capable of changing their shape. Gases are fluids that do not have constant shape or volume so they take up as much space as they can within a given container.


29.2: Electrocyclic Reactions
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- Steven Farmer, Dietmar Kennepohl, William Reusch, & Kevin M. Shea
- University of Illinois Springfield
An electrocyclic reaction is the concerted cyclization of a conjugated π-electron system by converting one π-bond to a ring forming σ-bond. The key sigma bond must be formed at the terminus of a pi system. These reactions classified by the number of pi electrons involved. Thus, 4 pi reactions form 4 membered rings, as in a conjugated diene can being converted into a cyclobutene. Also, 6 pi reactions form 6 membered rings as in a conjugated triene can be converted into a cyclohexadiene. These reactions are often reversible with the r everse reaction may be called electrocyclic ring opening . Although more more pi electrons can be used, the 4 pi and 6 pi variants are by far the most common and are illustrated below with the key sigma bond highlighted in magenta.
A striking feature of electrocyclic reactions that proceed by concerted mechanisms is their high degree of stereospecificity. For example, 2- trans, 4-cis, 6-trans -2,4,6-octatriene undergoes ring closure to cis -5,6-dimethyl-1,3-cyclohexadiene under thermal conditions i.e. when heated. Similarly the isomeric 2- trans, 4-cis, 6-cis -2,4,6-octatriene produces trans -5,6-dimethyl-1,3-cyclohexadiene, as noted below. However these results are completely reversed if the reaction is run under photochemical conditions (Irradiation with ultraviolet light). For example if 2- trans, 4-cis, 6-cis -2,4,6-octatriene is irradiated with UV light cis -5,6-dimethyl-1,3-cyclohexadiene would be produced.
Similar results are seen with the 4 pi electrocyclic reaction of cis , trans -2,4-hexadiene being heated to exclusively form cis -3,4-dimethylcyclobutene and being irradiated with UV light to exclusively form trans -3,4-dimethylcyclobutene. Likewise, trans , trans -2,4-hexadiene forms trans -3,4-dimethylcyclobutene when heated and cis -3,4-dimethylcyclobutene when being irradiated with UV light.
The stereospecificity of electrocyclic reaction can be explained by considering the terminal lobes of the molecular orbital fo the conjugated π-electron system. For electrocyclic reactions of occur, molecular orbital lobes with the same sign from the HOMO of the molecule must rotate to form/break the key ring sigma bond. If the orbital lobes involved both rotate in the same direction (both counterclockwise or both clockwise), the process is called conrotatory. This typically occurs when orbital lobes of the same sign are on opposite sides of the molecule.
If the orbitals involved rotate in opposite directions (one clockwise and one counterclockwise), the process is called disrotatory. These differences in rotation are critically important when stereocenters are formed or broken. This typically occurs when orbital lobes of the same sign are on the same side of the molecule.


7.4: Photosynthesis and the Importance of Light
- Describe the function and locations of photosynthetic pigments in eukaryotes and prokaryotes
- Describe the major products of the light-dependent and light-independent reactions
- Describe the reactions that produce glucose in a photosynthetic cell
- Compare and contrast cyclic and noncyclic photophosphorylation
Heterotrophic organisms ranging from E. coli to humans rely on the chemical energy found mainly in carbohydrate molecules. Many of these carbohydrates are produced by photosynthesis, the biochemical process by which phototrophic organisms convert solar energy (sunlight) into chemical energy. Although photosynthesis is most commonly associated with plants, microbial photosynthesis is also a significant supplier of chemical energy, fueling many diverse ecosystems. In this section, we will focus on microbial photosynthesis.
Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light-independent reactions (Figure \(\PageIndex{1}\)). In the light-dependent reactions, energy from sunlight is absorbed by pigment molecules in photosynthetic membranes and converted into stored chemical energy. In the light-independent reactions, the chemical energy produced by the light-dependent reactions is used to drive the assembly of sugar molecules using CO 2 ; however, these reactions are still light dependent because the products of the light-dependent reactions necessary for driving them are short-lived. The light-dependent reactions produce ATP and either NADPH or NADH to temporarily store energy. These energy carriers are used in the light-independent reactions to drive the energetically unfavorable process of “fixing” inorganic CO 2 in an organic form, sugar.
Photosynthetic Structures in Eukaryotes and Prokaryotes
In all phototrophic eukaryotes, photosynthesis takes place inside a chloroplast, an organelle that arose in eukaryotes by endosymbiosis of a photosynthetic bacterium. These chloroplasts are enclosed by a double membrane with inner and outer layers. Within the chloroplast is a third membrane that forms stacked, disc-shaped photosynthetic structures called thylakoids (Figure \(\PageIndex{2}\)). A stack of thylakoids is called a granum, and the space surrounding the granum within the chloroplast is called stroma.
Photosynthetic membranes in prokaryotes, by contrast, are not organized into distinct membrane-enclosed organelles; rather, they are infolded regions of the plasma membrane. In cyanobacteria, for example, these infolded regions are also referred to as thylakoids. In either case, embedded within the thylakoid membranes or other photosynthetic bacterial membranes are photosynthetic pigment molecules organized into one or more photosystems, where light energy is actually converted into chemical energy.
Photosynthetic pigments within the photosynthetic membranes are organized into photosystems, each of which is composed of a light-harvesting (antennae) complex and a reaction center. The light-harvesting complex consists of multiple proteins and associated pigments that each may absorb light energy and, thus, become excited. This energy is transferred from one pigment molecule to another until eventually (after about a millionth of a second) it is delivered to the reaction center. Up to this point, only energy—not electrons—has been transferred between molecules. The reaction center contains a pigment molecule that can undergo oxidation upon excitation, actually giving up an electron. It is at this step in photosynthesis that light energy is converted into an excited electron.
Different kinds of light-harvesting pigments absorb unique patterns of wavelengths (colors) of visible light. Pigments reflect or transmit the wavelengths they cannot absorb, making them appear the corresponding color. Examples of photosynthetic pigments (molecules used to absorb solar energy) are bacteriochlorophylls (green, purple, or red), carotenoids (orange, red, or yellow), chlorophylls (green), phycocyanins (blue), and phycoerythrins (red). By having mixtures of pigments, an organism can absorb energy from more wavelengths. Because photosynthetic bacteria commonly grow in competition for sunlight, each type of photosynthetic bacteria is optimized for harvesting the wavelengths of light to which it is commonly exposed, leading to stratification of microbial communities in aquatic and soil ecosystems by light quality and penetration.
Once the light harvesting complex transfers the energy to the reaction center, the reaction center delivers its high-energy electrons, one by one, to an electron carrier in an electron transport system, and electron transfer through the ETS is initiated. The ETS is similar to that used in cellular respiration and is embedded within the photosynthetic membrane. Ultimately, the electron is used to produce NADH or NADPH. The electrochemical gradient that forms across the photosynthetic membrane is used to generate ATP by chemiosmosis through the process of photophosphorylation, another example of oxidative phosphorylation (Figure \(\PageIndex{3}\)).
In a phototrophic eukaryote, where does photosynthesis take place?
Oxygenic and Anoxygenic Photosynthesis
For photosynthesis to continue, the electron lost from the reaction center pigment must be replaced. The source of this electron (H 2 A) differentiates the oxygenic photosynthesis of plants and cyanobacteria from anoxygenic photosynthesis carried out by other types of bacterial phototrophs (Figure \(\PageIndex{4}\)). In oxygenic photosynthesis, H 2 O is split and supplies the electron to the reaction center. Because oxygen is generated as a byproduct and is released, this type of photosynthesis is referred to as oxygenic photosynthesis. However, when other reduced compounds serve as the electron donor, oxygen is not generated; these types of photosynthesis are called anoxygenic photosynthesis. Hydrogen sulfide (H 2 S) or thiosulfate (S2O2−3) can serve as the electron donor, generating elemental sulfur and sulfate (SO2−4) ions, respectively, as a result.
Photosystems have been classified into two types: photosystem I (PSI) and photosystem II (PSII) (Figure \(\PageIndex{5}\)). Cyanobacteria and plant chloroplasts have both photosystems, whereas anoxygenic photosynthetic bacteria use only one of the photosystems. Both photosystems are excited by light energy simultaneously. If the cell requires both ATP and NADPH for biosynthesis, then it will carry out noncyclic photophosphorylation. Upon passing of the PSII reaction center electron to the ETS that connects PSII and PSI, the lost electron from the PSII reaction center is replaced by the splitting of water. The excited PSI reaction center electron is used to reduce NADP + to NADPH and is replaced by the electron exiting the ETS. The flow of electrons in this way is called the Z-scheme.If a cell’s need for ATP is significantly greater than its need for NADPH, it may bypass the production of reducing power through cyclic photophosphorylation. Only PSI is used during cyclic photophosphorylation; the high-energy electron of the PSI reaction center is passed to an ETS carrier and then ultimately returns to the oxidized PSI reaction center pigment, thereby reducing it.
Why would a photosynthetic bacterium have different pigments?
Light-Independent Reactions
After the energy from the sun is converted into chemical energy and temporarily stored in ATP and NADPH molecules (having lifespans of millionths of a second), photoautotrophs have the fuel needed to build multicarbon carbohydrate molecules, which can survive for hundreds of millions of years, for long-term energy storage. The carbon comes from CO 2 , the gas that is a waste product of cellular respiration.
The Calvin-Benson cycle (named for Melvin Calvin [1911–1997] and Andrew Benson [1917–2015]), the biochemical pathway used for fixation of CO 2 , is located within the cytoplasm of photosynthetic bacteria and in the stroma of eukaryotic chloroplasts. The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration.
- Fixation : The enzyme ribulose bisphosphate carboxylase (RuBisCO) catalyzes the addition of a CO 2 to ribulose bisphosphate (RuBP). This results in the production of 3-phosphoglycerate (3-PGA).
- Reduction : Six molecules of both ATP and NADPH (from the light-dependent reactions) are used to convert 3-PGA into glyceraldehyde 3-phosphate (G3P). Some G3P is then used to build glucose.
- Regeneration : The remaining G3P not used to synthesize glucose is used to regenerate RuBP, enabling the system to continue CO 2 fixation. Three more molecules of ATP are used in these regeneration reactions.
The Calvin cycle is used extensively by plants and photoautotrophic bacteria, and the enzyme RuBisCO is said to be the most plentiful enzyme on earth, composing 30%–50% of the total soluble protein in plant chloroplasts. 1 However, besides its prevalent use in photoautotrophs, the Calvin cycle is also used by many nonphotosynthetic chemoautotrophs to fix CO 2 . Additionally, other bacteria and archaea use alternative systems for CO 2 fixation. Although most bacteria using Calvin cycle alternatives are chemoautotrophic, certain green sulfur photoautotrophic bacteria have been also shown to use an alternative CO 2 fixation pathway.
Describe the three stages of the Calvin cycle.
Although there is a DNA test specific for Neisseria meningitidis , it is not practical for use in some developing countries because it requires expensive equipment and a high level of expertise to perform. The hospital in Banjul was not equipped to perform DNA testing. Biochemical testing, however, is much less expensive and is still effective for microbial identification.
Fortunately for Hannah, her symptoms began to resolve with antibiotic therapy. Patients who survive bacterial meningitis often suffer from long-term complications such as brain damage, hearing loss, and seizures, but after several weeks of recovery, Hannah did not seem to be exhibiting any long-term effects and her behavior returned to normal. Because of her age, her parents were advised to monitor her closely for any signs of developmental issues and have her regularly evaluated by her pediatrician.
N. meningitidis is found in the normal respiratory microbiota in 10%–20% of the human population.[2] In most cases, it does not cause disease, but for reasons not fully understood, the bacterium can sometimes invade the bloodstream and cause infections in other areas of the body, including the brain. The disease is more common in infants and children, like Hannah.
The prevalence of meningitis caused by N. meningitidis is particularly high in the so-called meningitis belt, a region of sub-Saharan African that includes 26 countries stretching from Senegal to Ethiopia (Figure 8.27). The reasons for this high prevalence are not clear, but several factors may contribute to higher rates of transmission, such as the dry, dusty climate; overcrowding and low standards of living; and the relatively low immunocompetence and nutritional status of the population.[3]
A vaccine against four bacterial strains of N. meningitidis is available. Vaccination is recommended for 11- and 12-year-old children, with a booster at age 16 years. Vaccination is also recommended for young people who live in close quarters with others (e.g., college dormitories, military barracks), where the disease is more easily transmitted. Travelers visiting the “meningitis belt” should also be vaccinated, especially during the dry season (December through June) when the prevalence is highest.[4][5]
Figure \(\PageIndex{7}\) (a) Neisseria meningitidis is a gram-negative diplococcus, as shown in this gram-stained sample. (b) The “meningitis belt” is the area of sub-Saharan Africa with high prevalence of meningitis caused by N. meningitidis . Control and Prevention)
Key Concepts and Summary
- Heterotrophs depend on the carbohydrates produced by autotrophs, many of which are photosynthetic, converting solar energy into chemical energy.
- Different photosynthetic organisms use different mixtures of photosynthetic pigments , which increase the range of the wavelengths of light an organism can absorb.
- Photosystems (PSI and PSII) each contain a light-harvesting complex , composed of multiple proteins and associated pigments that absorb light energy. The light-dependent reactions of photosynthesis convert solar energy into chemical energy, producing ATP and NADPH or NADH to temporarily store this energy.
- In oxygenic photosynthesis , H 2 O serves as the electron donor to replace the reaction center electron, and oxygen is formed as a byproduct. In anoxygenic photosynthesis , other reduced molecules like H 2 S or thiosulfate may be used as the electron donor; as such, oxygen is not formed as a byproduct.
- Noncyclic photophosphorylation is used in oxygenic photosynthesis when there is a need for both ATP and NADPH production. If a cell’s needs for ATP outweigh its needs for NADPH, then it may carry out cyclic photophosphorylation instead, producing only ATP.
- The light-independent reactions of photosynthesis use the ATP and NADPH from the light-dependent reactions to fix CO 2 into organic sugar molecules.
Footnotes
- A. Dhingra et al. “Enhanced Translation of a Chloroplast-Expressed Rbc S Gene Restores Small Subunit Levels and Photosynthesis in Nuclear Rbc S Antisense Plants.” Proceedings of the National Academy of Sciences of the United States of America 101 no. 16 (2004):6315–6320.
- Centers for Disease Control and Prevention. “Meningococcal Disease: Causes and Transmission.” http://www.cdc.gov/meningococcal/abo...nsmission.html . Accessed September 12, 2016.
- Centers for Disease Control and Prevention. “Meningococcal Disease in Other Countries.” http://www.cdc.gov/meningococcal/global.html . Accessed September 12, 2016.
- Centers for Disease Control and Prevention. “Health Information for Travelers to the Gambia: Traveler View.” http://wwwnc.cdc.gov/travel/destinat...one/the-gambia . Accessed September 12, 2016.
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Centers for Disease Control and Prevention. “Meningococcal: Who Needs to Be Vaccinated?”
http://www.cdc.gov/vaccines/vpd-vac/
mening/who-vaccinate.htm. Accessed September 12, 2016.
Contributors and Attributions
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Nina Parker, (Shenandoah University), Mark Schneegurt (Wichita State University), Anh-Hue Thi Tu (Georgia Southwestern State University), Philip Lister (Central New Mexico Community College), and Brian M. Forster (Saint Joseph’s University) with many contributing authors. Original content via Openstax (CC BY 4.0; Access for free at https://openstax.org/books/microbiology/pages/1-introduction )


11.4: Special-purpose Batteries
Back in the early days of electrical measurement technology, a special type of battery known as a mercury standard cell was popularly used as a voltage calibration standard. The output of a mercury cell was 1.0183 to 1.0194 volts DC (depending on the specific design of cell), and was extremely stable over time. Advertised drift was around 0.004 percent of rated voltage per year. Mercury standard cells were sometimes known as Weston cells or cadmium cells .
Unfortunately, mercury cells were rather intolerant of any current drain and could not even be measured with an analog voltmeter without compromising accuracy. Manufacturers typically called for no more than 0.1 mA of current through the cell, and even that figure was considered a momentary , or surge maximum! Consequently, standard cells could only be measured with a potentiometric (null-balance) device where current drain is almost zero. Short-circuiting a mercury cell was prohibited, and once short-circuited, the cell could never be relied upon again as a standard device.
Mercury standard cells were also susceptible to slight changes in voltage if physically or thermally disturbed. Two different types of mercury standard cells were developed for different calibration purposes: saturated and unsaturated . Saturated standard cells provided the greatest voltage stability over time, at the expense of thermal instability. In other words, their voltage drifted very little with the passage of time (just a few microvolts over the span of a decade!), but tended to vary with changes in temperature (tens of microvolts per degree Celsius). These cells functioned best in temperature-controlled laboratory environments where long-term stability is paramount. Unsaturated cells provided thermal stability at the expense of stability over time, the voltage remaining virtually constant with changes in temperature but decreasing steadily by about 100 µV every year. These cells functioned best as “field” calibration devices where ambient temperature is not precisely controlled. Nominal voltage for a saturated cell was 1.0186 volts, and 1.019 volts for an unsaturated cell.
Modern semiconductor voltage (zener diode regulator) references have superseded standard cell batteries as laboratory and field voltage standards.
A fascinating device closely related to primary-cell batteries is the fuel cell , so-called because it harnesses the chemical reaction of combustion to generate an electric current. The process of chemical oxidation (oxygen ionically bonding with other elements) is capable of producing an electron flow between two electrodes just as well as any combination of metals and electrolytes. A fuel cell can be thought of as a battery with an externally supplied chemical energy source.
To date, the most successful fuel cells constructed are those which run on hydrogen and oxygen, although much research has been done on cells using hydrocarbon fuels. While “burning” hydrogen, a fuel cell’s only waste byproducts are water and a small amount of heat. When operating on carbon-containing fuels, carbon dioxide is also released as a byproduct. Because the operating temperature of modern fuel cells is far below that of normal combustion, no oxides of nitrogen (NO x ) are formed, making it far less polluting, all other factors being equal.
The efficiency of energy conversion in a fuel cell from chemical to electrical far exceeds the theoretical Carnot efficiency limit of any internal-combustion engine, which is an exciting prospect for power generation and hybrid electric automobiles.
Another type of “battery” is the solar cell , a by-product of the semiconductor revolution in electronics. The photoelectric effect , whereby electrons are dislodged from atoms under the influence of light, has been known in physics for many decades, but it has only been with recent advances in semiconductor technology that a device existed capable of harnessing this effect to any practical degree. Conversion efficiencies for silicon solar cells are still quite low, but their benefits as power sources are legion: no moving parts, no noise, no waste products or pollution (aside from the manufacture of solar cells, which is still a fairly “dirty” industry), and indefinite life.
Specific cost of solar cell technology (dollars per kilowatt) is still very high, with little prospect of significant decrease barring some kind of revolutionary advance in technology. Unlike electronic components made from semiconductor material, which can be made smaller and smaller with less scrap as a result of better quality control, a single solar cell still takes the same amount of ultra-pure silicon to make as it did thirty years ago. Superior quality control fails to yield the same production gain seen in the manufacture of chips and transistors (where isolated specks of impurity can ruin many microscopic circuits on one wafer of silicon). The same number of impure inclusions does little to impact the overall efficiency of a 3-inch solar cell.
Yet another type of special-purpose “battery” is the chemical detection cell . Simply put, these cells chemically react with specific substances in the air to create a voltage directly proportional to the concentration of that substance. A common application for a chemical detection cell is in the detection and measurement of oxygen concentration. Many portable oxygen analyzers have been designed around these small cells. Cell chemistry must be designed to match the specific substance(s) to be detected, and the cells do tend to “wear out,” as their electrode materials deplete or become contaminated with use.
Review
- mercury standard cells are special types of batteries which were once used as voltage calibration standards before the advent of precision semiconductor reference devices.
- A fuel cell is a kind of battery that uses a combustible fuel and oxidizer as reactants to generate electricity. They are promising sources of electrical power in the future, “burning” fuels with very low emissions.
- A solar cell uses ambient light energy to motivate electrons from one electrode to the other, producing voltage (and current, providing an external circuit).
- A chemical detection cell is a special type of voltaic cell which produces voltage proportional to the concentration of an applied substance (usually a specific gas in ambient air).


6.4: Language, Community, and Culture
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- Jennifer Hasty, David G. Lewis, & Marjorie M. Snipes
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Learning Objectives
By the end of this section, you will be able to:
- Explain the role of culture in the acquisition of language.
- Describe how language can form the foundation of sociocultural groups in speech communities.
- Describe how people code-switch among speech communities.
While language is critical to individual human thought, its basic function is to communicate messages in human communities. That is, language is fundamentally social. Through social interaction, humans learn the language of their community. And through language, humans express community identity and coordinate their activities.
 What would you do?
Likely, you’d start by teaching the baby your language. Without language, it’s pretty hard to teach rules and values (unless you are a really good mime). Luckily, babies come into the world with special cognitive abilities that make them ready to learn language. Most babies undergo a rapid process of language learning between the ages of nine months and three years. Babies proceed through a set of stages that allow them to learn language just by being exposed to surrounding talk. Many scholars study the problem of language acquisition , examining precisely how humans manage to learn language in a diversity of sociocultural contexts.
So your babbling baby would probably learn language just by being exposed to it. But what if someone wanted to hasten the process or make sure their baby was particularly excellent with language?
An American would probably interact with the baby in a particular way, sitting the baby on their lap facing them, pointing to objects and asking basic questions in a quiz-like fashion. “See the cookie? Where did the cookie go? In my tummy!” The person might say these types of things while talking in a high-pitched, sing-song voice. Linguists call this type of talk “motherese.” In many other cultures, caregivers do not interact with babies in this way. In some cultures, oversimplified “baby talk” is considered detrimental to language learning. The context of language learning might involve a whole host of characters beyond the baby and the caregiver, encompassing all household relatives, neighbors, visitors, and even strangers. Language is not always “taught” to babies, but is often witnessed and overheard.  In West Africa, babies spend large parts of the day wrapped on the backs of their mothers where face-to-face interaction with her is impossible. But they overhear the talk around them all day long, and people frequently engage their attention in brief interactions. In the field of language socialization , researchers go beyond the various stages of language learning to focus on the social contexts in which language is acquired. As social contexts shape the way children learn language, language itself becomes a means of learning about sociocultural life.
Whether facing their caregivers or facing out to the social world around them, babies in all cultures learn to be proficient in their languages. And yet, in American culture, the notion persists that language proficiency relies on very precise forms of interaction between caregiver and baby, the American model of motherese. Every culture has specific ideas about language, how it is acquired, how it varies across social groups, how it changes over time, etc. These ideas are termed language ideologies . Some of these ideas, like the notion that babies have a special “window” of opportunity for learning language, are supported by linguistic research. Others, however, are challenged by ethnographic and cross-cultural research.
Speech Communities and Code Switching
A ten-year-old girl described one of her stuffed animals as “derpy.” Here is a snippet of her conversation with her mother:
Thisbe: Look at his face. He’s so derpy.
Jennifer: Derpy? I don’t know that word. What does it mean?
 Kind of dumb.
Jennifer: Oh, ok. Like Clover [our dog], when she fell off the couch. Was that derpy?
Thisbe: No, that’s not derpy! It’s like ... Mom, I just can’t explain it to you. You just have to know.
All speakers of a particular language form a hypothetical community, sharing a common grammar and vocabulary, as well as a set of understandings about how language is used in different situations. Within this large group are smaller groups of speakers who use the common language in special ways unique to that group. Anthropologists use the term speech community to describe such a group (Muehlmann 2014). Speech communities often have distinctive vocabularies, grammatical forms, and intonation patterns. Using these features appropriately, members of the speech community demonstrate their membership in the group.
The concept of speech community was originally used to describe the distribution of dialects in a language. A dialect is a form of language specific to a particular region. For instance, in the Philadelphia metropolitan area, it’s common for local people to pronounce the word “water” as “woohder,” as if it nearly rhymes with the word “order.” It’s also common to use the phrase “yooz” for the second-person plural (as in, “Yooz better drink some woohder!”). Linguists William Labov, Sharon Ash, and Charles Boberg famously mapped out these dialectical differences in different regions of the United States (2006). Over time, a dialect can accumulate such unique linguistic features that it develops into a separate language. Indeed, the distinction between a well-developed dialect and a language is largely political. Nation-states may downplay regional differences as mere dialects in order to maintain linguistic unity, while separatist political movements may champion their way of speaking as an entirely different language in order to justify their demands for independence.
Other researchers have focused on the speech communities of ethnic groups and immigrants. Researchers use the term vernacular to describe dialects that are not necessarily regional but associated with specific social categories, such as groups based on ethnicity, age, or gender. Anthropological research on African American Vernacular English (AAE), Chicano English, and Native American English have all shown how these vernaculars shape distinctive forms of storytelling, arguing, and criticism (Chun and Lo 2015). Rather than seeing ethnic vernaculars as “incorrect” forms of English, researchers demonstrate how vernaculars like AAE are highly structured linguistic systems with regular grammatical patterns and innovative vocabularies (Labov 1972a). In formal settings like American classrooms and courtrooms, these alternative ways of using English are too often stigmatized as lazy, unintelligent, or just plain wrong. Believing their own English to be the “correct” form, authority figures often forbid the use of alternative vernaculars of English and refuse to engage in any effort to understand those forms.
More recent research on vernaculars has explored how speakers maneuver among the styles of language they encounter in their daily lives, engaging in various languages, dialects, vernaculars, and other elements of style. We all use a variety of linguistic styles, and many speak more than one language. Addressing different audiences, U.S. President Barack Obama used linguistic strategies to “Whiten,” “Blacken,” “Americanize,” and “Christianize” his public identity, thus subverting racial stereotypes and indicating his membership in a diversity of communities (Alim and Smitherman 2012). In parts of the world that were previously colonized by Europeans, European languages have been maintained as the formal language of government and education even as most people speak local languages in their everyday interactions with kin, neighbors, merchants, and other community members. In these postcolonial contexts, people tack back and forth between various styles of their local languages as well as shifting between the local language and the European one. Such strategic maneuvering among linguistic styles, called code-switching , is done by people in many difference contexts.
For many people, the style of language spoken in elite settings such as schools and government institutions has the effect of disempowering and marginalizing them. Linguistic anthropologists examine how vernaculars associated with elite and professional groups become a means of in-group solidarity and out-group exclusion. Anthropologist and lawyer Elizabeth Mertz (2007) conducted participant observation in first-year classes at several American law schools, looking at how law students are taught to “think like a lawyer.” Using a version of the Socratic method, law professors teach their students to set aside the moral and emotional elements of cases to view them purely as texts subject to abstract, professional analysis. The ability to master the linguistic maneuvering and arcane vocabulary of this form of analysis becomes a prerequisite for becoming a lawyer. The American justice system is thus dominated by people who are trained to set aside humanistic concerns in favor of textual authority and manipulation. Mertz’s study shows how people are socialized by language throughout their lives, not just in childhood. And it alerts us to the way that language can be used to elevate the learned perspectives of elites, dismissing the moral and emotional perspectives of others.


11.3: Sexual Reproduction
- Explain that meiosis and sexual reproduction are evolved traits
- Identify variation among offspring as a potential evolutionary advantage to sexual reproduction
- Describe the three different life-cycle types among sexual multicellular organisms and their commonalities
Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. It appears to have been very successful because most eukaryotes are able to reproduce sexually, and in many animals, it is the only mode of reproduction.  On the surface, creating offspring that are genetic clones of the parent appears to be a better system. If the parent organism is successfully occupying a habitat, offspring with the same traits would be similarly successful. There is also the obvious benefit to an organism that can produce offspring whenever circumstances are favorable by asexual budding, fragmentation, or asexual eggs. These methods of reproduction do not require another organism of the opposite sex. Indeed, some organisms that lead a solitary lifestyle have retained the ability to reproduce asexually. In addition, in asexual populations, every individual is capable of reproduction. In sexual populations, the males are not producing the offspring themselves, so in theory an asexual population could grow twice as fast.
However, multicellular organisms that exclusively depend on asexual reproduction are exceedingly rare. Why is sexuality (and meiosis) so common? This is one of the important unanswered questions in biology and has been the focus of much research beginning in the latter half of the twentieth century. There are several possible explanations, one of which is that the variation that sexual reproduction creates among offspring is very important to the survival and reproduction of the population. Thus, on average, a sexually reproducing population will leave more descendants than an otherwise similar asexually reproducing population. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms, but in addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes and the genes are mixed into different combinations by crossovers during prophase I and random assortment at metaphase I.
It is not in dispute that sexual reproduction provides evolutionary advantages to organisms that employ this mechanism to produce offspring.  Variation is the outcome of sexual reproduction, but why are ongoing variations necessary? Enter the Red Queen hypothesis, first proposed by Leigh Van Valen in 1973. 1 The concept was named in reference to the Red Queen's race in Lewis Carroll's book, Through the Looking-Glass.
All species co-evolve with other organisms; for example predators evolve with their prey, and parasites evolve with their hosts. Each tiny advantage gained by favorable variation gives a species an edge over close competitors, predators, parasites, or even prey. The only method that will allow a co-evolving species to maintain its own share of the resources is to also continually improve its fitness. As one species gains an advantage, this increases selection on the other species; they must also develop an advantage or they will be outcompeted. No single species progresses too far ahead because genetic variation among the progeny of sexual reproduction provides all species with a mechanism to improve rapidly. Species that cannot keep up become extinct. The Red Queen’s catchphrase was, “It takes all the running you can do to stay in the same place.” This is an apt description of co-evolution between competing species.
Life Cycles of Sexually Reproducing Organisms
Fertilization and meiosis alternate in sexual life cycles . What happens between these two events depends on the organism. The process of meiosis reduces the chromosome number by half. Fertilization, the joining of two haploid gametes, restores the diploid condition. There are three main categories of life cycles in multicellular organisms: diploid-dominant , in which the multicellular diploid stage is the most obvious life stage, such as with most animals including humans; haploid-dominant , in which the multicellular haploid stage is the most obvious life stage, such as with all fungi and some algae; and alternation of generations , in which the two stages are apparent to different degrees depending on the group, as with plants and some algae.
Diploid-Dominant Life Cycle
Nearly all animals employ a diploid-dominant life-cycle strategy in which the only haploid cells produced by the organism are the gametes. Early in the development of the embryo, specialized diploid cells, called germ cells , are produced within the gonads, such as the testes and ovaries. Germ cells are capable of mitosis to perpetuate the cell line and meiosis to produce gametes. Once the haploid gametes are formed, they lose the ability to divide again. There is no multicellular haploid life stage. Fertilization occurs with the fusion of two gametes, usually from different individuals, restoring the diploid state (Figure \(\PageIndex{1}\)).
Haploid-Dominant Life Cycle
Most fungi and algae employ a life-cycle type in which the “body” of the organism—the ecologically important part of the life cycle—is haploid. The haploid cells that make up the tissues of the dominant multicellular stage are formed by mitosis. During sexual reproduction, specialized haploid cells from two individuals, designated the (+) and (−) mating types, join to form a diploid zygote. The zygote immediately undergoes meiosis to form four haploid cells called spores. Although haploid like the “parents,” these spores contain a new genetic combination from two parents. The spores can remain dormant for various time periods. Eventually, when conditions are conducive, the spores form multicellular haploid structures by many rounds of mitosis (Figure \(\PageIndex{2}\)).
Alternation of Generations
The third life-cycle type, employed by some algae and all plants, is a blend of the haploid-dominant and diploid-dominant extremes. Species with alternation of generations have both haploid and diploid multicellular organisms as part of their life cycle. The haploid multicellular plants are called gametophytes , because they produce gametes from specialized cells. Meiosis is not directly involved in the production of gametes in this case, because the organism that produces the gametes is already a haploid. Fertilization between the gametes forms a diploid zygote. The zygote will undergo many rounds of mitosis and give rise to a diploid multicellular plant called a sporophyte . Specialized cells of the sporophyte will undergo meiosis and produce haploid spores. The spores will subsequently develop into the gametophytes (Figure \(\PageIndex{3}\)).
Although all plants utilize some version of the alternation of generations, the relative size of the sporophyte and the gametophyte and the relationship between them vary greatly. In plants such as moss, the gametophyte organism is the free-living plant, and the sporophyte is physically dependent on the gametophyte. In other plants, such as ferns, both the gametophyte and sporophyte plants are free-living; however, the sporophyte is much larger. In seed plants, such as magnolia trees and daisies, the gametophyte is composed of only a few cells and, in the case of the female gametophyte, is completely retained within the sporophyte.
Sexual reproduction takes many forms in multicellular organisms. However, at some point in each type of life cycle, meiosis produces haploid cells that will fuse with the haploid cell of another organism. The mechanisms of variation—crossover, random assortment of homologous chromosomes, and random fertilization—are present in all versions of sexual reproduction. The fact that nearly every multicellular organism on Earth employs sexual reproduction is strong evidence for the benefits of producing offspring with unique gene combinations, though there are other possible benefits as well.
 The variation introduced into the reproductive cells by meiosis appears to be one of the advantages of sexual reproduction that has made it so successful. Meiosis and fertilization alternate in sexual life cycles. The process of meiosis produces unique reproductive cells called gametes, which have half the number of chromosomes as the parent cell. Fertilization, the fusion of haploid gametes from two individuals, restores the diploid condition. Thus, sexually reproducing organisms alternate between haploid and diploid stages. However, the ways in which reproductive cells are produced and the timing between meiosis and fertilization vary greatly. There are three main categories of life cycles: diploid-dominant, demonstrated by most animals; haploid-dominant, demonstrated by all fungi and some algae; and the alternation of generations, demonstrated by plants and some algae.

- Sexual reproduction involves fewer steps.
- There is a lower chance of using up the resources in a given environment.
- Sexual reproduction results in variation in the offspring.
- Sexual reproduction is more cost-effective.
- Answer
-
Answer: C
Which type of life cycle has both a haploid and diploid multicellular stage?
- asexual
- diploid-dominant
- haploid-dominant
- alternation of generations
- Answer
-
Answer: D
Fungi typically display which type of life cycle?
- diploid-dominant
- haploid-dominant
- alternation of generations
- asexual
- Answer
-
Answer: B
A diploid, multicellular life-cycle stage that gives rise to haploid cells by meiosis is called a ________.
- sporophyte
- gametophyte
- spore
- gamete
- Answer
-
Answer: A
Free Response
List and briefly describe the three processes that lead to variation in offspring with the same parents.
- Answer
-
Answer: a. Crossover occurs in prophase I between non-sister homologous chromosomes. Segments of DNA are exchanged between maternally derived and paternally derived chromosomes, and new gene combinations are formed. b. Random alignment during metaphase I leads to gametes that have a mixture of maternal and paternal chromosomes. c. Fertilization is random, in that any two gametes can fuse.
Compare the three main types of life cycles in multicellular organisms and give an example of an organism that employs each.
- Answer
-
Answer: a. In the haploid-dominant life cycle, the multicellular stage is haploid. The diploid stage is a spore that undergoes meiosis to produce cells that will divide mitotically to produce new multicellular organisms. Fungi have a haploid-dominant life cycle. b. In the diploid-dominant life cycle, the most visible or largest multicellular stage is diploid. The haploid stage is usually reduced to a single cell type, such as a gamete or spore. Animals, such as humans, have a diploid-dominant life cycle. c. In the alternation of generations life cycle, there are both haploid and diploid multicellular stages, although the haploid stage may be completely retained by the diploid stage. Plants have a life cycle with alternation of generations.
Art Connections
Figure \(\PageIndex{2}\): If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce?
- Answer
-
Answer: Yes, it will be able to reproduce asexually.
Footnotes
- 1 Leigh Van Valen, “A New Evolutionary Law,” Evolutionary Theory 1 (1973): 1–30
Glossary
- alternation of generations
- life-cycle type in which the diploid and haploid stages alternate
- diploid-dominant
- life-cycle type in which the multicellular diploid stage is prevalent
- haploid-dominant
- life-cycle type in which the multicellular haploid stage is prevalent
- gametophyte
- a multicellular haploid life-cycle stage that produces gametes
- germ cells
- specialized cell line that produces gametes, such as eggs or sperm
- life cycle
- the sequence of events in the development of an organism and the production of cells that produce offspring
- sporophyte
- a multicellular diploid life-cycle stage that produces haploid spores by meiosis
Contributors and Attributions
-
Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at<EMAIL_ADDRESS>).


25.6.0: Review Questions
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Review Questions
1 .
Tendons provide what component of musculoskeletal structure?
-
joining of two or more muscles
-
connection of ligaments and muscles
-
attachment of bone to muscle
-
linking vertebrae together
2 .
The hip has what type of joint?
-
plane joint
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saddle joint
-
pivot joint
-
ball-and-socket joint
3 .
A nurse is caring for a 6-year-old child who has a history of bleeding, bruising, and fatigue. The child may have what type of disorder?
-
electrolyte
-
bone marrow
-
cardiovascular
-
adrenal
4 .
The new graduate nurse recalls what number of cardinal signs of inflammation?
-
three
-
four
-
five
-
six
5 .
A nurse notices a patient’s knees creak with bending. This will be documented as what finding?
-
dislocation
-
crepitus
-
impaired ROM
-
asymmetry
6 .
An older woman has experienced spontaneous fractures. The nurse associates what disorder as a probable contributor to her bone weakness?
-
hip dysplasia
-
scoliosis
-
sarcopenia
-
osteoporosis
7 .
A nurse recommends what action for a patient concerned about sarcopenia-related frailty?
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reducing protein intake
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swimming more often
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thrice weekly stair-stepper
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high-carbohydrate diet
8 .
A nurse is caring for a patient who has had surgical repair of a fractured right radius. The nurse notices the right forearm is edematous and firm. What should be the nurse’s first action?
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Notify the charge nurse immediately.
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Call the surgeon about possible infection.
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Document the normal findings.
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Palpate for a radial pulse.
9 .
When reviewing a student nurse’s planned documentation of a postoperative hip replacement patient, the nurse will reassure the student the CMS assessment includes what item?
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bowel sounds
-
capillary refill
-
level of consciousness
-
urinary output
10 .
The atlas rests on what spinal structure?
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spinous process
-
intervertebral disk
-
vertebral foramen
-
second cervical vertebra
11 .
Flatback syndrome is characterized by a loss of what normal spinal curve?
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kyphotic curve
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lordotic curve
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cervical curve
-
sacral curve
12 .
The occurrence of gout is associated with what abnormal laboratory test?
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hyperuricemia
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hypophosphatemia
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hypernatremia
-
hypomagnesemia
13 .
Ankylosing spondylitis is an inflammatory arthritic disorder with a potential for causing what diagnosis of the eye?
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macular degeneration
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retinal detachment
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anterior uveitis
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astigmatism


18.4B: Distribution of Blood
Humans have a closed cardiovascular system, meaning that blood never leaves the network of arteries, veins, and capillaries.
- List the components of blood flow distribution
Key Points
- In humans, blood is pumped from the strong left ventricle of the heart through arteries to peripheral tissues and returns to the right atrium of the heart through veins.
- After blood returns to the right atrium, it enters the right ventricle and is pumped through the pulmonary artery to the lungs, then returns to the left atrium through the pulmonary veins. Blood then enters the left ventricle to be circulated through the systemic circulation again.
- The closing of blood vessels is termed vasoconstriction. Vasoconstriction occurs through contraction of the muscular walls of vessels and results in increased blood pressure.
- Vasoconstriction is important for minimizing acute blood loss in the event of hemorrhage as well as retaining body heat and regulating mean arterial pressure.
- Dilation, or opening of blood vessels, is termed vasodilation. Vasodilation occurs through relaxation of smooth muscle cells within vessel walls.
- Vasodilation increases blood flow by reducing vascular resistance. Therefore, dilation of arterial blood vessels (mainly arterioles ) causes a decrease in blood pressure.
Key Terms
- vasoconstriction : The constriction of the blood vessels.
- vascular resistance : The resistance to flow that must be overcome to push blood through the circulatory system. The resistance offered by the peripheral circulation is known as the systemic vascular resistance (SVR), while the resistance offered by the vasculature of the lungs is known as the pulmonary vascular resistance (PVR).
- vasodilation : The dilation of the blood vessels.
- mean arterial pressure : The average arterial pressure during a single cardiac cycle.
Humans have a closed cardiovascular system, meaning that the blood never leaves the network of arteries, veins, and capillaries. Blood is circulated through blood vessels by the pumping action of the heart, pumped from the left ventricle through arteries to peripheral tissues and returning to the right atrium through veins. It then enters the right ventricle and is pumped through the pulmonary artery to the lungs and returns to the left atrium through the pulmonary veins. Blood then enters the left ventricle to be circulated again.
Pulmonary circuit : Diagram of pulmonary circulation. Oxygen-rich blood is shown in red; oxygen-depleted blood in blue.
Distribution of blood can be modulated by many factors, including increasing or decreasing heart rate and dilation or constriction of blood vessels.
Vasoconstriction
Blood distribution : Oxygenated arterial blood (red) and deoxygenated venous blood (blue) are distributed around the body.
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in staunching hemorrhage and acute blood loss. When blood vessels constrict, the flow of blood is restricted or decreased, thus retaining body heat or increasing vascular resistance. This makes the skin turn paler because less blood reaches the surface, reducing the radiation of heat.
On a larger level, vasoconstriction is one mechanism by which the body regulates and maintains mean arterial pressure. Substances causing vasoconstriction are called vasoconstrictors or vasopressors. Generalized vasoconstriction usually results in an increase in systemic blood pressure, but it may also occur in specific tissues, causing a localized reduction in blood flow. The extent of vasoconstriction may be slight or severe depending on the substance or circumstance.
Vasodilation
Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large veins, large arteries, and smaller arterioles. The process is essentially the opposite of vasoconstriction. When blood vessels dilate, the flow of blood is increased due to a decrease in vascular resistance. Therefore, dilation of arterial blood vessels (mainly the arterioles) causes a decrease in blood pressure. The response may be intrinsic (due to local processes in the surrounding tissue) or extrinsic (due to hormones or the nervous system). Additionally, the response may be localized to a specific organ (depending on the metabolic needs of a particular tissue, as during strenuous exercise), or it may be systemic (seen throughout the entire systemic circulation). Substances that cause vasodilation are termed vasodilators.
LICENSES AND ATTRIBUTIONS
CC LICENSED CONTENT, SHARED PREVIOUSLY
- Curation and Revision. Authored by : Boundless.com. Provided by : Boundless.com. License : CC BY-SA: Attribution-ShareAlike
CC LICENSED CONTENT, SPECIFIC ATTRIBUTION
- Anatomy and Physiology of Animals/Cardiovascular System/Blood circulation. Provided by : Wikibooks. Located at : en.wikibooks.org/wiki/Anatomy_and_Physiology_of_Animals/Cardiovascular_System/Blood_circulation . License : CC BY-SA: Attribution-ShareAlike
- Boundless. Provided by : Boundless Learning. Located at : www.boundless.com//physiology...tolic-pressure . License : CC BY-SA: Attribution-ShareAlike
- Boundless. Provided by : Boundless Learning. Located at : www.boundless.com//physiology...tolic-pressure . License : CC BY-SA: Attribution-ShareAlike
- hypotension. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/hypotension . License : CC BY-SA: Attribution-ShareAlike
- Illu pulmonary circuit. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Il...ry_circuit.jpg . License : Public Domain: No Known Copyright
- Circulatory system. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Circulatory_system . License : CC BY-SA: Attribution-ShareAlike
- Vasodilation. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Vasodilation . License : CC BY-SA: Attribution-ShareAlike
- Vein. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Vein . License : CC BY-SA: Attribution-ShareAlike
- Venoconstriction. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Venoconstriction . License : CC BY-SA: Attribution-ShareAlike
- Blood. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Blood . License : CC BY-SA: Attribution-ShareAlike
- vasodilation. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/vasodilation . License : CC BY-SA: Attribution-ShareAlike
- mean arterial pressure. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/mean%20...ial%20pressure . License : CC BY-SA: Attribution-ShareAlike
- vascular resistance. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/vascular%20resistance . License : CC BY-SA: Attribution-ShareAlike
- Illu pulmonary circuit. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Il...ry_circuit.jpg . License : Public Domain: No Known Copyright
- Blutkreislauf. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Blutkreislauf.png . License : CC BY-SA: Attribution-ShareAlike
- Illu pulmonary circuit. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Illu_pulmonary_circuit.jpg . License : Public Domain: No Known Copyright


12.4: Fugue
Introduction
In music, a fugue is a contrapuntal compositional technique in two or more voices, built on a subject (theme) that is introduced at the beginning in imitation (repetition at different pitches) and recurs frequently in the course of the composition.
The English term fugue originated in the sixteenth century and is derived from the French word fugue or the Italian fuga . This in turn comes from Latin, also fuga , which is itself related to both fugere (“to flee”) and fugare (“to chase”). The adjectival form is fugal . Variants include fughetta (literally, “a small fugue”) and fugato (a passage in fugal style within another work that is not a fugue).
A fugue usually has three sections: an exposition, a development, and finally, a recapitulation that contains the return of the subject in the fugue’s tonic key, though not all fugues have a recapitulation. In the Middle Ages, the term was widely used to denote any works in canonic style; by the Renaissance, it had come to denote specifically imitative works. Since the seventeenth century, has described what is commonly regarded as the most fully developed procedure of imitative counterpoint.
Most fugues open with a short main theme, the subject, which then sounds successively in each voice (after the first voice is finished stating the subject, a second voice repeats the subject at a different pitch, and other voices repeat in the same way); when each voice has entered, the exposition is complete. This is often followed by a connecting passage, or episode , developed from previously heard material; further “entries” of the subject then are heard in related keys. Episodes (if applicable) and entries are usually alternated until the “final entry” of the subject, by which point the music has returned to the opening key, or tonic, which is often followed by closing material, the coda. In this sense, a fugue is a style of composition, rather than a fixed structure.
Exposition
The table below illustrates the structure of the fugue exposition:
| Voice | Themes played | Themes played | Themes played | Themes played |
|---|---|---|---|---|
| Soprano | Subject | Counter subject 1 | Counter subject 2 | Answer |
| Alto | Answer | Counter subject 1 | Counter subject 2 | |
| Bass | Subject | Counter subject 1 |
Read “Forms: Contrapuntal Composition Techniques: The Fugue” here .
Listen to J. S. Bach’s, “Little” Fugue (G minor, BWV 578) below; the different colors represent the voices of the fugue. See if you can identify the subject and answers throughout the piece.
After the Exposition: Episodes, Development
Read “Forms: Contrapuntal Composition Techniques: After the Exposition” here .
Please listen to the following along with the score:
J. S. Bach, Brandenburg Concerto No. 4 , 3rd Movement, Presto
Key Terms
-
Exposition – the opening section of the fugue, ends when the theme is presented in each voice.
- Subject – the main theme of the fugue.
- Answer – subject imitated in another voice.
- Countersubject – new material in the voice in which the subject was previously stated.
- Episodes – transitions based on the exposition material.
- Development – subject and answer being developed.
Contributors and Attributions
- Revision and adaptation. Provided by : Lumen Learning and Natalia Kuznetsova. License : CC BY-SA: Attribution-ShareAlike
- Fugue. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Fugue . License : CC BY-SA: Attribution-ShareAlike
- Manuscript page from Ricercar by J.S. Bach. Located at : https://commons.wikimedia.org/wiki/File:Ricercare_a_6_from_The_Musical_Offering.jpg . License : Public Domain: No Known Copyright


18.3: Conditional Statements
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A second kind of flow control that programming languages provide is the ability to evaluate
conditional statements
. Unlike loops, which can repeat over and over again, a conditional statement only executes once, but it can switch between different possible commands depending on a CONDITION that is specified by the programmer. The power of these commands is that they allow the program itself to make choices, and in particular, to make different choices depending on the context in which the program is run. The most prominent of example of a conditional statement is the
if
statement, and the accompanying
else
statement. The basic format of an
if
statement in R is as follows:
if ( CONDITION ) {
STATEMENT1
STATEMENT2
ETC
}
And the execution of the statement is pretty straightforward. If the CONDITION is true, then R will execute the statements contained in the curly braces. If the CONDITION is false, then it dose not. If you want to, you can extend the
if
statement to include an
else
statement as well, leading to the following syntax:
if ( CONDITION ) {
STATEMENT1
STATEMENT2
ETC
} else {
STATEMENT3
STATEMENT4
ETC
}
As you’d expect, the interpretation of this version is similar. If the CONDITION is true, then the contents of the first block of code (i.e., STATEMENT1, STATEMENT2, ETC) are executed; but if it is false, then the contents of the second block of code (i.e., STATEMENT3, STATEMENT4, ETC) are executed instead.
To give you a feel for how you can use
if
and
else
to do something useful, the example that I’ll show you is a script that prints out a different message depending on what day of the week you run it. We can do this making use of some of the tools that we discussed in Section 7.11.3. Here’s the script:
## --- ifelseexample.R
# find out what day it is...
today <- Sys.Date() # pull the date from the system clock
day <- weekdays( today ) # what day of the week it is_
# now make a choice depending on the day...
if ( day == "Monday" ) {
print( "I don't like Mondays" )
} else {
print( "I'm a happy little automaton" )
}
## [1] "I'm a happy little automaton"
Since today happens to be a Sunday, when I run the script here’s what happens:
source( "./rbook-master/scripts/ifelseexample.R" )
## [1] "I'm a happy little automaton"
There are other ways of making conditional statements in R. In particular, the
ifelse()
function and the
switch()
functions can be very useful in different contexts. However, my main aim in this chapter is to briefly cover the very basics, so I’ll move on.


11.3: Quiz 2-Safety Housekeeping and Accident Prevention
TRUE OR FALSE
- True or False...Even though many jobs are different, there are common safety practices we should follow in all of them?
- True or False... No matter how much work we have to get out, sometimes we need to take "breaks" to avoid mental or physical stres
- True or False...When you are pressed for time, the best thing to do is to improvise with your tools, such as using a screwdriver as a chisel?
- True or False... It is all right to store food or drink next to chemicals, as long as the area is refrigerated
- True or False...As long as the shelving is rated for the containers' total weight, it doesn't matter what chemicals are stored next to each other?
- True or False...A dull knife is more dangerous than a sharp one?
MULTIPLE CHOICE
- The abbreviation SDS stands for…?
________ Security data storage
________ Source definition sheet.
________ Safety Data Sheet.