16.E: Antimicrobial Drugs (Exercises)
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- Ying Liu
- City College of San Francisco
14.1: Discovering Antimicrobial Drugs
Antimicrobial drugs produced by purposeful fermentation and/or contained in plants have been used as traditional medicines in many cultures for millennia. The purposeful and systematic search for a chemical “magic bullet” that specifically target infectious microbes was initiated by Paul Ehrlich in the early 20th century. The discovery of the natural antibiotic, penicillin, by Alexander Fleming in 1928 started the modern age of antimicrobial discovery and research.
Multiple Choice
A scientist discovers that a soil bacterium he has been studying produces an antimicrobial that kills gram-negative bacteria. She isolates and purifies the antimicrobial compound, then chemically converts a chemical side chain to a hydroxyl group. When she tests the antimicrobial properties of this new version, she finds that this antimicrobial drug can now also kill gram-positive bacteria. The new antimicrobial drug with broad-spectrum activity is considered to be which of the following?
- resistant
- semisynthetic
- synthetic
- natural
- Answer
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B
Which of the following antimicrobial drugs is synthetic?
- sulfanilamide
- penicillin
- actinomycin
- neomycin
- Answer
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A
Fill in the Blank
The group of soil bacteria known for their ability to produce a wide variety of antimicrobials is called the ________.
- Answer
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actinomycetes
Short Answer
Where do antimicrobials come from naturally? Why?
Why was Salvarsan considered to be a “magic bullet” for the treatment of syphilis?
Critical Thinking
In nature, why do antimicrobial-producing microbes commonly also have antimicrobial resistance genes?
14.2: Antibacterial Drugs
Antimicrobial drugs can be bacteriostatic or bactericidal, and these characteristics are important considerations when selecting the most appropriate drug. The use of narrow-spectrum antimicrobial drugs is preferred in many cases to avoid superinfection and the development of antimicrobial resistance. Broad-spectrum antimicrobial use is warranted for serious systemic infections when there is no time to determine the causative agent or when narrow-spectrum antimicrobials fail.
Multiple Choice
Which of the following combinations would most likely contribute to the development of a superinfection?
- long-term use of narrow-spectrum antimicrobials
- long-term use of broad-spectrum antimicrobials
- short-term use of narrow-spectrum antimicrobials
- short-term use of broad-spectrum antimicrobials
- Answer
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B
Which of the following routes of administration would be appropriate and convenient for home administration of an antimicrobial to treat a systemic infection?
- oral
- intravenous
- topical
- parenteral
- Answer
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A
Which clinical situation would be appropriate for treatment with a narrow-spectrum antimicrobial drug?
- treatment of a polymicrobic mixed infection in the intestine
- prophylaxis against infection after a surgical procedure
- treatment of strep throat caused by culture identified Streptococcus pyogenes
- empiric therapy of pneumonia while waiting for culture results
- Answer
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C
Fill in the Blank
The bacterium known for causing pseudomembranous colitis, a potentially deadly superinfection, is ________.
- Answer
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Clostridium difficile
True/False
Narrow-spectrum antimicrobials are commonly used for prophylaxis following surgery.
- Answer
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False
Short Answer
When prescribing antibiotics, what aspects of the patient’s health history should the clinician ask about and why?
When is using a broad-spectrum antimicrobial drug warranted?
Critical Thinking
Why are yeast infections a common type of superinfection that results from long-term use of broad-spectrum antimicrobials?
Too often patients will stop taking antimicrobial drugs before the prescription is finished. What are factors that cause a patient to stop too soon, and what negative impacts could this have?
14.3: Drugs Targeting Other Microorganisms
Antibacterial compounds exhibit selective toxicity, largely due to differences between prokaryotic and eukaryotic cell structure. Cell wall synthesis inhibitors, including the β-lactams, the glycopeptides, and bacitracin, interfere with peptidoglycan synthesis, making bacterial cells more prone to osmotic lysis. There are a variety of broad-spectrum, bacterial protein synthesis inhibitors that selectively target the prokaryotic 70S ribosome, including those that bind to the 30S and 50S subunits.
Multiple Choice
Which of the following terms refers to the ability of an antimicrobial drug to harm the target microbe without harming the host?
- mode of action
- therapeutic level
- spectrum of activity
- selective toxicity
- Answer
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D
Which of the following is not a type of β-lactam antimicrobial?
- penicillins
- glycopeptides
- cephalosporins
- monobactams
- Answer
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B
Which of the following does not bind to the 50S ribosomal subunit?
- tetracyclines
- lincosamides
- macrolides
- chloramphenicol
- Answer
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A
Which of the following antimicrobials inhibits the activity of DNA gyrase?
- polymyxin B
- clindamycin
- nalidixic acid
- rifampin
- Answer
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C
Fill in the Blank
Selective toxicity antimicrobials are easier to develop against bacteria because they are ________ cells, whereas human cells are eukaryotic.
- Answer
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prokaryotic
True/False
β-lactamases can degrade vancomycin.
- Answer
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false
Short Answer
If human cells and bacterial cells perform transcription, how are the rifamycins specific for bacterial infections?
What bacterial structural target would make an antibacterial drug selective for gram-negative bacteria? Provide one example of an antimicrobial compound that targets this structure.
Critical Thinking
In considering the cell structure of prokaryotes compared with that of eukaryotes, propose one possible reason for side effects in humans due to treatment of bacterial infections with protein synthesis inhibitors.
14.4: Clinical Considerations
Because fungi, protozoans, and helminths are eukaryotic organisms like human cells, it is more challenging to develop antimicrobial drugs that specifically target them.
Multiple Choice
Which of the following is not an appropriate target for antifungal drugs?
- ergosterol
- chitin
- cholesterol
- β(1→3) glucan
- Answer
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C
Which of the following drug classes specifically inhibits neuronal transmission in helminths?
- quinolines
- avermectins
- amantadines
- imidazoles
- Answer
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B
Which of the following is a nucleoside analog commonly used as a reverse transcriptase inhibitor in the treatment of HIV?
- acyclovir
- ribavirin
- adenine-arabinoside
- azidothymidine
- Answer
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D
Which of the following is an antimalarial drug that is thought to increase ROS levels in target cells?
- artemisinin
- amphotericin b
- praziquantel
- pleconaril
- Answer
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A
Fill in the Blank
Antiviral drugs, like Tamiflu and Relenza, that are effective against the influenza virus by preventing viral escape from host cells are called ________.
- Answer
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neuraminidase inhibitors
True/False
Echinocandins, known as “penicillin for fungi,” target β(1→3) glucan in fungal cell walls.
- Answer
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true
Short Answer
How does the biology of HIV necessitate the need to treat HIV infections with multiple drugs?
Niclosamide is insoluble and thus is not readily absorbed from the stomach into the bloodstream. How does the insolubility of niclosamide aid its effectiveness as a treatment for tapeworm infection?
Critical Thinking
Which of the following molecules is an example of a nucleoside analog?
Why can’t drugs used to treat influenza, like amantadines and neuraminidase inhibitors, be used to treat a wider variety of viral infections?
14.5: Testing the Effectiveness of Antimicrobials
Antimicrobial resistance is on the rise and is the result of selection of drug-resistant strains in clinical environments, the overuse and misuse of antibacterials, the use of subtherapeutic doses of antibacterial drugs, and poor patient compliance with antibacterial drug therapies. Drug resistance genes are often carried on plasmids or in transposons that can undergo vertical transfer easily and between microbes through horizontal gene transfer.
Multiple Choice
Which of the following resistance mechanisms describes the function of β-lactamase?
- efflux pump
- target mimicry
- drug inactivation
- target overproduction
- Answer
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C
Which of the following resistance mechanisms is commonly effective against a wide range of antimicrobials in multiple classes?
- efflux pump
- target mimicry
- target modification
- target overproduction
- Answer
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A
Which of the following resistance mechanisms is the most nonspecific to a particular class of antimicrobials?
- drug modification
- target mimicry
- target modification
- efflux pump
- Answer
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D
Which of the following types of drug-resistant bacteria do not typically persist in individuals as a member of their intestinal microbiota?
- MRSA
- VRE
- CRE
- ESBL-producing bacteria
- Answer
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A
Fill in the Blank
Staphylococcus aureus , including MRSA strains, may commonly be carried as a normal member of the ________ microbiota in some people.
- Answer
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nasal
Short Answer
Why does the length of time of antimicrobial treatment for tuberculosis contribute to the rise of resistant strains?
What is the difference between multidrug resistance and cross-resistance?
14.6: The Emergence of Drug Resistance
The Kirby-Bauer disk diffusion test helps determine the susceptibility of a microorganism to various antimicrobial drugs. However, the zones of inhibition measured must be correlated to known standards to determine susceptibility and resistance, and do not provide information on bactericidal versus bacteriostatic activity, or allow for direct comparison of drug potencies. Antibiograms are useful for monitoring local trends in antimicrobial resistance/susceptibility.
Multiple Choice
In the Kirby-Bauer disk diffusion test, the _______ of the zone of inhibition is measured and used for interpretation.
- diameter
- microbial population
- circumference
- depth
- Answer
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A
Which of the following techniques cannot be used to determine the minimum inhibitory concentration of an antimicrobial drug against a particular microbe?
- Etest
- microbroth dilution test
- Kirby-Bauer disk diffusion test
- macrobroth dilution test
- Answer
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C
The utility of an antibiogram is that it shows antimicrobial susceptibility trends
- over a large geographic area.
- for an individual patient.
- in research laboratory strains.
- in a localized population.
- Answer
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D
Fill in the Blank
The method that can determine the MICs of multiple antimicrobial drugs against a microbial strain using a single agar plate is called the ________.
- Answer
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Etest
True/False
If drug A produces a larger zone of inhibition than drug B on the Kirby-Bauer disk diffusion test, drug A should always be prescribed.
- Answer
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false
Short Answer
How is the information from a Kirby-Bauer disk diffusion test used for the recommendation of the clinical use of an antimicrobial drug?
What is the difference between MIC and MBC?
Critical Thinking
Can an Etest be used to find the MBC of a drug? Explain.
14.7: Current Strategies for Antimicrobial Discovery
With the continued evolution and spread of antimicrobial resistance, and now the identification of pan-resistant bacterial pathogens, the search for new antimicrobials is essential for preventing the postantibiotic era.
Multiple Choice
Which of the following has yielded compounds with the most antimicrobial activity?
- water
- air
- volcanoes
- soil
- Answer
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D
True/False
The rate of discovery of antimicrobial drugs has decreased significantly in recent decades.
- Answer
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true
Critical Thinking
Who should be responsible for discovering and developing new antibiotics? Support your answer with reasoning.


7.2.41: Sort Paragraphs (Usable with Workarounds)
Query \(\PageIndex{1}\)
Overall Usability
Usable with Workarounds:
- The activity requires significant adjustments by content authors.
Important Reminders
Begin the activity with a correctly structured heading.
Include instructions for using the activity with the keyboard: "To use the keyboard to move a paragraph, select it by typing the Space or Enter key, then use the Up or Down arrow key to move the paragraph into position. Drop the paragraph by typing the Space or Enter key. To review correct and incorrect answers, users of screen reading software must read the paragraphs using forms mode."
Users who require good color contrast may require an alternative version of the activity
Visible Indication of Focus
The activity buttons have a visible indication of focus.
Color Contrast
The visible indication of focus has good contrast. When a paragraph is selected, the text does not have good color contrast. Users who require good color contrast may require an alternative version of the activity.
Keyboard Usability
The activity is usable with the keyboard.
No Keyboard Traps
There are no keyboard traps.
Magnification
The activity supports both magnification up to 200% and reflow of content with magnification up to 400% without a loss of content or functionality and without requiring horizontal scrolling.
Usability with Screen Reading Software
The activity is usable with screen reading software.
To review correct and incorrect answers, users of screen reading software must read the paragraphs using forms mode.


58: Minorities Face More Obstacles to a Lifesaving Organ Transplant (Nonterah)
Camilla Nonterah
#health #business #systemanalysis #research #science #sharedvalues #proposal
Patients who experience organ failure need a transplant to improve their odds of survival and to achieve a better quality of life.
However, getting an organ transplant is often accompanied by several challenges, many of which can be attributed to factors like the state of an individual’s living circumstances, their economic status and where they were born .
As a result, many racial and ethnic minorities, such as African Americans, Latinx individuals and Native Americans, must unjustly wait longer for a much-needed new organ – or never receive one at all because of these barriers to care.
Research shows that these disparities are avoidable, especially with changes at the institutional level .
Which groups are less likely to get a transplant?
Transplant trends from the United Network of Organ Sharing indicate that approximately 113,600 people are in need of a lifesaving solid organ as of June 2019 . The majority have been diagnosed with kidney disease and liver disease.
The most recent data shows that, in 2016, the rate of kidney failure was highest among minority groups. For example, compared to whites, kidney failure was 9.5 times higher among Native Hawaiians and Pacific Islanders. Latinx individuals were over 50% more likely to be diagnosed with kidney failure than those who did not identify as Latinx.
Although minorities are more likely to be diagnosed with kidney failure, they are less likely to be transplanted. The majority of transplants in the U.S. go to whites.
These trends are also evident in groups suffering from liver disease. Asians and Latinx individuals are more likely to be diagnosed with liver failure , but less likely to receive a transplant .
What’s causing these disparities?
A patient has to undergo several steps before they can receive a transplant .
These steps include a physician deciding that a transplant is medically suitable, the patient demonstrating interest in a transplant, a referral to a transplant center, completion of a pre-transplant evaluation and identification of a suitable living donor.
At each point of the transplant preparation process, there are opportunities for barriers to occur as a result of patient, provider, community and institutional factors. Together, these potentially create disparities in access.
Income level may play a role. Patients with organ failure who experience poverty, for instance, may face challenges covering the cost of their insurance co-payments , especially when they do not have comprehensive insurance or private insurance.
Literacy issues , such as gaps in formal education or English as a second language, may also impact a patient’s ability to understand the medical terminology involved in their treatment. This would affect their ability to communicate effectively with their providers.
Limited knowledge of the benefits of transplantation can also affect patients’ ability to access transplants. Patients who are unaware that transplantation is the preferred treatment may not complete the steps to transplant and instead remain on dialysis.
Providers can also play a role in limiting access. For example, doctors may not provide patients with the referral they need or wait longer to provide it .
Given negative historical experiences, such as the Tuskegee Syphilis Study , some patients, especially those who have been historically disadvantaged or are currently marginalized, mistrust medical providers . As a result, they are less likely to seek medical assistance or trust that their providers are giving them accurate information.
Also, patients who report experiences of discrimination by their medical providers are less likely to seek transplantation. They may be discouraged from seeking further medical care because they expect poor treatment by providers.
Low rates of organ donation also influence transplant rates. Although about 95% of Americans are in favor of organ donation, only 58% of them are registered as organ donors . These low donation rates are pronounced among racial/ethnic minorities. This could be attributed to factors such as not knowing other registered donors in one’s community and mistrust of providers .
How can medical providers close the gap?
I am a counseling psychologist whose research examines health inequities and treatment. Given the enormity of these factors, I conducted a study with my colleague, Heather Gardiner , director of the Health Disparities Research Lab at Temple University.
We sought to identify barriers to the pre-transplant evaluation for African American kidney patients. Patients who complete this evaluation successfully become active on the waitlist.
We looked at barriers at several levels: individual barriers, such as limited income; health barriers, such as having multiple health conditions in addition to kidney disease; educational barriers, such as limited knowledge about the kidney transplant process; and systemic barriers, such as long wait times for medical appointments. We also asked people what motivated them to pursue a transplant.
Our research leads us to believe that changing systemic problems will help address problems at the other levels.
For example, medical providers could consider condensing the medical appointments and testing period for the pre-transplant evaluation. Patients who are motivated to get off dialysis will be more motivated to complete the pre-transplant evaluation if they are able to complete the majority of their medical testing at one place over a short period, rather than having to attend several medical appointments over a long period of time.
Policy changes also matter
In order to decide who gets an organ, medical providers give liver patients a MELD score that indicates the severity of their disease.
The introduction of the current liver allocation system in 2002 reduced the number of people from minority groups who died waiting for an organ .
Under the previous system, African Americans were more likely to die waiting for a liver transplant, because they generally had higher MELD scores, indicating that their disease was becoming worse. However, the current system prioritizes patients with high MELD scores, which has improved liver transplant rates for this group.
The 2014 policy change in kidney allocation allowed patients to count time spent on dialysis toward their total time spent on the waitlist, thereby reducing racial and ethnic disparities.
The success of these systemic changes illustrates the effectiveness of policy change. In my view, policies such as comprehensive Medicare coverage – with transportation assistance for all patients with kidney disease, for example – could potentially reduce many of the disparities along the steps to a successful transplant.
Countries such as Austria and Norway have seen significant improvements in their organ donation rates by using an opt-out system, which is based on the assumption that everyone consents unless an individual notes otherwise . Although this topic may be somewhat controversial in the U.S., I feel that the potential benefits of an opt-out policy are worth exploring.
____________________
Camilla Nonterah is Assistant Professor of Health Psychology, University of Richmond. Her essay was originally published in The Conversation .
Minorities Face More Obstacles to a Lifesaving Organ Transplant by Camilla Nonterah is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License .


7.4: Three-wire Power Supply System
Electrical energy to most individual and small commercial buildings in North America is distributed through a 120 V/240 V AC, single-phase, three-wire system.
Several advantages are gained by using this method of distribution:
- Copper conductor current requirements can be reduced.
- Two different voltages (120 V and 240 V) are available.
- Improved safety is established through grounding the neutral.
Source connections
A three-wire circuit is accomplished by connecting two 120 V sources in a series-aiding configuration. The conductor taken from the common point between the two sources is called the neutral conductor . Conductors taken from the two outer points are called the line or hot conductors .
As shown in Figure \(\PageIndex{1}\):
- Voltage measured line-to-line is 240 V.
- Voltage measured from either line to neutral is 120 V.
This allows connection to either 120 V loads (such as lighting) or 240 V loads (such as ranges or clothes dryers). See Figure \(\PageIndex{2}\).
Note that polarities shown in Figure \(\PageIndex{1}\) change every 120th of a second for a 60 hertz AC power supply.
For safety reasons, it is important that circuit conductors are identified by colour:
- Insulation on the two-line conductors is usually black (or sometimes one is black and one is red).
- The neutral always has white insulation.
The neutral is also grounded (directly connected to earth) at the source of supply.
Grounding the neutral conductor
Earth is a conductor of electricity. Therefore, to reduce the hazards of electrical shock and improve safety, electrical distribution systems usually have one of the circuit conductors connected to Earth, or as we say, grounded.
In most electrical systems, the neutral conductor is grounded at the supply by directly connecting it to Earth by another conductor (called the system grounding conductor) or by an electrode. Although grounding electrical distribution systems is an elaborate topic, consider the following simplified example.
Example
The fundamental purpose of grounding is to guard against electrical shocks and fire hazards. But what makes a grounded electrical system safer? Consider an ungrounded 120 V/240 V wiring system with a fault, as shown in Figure \(\PageIndex{3}\). Theoretically, if an insulation fault occurs at a piece of equipment (so that a line conductor makes accidental contact with the metal frame), nothing should happen. However, if an accidental ground should occur and a person comes in contact with the faulty equipment and ground, that person will experience a shock of 240 V (the line-to-line voltage).
Now look at the same wiring system with the neutral purposely grounded, as shown in Figure \(\PageIndex{4}\).
With the neutral grounded and the same equipment fault as previously described, the person coming in contact with both the metal frame of the equipment and the Earth would experience a shock of only 120 V (which is the line-to-neutral voltage). The shock voltage has been reduced by 50%.
To further minimize shock hazard, not only is the wiring system grounded but also all metallic, non-current-carrying parts of the equipment are grounded by using a bonding conductor. This is an important step if maximum safety is to be achieved.
As shown in Figure \(\PageIndex{5}\), if the equipment is also grounded intentionally, then a line-to-frame fault condition offers a low-resistance path for current flow back to the system neutral. Essentially this is a line-to-neutral short circuit, which causes the circuit overcurrent device to trip, thus eliminating the shock hazard from the system.
Although properly grounded wiring systems do not eliminate shock hazard, they certainly lower the odds of being shocked!
Now complete the Learning Task Self-Test.


6.6: Exercise - Looking at the Averaged ERPs
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Let’s make averaged ERPs for the bins we created. We still have continuous EEG data, so we first need to divide the data into epochs, with the time-locking event code as time zero. Make sure that the correct dataset is active ( 12_P3_corrected_elist_bins ) and select EEGLAB > ERPLAB > Extract bin-based epochs . Use the default epoch of -200 to 800 ms and the prestimulus interval as the baseline correction period. Click RUN and keep the default name of 12_P3_corrected_elist_bins_be for the new dataset. Take a look at the epoched data (using EEGLAB > Plot > Channel data (scroll) ) to make sure everything looks okay. As you may recall from Chapter 2, EEGLAB plots 5 epochs on a screen by default, making the epoched data look a lot like continuous data—you need to look closely to see the boundaries between the epochs.
Once you’ve looked at the EEG epochs, select EEGLAB > ERPLAB > Compute averaged ERPs . You should be able to use the default settings and just click RUN . Name the resulting ERPset 12_P3 , and save the ERPset as a file named 12_P3.erp . Now plot the ERPs (using EEGLAB > ERPLAB > Plot ERP > Plot ERP waveforms) . It’s a good idea to click the RESET button in the plotting GUI to get rid of any custom settings from the last time you plotted ERPs. We only have two bins, so you can keep it set to plot all bins . You should see something like Screenshot 6.2.
Compare the waveforms at Pz with the grand average waveforms shown in Figure 6.2. Pretty similar! But that’s only because I intentionally chose a participant whose ERPs looked like the grand average for the exercises in this chapter. There are tremendous individual differences in ERP waveforms (largely due to nonfunctional differences in biophysical factors like skull thickness), and the ERPs for most of the participants in this study don’t look this much like the grand average. Averaging (whether across trials or across participants) is often necessary, but the result is something of a fiction.
Although published papers often focus on just a few electrode sites, you should always look at the whole set of channels to verify that the scalp distribution is sensible. With a reference at or near the mastoids, the P3b effect (defined as the difference between Rare and Frequent) should be biggest along the midline near Cz and Pz. This participant’s P3b is a little more frontal than is typical for a visual paradigm, and I would ordinarily expect a smaller effect at Fz and a larger effect at Oz. But given the large range of individual differences in ERPs, this participant’s data look pretty normal.
You can also see quite a bit of high-frequency noise in the lateral frontal and central channels over the right hemisphere (especially F8). The noise in F8 and surrounding channels is probably EMG from the temporalis muscle (the muscle near the temples that is used to contract the jaws). If you scroll through the original EEG data, you can also see the high-frequency noise in the single trials. My guess is that this participant was clenching their jaw just a little bit, mainly on the right side.


15.9: Antisocial Behavior in Adolescence
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Bullies, Victims, and the Bystander
Bullying is defined as unwanted, aggressive behavior among school aged children that involves a real or perceived power imbalance. Further, the aggressive behavior happens more than once or has the potential to be repeated. There are different types of bullying. They are detailed in the table below.
| Type of Bullying | Description |
|---|---|
| Verbal Bullying | Includes saying or writing mean things, teasing, name calling, taunting, threatening, or making inappropriate sexual comments. |
| Social bullying (also referred to as relational bullying) | Includes spreading rumors, purposefully excluding someone from a group, or embarrassing someone on purpose. |
| Physical Bullying | Includes hurting a person’s body or possessions. |
| Cyberbullying | Involves electronic technology. Examples of cyberbullying include sending mean text messages or emails, creating fake profiles, and posting embarrassing pictures, videos or rumors on social networking sites. |
The Bystander Effect
The discussion of bullying highlights the problem of witnesses not intervening to help a victim. Researchers Latané and Darley (1968) described a phenomenon called the bystander effect . The bystander effect is a phenomenon in which a witness or bystander does not volunteer to help a victim or person in distress. Instead, they just watch what is happening. Social psychologists hold that we make these decisions based on the social situation, not our own personality variables. Why do you think bystanders don’t get help? What are the benefits to helping? What are the risks? It is very likely you listed more costs than benefits to helping. In many situations, bystanders likely feared for their own lives—if they went to help, the attacker might harm them. However, how difficult would it be to make a phone call to the police? Social psychologists claim that diffusion of responsibility is the likely explanation. Diffusion of responsibility is the tendency for no one in a group to help because the responsibility to help is spread throughout the group (Bandura, 1999). Have you ever passed an accident on the freeway and assumed that a victim or certainly another motorist has already reported the accident? In general, the greater the number of bystanders, the less likely any one person will help. 67
Contributors and Attributions
67. Psychology – 12.6 Aggression by OpenStax is licensed under CC BY 4.0


25.5: Microscopic Anatomy of the Kidney
By the end of this section, you will be able to:
- Distinguish the histological differences between the renal cortex and medulla
- Describe the structure of the filtration membrane
- Identify the major structures and subdivisions of the renal corpuscles, renal tubules, and renal capillaries
- Discuss the function of the peritubular capillaries and vasa recta
- Identify the location of the juxtaglomerular apparatus and describe the cells that line it
- Describe the histology of the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting ducts
The renal structures that conduct the essential work of the kidney cannot be seen by the naked eye. Only a light or electron microscope can reveal these structures. Even then, serial sections and computer reconstruction are necessary to give us a comprehensive view of the functional anatomy of the nephron and its associated blood vessels.
Nephrons: The Functional Unit
Nephrons take a simple filtrate of the blood and modify it into urine. Many changes take place in the different parts of the nephron before urine is created for disposal. The term forming urine will be used hereafter to describe the filtrate as it is modified into true urine. The principle task of the nephron population is to balance the plasma to homeostatic set points and excrete potential toxins in the urine. They do this by accomplishing three principle functions—filtration, reabsorption, and secretion. They also have additional secondary functions that exert control in three areas: blood pressure (via production of renin ), red blood cell production (via the hormone EPO), and calcium absorption (via conversion of calcidiol into calcitriol, the active form of vitamin D).
Renal Corpuscle
As discussed earlier, the renal corpuscle consists of a tuft of capillaries called the glomerulus that is largely surrounded by Bowman’s (glomerular) capsule. The glomerulus is a high-pressure capillary bed between afferent and efferent arterioles. Bowman’s capsule surrounds the glomerulus to form a lumen, and captures and directs this filtrate to the PCT. The outermost part of Bowman’s capsule, the parietal layer, is a simple squamous epithelium. It transitions onto the glomerular capillaries in an intimate embrace to form the visceral layer of the capsule. Here, the cells are not squamous, but uniquely shaped cells ( podocytes ) extending finger-like arms ( pedicels ) to cover the glomerular capillaries (Figure \(\PageIndex{1}\) ). These projections interdigitate to form filtration slits , leaving small gaps between the digits to form a sieve. As blood passes through the glomerulus, 10 to 20 percent of the plasma filters between these sieve-like fingers to be captured by Bowman’s capsule and funneled to the PCT. Where the fenestrae (windows) in the glomerular capillaries match the spaces between the podocyte “fingers,” the only thing separating the capillary lumen and the lumen of Bowman’s capsule is their shared basement membrane (Figure \(\PageIndex{2}\) ). These three features comprise what is known as the filtration membrane. This membrane permits very rapid movement of filtrate from capillary to capsule though pores that are only 70 nm in diameter.
The fenestrations prevent filtration of blood cells or large proteins, but allow most other constituents through. These substances cross readily if they are less than 4 nm in size and most pass freely up to 8 nm in size. An additional factor affecting the ability of substances to cross this barrier is their electric charge. The proteins associated with these pores are negatively charged, so they tend to repel negatively charged substances and allow positively charged substances to pass more readily. The basement membrane prevents filtration of medium-to-large proteins such as globulins. There are also mesangial cells in the filtration membrane that can contract to help regulate the rate of filtration of the glomerulus. Overall, filtration is regulated by fenestrations in capillary endothelial cells, podocytes with filtration slits, membrane charge, and the basement membrane between capillary cells. The result is the creation of a filtrate that does not contain cells or large proteins, and has a slight predominance of positively charged substances.
Lying just outside Bowman’s capsule and the glomerulus is the juxtaglomerular apparatus (JGA) (Figure \(\PageIndex{3}\)). At the juncture where the afferent and efferent arterioles enter and leave Bowman’s capsule, the initial part of the distal convoluted tubule (DCT) comes into direct contact with the arterioles. The wall of the DCT at that point forms a part of the JGA known as the macula densa . This cluster of cuboidal epithelial cells monitors the fluid composition of fluid flowing through the DCT. In response to the concentration of Na + in the fluid flowing past them, these cells release paracrine signals. They also have a single, nonmotile cilium that responds to the rate of fluid movement in the tubule. The paracrine signals released in response to changes in flow rate and Na + concentration are adenosine triphosphate (ATP) and adenosine.
A second cell type in this apparatus is the juxtaglomerular cell . This is a modified, smooth muscle cell lining the afferent arteriole that can contract or relax in response to ATP or adenosine released by the macula densa. Such contraction and relaxation regulate blood flow to the glomerulus. If the osmolarity of the filtrate is too high (hyperosmotic), the juxtaglomerular cells will contract, decreasing the glomerular filtration rate (GFR) so less plasma is filtered, leading to less urine formation and greater retention of fluid. This will ultimately decrease blood osmolarity toward the physiologic norm. If the osmolarity of the filtrate is too low, the juxtaglomerular cells will relax, increasing the GFR and enhancing the loss of water to the urine, causing blood osmolarity to rise. In other words, when blood osmolarity goes up, filtration and urine formation decrease and water is retained. When blood osmolarity goes down, filtration and urine formation increase and water is lost by way of the urine. The net result of these opposing actions is to keep the rate of filtration relatively constant. A second function of the macula densa cells is to regulate renin release from the juxtaglomerular cells of the afferent arteriole (Figure \(\PageIndex{4}\)). Active renin is a protein comprised of 304 amino acids that cleaves several amino acids from angiotensinogen to produce angiotensin I . Angiotensin I is not biologically active until converted to angiotensin II by angiotensin-converting enzyme (ACE) from the lungs. Angiotensin II is a systemic vasoconstrictor that helps to regulate blood pressure by increasing it. Angiotensin II also stimulates the release of the steroid hormone aldosterone from the adrenal cortex. Aldosterone stimulates Na + reabsorption by the kidney, which also results in water retention and increased blood pressure.
Proximal Convoluted Tubule (PCT)
Filtered fluid collected by Bowman’s capsule enters into the PCT. It is called convoluted due to its tortuous path. Simple cuboidal cells form this tubule with prominent microvilli on the luminal surface, forming a brush border . These microvilli create a large surface area to maximize the absorption and secretion of solutes (Na + , Cl – , glucose, etc.), the most essential function of this portion of the nephron. These cells actively transport ions across their membranes, so they possess a high concentration of mitochondria in order to produce sufficient ATP.
Loop of Henle
The descending and ascending portions of the loop of Henle (sometimes referred to as the nephron loop) are, of course, just continuations of the same tubule. They run adjacent and parallel to each other after having made a hairpin turn at the deepest point of their descent. The descending loop of Henle consists of an initial short, thick portion and long, thin portion, whereas the ascending loop consists of an initial short, thin portion followed by a long, thick portion. The descending thick portion consists of simple cuboidal epithelium similar to that of the PCT. The descending and ascending thin portions consists of simple squamous epithelium. As you will see later, these are important differences, since different portions of the loop have different permeabilities for solutes and water. The ascending thick portion consists of simple cuboidal epithelium similar to the DCT.
Distal Convoluted Tubule (DCT)
The DCT, like the PCT, is very tortuous and formed by simple cuboidal epithelium, but it is shorter than the PCT. These cells are not as active as those in the PCT; thus, there are fewer microvilli on the apical surface. However, these cells must also pump ions against their concentration gradient, so you will find of large numbers of mitochondria, although fewer than in the PCT.
Collecting Ducts
The collecting ducts are continuous with the nephron but not technically part of it. In fact, each duct collects filtrate from several nephrons for final modification. Collecting ducts merge as they descend deeper in the medulla to form about 30 terminal ducts, which empty at a papilla. They are lined with simple squamous epithelium with receptors for ADH. When stimulated by ADH, these cells will insert aquaporin channel proteins into their membranes, which as their name suggests, allow water to pass from the duct lumen through the cells and into the interstitial spaces to be recovered by the vasa recta. This process allows for the recovery of large amounts of water from the filtrate back into the blood. In the absence of ADH, these channels are not inserted, resulting in the excretion of water in the form of dilute urine. Most, if not all, cells of the body contain aquaporin molecules, whose channels are so small that only water can pass. At least 10 types of aquaporins are known in humans, and six of those are found in the kidney. The function of all aquaporins is to allow the movement of water across the lipid-rich, hydrophobic cell membrane (Figure \(\PageIndex{5}\)).


20.10: The Limits of Selection
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Learning Objectives
- Explain the limitations encountered in natural selection
No Perfect Organism
Natural selection is a driving force in evolution and can generate populations that are adapted to survive and successfully reproduce in their environments. However, natural selection cannot produce the perfect organism. Natural selection can only select on existing variation in the population; it cannot create anything from scratch. Therefore, the process of evolution is limited by a population’s existing genetic variance, the physical proximity of alleles, non-beneficial intermediate morphs in a polymorphic population, and non-adaptive evolutionary forces.
Natural Selection Acts on Individuals, not Alleles
Natural selection is also limited because it acts on the phenotypes of individuals, not alleles. Some alleles may be more likely to be passed on with alleles that confer a beneficial phenotype because of their physical proximity on the chromosomes. Alleles that are carried together are in linkage disequilibrium. When a neutral allele is linked to beneficial allele, consequently meaning that it has a selective advantage, the allele frequency can increase in the population through genetic hitchhiking (also called genetic draft).
Any given individual may carry some beneficial alleles and some unfavorable alleles. Natural selection acts on the net effect of these alleles and corresponding fitness of the phenotype. As a result, good alleles can be lost if they are carried by individuals that also have several overwhelmingly bad alleles; similarly, bad alleles can be kept if they are carried by individuals that have enough good alleles to result in an overall fitness benefit.
Polymorphism
Furthermore, natural selection can be constrained by the relationships between different polymorphisms. One morph may confer a higher fitness than another, but may not increase in frequency because the intermediate morph is detrimental.
Polymorphism in the grove snail : Color and pattern morphs of the grove snail, Cepaea nemoralis.The polymorphism, when two or more different genotypes exist within a given species, in grove snails seems to have several causes, including predation by thrushes.
For example, consider a hypothetical population of mice that live in the desert. Some are light-colored and blend in with the sand, while others are dark and blend in with the patches of black rock. The dark-colored mice may be more fit than the light-colored mice, and according to the principles of natural selection the frequency of light-colored mice is expected to decrease over time. However, the intermediate phenotype of a medium-colored coat is very bad for the mice: these cannot blend in with either the sand or the rock and will more vulnerable to predators. As a result, the frequency of a dark-colored mice would not increase because the intermediate morphs are less fit than either light-colored or dark-colored mice. This a common example of disruptive selection.
Not all Evolution is Adaptive
Finally, it is important to understand that not all evolution is adaptive. While natural selection selects the fittest individuals and often results in a more fit population overall, other forces of evolution, including genetic drift and gene flow, often do the opposite by introducing deleterious alleles to the population’s gene pool. Evolution has no purpose. It is not changing a population into a preconceived ideal. It is simply the sum of various forces and their influence on the genetic and phenotypic variance of a population.
Contributions and Attributions
- natural selection. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/natural_selection . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Darwinian fitness. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Darwinian%20fitness . License : CC BY-SA: Attribution-ShareAlike
- fecundity. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/fecundity . License : CC BY-SA: Attribution-ShareAlike
- Evolution sm. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Adaptiv...olution_sm.png . License : Public Domain: No Known Copyright
- Galu00e1pagos with David Attenborough. Located at : http://www.youtube.com/watch?v=czpPbDGHOZA . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. October 23, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- stabilizing selection. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/stabilizing%20selection . License : CC BY-SA: Attribution-ShareAlike
- directional selection. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/directional%20selection . License : CC BY-SA: Attribution-ShareAlike
- disruptive selection. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/disruptive%20selection . License : CC BY-SA: Attribution-ShareAlike
- Evolution sm. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Adaptiv...olution_sm.png . License : Public Domain: No Known Copyright
- Galu00e1pagos with David Attenborough. Located at : http://www.youtube.com/watch?v=czpPbDGHOZA . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- Peppered moth evolution. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Peppered_moth_evolution . License : Public Domain: No Known Copyright
- OpenStax College, Biology. November 9, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Frequency-dependent selection. Provided by : genetics-notes Wikispace. Located at : http://genetics-notes.wikispaces.com...dent+selection . License : CC BY-SA: Attribution-ShareAlike
- polygynous. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/polygynous . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Frequency-dependent selection. Provided by : WIKIPEDIA. Located at : en.Wikipedia.org/wiki/Frequen...dent_selection . License : CC BY-SA: Attribution-ShareAlike
- frequency-dependent selection. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/frequen...nt%20selection . License : CC BY-SA: Attribution-ShareAlike
- Evolution sm. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Adaptiv...olution_sm.png . License : Public Domain: No Known Copyright
- Galu00e1pagos with David Attenborough. Located at : http://www.youtube.com/watch?v=czpPbDGHOZA . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- Peppered moth evolution. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Peppered_moth_evolution . License : Public Domain: No Known Copyright
- OpenStax College, Biology. November 9, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Coral snake. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Coral_009.jpg . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Adaptive Evolution. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...e_19_03_02.jpg . License : CC BY: Attribution
- Lampropeltis elapsoides. Provided by : WikiPedia. Located at : en.Wikipedia.org/wiki/File:G-Bartolotti_SK.jpg . License : CC BY-SA: Attribution-ShareAlike
- sexual dimorphism. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/sexual_dimorphism . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Boundless. Provided by : Boundless Learning. Located at : www.boundless.com//biology/de...icap-principle . License : CC BY-SA: Attribution-ShareAlike
- Sexual Selection. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Sexual_selection .  Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/sexual_selection . License : CC BY-SA: Attribution-ShareAlike
- Evolution sm. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Adaptiv...olution_sm.png . License : Public Domain: No Known Copyright
- Galu00e1pagos with David Attenborough. Located at : http://www.youtube.com/watch?v=czpPbDGHOZA . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- Peppered moth evolution. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Peppered_moth_evolution . License : Public Domain: No Known Copyright
- OpenStax College, Biology. November 9, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Coral snake. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Coral_009.jpg . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Adaptive Evolution. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...e_19_03_02.jpg . License : CC BY: Attribution
- Lampropeltis elapsoides. Provided by : WikiPedia. Located at : en.Wikipedia.org/wiki/File:G-Bartolotti_SK.jpg . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Adaptive Evolution. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...9_03_03abc.jpg . License : CC BY: Attribution
- Bull elk bugling during the fall mating season. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/File:Bu...ing_season.jpg . License : Public Domain: No Known Copyright
- Ribbon-tailed Astrapia. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Bird-of...d_Astrapia.jpg . License : CC BY-SA: Attribution-ShareAlike
- BBC Planet Earth - Birds of Paradise mating dance. Located at : http://www.youtube.com/watch?v=W7QZnwKqopo . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- linkage disequilibrium. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/linkage_disequilibrium . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- polymorphism. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/polymorphism . License : CC BY-SA: Attribution-ShareAlike
- Genetic Hitchhiking. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Genetic_draft . License : CC BY-SA: Attribution-ShareAlike
- Evolution sm. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Adaptiv...olution_sm.png . License : Public Domain: No Known Copyright
- Galu00e1pagos with David Attenborough. Located at : http://www.youtube.com/watch?v=czpPbDGHOZA . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- Peppered moth evolution. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Peppered_moth_evolution . License : Public Domain: No Known Copyright
- OpenStax College, Biology. November 9, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...ol11448/latest . License : CC BY: Attribution
- Coral snake. Provided by : Wikipedia. Located at : http://en.Wikipedia.org/wiki/File:Coral_009.jpg . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Adaptive Evolution. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...e_19_03_02.jpg . License : CC BY: Attribution
- Lampropeltis elapsoides. Provided by : WikiPedia. Located at : en.Wikipedia.org/wiki/File:G-Bartolotti_SK.jpg . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Adaptive Evolution. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44586/latest...9_03_03abc.jpg . License : CC BY: Attribution
- Bull elk bugling during the fall mating season. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/File:Bu...ing_season.jpg . License : Public Domain: No Known Copyright
- Ribbon-tailed Astrapia. Provided by : Wikimedia. Located at : en.Wikipedia.org/wiki/Bird-of...d_Astrapia.jpg . License : CC BY-SA: Attribution-ShareAlike
- BBC Planet Earth - Birds of Paradise mating dance. Located at : http://www.youtube.com/watch?v=W7QZnwKqopo . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- Polymorphism in Cepaea nemoralis. Provided by : Wikimedia. Located at : commons.wikimedia.org/wiki/Fi..._nemoralis.jpg . License : CC BY-SA: Attribution-ShareAlike
Key Points
- Natural selection is limited by a population ‘s existing genetic variation.
- Natural selection is limited through linkage disequilibrium, where alleles that are physically proximate on the chromosome are passed on together at greater frequencies.
- In a polymorphic population, two phenotypes may be maintained in the population despite the higher fitness of one morph if the intermediate phenotype is detrimental.
- Evolution is not purposefully adaptive; it is the result of various selection forces working together to influence genetic and phenotypical variances within a population.
Key Terms
- linkage disequilibrium : a non-random association of two or more alleles at two or more loci; normally caused by an interaction between genes
- genetic hitchhiking : changes in the frequency of an allele because of linkage with a positively or negatively selected allele at another locus
- polymorphism : the regular existence of two or more different genotypes within a given species or population


15.3: Launching Your Venture
By the end of this section, you will be able to:
- Explain the importance of creating and discussing the vision statement
- Determine the documents necessary for managing risks
- Describe company culture and the purpose of a code of conduct
- Summarize how to outline and schedule the operational steps of the launch
The big day has arrived. Your opportunity recognition process noted that your idea solves a significant problem or need, you double-checked that the target market is large enough for potential profitability, you have a method to reach this target market, you have a passion to start this company, and you found resources to support the start-up. Knowing that you analyzed and addressed these topics, you now need to consider some of the more sensitive topics regarding the agreements within your team. Many entrepreneurs overlook the issues discussed here or act on them in a generic manner instead of fitting them to the specific needs of the venture. This lack of due diligence can be detrimental to the success of the business. The advice presented here can help you avoid those same mistakes.
To protect the interests of all parties involved at launch, the team should develop several important documents, such as a founders’ agreement, nondisclosure and noncompete forms, and a code of conduct. Before these are drafted, the team should ensure the venture’s vision statement is agreed upon. (See Entrepreneurial Vision and Goals for a discussion around creating a vision statement.) The entrepreneurship team needs to be in complete agreement on the vision of the venture before they can successfully create the founders’ agreement. If some team members have an interest in creating a lifestyle business (a venture that provides an income that replaces other types of employment), while other team members want to harvest the venture with significant returns, there is a clash between these expectations. An angel investor will also have a strong opinion on the vision for the venture.
Founder’s Agreement, Nondisclosure Agreement, and Noncompete Agreement
Honest and open discussions between the entrepreneurial team members, including your angel investor if an angel investor is part of your initial funding, must take place before opening the venture. These frank discussions need to include a founders’ agreement as well as the identified vision for the venture. The founders’ agreement should describe how individual contributions are valued and fit into the compensation plan and should consider and answer these questions:
- Will the entrepreneurial team members receive a monthly compensation?
- Is there a vesting plan with defined timelines aligned with equity percentages?
- What happens if a team member decides to leave the venture before an exit event? How will that team member be compensated, if at all?
Discussing the entrepreneurial team members’ expectations avoids the problem of an entrepreneurial team member expecting a large equity stake in the company for a short-term commitment to the venture, and other misguided expectations. Such problems can be avoided by addressing the following questions:
- What activities and responsibilities are expected from each team member, and what is the process or action when individual overstep their authority?
- Is there an evaluation period during which the team members discuss each other’s performance? If so, how is that discussion managed, and is there a formal process?
- What happens if a team member fails to deliver on expected actions, or if an unexpected life event occurs?
The founders’ agreement should also outline contingency plans if the business does not continue. The following questions help define those next steps and need to be answered prior to opening the venture:
- If the venture is unsuccessful, how will the dissolution of the venture be conducted?
- What happens to the assets, and how are the liabilities paid?
- How is the decision made to liquidate the venture?
- What happens to the originally identified opportunity? Does a team member have access to that idea, but with a different team, or implemented using a different business model?
Once the venture opens, discussing these topics becomes more complicated because the entrepreneurial team is immersed in various start-up activities, and new information affects their thoughts on these issues. Along with these topics, the founders’ agreement should also state the legal form of ownership, division of ownership (this refers to the division of equity at either the next round of financing, or harvesting of the company), as well as the buyout, or buyback clause. (See Entrepreneurial Journey and Pathways for a discussion on the life cycle stages of a venture, including end stages of harvesting, transition, and reincarnation of the business.)
The buyback clause addresses the situations in which a team member exits the venture prior to the next financing round or harvesting due to internal disputes with team members, illness, death, or other circumstances, clearly stating compensation and profit distribution (with consideration of what is reinvested into the venture). Discussing these topics provides agreement between all team members about how to address these types of situations. The buyback clause should also include a dispute resolution process with agreement on how the dispute solution is implemented. Identifying exactly how these items are handled within the founders’ agreement prevents future conflicts and even legal disputes.
If the entrepreneurship team includes an angel investor, the angel investor typically has the final say in these questions. In the best possible scenario, the angel investor has experience creating a founders’ agreement and can provide valuable insights into working through this document. One common approach to creating this document, given the angel investor’s available time, is for the entrepreneurship team to discuss and agree on the final document, then have the angel investor review the document for final approval. Making Difficult Business Decisions in Response to Challenges will help in finalizing your founders’ agreement.
After completing the formal vision statement and the founders’ agreement, you might want to have an attorney evaluate the documents. This checkpoint can identify gaps or decisions that were not stated clearly. After receiving the examined documents back, the team should once again review the documents for agreement. If everyone is satisfied with the documents, each entrepreneurship team member should sign the document and receive a copy. If, later, the entrepreneurship team decides a change needs to be made to either the vision statement or the founders’ agreement, an addendum can be created, again with all parties agreeing to any changes.
Two other formal documents your team might want to consider include a nondisclosure agreement and a noncompete agreement. These documents can be applied to all employees, including the startup team, with consideration of extending to other contributors such as contractual personnel. A nondisclosure agreement agrees to refrain from disclosing information about the venture. Topics that might be included in this document include trade secrets, key accounts, or any other information of high value to the venture or potentially useful to a competitor. A noncompete agreement states that the person signing the agreement will not work for a competing organization while working for the venture, and generally for a set length of time after leaving the venture. Often, this time period is one year, but it can be longer depending on the know-how or intellectual property the exiting team member has.
Company Culture and Code of Conduct
In conjunction with these formal documents, the founding team should determine the culture they would like to build for their venture. Ideally, the organization’s company culture is made up of the behaviors and beliefs that support the success of the organization. For example, when you walk into a business, is there a bustle of noise and activity, or is the business calm and restrained? This impression results from the organization’s culture. We could compare the difference between walking into a high-end jewelry store and walking into a fast food restaurant. Both businesses have distinctly different cultures. If the venture is highly dynamic with fast-paced decisions and constant change, then the culture should support this type of venture. Perhaps the team wants to create a work hard, play hard culture. In that case, standards that support ad hoc team creation for impromptu discussions should be encouraged, rather than setting up a bureaucratic culture that requires approval of all meetings and deliberation of decisions prior to action. Many tech companies support a work hard, play hard culture. This culture is reinforced with open office spaces that provide opportunities to collaborate with colleagues. Or perhaps ping pong tables and kitchens are provided to encourage interaction. Even the hours of operation contribute to culture creation by either encouraging employees to set their own hours or restricting work hours through regulated entry. In contrast, a more bureaucratically structured environment may fit a venture whose success relies upon compliance with external regulations and the use of highly sensitive or private information. An example of a bureaucratic culture aligns with many financial institutions. The culture within a bank conveys security of our deposited funds; we want a bank to have processes and systems in place that reinforce that we can trust the bank with our finances.
The culture-defining process should include the entrepreneurship team’s creation of a code of conduct . Some organizations develop a code of conduct that includes guiding principles, while other organizations create detailed descriptions of what is acceptable and what isn’t acceptable. Your venture’s code of conduct should fit with your venture’s vision, the culture desired, and the entrepreneurship team’s values. Codes of conduct should be created as documents that include a sensitivity to people within the company as well as the greater community. A code of conduct addresses the values that the organization supports, as well as ethical considerations. The purpose of a code of conduct is to help guide employee actions to align with the desired behavior. Including uniquely specific examples that align with the specific venture, can further communicate the desired behaviors. There are many varieties of codes of conduct; the main point is to create a code that supports the values and behaviors that you want to advance throughout your organization. Figure 15.2 and Figure 15.3 show two approaches to developing a code of conduct that fits the company’s culture and vision. The first example might be used by an advocacy-based venture that desires a principle-based approach to guiding employee behaviors through a code of conduct that provides general guidelines, rather than a more rule-based approach as presented in the second example. These two examples highlight the importance of creating a code of conduct that fits the beliefs and culture that you want to encourage within your venture.
Earlier, we discussed the importance of the lead entrepreneur taking the initiative to discover the investor’s business knowledge and learning about the investor’s previous experience in funding an entrepreneurial venture. The code of conduct is another area that entrepreneurial teams frequently skip over by accepting a generic code of conduct rather than recognizing that there are a multitude of topics, phrases, and principles that should be uniquely designed to fit the venture. These two examples demonstrate the vastly different topics addressed within a code of conduct as evidence for why your code of conduct must fit your intentions for how you will conduct business and support the success of your venture.
These preparatory documents should be personalized to align with the entrepreneurial team and desired behaviors that support the success of the venture. Although standard language and forms addressing these topics are available online, these generic models aren’t intended to meet your unique venture’s needs or the entrepreneurial team’s needs. Taking the time to discuss and prepare these documents pays off in well-crafted documents and aligns the entrepreneurship teams’ vison, goals, and dreams for their venture.
Google’s code of conduct
Review Google’s code of conduct as you think about developing your own code of conduct. What do you like about Google’s code of conduct? What would you change? How does this example help you in creating a code of conduct for your venture?
Operational Steps to Launch
The next action is outlining the operational steps in the venture creation process. A good approach is to create a chart that identifies how you should proceed. The goal in creating this chart is to recognize what actions need to be taken first. For example, if you need a convection oven for your business, what is the timeline between ordering and receiving the oven? If you need ten employees to manually prepare and package your product, how long will it take to interview and hire each person? According to Glassdoor, the hiring process took 23 days in 2014 and appears to be lengthening in time as organizations become more aware of the importance of hiring the right person. 2 What about training? Will your employees need training on your product or processes before starting the venture? These necessary outcomes need to be identified and then tracked backwards from the desired start date to include the preparatory actions that support the success of the business. You’ve probably heard the phrase that timing is everything. Not only do entrepreneurs need to be concerned about finding the right time to start the venture, they also need the right timing to orchestrate the start-up of the venture.
Below is a sample Gantt chart , a method to track a list of tasks or activities aligned with time intervals. You can use this tool to help identify and schedule the operational steps that need to be completed to launch the venture. One approach to creating a Gantt chart is for each team member to independently create a list of operational activities or tasks required to start the venture that fall under their area of involvement. Then the team can create a master list of activities to discuss: This helps clarify who is contributing to or owning each task. Next, have all team members create their own Gantt chart based on their task list: That is, the time required for each task should be spelled out, including steps that must happen sequentially (when one task cannot be started until another step is complete). Once again, bring all team members together to create one master Gantt chart. This will help ensure that dependencies from member to member are accounted for in the planning. These contingencies and dependencies need to be identified and accommodated for in the master schedule. For example, in Figure 15.4 , we see that Mike Smith cannot perform system testing until Sam Watson has developed the system modules, and in turn, that task can’t be done until Mike Smith has documented the current systems. After completing the chart, agree on assignments of responsibility to follow through on the activities, based on the timelines from the Gantt chart.
See the Suggested Resources for more information on how to use a Gantt chart to assist in tracking the actions needed to support the start-up of your venture and to organize each action based on your necessary timelines. You might want to reach out to other sources to find examples of how other entrepreneurs worked through their operational start-up steps.
This TED Talk features Paul Tasner sharing how he found himself changing his career at the age of 66, reinforcing the idea that the world of entrepreneurship is open to all people regardless of age, race, background, health, or geographic location. In this presentation, he references a variety of activities he needed to experience in order to understand the process of starting his venture. Regardless of what we learned in our past experiences, launching a new venture includes new experiences and decisions.
After watching this video, do you have some ideas regarding starting a new venture around the idea of senior entrepreneurs? How could you support this group or build a network that creates a community of support for this large population?
Launch Considerations
Sage advice in launching the new venture is to quickly recognize when you don’t have the answer or information to make the best decisions. In the early stage of launching the venture, the level of uncertainty is high, as is the need for agility and spontaneity. Even identifying the actual moment when the venture becomes a new venture can be difficult to determine. Should the venture be recognized as a new venture after receiving the necessary licenses or tax identification number, or when the first sale occurs, or when funds are first invested, or by some other method?
It is also important to keep in mind the end goal of the venture, often referred to as "begin with the end in mind." For example, many highly successful ventures never earn a dollar in sales. Depending on the entrepreneurial team’s vision and the business model selected, the venture could be highly valuable from a harvest, or sale of the venture, perspective. Frequently, this decision is dictated by the angel investor. These people frequently started their own venture, harvested the venture, and as a result have funds available to invest in other new ventures. In most cases, the angel investor expects to cash out of the venture at some point in the future. These are investors who are not interested in holding a long-term equity position but rather expect to grow the venture into a position where another company buys out the venture. This buyout is also known as the harvesting of the venture and the point at which the angel investor receives a percentage of the harvested dollar sale to cover the equity stake in the new venture. Because of this pattern, entrepreneurs are often advised to “begin with the end in mind” when launching a new venture. If the goal is to sell the venture to another company, we want to identify that company before launching the venture. Of course, at this point, this is only a desire or hope, as you cannot require or expect another company to have an interest in your new venture. But you can design the new venture to align with this end goal by making decisions that support this end goal.
Consider the example of YouTube, a startup with zero dollars in sales but with a harvest price of $1.65 billion in stock from Google. The startup team, former PayPal colleagues, understood that the technology was being developed for video searching and recognized that creating a platform to house video-sharing would be desired by companies such as Google at some point in the future. Consider the tight timeline between 2005 when YouTube began supporting video sharing, and the harvest of YouTube to Google in 2006, 21 months later. This example clearly points to the importance of beginning with the end in mind.
A New Greeting Card Concept
Is there a connection between ship architecture and greeting cards? Most people would quickly say there isn’t any connection between these two disparate ideas. However, Wombi Rose and John Wise studied ship architecture, with Wise moving on to a boat-building start-up in Louisiana when they reconnected and decided to start a new venture. While traveling in Vietnam, the two ship architects came across the paper-cutting process of kirigami, similar to origami, but rather than folding paper, the paper is cut. The two engineers realized that the same design software used in building ships could also be used in creating these three-dimensional paper objects. Despite the declining greeting card industry’s sales, these two entrepreneurs decided to enter the greeting card industry with a new approach to greeting cards. Pop-up kirigami art folds flat until the envelope opens, and a kirigami object pops up. Lovepop, the name of their greeting card line, has grown to 30 employees and $6.7 million in revenue. 3
What evidence is there that Rose and Wise followed the concept of “begin with the end in mind”? If Rose and Wise followed this advice, and you were a part of this team, at what point would you begin seeking a buyer for this company? What milestones might you select for harvesting the company? Consider what actions you would accomplish to increase the sale amount to the maximum amount.
Launching your venture is a unique experience for every entrepreneurial team and for every venture. These novel situations and uncertainties create both challenges and new learning opportunities. Accepting that a multitude of possibilities exists and recognizing the importance of researching and discussing actions are valuable to the success of the team. Angel investors hold a wealth of knowledge, and with an equity stake in the venture, these investors should be included in all discussions. If you have an angel investor on your team, you have an added advantage to tap into the expertise available to support the venture. In conjunction with a well-aligned angel investor, conducting research to explore decisions will improve your venture’s success. Although these decisions might seem difficult, the next section addresses how to approach difficult decisions and the role emotional connections for the venture and its team play in those decisions.


14.4: The Yoga Sutras of Patanjali
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An early translation of the Yoga Sutras lists 195 sutras in the four books, totaling only sixteen pages (Bailey, 1927). And yet, the philosophy contained within them is amazing, although somewhat difficult to understand without having prepared oneself for this very different Eastern philosophy. A more Americanized version of the Yoga Sutras has recently been provided by Hartranft (2003), along with a section by section interpretation of the text.
The first verse of the first book states very clearly what Yoga is about. “Aum. The following instruction concerneth the Science of Union.” ( Yoga Sutras I:1; Bailey, 1927). Aum, or Om , is the sound of creation, which many Christians may relate to the Word of God in the New Testament (John 1:1; Holy Bible, 1962). The union refers to the union of the individual with the divine creator. Don’t be confused by the fact that Hindus believe in many gods. In reality, they view those lesser gods as aspects or manifestations of the one true God, much as Christians believe in one God but refer often to Father, Son, and Holy Spirit (the Holy Trinity) and the angels and demons (including Satan).
The second and third verses then set the stage for the purpose of practicing Yoga: restraining one’s inquisitive nature and controlling the mind, so that we might see ourselves realistically. The primary way in which we control the mind is to meditate. The remaining verses describe the nature of man, the universe, and the divine, the proper practice of Yoga through meditation , the challenges one is likely to face along the way, and the marvelous benefits of Yoga. Thousands of books, describing many different approaches to Yoga, have followed these simple and straightforward guidelines. No matter which type of Yoga one may choose to study, it would be valuable for anyone to return to this primary source of information to be reminded of the basic goal and purpose of Yoga.


17: Two Independent Sample Means Comparison Given Data
Two Independent Samples Means Comparison Given Data
This calculator performs the hypothesis test and also constructs a confidence interval for \(\mu_1\)−\(\mu_2\) given data. Please report the error to Dr. Jessica Kuang at jkuangATvcccd.edu.
To learn how to use this calculator, please watch a s hort video here (coming up).
Input
Type in the values from the two data sets separated by commas, for example, 2,4,5,8,11,2. Enter the statistics, the tail type, and the confidence level then hit Calculate. The test statistic, p-value, and the boundaries for the confidence interval. Be sure to enter the confidence level as a decimal, e.g., 95% should be entered as 0.95.
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Data 1: |
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choose a test \(\lt\) \(\gt\) \(\neq\) |
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Data 2: |
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Confidence Level (enter a decimal):
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Output
| Test Statistics (t): | p-value | Lower bound | Upper Bound |
(Powered by Desmos)


3.7: Introduction to Using the Right Communication Channel
What you’ll learn to do: Determine the appropriate communication channel for a specific type of message
How do I match the electronic communication channel with the audience and the message? Given all of the techniques we have discussed in this module, what is the most effective technique based on the situation available today?
Contributors and Attributions
CC licensed content, Original
- Introduction to Using the Right Communication Channel. Authored by : Robert Danielson. Provided by : Lumen Learning. License : CC BY: Attribution
CC licensed content, Shared previously
- communication icons. Authored by : eConnekt. Provided by : Pixabay. Located at : pixabay.com/en/communication-disability-3213920/. License : CC0: No Rights Reserved


3.4: Purpose of Communication
The purpose of communication is to inquire, inform, persuade, entertain, request and investigate. A single message can have one or more of the following purposes:
- To convey information/opinion, for example, “I have headache” or “I am here to give you medication”.
- To request information/opinion/behavior, for example, “Are you allergic to penicillin?” or “Tell me more about the injury”.
- To give social acknowledgement, for example, “Hello” or “Good morning”.
These three primary types of messages can be combined in many ways so that they form an interaction (conversation). The goals of the interaction can be comprehensive. Nurses strive to make all their communication with patients therapeutic, that is, their communication is purposefully and consciously planned to promote the patient’s health and wellbeing.


1.4: Carbon and Functional Groups
Skills to Develop
- Explain why carbon is important for life
- Describe the role of functional groups in biological molecules
Cells are made of many complex molecules called macromolecules, such as proteins, nucleic acids (RNA and DNA), carbohydrates, and lipids.  The fundamental component for all of these macromolecules is carbon. The carbon atom has unique properties that allow it to form covalent bonds to as many as four different atoms, making this versatile element ideal to serve as the basic structural component, or “backbone,” of the macromolecules.
Individual carbon atoms have an incomplete outermost electron shell. With an atomic number of 6 (six electrons and six protons), the first two electrons fill the inner shell, leaving four in the second shell. Therefore, carbon atoms can form up to four covalent bonds with other atoms to satisfy the octet rule. The methane molecule provides an example: it has the chemical formula CH 4 . Each of its four hydrogen atoms forms a single covalent bond with the carbon atom by sharing a pair of electrons. This results in a filled outermost shell.
Hydrocarbons
Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen, such as methane (CH 4 ) described above. We often use hydrocarbons in our daily lives as fuels—like the propane in a gas grill or the butane in a lighter. The many covalent bonds between the atoms in hydrocarbons store a great amount of energy, which is released when these molecules are burned (oxidized). Methane, an excellent fuel, is the simplest hydrocarbon molecule, with a central carbon atom bonded to four different hydrogen atoms, as illustrated in Figure \(\PageIndex{1}\). The geometry of the methane molecule, where the atoms reside in three dimensions, is determined by the shape of its electron orbitals. The carbons and the four hydrogen atoms form a shape known as a tetrahedron, with four triangular faces; for this reason, methane is described as having tetrahedral geometry.
Figure \(\PageIndex{1}\): Methane has a tetrahedral geometry, with each of the four hydrogen atoms spaced 109.5° apart.As the backbone of the large molecules of living things, hydrocarbons may exist as linear carbon chains, carbon rings, or combinations of both. Furthermore, individual carbon-to-carbon bonds may be single, double, or triple covalent bonds, and each type of bond affects the geometry of the molecule in a specific way. This three-dimensional shape or conformation of the large molecules of life (macromolecules) is critical to how they function.
Hydrocarbon Chains
Hydrocarbon chains are formed by successive bonds between carbon atoms and may be branched or unbranched. Furthermore, the overall geometry of the molecule is altered by the different geometries of single, double, and triple covalent bonds, illustrated in Figure \(\PageIndex{2}\). The hydrocarbons ethane, ethene, and ethyne serve as examples of how different carbon-to-carbon bonds affect the geometry of the molecule. The names of all three molecules start with the prefix “eth-,” which is the prefix for two carbon hydrocarbons. The suffixes “-ane,” “-ene,” and “-yne” refer to the presence of single, double, or triple carbon-carbon bonds, respectively. Thus, propane, propene, and propyne follow the same pattern with three carbon molecules, butane, butane, and butyne for four carbon molecules, and so on. Double and triple bonds change the geometry of the molecule: single bonds allow rotation along the axis of the bond, whereas double bonds lead to a planar configuration and triple bonds to a linear one. These geometries have a significant impact on the shape a particular molecule can assume.
Figure \(\PageIndex{2}\): When carbon forms single bonds with other atoms, the shape is tetrahedral. When two carbon atoms form a double bond, the shape is planar, or flat. Single bonds, like those found in ethane, are able to rotate. Double bonds, like those found in ethene cannot rotate, so the atoms on either side are locked in place.Hydrocarbon Rings
So far, the hydrocarbons we have discussed have been aliphatic hydrocarbons , which consist of linear chains of carbon atoms. Another type of hydrocarbon, aromatic hydrocarbons , consists of closed rings of carbon atoms. Ring structures are found in hydrocarbons, sometimes with the presence of double bonds, which can be seen by comparing the structure of cyclohexane to benzene in Figure \(\PageIndex{3}\). Examples of biological molecules that incorporate the benzene ring include some amino acids and cholesterol and its derivatives, including the hormones estrogen and testosterone. The benzene ring is also found in the herbicide 2,4-D. Benzene is a natural component of crude oil and has been classified as a carcinogen. Some hydrocarbons have both aliphatic and aromatic portions; beta-carotene is an example of such a hydrocarbon.
Figure \(\PageIndex{3}\): Carbon can form five-and six membered rings. Single or double bonds may connect the carbons in the ring, and nitrogen may be substituted for carbon.Isomers
The three-dimensional placement of atoms and chemical bonds within organic molecules is central to understanding their chemistry. Molecules that share the same chemical formula but differ in the placement (structure) of their atoms and/or chemical bonds are known as isomers . Structural isomers (like butane and isobutene shown in Figure \(\PageIndex{4}\)a differ in the placement of their covalent bonds: both molecules have four carbons and ten hydrogens (C 4 H 10 ), but the different arrangement of the atoms within the molecules leads to differences in their chemical properties. For example, due to their different chemical properties, butane is suited for use as a fuel for cigarette lighters and torches, whereas isobutene is suited for use as a refrigerant and a propellant in spray cans.
Geometric isomers , on the other hand, have similar placements of their covalent bonds but differ in how these bonds are made to the surrounding atoms, especially in carbon-to-carbon double bonds. In the simple molecule butene (C 4 H 8 ), the two methyl groups (CH 3 ) can be on either side of the double covalent bond central to the molecule, as illustrated in Figure \(\PageIndex{4}\)b. When the carbons are bound on the same side of the double bond, this is the cis configuration; if they are on opposite sides of the double bond, it is a trans configuration. In the trans configuration, the carbons form a more or less linear structure, whereas the carbons in the cis configuration make a bend (change in direction) of the carbon backbone.
Art Connection
Figure \(\PageIndex{4}\): Molecules that have the same number and type of atoms arranged differently are called isomers. (a) Structural isomers have a different covalent arrangement of atoms. (b) Geometric isomers have a different arrangement of atoms around a double bond. (c) Enantiomers are mirror images of each other.Which of the following statements is false?
- Molecules with the formulas CH 3 CH 2 COOH and C 3 H 6 O 2 could be structural isomers.
- Molecules must have a double bond to be cis-trans isomers.
- To be enantiomers, a molecule must have at least three different atoms or groups connected to a central carbon.
- To be enantiomers, a molecule must have at least four different atoms or groups connected to a central carbon.
In triglycerides (fats and oils), long carbon chains known as fatty acids may contain double bonds, which can be in either the cis or trans configuration, illustrated in Figure \(\PageIndex{5}\). Fats with at least one double bond between carbon atoms are unsaturated fats. When some of these bonds are in the cis configuration, the resulting bend in the carbon backbone of the chain means that triglyceride molecules cannot pack tightly, so they remain liquid (oil) at room temperature. On the other hand, triglycerides with trans double bonds (popularly called trans fats), have relatively linear fatty acids that are able to pack tightly together at room temperature and form solid fats. In the human diet, trans fats are linked to an increased risk of cardiovascular disease, so many food manufacturers have reduced or eliminated their use in recent years. In contrast to unsaturated fats, triglycerides without double bonds between carbon atoms are called saturated fats, meaning that they contain all the hydrogen atoms available. Saturated fats are a solid at room temperature and usually of animal origin.
Figure \(\PageIndex{5}\): These space-filling models show a cis (oleic acid) and a trans (eliadic acid) fatty acid. Notice the bend in the molecule cause by the cis configuration.Enantiomers
Enantiomers are molecules that share the same chemical structure and chemical bonds but differ in the three-dimensional placement of atoms so that they are mirror images. As shown in Figure \(\PageIndex{6}\), an amino acid alanine example, the two structures are non-superimposable. In nature, only the L-forms of amino acids are used to make proteins. Some D forms of amino acids are seen in the cell walls of bacteria, but never in their proteins. Similarly, the D-form of glucose is the main product of photosynthesis and the L-form of the molecule is rarely seen in nature.
Figure \(\PageIndex{6}\): D-alanine and L-alanine are examples of enantiomers or mirror images. Only the L-forms of amino acids are used to make proteins.Functional Groups
Functional groups are groups of atoms that occur within molecules and confer specific chemical properties to those molecules. They are found along the “carbon backbone” of macromolecules. This carbon backbone is formed by chains and/or rings of carbon atoms with the occasional substitution of an element such as nitrogen or oxygen. Molecules with other elements in their carbon backbone are substituted hydrocarbons .
The functional groups in a macromolecule are usually attached to the carbon backbone at one or several different places along its chain and/or ring structure. Each of the four types of macromolecules—proteins, lipids, carbohydrates, and nucleic acids—has its own characteristic set of functional groups that contributes greatly to its differing chemical properties and its function in living organisms.
A functional group can participate in specific chemical reactions. Some of the important functional groups in biological molecules are shown in Figure \(\PageIndex{7}\); they include: hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl. These groups play an important role in the formation of molecules like DNA, proteins, carbohydrates, and lipids. Functional groups are usually classified as hydrophobic or hydrophilic depending on their charge or polarity characteristics. An example of a hydrophobic group is the non-polar methane molecule. Among the hydrophilic functional groups is the carboxyl group found in amino acids, some amino acid side chains, and the fatty acids that form triglycerides and phospholipids. This carboxyl group ionizes to release hydrogen ions (H + ) from the COOH group resulting in the negatively charged COO - group; this contributes to the hydrophilic nature of whatever molecule it is found on. Other functional groups, such as the carbonyl group, have a partially negatively charged oxygen atom that may form hydrogen bonds with water molecules, again making the molecule more hydrophilic.
Figure \(\PageIndex{7}\): The functional groups shown here are found in many different biological molecules.Hydrogen bonds between functional groups (within the same molecule or between different molecules) are important to the function of many macromolecules and help them to fold properly into and maintain the appropriate shape for functioning. Hydrogen bonds are also involved in various recognition processes, such as DNA complementary base pairing and the binding of an enzyme to its substrate, as illustrated in Figure \(\PageIndex{8}\).
Figure \(\PageIndex{8}\): Hydrogen bonds connect two strands of DNA together to create the double-helix structure.Summary
The unique properties of carbon make it a central part of biological molecules. Carbon binds to oxygen, hydrogen, and nitrogen covalently to form the many molecules important for cellular function. Carbon has four electrons in its outermost shell and can form four bonds. Carbon and hydrogen can form hydrocarbon chains or rings. Functional groups are groups of atoms that confer specific properties to hydrocarbon (or substituted hydrocarbon) chains or rings that define their overall chemical characteristics and function.
Art Connections
Figure \(\PageIndex{4}\): Which of the following statements is false?
- Molecules with the formulas CH 3 CH 2 COOH and C 3 H 6 O 2 could be structural isomers.
- Molecules must have a double bond to be cis - trans isomers.
- To be enantiomers, a molecule must have at least three different atoms or groups connected to a central carbon.
- To be enantiomers, a molecule must have at least four different atoms or groups connected to a central carbon.
- Answer
-
C
Glossary
- aliphatic hydrocarbon
- hydrocarbon consisting of a linear chain of carbon atoms
- aromatic hydrocarbon
- hydrocarbon consisting of closed rings of carbon atoms
- enantiomers
- molecules that share overall structure and bonding patterns, but differ in how the atoms are three dimensionally placed such that they are mirror images of each other
- functional group
- group of atoms that provides or imparts a specific function to a carbon skeleton
- geometric isomer
- isomer with similar bonding patterns differing in the placement of atoms alongside a double covalent bond
- hydrocarbon
- molecule that consists only of carbon and hydrogen
- isomers
- molecules that differ from one another even though they share the same chemical formula
- organic molecule
- any molecule containing carbon (except carbon dioxide)
- structural isomers
- molecules that share a chemical formula but differ in the placement of their chemical bonds
- substituted hydrocarbon
- hydrocarbon chain or ring containing an atom of another element in place of one of the backbone carbons


Having just completed a course on food and agricultural marketing, you notice immediately that each of these questions pertains to a variable that can influence market demand. Question 1 deals with the own-price relationship, question 2 with cross-price relationships, question 3 with an income relationship, and question 4 with the potential for advertising expenditures to exert a favorable influence on consumer preferences.
You are pleased to have been given such a straightforward assignment and begin to draft a memo that provides sensible answers to each question. In response to question 1, you explain that as the price of beef increases, quantity demanded will fall. After all, there is this little idea called “the law of demand” that your professor kept blabbering about. Question 2 is also easy. You simply argue that pork, poultry, lamb, or fish are usually presented as alternative protein choices to beef. Because of this, each can be classified as a substitute to beef. You conclude that as the price of one or more of these products increases, beef demand would increase as well. You find the income question to be a little harder. Nevertheless, being a resourceful person, you log into the University Libraries and locate a study showing that as incomes rise, consumers increase visits to higher-end restaurants. Since these restaurants are more likely to serve expensive table cuts from the loin and rib, you reason that this study provides the evidence you need to make a case that beef is a normal good. As such, you argue that beef demand will increase as consumer incomes rise. Finally, on question 4, you state: “If the NCBA launches a new advertising campaign, it is reasonable to expect beef demand to increase. Especially if the campaign is successful in convincing consumers that beef is a nutritious and convenient menu choice.” You proofread your memo and send it off to your supervisor in an email. She acknowledges receipt with a short reply: “Wow. That was fast. I’ll look at this tonight.”
The next morning you arrive at work and see a hard copy of the memo on your desk. On it is a hand-written note that says: “Tell me something I don’t already know.” Ouch! So much for making a good first impression.
The answers you developed were correct. The problem is that answers this simple are usually not specific enough to support policy or marketing decisions. Your supervisor already had a good idea of the direction of the demand changes. What she really wanted was a better idea about the magnitude of these changes. This is where elasticities can be useful. The aim of this chapter is to help you understand how to compute and use demand and supply elasticities. You will use elasticities to address some basic decision problems in the problem sets of this chapter but will put this knowledge to work in earnest in the next chapter.
The learning objectives for this chapter are as follows: