7.5: Introduction to Tuberculosis and Antitubercular Drugs
By the end of this section, you should be able to:
- 7.4.1 Describe the pathophysiology of common sexually transmitted infections.
- 7.4.2 Identify clinical manifestations related to common sexually transmitted infections.
- 7.4.3 Identify the etiology and diagnostic studies related to common sexually transmitted infections.
- 7.4.4 Identify various methods to prevent the transmission of sexually transmitted infections.
- 7.4.5 Identify the characteristics of drugs used to treat common sexually transmitted infections.
- 7.4.6 Explain the indications, actions, adverse reactions, and interactions of drugs used to treat common sexually transmitted infections.
- 7.4.7 Describe nursing implications of drugs used to treat common sexually transmitted infections.
- 7.4.8 Explain the client education related to drugs used to treat common sexually transmitted infections.
According to the World Health Organization, more than 1 million sexually transmitted infections (STIs) are acquired every day (2023b). Many of these are asymptomatic, which accounts for their rapid spread between sexual partners. The consequences of not appropriately preventing, screening for, and treating STIs are numerous and include complications such as infertility, cancer, pregnancy complications, and increased risk for HIV infection. Due to the societal stigma around STIs, many people may be hesitant to seek out care for STIs because of perceived judgement from friends, family, and health care professionals. Nurses should always adopt a curious, nonjudgmental approach with clients to encourage open and honest communication so that clients get the care they need and deserve.
Bacterial Infections
Bacteria are known to cause several STIs, and they respond well to antibiotics covered previously in this chapter. One ongoing concern with the treatment of bacterial STIs is the development of drug-resistant bacteria that do not respond to traditional therapies. Health care professionals should follow the latest clinical guidelines from the Centers for Disease Control and Prevention .
Bacterial Vaginosis
Bacterial vaginosis (BV) is a common cause of vaginal discharge and occurs when the normal bacterial flora of the vagina shift from the normally dominant lactobacilli to other pathogenic species. Disruption of the normal vaginal flora can occur for a variety of reasons, but sex with multiple partners, douching, and not using condoms are cited as the most common risk factors. Individuals with BV may be asymptomatic or can have signs and symptoms such as vaginal discharge and fishy odor. Treatment is necessary to prevent outcomes such as acquisition of other STIs, pelvic inflammatory disease (PID), and preterm delivery if pregnant.
Chlamydia
Chlamydia is one of the most reported STIs in the United States, with more than 1.6 million cases being reported in 2021 (CDC, 2023a). The condition is caused by the organism Chlamydia trachomatis , which can spread during sexual intercourse. Clients with chlamydia may present with painful urination and urethral discharge in males or vaginal discharge in females. However, many affected individuals are asymptomatic and are diagnosed only if screened. Screening usually includes a nucleic acid amplification test (NAAT) to look for the presence of the organism. Untreated cases of chlamydia can progress to PID in female clients, which may result in chronic pain and infertility.
Gonorrhea
Gonorrhea is the second most reported STI in the United States, with over 700,000 cases being reported in 2021 (CDC, 2023a). The condition is caused by Neisseria gonorrhoeae , which is transmitted during sexual contact. As with chlamydia, some clients will remain asymptomatic, which aids in the spread to sexual partners. The most common presenting symptoms include mucopurulent penile discharge and painful urination. Diagnosis is made using a NAAT to look for presence of the organism. Complications from untreated cases of gonorrhea include PID, infertility, and increased risk for HIV infection.
Syphilis
Syphilis is a bacterial infection caused by the spirochete Treponema pallidum . It can be transmitted perinatally and through sexual contact. Syphilis can present in a variety of ways depending on the stage to which it has advanced. Primary syphilis is associated with a painless chancre on tissue that was exposed to the organism (usually the genital tissue). Secondary syphilis occurs as the organism spreads through the lymph system, producing skin lesions throughout the body. The third stage of syphilis is the latent phase, when the symptoms of the secondary stage disappear. In the most advanced stage, the organism can invade the body’s organ systems, including the central nervous system (neurosyphilis) and the cardiovascular system (cardiovascular syphilis) and can result in stroke, seizures, vision problems, and death. Several tests can be performed to diagnose syphilis; the rapid plasma reagin (RPR) and venereal disease research laboratory (VDRL) tests are the most common.
Trending Today
Increasing Rates of STIs
The CDC tracks STI rates year to year and documented over 2.5 million cases in 2021, which is a marked increase from 2020 (CDC, 2023b). Although rates rose in all parts of the United States, certain populations were disproportionately affected, including gay and bisexual males; and females who belong to racial and ethnic minorities . The changes included more cases of gonorrhea and chlamydia and a 32.5% increase in congenital syphilis cases. Congenital syphilis occurs when an infant acquires the infection in utero from the birthing parent, and it is a cause of stillbirths and infant deaths. The CDC has called for an increased commitment to educating, preventing, and treating these infections to help reverse this trend. All health care professionals should be able to discuss sexual health topics with clients to increase disease awareness and teach them about safe practices to help prevent future cases of STIs.
Viral Infections
Viruses cause some STIs and may exist alongside the various bacterial organisms discussed previously. Unlike bacterial STIs, most of the viral STIs do not have definitive curative therapy, meaning these infections may become lifelong conditions to manage.
Herpes Simplex
Herpes simplex virus (HSV) , discussed earlier in the chapter, is a major cause of genital ulcerations in the United States, with an estimated 572,000 cases reported each year (CDC, 2021). Despite its prevalence, many individuals are asymptomatic, leading to transmission of the condition without the person’s knowledge. Ulcerations are often painful and can occur in multiple episodes per year in susceptible individuals. Individuals with HSV infection are also more susceptible to HIV infection.
Human Papillomavirus
Human papillomavirus (HPV) is a DNA virus that spreads through skin-to-skin contact. HPV infection is also prevalent; an estimated 42.5 million people contracted the virus in 2018 (CDC, 2021). Most individuals who contract HPV remain asymptomatic; however, the signs and symptoms include genital warts, which can produce varying levels of discomfort. Many subtypes of HPV exist and are linked to different types of cancer, including cervical, anal, vaginal, and oropharyngeal cancers. This association prompted development of an HPV vaccine that protects against nine strains of the virus. The vaccine protects against cervical, vulvar, and vaginal cancer in females along with anal cancer and genital warts in both females and males.
Other Pathogenic Infections
A variety of other microorganisms are responsible for STIs, including trichomoniasis , a genitourinary infection that is caused by the protozoan parasite Trichomonas vaginalis. It is the most common nonviral STI; the CDC estimated that 6.9 million cases occurred in 2018 (CDC, 2021). Trichomoniasis infections are spread through sexual contact and typically present with purulent vaginal discharge and painful urination. As with many other conditions discussed, untreated trichomoniasis can lead to PID, infertility, and increased risk for HIV infection. A NAAT is available for screening clients for trichomoniasis to aid in diagnosis.
Preventing Transmission of STIs
Preventing STI transmission is the single best step individuals can take to protect their sexual health. Several strategies are available and should be discussed with clients to help prevent future infections from occurring. The most important way to prevent the spread of STIs is through education. Nurses should teach clients how STIs are transmitted and how they prevent infections.
STIs can be transmitted to anyone who has sexual contact (oral, vaginal, anal) with an infected individual, so one way to prevent transmission is to reduce unprotected contact. Correct and consistent use of barrier methods of protection, such as condoms, can reduce the risk for STI transmission. Clients should be instructed to use either latex or polyisoprene condoms because lambskin condoms are too porous to prevent the transmission of many organisms that cause STIs. Routine screening for individuals who do not use barrier methods of protection or who have multiple sexual partners can also detect STIs earlier, allowing earlier treatment and prevention of asymptomatic transmission to other individuals. Reducing the number of sexual partners can also decrease the risk for transmission. Finally, vaccination can help prevent several STIs, including HPV and HBV infections. Vaccines should be given before the onset of sexual activity because they will have little efficacy if the client has already been infected.
When diagnosed with an STI, the client should be encouraged to have their sexual partners tested as well because many infections may be asymptomatic. In addition, an asymptomatic infection may serve as a reservoir for transmission back to the client or to other sexual partners. Clients should also be educated to refrain from sexual activity while being treated for an STI to prevent transmission.
  By communicating openly, partners can share information about their STI status, discuss previous experiences, and make informed decisions together about contraception and safer sex practices. It is important for nurses to help create a nonjudgmental and supportive environment in which individuals feel comfortable discussing their sexual health concerns and seeking appropriate medical care when needed.
Special Considerations
Sexually Transmitted Infections
Health equity refers to the equal chance of every person to be healthy regardless of race, ethnicity, income, gender, religion, sexual identity, or disability. Unfortunately, data have shown that certain groups are more prone to STIs and encounter various structural and cultural barriers that prevent them from accessing the care they deserve (Norris et al., 2019). Notable groups disproportionately affected by STIs include females and some members of ethnic and racial minority groups. The reasons for this disparity are complex and multifactorial but include having insufficient financial support to access health care, being generally distrustful of the health care system, and being sexually active in communities in which sexual partners are more likely to have an STI. No single health care professional will be able to fix these problems, but they can educate and foster open and honest communication with their clients. This includes teaching them strategies to reduce the risk for acquiring an STI, directing the client to resources for preventive devices such as condoms, and fostering a nonjudgmental environment to encourage client honesty about their sexual health.
(Source: CDC, 2023c)
Drugs to Treat STIs
A variety of drugs are used to treat STIs in clinical practice; many were discussed in the previous sections. This section presents the agents that are appropriate for specific STIs and the concerns regarding resistance issues that have developed over time.
Antimicrobials
The ideal antimicrobial to treat an STI is one that is effective, has few adverse effects, is inexpensive, and can be given as a single dose or short course to ensure adherence. However, drug resistance continues to be problematic for drugs used to treat STIs. Therefore, nurses should make sure to regularly review current guidelines for the treatment of STIs. The following are common antimicrobials used to treat STIs:
- Metronidazole: Metronidazole has good activity against anaerobic bacteria and protozoa. For this reason, metronidazole is recommended for treatment of BV and trichomoniasis. The client’s sexual partners should also be treated with metronidazole to prevent reinfection. Metronidazole may be given either orally or as a vaginal gel.
- Clindamycin: Clindamycin is an alternative treatment for BV if metronidazole cannot be used. It can be given orally or as a vaginal cream. Oral options are less preferred due to the risk for C. difficile infection and severe diarrhea.
- Penicillin: Penicillin is considered the treatment of choice for syphilis. It can be given as a single-dose, long-acting intramuscular injection to assist with client adherence. Continuous intravenous infusion may be necessary to treat neurosyphilis.
- Ciprofloxacin: Ciprofloxacin is a fluoroquinolone antibiotic that has some activity against N. gonorrhea and C. trachomatis . Due to fluoroquinolone overuse, antimicrobial resistance is a major issue with continued use of this drug, and guidelines list ciprofloxacin only as an alternative agent if clients cannot receive other first-line therapies such as ceftriaxone or doxycycline. Clients should be educated to avoid taking ciprofloxacin with any multivitamins or dairy products because iron and calcium can bind to the drug and render it ineffective.
- Ceftriaxone: Ceftriaxone is the treatment of choice for gonorrhea. It can be given as a single intramuscular injection for most cases of uncomplicated gonorrhea. The main adverse effect expected with this treatment is pain at the injection site, which can be offset by mixing ceftriaxone with a local anesthetic such as lidocaine.
- Doxycycline: Doxycycline is a tetracycline antibiotic that is the treatment of choice for chlamydia. Single doses of the macrolide azithromycin used to be the preferred therapy, but due to rising chlamydial resistance, doxycycline is now considered first-line therapy. The downside of doxycycline is that it must be given twice daily over 7 days, so nurses should impress upon the client the need to take all doses to prevent treatment failure and to control resistance.
Safety Alert
Doxycycline
It is important to educate clients using doxycycline to avoid taking the medication with calcium- or iron-containing products to ensure absorption. Clients should also be instructed to avoid prolonged sun exposure and to use appropriate sun protection (e.g., physical coverings, sunscreen) to prevent sunburn.
- Erythromycin: Erythromycin is a macrolide antibiotic that can be used for treating neonatal gonococcal and chlamydial infections acquired perinatally from the birthing parent. Known or suspected infections can be treated with systemically administered erythromycin, and ophthalmic ointment administered to newborns as prophylaxis is standard of care in many U.S. hospitals. Approximately 1 cm in length of ointment should be administered into each lower conjunctival sac. The ointment should not be flushed from the eye following instillation. A new tube should be used for each infant.
Antivirals
Although not curative for any viral STIs, the antivirals acyclovir, valacyclovir, and famciclovir are used to help manage the symptoms of HSV and prevent spread to sexual partners. Nurses should inform clients taking antivirals for STIs that even if they do not have active lesions, viral shedding can still occur and thereby spread the infection to partners. If clients are taking antivirals for episodic management of HSV-related lesions, they should begin therapy within 24 hours of symptom onset to ensure drug efficacy. Chronic suppressive therapy, in which clients take the medication every day regardless of symptom status, can help prevent spread to sexual partners, but nurses should instruct clients to use additional protective measures such as condoms if the partner does not have HSV.
Table 7.11 lists commonly used medications to treat STIs and typical routes and dosing for adult clients.
| Drug | Routes and Dosage Ranges |
|---|---|
|
Acyclovir
( Zovirax ) |
Herpes simplex virus, mucocutaneous infection: 400 mg orally 3 times daily for 7–10 days. |
|
Ceftriaxone
( Rocephin ) |
Gonococcal infection: 500 mg intramuscularly once. |
|
Clindamycin
( Cleocin ) |
Bacterial vaginosis: 300 mg orally twice daily for 7 days. |
|
Doxycycline
( Vibramycin ) |
Chlamydia: 100 mg orally twice daily for 7 days. |
|
Metronidazole
( Flagyl ) |
Trichomoniasis: 500 mg orally twice daily for 7 days. |
|
Penicillin G benzathine
( Bicillin L-A ) |
Syphilis: 2.4 million units intramuscularly once. |
Nursing Implications
The nurse should do the following for clients who are taking medications for STIs:
- Monitor for signs and symptoms of anaphylaxis (e.g., shortness of breath, difficulty breathing, difficulty swallowing).
- Advise the client to take the entire prescribed course of the drug to ensure adequate treatment and to reduce the development of drug resistance.
- Instruct the client to maintain adequate hydration; monitor kidney function for renally eliminated medications such as penicillin and ciprofloxacin.
- Educate about safer sex practices and ways to avoid STIs in the future.
- Mix ceftriaxone with lidocaine, as ordered, to reduce the pain of intramuscular injections for treatment of gonorrhea.
- Provide client teaching regarding the drug and when to call the health care provider. See below for client teaching guidelines.
Client Teaching Guidelines
The client taking a medication for an STI should:
- Alert their health care provider about any signs of allergic reactions, including throat swelling, severe itching, rash, or chest tightness.
- Alert their health care provider that they are taking these medications, including the dose and frequency.
- Take the drug with food if it causes an upset stomach.
- Take a missed dose as soon as they remember; however, they should not take double doses.
- Avoid consuming alcohol when receiving metronidazole/tinidazole treatment.
- Avoid taking ciprofloxacin or doxycycline with iron- or calcium-containing products because they will prevent the drug from being absorbed.
- Use sunscreen or protective coverings while out in the sun to prevent rash or sunburn when taking doxycycline.
- Refrain from sexual activity while taking medications for an STI.
- Use barrier methods such as condoms to help prevent transmission of HSV because transmission can occur even when no active lesions are present.
- Encourage all sexual partners to be tested as well to determine whether they also require treatment.


20.3B: Types of Adaptive Immunity
The adaptive immune response is mediated by B and T cells and creates immunity memory.
- Distinguish between the types of adaptive immunity
Key Points
- B cells and T cells, the major types of lymphocytes, are very important in the adaptive immune system.
- B cells, type 2 helper T cells, antibodies, mast cells, and eosinophils are involved in the humoral immune response.
- Type 1 helper T cells and cytoxic T-cells are involved in cell-mediated immune response.
- Cytotoxic T cells kill pathogens through release of perforin, granzymes, and proteases, which cause the target cell to undergo apoptosis.
- Antibodies bind to pathogens to opsonize them, neutralize pathogen toxins, and activate the complement complex system. IgE also alerts circulating mast cells and eosinophils of known antigens, which causes a rapid inflammatory response.
Key Terms
- cell-mediated immunity : Adaptive immunity that is not controlled by antibodies and is instead mediated directly by immune cells themselves, most notably type 1 helper T cells and cytotoxic T-cells.
- humoral immunity : Adaptive immunity that refers to antigen-specific components flowing through the plasma, such as antibodies, their function, and the cells that produce them.
The adaptive immune system mounts a stronger, antigen-specific immune response after the innate immune response fails to prevent a pathogen from causing an infection. There are two subdivisions of the adaptive immune system: cell-mediated immunity and humoral immunity.
Cell-Mediated Immunity
Cell mediated immunity is controlled by type 1 helper T cells (T h 1) and cytotoxic T cells. These cells are activated by antigen-presenting cells, which causes them to rapidly mature into forms specific to that antigen. T cells then circulate through the body to destroy pathogens in several ways. Helper T cells facilitate the immune response by guiding cytotoxic T cells to pathogens or pathogen-infected cells, which they will then destroy.
Cytotoxic T cells kill pathogens in several ways, including the release of granules that contain the cytotoxins perforin and granzyme, which lyse small pores in the membrane of a pathogen. Then T-cell produced proteases enter the pathogen and induce an apoptosis response within the cell. Helper T cells secrete cytokines such as interferon-gamma, which can activate cytotoxic T cells and macrophages.
Humoral Immunity
Humoral immunity refers to the component of the adaptive immune response that is caused by B cells, antibodies, and type 2 helper T cells (T h 2), as well as circulating mast cells and eosinophils to a lesser extent. Its name comes from the idea that blood is one of the humors of the body, since antibodies provide passive or active immunity through circulation in the bloodstream.
Type 2 helper T cells are included in the humoral immune system because they present antigens to immature B-cells, which undergo proliferation to become specific to the presented antigen. The B cells then rapidly produce a large number of antibodies that circulate through the body’s plasma.
Antibodies provide a number of functions in humoral immunity. Six different classes of antibodies provide distinct functions and interact with different cells in the immune system. All antibodies bind to pathogens to opsonize them, which makes it easier for phagocytic cells to bind to and destroy the pathogen. They also neutralize the toxins produced by certain pathogens and provide complement pathway activation, in which circulating proteins are combined in a complex cascade that forms a membrane attack complex on a pathogen cell membrane, which lyses the cell.
Mast cells and eosinophils are considered part of the humoral immune system because they can be sensitized towards certain antigens through circulating immunoglobin E (IgE), a specific type of antibody produced by B cells. IgE binds to the mast cells and eosinophils when an antigen is detected, using a type of Fc receptor on the mast cell or eosinophil that has a high-binding affinity with IgE. This binding will cause degranulation and release of inflammatory mediators that start an immune response against the antigen. This process is the reason why memory B cells can cause hypersensitivity (allergy) formation, as circulating IgE from those memory cells will activate a rapid inflammatory and immune response.
Types of Adaptive Immunity : This diagram of adaptive immunity indicates the flow from antigen to APC, MHC2, CD4+, T helper cells, B cells, antibodies, macrophages, and killer T cells.


5.7: Writing Purpose
You should identify your purpose before you start writing. This purpose will guide your writing process and your decisions about how to write and what to include. Sometimes your instructor will provide a purpose for your writing. Other times, your purpose will depend on what effect you want your writing to have on your audience. What is your goal? What do you hope for your audience to think, feel, or do after reading it?
To figure out your purpose, start by looking at the course assignment guidelines. The verbs in your guidelines can help you determine the purpose of your writing. Once you know your ultimate goal, you can choose appropriate language. The verbs that you use will help your audience anticipate the direction of your work and also ensure congruence in your writing. For example, if your purpose is to argue, the audience can expect a debate with information strategically presented to convey a point of view. Instead, if your purpose is to inform the audience, your writing may be neutral with no specific point of view.
Here are a few possible purposes:
- Persuade/inspire your audience to act or think about an issue from your point of view.
- Challenge your audience or make them question their thinking or behaviour.
- Argue for or against something your audience believes or change their minds or behaviour.
- Inform/teach your audience about a topic they don’t know much about.
- Connect with your audience emotionally and help them feel understood.
- Motivate your audience to continue to research/investigate and learn about the topic.
- Inspire your audience to share and apply what they learn to their nursing practice.
Student Tip
Purpose Statement
When writing a purpose statement , consider the audience. Write your purpose clearly and concisely. As you do this, choose your verbs purposefully and limit the number of verbs you use.
Attribution statement
Content from this page was remixed with our own original content, and with editorial changes, adapted from:
The Word on College Reading and Writing by Carol Burnell, Jaime Wood, Monique Babin, Susan Pesznecker, and Nicole Rosevear, licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.Download for free at: https://openoregon.pressbooks.pub/wrd/


21.4: Western Canada during the Mesozoic
The Mesozoic extends over 187 million years from the beginning of the Triassic (252 Ma) to the end of the Cretaceous (65.5 Ma). It was a particularly important period for the geology of western Canada. During this time, several continental collisions occurred along the west coast, resulting in the formation of the Rocky Mountains and the accretion (addition) of much of the land mass of British Columbia, and continuing deposition within the WCSB.
Terrane Accretion in British Columbia and Yukon
Continued subduction along the western edge of North America carried a number of continental terranes toward the coast, with the first collisions taking place in the early part of the Triassic, as the Quesnel, Cache Creek, and Stikine Terranes combined to form the Intermontane Superterrane, so named because it forms the interior plateau of British Columbia, between the Rockies to the east and the Coast Range to the west (Figure \(\PageIndex{1}\)).
Approximately 100 million years later, another pair of terranes—Alexander and Wrangellia—collided to form most of Vancouver Island and Haida Gwaii, plus a significant part of Alaska. During the Cenozoic, additional terranes (the Outboard terranes) were added to the western edge of North America. An overview of the accreted terranes of B.C., Yukon, and Alaska is given in Figure \(\PageIndex{2}\).
During the Jurassic, the Intermontane Superterrane acted like a giant bulldozer, pushing, folding, and thrusting the existing Proterozoic and Paleozoic west coast sediments eastward and upward to form the Rocky Mountains (Figure \(\PageIndex{3}\)). The same process continued into the Cretaceous as the Insular Superterrane collided with North America and pushed the Intermontane Superterrane farther east. Folding in Rocky Mountain rocks, like that shown in Figures 21.4.4 and 21.4.5, is one of the results of this process.
Thrusting is another important process in the formation of fold-belt mountains, as described in Chapter 12. During plate convergence, entire sheets of sedimentary rock are slowly pushed over top of other sheets, resulting in situations where older rocks lie on top of younger ones. One of the best known examples of this is at Mt. Yamnuska, near Exshaw, Alberta (Figure \(\PageIndex{6}\)), where the older Cambrian rocks were pushed east by a total of 40 km, over top of younger rocks.
In the area near the U.S. border, within B.C., Alberta, and Montana, a sheet of Paleozoic rocks has been thrust about 80 km east over top of Cretaceous rocks along the Lewis Fault (Figure \(\PageIndex{7}\)).
Not only did the subduction of oceanic crust beneath North America during the Mesozoic deliver geologically exotic terranes to the western edge of the continent, it also resulted in massive amounts of volcanism along the boundary (Figure \(\PageIndex{1}\)). The upper-crustal magma chambers that fed those now-eroded volcanoes slowly cooled into granitic and dioritic stocks, and those stocks gradually coalesced into batholiths that extend from the southwest corner of B.C. all the way into Yukon and Alaska (Figures 21.4.8 and 21.4.9). Most of the granitic rocks of this region fall into two main age ranges: many are middle-Jurassic to early Cretaceous in age (~ 170 Ma to 140 Ma), while others are late Cretaceous to Paleogene (~50 Ma to 90 Ma). Many of the older bodies intruded into the terranes they are on before they arrived on the North America coast. This applies to those on Vancouver Island and Haida Gwaii. Some of the older ones formed in situ when the subduction zone was farther east (see Figure \(\PageIndex{1}\)). Most of the younger bodies formed in situ when the subduction zone was close to where it is now (west of Vancouver Island) or slightly to the east.
Although these intrusive igneous rocks cooled at depth in the upper crust, they now form some of the highest peaks in Canada, many of them hundreds of meters higher than those of the Rocky Mountains (including Mt. Waddington, the highest peak entirely within British Columbia at 4,091 m). It is estimated that over the past 100 million years some of these igneous bodies have been uplifted in the order of 8,000 m. Much of that uplift is a result of the relative low density of the granitic rocks compared with the surrounding rocks.
The Western Canada Sedimentary Basin during the Mesozoic
The construction of the Rocky Mountains during the Jurassic and Cretaceous—and their ensuing erosion—created a significant new source of sediments for the WCSB. Based on the ages, distributions, and thicknesses of the sedimentary layers (Figure \(\PageIndex{11}\)), it is evident that the greatest volumes of sediment were produced in the Upper Cretaceous (100 Ma to 65 Ma) and into the Paleocene (65 Ma to 55 Ma). The sediments accumulated in a basin that is thought to have been at least partly formed by the presence of a subducting slab of oceanic lithosphere underneath this part of North America. However, the ongoing uplift of the Rockies through this time period also led to isostatic depression of the crust. The western edge of the basin, which has about 4,500 m of Mesozoic rock alone, is a foreland basin. (See Chapter 6 for more on the origins of basins.)
From time to time during the Mesozoic, the WCSB was filled to varying degrees with marine water. The Jurassic rocks at the base of the sequence are marine in origin, although the Jurassic sequence in Manitoba also includes evaporite layers. Most of the Middle Cretaceous rocks across the basin are marine, but the majority of the Upper Cretaceous rocks are of terrestrial origin, deposited within the flood plains and deltas of rivers. Some of these terrestrial sediments include coal layers; as described in Chapter 20, there are significant coal deposits in central Alberta.
The Paleozoic sediments within the WCSB were buried deeply beneath the Mesozoic sediments and were heated enough to form both oil and gas. There are large petroleum resources in reservoir rocks of various ages extending from northeastern B.C. to southwestern Manitoba.
Several of the terrestrial Cretaceous formations in the WCSB are host to important dinosaur fossils. Some are within B.C. and Saskatchewan, but the most famous are in Alberta, including the Dinosaur Park Formation ( Figure \(\PageIndex{1}\) ), the Scollard Formation, and the Horseshoe Canyon Formation (Figure \(\PageIndex{12}\)). The Dinosaur Park Formation has one of the greatest concentrations of dinosaur fossils of any rock on Earth, with at least 50 genera of dinosaurs represented, ranging from tiny Hesperonychus to giant Albertosaurus. The Hilda Bone Bed, situated about 80 km to the east of Dinosaur Park, is estimated to have the remains of approximately 1500 ceratopsians, all of which are interpreted to have died in a flood related to a tropical storm . A few of the larger herbivorous dinosaurs found at Dinosaur Park are illustrated in Figure \(\PageIndex{13}\).
The photo is from the Cretaceous Dinosaur Park Formation in Alberta. What characteristic of this rock tells you that it might be suitable for the discovery of the fossils of dinosaurs or other terrestrial organisms?
See Appendix 3 for Exercise 21.4 answers.
Several important depositional basins existed in British Columbia during the Mesozoic, including the large Jurassic-aged Bowser Basin north of Terrace, and the smaller late-Cretaceous Nanaimo Basin between Vancouver Island and the mainland. In both cases, the rocks are mostly clastic, with both terrestrial and marine deposition.
Image Descriptions
Figure \(\PageIndex{1}\) image description: During the early Triassic period (around 250 Ma), subduction along the west coast of North America caused the Quesnel, Cache Creek, and Stikine Terranes to collide with the continent. By the Jurassic persion (180 Ma), the collision had caused the formation of mountains along the coast and the creation of the Intermontane Superterrane, the present interior plateau of British Columbia. The Alexander and Wrangellia Terranes were also pulled towards the coast and by the Cretaceous period (around 90 Ma), they had formed the Insular Superterrane. [Return to Figure \(\PageIndex{1}\)]
Figure \(\PageIndex{2}\) image description: This image shows two groups of terranes, the Intermontane terranes and the Insular terranes. The Intermontane terranes make up the interior portions of present-day British Columbia and the Yukon. The Yukon-Tanana terrane in the Yukon and the Quesnel terrane in BC are the farthest inland. As you move closer to the coast, there is the Cache Creek terrane and the Stikine terrane. Then comes the Insular terrane group. This includes the Alexander terrane and the Wrangellia terrane, which make up the coast and islands of British Columbia. [Return to Figure \(\PageIndex{2}\)]
Figure \(\PageIndex{8}\) image description: Cretaceous rocks cover a lot of the southwest coast of BC and a bit in the north. Jurassic rocks can be found on the northwest coast of BC, scattered sparsely through the interior, and a bit on Haida Gwaii, and Vancouver Island. [Return to Figure \(\PageIndex{8}\)]
| Period/Era/Epoch | Age (Ma) | Location of sedimentary rocks |
|---|---|---|
| Paleozoic Era | 540 to 251 |
|


Unit 5: Molecular Orbitals
Molecular Orbital Theory
Molecular Orbital (MO) Theory is a sophisticated bonding model. It is generally considered to be more powerful than Lewis and Valence Bond Theories for predicting molecular properties; however, this power comes at the price of complexity. In its full development, MO Theory requires complex mathematics, though the ideas behind it are simple. Atomic orbitals (AOs) that are localized on individual atoms combine to make molecular orbitals (MOs) that are distributed over the molecule. The simplest example is the molecule dihydrogen (H 2 ), in which two independent hydrogen 1s orbitals combine to form the \(\sigma\) bonding MO and the \(\sigma\) antibonding MO of the dihydrogen molecule (see figure). The MO’s are also called Linear Combinations of Atomic Orbitals (LCAO).
-
- 5.3: Diatomic MO Diagrams
-
- 5.3.1: Homonuclear Diatomic Molecules
- <IP_ADDRESS>: Molecular Orbitals
- <IP_ADDRESS>: Orbital Mixing
- <IP_ADDRESS>: Diatomic Molecules of the First and Second Periods
- <IP_ADDRESS>: Photoelectron Spectroscopy
- 5.3.2: Heteronuclear Diatomic Molecules
- <IP_ADDRESS>: Orbital ionization energies
- <IP_ADDRESS>: Polar bonds
- <IP_ADDRESS>: Ionic Compounds and Molecular Orbitals


3.5: Assessing the Fit of a Line (2 of 4)
Learning Objectives
- Use residuals, standard error, and r 2 to assess the fit of a linear model.
Introduction
Now we move from calculating the residual for an individual data point to creating a graph of the residuals for all the data points. We use residual plots to determine if the linear model fits the data well.
Residual Plots
The graph below shows a scatterplot and the regression line for a set of 10 points. The blue points represent our original data set, that is, our observed values. The red points, lying directly on the regression line, are the predicted values.
The vertical arrows from the predicted to observed values represent the residuals. The up arrows correspond to positive residuals, and the down arrows correspond to negative residuals.
Now consider the following pair of graphs. The top graph is a copy of the graph we looked at above. In the graph below, we plotted the values of the residuals on their own. (The explanatory variable is still plotted on the horizontal axis, though it is not indicated this here.) This is called a residual plot .
In the residual plot, each point with a value greater than zero corresponds to a data point in the original data set where the observed value is greater than the predicted value. Similarly, negative values correspond to data points where the observed value is less than the predicted value.
What are we looking for in a residual plot?
We use residual plots to determine if a linear model is appropriate. In particular, we look for any unexpected patterns in the residuals that may suggest that the data is not linear in form.
To help us identify an unexpected pattern, we start by looking at what we expect to see in a residual plot when the form is linear.
Example
No Pattern in Residual Plot
Consider the pair of graphs below. Here we have a scatterplot for a data set consisting of 400 observations. The regression line is shown in the scatterplot. The residual plot is below the scatterplot.
In this example, the line in the scatterplot is a good summary of the positive linear pattern in the data. Notice that the points in the residual plot seem to be randomly scattered. As we examine the residuals from left to right, they don’t appear to follow a particular path, nor does the cloud of points widen or narrow in any systematic way. We see no particular pattern. Thus, in the ideal case, when a linear model is really a good fit, we expect to see no pattern in the residual plot.
Our general principle when looking at residual plots, then, is that a residual plot with no pattern is good because it suggests that our use of a linear model is appropriate.
However, we must be flexible in applying this principle because what we see usually lies somewhere between the extremes of no pattern and a clear pattern. Let’s look at some specific examples.
Example
Patterns in Residual Plots
At first glance, the scatterplot appears to show a strong linear relationship. The correlation is r = 0.84. However, when we examine the residual plot, we see a clear U-shaped pattern. Looking back at the scatterplot, this movement of the data points above, below and then above the regression line is noticeable. The residual plot, particularly when graphed at a finer scale, helps us to focus on this deviation from linearity.
The pattern in the residual plot suggests that our linear model may not be appropriate because the model predictions will be too high for values in the middle of the range of the explanatory variable and too low for values at the two ends of that range. A model with a curvilinear form may be more appropriate.
Example
Patterns in Residual Plots 2
This scatterplot is based on datapoints that have a correlation of r = 0.75. In the residual plot, we see that residuals grow steadily larger in absolute value as we move from left to right. In other words, as we move from left to right, the observed values deviate more and more from the predicted values. Again, we have chosen a smaller vertical scale for the residual plot to help amplify the pattern to make it easier to see.
The pattern in the residual plot suggests that predictions based on the linear regression line will result in greater error as we move from left to right through the range of the explanatory variable.
Example
Highway Sign Visibility
Let’s return now to our original example and take a look at what the residual plot tell us about the appropriateness of applying a linear model to this data.
Note that the residuals are fairly randomly dispersed. However, they seem to be a bit more spread out on the left and right than they are in the middle. As we look at higher ages, there seems to be greater variation in the residuals, which suggests that we may want to be more cautious if we are trying to predict distances for older drivers. And the risks associated with extrapolation beyond the range of the data seem to be even greater here. In this case, we may still use this linear model but condition the use of it on our analysis of the residual plot.
Here again are four scatterplots with regression lines shown and four corresponding residual plots.
Contributors and Attributions
- Concepts in Statistics. Provided by : Open Learning Initiative. Located at : http://oli.cmu.edu . License : CC BY: Attribution


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1: Topics in General Chemistry I
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1.1: Expressing Numbers - Significant Figures
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Significant figures properly report the number of measured and an estimated digit in a measurement. There are rules for applying significant figures in calculations.
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1.2: Expressing Numbers - Scientific Notation
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Scientific notation is a system for expressing very large or very small numbers as a simple number multiplied by 10 raised to a certain exponent, or power. Scientific notation expressed numbers using powers of 10.
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1.3: Converting Units-Dimensional Analysis
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The ability to convert from one unit to another is an important skill. A unit can be converted to another unit of the same type with a conversion factor.
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1.4: States of Matter - Solid, Liquid, and Gas
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Three states of matter exist: solid, liquid, and gas. Solids have a definite shape and volume. Liquids have a definite volume, but take the shape of the container. Gases have no definite shape or volume
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1.5: Energy
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When we speak of using energy, we are really referring to transferring energy from one place to another. Although energy is used in many kinds of different situations, all of these uses rely on energy being transferred in one of two ways. Energy can be transferred as heat or as work.
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1.6: Measurements and Units
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Chemists measure the properties of matter and express these measurements with a number and a unit. The basic units in the SI system of mass, length, temperature, time, and amount of substance are commonly used in chemistry.
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1.7: Temperature - Motion of Molecules and Atoms
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Three different scales are commonly used to measure temperature: Fahrenheit (°F), Celsius (°C), and Kelvin (K).
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1.8: Density and Specific Gravity
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Density is the ratio of the mass of an object to its volume. Specific gravity is the ratio of the density of a substance to the density of water.
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1.9: Dosage Calculations I
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Conversion factors are important in calculating dosages of medications administered to patients.
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1.10: Metric Prefixes
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Metric prefixes derive from Latin or Greek terms. The prefixes are used to make the units manageable. The SI system is based on multiples of ten.
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1.11: Dosage Calculations II
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Drug dosage calculation is required if the physician’s order is different from what is available. We will see examples where the medications are administered as fluids or tablets.
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1.12: End of Chapter Problems I
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This problem set is based on Chapter 1 topics.
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1.13: End of Chapter Problems II
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This problem set is based on simple one-step dosage calculations.
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1.14: End of Chapter Problems III
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This problem set is based on metric prefixes and multi-step dosage calculations.


4: Microsoft Word Intermediate Skills Last updated Save as PDF Page ID 46380 Learning Objectives Change page layout Create and modify text boxes Create tables to organize information in a Word document Place images in a Word document Add a hyperlink 4.1: Why It Matters- Microsoft Word Intermediate Skills 4.2: Introduction to Page Layout 4.3: Tab Stops 4.4: Columns 4.5: Headers and Footers 4.6: Introduction to Text Boxes 4.7: Text Boxes 4.8: Introduction to Tables 4.9: Creating Tables 4.10: Converting Text to a Table 4.11: Formatting Tables 4.12: Introduction to Images 4.13: Adding Images 4.14: Text Wrap 4.15: Introduction to Hyperlinks 4.16: Hyperlinks 4.17: Putting It Together- Microsoft Word Intermediate Skills 4.18: Assignment- Create Document with Tables and Images 4.19: Discussion- Cover Pages


23.5F: Control of Catabolic Pathways
Catabolic pathways are controlled by enzymes, proteins, electron carriers, and pumps that ensure that the remaining reactions can proceed.
- Explain how catabolic pathways are controlled
Key Points
- Glycolysis, the citric acid cycle, and the electron transport chain are catabolic pathways that bring forth non-reversible reactions.
- Glycolysis control begins with hexokinase, which catalyzes the phosphorylation of glucose; its product is glucose-6- phosphate, which accumulates when phosphofructokinase is inhibited.
- The citric acid cycle is controlled through the enzymes that break down the reactions that make the first two molecules of NADH.
- The rate of electron transport through the electron transport chain is affected by the levels of ADP and ATP, whereas specific enzymes of the electron transport chain are unaffected by feedback inhibition.
Key Terms
- phosphofructokinase : any of a group of kinase enzymes that convert fructose phosphates to biphosphate
- glycolysis : the cellular metabolic pathway of the simple sugar glucose to yield pyruvic acid and ATP as an energy source
- kinase : any of a group of enzymes that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific target molecules (substrates); the process is termed phosphorylation
Control of Catabolic Pathways
Enzymes, proteins, electron carriers, and pumps that play roles in glycolysis, the citric acid cycle, and the electron transport chain tend to catalyze non-reversible reactions. In other words, if the initial reaction takes place, the pathway is committed to proceeding with the remaining reactions. Whether a particular enzyme activity is released depends upon the energy needs of the cell (as reflected by the levels of ATP, ADP, and AMP).
Glycolysis
The control of glycolysis begins with the first enzyme in the pathway, hexokinase. This enzyme catalyzes the phosphorylation of glucose, which helps to prepare the compound for cleavage in a later step. The presence of the negatively-charged phosphate in the molecule also prevents the sugar from leaving the cell. When hexokinase is inhibited, glucose diffuses out of the cell and does not become a substrate for the respiration pathways in that tissue. The product of the hexokinase reaction is glucose-6-phosphate, which accumulates when a later enzyme, phosphofructokinase, is inhibited.
Glycolysis : The glycolysis pathway is primarily regulated at the three key enzymatic steps (1, 2, and 7) as indicated. Note that the first two steps that are regulated occur early in the pathway and involve hydrolysis of ATP.
Phosphofructokinase is the main enzyme controlled in glycolysis. High levels of ATP, citrate, or a lower, more acidic pH decrease the enzyme’s activity. An increase in citrate concentration can occur because of a blockage in the citric acid cycle. Fermentation, with its production of organic acids like lactic acid, frequently accounts for the increased acidity in a cell; however, the products of fermentation do not typically accumulate in cells.
The last step in glycolysis is catalyzed by pyruvate kinase. The pyruvate produced can proceed to be catabolized or converted into the amino acid alanine. If no more energy is needed and alanine is in adequate supply, the enzyme is inhibited. The enzyme’s activity is increased when fructose-1,6-bisphosphate levels increase. (Recall that fructose-1,6-bisphosphate is an intermediate in the first half of glycolysis. ) The regulation of pyruvate kinase involves phosphorylation, resulting in a less-active enzyme. Dephosphorylation by a phosphatase reactivates it. Pyruvate kinase is also regulated by ATP (a negative allosteric effect).
If more energy is needed, more pyruvate will be converted into acetyl CoA through the action of pyruvate dehydrogenase. If either acetyl groups or NADH accumulate, there is less need for the reaction and the rate decreases. Pyruvate dehydrogenase is also regulated by phosphorylation: a kinase phosphorylates it to form an inactive enzyme, and a phosphatase reactivates it. The kinase and the phosphatase are also regulated.
Citric Acid Cycle
The citric acid cycle is controlled through the enzymes that catalyze the reactions that make the first two molecules of NADH. These enzymes are isocitrate dehydrogenase and α-ketoglutarate dehydrogenase. When adequate ATP and NADH levels are available, the rates of these reactions decrease. When more ATP is needed, as reflected in rising ADP levels, the rate increases. α-Ketoglutarate dehydrogenase will also be affected by the levels of succinyl CoA, a subsequent intermediate in the cycle, causing a decrease in activity. A decrease in the rate of operation of the pathway at this point is not necessarily negative as the increased levels of the α-ketoglutarate not used by the citric acid cycle can be used by the cell for amino acid (glutamate) synthesis.
Citric Acid Cycle : Enzymes, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, catalyze the reactions that make the first two molecules of NADH in the citric acid cycle. Rates of the reaction decrease when sufficient ATP and NADH levels are reached.
Electron Transport Chain
Specific enzymes of the electron transport chain are unaffected by feedback inhibition, but the rate of electron transport through the pathway is affected by the levels of ADP and ATP. Greater ATP consumption by a cell is indicated by a buildup of ADP. As ATP usage decreases, the concentration of ADP decreases: ATP begins to build up in the cell. This change in the relative concentration of ADP to ATP triggers the cell to slow down the electron transport chain.
Electron Chain Transport : Levels of ADP and ATP affect the rate of electron transport through this type of chain transport.


18: Disease and Epidemiology (Part A)
In the United States and other developed nations, public health is a key function of government. A healthy citizenry is more productive, content, and prosperous; high rates of death and disease, on the other hand, can severely hamper economic productivity and foster social and political instability. The burden of disease makes it difficult for citizens to work consistently, maintain employment, and accumulate wealth to better their lives and support a growing economy.
In this chapter, we will explore the intersections between microbiology and epidemiology , the science that underlies public health. Epidemiology studies how disease originates and spreads throughout a population, with the goal of preventing outbreaks and containing them when they do occur. Over the past two centuries, discoveries in epidemiology have led to public health policies that have transformed life in developed nations, leading to the eradication (or near eradication) of many diseases that were once causes of great human suffering and premature death. However, the work of epidemiologists is far from finished. Numerous diseases continue to plague humanity, and new diseases are always emerging. Moreover, in the developing world, lack of infrastructure continues to pose many challenges to efforts to contain disease.
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- 18.1: How Diseases Spread
- Pathogens often have elaborate adaptations to exploit host biology, behavior, and ecology to live in and move between hosts. Hosts have evolved defenses against pathogens, but because their rates of evolution are typically slower than their pathogens (because their generation times are longer), hosts are usually at an evolutionary disadvantage. This section will explore where pathogens survive—both inside and outside hosts—and some of the many ways they move from one host to another.
Thumbnail: The biohazard symbol was developed by the Dow Chemical Company in 1966 for their containment products. It is used in the labeling of biological materials that carry a significant health risk. (Public Domain; Silsor).


34.8: Madison Unchained
As modern technology increases and evolves within the U.S., old traditions such as reading literature have begun to fade. As screens take over our lives, people are less inclined to pick up a book and read for pleasure or learning. This is not to say that reading has become obsolete, but it is becoming more and more evident that young Americans would much rather watch a movie, a television show, or a documentary than read a book. Despite the fact that people may not read as often as they used to, the movies and shows that they watch now are still based upon written works: the screenplays. Writers can still present knowledge, allegory, themes, and ideas in their work and attract a wide audience through live action film. For instance, Quentin Tarantino’s Django Unchained deals with themes such as slavery and abolitionism much like early American works of literature such as The Heroic Slave .
In the U.S. today, it seems as if practically every household has access to the internet. The internet has an infinite supply of sources which makes gaining information so much easier than it was in the eighteen-hundreds when The Heroic Slave was written. In that time, not everyone was literate and therefore many people were unable to educate themselves. Books were a luxury; not every household had the means to worry about building their personal library. The Heroic Slave was written with the intent to shed light on slavery from the perspective of a slave who was a human with thoughts, emotions, and good morals. It was to show that slaves weren’t just livestock or property, but that they were people who deserved their freedom. In fact, the novel opens up with a soliloquy as the protagonist laments over the fact that a snake is born with more freedom than himself, “here I am, a man—yes, a man! —with thoughts and wishes, with powers and faculties as far as angel’s flight above that hated reptile, yet he is my superior” (5). The novel, however, could only reach a limited audience because racism was far more prominent; people were much less likely to pick up a book written by a black author, and a large portion of the populace was illiterate leaving them unable to read at all. Education in America has immensely improved throughout the centuries and although most people can read, it is not a favored pastime. That is why a movie like Django is able to capture such a large audience in which it can pass on similar motifs and themes as The Heroic Slave . The entire film is available on YouTube for free, meaning that any person with access to the internet is able to view it; the movie already has 1.5 million views on YouTube and was only published on the site eight months ago.
Django Unchained is directed by the notorious Tarantino, who is famous for his gore-filled thrillers. Tarantino has had a very successful career in the film industry and has produced many cult-classics such as Pulp Fiction and Kill Bill. The popularity of these films shows how well gory films are received by an American audience. Violence sells. By combining elements of the classic spaghetti western with his own directorial flare, and America’s history with slavery, Tarantino creates an adaptation of classic slave literature in order to make a statement on America’s cruel past while simultaneously attracting a wide audience. While slavery has been abolished for centuries, it has seared some long-lasting effects into American society. Django Unchained reminds America of its horrid past with slavery as it follows Django on his journey to rescue his wife.
While Django Unchained is far more violent and vulgar than Frederick Douglass’s The Heroic Slave , the plotline still bears many similarities with Douglass’s novel. Both protagonists gain their freedom by escaping, both protagonists have the help of a white companion, and both protagonists risk their lives and their freedom in order to rescue their wives who are still enslaved.  Django meets a German man named Dr. Schultz who happens to be a bounty hunter that kills white criminals. Dr. Schultz does not agree with slavery and sees Django as what he truly is: another human being. Dr. Schultz actually frees Django when he kills the slave traders that had him in their captivity. He enlists Django as his partner and the two travel throughout the south. Django eventually trusts Dr. Schultz enough to tell him about his wife, Brunhilda, and Schultz agrees to help him rescue her from slavery. The scene where Django tells of Brunhilda is very reminiscent of Madison telling Mr. Listwell about his attempt to save his wife, “I could not bear the thought of leaving her in the cruel jaws of slavery, without making an effort to rescue her” (36). Both characters’ freedom means nothing to them while their lives are still enslaved.
One of the main differences between Django and The Heroic Slave is the bloody twist, as it is an action movie directed by Tarantino. When Django becomes a bounty hunter, he soon realizes that he is a skilled sharpshooter. He is able to draw his gun in a flash and shoot with precise accuracy. Throughout the film, it becomes clear that Django takes pride in this skill and actually enjoys slaughtering white men. Though they are killing lawfully (they only kill criminals who are wanted dead or alive) it seems as though Django is also killing for revenge.  Madison, on the other hand, strictly made it a point not to kill for revenge during his slave rebellion, “God is my witness that liberty , not malice , is the motive for this night’s work… we do not thirst for your blood, we demand only our rightful freedom” (48-49). Many of Tarantino’s other films focus on revenge as a theme, such as Kill Bill . A mission of revenge is something people like to watch on the big screen, and while Django’s thirst for revenge is a character flaw, it is that mission of revenge that the American audience is attracted to.
Today we are able to gain knowledge in so many different forms through technology. For example, the online anthology used in Rethinking American Literature makes obtaining required texts much easier for students. Many students are on a tight budget and any text the students can use online for free helps immensely. Many other sources beyond books can help spread knowledge as well; almost any film or documentary is out on the internet somewhere ready to be downloaded or streamed. YouTube is a favored tool of both students and teachers alike as it has many contributors producing educational content as well as pop culture. As technology advances, students have access to a plethora of sources that can enhance their learning experience in any field of study.
#slavery #technology #education #adaptation
Django Unchained Full Film: https://www.youtube.com/watch?v=PuxxKDbh7AE


14.21: Assignment- Create Queries for Access Database
In this assignment you’ll import and existing database of past orders from a bakery and use the skills you have learned in this module to create a query in the data table.
To complete this assignment, download the Excel file here . [1] Follow the directions, then submit your assignment. If you get stuck on a step, review this module and ask your classmates for help in the discussion forum.
- Open a new Access database and save the new Module 14 assignment file to the Rowan folder on your desktop as BA132_LastName_QueryDB.accdb, replacing “LastName” with your own last name. (Example: BA132_Hywater_Memo) It is a good idea to save your work periodically.
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Import External Data:
With the Access new database open import the Excel data file into Access.
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Import Wizard:
Set up the imported data into a new table, make sure the box with first row with column heading is checked and let Access add the primary key, and name the table.
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Create a Query:
Use the Query Wizard and created a query that is a simple query and uses the ‘Product TableProduct Name’ and the ‘Quantity’ sections of the table.
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Resize Columns of Query:
Resize the first column to be able to read the names of all the products.
- Query Design: Now create a second query, but this time from when you run the wizard button choose to ‘Modify the query design’.
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Add New Criteria:
Now you wish just to see the number of orders that were chocolate chip cookies. Enter that in the criteria field.
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Run Query:
Run the query, resize the first column and see how many orders there were for chocolate chip cookies.
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Run Third Query:
Now, run another query but this time for “pecan” and when the results are displayed, add in an Autosum total at the bottom and see how many pecan orders have been placed. Save this query.
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Rename Queries:
Rename the queries to match what is queried to better remember for what they are searching.
- Save: Save the file as an Access database and make sure all the queries have been saved as well.
- Submit the presentation file in your course online.
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Data source: GCFLearnFree.org.
Access – Designing a Simple Query.
Database sample
↵
Contributors and Attributions
CC licensed content, Original
- Assignment: Create Queries for Access Database. Authored by : Sherri Pendleton. Provided by : Lumen Learning. License : CC BY: Attribution


9.3A: Force of Muscle Contraction
The force a muscle generates is dependent on its length and shortening velocity.
- Differentiate between force-length and force-velocity of muscle contraction
Key Points
- The force -length relationship indicates that muscles generate the greatest force when at their resting (ideal) length, and the least amount of force when shortened or stretched relative to the resting length.
- The force-velocity relationship demonstrates that power produced is controlled by the velocity and force of muscle contraction, with an optimum power output at one third of maximum velocity.
Key Terms
- force : Any influence that causes an object to undergo a certain change concerning its movement, direction, or geometrical construction.
- resting length : Often the ideal length of a muscle and the length at which it can create the greatest active force.
- power : A measure of force x velocity, a measurable output for muscle contraction
- Force-Velocity Relationship : The relationship between the speed and force of muscle contraction, outputted as power.
- Force-Length Relationship : The relationship between sarcomere length and force produced in the muscle, modulated by actin and myosin myofilament overlap.
Muscle Force Generation
The force a muscle generates is dependent on the length of the muscle and its shortening velocity. These two fundamental properties limit many key biomechanical properties, including running speed, strength, and jumping distance.
Force-Length Relationship
Due to the presence of titin, muscles are innately elastic. Skeletal muscles are attached to bones via tendons that maintain the muscle under a constant level of stretch called the resting length. If this attachment was removed, for example if the bicep was detached from the scapula or radius, the muscle would shorten in length.
The Ideal Length of a Sarcomere : Sarcomeres produce maximal tension when thick and thin filaments overlap between about 80 percent to 120 percent, approximately 1.6 to 2.6 micrometers.
Muscles exist in this state to optimize the force produced during contraction, which is modulated by the interlaced myofilaments of the sarcomere. When a sarcomere contracts, myosin heads attach to actin to form cross-bridges. Then, the thin filaments slide over the thick filaments as the heads pull the actin. This results in sarcomere shortening, creating the tension of the muscle contraction. If a sarcomere is stretched too far, there will be insufficient overlap of the myofilaments and the less force will be produced. If the muscle is over-contracted, the potential for further contraction is reduced, which in turn reduces the amount of force produced.
Simply put, the tension generated in skeletal muscle is a function of the magnitude of overlap between actin and myosin myofilaments.
In mammals, there is a strong overlap between the optimum and actual resting length of sarcomeres.
Force-Velocity Relationship
Force-Velocity Relationship : As velocity increases force and therefore power produced is reduced. Although force increases due to stretching with no velocity, zero power is produced. Maximum power is generated at one-third of maximum shortening velocity.
The force-velocity relationship in muscle relates the speed at which a muscle changes length with the force of this contraction and the resultant power output (force x velocity = power). The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force. However, cross-bridge formation is not immediate, so if myofilaments slide over each other at a faster rate the ability to form cross bridges and resultant force are both reduced.
At maximum velocity no cross-bridges can form, so no force is generated, resulting in the production of zero power (right edge of graph). The reverse is true for stretching of muscle. Although the force of the muscle is increased, there is no velocity of contraction and zero power is generated (left edge of graph). Maximum power is generated at approximately one-third of maximum shortening velocity.


14.2: How Microscopes Work
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Learning Objectives
- Identify and define the characteristics of electromagnetic radiation (EMR) used in microscopy
- Explain how lenses are used in microscopy to manipulate visible and ultraviolet (UV) light
- Describe historical developments and individual contributions that led to the invention and development of the microscope
- Compare and contrast the features of simple and compound microscopes
- Identify and describe the parts of a brightfield microscope
- Calculate total magnification for a compound microscope
- Describe the distinguishing features and typical uses for various types of light microscopes, and electron microscopes.
Clinical Focus: part 1
Cindy, a 17-year-old counselor at a summer sports camp, scraped her knee playing basketball 2 weeks ago. At the time, she thought it was only a minor abrasion that would heal, like many others before it. Instead, the wound began to look like an insect bite and has continued to become increasingly painful and swollen.
The camp nurse examines the lesion and observes a large amount of pus oozing from the surface. Concerned that Cindy may have developed a potentially aggressive infection, she swabs the wound to collect a sample from the infection site. Then she cleans out the pus and dresses the wound, instructing Cindy to keep the area clean and to come back the next day. When Cindy leaves, the nurse sends the sample to the closest medical lab to be analyzed under a microscope.
Exercise \(\PageIndex{1}\)
What are some things we can learn about these bacteria by looking at them under a microscope?
Visible light consists of electromagnetic waves that behave like other waves. Hence, many of the properties of light that are relevant to microscopy can be understood in terms of light’s behavior as a wave. An important property of light waves is the wavelength, or the distance between one peak of a wave and the next peak. The height of each peak (or depth of each trough) is called the amplitude. In contrast, the frequency of the wave is the rate of vibration of the wave, or the number of wavelengths within a specified time period (Figure \(\PageIndex{1}\)).
Interactions of Light
Light waves interact with materials by being reflected, absorbed, or transmitted. Reflection occurs when a wave bounces off of a material. For example, a red piece of cloth may reflect red light to our eyes while absorbing other colors of light. Absorbance occurs when a material captures the energy of a light wave. In the case of glow-in-the-dark plastics, the energy from light can be absorbed and then later re-emitted as another form of phosphorescence. Transmission occurs when a wave travels through a material, like light through glass (the process of transmission is called transmittance). When a material allows a large proportion of light to be transmitted, it may do so because it is thinner, or more transparent (having more transparency and less opacity). Figure \(\PageIndex{2}\) illustrates the difference between transparency and opacity.
Exercise \(\PageIndex{2}\)
- If a light wave has a long wavelength, is it likely to have a low or high frequency?
- If an object is transparent, does it reflect, absorb, or transmit light?
Lenses and Refraction
In the context of microscopy, refraction is perhaps the most important behavior exhibited by light waves. Refraction occurs when light waves change direction as they enter a new medium (Figure \(\PageIndex{3}\)). Different transparent materials transmit light at different speeds; thus, light can change speed when passing from one material to another. This change in speed usually also causes a change in direction (refraction), with the degree of change dependent on the angle of the incoming light.
The extent to which a material slows transmission speed relative to empty space is called the refractive index of that material. Large differences between the refractive indices of two materials will result in a large amount of refraction when light passes from one material to the other. For example, light moves much more slowly through water than through air, so light entering water from air can change direction greatly. We say that the water has a higher refractive index than air (Figure \(\PageIndex{4}\)).
When light crosses a boundary into a material with a higher refractive index, its direction turns to be closer to perpendicular to the boundary (i.e., more toward a normal- the same angle- to that boundary; Figure \(\PageIndex{5}\)). This is the principle behind lenses. We can think of a lens as an object with a curved boundary (or a collection of prisms) that collects all of the light that strikes it and refracts it so that it all meets at a single point called the focus point (or image point). A convex lens can be used to magnify because it can focus at closer range than the human eye, producing a larger image. Concave lenses and mirrors can also be used in microscopes to redirect the light path. Figure \(\PageIndex{5}\) shows the focal point (the image point when light entering the lens is parallel) and the focal length (the distance to the focal point) for convex and concave lenses.
The human eye contains a lens that enables us to see images.  Artificial lenses placed in front of the eye (contact lenses, glasses, or microscopic lenses) focus light before it is focused (again) by the lens of the eye, manipulating the image that ends up on the retina (e.g., by making it appear larger).
Images are commonly manipulated by controlling the distances between the object, the lens, and the screen, as well as the curvature of the lens. For example, for a given amount of curvature, when an object is closer to the lens, the focal points are farther from the lens. As a result, it is often necessary to manipulate these distances to create a focused image on a screen. Similarly, more curvature creates image points closer to the lens and a larger image when the image is in focus. This property is often described in terms of the focal distance, or distance to the focal point.
Exercise \(\PageIndex{3}\)
- Explain how a lens focuses light at the image point.
- Name some factors that affect the focal length of a lens.
Electromagnetic Spectrum and Color
Visible light is just one form of electromagnetic radiation (EMR), a type of energy that is all around us. Other forms of EMR include microwaves, X-rays, and radio waves, among others. The different types of EMR fall on the electromagnetic spectrum, which is defined in terms of wavelength and frequency. The spectrum of visible light occupies a relatively small range of frequencies between infrared and ultraviolet light (Figure \(\PageIndex{6}\)).
Whereas wavelength represents the distance between adjacent peaks of a light wave, frequency, in a simplified definition, represents the rate of oscillation. Waves with higher frequencies have shorter wavelengths and, therefore, have more oscillations per unit time than lower-frequency waves. Higher-frequency waves also contain more energy than lower-frequency waves. This energy is delivered as elementary particles called photons. Higher-frequency waves deliver more energetic photons than lower-frequency waves.
Photons with different energies interact differently with the retina. In the spectrum of visible light, each color corresponds to a particular frequency and wavelength (Figure \(\PageIndex{6}\)).The lowest frequency of visible light appears as the color red, whereas the highest appears as the color violet. When the retina receives visible light of many different frequencies, we perceive this as white light. However, white light can be separated into its component colors using refraction. If we pass white light through a prism, different colors will be refracted in different directions, creating a rainbow-like spectrum on a screen behind the prism. This separation of colors is called dispersion, and it occurs because, for a given material, the refractive index is different for different frequencies of light.
Certain materials can refract nonvisible forms of EMR and, in effect, transform them into visible light. Certain fluorescent dyes, for instance, absorb ultraviolet or blue light and then use the energy to emit photons of a different color, giving off light rather than simply vibrating. This occurs because the energy absorption causes electrons to jump to higher energy states, after which they then almost immediately fall back down to their ground states, emitting specific amounts of energy as photons. Not all of the energy is emitted in a given photon, so the emitted photons will be of lower energy and, thus, of lower frequency than the absorbed ones. Thus, a dye such as Texas red may be excited by blue light, but emit red light; or a dye such as fluorescein isothiocyanate (FITC) may absorb (invisible) high-energy ultraviolet light and emit green light (Figure \(\PageIndex{7}\)). In some materials, the photons may be emitted following a delay after absorption; in this case, the process is called phosphorescence. Glow-in-the-dark plastic works by using phosphorescent material.
Exercise \(\PageIndex{4}\)
- Which has a higher frequency: red light or green light?
- Explain why dispersion occurs when white light passes through a prism.
- Why do fluorescent dyes emit a different color of light than they absorb?
Magnification, Resolution, and Contrast
Microscopes magnify images and use the properties of light to create useful images of small objects. Magnification is defined as the ability of a lens to enlarge the image of an object when compared to the real object. For example, a magnification of 10⨯ means that the image appears 10 times the size of the object as viewed with the naked eye.
Greater magnification typically improves our ability to see details of small objects, but magnification alone is not sufficient to make the most useful images. It is often useful to enhance the resolution of objects: the ability to tell that two separate points or objects are separate. A low-resolution image appears fuzzy, whereas a high-resolution image appears sharp. Two factors affect resolution. The first is wavelength. Shorter wavelengths are able to resolve smaller objects; thus, an electron microscope has a much higher resolution than a light microscope, since it uses an electron beam with a very short wavelength, as opposed to the long-wavelength visible light used by a light microscope. The second factor that affects resolution is numerical aperture, which is a measure of a lens’s ability to gather light. The higher the numerical aperture, the better the resolution.
Even when a microscope has high resolution, it can be difficult to distinguish small structures in many specimens because microorganisms are relatively transparent. It is often necessary to increase contrast to detect different structures in a specimen. Various types of microscopes use different features of light or electrons to increase contrast—visible differences between the parts of a specimen. Additionally, dyes that bind to some structures but not others can be used to improve the contrast between images of relatively transparent objects.
Exercise \(\PageIndex{5}\)
- Explain the difference between magnification and resolution.
- Explain the difference between resolution and contrast.
- Name two factors that affect resolution.
The Early Microscope
Some of the fundamental characteristics and functions of microscopes can be understood in the context of the history of their use. Italian scholar Girolamo Fracastoro is regarded as the first person to formally postulate that disease was spread by tiny invisible seminaria , or “seeds of the contagion.” In his book De Contagione (1546), he proposed that these seeds could attach themselves to certain objects (which he called fomes [cloth]) that supported their transfer from person to person. However, since the technology for seeing such tiny objects did not yet exist, the existence of the seminaria remained hypothetical for a little over a century—an invisible world waiting to be revealed.
Who Invented the Microscope?
While Antonie van Leeuwenhoek and Robert Hooke generally receive much of the credit for early advances in microscopy, neither can claim to be the inventor of the microscope. While van Leeuwenhoek is credited with the discovery of microorganisms, others before him had contributed to the development of the microscope. These included the Italian astronomer Galileo Galilei, who used a compound microscope to examine insect parts . Whereas van Leeuwenhoek used a simple microscope, in which light is passed through just one lens, Galileo’s compound microscope was more sophisticated, passing light through two sets of lenses.
Some argue that this designation of inventor should belong to Hans and Zaccharias Janssen, Dutch spectacle-makers who may have invented the telescope, the simple microscope, and the compound microscope during the late 1500s or early 1600s (Figure \(\PageIndex{8}\)). Unfortunately, little is known for sure about the Janssens, not even the exact dates of their births and deaths. The Janssens were secretive about their work and never published. It is also possible that the Janssens did not invent anything at all; their neighbor, Hans Lippershey, also developed microscopes and telescopes during the same time frame, and he is often credited with inventing the telescope. The historical records from the time are as fuzzy and imprecise as the images viewed through those early lenses, and any archived records have been lost over the centuries.
By contrast, van Leeuwenhoek and Hooke can thank ample documentation of their work for their respective legacies. Like Janssen, van Leeuwenhoek began his work in obscurity, leaving behind few records. However, his friend, the prominent physician Reinier de Graaf, wrote a letter to the editor of the Philosophical Transactions of the Royal Society of London calling attention to van Leeuwenhoek’s powerful microscopes. From 1673 onward, van Leeuwenhoek began regularly submitting letters to the Royal Society detailing his observations. In 1674, his report describing single-celled organisms produced controversy in the scientific community, but his observations were soon confirmed when the society sent a delegation to investigate his findings. He subsequently enjoyed considerable celebrity, at one point even entertaining a visit by the czar of Russia.
Similarly, Robert Hooke had his observations using microscopes published by the Royal Society in a book called Micrographia in 1665. The book became a bestseller and greatly increased interest in microscopy throughout much of Europe.
Modern Microscopy
The early pioneers of microscopy opened a window into the invisible world of microorganisms. But microscopy continued to advance in the centuries that followed. In 1830, Joseph Jackson Lister created an essentially modern light microscope. The 20th century saw the development of microscopes that leveraged nonvisible light, such as fluorescence microscopy, which uses an ultraviolet light source, and electron microscopy, which uses short-wavelength electron beams. These advances led to major improvements in magnification, resolution, and contrast. By comparison, the relatively rudimentary microscopes of van Leeuwenhoek and his contemporaries were far less powerful than even the most basic microscopes in use today. In this section, we will focus on the most common and applications for each type of microscope.
Light Microscopy
Many types of microscopes fall under the category of light microscopes, which use light to visualize images. Examples of light microscopes include brightfield microscopes, darkfield microscopes, phase-contrast microscopes, differential interference contrast microscopes, fluorescence microscopes, confocal scanning laser microscopes, and two-photon microscopes. These various types of light microscopes can be used to complement each other in diagnostics and research. We will just focus on brightfield, the most common type to be used in labs.
Components of a Typical Brightfield Microscope
The item being viewed is called a specimen. The specimen is placed on a glass slide, which is then clipped into place on the stage(a platform) of the microscope. Once the slide is secured, the specimen on the slide is positioned over the light using the x-y mechanical stage knobs. These knobs move the slide on the surface of the stage, but do not raise or lower the stage. Once the specimen is centered over the light, the stage position can be raised or lowered to focus the image. The coarse focusing knob is used for large-scale movements with 4⨯ and 10⨯ objective lenses; the fine focusing knob is used for small-scale movements, especially with 40⨯ or 100⨯ objective lenses.
When images are magnified, they become dimmer because there is less light per unit area of image. Highly magnified images produced by microscopes, therefore, require intense lighting. In a brightfield microscope, this light is provided by an illuminator, which is typically a high-intensity bulb below the stage. Light from the illuminator passes up through condenser lens (located below the stage), which focuses all of the light rays on the specimen to maximize illumination. The position of the condenser can be optimized using the attached condenser focus knob; once the optimal distance is established, the condenser should not be moved to adjust the brightness. If less-than-maximal light levels are needed, the amount of light striking the specimen can be easily adjusted by opening or closing a diaphragm between the condenser and the specimen. In some cases, brightness can also be adjusted using the rheostat, a dimmer switch that controls the intensity of the illuminator.
A brightfield microscope creates an image by directing light from the illuminator at the specimen; this light is differentially transmitted, absorbed, reflected, or refracted by different structures. Different colors can behave differently as they interact with chromophores (pigments that absorb and reflect particular wavelengths of light) in parts of the specimen. Often, chromophores are artificially added to the specimen using stains, which serve to increase contrast and resolution. In general, structures in the specimen will appear darker, to various extents, than the bright background, creating maximally sharp images at magnifications up to about 1000⨯. Further magnification would create a larger image, but without increased resolution. This allows us to see objects as small as bacteria, which are visible at about 400⨯ or so, but not smaller objects such as viruses.
At very high magnifications, resolution may be compromised when light passes through the small amount of air between the specimen and the lens. This is due to the large difference between the refractive indices of air and glass; the air scatters the light rays before they can be focused by the lens. To solve this problem, a drop of oil can be used to fill the space between the specimen and an oil immersion lens, a special lens designed to be used with immersion oils. Since the oil has a refractive index very similar to that of glass, it increases the maximum angle at which light leaving the specimen can strike the lens. This increases the light collected and, thus, the resolution of the image (Figure \(\PageIndex{10}\)). A variety of oils can be used for different types of light.
Brightfield Microscopes
The brightfield microscope, perhaps the most commonly used type of microscope, is a compound microscope with two or more lenses that produce a dark image on a bright background. Some brightfield microscopes are monocular (having a single eyepiece), though most newer brightfield microscopes are binocular (having two eyepieces), like the one shown in Figure \(\PageIndex{9}\); in either case, each eyepiece contains a lens called an ocular lens. The ocular lenses typically magnify images 10 times (10⨯). At the other end of the body tube are a set of objective lenses on a rotating nosepiece. The magnification of these objective lenses typically ranges from 4⨯ to 100⨯, with the magnification for each lens designated on the metal casing of the lens. The ocular and objective lenses work together to create a magnified image. The total magnification is the product of the ocular magnification times the objective magnification:
\[\text{ocular magnification}\; \times\; \text{objective magnification}\]
For example, if a 40⨯ objective lens is selected and the ocular lens is 10⨯, the total magnification would be
(40×)(10×)=400×
Microscope Maintenance: Best Practices
Even a very powerful microscope cannot deliver high-resolution images if it is not properly cleaned and maintained. Since lenses are carefully designed and manufactured to refract light with a high degree of precision, even a slightly dirty or scratched lens will refract light in unintended ways, degrading the image of the specimen. In addition, microscopes are rather delicate instruments, and great care must be taken to avoid damaging parts and surfaces. Among other things, proper care of a microscope includes the following:
- cleaning the lenses with lens paper
- not allowing lenses to contact the slide (e.g., by rapidly changing the focus)
- protecting the bulb (if there is one) from breakage
- not pushing an objective into a slide
- not using the coarse focusing knob when using the 40⨯ or greater objective lenses
- only using immersion oil with a specialized oil objective, usually the 100⨯ objective
- cleaning oil from immersion lenses after using the microscope
- cleaning any oil accidentally transferred from other lenses
- covering the microscope and/or placing it in a cabinet when not in use
Electron Microscopy
The maximum theoretical resolution of images created by light microscopes is ultimately limited by the wavelengths of visible light. Most light microscopes can only magnify 1000⨯, and a few can magnify up to 1500⨯, but this does not begin to approach the magnifying power of an electron microscope (EM), which uses short-wavelength electron beams rather than light to increase magnification and resolution.
Electrons, like electromagnetic radiation, can behave as waves, but with wavelengths of 0.005 nm, they can produce much better resolution than visible light. An EM can produce a sharp image that is magnified up to 100,000⨯. Thus, EMs can resolve subcellular structures as well as some molecular structures (e.g., single strands of DNA); however, electron microscopy cannot be used on living material because of the methods needed to prepare the specimens.
There are two basic types of EM: the transmission electron microscope (TEM) and the scanning electron microscope (SEM)(Figure \(\PageIndex{11}\)). The TEM is somewhat analogous to the brightfield light microscope in terms of the way it functions. However, it uses an electron beam from above the specimen that is focused using a magnetic lens (rather than a glass lens) and projected through the specimen onto a detector. Electrons pass through the specimen, and then the detector captures the image (Figure \(\PageIndex{12}\)).
For electrons to pass through the specimen in a TEM, the specimen must be extremely thin (20–100 nm thick). The image is produced because of varying opacity in various parts of the specimen. This opacity can be enhanced by staining the specimen with materials such as heavy metals, which are electron dense. TEM requires that the beam and specimen be in a vacuum and that the specimen be very thin and dehydrated. The specific steps needed to prepare a specimen for observation under an EM are discussed in detail in the next section.
SEMs form images of surfaces of specimens, usually from electrons that are knocked off of specimens by a beam of electrons. This can create highly detailed images with a three-dimensional appearance that are displayed on a monitor (Figure \(\PageIndex{13}\)). Typically, specimens are dried and prepared with fixatives that reduce artifacts, such as shriveling, that can be produced by drying, before being sputter-coated with a thin layer of metal such as gold. Whereas transmission electron microscopy requires very thin sections and allows one to see internal structures such as organelles and the interior of membranes, scanning electron microscopy can be used to view the surfaces of larger objects (such as a pollen grain) as well as the surfaces of very small samples (Figure \(\PageIndex{14}\)). Some EMs can magnify an image up to 2,000,000⨯. 1
Exercise \(\PageIndex{6}\)
- What are some advantages and disadvantages of electron microscopy, as opposed to light microscopy, for examining microbiological specimens?
- What kinds of specimens are best examined using TEM? SEM?
Key Concepts and Summary
- Light waves interacting with materials may be reflected, absorbed, or transmitted, depending on the properties of the material.
- Light waves can interact with each other (interference) or be distorted by interactions with small objects or openings (diffraction).
- Refraction occurs when light waves change speed and direction as they pass from one medium to another. Differences in the refraction indices of two materials determine the magnitude of directional changes when light passes from one to the other.
- A lens is a medium with a curved surface that refracts and focuses light to produce an image.
- Visible light is part of the electromagnetic spectrum; light waves of different frequencies and wavelengths are distinguished as colors by the human eye.
- A prism can separate the colors of white light (dispersion) because different frequencies of light have different refractive indices for a given material.
- Fluorescent dyes and phosphorescent materials can effectively transform nonvisible electromagnetic radiation into visible light.
- The power of a microscope can be described in terms of its magnification and resolution.
- Resolution can be increased by shortening wavelength, increasing the numerical aperture of the lens, or using stains that enhance contrast.
- Antonie van Leeuwenhoek is credited with the first observation of microbes, including protists and bacteria, with simple microscopes that he made.
- Robert Hooke was the first to describe what we now call cells.
- Simple microscopes have a single lens, while compound microscopes have multiple lenses.
- Numerous types of microscopes use various technologies to generate micrographs. Most are useful for a particular type of specimen or application.
- Light microscopy uses lenses to focus light on a specimen to produce an image. Commonly used light microscopes include brightfield, darkfield, phase-contrast, differential interference contrast, fluorescence, confocal, and two-photon microscopes.
- Electron microscopy focuses electrons on the specimen using magnets, producing much greater magnification than light microscopy. The transmission electron microscope (TEM) and scanning electron microscope (SEM) are two common forms.
Glossary
- absorbance
- when a molecule captures energy from a photon and vibrates or stretches, using the energy
- amplitude
- the height of a wave
- brightfield microscope
- a compound light microscope with two lenses; it produces a dark image on a bright background
- chromophores
- pigments that absorb and reflect particular wavelengths of light (giving them a color)
- coarse focusing knob
- a knob on a microscope that produces relatively large movements to adjust focus
- condenser lens
- a lens on a microscope that focuses light from the light source onto the specimen
- contrast
- visible differences between parts of a microscopic specimen
- compound microscope
- a microscope that uses multiple lenses to focus light from the specimen
- diaphragm
- a component of a microscope; typically consists of a disk under the stage with holes of various sizes; can be adjusted to allow more or less light from the light source to reach the specimen
- diffraction
- the changing of direction (bending or spreading) that occurs when a light wave interacts with an opening or barrier
- dispersion
- the separation of light of different frequencies due to different degrees of refraction
- electron microscope
- a type of microscope that uses short-wavelength electron beams rather than light to increase magnification and resolution
- fine focusing knob
- a knob on a microscope that produces relatively small movements to adjust focus
- fluorescent
- the ability of certain materials to absorb energy and then immediately release that energy in the form of light
- focal length
- the distance from the lens to the image point when the object is at a definite distance from the lens (this is also the distance to the focal point)
- focal point
- a property of the lens; the image point when light entering the lens is parallel (i.e., the object is an infinite distance from the lens)
- frequency
- the rate of vibration for a light wave or other electromagnetic wave
Footnotes
- illuminator
- the light source on a microscope
- image point (focus)
- a property of the lens and the distance of the object to the lens; the point at which an image is in focus (the image point is often called the focus)
- interference
- distortion of a light wave due to interaction with another wave
- magnification
- the power of a microscope (or lens) to produce an image that appears larger than the actual specimen, expressed as a factor of the actual size
- numerical aperture
- a measure of a lens’s ability to gather light
- objective lenses
- on a light microscope, the lenses closest to the specimen, typically located at the ends of turrets
- ocular lens
- on a microscope, the lens closest to the eye (also called an eyepiece)
- oil immersion lens
- a special objective lens on a microscope designed to be used with immersion oil to improve resolution
- opacity
- the property of absorbing or blocking light
- phosphorescence
- the ability of certain materials to absorb energy and then release that energy as light after a delay
- reflection
- when light bounces back from a surface
- refraction
- bending of light waves, which occurs when a light wave passes from one medium to another
- refractive index
- a measure of the magnitude of slowing of light waves by a particular medium
- resolution
- the ability to distinguish between two points in an image
- rheostat
- a dimmer switch that controls the intensity of the illuminator on a light microscope
- scanning electron microscope (SEM)
- a type of electron microscope that bounces electrons off of the specimen, forming an image of the surface
- simple microscope
- a type of microscope with only one lens to focus light from the specimen
- stage
- the platform of a microscope on which slides are placed
- total magnification
- in a light microscope is a value calculated by multiplying the magnification of the ocular by the magnification of the objective lenses
- transmission electron microscope (TEM)
- a type of electron microscope that uses an electron beam, focused with magnets, that passes through a thin specimen
- transmittance
- the amount of light that passes through a medium
- transparency
- the property of allowing light to pass through
- wavelength
- the distance between one peak of a wave and the next peak
- x-y mechanical stage knobs
- knobs on a microscope that are used to adjust the position of the specimen on the stage surface, generally to center it directly above the light
- 1 “JEM-ARM200F Transmission Electron Microscope,” JEOL USA Inc , www.jeolusa.com/PRODUCTS/Tran...specifications. Accessed 8/28/2015.
Contributor
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Nina Parker, (Shenandoah University), Mark Schneegurt (Wichita State University), Anh-Hue Thi Tu (Georgia Southwestern State University), Philip Lister (Central New Mexico Community College), and Brian M. Forster (Saint Joseph’s University) with many contributing authors. Original content via Openstax (CC BY 4.0; Access for free at https://openstax.org/books/microbiology/pages/1-introduction )