16.21: Putting It Together- Grammar
Grammar is made up of lots of little rules that work together to create a language. Since there are so many rules, you can’t expect to remember everything, especially not at once. No one can, not even professional writers and editors, who typically have at least three reference books and style manuals at their fingertips. Feel free to come back and reference the material taught in this modules as often as you need.
Here’s a quick recap of the parts of speech we learned about in this module:
https://lumenlearning.h5p.com/content/1290928710549160118/embed
Remember, language is always changing: new words are being created (e.g., google , selfie ), and words are changing meaning (e.g., they , literally ). This kind of change is how these are all from the same language:
- Hwæt, we gar-dena in geardagum, þeodcyninga þrym gefrunon, hu ða æþelingas ellen fremedon! ( Beowulf , the Beowulf poet, c. 700 AD)
- Thanne kam þer a Kyng: Knyȝthod hym ladde; Might of þe communes made hym to regne. ( Piers Plowman , William Langland, c. 1300 AD)
- And for myself, foe as he was to me, Might liquid tears or heart-offending groans Or blood-consuming sighs recall his life. (Henry VI, William Shakespeare, c. 1550 AD)
- Never do anything by halves if you want to get away with it. Be outrageous. Go the whole hog.  ( Matilda , Roald Dahl, 1988)
In another couple hundred years, the things we say right now will be just as incomprehensible to people as the things Shakespeare wrote are to us.
Contributors and Attributions
- Putting It Together: Grammar. Provided by : Lumen Learning. License : CC BY: Attribution
- Grammar Essentials. Provided by : Excelsior College Online Writing Lab. Located at : https://owl.excelsior.edu/grammar-essentials/parts-of-speech/parts-of-speech-putting-it-all-together/ . License : CC BY: Attribution


21.7: Loading an Array from a Text File
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Overview
Loading an array from a text file requires several steps, including: opening the file, reading the records, parsing (splitting) the records into fields, adding the fields to an array, and closing the file. The file may be read all at once and then parsed, or processed line by line. The array must either be at least as large as the number of records in the file, or must be generated dynamically.
Discussion
Loading an array from a file presents an interesting dilemma. The problem resolves around how many elements you should plan for in the array. Let’s say 100, but what if the file has fewer or more than 100 values. How can the program handle it correctly?
Either:
- Read the file and count the number of records.
- Create a static array of that size.
- Read the file again and add each record to the array.
Or:
- Read the file and dynamically add the records to the array.
Processing Records
There are two options for file processing:
- Read the entire file into memory, split the records and then process each record.
- Read the file line by line and process one record at a time.
Which of these approaches is better will depend on the size of the file and the types of file and string processing supported by your programming language. Reading the entire file at once may be faster for small files. Very large files must be processed line by line.
Processing Fields
Processing fields requires splitting records based on the given file format. For example, a comma-separated-values file might be formatted as:
Celsius,Fahrenheit 0.0,32.0 1.0,33.8 2.0,35.6
The first line contains field names separated by commas. Following lines contain a value for each of the fields, separated by commas. Note that all text file input is strings. Each line must be split on the field separator (comma), and then numeric fields must be converted to integer or floating point values for processing.
Pseudocode
Static Array Processing
Open file Read header While Not End-Of-File Read line Increment record count Close file Declare array with length based on record count Read Header While Not End-Of-File Read line Split line into field(s) Convert numeric values to numeric data types Add field(s) to array or parallel arrays Close file
Dynamic Array Processing
Declare empty array Open file Read Header While Not End-Of-File Read line Split line into field(s) Convert numeric values to numeric data types Add field(s) to array or parallel arrays Close file
Key Terms
- dynamic memory
- Aka stack created memory associated with local scope.
- static memory
- Aka data area memory associated with global scope.


17.6: Checklist for NG Suction
Use the checklist below to review the steps for completion of the “NG Suction.”
Steps
Disclaimer: Always review and follow agency policy regarding this specific skill.
- Verify the provider’s order.
- Gather supplies: nonsterile gloves.
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Perform safety steps:
- Perform hand hygiene.
- Check the room for transmission-based precautions.
- Introduce yourself, your role, the purpose of your visit, and an estimate of the time it will take.
- Confirm patient ID using two patient identifiers (e.g., name and date of birth).
- Explain the process to the patient and ask if they have any questions.
- Be organized and systematic.
- Use appropriate listening and questioning skills.
- Listen and attend to patient cues.
- Ensure the patient’s privacy and dignity.
- Assess ABCs.
- Don the appropriate PPE as indicated.
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Perform abdominal and nasogastric tube assessment:
- Assess skin integrity on the nose and ensure the tube is securely attached.
- Use a flashlight to look in the nares to assess swelling, redness, or bleeding.
- Ask the patient to open their mouth and look for curling of the tube in the patient’s mouth. The tube should go straight down into the esophagus.
- Lower the blankets and move the gown up to expose the abdomen. Inspect from two locations.
- Auscultate bowel sounds and then palpate the abdomen.
Rationale: Performing a nasogastric and abdominal assessment is important for determining signs of complications such as skin breakdown and necessity for suction.
- Don gloves.
- Attach the NG tube to the suction canister.
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Set the rate of suction according to provider order:
- Low intermittent suction is usually ordered. Low range on the suction device is from 0 to 80 mmHg. Starting between 40-60 mmHg is recommended. The suction level should not exceed 80 mmHg.
- Observe for the gastric content to flow into the tubing and then the canister.
- Monitor canister output and document color, odor, consistency, and amount.
- Perform hand hygiene.
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Ensure safety measures when leaving the room:
- CALL LIGHT: Within reach
- BED: Low and locked (in lowest position and brakes on)
- SIDE RAILS: Secured
- TABLE: Within reach
- ROOM: Risk-free for falls (scan room and clear any obstacles)
- Document the procedure and related assessment findings. Report any concerns according to agency policy.


12.1: Introduction to Probability
The probability of a specified event is the chance or likelihood that it will occur. There are several ways of viewing probability. One would be experimental in nature, where we repeatedly conduct an experiment. Suppose we flipped a coin over and over and over again and it came up heads about half of the time; we would expect that in the future whenever we flipped the coin it would turn up heads about half of the time. When a weather reporter says “there is a 10% chance of rain tomorrow,” she is basing that on prior evidence; that out of all days with similar weather patterns, it has rained on 1 out of 10 of those days.
Another view would be subjective in nature, in other words an educated guess. If someone asked you the probability that the Seattle Mariners would win their next baseball game, it would be impossible to conduct an experiment where the same two teams played each other repeatedly, each time with the same starting lineup and starting pitchers, each starting at the same time of day on the same field under the precisely the same conditions. Since there are so many variables to take into account, someone familiar with baseball and with the two teams involved might make an educated guess that there is a 75% chance they will win the game; that is, if the same two teams were to play each other repeatedly under identical conditions, the Mariners would win about three out of every four games. But this is just a guess, with no way to verify its accuracy, and depending upon how educated the educated guesser is, a subjective probability may not be worth very much.
We will return to the experimental and subjective probabilities from time to time, but in this course we will mostly be concerned with theoretical probability, which is defined as follows: Suppose there is a situation with \(n\) equally likely possible outcomes and that m of those \(n\) outcomes correspond to a particular event; then the probability of that event is defined as \(\frac{m}{n}\).


13.2: The Research Process- How to Create Sources
By the end of this section, you will be able to:
- Locate and create primary research materials.
- Apply methods and technologies used for research and communication in various fields.
Introducing Research as Evidence and Compiling Sources for an Annotated Bibliography explain the difference between primary and secondary sources in the research process. Almost all of the source-gathering information in this chapter thus far has focused on gathering secondary sources. However, your research assignment may require that you use primary sources—not only those you find in the library but also those you create yourself, outside the library, by doing field research , also called fieldwork .
Conducting Field Research
If not applicable for this class, you may be asked at some point in your college career to conduct fieldwork, which is considered primary research (the collection or development of primary sources). You may already have engaged in primary research by performing experiments in a laboratory for a science course or by documenting your observation of a musical or artistic performance.
Fieldwork is the kind of research done when a person goes out into the “field” to collect data. This term is often used by both biologists, who may observe nature to understand plant growth, and anthropologists, who observe people to understand human cultural habits. Social scientists interested in language use and development, for example, have borrowed the term fieldwork to describe the ways they collect data about how people learn or use language. In fact, fieldwork is common to subjects such as education, medicine, engineering, sociology, journalism, criminology, and advertising.
Different disciplines—and different rhetorical situations—require different kinds of fieldwork. If your task, for instance, is to find out what consumers think of a new product, you may need to create and distribute a survey or questionnaire. If you want to find out how many people stop at a certain fast-food restaurant along the highway just to use the restroom, as compared with the number of customers who purchase food, you will have to spend some time observing the location.
No matter what kind of data you collect, the way you represent your research in your written work requires careful attention to fairness and accuracy. These ideas are particularly important when you write about the people you interview or observe. The way you represent them, as well as their words and actions, may present challenges. Be aware of those challenges by considering personal biases as you write about your research participants. Finally, be considerate of interviewees’ time, and acknowledge their help by sending a follow-up email thanking them.
Planning Field Research
Unlike a library, which bundles millions of bits of every kind of information in a single location, “fields” are everywhere, including the campus of your university (academic departments, administrative offices, labs, libraries, dining and sports facilities, and dormitories) as well as the neighborhood beyond the campus (theaters, restaurants, malls, parks, playgrounds, farms, factories, schools, and so on). Field information is not cataloged, organized, indexed, or shelved for your convenience. Obtaining it requires diligence, energy, and careful planning. Some considerations are listed below:
- Think about your research question. What field sources might strengthen your argument or add to your report?
- Select your contacts and sites. Find the person, place, thing, or event that you would see as most helpful to you. Will you set up observations, conduct interviews, distribute surveys, or use a combination of methods?
- Schedule research in advance. Interviews, trips, and events don’t always work out according to plans. Allow time for glitches, such as having to reschedule an interview or return for more information.
- Do your homework. Visit the library or do a Google search before conducting extensive field research. No matter from whom or from where you intend to collect information, having background knowledge can help you make more insightful observations and formulate better interview questions.
- Log what you find. Record visits, questions, phone calls, and conversations in a research log ( https://openstax.org/r/reasearchlog ). From the very beginning of your research, enter information about topics, questions, methods, and answers into a journal, or use another record-keeping method. Record even dead-end searches to remind yourself that you tried them. This method of organizing information is the writing task for this chapter and will be discussed at length in Glance at the Research Process: Key Skills and Annotated Student Sample.
Figure \(13.5\) Biologists work in the field to gather samples for further study. (credit: “Biologists track frogs in Eastern Oregon desert” by U.S. Bureau of Land Management/Maria Thi Mai/Wikimedia Commons, CC BY 2.0)
Observation
In general, fieldwork that relies on observation as a method of data collection involves taking notes while observing events, activities, people, places, animals, and so on. Observations can range from a single visit to one event or location to several visits over an extended period. Consider your research question and topic to determine whether you need to observe over time or just once to get the information you need. You can prepare for your observation by doing some of the preliminary work in your research log. At this time, consider the limitations of only one observation session, which may yield only partial information.
As you plan for your observation, and before you arrive, decide whether you will be a participant observer , which involves taking part in what you are observing. For example, if you observed a volleyball club meeting that you attend regularly, and thus know most of its members or join in activities, you would be a participant observer. You will need to consider, though, how well you will be able to focus on the observation tasks. How actively will you participate in the group/event? While participating, how frequently will you be able to jot down notes or otherwise document your experience? Might you become distracted and forget your observation tasks, and if so, how will you handle that possibility?
Another option is to be a nonparticipant observer. In this capacity, you try to let your presence go unnoticed. Although you are there and observing, you do not influence the situation in any way. If you sat in a corner of an art class at your university to observe what materials students use, for example, you would be an unobtrusive and nonparticipant observer.
When you observe, take detailed notes; without them, you may forget much of what you observed after you leave a site. After recording your notes in your research log, review and rewrite your observation notes as soon after your site visit as possible. Take precise notes, indicating the color, shape, size, texture, and arrangement of everything relevant as applicable. Pay special attention to any anomalies you notice in a situation. Visual images provide excellent memory aids, so consider sketching, photographing, or videotaping the site you visit. If you speak your notes into a recording device, you will also pick up the characteristic sounds of the site.
Your observation notes will become very important as you begin to analyze your data. When you have finished observing, review your notes to consider them for analysis. Ask yourself what kinds of questions or conclusions your observations raise. Record your questions and conclusions in the speculations section of your research log; this material serves as your tentative interpretation of observation notes. These questions and conclusions can help direct further analysis of what you have observed and what you write based on those observations.
Your observation notes will become very important as you begin to analyze your data. When you have finished observing, review your notes to consider them for analysis. Ask yourself what kinds of questions or conclusions your observations raise. Record your questions and conclusions in the speculations section of your research log; this material serves as your tentative interpretation of observation notes. These questions and conclusions can help direct further analysis of what you have observed and what you write based on those observations.
For example, consider that you want to determine whether seating is an issue for students eating in on-campus restaurants. You might organize your observations, questions, and speculations as shown in Table \(13.2\).
| Observations |
Questions and Speculation |
| Student enters campus restaurant with friends. Friends look around for seating before rejoining student at the counter. Friends take over five minutes to find an empty table that will seat them. Both the students searching for tables and the student at the counter keep checking their watches. The time is between classes but later in the afternoon than normal lunch time: 2:30. | How many seats are available in the campus restaurant? Are students at the tables eating, studying, or both? The students appear concerned about time and the opportunity to eat as a group. |
In the “Observations” column, the writer describes, whereas in the “Questions and Speculation” column, the writer evaluates the situation. The “Questions and Speculation” section is particularly important, as different observers usually will have different interpretations. Moreover, both columns might be different at different times of the day or on different days of the week.
Surverys
Researchers in the social sciences often use surveys to collect data from a large number of individuals or from groups of people. A survey is a structured interview in which respondents are all asked the same questions and their answers are tabulated and interpreted. A survey would be a good source of data if, for example, you were comparing the eating habits of students who eat off campus with those of students who eat in college dining facilities. Or you may want to conduct research that compares the overall eating habits of students in one on-campus dining facility with those of students in another. You might ask questions such as these:
- How often do you eat at a campus facility? This question could provide several options to assist survey takers with some ranges.
- When you eat on campus, which of these dining facilities do you choose? A list of the dining facilities you are comparing would follow this question to refamiliarize survey takers with the names of the venues.
For research purposes, respondents to surveys can be treated as experts because they are being asked for opinions or information about their own behavior. Design your survey questions to be answered quickly and to generate useful information about your topic. To get this kind of information, ask questions skillfully. What and who questions are easy for respondents to answer easily and accurately. Less valuable for a survey is a why question, which requires a more thorough and planned answer. Respondents are less likely to give the proper attention to a why question for this reason. Furthermore, wording that suggests a right or wrong answer reveals the researcher’s biases more than the subject’s candid responses.
The format of the questioning and the way the research is conducted also influence responses. For example, to get complete and honest answers about a sensitive or highly personal issue, the researcher would probably use anonymous written surveys to ensure confidentiality. Other survey techniques include oral interviews in which the researcher records each subject’s responses on a written form. Surveys are usually brief in order to gain the cooperation of a sufficiently large number of respondents. To enable the researcher to compare answers, the questions are usually closed, although researchers may sometimes ask open-ended questions to gain additional information or insights. Treated briefly here, surveys involve complex procedures for the designing of questions, distribution of the survey, and assessment of the results.
A complication arises when a survey requests sensitive information, such as personal experience with drugs, alcohol, or sex, from identifiable subjects. Colleges and universities have “human subject” boards or committees that need to approve any research that could compromise the privacy of students, staff, or faculty. Consequently, consult your instructor before launching any survey on or off campus. However, the simple, informal polling of people to request opinions takes place quite often in daily college life, such as every time a class takes a vote or an instructor asks the class for opinions or interpretations of texts.
In one case, a student who was writing a self-profile wanted to find out how others perceived her. First, she listed 10 people who knew her in different ways—her mother, father, older sister, roommate, best friend, favorite teacher, and so on. Next, she invited each to list five words that best characterized her. Finally, she asked each to call her answering machine on a day when she knew she would not be home and name those five words. ln this way, she was able to collect original outside opinion (fieldwork research) in a nonthreatening manner. She then wove those opinions into her profile paper, combining them with her own self-assessment. The external points of view added an interesting (and sometimes surprising) view of herself as well as other voices to her paper.
Interviews
Conducting interviews is another method of gathering information. Consulting, interviewing, and using information gathered from professionals in specific fields can offer authoritative perspectives. Other possibilities include interviewing people who have direct experience with your research topic.
 In many respects, a good interview is simply a good conversation. If you consider yourself shy, don’t worry; you can still learn how to ask insightful interview questions that will elicit useful answers. Before conducting an interview, determine whether it is more appropriate to use a formal question-and-answer session, an informal exchange of ideas, or something in between.
Your chances of gathering helpful interview material increase dramatically when you prepare ahead of time and formulate the questions you want to ask. Consider the following guidelines:
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Select the right person. People differ in both the amount and the kind of knowledge they have. Not everyone who knows something about your research topic will be able to provide the information you need. Ask yourself
- what information you need;
- why you need it;
- who is likely to have it; and
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how you might gain it.
Most research projects benefit from more than one perspective, so plan on more than one interview. For example, to research Lake Erie pollution, you could interview someone who lives on the shore, a chemist who knows about pesticide decomposition, a vice president of a nearby paper company, and people who frequent the waterfront.
- Know your subject. Before you talk to an expert about your topic, make sure you know something about it yourself. Be prepared to explain your interest in it, know the general issues, and learn what your interview subject has already said about it in books, articles, or interviews. ln this way, you will ask sharper questions, get to the point faster, and be more interesting for your subject to talk with.
- Create a working script. A good interview doesn’t follow a script, but it usually starts with one. Before you begin an interview, write the questions you plan to ask, and arrange them so that they build on each other—general questions first, specific ones later. Your written questions can remind you to get back on track, should you or your subject digress.
- Ask both open and closed questions. Different kinds of questions elicit different kinds of information. Open questions place few limits on the answers given: Why did you decide to major in business? What are your plans for the future? Closed questions specify the information you want and usually elicit brief responses: When did you receive your degree? From what college? Open questions usually provide general information; closed questions supply details.
- Ask follow-up questions. Listen closely to the answers you receive. When the information is incomplete or confusing, ask follow-up questions to request clarification. Such questions are seldom scripted, so plan on using your wits to direct your subject toward the information you consider most important.
- Use silence. If you don’t get an immediate response to a question, wait a bit before asking another one. ln some cases, your question may not have been clear, and you will need to rephrase it. But in many cases, your interview subject is simply collecting their thoughts, not ignoring you. After a slight pause, you may hear answers worth waiting for.
- Read body language. Be aware of what your subject is doing while answering questions. Does the subject look you in the eye? Fidget and squirm? Look distracted or bored? Smile? From these visual cues, you may be able to infer when your subject is speaking most frankly, doesn’t want to give more information, or is tired of answering questions.
- Take content notes. Many interviewers take notes on a pad that is spiral bound on top and thus allows for quick page flipping. Don’t try to write down everything, just major ideas and telling statements in the subject’s own words that you might want to use as quotations in your paper. Omitting small words, focusing on the most distinctive and precise language, and using common abbreviations are all techniques to make taking notes more efficient.
- Take context notes. Note your subject’s physical appearance, facial expressions, and clothing as well as the interview setting itself. These details will be useful later when you reconstruct the interview, helping you represent it more vividly in your paper.
- Record audio with permission only. If you plan to record the interview, ask for permission in advance. The advantage of recording is that you have a complete record of the conversation. Sometimes, when hearing the interview subject a second time, you notice important things you missed earlier. However, recording devices may make subjects nervous. Be aware, too, that transcribing a recording is time consuming. It’s a good idea to have a pen in hand to catch highlights or jot down additional questions.
- Confirm important assertions. When your subject says something especially important or controversial, read back your notes aloud to check for accuracy and to allow your subject to elaborate. Some interviewers do this during the interview, while others do it at the end.
- Review your notes. Notes taken during an interview are brief reminders of what your subject has said, not complete quotations. Write out the complete information as soon after the interview as you can, certainly within 24 hours. Supplement the notes with other remembered details while they are still fresh, recording them in your research log or directly into a computer file that you can refer to as you write your paper.
- Interview electronically. It is possible, and useful, to contact individuals electronically. Phone interviews are quick and obvious ways of finding out information on short notice. Even better is asking questions via email, which is less intrusive than telephoning, as your subject can answer quickly, specifically, and in writing at a convenient time. Other electronic media for interviews include Skype, Zoom, Google Meet, and Microsoft Teams. All of these tools allow you to see the interviewee physically without having to travel for an in-person interview.


3.5: Industrial Revolution
While smallpox continued to devastate indigenous and enslaved populations, one of the reasons many Europeans had immunity to it by this time, was due to a popular medical practice called variolation . This process involved gathering fluid from smallpox pustules of a currently infected person and inoculating the next person by rubbing the material into small scratches in the skin. The purpose was to cause a milder form of the disease in the recipient which would be far less deadly. Although the workings of the human immune system were not yet understood, the process worked for the most part, although it was still risky (Contributors to Wikimedia projects, Variolation, 2023d). In 1796, an English doctor named Edward Jenner discovered that cowpox infections could provide immunity against smallpox as well. This discovery led to the development of the first vaccine - which was eventually provided freely by the English government and adopted across Europe (Contributors to Wikimedia projects, Edward Jenner, 2023g). Due to worldwide vaccination efforts over the next two centuries, the World Health Organization declared smallpox completely eradicated in 1980 (Tulchinsky & Varavikova, 2014, p. 11). The eradication of smallpox is considered one of the greatest achievements of global public health efforts.
Along with the aforementioned effects of colonization, enslavement, and westward expansion on the spread of disease, now the consequences of the industrial revolution further exacerbated disease transmission and created new health concerns. Factory jobs often utilized dangerous machinery and had little oversight to occupational safety. These same jobs brought more people into cities with crowded living quarters. In the 1830’s, Edwin Chadwick, a British Lawyer, gathered data and demonstrated the correlation between poverty, poor living conditions, and disease. He also advocated for better sanitation to prevent the spread of infectious diseases. Chadwick and others began what historians refer to as the sanitary movement - public and private efforts to improve health by improving living conditions related to clean water, plumbing, and waste removal. This prompted cities to rebuild whole neighborhoods throughout Europe and North America ( HIST 234 - Lecture 11 - The Sanitary Movement and the “Filth Theory of Disease,” n.d.).
These social determinants of health like poverty, environment, and education, have been recognized for centuries, and those who advocated for the remedies to health disparities were often considered politically radical. In 1848 there was a Typhus outbreak in a rural area among an ethnic Polish community. A young and politically active doctor, Rudolph Virchow, was tasked by the Prussian government with determining the cause of this outbreak. Although Virchow was notably obsessed with cellular pathology in his other work, he identified social, environmental and political factors as the causes of disease in his report on the Typhus outbreak. “Medicine is a social science, and politics nothing but medicine on a grand scale,” noted Virchow (Taylor & Rieger, 1985, p. 548). In his report, he advocated that diseases could be reduced with adequate employment and income, sufficient housing and sanitation, and proper nutrition. Although he disagreed with Louis Pastuer’s germ theory that bacteria were the cause of infectious diseases like typhus, we now recognize that both social-economic determinants and infectious pathogens are causal factors in outbreaks of communicable diseases. Virchow is perhaps most well-known for proposing the philosophy of health as a human right - a concept that can still seem revolutionary. A century later, it was one of the founding principles of the constitution of the World Health Organization (WHO): “The enjoyment of the highest attainable standard of health is one of the fundamental rights of every human being without distinction of race, religion, political belief, economic or social condition.” (World Health Organization, n.d.-a).
In the early 1800s a cholera epidemic broke out in India and was soon transported to Europe and North America. In London, a young doctor by the name of John Snow began one of the first epidemiological surveillance projects in 1854. Through door-to-door interviews, Snow determined that the rates of cholera were higher in specific neighborhoods. He found that the homes with higher infection rates had been provided with water by one of the water supply companies, which had an intake valve in a particularly polluted section of the Thames river. Without understanding the microorganism that causes cholera (this would not be discovered for another 20 years), he gathered sufficient evidence to convince authorities to remove the handle of the Broad Street water pump. This effectively decreased the cholera cases in those homes, demonstrating that public health actions to benefit the community could be taken even without a complete causal explanation of the disease. Snow’s actions also assisted in the discovery of waterborne pathogens, reinforced the sanitation movement, and prompted filtration requirements for public water. A replica of the Broad Street pump stands to this day as a memorial of this feat of public health (Seabert et al., 2021, Tulchinsky & Varavikova, 2014).


The topic of money management is a broad and sometimes complex one. Ultimately, personal money management involves managing both our debt and also our savings and investments.
In 2021, the average American had consumer debt balance of $96,371. Nearly $100,000 per person. And less than 25% of Americans are debt free. Consumer debt can include mortgages, credit cards, as well as student loans. A key question all consumers should consider is how to manage debt and not become overburdened by it. The first step is to create a budget, which puts earnings into perspective, indicating what we can, and cannot, afford. A budget also entails setting aside certain funds for savings and investment, which help us achieve our short- and long-term goals.


7.9A: The Role of the Cell Cycle
The cell cycle allows multiicellular organisms to grow and divide and single-celled organisms to reproduce.
LEARNING OBJECTIVES
Explain the role of the cell cycle in carrying out the cell’s essential functions
Key Takeaways
Introduction: Cell Division and Reproduction
A human, as well as every sexually-reproducing organism, begins life as a fertilized egg or zygote. Trillions of cell divisions subsequently occur in a controlled manner to produce a complex, multicellular human. In other words, that original single cell is the ancestor of every other cell in the body. Once a being is fully grown, cell reproduction is still necessary to repair or regenerate tissues. For example, new blood and skin cells are constantly being produced. All multicellular organisms use cell division for growth and the maintenance and repair of cells and tissues. Cell division is tightly regulated because the occasional failure of regulation can have life-threatening consequences. Single-celled organisms use cell division as their method of reproduction.
While there are a few cells in the body that do not undergo cell division, most somatic cells divide regularly. A somatic cell is a general term for a body cell: all human cells, except for the cells that produce eggs and sperm (which are referred to as germ cells), are somatic cells. Somatic cells contain two copies of each of their chromosomes (one copy received from each parent). Cells in the body replace themselves over the lifetime of a person. For example, the cells lining the gastrointestinal tract must be frequently replaced when constantly “worn off” by the movement of food through the gut. But what triggers a cell to divide and how does it prepare for and complete cell division?
The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produces two identical (clone) cells. The cell cycle has two major phases: interphase and the mitotic phase. During interphase, the cell grows and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated and the cell divides.
Key Points
- All multicellular organisms use cell division for growth and the maintenance and repair of cells and tissues.
- Single-celled organisms use cell division as their method of reproduction.
- Somatic cells divide regularly; all human cells (except for the cells that produce eggs and sperm) are somatic cells.
- Somatic cells contain two copies of each of their chromosomes (one copy from each parent).
- The cell cycle has two major phases: interphase and the mitotic phase.
- During interphase, the cell grows and DNA is replicated; during the mitotic phase, the replicated DNA and cytoplasmic contents are separated and the cell divides.
Key Terms
- somatic cell : any normal body cell of an organism that is not involved in reproduction; a cell that is not on the germline
- interphase : the stage in the life cycle of a cell where the cell grows and DNA is replicated
- mitotic phase : replicated DNA and the cytoplasmic material are divided into two identical cells


9.2: Hybrid Atomic Orbitals
- Explain the concept of atomic orbital hybridization
- Determine the hybrid orbitals associated with various molecular geometries
Thinking in terms of overlapping atomic orbitals is one way for us to explain how chemical bonds form in diatomic molecules. However, to understand how molecules with more than two atoms form stable bonds, we require a more detailed model. As an example, let us consider the water molecule, in which we have one oxygen atom bonding to two hydrogen atoms. Oxygen has the electron configuration 1 s 2 2 s 2 2 p 4 , with two unpaired electrons (one in each of the two 2 p orbitals). Valence bond theory would predict that the two O–H bonds form from the overlap of these two 2 p orbitals with the 1 s orbitals of the hydrogen atoms. If this were the case, the bond angle would be 90°, as shown in Figure \(\PageIndex{1}\), because p orbitals are perpendicular to each other. Experimental evidence shows that the bond angle is 104.5°, not 90°. The prediction of the valence bond theory model does not match the real-world observations of a water molecule; a different model is needed.
Quantum-mechanical calculations suggest why the observed bond angles in H 2 O differ from those predicted by the overlap of the 1 s orbital of the hydrogen atoms with the 2 p orbitals of the oxygen atom. The mathematical expression known as the wave function, ψ , contains information about each orbital and the wavelike properties of electrons in an isolated atom. When atoms are bound together in a molecule, the wave functions combine to produce new mathematical descriptions that have different shapes. This process of combining the wave functions for atomic orbitals is called hybridization and is mathematically accomplished by the linear combination of atomic orbitals , LCAO, (a technique that we will encounter again later). The new orbitals that result are called hybrid orbitals . The valence orbitals in an isolated oxygen atom are a 2 s orbital and three 2 p orbitals. The valence orbitals in an oxygen atom in a water molecule differ; they consist of four equivalent hybrid orbitals that point approximately toward the corners of a tetrahedron (Figure \(\PageIndex{2}\)). Consequently, the overlap of the O and H orbitals should result in a tetrahedral bond angle (109.5°). The observed angle of 104.5° is experimental evidence for which quantum-mechanical calculations give a useful explanation: Valence bond theory must include a hybridization component to give accurate predictions.
The following ideas are important in understanding hybridization:
- Hybrid orbitals do not exist in isolated atoms. They are formed only in covalently bonded atoms.
- Hybrid orbitals have shapes and orientations that are very different from those of the atomic orbitals in isolated atoms.
- A set of hybrid orbitals is generated by combining atomic orbitals. The number of hybrid orbitals in a set is equal to the number of atomic orbitals that were combined to produce the set.
- All orbitals in a set of hybrid orbitals are equivalent in shape and energy.
- The type of hybrid orbitals formed in a bonded atom depends on its electron-pair geometry as predicted by the VSEPR theory.
- Hybrid orbitals overlap to form σ bonds. Unhybridized orbitals overlap to form π bonds.
In the following sections, we shall discuss the common types of hybrid orbitals.
sp Hybridization
The beryllium atom in a gaseous BeCl 2 molecule is an example of a central atom with no lone pairs of electrons in a linear arrangement of three atoms. There are two regions of valence electron density in the BeCl 2 molecule that correspond to the two covalent Be–Cl bonds. To accommodate these two electron domains, two of the Be atom’s four valence orbitals will mix to yield two hybrid orbitals. This hybridization process involves mixing of the valence s orbital with one of the valence p orbitals to yield two equivalent sp hybrid orbitals that are oriented in a linear geometry (Figure \(\PageIndex{3}\)). In this figure, the set of sp orbitals appears similar in shape to the original p orbital, but there is an important difference. The number of atomic orbitals combined always equals the number of hybrid orbitals formed. The p orbital is one orbital that can hold up to two electrons. The sp set is two equivalent orbitals that point 180° from each other. The two electrons that were originally in the s orbital are now distributed to the two sp orbitals, which are half filled. In gaseous BeCl 2 , these half-filled hybrid orbitals will overlap with orbitals from the chlorine atoms to form two identical σ bonds.
We illustrate the electronic differences in an isolated Be atom and in the bonded Be atom in the orbital energy-level diagram in Figure \(\PageIndex{4}\). These diagrams represent each orbital by a horizontal line (indicating its energy) and each electron by an arrow. Energy increases toward the top of the diagram. We use one upward arrow to indicate one electron in an orbital and two arrows (up and down) to indicate two electrons of opposite spin.
When atomic orbitals hybridize, the valence electrons occupy the newly created orbitals. The Be atom had two valence electrons, so each of the sp orbitals gets one of these electrons. Each of these electrons pairs up with the unpaired electron on a chlorine atom when a hybrid orbital and a chlorine orbital overlap during the formation of the Be–Cl bonds. Any central atom surrounded by just two regions of valence electron density in a molecule will exhibit sp hybridization. Other examples include the mercury atom in the linear HgCl 2 molecule, the zinc atom in Zn(CH 3 ) 2 , which contains a linear C–Zn–C arrangement, and the carbon atoms in HCCH and CO 2 .
sp 2 Hybridization
The valence orbitals of a central atom surrounded by three regions of electron density consist of a set of three sp 2 hybrid orbitals and one unhybridized p orbital. This arrangement results from sp 2 hybridization, the mixing of one s orbital and two p orbitals to produce three identical hybrid orbitals oriented in a trigonal planar geometry (Figure \(\PageIndex{5}\)).
Although quantum mechanics yields the “plump” orbital lobes as depicted in Figure \(\PageIndex{5}\), sometimes for clarity these orbitals are drawn thinner and without the minor lobes, as in Figure \(\PageIndex{6}\), to avoid obscuring other features of a given illustration. We will use these “thinner” representations whenever the true view is too crowded to easily visualize.
The observed structure of the borane molecule, BH 3 , suggests sp 2 hybridization for boron in this compound. The molecule is trigonal planar, and the boron atom is involved in three bonds to hydrogen atoms ( Figure \(\PageIndex{7}\)).
We can illustrate the comparison of orbitals and electron distribution in an isolated boron atom and in the bonded atom in BH 3 as shown in the orbital energy level diagram in Figure \(\PageIndex{8}\). We redistribute the three valence electrons of the boron atom in the three sp 2 hybrid orbitals, and each boron electron pairs with a hydrogen electron when B–H bonds form.
Any central atom surrounded by three regions of electron density will exhibit sp 2 hybridization. This includes molecules with a lone pair on the central atom, such as ClNO (Figure \(\PageIndex{9}\)), or molecules with two single bonds and a double bond connected to the central atom, as in formaldehyde, CH 2 O, and ethene, H 2 CCH 2 .
sp 3 Hybridization
The valence orbitals of an atom surrounded by a tetrahedral arrangement of bonding pairs and lone pairs consist of a set of four sp 3 hybrid orbitals . The hybrids result from the mixing of one s orbital and all three p orbitals that produces four identical sp 3 hybrid orbitals (Figure \(\PageIndex{10}\)). Each of these hybrid orbitals points toward a different corner of a tetrahedron.
A molecule of methane, CH 4 , consists of a carbon atom surrounded by four hydrogen atoms at the corners of a tetrahedron. The carbon atom in methane exhibits sp 3 hybridization. We illustrate the orbitals and electron distribution in an isolated carbon atom and in the bonded atom in CH 4 in Figure \(\PageIndex{11}\). The four valence electrons of the carbon atom are distributed equally in the hybrid orbitals, and each carbon electron pairs with a hydrogen electron when the C–H bonds form.
In a methane molecule, the 1 s orbital of each of the four hydrogen atoms overlaps with one of the four sp 3 orbitals of the carbon atom to form a sigma (σ) bond. This results in the formation of four strong, equivalent covalent bonds between the carbon atom and each of the hydrogen atoms to produce the methane molecule, CH 4 .
The structure of ethane, C 2 H 6 , is similar to that of methane in that each carbon in ethane has four neighboring atoms arranged at the corners of a tetrahedron—three hydrogen atoms and one carbon atom (Figure \(\PageIndex{10}\)). However, in ethane an sp 3 orbital of one carbon atom overlaps end to end with an sp 3 orbital of a second carbon atom to form a σ bond between the two carbon atoms. Each of the remaining sp 3 hybrid orbitals overlaps with an s orbital of a hydrogen atom to form carbon–hydrogen σ bonds. The structure and overall outline of the bonding orbitals of ethane are shown in Figure \(\PageIndex{12}\). The orientation of the two CH 3 groups is not fixed relative to each other. Experimental evidence shows that rotation around σ bonds occurs easily.
An sp 3 hybrid orbital can also hold a lone pair of electrons. For example, the nitrogen atom in ammonia is surrounded by three bonding pairs and a lone pair of electrons directed to the four corners of a tetrahedron. The nitrogen atom is sp 3 hybridized with one hybrid orbital occupied by the lone pair.
The molecular structure of water is consistent with a tetrahedral arrangement of two lone pairs and two bonding pairs of electrons. Thus we say that the oxygen atom is sp 3 hybridized, with two of the hybrid orbitals occupied by lone pairs and two by bonding pairs. Since lone pairs occupy more space than bonding pairs, structures that contain lone pairs have bond angles slightly distorted from the ideal. Perfect tetrahedra have angles of 109.5°, but the observed angles in ammonia (107.3°) and water (104.5°) are slightly smaller. Other examples of sp 3 hybridization include CCl 4 , PCl 3 , and NCl 3 .
sp 3 d and sp 3 d 2 Hybridization
To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell atomic orbitals (the s orbital, the three p orbitals, and one of the d orbitals), which gives five sp 3 d hybrid orbitals . With an octahedral arrangement of six hybrid orbitals, we must use six valence shell atomic orbitals (the s orbital, the three p orbitals, and two of the d orbitals in its valence shell), which gives six sp 3 d 2 hybrid orbitals . These hybridizations are only possible for atoms that have d orbitals in their valence subshells (that is, not those in the first or second period).
In a molecule of phosphorus pentachloride, PCl 5 , there are five P–Cl bonds (thus five pairs of valence electrons around the phosphorus atom) directed toward the corners of a trigonal bipyramid. We use the 3 s orbital, the three 3 p orbitals, and one of the 3 d orbitals to form the set of five sp 3 d hybrid orbitals (Figure \(\PageIndex{13}\)) that are involved in the P–Cl bonds. Other atoms that exhibit sp 3 d hybridization include the sulfur atom in SF 4 and the chlorine atoms in ClF 3 and in \(\ce{ClF4+}\). (The electrons on fluorine atoms are omitted for clarity.)
The sulfur atom in sulfur hexafluoride, SF 6 , exhibits sp 3 d 2 hybridization. A molecule of sulfur hexafluoride has six bonding pairs of electrons connecting six fluorine atoms to a single sulfur atom. There are no lone pairs of electrons on the central atom. To bond six fluorine atoms, the 3 s orbital, the three 3 p orbitals, and two of the 3 d orbitals form six equivalent sp 3 d 2 hybrid orbitals, each directed toward a different corner of an octahedron. Other atoms that exhibit sp 3 d 2 hybridization include the phosphorus atom in \(\ce{PCl6-}\), the iodine atom in the interhalogens \(\ce{IF6+}\), IF 5 , \(\ce{ICl4-}\), \(\ce{IF4-}\) and the xenon atom in XeF 4 .
Assignment of Hybrid Orbitals to Central Atoms
The hybridization of an atom is determined based on the number of regions of electron density that surround it. The geometrical arrangements characteristic of the various sets of hybrid orbitals are shown in Figure \(\PageIndex{16}\). These arrangements are identical to those of the electron-pair geometries predicted by VSEPR theory. VSEPR theory predicts the shapes of molecules, and hybrid orbital theory provides an explanation for how those shapes are formed. To find the hybridization of a central atom, we can use the following guidelines:
- Determine the Lewis structure of the molecule.
- Determine the number of regions of electron density around an atom using VSEPR theory, in which single bonds, multiple bonds, radicals, and lone pairs each count as one region.
- Assign the set of hybridized orbitals from Figure \(\PageIndex{16}\) that corresponds to this geometry.
It is important to remember that hybridization was devised to rationalize experimentally observed molecular geometries, not the other way around.
Ammonium sulfate is important as a fertilizer. What is the hybridization of the sulfur atom in the sulfate ion, \(\ce{SO4^2-}\)?
S olution
The Lewis structure of sulfate shows there are four regions of electron density.
What is the hybridization of the selenium atom in SeF 4 ?
- Answer
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The selenium atom is sp 3 d hybridized.
Urea, NH 2 C(O)NH 2 , is sometimes used as a source of nitrogen in fertilizers. What is the hybridization of each nitrogen and carbon atom in urea?
Solution
The Lewis structure of urea is
The carbon atom is surrounded by three regions of electron density, positioned in a trigonal planar arrangement. The hybridization in a trigonal planar electron pair geometry is sp 2 (Figure \(\PageIndex{16}\)), which is the hybridization of the carbon atom in urea.
The nitrogen atoms are both surrounded by four regions of electron density, three bonds and a lone pair of electrons. This results in a tetrahedral geometry and requires sp 3 hybridization.
Acetic acid, H 3 CC(O)OH, is the molecule that gives vinegar its odor and sour taste. What is the hybridization of the two carbon atoms in acetic acid?
- Answer
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H 3 C , sp 3 ; C (O)OH, sp 2
Summary
We can use hybrid orbitals, which are mathematical combinations of some or all of the valence atomic orbitals, to describe the electron density around covalently bonded atoms. These hybrid orbitals either form sigma (σ) bonds directed toward other atoms of the molecule or contain lone pairs of electrons. We can determine the type of hybridization around a central atom from the geometry of the regions of electron density about it. Two such regions imply sp hybridization; three, sp 2 hybridization; four, sp 3 hybridization; five, sp 3 d hybridization; and six, sp 3 d 2 hybridization. Pi (π) bonds are formed from unhybridized atomic orbitals ( p or d orbitals).
Footnotes
- Note that orbitals may sometimes be drawn in an elongated “balloon” shape rather than in a more realistic “plump” shape in order to make the geometry easier to visualize.
Glossary
- hybrid orbital
- orbital created by combining atomic orbitals on a central atom
- hybridization
- model that describes the changes in the atomic orbitals of an atom when it forms a covalent compound
- sp hybrid orbital
- one of a set of two orbitals with a linear arrangement that results from combining one s and one p orbital
- sp 2 hybrid orbital
- one of a set of three orbitals with a trigonal planar arrangement that results from combining one s and two p orbitals
- sp 3 hybrid orbital
- one of a set of four orbitals with a tetrahedral arrangement that results from combining one s and three p orbitals
- sp 3 d hybrid orbital
- one of a set of five orbitals with a trigonal bipyramidal arrangement that results from combining one s , three p , and one d orbital
- sp 3 d 2 hybrid orbital
- one of a set of six orbitals with an octahedral arrangement that results from combining one s , three p , and two d orbitals


22.7D: Blood Supply to the Liver
In the hepatic portal system, the liver receives a dual blood supply from the hepatic portal vein and the hepatic arteries.
- Outline the blood flow to and from the liver
Key Points
- The hepatic portal vein supplies 75% of the blood to the liver, while the hepatic arteries supply the remaining 25%.
- Approximately half of the liver’s oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries.
- The hepatic portal system connects the capillaries of the gastrointestinal tract with the capillaries in the liver. Nutrient-rich blood leaves the gastrointestinal tract and is first brought to the liver for processing before being sent to the heart.
Key Terms
- hepatic arteries : A blood vessel that supplies oxygenated blood to the liver.
- hepatic portal vein : A vessel located in the abdominal cavity that is formed by the union of the superior mesenteric and splenic veins that channel blood from the gastrointestinal tract and spleen to the capillary beds in the liver.
- cofactors : A substance, especially a coenzyme or a metal, that must be present for an enzyme to function.
In the hepatic portal system, the liver receives a dual blood supply from the hepatic portal vein and hepatic arteries. The hepatic portal vein carries venous blood drained from the spleen, gastrointestinal tract and its associated organs; it supplies approximately 75% of the liver’s blood. The hepatic arteries supply arterial blood to the liver and account for the remainder of its blood flow.
Oxygen is provided from both sources; approximately half of the liver’s oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries. Blood flows through the liver tissue and empties into the central vein of each lobule. The central veins coalesce into hepatic veins that collect the blood leaving the liver and bring it to the heart.
Hepatic veins : An image of a liver with the hepatic veins labeled. They are located in the inferior vena cava.
A portal system is a venous structure that enables blood from one set of capillary beds to drain into another set of capillary beds, without first returning this blood to the heart. The majority of capillaries in the body drain directly into the heart, so portal systems are unusual.
The hepatic portal system connects the capillaries of the gastrointestinal tract with the capillaries in the liver. Nutrient-rich blood leaves the gastrointestinal tract and is first brought to the liver for processing before being sent to the heart. Here, carbohydrates and amino acids can be stored or used to make new proteins and carbohydrates.
The liver also removes vitamins and cofactors from the blood for storage, as well as filters any toxins that may have been absorbed along with the food. When any of these stored substances are needed, the liver releases them back into circulation through the hepatic veins.
Hepatic portal circulation : A diagram that shows the hepatic portal vein and its territory.


24.4: Type IV Hypersensitivities
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Learning Objectives
- Describe the three subtypes of type IV hypersensitivity
- Explain how T cells contribute to tissue damage in type IV hypersensitivity
Type IV Hypersensitivities
Type IV hypersensitivities are not mediated by antibodies like the other three types of hypersensitivities. Rather, type IV hypersensitivities are regulated by T cells and involve the action of effector cells. These types of hypersensitivities can be organized into three subcategories based on T-cell subtype, type of antigen, and the resulting effector mechanism (Table \(\PageIndex{5}\)).
In the first type IV subcategory, CD4 T H 1-mediated reactions are described as delayed-type hypersensitivities (DTH). The sensitization step involves the introduction of antigen into the skin and phagocytosis by local antigen presenting cells (APCs). The APCs activate helper T cells, stimulating clonal proliferation and differentiation into memory T H 1 cells. Upon subsequent exposure to the antigen, these sensitized memory T H 1 cells release cytokines that activate macrophages, and activated macrophages are responsible for much of the tissue damage. Examples of this T H 1-mediated hypersensitivity are observed in tuberculin the Mantoux skin test and contact dermatitis , such as occurs in latex allergy reactions.
In the second type IV subcategory, CD4 T H 2-mediated reactions result in chronic asthma or chronic allergic rhinitis. In these cases, the soluble antigen is first inhaled, resulting in eosinophil recruitment and activation with the release of cytokines and inflammatory mediators.
In the third type IV subcategory, CD8 cytotoxic T lymphocyte (CTL)-mediated reactions are associated with tissue transplant rejection and contact dermatitis (Figure \(\PageIndex{7}\)). For this form of cell-mediated hypersensitivity, APCs process and present the antigen with MHC I to naïve CD8 T cells. When these naïve CD8 T cells are activated, they proliferate and differentiate into CTLs. Activated T H 1 cells can also enhance the activation of the CTLs. The activated CTLs then target and induce granzyme-mediated apoptosis in cells presenting the same antigen with MHC I. These target cells could be “self” cells that have absorbed the foreign antigen (such as with contact dermatitis due to poison ivy), or they could be transplanted tissue cells displaying foreign antigen from the donor.
| Subcategory | Antigen | Effector Mechanism | Examples |
|---|---|---|---|
| 1 | Soluble antigen | Activated macrophages damage tissue and promote inflammatory response | Contact dermatitis (e.g., exposure to latex) and delayed-type hypersensitivity (e.g., tuberculin reaction) |
| 2 | Soluble antigen | Eosinophil recruitment and activation release cytokines and pro-inflammatory chemicals | Chronic asthma and chronic allergic rhinitis |
| 3 | Cell-associated antigen | CTL-mediated cytotoxicity | Contact dermatitis (e.g., contact with poison ivy) and tissue-transplant rejection |
Query \(\PageIndex{1}\)
Query \(\PageIndex{1}\)
Using Delayed Hypersensitivity to Test for TB
Austrian pediatrician Clemans von Pirquet (1874–1929) first described allergy mechanisms, including type III serum sickness. 9 His interest led to the development of a test for tuberculosis (TB), using the tuberculin antigen, based on earlier work identifying the TB pathogen performed by Robert Koch. Pirquet’s method involved scarification, which results in simultaneous multiple punctures, using a device with an array of needles to break the skin numerous times in a small area. The device Pirquet used was similar to the tine testdevice with four needles seen in Figure \(\PageIndex{8}\).
The tips of all the needles in the array are coated with tuberculin, a protein extract of TB bacteria, effectively introducing the tuberculin into the skin. One to 3 days later, the area can be examined for a delayed hypersensitivity reaction, signs of which include swelling and redness.
As you can imagine, scarification was not a pleasant experience, 10 and the numerous skin punctures put the patient at risk of developing bacterial infection of the skin. Mantoux modified Pirquet’s test to use a single subcutaneous injection of purified tuberculin material. A positive test, which is indicated by a delayed localized swelling at the injection site, does not necessarily mean that the patient is currently infected with active TB. Because type IV (delayed-type) hypersensitivity is mediated by reactivation of memory T cells, such cells may have been created recently (due to an active current infection) or years prior (if a patient had TB and had spontaneously cleared it, or if it had gone into latency). However, the test can be used to confirm infection in cases in which symptoms in the patient or findings on a radiograph suggest its presence.
Key Concepts and Summary
- Type IV hypersensitivities are not mediated by antibodies, but by helper T-cell activation of macrophages, eosinophils, and cytotoxic T cells.
Footnotes
- B. Huber “100 Jahre Allergie: Clemens von Pirquet–sein Allergiebegriff und das ihm zugrunde liegende Krankheitsverständnis.” Wiener Klinische Wochenschrift 118 no. 19–20 (2006):573–579.
- C.A. Stewart. “The Pirquet Test: Comparison of the Scarification and the Puncture Methods of Application.” Archives of Pediatrics & Adolescent Medicine 35 no. 3 (1928):388–391.


18.6: Fluvial Processes in Dry Regions
Though uncommon, when precipitation comes to the desert it can do so in torrential downpours sending a flash flood churning down dry streambeds known as a wash , arroyo or wadi depending on region. Salt encrusted soils result as water rapidly evaporates in the desert climate. A playa forms as an ephemeral lake in a low region of closed drainage. Permanent lakes and perennially running stream are rare in deserts. Many rivers are exotic streams , rivers whose head waters lie in a wetter region and the majority of which flows through a desert.
Alluvial fans are another prominent feature of many desert regions. Alluvial fans are fan-shaped alluvial deposits generally found where a mountain stream runs on to a flatter surface at the front of a mountain system. Mountain streams carrying a heavy stream load loses their kinetic energy as they flow out on to the flat plain depositing alluvium. Alluvial fans are quite common in arid regions where water is lost to evaporation and infiltration into coarse surface material when the stream exits the mountain front. Deposition of the sediment cause the channel to migrate horizontally depositing alluvium. Through time the channel migrates back and forth depositing sediment until a fan-shaped deposit is formed. A bajada forms when several individual alluvial fans merge into one broadly sloping surface.


13.2: What Programs Can Do to Support Children with Religious Differences
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Early childhood education programs are often the first context in which children are confronted with different religions and religious attitudes than those experienced in their family environment, and it is very important that they learn to treat each other with respect and to be sensitive to differences. Taking children’s opinions and interests into account and exploring how early childhood educational institutions deal with religious differences contributes to both childhood research and raising awareness of aspects of dealing with religious differences in educational institutions, which has not often been researched.
Young children notice religious differences, even when they don’t quite understand it or may not have the language to fully explain it. Even though it is noticeable, religious differences are often overlooked in early childhood education. “Many teachers are uncomfortable talking about religion in their classrooms, yet many schools continue to celebrate the traditional Christian holidays, such as Easter and Christmas, which further marginalizes non-Christian students.” [184]
Communication plays a key role in dealing with religious difference. Religious difference increases the need for communication about religion and religions. People get to know each other in two-way conversations. “Otherness is not threatening, but awakens the desire for communication. It is precisely because one or the other is different that we need communication.”
 If the staff and/or families in an early childhood program have different religious affiliations, communication about their different religious traditions makes sense in the kindergarten.
Questions early childhood education programs should ask themselves, include:
Values
Policy
Program Recognition
Curriculum
Professional Development of Teachers
Communication about religious difference
Communication about religious difference can bring challenges. But when programs create trusting, reciprocal relationships with families, dealing with conflicts, including dealing with religious conflicts, offers the opportunities for programs to become more culturally responsive. [185]
In education, including early childhood education, there is a tendency to focus exclusively on the major religion, but not on the minor religions and religious differences. Research has found that children of the minor religions often do not feel comfortable expressing themselves about their religion or their religious expressions and that their religion is given little attention by early childhood education programs in general or in the behavior of the teachers. Inclusion and integration of all religions, both major and minor. Children should be not be expected to assimilate to the major religion. Religious students should have the opportunity to address their religious perspective and not hide it. When children of different world religions live together in the group, the children have a right to be heard and told about their respective traditions. [186]
Children and adults belonging to a religion are also different in their religiousness, which can be seen in different forms of expression. It is important for early childhood educators to remember that how families observe and express their religion will vary, even within the same religion. [187]
Even if complete equity cannot be achieved in early childhood education, it is important to strive for it and to develop a safe space in which children are recognized in their individuality and their difference and in which they can address topics that concern them. While most early childhood settings appear to be calm and friendly places on the surface, there may be a great deal of underlying inequity in practice, as both adults and children inevitably bring with them their own perceptions and prejudices to the setting and in their interactions with one another. [188]
If the children’s religion and the resulting religious difference have no place in the kindergarten – if it is important to them – a part of them has no place. [189]
The naturalness and curiosity with which children encounter religious difference is a good foundation or learning processes about religious difference. The children’s conversations or questions that suddenly arise during the program day can, provided that they are perceived and sensitively taken up by the educators, be opportunities for learning, in which an examination of religious difference can take place. [190] “For young children, sharing their stories can be a vehicle to open conversations about religion and diversity.” [191]
Early childhood education programs should provide food that can be enjoyed by all children. Mealtimes offer a chance to make religious differences visible in the different eating habits of the children. It is critical that cultural (and religious) differences in food and meals be understood and respected by the program. How religious eating habits are dealt with in meals can therefore be an important indication of how religious differences are dealt with by the program in general. [192]
Some families may have religious practices that prescribe specific clothing, hairstyle, or head coverings. Early childhood education programs must learn about these practices from the families and help children follow these practices while the child is in the care of the program. [193]
“Holidays and celebrations are important topics in schools because they offer interesting and relevant opportunities for students to learn about cultures different than their own and to develop awareness of how religion influences cultures.” [195] Early childhood education programs should be careful that the celebrations they observe are authentic and reflect the values and beliefs of the families, they serve. The unique celebration of a festival of another religion without other consideration of religious difference in the program seems to miss the desired intentions despite the positive intentions. When festivals are celebrated, the question arises how this is done so that the celebration is not perceived as an “exotic activity” but is based on the recognition of religious difference in the program. [196]
Multicultural children‘s literature can be used to help children become more aware of the many religions and religious traditions. “Reading and discussing multicultural literature fosters opportunities for students to not only learn about world religions, but to explore commonalities and differences amongst people from a variety of places and religious practices (Dever, Whitaker, & Byrnes, 2001).” [197]
Children need explanations from adults in order to understand religious differences they notice. Children are often not given an explanation on the religious background of some children who observe different religious traditions. If the children do not know the reason for the difference, they may unintentionally find an explanation that is hurtful or irritating for the children concerned.
Due to the importance of teachers in early childhood institutions and the teacher’s diverse tasks in dealing with religious differences, teachers require interreligious competence. [198]
Early childhood educators often experience insecurity and fear of dealing with conflict or challenging situations, including those surrounding religious differences. Training of awareness of religious difference and the expansion of knowledge about different religions can take place to help build knowledge. Through support and professional development opportunities, the fears and concerns of the teachers and administrators can be addressed. This can lead to increased comfort surrounding addressing religious differences.
Staff meetings in which opportunities and challenges are discussed together make it clear that religious difference is not the concern of a single person in the program, but rather a common concern. Further training dedicated to the desires of the staff can be context-sensitive to the specific program and its situation.
One area that deserves further attention and training is that examination of one’s own prejudices, as is implemented in an anti-bias approach. [199]
In addition to knowledge, it is important for educators to examine their own values and attitudes in order to develop a sensitivity to different religions and world views. Dealing with one’s own religion and religiousness is important to
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Think About It… How might it feel if you are caring for a child with different religious beliefs than your own (maybe even contradictory)? What would you need to do to ensure the child and family’s beliefs are respected and honored in your classroom? |


10.0: Introduction
As you embark on your educational journey to becoming a nurse, you will quickly discover that effective clinical care relies on not only compassionate patient interactions but also the acquisition of critical clinical skills. One of the foundational components of nursing practice is specimen collection. This chapter explores the collection and handling of various clinical specimens, including urine, stool, sputum , and blood. Mastery of these skills is critical, as accurate specimen collection is the first step in generating valuable diagnostic data that inform patient care decisions.
This chapter delves into the rationale behind each type of specimen collection, its clinical significance, and its role in identifying and managing a wide range of medical conditions. Proper techniques for collecting specimens are explored, emphasizing the importance of hygiene, patient communication, and safety throughout the process. These are foundational skills that lay the groundwork for your future nursing practice in providing high-quality patient care.


13.1: Introduction
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Imagine a beach populated with sunbathers and swimmers. As those basking in the sun get too hot, they enter the surf to swim and cool off. As the swimmers tire, they return to the beach to rest. If the rate at which sunbathers enter the surf were to equal the rate at which swimmers return to the sand, then the numbers (though not the identities) of sunbathers and swimmers would remain constant. This scenario illustrates a dynamic phenomenon known as equilibrium , in which opposing processes occur at equal rates. Chemical and physical processes are subject to this phenomenon; these processes are at equilibrium when the forward and reverse reaction rates are equal. Equilibrium systems are pervasive in nature; the various reactions involving carbon dioxide dissolved in blood are examples (see Figure \(\PageIndex{1}\)). This chapter provides a thorough introduction to the essential aspects of chemical equilibria.


46.2: Energy Flow through Ecosystems
Learning Objectives
- Describe how organisms acquire energy in a food web and in associated food chains
- Explain how the efficiency of energy transfers between trophic levels affects ecosystem structure and dynamics
- Discuss trophic levels and how ecological pyramids are used to model them
All living things require energy in one form or another. Energy is required by most complex metabolic pathways (often in the form of adenosine triphosphate, ATP), especially those responsible for building large molecules from smaller compounds, and life itself is an energy-driven process. Living organisms would not be able to assemble macromolecules (proteins, lipids, nucleic acids, and complex carbohydrates) from their monomeric subunits without a constant energy input.
It is important to understand how organisms acquire energy and how that energy is passed from one organism to another through food webs and their constituent food chains. Food webs illustrate how energy flows directionally through ecosystems, including how efficiently organisms acquire it, use it, and how much remains for use by other organisms of the food web.
How Organisms Acquire Energy in a Food Web
Energy is acquired by living things in three ways: photosynthesis, chemosynthesis, and the consumption and digestion of other living or previously living organisms by heterotrophs.
Photosynthetic and chemosynthetic organisms are both grouped into a category known as autotrophs: organisms capable of synthesizing their own food (more specifically, capable of using inorganic carbon as a carbon source). Photosynthetic autotrophs (photoautotrophs) use sunlight as an energy source, whereas chemosynthetic autotrophs (chemoautotrophs) use inorganic molecules as an energy source. Autotrophs are critical for all ecosystems. Without these organisms, energy would not be available to other living organisms and life itself would not be possible.
Photoautotrophs, such as plants, algae, and photosynthetic bacteria, serve as the energy source for a majority of the world’s ecosystems. These ecosystems are often described by grazing food webs. Photoautotrophs harness the solar energy of the sun by converting it to chemical energy in the form of ATP (and NADP). The energy stored in ATP is used to synthesize complex organic molecules, such as glucose.
Chemoautotrophs are primarily bacteria that are found in rare ecosystems where sunlight is not available, such as in those associated with dark caves or hydrothermal vents at the bottom of the ocean (Figure \(\PageIndex{1}\)). Many chemoautotrophs in hydrothermal vents use hydrogen sulfide (H 2 S), which is released from the vents as a source of chemical energy. This allows chemoautotrophs to synthesize complex organic molecules, such as glucose, for their own energy and in turn supplies energy to the rest of the ecosystem.
Productivity within Trophic Levels
Productivity within an ecosystem can be defined as the percentage of energy entering the ecosystem incorporated into biomass in a particular trophic level. Biomass is the total mass, in a unit area at the time of measurement, of living or previously living organisms within a trophic level. Ecosystems have characteristic amounts of biomass at each trophic level. For example, in the English Channel ecosystem the primary producers account for a biomass of 4 g/m 2 (grams per meter squared), while the primary consumers exhibit a biomass of 21 g/m 2 .
The productivity of the primary producers is especially important in any ecosystem because these organisms bring energy to other living organisms by photoautotrophy or chemoautotrophy. The rate at which photosynthetic primary producers incorporate energy from the sun is called gross primary productivity . An example of gross primary productivity is shown in the compartment diagram of energy flow within the Silver Springs aquatic ecosystem as shown ( Figure 46.1.7 ). In this ecosystem, the total energy accumulated by the primary producers (gross primary productivity) was shown to be 20,810 kcal/m 2 /yr.
Because all organisms need to use some of this energy for their own functions (like respiration and resulting metabolic heat loss) scientists often refer to the net primary productivity of an ecosystem. Net primary productivity is the energy that remains in the primary producers after accounting for the organisms’ respiration and heat loss. The net productivity is then available to the primary consumers at the next trophic level. In our Silver Spring example, 13,187 of the 20,810 kcal/m 2 /yr were used for respiration or were lost as heat, leaving 7,632 kcal/m 2 /yr of energy for use by the primary consumers.
Ecological Efficiency: The Transfer of Energy between Trophic Levels
As illustrated in Figure 46.1.7 , large amounts of energy are lost from the ecosystem from one trophic level to the next level as energy flows from the primary producers through the various trophic levels of consumers and decomposers. The main reason for this loss is the second law of thermodynamics, which states that whenever energy is converted from one form to another, there is a tendency toward disorder (entropy) in the system. In biologic systems, this means a great deal of energy is lost as metabolic heat when the organisms from one trophic level consume the next level. In the Silver Springs ecosystem example ( Figure 46.1.7 ), we see that the primary consumers produced 1103 kcal/m 2 /yr from the 7618 kcal/m 2 /yr of energy available to them from the primary producers. The measurement of energy transfer efficiency between two successive trophic levels is termed the trophic level transfer efficiency (TLTE) and is defined by the formula:
\[\text{TLTE} = \frac{\text{production at present trophic level}}{\text{production at previous trophic level}} * 100 \nonumber\]
In Silver Springs, the TLTE between the first two trophic levels was approximately 14.8 percent. The low efficiency of energy transfer between trophic levels is usually the major factor that limits the length of food chains observed in a food web. The fact is, after four to six energy transfers, there is not enough energy left to support another trophic level. In the Lake Ontario example shown in Figure 46.1.5 , only three energy transfers occurred between the primary producer, (green algae), and the apex consumer (Chinook salmon).
Ecologists have many different methods of measuring energy transfers within ecosystems. Some transfers are easier or more difficult to measure depending on the complexity of the ecosystem and how much access scientists have to observe the ecosystem. In other words, some ecosystems are more difficult to study than others, and sometimes the quantification of energy transfers has to be estimated.
Another main parameter that is important in characterizing energy flow within an ecosystem is the net production efficiency. Net production efficiency (NPE) allows ecologists to quantify how efficiently organisms of a particular trophic level incorporate the energy they receive into biomass; it is calculated using the following formula:
\[\text{NPE} = \frac{\text{net consumer productivity}}{\text{assimilation}} * 100 \nonumber\]
Net consumer productivity is the energy content available to the organisms of the next trophic level. Assimilation is the biomass (energy content generated per unit area) of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste. Incomplete ingestion refers to the fact that some consumers eat only a part of their food. For example, when a lion kills an antelope, it will eat everything except the hide and bones. The lion is missing the energy-rich bone marrow inside the bone, so the lion does not make use of all the calories its prey could provide.
Thus, NPE measures how efficiently each trophic level uses and incorporates the energy from its food into biomass to fuel the next trophic level. In general, cold-blooded animals (ectotherms), such as invertebrates, fish, amphibians, and reptiles, use less of the energy they obtain for respiration and heat than warm-blooded animals (endotherms), such as birds and mammals. The extra heat generated in endotherms, although an advantage in terms of the activity of these organisms in colder environments, is a major disadvantage in terms of NPE. Therefore, many endotherms have to eat more often than ectotherms to get the energy they need for survival. In general, NPE for ectotherms is an order of magnitude (10x) higher than for endotherms. For example, the NPE for a caterpillar eating leaves has been measured at 18 percent, whereas the NPE for a squirrel eating acorns may be as low as 1.6 percent.
The inefficiency of energy use by warm-blooded animals has broad implications for the world's food supply. It is widely accepted that the meat industry uses large amounts of crops to feed livestock, and because the NPE is low, much of the energy from animal feed is lost. For example, it costs about 1¢ to produce 1000 dietary calories (kcal) of corn or soybeans, but approximately $0.19 to produce a similar number of calories growing cattle for beef consumption. The same energy content of milk from cattle is also costly, at approximately $0.16 per 1000 kcal. Much of this difference is due to the low NPE of cattle. Thus, there has been a growing movement worldwide to promote the consumption of non-meat and non-dairy foods so that less energy is wasted feeding animals for the meat industry.
Modeling Ecosystems Energy Flow: Ecological Pyramids
The structure of ecosystems can be visualized with ecological pyramids, which were first described by the pioneering studies of Charles Elton in the 1920s. Ecological pyramids show the relative amounts of various parameters (such as number of organisms, energy, and biomass) across trophic levels.
Pyramids of numbers can be either upright or inverted, depending on the ecosystem. As shown in Figure \(\PageIndex{2}\), typical grassland during the summer has a base of many plants and the numbers of organisms decrease at each trophic level. However, during the summer in a temperate forest, the base of the pyramid consists of few trees compared with the number of primary consumers, mostly insects. Because trees are large, they have great photosynthetic capability, and dominate other plants in this ecosystem to obtain sunlight. Even in smaller numbers, primary producers in forests are still capable of supporting other trophic levels.
Another way to visualize ecosystem structure is with pyramids of biomass. This pyramid measures the amount of energy converted into living tissue at the different trophic levels. Using the Silver Springs ecosystem example, this data exhibits an upright biomass pyramid (Figure \(\PageIndex{2}\)), whereas the pyramid from the English Channel example is inverted. The plants (primary producers) of the Silver Springs ecosystem make up a large percentage of the biomass found there. However, the phytoplankton in the English Channel example make up less biomass than the primary consumers, the zooplankton. As with inverted pyramids of numbers, this inverted pyramid is not due to a lack of productivity from the primary producers, but results from the high turnover rate of the phytoplankton. The phytoplankton are consumed rapidly by the primary consumers, thus, minimizing their biomass at any particular point in time. However, phytoplankton reproduce quickly, thus they are able to support the rest of the ecosystem.
Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels. Notice that these numbers are the same as those used in the energy flow compartment diagram in Figure 46.1.7 . Pyramids of energy are always upright, and an ecosystem without sufficient primary productivity cannot be supported. All types of ecological pyramids are useful for characterizing ecosystem structure. However, in the study of energy flow through the ecosystem, pyramids of energy are the most consistent and representative models of ecosystem structure (Figure \(\PageIndex{2}\)).
Exercise
Pyramids depicting the number of organisms or biomass may be inverted, upright, or even diamond-shaped. Energy pyramids, however, are always upright. Why?
- Answer
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Pyramids of organisms may be inverted or diamond-shaped because a large organism, such as a tree, can sustain many smaller organisms. Likewise, a low biomass of organisms can sustain a larger biomass at the next trophic level because the organisms reproduce rapidly and thus supply continuous nourishment. Energy pyramids, however, must always be upright because of the laws of thermodynamics. The first law of thermodynamics states that energy can neither be created nor destroyed; thus, each trophic level must acquire energy from the trophic level below. The second law of thermodynamics states that, during the transfer of energy, some energy is always lost as heat; thus, less energy is available at each higher trophic level.
Consequences of Food Webs: Biological Magnification
One of the most important environmental consequences of ecosystem dynamics is biomagnification. Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each trophic level, from the primary producers to the apex consumers. Many substances have been shown to bioaccumulate, including classical studies with the pesticide d ichloro d iphenyl t richloroethane (DDT), which was published in the 1960s bestseller, Silent Spring , by Rachel Carson. DDT was a commonly used pesticide before its dangers became known. In some aquatic ecosystems, organisms from each trophic level consumed many organisms of the lower level, which caused DDT to increase in birds (apex consumers) that ate fish. Thus, the birds accumulated sufficient amounts of DDT to cause fragility in their eggshells. This effect increased egg breakage during nesting and was shown to have adverse effects on these bird populations. The use of DDT was banned in the United States in the 1970s.
Other substances that biomagnify are polychlorinated biphenyls (PCBs), which were used in coolant liquids in the United States until their use was banned in 1979, and heavy metals, such as mercury, lead, and cadmium. These substances were best studied in aquatic ecosystems, where fish species at different trophic levels accumulate toxic substances brought through the ecosystem by the primary producers. As illustrated in a study performed by the National Oceanic and Atmospheric Administration (NOAA) in the Saginaw Bay of Lake Huron (Figure \(\PageIndex{3}\)), PCB concentrations increased from the ecosystem’s primary producers (phytoplankton) through the different trophic levels of fish species. The apex consumer (walleye) has more than four times the amount of PCBs compared to phytoplankton. Also, based on results from other studies, birds that eat these fish may have PCB levels at least one order of magnitude higher than those found in the lake fish.
Other concerns have been raised by the accumulation of heavy metals, such as mercury and cadmium, in certain types of seafood. The United States Environmental Protection Agency (EPA) recommends that pregnant women and young children should not consume any swordfish, shark, king mackerel, or tilefish because of their high mercury content. These individuals are advised to eat fish low in mercury: salmon, tilapia, shrimp, pollock, and catfish. Biomagnification is a good example of how ecosystem dynamics can affect our everyday lives, even influencing the food we eat.
Summary
Organisms in an ecosystem acquire energy in a variety of ways, which is transferred between trophic levels as the energy flows from the bottom to the top of the food web, with energy being lost at each transfer. The efficiency of these transfers is important for understanding the different behaviors and eating habits of warm-blooded versus cold-blooded animals. Modeling of ecosystem energy is best done with ecological pyramids of energy, although other ecological pyramids provide other vital information about ecosystem structure.
Glossary
- assimilation
- biomass consumed and assimilated from the previous trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste
- biomagnification
- increasing concentrations of persistent, toxic substances in organisms at each trophic level, from the primary producers to the apex consumers
- biomass
- total weight, at the time of measurement, of living or previously living organisms in a unit area within a trophic level
- chemoautotroph
- organism capable of synthesizing its own food using energy from inorganic molecules
- ecological pyramid
- (also, Eltonian pyramid) graphical representation of different trophic levels in an ecosystem based of organism numbers, biomass, or energy content
- gross primary productivity
- rate at which photosynthetic primary producers incorporate energy from the sun
- net consumer productivity
- energy content available to the organisms of the next trophic level
- net primary productivity
- energy that remains in the primary producers after accounting for the organisms’ respiration and heat loss
- net production efficiency (NPE)
- measure of the ability of a trophic level to convert the energy it receives from the previous trophic level into biomass
- trophic level transfer efficiency (TLTE)
- energy transfer efficiency between two successive trophic levels


28.6: Chapter Summary
Everyone has their own definition of family. Whatever that definition, the nurse must work with the family and their dynamics. Regardless of the structure, families share certain common functions and characteristics. The functions and characteristics of the family can and will affect the health of the individual. Nurses must educate families on self-care, health promotion, and disease prevention.
Families go through life cycles, from starting a family to growing old. Each family may go through certain developmental tasks at their own pace. Nurses need to differentiate these tasks to formulate a holistic perspective on the family. Certain frameworks and theories help guide nurses in caring for families and help nurses understand how these familes operate as a social system. These include the socioecological framework, the transactional model, general systems theory, the Calgary Family Assessment model, and the Calgary Family Intervention model.
In family health nursing, the nurse focuses on viewing the “client” as one unit or group of people. Family health nurses work in a variety of settings such as home care agencies; local, state, or national agencies or organization; or hospital systems. Family health reflects the family’s ability to meet each family member’s physical, psychological, spiritual, safety, economic, emotional, and intellectual needs. A family’s ability to meet these needs is affected by the SDOH.
A family health assessment is a systemized process of collecting and organizing data nurses may use to determine a family’s strengths and areas of concern. Nurses gather information through interviews with the family and observation of the family’s environment and by collecting community data. Specific tools, including ecomaps and genograms, can help nurses conduct family assessments, and it may take more than one interview to collect the necessary data. Once the nurse conducts the family health assessment, they must formulate a nursing care plan that includes assessment, diagnosis, planning, and evaluation.
Families may experience developmental or situational crises. Families may also experience IPV, abuse, and/or neglect. Nurses must understand the different types of abuse (physical, sexual, or psychological) and their signs and symptoms. Nurses have an ethical role in preventing and intervening in any abuse. Nurses can implement strategies at all levels to help families that are in crisis and prevent abuse and neglect.


7.4.1: Electron Donors and Acceptors in Anaerobic Respiration
In anaerobic respiration, a molecule other than oxygen is used as the terminal electron acceptor in the electron transport chain.
- Describe various types of electron acceptors and donors including: nitrate, sulfate, hydrgoen, carbon dioxide and ferric iron
Key Points
- Both inorganic and organic compounds may be used as electron acceptors in anaerobic respiration. Inorganic compounds include sulfate (SO 4 2- ), nitrate (NO 3 – ), and ferric iron (Fe 3+ ). Organic compounds include DMSO.
- These molecules have a lower reduction potential than oxygen. Therefore, less energy is formed per molecule of glucose in anaerobic versus aerobic conditions.
- The reduction of certain inorganic compounds by anaerobic microbes is often ecologically significant.
Key Terms
- anaerobic : Without oxygen; especially of an environment or organism.
- reduction : A reaction in which electrons are gained and valence is reduced; often by the removal of oxygen or the addition of hydrogen.
- anaerobic respiration : metabolic reactions and processes that take place in the cells of organisms that use electron acceptors other than oxygen
Anaerobic respiration is the formation of ATP without oxygen. This method still incorporates the respiratory electron transport chain, but without using oxygen as the terminal electron acceptor. Instead, molecules such as sulfate (SO 4 2 - ), nitrate (NO 3 – ), or sulfur (S) are used as electron acceptors. These molecules have a lower reduction potential than oxygen; thus, less energy is formed per molecule of glucose in anaerobic versus aerobic conditions.
Many different types of electron acceptors may be used for anaerobic respiration. Denitrification is the utilization of nitrate (NO 3 − ) as the terminal electron acceptor. Nitrate, like oxygen, has a high reduction potential. This process is widespread, and used by many members of Proteobacteria. Many denitrifying bacteria can also use ferric iron (Fe 3 + ) and different organic electron acceptors.
Sulfate reduction uses sulfate (SO 2 −4 ) as the electron acceptor, producing hydrogen sulfide (H 2 S) as a metabolic end product. Sulfate reduction is a relatively energetically poor process, and is used by many Gram negative bacteria found within the δ-Proteobacteria. It is also used in Gram-positive organisms related to Desulfotomaculum or the archaeon Archaeoglobus.
Sulfate reduction requires the use of electron donors, such as the carbon compounds lactate and pyruvate (organotrophic reducers), or hydrogen gas (lithotrophic reducers). Some unusual autotrophic sulfate-reducing bacteria, such as Desulfotignum phosphitoxidans, can use phosphite (HPO 3 – ) as an electron donor. Others, such as certain Desulfovibrio species, are capable of sulfur disproportionation (splitting one compound into an electron donor and an electron acceptor) using elemental sulfur (S0), sulfite (SO 3 −2 ), and thiosulfate (S 2 O 3 2 - ) to produce both hydrogen sulfide (H 2 S) and sulfate (SO 2 − ).
Acetogenesis is a type of microbial metabolism that uses hydrogen (H 2 ) as an electron donor and carbon dioxide (CO 2 ) as an electron acceptor to produce acetate, the same electron donors and acceptors used in methanogenesis.
Ferric iron (Fe 3 + ) is a widespread anaerobic terminal electron acceptor used by both autotrophic and heterotrophic organisms. Electron flow in these organisms is similar to those in electron transport, ending in oxygen or nitrate, except that in ferric iron-reducing organisms the final enzyme in this system is a ferric iron reductase. Since some ferric iron-reducing bacteria ( e.g.G. metallireducens ) can use toxic hydrocarbons ( e.g. toluene) as a carbon source, there is significant interest in using these organisms as bioremediation agents in ferric iron contaminated aquifers.
Other inorganic electron acceptors include the reduction of Manganic ion (Mn 4 + ) to manganous (Mn 2 + ), Selenate (SeO 4 2 − ) to selenite (SeO 3 2 − ) to selenium (Se), Arsenate (AsO 4 3 − ) to arsenite (AsO 3 3 - ), and Uranyl (UO 2 2 + ) to uranium dioxide (UO 2 )
Organic compounds may also be used as electron acceptors in anaerobic respiration. These include the reduction of fumarate to succinate, Trimethylamine N-oxide (TMAO) to trimethylamine (TMA), and Dimethyl sulfoxide (DMSO) to Dimethyl sulfide (DMS).