6.3: The pH Scale
You may have heard of pH levels in chemistry. pH is a measure of how acidic or basic a solution is. The pH scale is actually a logarithmic scale, similar to the Richter scale studied in the previous section. In chemistry, the level of acidity depends on the molar concentration of hydrogen ions in a given solution. The more hydrogen ions there are, the more acidic the solution is. But the concentrations are really, really small fractions, like 1/10,000,000 for pure water. Because this denominator ranges drastically, it is convenient to use a logarithmic scale.
pH is a logarithmic function of [\(\ce {H+}\)], where [\(\ce {H+}\)] is the concentration of the hydrogen ion [\(\ce {H+}\)].
\[pH = −\log[\ce {H+}]\]
pH is usually between 0 and 14. Knowing the dependence of pH on [ \(\ce {H+}\) ], we can summarize as follows:
- If pH < 7, then the solution is acidic.
- If pH = 7, then the solution is neutral.
- If pH > 7, then the solution is basic.
This is known as the pH scale. You can use pH to make a quick determination of whether a given water based solution is acidic, basic, or neutral.
Example \(\PageIndex{1}\)
Label each solution as acidic, basic, or neutral based only on the stated pH.
- milk of magnesia, pH = 10.5
- pure water, pH = 7
- wine, pH = 3.0
Solution
- With a pH greater than 7, milk of magnesia is basic. (Milk of magnesia is largely \(\ce {Mg(OH)2} \).)
- Pure water, with a pH of 7, is neutral.
- With a pH of less than 7, wine is acidic.
Example \(\PageIndex{2}\)
Identify each substance as acidic, basic, or neutral based only on the stated pH.
- human blood, pH = 7.4
- household ammonia, pH = 11.0
- cherries, pH = 3.6
Solution
- basic
- basic (very)
- acidic
The table below gives the typical pH values of some common substances. Note that several food items are on the list, and most of them are acidic.
|
Substance |
pH |
|---|---|
|
stomach acid |
1.7 |
|
lemon juice |
2.2 |
|
vinegar |
2.9 |
|
soda |
3.0 |
|
wine |
3.5 |
|
coffee, black |
5.0 |
|
milk |
6.9 |
|
pure water |
7.0 |
|
blood |
7.4 |
|
seawater |
8.5 |
|
milk of magnesia |
10.5 |
|
ammonia solution |
12.5 |
|
1.0 M \(\ce{NaOH}\) |
14.0 |
|
*Actual values may vary depending on conditions. |
pH is a logarithmic scale, a solution that has a pH of 1.0 has 10 times the [\(\ce {H+}\)] as a solution with a pH of 2.0, which in turn has 10 times the [\(\ce {H+}\)] as a solution with a pH of 3.0 and so forth.
Using the definition of pH, it is also possible to calculate [\(\ce {H+}\)] from pH and vice versa. The general formula for determining [\(\ce {H+}\)] from pH is as follows:
\[\left[\ce {H+}\right]=10^{-\text {pH}} \nonumber \]
You need to determine how to evaluate the above expression on your calculator. Ask your instructor if you have any questions. The other issue that concerns us here is significant figures. Because the number(s) before the decimal point in a logarithm relate to the power on 10, the number of digits after the decimal point is what determines the number of significant figures in the final answer.
Example \(\PageIndex{2}\)
What is [\(\ce {H+}\)] for an acid solution whose pH is 4.88?
Solution
We need to evaluate the expression
\[\left[\ce {H+}\right]=10^{-4.88} \nonumber \]
Depending on the calculator you use, the method for solving this problem will vary. In some cases, the “−4.88” is entered and a “\(10^x\)” key is pressed; for other calculators, the sequence of keystrokes is reversed. In any case, the correct numerical answer is as follows:
\[\left[\ce {H+}\right]=10^{-4.88}=0.0001318 \ldots \approx 1.32 \times 10^{-5} \nonumber \]
Exercises
-
Marko currently has 20 tulips in his yard. Each year he plants 5 more.
- Write a recursive formula for the number of tulips Marko has
- Write an explicit formula for the number of tulips Marko has
-
Pam is a Disc Jockey. Every week she buys 3 new albums to keep her collection current. She currently owns 450 albums.
- Write a recursive formula for the number of albums Pam has
- Write an explicit formula for the number of albums Pam has
-
A store’s sales (in thousands of dollars) grow according to the recursive rule \(P_{n}=P_{n-1}+15\), with initial population \(P_0=40\).
- Calculate \(P_1\) and \(P_2\)
- Find an explicit formula for \(P_n\)
- Use your formula to predict the store’s sales in 10 years
- When will the store’s sales exceed $100,000?
-
The number of houses in a town has been growing according to the recursive rule \(P_{n}=P_{n-1}+30\), with initial population \(P_0=200\).
- Calculate \(P_1\) and \(P_2\)
- Find an explicit formula for \(P_n\)
- Use your formula to predict the number of houses in 10 years
- When will the number of houses reach 400 houses?
-
A population of beetles is growing according to a linear growth model. The initial population (week 0) was \(P_0=3\), and the population after 8 weeks is \(P_8=67\).
- Find an explicit formula for the beetle population in week \(n\).
- After how many weeks will the beetle population reach 187?
-
The number of streetlights in a town is growing linearly. Four months ago (\(n = 0\)) there were 130 lights. Now (\(n = 4\)) there are 146 lights. If this trend continues,
- Find an explicit formula for the number of lights in month \(n\).
- How many months will it take to reach 200 lights?
-
Tacoma's population in 2000 was about 200 thousand, and had been growing by about 9% each year.
- Write a recursive formula for the population of Tacoma
- Write an explicit formula for the population of Tacoma
- If this trend continues, what will Tacoma's population be in 2016?
- When does this model predict Tacoma’s population to exceed 400 thousand?
-
Portland's population in 2007 was about 568 thousand, and had been growing by about 1.1% each year.
- Write a recursive formula for the population of Portland
- Write an explicit formula for the population of Portland
- If this trend continues, what will Portland's population be in 2016?
- If this trend continues, when will Portland’s population reach 700 thousand?
- Diseases tend to spread according to the exponential growth model. In the early days of AIDS, the growth rate was around 190%. In 1983, about 1700 people in the U.S. died of AIDS. If the trend had continued unchecked, how many people would have died from AIDS in 2005?
- The population of the world in 1987 was 5 billion and the annual growth rate was estimated at 2 percent per year. Assuming that the world population follows an exponential growth model, find the projected world population in 2015.
-
A bacteria culture is started with 300 bacteria. After 4 hours, the population has grown to 500 bacteria. If the population grows exponentially,
- Write a recursive formula for the number of bacteria
- Write an explicit formula for the number of bacteria
- If this trend continues, how many bacteria will there be in 1 day?
- How long does it take for the culture to triple in size?
-
A native wolf species has been reintroduced into a national forest. Originally 200 wolves were transplanted. After 3 years, the population had grown to 270 wolves. If the population grows exponentially,
- Write a recursive formula for the number of wolves
- Write an explicit formula for the number of wolves
- If this trend continues, how many wolves will there be in 10 years?
- If this trend continues, how long will it take the population to grow to 1000 wolves?
-
One hundred trout are seeded into a lake. Absent constraint, their population will grow by 70% a year. The lake can sustain a maximum of 2000 trout. Using the logistic growth model,
- Write a recursive formula for the number of trout
- Calculate the number of trout after 1 year and after 2 years.
-
Ten blackberry plants started growing in my yard. Absent constraint, blackberries will spread by 200% a month. My yard can only sustain about 50 plants. Using the logistic growth model,
- Write a recursive formula for the number of blackberry plants in my yard
- Calculate the number of plants after 1, 2, and 3 months
-
In 1968, the U.S. minimum wage was $1.60 per hour. In 1976, the minimum wage was $2.30 per hour. Assume the minimum wage grows according to an exponential model where \(n\) represents the time in years after 1960.
- Find an explicit formula for the minimum wage.
- What does the model predict for the minimum wage in 1960?
- If the minimum wage was $5.15 in 1996, is this above, below or equal to what the model predicts?
- The population of a small town can be described by the equation \(P_{n}=4000+70 n\), where \(n\) is the number of years after 2005. Explain in words what this equation tells us about how the population is changing.
- The population of a small town can be described by the equation \(P_n=4000(1.04)^{n}\), where \(n\) is the number of years after 2005. Explain in words what this equation tells us about how the population is changing.
Most of the examples in the text examined growing quantities, but linear and exponential equations can also describe decreasing quantities, as the next few problems will explore.
- A new truck costs $32,000. The car’s value will depreciate over time, which means it will lose value. For tax purposes, depreciation is usually calculated linearly. If the truck is worth $24,500 after three years, write an explicit formula for the value of the car after \(n\) years.
- Inflation causes things to cost more, and for our money to buy less (hence your grandparents saying, "In my day, you could buy a cup of coffee for a nickel"). Suppose inflation decreases the value of money by 5% each year. In other words, if you have $1 this year, next year it will only buy you $0.95 worth of stuff. How much will $100 buy you in 20 years?
- Suppose that you have a bowl of 500 M&M candies, and each day you eat ¼ of the candies you have. Is the number of candies left changing linearly or exponentially? Write an equation to model the number of candies left after \(n\) days.
-
A warm object in a cooler room will decrease in temperature exponentially, approaching the room temperature according to the formula \(T_{n}=a(1-r)^{n}+T_{r}\) where \(T_{n}\) is the temperature after \(n\) minutes, \(r\) is the rate at which temperature is changing, \(a\) is a constant, and \(T_{r}\) is the temperature of the room.
Forensic investigators can use this to predict the time of death of a homicide victim. Suppose that when a body was discovered (\(n=0\)) it was 85 degrees. After 20 minutes, the temperature was measured again to be 80 degrees. The body was in a 70 degree room.
- Use the given information with the formula provided to find a formula for the temperature of the body.
- When did the victim die, if the body started at 98.6 degrees?
-
Recursive equations can be very handy for modeling complicated situations for which explicit equations would be hard to interpret. As an example, consider a lake in which 2000 fish currently reside. The fish population grows by 10% each year, but every year 100 fish are harvested from the lake by people fishing.
- Write a recursive equation for the number of fish in the lake after \(n\) years.
- Calculate the population after 1 and 2 years. Does the population appear to be increasing or decreasing?
- What is the maximum number of fish that could be harvested each year without causing the fish population to decrease in the long run?
-
The number of Starbucks stores grew after first opened. The number of stores from 1990-2007, as reported on their corporate website,
2
is shown below.
- Carefully plot the data. Does is appear to be changing linearly or exponentially?
- Try finding an equation to model the data by picking two points to work from. How well does the equation model the data?
- Try using an equation of the form \(P_{n}=P_{0} n^{k}\), where \(k\) is a constant, to model the data. This type of model is called a Power model. Compare your results to the results from part b. Note: to use this model, you will need to have 1990 correspond with \(n=1\) rather than \(n=0\) .
|
Year |
Number of Starbucks stores |
|---|---|
|
1990 |
84 |
|
1991 |
116 |
|
1992 |
165 |
|
1993 |
272 |
|
1994 |
425 |
|
1995 |
677 |
|
1996 |
1015 |
|
1997 |
1412 |
|
1998 |
1886 |
|
1999 |
2498 |
|
2000 |
3501 |
|
2001 |
4709 |
|
2002 |
5886 |
|
2003 |
7225 |
|
2004 |
8569 |
|
2005 |
10241 |
|
2006 |
12440 |
|
2007 |
15756 |
-
Thomas Malthus was an economist who put forth the principle that population grows based on an exponential growth model, while food and resources grow based on a linear growth model. Based on this, Malthus predicted that eventually demand for food and resources would out outgrow supply, with doom-and-gloom consequences. Do some research about Malthus to answer these questions.
- What societal changes did Malthus propose to avoid the doom-and-gloom outcome he was predicting?
- Why do you think his predictions did not occur?
- What are the similarities and differences between Malthus's theory and the logistic growth model?
- What is a base \(b\) logarithm? Discuss the meaning by interpreting each part of the equivalent equations \(b^{y}=x\) and \(\log _{b} x=y\) for \(b>0, b \neq 1\)
-
How is the logarithmic function \(f(x)=\log _{b} x\) related to the exponential function \(g(x)=b^{x}\) What is the result of composing these two functions?
- How can the logarithmic equation \(\log _{b} x=y\) be solved using the properties of exponents?
-
Discuss the meaning of the common logarithm. What is its relationship to a logarithm with base \(b\), and how does the notation differ?
- Discuss the meaning of the natural logarithm. What is its relationship to a logarithm with base \(b\), and how does the notation differ?
For the following exercises, rewrite each equation in exponential form.
-
\(\log _{4}(q)=m\)
- \(\log _{a}(b)=c\)
-
\(\log _{16}(y)=x\)
- \(\log _{x}(64)=y\)
-
\(\log _{16}(y)=x\)
- \(\log _{x}(64)=y\)
-
\(\log _{y}(x)=-11\)
- \(\log _{15}(a)=b\)
-
\(\log _{y}(137)=x\)
- \(\log _{13}(142)=a\)
-
\(\log (v)=t\)
- \(\ln (w)=n\)
For the following exercises, rewrite each equation in logarithmic form.
-
The exposure index \(EI\) for a 35 millimeter camera is a measurement of the amount of light that hits the film. It is determined by the equation \(E I=\log _{2}\left(\dfrac{f^{2}}{t}\right)\), where \(f\) is the “f-stop” setting on the camera, and \(t\) is the exposure time in seconds. Suppose the f-stop setting is 8 and the desired exposure time is 2 seconds. What will the resulting exposure index be?
- Suppose the light meter on a camera indicates an \(EI\) of -2, and the desired exposure time is 16 seconds. What should the f-stop setting be?
- Describe, using your own words, what happens to the energy of an earthquake each time the magnitude on the Richter scale increases by 1.
-
Remember that \(\log (M)\) is the exponent so that 10 to that exponent is \(M\). Given this fact, find
- \(\log (1000) \)
- \(\log (10) \)
- \(\log (10,000,000) \)
- As mentioned in the text, the 1994 Northridge Earthquake registered a 6.7 on the Richter scale. In July, 2019, there was a major earthquake in Ridgecrest, California, with a magnitude of 7.1. How much bigger was the Ridgecrest quake compared to the Northridge Earthquake 25 years before (in terms of the energy released)? Use a calculator.
-
The pH level of lemon juice is 2.2 while the pH level of a typical wine is 3.5. They are both acidic, but one is much more acid than the other.
- Which one is more acidic?
- Compare the concentration of hydrogen ions between these two liquids. (How many times as much?) Hint: use the same method applied in the previous section to compare two earthquakes. The mathematics is the same.
- Many orange farmers pay attention to the pH level of their oranges. If an orange produces a juice with a pH level of 4.0, how much is the concentration of hydrogen ions in that juice compared a lemon juice with a pH level of 2.2?
Reference
- References (15)
- www.starbucks.com/aboutus/Company_Timeline.pdf retrieved May 2009
Contributors and Attributions
-
Saburo Matsumoto
CC-BY-4.0


12.5: Cancer
-
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What Is Cancer?
Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.
Figure \(\PageIndex{1}\). Cancerous Cells
When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors. Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor. Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening.
Key Cancer Terms
- Neoplasms : clusters of abnormal cells; aka “tumors.” When the neoplasms or tumors grow out and replace normal cells they are said to be “infiltrating” or “metastasizing” which means traveling to other parts of the body via the blood or lymph.
- Carcinoma : most common form; starts in the epithelium.
- Sarcoma: forms in connective tissue: bones, muscles, blood vessels.
- Leukemias: form in blood-forming tissues: bone marrow, lymph nodes, and the spleen.
- Lymphomas : form in the cells of the lymph system (the system that filters out impurities and/or infection).
- Conceptually, cancer is thought to develop via the turning on of genes called “ oncogenes ” or genes that have gone awry. The DNA in these cells replicates at an accelerated rate. “Tumor suppressor genes”, which are present in all of us, fail to stop these cells from dividing thereby allowing a tumor to form.
- A “ malignant ” tumor is a cancerous tumor, whereas a “benign” tumor is not cancerous and of no imminent danger to the body.
How Cancer Arises
Cancer is caused by changes to genes that control the way our cells function, especially how they grow and divide.
Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.
When Cancer Spreads
In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumors (metastatic tumors) in other parts of the body. The metastatic tumor is the same type of cancer as the primary tumor.
A cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.
Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer.
Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
Cancer Stages
Cancers are staged 1-3/4, depending on the cancer and the severity. When detected at stage 1, a person suffering from most types of cancer has about a 95% of surviving. The odds go down as you get to stage 3 or 4 (some cancers only have 3 stages, others 4). Doctors will often add an ‘A’ or ‘B’ to the staging as well, and this can relate to whether or not the cancer has invaded other tissues.
Tissue Changes That Are Not Cancer
Not every change in the body’s tissues is cancer. Some tissue changes may develop into cancer if they are not treated, however. Here are some examples of tissue changes that are not cancer but, in some cases, are monitored:
Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up, or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.
Dysplasia is a more serious condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form.
Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not.
Normal cells may become cancer cells. Before cancer cells form in tissues of the body, the cells go through abnormal changes called hyperplasia and dysplasia. In hyperplasia, there is an increase in the number of cells in an organ or tissue that appear normal under a microscope. In dysplasia, the cells look abnormal under a microscope but are not cancer. Hyperplasia and dysplasia may or may not become cancer.
Types of Cancer
There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain. Cancers also may be described by the type of cell that formed them, such as an epithelial cell or a squamous cell.
Common Cancer Types
This list of common cancer types includes cancers that are diagnosed with the greatest frequency in the United States, excluding non-melanoma skin cancers:
- Bladder Cancer: The most common type of bladder cancer is transitional cell carcinoma, also called urothelial carcinoma. Smoking is a major risk factor for bladder cancer. Bladder cancer is often diagnosed at an early stage.
- Breast Cancer : Breast cancer is the second most common cancer in women after skin cancer. Mammograms can detect breast cancer early, possibly before it has spread.
- Colon and Rectal Cancer: Colorectal cancer often begins as a growth called a polyp inside the colon or rectum. Finding and removing polyps can prevent colorectal cancer.
- Endometrial Cancer: Uterine cancers can be of two types: endometrial cancer (common) and uterine sarcoma (rare). Endometrial cancer can often be cured. Uterine sarcoma is often more aggressive and harder to treat.
- Kidney Cancer: Kidney cancer can develop in adults and children. The main types of kidney cancer are renal cell cancer, transitional cell cancer, and Wilms tumor. Certain inherited conditions increase the risk of kidney cancer.
- Leukemia: Leukemia is a broad term for cancers of the blood cells. The type of leukemia depends on the type of blood cell that becomes cancer and whether it grows quickly or slowly. Leukemia occurs most often in adults older than 55, but it is also the most common cancer in children younger than 15.
- Lung Cancer: Lung cancer includes two main types: non-small cell lung cancer and small cell lung cancer. Smoking causes most lung cancers, but nonsmokers can also develop lung cancer.
- Melanoma: Skin cancer is the most common type of cancer. The main types of skin cancer are squamous cell carcinoma, basal cell carcinoma, and melanoma. Melanoma is much less common than the other types but much more likely to invade nearby tissue and spread to other parts of the body. Most deaths from skin cancer are caused by melanoma.
- Non-Hodgkin Lymphoma: Lymphoma is a broad term for cancer that begins in cells of the lymph system. The two main types are Hodgkin lymphoma and nonHodgkin lymphoma (NHL). Hodgkin lymphoma can often be cured. The prognosis of NHL depends on the specific type.
- Pancreatic Cancer: Pancreatic cancer can develop from two kinds of cells in the pancreas: exocrine cells and neuroendocrine cells, such as islet cells. The exocrine type is more common and is usually found at an advanced stage. Pancreatic neuroendocrine tumors (islet cell tumors) are less common but have a better prognosis.
- Prostate Cancer: Prostate cancer is the most common cancer and the second leading cause of cancer death among men in the United States. Prostate cancer usually grows very slowly, and finding and treating it before symptoms occur may not improve men's health or help them live longer.
- Thyroid Cancer: Thyroid cancer can be of four main types, which vary in their aggressiveness. Anaplastic thyroid cancer is hard to cure with current treatments, whereas papillary (the most common), follicular, and medullary thyroid cancer can usually be cured.
Cancer incidence and mortality statistics reported by the American Cancer Society and other resources were used to create the list. To qualify as a common cancer for the list, the estimated annual incidence for 2016 had to be 40,000 cases or more.
The most common type of cancer on the list is breast cancer, with more than 249,000 new cases expected in the United States in 2016. The next most common cancers are lung cancer and prostate cancer.
Because colon and rectal cancers are often referred to as “colorectal cancers,” these two cancer types are combined for the list. For 2016, the estimated number of new cases of colon cancer and rectal cancer are 95,270 and 39,220, respectively, adding to a total of 134,490 new cases of colorectal cancer.
The following table gives the estimated numbers of new cases and deaths for each common cancer type:
Table \(\PageIndex{1}\). Cancer Types
| Cancer Type | Estimated New Cases | Estimated Deaths |
| Bladder | 76,960 | 16,390 |
| Breast (Female - Male) | 246,660 - 2,600 | 40,450 - 440 |
| Colon and Rectal (Combined) | 134,490 | 49,190 |
| Endometrial | 60,050 | 10,470 |
| Kidney (Renal Cell and Renal Pelvis) Cancer | 62,700 | 14,240 |
| Leukemia (All Types) | 60,140 | 24,400 |
| Lung (Including Bronchus) | 224,390 | 158,080 |
| Melanoma | 76,380 | 10,130 |
| Non-Hodgkin Lymphoma | 72,580 | 20,150 |
| Pancreatic | 53,070 | 41,780 |
| Prostate | 180,890 | 26,120 |
| Thyroid | 64,300 | 1,980 |
Risk Factors for Cancer
It is usually not possible to know exactly why one person develops cancer and another doesn’t. But research has shown that certain risk factors may increase a person’s chances of developing cancer. (There are also factors that are linked to a lower risk of cancer. These are called protective factors.)
Cancer risk factors include exposure to chemicals or other substances, as well as certain behaviors. They also include things people cannot control, like age and family history. A family history of certain cancers can be a sign of a possible inherited cancer syndrome.
Most cancer risk (and protective) factors are initially identified in epidemiology studies. In these studies, scientists look at large groups of people and compare those who develop cancer with those who don’t. These studies may show that the people who develop cancer are more or less likely to behave in certain ways or to be exposed to certain substances than those who do not develop cancer.
Such studies, on their own, cannot prove that a behavior or substance causes cancer. For example, the finding could be a result of chance, or the true risk factor could be something other than the suspected risk factor. But findings of this type sometimes get attention in the media, and this can lead to wrong ideas about how cancer starts and spreads.
When many studies all point to a similar association between a potential risk factor and an increased risk of cancer, and when a possible mechanism exists that could explain how the risk factor could actually cause cancer, scientists can be more confident about the relationship between the two.
The list below includes the most studied known or suspected risk factors for cancer:
- Age
- Alcohol
- Cancer-Causing Substances
- Chronic Inflammation
- Diet
- Hormones
- Immunosuppression
- Infectious Agents
- Obesity
- Radiation
- Sunlight
- Tobacco
Figure \(\PageIndex{2}\). CDC Advertisement
Although some of these risk factors can be avoided, others—such as growing older— cannot. Limiting your exposure to avoidable risk factors may lower your risk of developing certain cancers.
TOBACCO
Tobacco use is a leading cause of cancer and of death from cancer. People who use tobacco products or who are regularly around environmental tobacco smoke (also called secondhand smoke) have an increased risk of cancer because tobacco products and secondhand smoke have many chemicals that damage DNA.
Tobacco use causes many types of cancer, including cancer of the lung, larynx (voice box), mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon and rectum, and cervix, as well as acute myeloid leukemia. People who use smokeless tobacco (snuff or chewing tobacco) have increased risks of cancers of the mouth, esophagus, and pancreas.
There is no safe level of tobacco use. People who use any type of tobacco product are strongly urged to quit. People who quit smoking, regardless of their age, have substantial gains in life expectancy compared with those who continue to smoke. Also, quitting smoking at the time of a cancer diagnosis reduces the risk of death.
Scientists believe that cigarette smoking causes about 30% of all cancer deaths in the United States.
Cancer Prevention
The number of new cancer cases can be reduced and many cancer deaths can be prevented. Research shows that screening for cervical and colorectal cancers as recommended helps prevent these diseases by finding precancerous lesions so they can be treated before they become cancerous. Screening for cervical, colorectal, and breast cancers also helps find these diseases at an early stage, when treatment works best.
Vaccines (shots) also help lower cancer risk. The human papillomavirus (HPV) vaccine helps prevent most cervical cancers and several other kinds of cancer, and the hepatitis B vaccine can help lower liver cancer risk.
A person’s cancer risk can be reduced with healthy choices like avoiding tobacco, limiting alcohol use, protecting your skin from the sun and avoiding indoor tanning, eating a diet rich in fruits and vegetables, keeping a healthy weight, and being physically active.
Avoiding Tobacco
Cigarette Smoking
Lung cancer is the leading cause of cancer death, and cigarette smoking causes almost all cases. Compared to nonsmokers, current smokers are about 25 times more likely to die from lung cancer. Smoking causes about 80% to 90% of lung cancer deaths. Smoking also causes cancer of the mouth and throat, esophagus, stomach, colon, rectum, liver, pancreas, voicebox (larynx), trachea, bronchus, kidney and renal pelvis, urinary bladder, and cervix, and causes acute myeloid leukemia.
Visit smokefree.gov to learn how you can quit smoking.
Secondhand Smoke
Adults who are exposed to secondhand smoke at home or at work increase their risk of developing lung cancer by 20% to 30%. Concentrations of many cancer-causing and toxic chemicals are higher in secondhand smoke than in the smoke inhaled by smokers.
Protecting Your Skin
Skin cancer is the most common kind of cancer in the United States. Exposure to ultraviolet (UV) rays from the sun and tanning beds appears to be the most important environmental factor involved with developing skin cancer. To help prevent skin cancer while still having fun outdoors, protect yourself by seeking shade, applying sunscreen, and wearing sunprotective clothing, a hat, and sunglasses.
DETECTING MELANOMA
Melanoma is the most serious type of skin cancer. Often the first sign of melanoma is a change in the size, shape, color, or feel of a mole. Most melanomas have a black or black-blue area. Melanoma may also appear as a new mole. It may be black, abnormal, or “ugly looking.”
Thinking of “ ABCDE ” can help you remember what to watch for:
- A symmetry – the shape of one half does not match the other
- B order – the edges are ragged, blurred or irregular
- C olor – the color is uneven and may include shades of black, brown and tan
- D iameter – there is a change in size, usually an increase (larger than 6 millimeters or about 1/4 inch)
- E volving – the mole has changed (in size, color, shape; it may start to itch or bleed) over the past few weeks or months
Limiting Alcohol Intake
Drinking alcohol raises the risk of some cancers. Drinking any kind of alcohol can contribute to cancers of the mouth and throat, larynx (voice box), esophagus, colon and rectum, liver, and breast (in women). The less alcohol you drink, the lower the risk of cancer.
Studies around the world have shown that drinking alcohol regularly increases the risk of getting mouth, voice box, and throat cancers.
A large number of studies provide strong evidence that drinking alcohol is a risk factor for primary liver cancer, and more than 100 studies have found an increased risk of breast cancer with increasing alcohol intake. The link between alcohol consumption and colorectal (colon) cancer has been reported in more than 50 studies.
Keeping a Healthy Weight
Research has shown that being overweight or obese substantially raises a person’s risk of getting endometrial (uterine), breast, prostate, and colorectal cancers. Overweight is defined as a body mass index (BMI) of 25 to 29, and obesity is defined as a BMI of 30 or higher. You can learn more about eating healthy and maintaining a healthy weight in chapters 9 and 10.
Types of Cancer Treatment
Figure \(\PageIndex{3}\). Source: National Cancer Institute - https://www.cancer.gov/about-cancer/treatment/types
There are many types of cancer treatment. The types of treatment will depend on the type of cancer and how advanced it is. Some people with cancer will have only one treatment. But most people have a combination of treatments, such as surgery with chemotherapy and/or radiation therapy.
Surgery
When used to treat cancer, surgery is a procedure in which a surgeon removes cancer from your body. Learn the different ways that surgery is used against cancer and what you can expect before, during, and after surgery.
 Learn about the types of radiation, why side effects happen, which ones you might have, and more.
 Learn how chemotherapy works against cancer, why it causes side effects, and how it is used with other cancer treatments.
Immunotherapy
Immunotherapy is a type of treatment that helps your immune system fight cancer. Get information about the types of immunotherapy and what you can expect during treatment.
Targeted Therapy
Targeted therapy is a type of cancer treatment that targets the changes in cancer cells that help them grow, divide, and spread. Learn how targeted therapy works against cancer and about common side effects that may occur.
Hormone Therapy
Hormone therapy is a treatment that slows or stops the growth of breast and prostate cancers that use hormones to grow. Learn about the types of hormone therapy and side effects that may happen.
Stem Cell Transplant
Figure \(\PageIndex{4}\). Stem Cell Transplant
Stem cell transplants are procedures that restore blood-forming stem cells in cancer patients who have had theirs destroyed by very high doses of chemotherapy or radiation therapy. Learn about the types of transplants, side effects that may occur, and how stem cell transplants are used in cancer treatment.
Precision Medicine
Precision medicine helps doctors select treatments that are most likely to help patients based on a genetic understanding of their disease. Learn about the role precision medicine plays in cancer treatment, including how genetic changes in a person's cancer are identified and used to select treatments.


9.5: Human Trafficking
By the end of this section, you will be able to:
- Discuss the definition of human trafficking, and describe at-risk populations, traffickers, and regional trafficking trends in the United States
- Describe the nursing care for the person who has been trafficked, including how to recognize and treat those people
- Construct a nursing care plan for the person who has been trafficked
Human trafficking is a crime that involves the exploitation of people for forced labor or commercial sex (United Nations Office on Drugs and Crime, 2020). Human trafficking is a global problem that includes women, children, and men. Nurses and health-care providers should identify and provide help for people being trafficked.
Human Trafficking: Definition
The targeting, relocation of, detention of, or receiving of a person by any means possible to achieve control over that person for exploitation is considered human trafficking (WHO, 2012). The National Human Trafficking Hotline (NHTH; 2024, p. 1) defines trafficking as “stealing freedom for profit.” People are trafficked for many different forms of forced labor and sexual exploitation. Victims of human trafficking are forced to work excessively long hours, live in overcrowded or unsafe conditions, experience physical abuse and malnourishment, and are unable to move freely or leave their place of work or residence (Hodge & Lietz, 2018; Piscitelli & Pienaar, 2019). Consequences of human trafficking include physical and relationship problems, psychologic issues, and chronic health conditions (CDC, 2022b).
Factors Related to Human Traffickers
Human traffickers do not have a common background, race, gender, or nationality. Traffickers can be strangers, family members, partners, or acquaintances. Signs of possible trafficking for labor situations include the following: a person in an overwhelming romantic relationship is suddenly showered with gifts and money by a person with a large age difference or large difference in financial status; a person is developing a close relationship with a person solely known on social media; a person is being offered a job that seems too good to be true; and a person is being recruited for a job that requires the person to move far away, but the recruiter is vague and reluctant to answer questions about the job (NHTH, 2023). People who are being trafficked for sex may want to stop participating in commercial sex but cannot leave the situation; they live where they work or are transported between home and workplace by guards. They may work in a strip club or illicit massage business where they are pressured to perform sex acts for money; or they have a controlling person (parent, guardian, partner, etc.) who will not allow them to speak or be alone with anyone (NHTH, 2023).
Populations at High Risk for Human Trafficking
Some groups are at higher risk for human trafficking, such as women and children. One-third of adolescents who have run away from home are recruited into sex trafficking within 48 hours of being homeless (Camak 2022). People living in poverty or unsafe situations, undocumented immigrants, and those with a history of abuse or trauma are at higher risk (CDC, 2022b; International Labour Organization, 2022). People of color and LGBTQIA+ persons are also at higher risk than other demographic groups (NHTH, 2023). Traffickers recognize and target people who are at higher risk, such as runaways, those with drug or alcohol use issues, or those with a caregiver or family member with substance use issues (NHTH, 2023). Identifying victims of human trafficking can be challenging because they may be kept in isolation , have limited contact with others, or be forced to deny their situation. Traffickers prey on populations at high risk for trafficking by developing trust, rescuing them from bad situations, helping them, and then demanding they “repay” the kindness through servitude (Camak, 2022).
Regional Trends in the United States of America
Human trafficking occurs everywhere; however, Asia and the Pacific region have the highest number of victims of human trafficking (McGeough & Van Schooneveld, 2023). Asia and the Pacific reported 29.3 million cases of human trafficking, while the Americas reported 5.1 million cases (McGeough & Van Schooneveld, 2023). In North America, most human trafficking victim s are women subjected to sexual trafficking (McGeough & Van Schooneveld, 2023).
In 2020, 2,198 people were referred to the U.S. Attorneys’ Department of Justice for human trafficking, which is a 62 percent increase in 10 years. Human trafficking cases have been reported in all 50 states, with an increase in trafficking by a family member, guardian, or intimate partner (U.S. Department of State, 2022). California, Texas, and Florida have the highest numbers of reported cases of human trafficking (National Human Trafficking Hotline, n.d.), likely due to their large populations, international borders, and transportation networks. Other areas with major urban centers (New York, Michigan, and Georgia) also attract traffickers (National Human Trafficking Hotline, n.d.).
Preventing Human Trafficking
Programs to increase community awareness of human trafficking and to address exploitation are designed to prevent trafficking (CDC, 2022b). Strategies to encourage healthy relationship behaviors, foster safe homes and neighborhoods, identify and address vulnerabilities during health-care visits, reduce demand for commercial sex, and end business profits from trafficking-related transactions have been suggested by the CDC (2022b). The United States enacted the Victims of Trafficking and Violence Protection Act of 2000 in an effort to prevent human trafficking (2000).
Nursing Care for the Person Who Has Been Trafficked
Nurses can help women subjected to trafficking by providing sensitive, empathetic care. The nurse is trained to recognize the signs of a person who is being trafficked in order to care for the person but also to report the trafficking incident. Nurses are required by law to report trafficking victims under the age of 18 years; unfortunately, nurses are not required to report adult victims of trafficking (Byrne et al., 2019; Camak, 2022). Intervening in cases of human trafficking is crucial to prevent further harm to victims. In some cases, it may be necessary to involve a professional interpreter, as victims may not speak the local language or be hesitant to share their experiences. Overall, nurses can raise awareness about human trafficking and take steps to identify victims and provide help.
How to Recognize Victims of Human Trafficking
Recognizing victims of human trafficking can be difficult for nurses and health-care providers due to the victims being threatened with physical violence or other consequences if they are discovered. Training can help nurses recognize signs of human trafficking, such as by looking closely at a patient’s location and occupation, by being attentive to behavioral and physical signs, and by using screening tools. For example, sex trafficking victims have been found on the street, in massage parlors, at escort services, at truck stops, and in hotels, brothels, and strip clubs (Camak, 2022). Behavioral signs that a person may be a victim of trafficking include acting fearful, anxious, depressed, submissive, or tense around someone they know; deferring to another person to speak for them; and avoiding eye contact (Department of Human Services [DHS], 2020). Physical signs can include evidence of physical or sexual abuse ; signs of physical restraint, confinement, or torture; or signs of being harmed or deprived of food, water, sleep, medical care, or personal possessions (DHS, 2020). Table 9.3 provides nurses with examples of red flags of potential victims of human trafficking.
| Patient | Red Flags |
|---|---|
| Physical signs of trafficking victims |
|
| Characteristics of trafficking victims |
|
| Child/adolescent trafficking victims |
|
| Other signs of trafficking victims |
|
| Characteristics of traffickers |
|
Nursing Assessment and Diagnosis
Recognizing a person who has been trafficked is the first goal of nursing care; 50 percent to 80 percent of trafficked people have seen a health-care provider while being trafficked (Byrne et al., 2019). The nurse must develop a level of trust prior to assessing for signs of abuse. Many times, a person being trafficked is not allowed to speak for themselves; therefore, the nurse should find a way to interview the patient in private. The nurse must create a safe, nonthreatening environment for the interview. The nurse assesses the patient’s living and working conditions, amount of control over their life, mental health status, physical health, and psychosocial health (Byrne et al., 2019). The nurse can ask the following questions during the interview:
- Can you leave your job if you want?
- Can you come and go as you please?
- Have you been threatened or physically harmed in any way?
- Where do you sleep or eat?
- Do you sleep in a bed, on a cot, or on the floor?
- Do you have to ask permission to go to the bathroom, eat, or sleep?
- Has anyone threatened your family?
- Is anyone forcing you to do anything you do not want to do? (Camak, 2022)
Nursing assessment findings may include physical and emotional red flags. A person’s medical history might also have clues to a history of human trafficking, such as repeat abortions; lack of medical care; and history of PTSD, suicide attempts, and alcohol or drug addiction (Byrne et al., 2019).
Nursing diagnoses are centered on the actual or potential needs related to the physical and psychologic needs of the person being trafficked. The most common nursing diagnoses include:
- risk for injury related to physical abuse
- ineffective coping related to fear, stress, and lack of support
- hopelessness related to feelings of wanting to escape trafficking
- risk for injury related to lack of shelter
The Action-Means-Purpose Model
The nurse can use the Action-Means-Purpose Model (AMP Model) to determine if a patient meets the federal definition of human trafficking. If the nurse can confirm one element from each area of the model, the legal definition has been met. The elements are as follows:
- Action: induces, recruits, harbors, transports, provides, or obtains
- Means: force, fraud, coercion
- Purpose: commercial sex, labor, or services
(National Human Trafficking Hotline, 2024)
Nursing Plan and Implementation
The nursing plan for persons being trafficked includes a team approach with health-care providers, social workers, counselors, and possibly law enforcement. Nursing interventions should be individualized and compassionate, helping the patient to reestablish control, a sense of safety, and independence (Camak, 2022). The nurse provides supportive care and reassurance. Interventions can include providing resources for shelters and support groups, encouraging counseling, educating the person on legal assistance, and preventing further abuse.


13.3: Hallmarks of Cancer
Researchers have identified six molecular and cellular traits that characterize most cancers. These six hallmarks of cancer are summarized in Table \(\PageIndex{1}\). In this chapter, we will focus on the first two hallmarks, namely growth signal autonomy and insensitivity to anti-‐growth signals.
|
Table \(\PageIndex{1}\) Ten Hallmarks of Cancer (Hanahan and Weinberg, 2000; Hanahan 2011) |
|
1. Growth signal autonomy Cancer cells can divide without the external signals normally required to stimulate division. 2. Insensitivity to growth inhibitory signals Cancer cells are unaffected by external signals that inhibit division of normal cells. 3. Evasion of apoptosis When excessive DNA damage and other abnormalities are detected, apoptosis (a type of programmed cell death) is induced in normal cells, but not in cancer cells. 4. Reproductive potential not limited by telomeres Each division of a normal cell reduces the length of its telomeres. Normal cells arrest further division once telomeres reach a certain length. Cancer cells avoid this arrest and/or maintain the length of their telomeres. 5. Sustained angiogenesis Most cancers require the growth of new blood vessels into the tumor. Normal angiogenesis is regulated by both inhibitory and stimulatory signals not required in cancer cells. 6. Tissue invasion and metastasis Normal cells generally do not migrate (except in embryo development). Cancer cells invade other tissues including vital organs. 7. Deregulated metabolic pathways Cancer cells use an abnormal metabolism to satisfy a high demand for energy and nutrients. 8. Evasion of the immune system Cancer cells are able to evade the immune system. 9. Chromosomal instability Severe chromosomal abnormalities are found in most cancers. 10. Inflammation Local chronic inflammation is associated with many types of cancer. |


3.9: Versions and Version History
By the end of this section, you will be able to:
- Access and use versioning features in Google Docs
- Access and use versioning features in Microsoft Word
This section delves into a feature of Microsoft Word and Google Docs called versioning . Versioning refers to the technology where programs store multiple iterations of files until they are approved and saved. Essentially, several edited versions of the file are maintained on an online server, as well as the original document. Versioning technology can give you some peace of mind that your original document is saved somewhere, and that any changes will need to be accepted (approved) before the final document is saved.
There are many user-friendly options in Docs’s versioning, as you can clearly see all of the changes created within each version, as well as the time stamps for when each version was made. With this versioning technology, your team can edit a document simultaneously, and everyone will see the changes happening and what changes were made before you started working with the document. You will also see when other collaborators add or edit the text. This sharing of the views of the document adds accountability to the work on the final version of the document. It can be used to enhance communication about the rationale for suggestions when comments are used. In Word, there are fewer options for accessing and using version history features, but they do exist if you keep your documents stored on Microsoft’s cloud service, OneDrive , or on a SharePoint server.
When you are creating the market trends report, you will be sending the draft to key personnel in various departments to contribute to the report. Using these collaboration features will help as the document moves through each stage toward a final, accurate report.
Versioning in Docs
With versioning, you no longer have to worry about losing your files if your laptop battery dies. You do not have to be concerned if your program suddenly shuts down before you had a chance to save that last paragraph you typed. Docs has a feature that, as long as you are connected to the internet, autosaves every change you make to the file. There is no Save or Save As command because Docs is constantly saving in Google Drive, which creates version histories. This version history can be accessed by going to the File menu, then hovering over Version history, then selecting See version history. A sidebar will spring up to the right, as shown in Figure 3.64, listing many versions of the file, each with a time stamp and the name of the person or people using it at the time it was saved. With this Docs feature, it is not necessary to save multiple drafts of the same document. An alternative way to access the version history is by clicking on the title bar that says, Last edit was . . ..
To quickly see new changes in a file, Docs has a See New Changes alert. It appears where the date normally appears, next to the Help menu. If you select that, you’ll be able to see the recent changes from other editors—specifically, you will see all the changes that you haven’t seen since the last time you opened the file. This functionality is useful for quickly and easily seeing changes from collaborators without having to access the version history.
Is Transparency Always the Right Choice?
Suggesting mode in Docs and Track Changes in Word serve the same purpose: Both help teams collaborate and share documents. These functions also help teams maintain accountability on the document’s grammar, usage, style, guidelines, and subject matter inaccuracies or faults. Google automatically logs the chain of events of the addition or editing of text by time and collaborator, tracking who made each change and when they did it. Between the Suggesting mode tool and Docs’s version history, the person in charge of the document or team can monitor the progression of the document and increase the efficiency and speed of its completion.
When sharing documents between a client and a vendor, there could be concerns about access to all the information in the document or the version history. Similarly, a supervisor might not want an employee to see the comments and edits in a document summarizing their job performance and proposed salary increase until they are ready to present it to the employee. That information might be important for the human resources department to keep but does not need to be shared with the employee. So, although Suggesting mode and Track Changes can assist with transparency and accountability, it can also be problematic if information is shared to the wrong audience or before the document is ready to be shared with others.
Now think about different circumstances in your life in which tracking changes and version history could be helpful, harmful, or both. How would you store your different versions?
Browsing Versions
In Docs, all these versions of the same file are organized by date, with the newest on top (Figure 3.65). The top version in the history is the most current and is open by default. You can check the date of the current version on the title bar, right beside the name of the file. You can check the name of the collaborator who made the edits by their name on the bottom of the time stamp, but also by the color of the circle next to the name, as each collaborator will have a different color circle. If multiple people worked on the file, their usernames will be listed below the time stamp, along with their color circle on the side.
The changes on the versions themselves are shown in highlighted font, similar to the Track Changes feature in Word. But unlike Track Changes, each editor’s changes will not be identified with a different color. Just the changes overall will be highlighted. If you want to find out who made the changes, hover the mouse above the text you want to query, and the name of the collaborator will appear. If you don’t want to look at this highlight, as it may be distracting, go to the bottom of the sidebar and uncheck Show changes.
Naming Versions
In Docs, the versions do not have a name; they simply just show a time stamp. If you like a certain version and want to keep it for future reference, or if you want to save it because it shows the progress of the file, select that particular version and give it a specific name so that it’s easy to find. Select the three dots next to the time stamp and a context menu will appear, from which you can choose to Name this version, as shown in Figure 3.67. As you finish typing the name, the time stamp will still appear, yet above it will be the name of that version. This will keep track of the important changes in a collaboration.
To name the current version, go to the File menu, then Version history, then Name current version. Next, type the name of this version in the dialog box and click Save.
After you finish your document, you might have named some of the versions, and you might just want to see only the named versions on the Version History sidebar. You can toggle the unidentified versions on and off, on the top of the sidebar with the option Only show named versions, as you can see in Figure 3.68.
Making a Copy of a Version
To make a copy of a version, you will also use the context menu for the specific version. The menu has the option to make a copy, in which you can make a new separate file from this document. (It is like Save As in Word, in which you can save a version with a different file name.) If you use the Name this version command, you will not create a separate file; it will still be the same document. However, it may be better in some situations to have separate files with descriptive names to them, as you would with different saved Word versions of a document. Many companies have file naming conventions to help them keep track of versions, such as “project#_document_name, ver#”, followed by the initials of the collaborators who made the changes (e.g., “WC05_Market_Trends_Report_ver1_AC”).
Having copies of the same file, but as different versions, is an option if you want to download these versions to your business’s computer desktop or hard drive, instead of keeping them online. Having a different version can also be useful if you want to send this version to a client or any third party. When a copy is made of any version of a document, it is saved as a new Doc, without the version history attached to it. The comments and suggestions are also not copied.
You might find that at some point, you would like to preserve some content from an older version, but not the whole document. In this case, you can go to the older version and look for the information that you want to keep, then right-click to show the context menu, and select Copy. Then, go to the newest version and place the cursor where you want the recovered paragraphs to be, and right-click to the context menu Paste. This will keep your newest version, while adding the older paragraphs.
In addition to saving a copy by the context menu of the three dots, there are other commands available in the list of versions. Right on top of the window of each version there are two different commands you can choose from, zoom in and print, as shown in Figure 3.69. Some people like to have hard copies of versions of documents for archiving purposes.
Restoring Versions
There may be instances when you want to revert to a previous version of the document. This is called version restore . This could occur for a variety of reasons. For example, you might realize some key information that is now needed was in a previous iteration of the document. Your team could also agree that a previous version might be preferred after additional edits are made. This feature of versioning in Docs can offer you some assurance that even if a document has gone through several stages, the previous work on the document is not lost and can be accessed through Restore.
On the main window, where the versions are being read, there is a notification on the top right corner displaying the number of edits of that particular session, as Figure 3.70 shows. Next to the number of edits are two arrows; these are toggles for viewing the session changes. The first change of the May 6, 6:19pm session was to change the date of the marketing report.
You can also restore a version without having it on the main window display by selecting the three dots beside the version and selecting Restore this version. The newer version will not be the current version anymore, as the older version now supersedes it.
If, after reviewing each change, you decide that one of the older versions is better than the current one, you can select the large Restore this version button at the top of the window (Figure 3.71).
Keep in mind that the number of versions displayed on the sidebar does not show all the versions available. If you go to the sidebar, you’ll see that the time stamps are typically a certain length of time apart, as you can see in Figure 3.72. That means that there are hidden versions from when the editing was taking place. Each version has many changes that were happening seconds or minutes apart. You can access these micro changes in each session by clicking on the triangle on the left of the version.
To quickly see new changes in a file, Docs has a See New Changes alert. It appears where the date normally appears, next to the Help menu. If you select that, you’ll be able to see the recent changes from other editors—specifically, you will see all the changes that you haven’t seen since the last time you opened the file. This functionality is useful for quickly and easily seeing changes from collaborators without having to access the version history.
Versioning in Microsoft Word
Microsoft Office has many options for accessing version histories but can be done only if the file is stored in OneDrive or SharePoint Figure 3.73.
If you have a desktop version of Word, you have to sign in to your Microsoft account. You will be able to access the last 25 versions of your file on OneDrive (that is, if your file is stored on OneDrive), as you can see in Figure 3.74.
You can access your version histories in Word by going to the File tab and selecting History. If you have a Microsoft 365 Word subscription, you can access the version history by going to the File tab, then Info, followed by Version History. There you can see the versions available and browse through them. You can also choose to restore a previous version, as Figure 3.75 shows. Moreover, if you have SharePoint Server or SharePoint365, the possibilities of versioning are much more powerful, allowing as many as 500 versions to be retained, as you can track a version’s history, view multiple earlier iterations, determine who can edit or write on the files, control the number of versions stored, and more.
SharePoint is more pliable than Google Drive, but it is not free. Unless your company is paying for a corporate license, you would need to pay a fee per month per user for the standard version (Plan 1), and you would need to have the desktop Microsoft 365. The current plans are priced between $5 and $23 per month. Visit the Microsoft page comparing SharePoint plan options for more information.
If you want the Microsoft 365 applications integrated with SharePoint, you should choose Office 365 E3. This article gives you an idea of the additional capabilities SharePoint has and how users can benefit from versioning.


6.2: Epidemiologic Triangle
Like the early epidemiologists, let’s start by looking at infectious diseases. If we’re trying to understand a certain infectious disease, we need to know the factors that lead to a person’s contracting it. The epidemiologic triangle is a good visual representation of the different factors required for an infectious disease to spread. There has to be some sort of pathogen that causes the disease - this is called the “agent”. This agent is usually one of the following pathogens: bacteria, virus, fungi, protozoa, or prion (we’ll go over these pathogens more in another chapter). This agent has to have a host in order to cause disease in that host. Assuming we are worried only about human hosts (not animals at this point), their risk and severity of disease is influenced by many factors, including their age, sex, susceptibility, immune system function, and other diseases or conditions that they might already have. The third corner of the triangle is the environment, and how it may encourage or discourage disease transmission. If the disease is transmitted through a vector (like a flea, tick, or mosquito bite, or another animal bite), then a fourth factor could be added to the middle of the triangle. The epidemiological triangle helps to identify questions that need to be answered in order to help prevent the spread of infectious diseases. See Fig. \(\PageIndex{1}\) for some examples.


2.4.13: Derivations with Identity predicate
Derivations with identity predicate require additional initial sequents and inference rules.
If \(t\) is a closed term, then \({} \Sequent \eq[t][t]\) is an initial sequent.
The rules for \(\eq[][]\) are ( \(t_1\) and \(t_2\) are closed terms):
If \(s\) and \(t\) are closed terms, then \(\eq[s][t], A(s) \Proves A(t)\) :
This may be familiar as the principle of substitutability of identicals, or Leibniz’ Law.
\(\Log{LK}\) proves that \(\eq[][]\) is symmetric and transitive:
In the proof on the left, the formula \(\eq[x][t_1]\) is our \(A(x)\) . On the right, we take \(A(x)\) to be \(\eq[t_1][x]\) .
Give derivations of the following sequents:
- \(\Sequent \lforall{x}{\lforall{y}{((x = y \land A(x)) \lif A(y))}}\)
- \(\lexists{x}{A(x)} \land \lforall{y}{\lforall{z}{((A(y) \land A(z)) \lif y = z)}} \Sequent \lexists{x}{(A(x) \land \lforall{y}{(A(y) \lif y = x)})}\)


4.6: Formation of the Solar System
Learning Objectives
By the end of this section, you will be able to:
- Describe the motion, chemical, and age constraints that must be met by any theory of solar system formation
- Summarize the physical and chemical changes during the solar nebula stage of solar system formation
- Explain the formation process of the terrestrial and giant planets
- Describe the main events of the further evolution of the solar system
As we have seen, the comets, asteroids, and meteorites are surviving remnants from the processes that formed the solar system. The planets, moons, and the Sun, of course, also are the products of the formation process, although the material in them has undergone a wide range of changes. We are now ready to put together the information from all these objects to discuss what is known about the origin of the solar system.
Observational Constraints
There are certain basic properties of the planetary system that any theory of its formation must explain. These may be summarized under three categories: motion constraints, chemical constraints, and age constraints. We call them constraints because they place restrictions on our theories; unless a theory can explain the observed facts, it will not survive in the competitive marketplace of ideas that characterizes the endeavor of science. Let’s take a look at these constraints one by one.
There are many regularities to the motions in the solar system. We saw that the planets all revolve around the Sun in the same direction and approximately in the plane of the Sun’s own rotation. In addition, most of the planets rotate in the same direction as they revolve, and most of the moons also move in counterclockwise orbits (when seen from the north). With the exception of the comets and other trans-neptunian objects, the motions of the system members define a disk or Frisbee shape. Nevertheless, a full theory must also be prepared to deal with the exceptions to these trends, such as the retrograde rotation (not revolution) of Venus.
In the realm of chemistry, we saw that Jupiter and Saturn have approximately the same composition—dominated by hydrogen and helium. These are the two largest planets, with sufficient gravity to hold on to any gas present when and where they formed; thus, we might expect them to be representative of the original material out of which the solar system formed. Each of the other members of the planetary system is, to some degree, lacking in the light elements. A careful examination of the composition of solid solar-system objects shows a striking progression from the metal-rich inner planets, through those made predominantly of rocky materials, out to objects with ice-dominated compositions in the outer solar system. The comets in the Oort cloud and the trans-neptunian objects in the Kuiper belt are also icy objects, whereas the asteroids represent a transitional rocky composition with abundant dark, carbon-rich material.
This general chemical pattern can be interpreted as a temperature sequence: hot near the Sun and cooler as we move outward. The inner parts of the system are generally missing those materials that could not condense (form a solid) at the high temperatures found near the Sun. However, there are (again) important exceptions to the general pattern. For example, it is difficult to explain the presence of water on Earth and Mars if these planets formed in a region where the temperature was too hot for ice to condense, unless the ice or water was brought in later from cooler regions. The extreme example is the observation that there are polar deposits of ice on both Mercury and the Moon; these are almost certainly formed and maintained by occasional comet impacts.
As far as age is concerned, we discussed that radioactive dating demonstrates that some rocks on the surface of Earth have been present for at least 3.8 billion years, and that certain lunar samples are 4.4 billion years old. The primitive meteorites all have radioactive ages near 4.5 billion years. The age of these unaltered building blocks is considered the age of the planetary system. The similarity of the measured ages tells us that planets formed and their crusts cooled within a few tens of millions of years (at most) of the beginning of the solar system. Further, detailed examination of primitive meteorites indicates that they are made primarily from material that condensed or coagulated out of a hot gas; few identifiable fragments appear to have survived from before this hot-vapor stage 4.5 billion years ago.
The Solar Nebula
All the foregoing constraints are consistent with the general idea, introduced in Other Worlds: An Introduction to the Solar System, that the solar system formed 4.5 billion years ago out of a rotating cloud of vapor and dust—which we call the solar nebula—with an initial composition similar to that of the Sun today. As the solar nebula collapsed under its own gravity, material fell toward the center, where things became more and more concentrated and hot. Increasing temperatures in the shrinking nebula vaporized most of the solid material that was originally present.
At the same time, the collapsing nebula began to rotate faster through the conservation of angular momentum (see Chapter 2). Like a figure skater pulling her arms in to spin faster, the shrinking cloud spun more quickly as time went on. Now, think about how a round object spins. Close to the poles, the spin rate is slow, and it gets faster as you get closer to the equator. In the same way, near the poles of the nebula, where orbits were slow, the nebular material fell directly into the center. Faster moving material, on the other hand, collapsed into a flat disk revolving around the central object (Figure \(\PageIndex{1}\)). The existence of this disk-shaped rotating nebula explains the primary motions in the solar system that we discussed in the previous section. And since they formed from a rotating disk, the planets all orbit the same way.
Picture the solar nebula at the end of the collapse phase, when it was at its hottest. With no more gravitational energy (from material falling in) to heat it, most of the nebula began to cool. The material in the center, however, where it was hottest and most crowded, formed a star that maintained high temperatures in its immediate neighborhood by producing its own energy. Turbulent motions and magnetic fields within the disk can drain away angular momentum, robbing the disk material of some of its spin. This allowed some material to continue to fall into the growing star, while the rest of the disk gradually stabilized.
The temperature within the disk decreased with increasing distance from the Sun, much as the planets’ temperatures vary with position today. As the disk cooled, the gases interacted chemically to produce compounds; eventually these compounds condensed into liquid droplets or solid grains. This is similar to the process by which raindrops on Earth condense from moist air as it rises over a mountain.
Let’s look in more detail at how material condensed at different places in the maturing disk (Figure \(\PageIndex{2}\)). The first materials to form solid grains were the metals and various rock-forming silicates. As the temperature dropped, these were joined throughout much of the solar nebula by sulfur compounds and by carbon- and water-rich silicates, such as those now found abundantly among the asteroids. However, in the inner parts of the disk, the temperature never dropped low enough for such materials as ice or carbonaceous organic compounds to condense, so they were lacking on the innermost planets.
Far from the Sun, cooler temperatures allowed the oxygen to combine with hydrogen and condense in the form of water (H 2 O) ice. Beyond the orbit of Saturn, carbon and nitrogen combined with hydrogen to make ices such as methane (CH 4 ) and ammonia (NH 3 ). This sequence of events explains the basic chemical composition differences among various regions of the solar system.
Example \(\PageIndex{1}\): rotation of the solar nebula
We can use the concept of angular momentum to trace the evolution of the collapsing solar nebula. The angular momentum of an object is proportional to the square of its size (diameter) divided by its period of rotation (\(D^2/P\)). If angular momentum is conserved, then any change in the size of a nebula must be compensated for by a proportional change in period, in order to keep \(D^2/P\) constant. Suppose the solar nebula began with a diameter of 10,000 AU and a rotation period of 1 million years. What is its rotation period when it has shrunk to the size of Pluto’s orbit, which Appendix F tells us has a radius of about 40 AU?
- Answer
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We are given that the final diameter of the solar nebula is about 80 AU. Noting the initial state before the collapse and the final state at Pluto’s orbit, then
\[\frac{P_{\text{final}}}{P_{\text{initial}}}= \left( \frac{D_{\text{final}}}{D_{\text{initial}}} \right)^2= \left( \frac{80}{10,000} \right)^2=(0.008)^2=0.000064 \nonumber\]
With \(P_{\text{initial}}\) equal to 1,000,000 years, \(P_{\text{final}}\), the new rotation period, is 64 years. This is a lot shorter than the actual time Pluto takes to go around the Sun, but it gives you a sense of the kind of speeding up the conservation of angular momentum can produce. As we noted earlier, other mechanisms helped the material in the disk lose angular momentum before the planets fully formed.
Exercise \(\PageIndex{1}\)
What would the rotation period of the nebula in our example be when it had shrunk to the size of Jupiter’s orbit?
- Answer
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The period of the rotating nebula is inversely proportional to \(D^2\). As we have just seen, \(\frac{P_{\text{final}}}{P_{\text{initial}}} = \left( \frac{D_{\text{final}}}{D_{\text{initial}}} \right)^2\). Initially, we have \(P_{\text{initial}} = 106 yr and \(D_{\text{initial}}\) = 104 AU. Then, if \(D_{\text{final}}\) is in AU, \(P_{\text{final}}\) (in years) is given by \(P_{\text{final}}=0.01D^2_{\text{final}}\). If Jupiter’s orbit has a radius of 5.2 AU, then the diameter is 10.4 AU. The period is then 1.08 years.
Formation of the Terrestrial Planets
The grains that condensed in the solar nebula rather quickly joined into larger and larger chunks, until most of the solid material was in the form of planetesimals, chunks a few kilometers to a few tens of kilometers in diameter. Some planetesimals still survive today as comets and asteroids. Others have left their imprint on the cratered surfaces of many of the worlds we studied in earlier chapters. A substantial step up in size is required, however, to go from planetesimal to planet.
Some planetesimals were large enough to attract their neighbors gravitationally and thus to grow by the process called accretion . While the intermediate steps are not well understood, ultimately several dozen centers of accretion seem to have grown in the inner solar system. Each of these attracted surrounding planetesimals until it had acquired a mass similar to that of Mercury or Mars. At this stage, we may think of these objects as protoplanets —“not quite ready for prime time” planets.
Each of these protoplanets continued to grow by the accretion of planetesimals. Every incoming planetesimal was accelerated by the gravity of the protoplanet, striking with enough energy to melt both the projectile and a part of the impact area. Soon the entire protoplanet was heated to above the melting temperature of rocks. The result was planetary differentiation , with heavier metals sinking toward the core and lighter silicates rising toward the surface. As they were heated, the inner protoplanets lost some of their more volatile constituents (the lighter gases), leaving more of the heavier elements and compounds behind.
Formation of the Giant Planets
In the outer solar system, where the available raw materials included ices as well as rocks, the protoplanets grew to be much larger, with masses ten times greater than Earth. These protoplanets of the outer solar system were so large that they were able to attract and hold the surrounding gas. As the hydrogen and helium rapidly collapsed onto their cores, the giant planets were heated by the energy of contraction. But although these giant planets got hotter than their terrestrial siblings, they were far too small to raise their central temperatures and pressures to the point where nuclear reactions could begin (and it is such reactions that give us our definition of a star). After glowing dull red for a few thousand years, the giant planets gradually cooled to their present state (Figure \(\PageIndex{3}\)).
The collapse of gas from the nebula onto the cores of the giant planets explains how these objects acquired nearly the same hydrogen-rich composition as the Sun. The process was most efficient for Jupiter and Saturn; hence, their compositions are most nearly “cosmic.” Much less gas was captured by Uranus and Neptune, which is why these two planets have compositions dominated by the icy and rocky building blocks that made up their large cores rather than by hydrogen and helium. The initial formation period ended when much of the available raw material was used up and the solar wind (the flow of atomic particles) from the young Sun blew away the remaining supply of lighter gases.
Further Evolution of the System
All the processes we have just described, from the collapse of the solar nebula to the formation of protoplanets, took place within a few million years. However, the story of the formation of the solar system was not complete at this stage; there were many planetesimals and other debris that did not initially accumulate to form the planets. What was their fate?
The comets visible to us today are merely the tip of the cosmic iceberg (if you’ll pardon the pun). Most comets are believed to be in the Oort cloud, far from the region of the planets. Additional comets and icy dwarf planets are in the Kuiper belt, which stretches beyond the orbit of Neptune. These icy pieces probably formed near the present orbits of Uranus and Neptune but were ejected from their initial orbits by the gravitational influence of the giant planets.
In the inner parts of the system, remnant planetesimals and perhaps several dozen protoplanets continued to whiz about. Over the vast span of time we are discussing, collisions among these objects were inevitable. Giant impacts at this stage probably stripped Mercury of part of its mantle and crust, reversed the rotation of Venus, and broke off part of Earth to create the Moon (all events we discussed in other chapters).
Smaller-scale impacts also added mass to the inner protoplanets. Because the gravity of the giant planets could “stir up” the orbits of the planetesimals, the material impacting on the inner protoplanets could have come from almost anywhere within the solar system. In contrast to the previous stage of accretion, therefore, this new material did not represent just a narrow range of compositions.
As a result, much of the debris striking the inner planets was ice-rich material that had condensed in the outer part of the solar nebula. As this comet-like bombardment progressed, Earth accumulated the water and various organic compounds that would later be critical to the formation of life. Mars and Venus probably also acquired abundant water and organic materials from the same source, as Mercury and the Moon are still doing to form their icy polar caps.
Gradually, as the planets swept up or ejected the remaining debris, most of the planetesimals disappeared. In two regions, however, stable orbits are possible where leftover planetesimals could avoid impacting the planets or being ejected from the system. These regions are the asteroid belt between Mars and Jupiter and the Kuiper belt beyond Neptune. The planetesimals (and their fragments) that survive in these special locations are what we now call asteroids, comets, and trans-neptunian objects.
Astronomers used to think that the solar system that emerged from this early evolution was similar to what we see today. Detailed recent studies of the orbits of the planets and asteroids, however, suggest that there were more violent events soon afterward, perhaps involving substantial changes in the orbits of Jupiter and Saturn. These two giant planets control, through their gravity, the distribution of asteroids. Working backward from our present solar system, it appears that orbital changes took place during the first few hundred million years. One consequence may have been scattering of asteroids into the inner solar system, causing the period of “heavy bombardment” recorded in the oldest lunar craters.
Key Concepts and Summary
A viable theory of solar system formation must take into account motion constraints, chemical constraints, and age constraints. Meteorites, comets, and asteroids are survivors of the solar nebula out of which the solar system formed. This nebula was the result of the collapse of an interstellar cloud of gas and dust, which contracted (conserving its angular momentum) to form our star, the Sun, surrounded by a thin, spinning disk of dust and vapor. Condensation in the disk led to the formation of planetesimals, which became the building blocks of the planets. Accretion of infalling materials heated the planets, leading to their differentiation. The giant planets were also able to attract and hold gas from the solar nebula. After a few million years of violent impacts, most of the debris was swept up or ejected, leaving only the asteroids and cometary remnants surviving to the present.
Glossary
- accretion
- the gradual accumulation of mass, as by a planet forming from colliding particles in the solar nebula
Contributors and Attributions
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Andrew Fraknoi (Foothill College), David Morrison (NASA Ames Research Center), Sidney C. Wolff (National Optical Astronomy Observatory) with many contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at https://openstax.org/details/books/astronomy ).


12.5.7: Summary
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Summary
The networking revolution has completely changed how the computer is used. Today, no one would imagine using a computer that was not connected to one or more networks. The development of the Internet and World Wide Web, combined with wireless access, has made information available at our fingertips. The Web 2.0 revolution has made us all authors of web content. As networking technology has matured, the use of Internet technologies has become a standard for every type of organization. The use of intranets and extranets has allowed organizations to deploy functionality to employees and business partners alike, increasing efficiencies and improving communications. Cloud computing has truly made information available everywhere and has serious implications for the role of the IT department.
Study Questions
- What were the first four locations hooked up to the Internet (ARPANET)?
- What does the term packet mean?
- Which came first, the Internet or the World Wide Web?
- What was revolutionary about Web 2.0?
- What was the so-called killer app for the Internet?
- What makes a connection a broadband connection?
- What does the term VoIP mean?
- What is an LAN?
- What is the difference between an intranet and an extranet?
- What is Metcalfe’s Law?
Exercises
- What is the IP address of your computer? How did you find out? What is the IP address of google.com? How did you find out? Did you get IPv4 or IPv6 addresses?
- What is the difference between the Internet and the World Wide Web? Create at least three statements that identify the differences between the two.
- Who are the broadband providers in your area? What are the prices and speeds offered?
- Pretend you are planning a trip to three foreign countries in the next month. Consult your wireless carrier to determine if your mobile phone would work properly in those countries. What would the costs be? What alternatives do you have if it would not work?
- "UN sets goal of bringing broadband to half developing world’s people by 2015.", UN News Center website, http://www.un.org/apps/news/story.as...1#.Ut7JOmTTk1J ↵