17.3: Landforms and Coastal Deposition
Some coastal areas are dominated by erosion, an example being the Pacific coast of Canada and the United States, while others are dominated by deposition, examples being the Atlantic and Caribbean coasts of the United States. But on almost all coasts, both deposition and erosion are happening to varying degrees most of the time, although in different places. This is clearly evident in the Tofino area of Vancouver Island (Figure \(\PageIndex{1}\)), where erosion is the predominant process on the rocky headlands, while depositional processes predominate within the bays. On deposition-dominant coasts, the coastal sediments are still being eroded from some areas and deposited in others.
A key factor in determining if a coast is dominated by erosion or deposition is its history of tectonic activity. A coast like that of British Columbia is tectonically active, and compression and uplift have been going on for tens of millions of years. This coast has also been uplifted during the past 15,000 years by isostatic rebound due to deglaciation. The coasts of the United States along the Atlantic and the Gulf of Mexico have not seen significant tectonic activity in a few hundred million years, and except in the northeast, have not experienced post-glacial uplift. These areas have relatively little topographic relief, and there is now minimal erosion of coastal bedrock. Another important factor is the supply of sediments. Unless there is a continuous supply of sandy and coarser sediment to a coast it will not be a depositional coast.
On coasts that are dominated by depositional processes, most of the sediment being deposited typically comes from large rivers. An obvious example is where the Mississippi River flows into the Gulf of Mexico at New Orleans; another is the Fraser River at Vancouver. There are no large rivers bringing sandy sediments to the west coast of Vancouver Island, but there are still long and wide sandy beaches there. In this area, most of the sand comes from glaciofluvial sand deposits situated along the shore behind the beach, and some comes from the erosion of the rocks on the headlands.
The components of a typical beach are shown in Figure \(\PageIndex{1}\). On a sandy marine beach, the beach face is the area between the low and high tide levels. A berm is a flatter region beyond the reach of high tides; this area stays dry except during large storms.
Most beaches go through a seasonal cycle because conditions change from summer to winter. In summer, sea conditions are relatively calm with long-wavelength, low-amplitude waves generated by distant winds. Winter conditions are rougher, with shorter-wavelength, higher-amplitude waves caused by strong local winds. As shown in Figure \(\PageIndex{2}\), the heavy seas of winter gradually erode sand from beaches, moving it to an underwater sandbar offshore from the beach. The gentler waves of summer gradually push this sand back toward the shore, creating a wider and flatter beach.
The evolution of sandy depositional features on sea coasts is primarily influenced by waves and currents, especially longshore currents. As sediment is transported along a shore, either it is deposited on beaches, or it creates other depositional features. A spit , for example is an elongated sandy deposit that extends out into open water in the direction of a longshore current. A good example is Goose Spit at Comox on Vancouver Island (Figure \(\PageIndex{3}\)). At this location, the longshore current typically flows toward the southwest, and the sand eroded from a 60 m high cliff of Pleistocene glaciofluvial Quadra Sand is pushed in that direction and then out into Comox Harbour.
The Quadra Sand at Comox is visible in Figure \(\PageIndex{4}\). There are numerous homes built at the top of the cliff, and the property owners have gone to considerable expense to reinforce the base of the cliff with large angular rocks ( rip-rap ) and concrete barriers so as to limit further erosion of their properties. One result of this will be to starve Goose Spit of sediments and eventually contribute to its erosion. Of course the rocks and concrete barriers are only temporary; they will be eroded by strong winter storms over the next few decades and the Quadra Sand will once again contribute to the maintenance of Goose Spit.
A spit that extends across a bay to the extent of closing, or almost closing it off, is known as a baymouth bar . Most bays have streams flowing into them, and since this water has to get out, it is rare that a baymouth bar will completely close the entrance to a bay. In areas where there is sufficient sediment being transported, and there are near-shore islands, a tombolo may form (Figure \(\PageIndex{5}\)).
Tombolos are common around the southern part of the coast of British Columbia, where islands are abundant, and they typically form where there is a wave shadow behind a nearshore island (Figure \(\PageIndex{6}\)). This becomes an area with reduced energy, and so the longshore current slows and sediments accumulate. Eventually enough sediments accumulate to connect the island to the mainland with a tombolo. There is a good example of a tombolo in Figure \(\PageIndex{1}\), and another in Figure \(\PageIndex{7}\).
In areas where coastal sediments are abundant and coastal relief is low (because there has been little or no recent coastal uplift), it is common for barrier islands to form. Barrier islands are elongated islands composed of sand that form a few kilometers away from the mainland. They are common along the U.S. Gulf Coast from Texas to Florida, and along the U.S. Atlantic Coast from Florida to Massachusetts (Figure \(\PageIndex{8}\)). North of Boston, the coast becomes rocky, partly because that area has been affected by post-glacial crustal rebound.
On the map, sketch where you would expect the following to form:
- A spit
- A baymouth bar
- A tombolo
What conditions might lead to the formation of barrier islands in this area?
See Appendix 3 for Exercise 17.3 answers .
Some coasts in tropical regions (between 30° S and 30° N) are characterized by carbonate reefs . Reefs form in relatively shallow marine water within a few hundred to a few thousand meters of shore in areas where the water is clear because there is little or no input of clastic sediments from streams, and marine organisms such as corals, algae, and shelled organisms can thrive. The associated biological processes are enhanced where upwelling currents bring chemical nutrients from deeper water (but not so deep that the water is cooler than about 25°C) (Figure \(\PageIndex{10}\)). Sediments that form in the back reef (shore side) and fore reef (ocean side) are typically dominated by carbonate fragments eroded from the reef and from organisms that thrive in the back-reef area that is protected from wave energy by the reef.
Image descriptions
Figure \(\PageIndex{1}\) image description: A berm, the part of a beach that is beyond the reach of high tide, is part of the backshore. The beach face, the part of the beach between low tide and high tide level, includes the swash zone and the foreshore. Beyond the swash zone is the surf zone and beyond that is the breaker zone. [Return to Figure \(\PageIndex{1}\)]
Media Attributions
- Figures 17.3.1, 17.3.2, 17.3.3, 17.3.4, 17.3.5, 17.3.6, 17.3.7, 17.3.9, 17.3.10: © Steven Earle. CC BY.
- Figure \(\PageIndex{8}\): “ Aerial view of Assateague Island ” by Susanne Bledsoe, U.S. Army Corps of Engineers. Public domain.


39.1: Systems of Gas Exchange
Skills to Develop
- Describe the passage of air from the outside environment to the lungs
- Explain how the lungs are protected from particulate matter
The primary function of the respiratory system is to deliver oxygen to the cells of the body’s tissues and remove carbon dioxide, a cell waste product. The main structures of the human respiratory system are the nasal cavity, the trachea, and lungs.
All aerobic organisms require oxygen to carry out their metabolic functions. Along the evolutionary tree, different organisms have devised different means of obtaining oxygen from the surrounding atmosphere. The environment in which the animal lives greatly determines how an animal respires. The complexity of the respiratory system is correlated with the size of the organism. As animal size increases, diffusion distances increase and the ratio of surface area to volume drops. In unicellular organisms, diffusion across the cell membrane is sufficient for supplying oxygen to the cell (Figure \(\PageIndex{1}\)). Diffusion is a slow, passive transport process. In order for diffusion to be a feasible means of providing oxygen to the cell, the rate of oxygen uptake must match the rate of diffusion across the membrane. In other words, if the cell were very large or thick, diffusion would not be able to provide oxygen quickly enough to the inside of the cell. Therefore, dependence on diffusion as a means of obtaining oxygen and removing carbon dioxide remains feasible only for small organisms or those with highly-flattened bodies, such as many flatworms (Platyhelminthes). Larger organisms had to evolve specialized respiratory tissues, such as gills, lungs, and respiratory passages accompanied by complex circulatory systems, to transport oxygen throughout their entire body.
Direct Diffusion
For small multicellular organisms, diffusion across the outer membrane is sufficient to meet their oxygen needs. Gas exchange by direct diffusion across surface membranes is efficient for organisms less than 1 mm in diameter. In simple organisms, such as cnidarians and flatworms, every cell in the body is close to the external environment. Their cells are kept moist and gases diffuse quickly via direct diffusion. Flatworms are small, literally flat worms, which ‘breathe’ through diffusion across the outer membrane (Figure \(\PageIndex{2}\)). The flat shape of these organisms increases the surface area for diffusion, ensuring that each cell within the body is close to the outer membrane surface and has access to oxygen. If the flatworm had a cylindrical body, then the cells in the center would not be able to get oxygen.
Skin and Gills
Earthworms and amphibians use their skin (integument) as a respiratory organ. A dense network of capillaries lies just below the skin and facilitates gas exchange between the external environment and the circulatory system. The respiratory surface must be kept moist in order for the gases to dissolve and diffuse across cell membranes.
Organisms that live in water need to obtain oxygen from the water. Oxygen dissolves in water but at a lower concentration than in the atmosphere. The atmosphere has roughly 21 percent oxygen. In water, the oxygen concentration is much smaller than that. Fish and many other aquatic organisms have evolved gills to take up the dissolved oxygen from water (Figure \(\PageIndex{3}\)). Gills are thin tissue filaments that are highly branched and folded. When water passes over the gills, the dissolved oxygen in water rapidly diffuses across the gills into the bloodstream. The circulatory system can then carry the oxygenated blood to the other parts of the body. In animals that contain coelomic fluid instead of blood, oxygen diffuses across the gill surfaces into the coelomic fluid. Gills are found in mollusks, annelids, and crustaceans.
The folded surfaces of the gills provide a large surface area to ensure that the fish gets sufficient oxygen. Diffusion is a process in which material travels from regions of high concentration to low concentration until equilibrium is reached. In this case, blood with a low concentration of oxygen molecules circulates through the gills. The concentration of oxygen molecules in water is higher than the concentration of oxygen molecules in gills. As a result, oxygen molecules diffuse from water (high concentration) to blood (low concentration), as shown in Figure \(\PageIndex{4}\). Similarly, carbon dioxide molecules in the blood diffuse from the blood (high concentration) to water (low concentration).
Tracheal Systems
Insect respiration is independent of its circulatory system; therefore, the blood does not play a direct role in oxygen transport. Insects have a highly specialized type of respiratory system called the tracheal system, which consists of a network of small tubes that carries oxygen to the entire body. The tracheal system is the most direct and efficient respiratory system in active animals. The tubes in the tracheal system are made of a polymeric material called chitin.
Insect bodies have openings, called spiracles, along the thorax and abdomen. These openings connect to the tubular network, allowing oxygen to pass into the body (Figure \(\PageIndex{5}\)) and regulating the diffusion of CO 2 and water vapor. Air enters and leaves the tracheal system through the spiracles. Some insects can ventilate the tracheal system with body movements.
Mammalian Systems
In mammals, pulmonary ventilation occurs via inhalation (breathing). During inhalation, air enters the body through the nasal cavity located just inside the nose (Figure \(\PageIndex{6}\)). As air passes through the nasal cavity, the air is warmed to body temperature and humidified. The respiratory tract is coated with mucus to seal the tissues from direct contact with air. Mucus is high in water. As air crosses these surfaces of the mucous membranes, it picks up water. These processes help equilibrate the air to the body conditions, reducing any damage that cold, dry air can cause. Particulate matter that is floating in the air is removed in the nasal passages via mucus and cilia. The processes of warming, humidifying, and removing particles are important protective mechanisms that prevent damage to the trachea and lungs. Thus, inhalation serves several purposes in addition to bringing oxygen into the respiratory system.
Art Connection
Which of the following statements about the mammalian respiratory system is false?
- When we breathe in, air travels from the pharynx to the trachea.
- The bronchioles branch into bronchi.
- Alveolar ducts connect to alveolar sacs.
- Gas exchange between the lung and blood takes place in the alveolus.
From the nasal cavity, air passes through the pharynx (throat) and the larynx (voice box), as it makes its way to the trachea (Figure \(\PageIndex{6}\)). The main function of the trachea is to funnel the inhaled air to the lungs and the exhaled air back out of the body. The human trachea is a cylinder about 10 to 12 cm long and 2 cm in diameter that sits in front of the esophagus and extends from the larynx into the chest cavity where it divides into the two primary bronchi at the midthorax. It is made of incomplete rings of hyaline cartilage and smooth muscle (Figure \(\PageIndex{7}\)). The trachea is lined with mucus-producing goblet cells and ciliated epithelia. The cilia propel foreign particles trapped in the mucus toward the pharynx. The cartilage provides strength and support to the trachea to keep the passage open. The smooth muscle can contract, decreasing the trachea’s diameter, which causes expired air to rush upwards from the lungs at a great force. The forced exhalation helps expel mucus when we cough. Smooth muscle can contract or relax, depending on stimuli from the external environment or the body’s nervous system.
Lungs: Bronchi and Alveoli
The end of the trachea bifurcates (divides) to the right and left lungs. The lungs are not identical. The right lung is larger and contains three lobes, whereas the smaller left lung contains two lobes (Figure \(\PageIndex{8}\)). The muscular diaphragm , which facilitates breathing, is inferior to (below) the lungs and marks the end of the thoracic cavity.
In the lungs, air is diverted into smaller and smaller passages, or bronchi . Air enters the lungs through the two primary (main) bronchi (singular: bronchus). Each bronchus divides into secondary bronchi, then into tertiary bronchi, which in turn divide, creating smaller and smaller diameter bronchioles as they split and spread through the lung. Like the trachea, the bronchi are made of cartilage and smooth muscle. At the bronchioles, the cartilage is replaced with elastic fibers. Bronchi are innervated by nerves of both the parasympathetic and sympathetic nervous systems that control muscle contraction (parasympathetic) or relaxation (sympathetic) in the bronchi and bronchioles, depending on the nervous system’s cues. In humans, bronchioles with a diameter smaller than 0.5 mm are the respiratory bronchioles . They lack cartilage and therefore rely on inhaled air to support their shape. As the passageways decrease in diameter, the relative amount of smooth muscle increases.
The terminal bronchioles subdivide into microscopic branches called respiratory bronchioles. The respiratory bronchioles subdivide into several alveolar ducts. Numerous alveoli and alveolar sacs surround the alveolar ducts. The alveolar sacs resemble bunches of grapes tethered to the end of the bronchioles (Figure \(\PageIndex{9}\)). In the acinar region, the alveolar ducts are attached to the end of each bronchiole. At the end of each duct are approximately 100 alveolar sacs , each containing 20 to 30 alveoli that are 200 to 300 microns in diameter. Gas exchange occurs only in alveoli. Alveoli are made of thin-walled parenchymal cells, typically one-cell thick, that look like tiny bubbles within the sacs. Alveoli are in direct contact with capillaries (one-cell thick) of the circulatory system. Such intimate contact ensures that oxygen will diffuse from alveoli into the blood and be distributed to the cells of the body. In addition, the carbon dioxide that was produced by cells as a waste product will diffuse from the blood into alveoli to be exhaled. The anatomical arrangement of capillaries and alveoli emphasizes the structural and functional relationship of the respiratory and circulatory systems. Because there are so many alveoli (~300 million per lung) within each alveolar sac and so many sacs at the end of each alveolar duct, the lungs have a sponge-like consistency. This organization produces a very large surface area that is available for gas exchange. The surface area of alveoli in the lungs is approximately 75 m 2 . This large surface area, combined with the thin-walled nature of the alveolar parenchymal cells, allows gases to easily diffuse across the cells.
Link to Learning
Watch the following video to review the respiratory system.
Protective Mechanisms
The air that organisms breathe contains particulate matter such as dust, dirt, viral particles, and bacteria that can damage the lungs or trigger allergic immune responses. The respiratory system contains several protective mechanisms to avoid problems or tissue damage. In the nasal cavity, hairs and mucus trap small particles, viruses, bacteria, dust, and dirt to prevent their entry.
If particulates do make it beyond the nose, or enter through the mouth, the bronchi and bronchioles of the lungs also contain several protective devices. The lungs produce mucus —a sticky substance made of mucin , a complex glycoprotein, as well as salts and water—that traps particulates. The bronchi and bronchioles contain cilia, small hair-like projections that line the walls of the bronchi and bronchioles (Figure \(\PageIndex{10}\)). These cilia beat in unison and move mucus and particles out of the bronchi and bronchioles back up to the throat where it is swallowed and eliminated via the esophagus.
In humans, for example, tar and other substances in cigarette smoke destroy or paralyze the cilia, making the removal of particles more difficult. In addition, smoking causes the lungs to produce more mucus, which the damaged cilia are not able to move. This causes a persistent cough, as the lungs try to rid themselves of particulate matter, and makes smokers more susceptible to respiratory ailments.
Summary
Animal respiratory systems are designed to facilitate gas exchange. In mammals, air is warmed and humidified in the nasal cavity. Air then travels down the pharynx, through the trachea, and into the lungs. In the lungs, air passes through the branching bronchi, reaching the respiratory bronchioles, which house the first site of gas exchange. The respiratory bronchioles open into the alveolar ducts, alveolar sacs, and alveoli. Because there are so many alveoli and alveolar sacs in the lung, the surface area for gas exchange is very large. Several protective mechanisms are in place to prevent damage or infection. These include the hair and mucus in the nasal cavity that trap dust, dirt, and other particulate matter before they can enter the system. In the lungs, particles are trapped in a mucus layer and transported via cilia up to the esophageal opening at the top of the trachea to be swallowed.
Art Connections
Figure \(\PageIndex{6}\): Which of the following statements about the mammalian respiratory system is false?
- When we breathe in, air travels from the pharynx to the trachea.
- The bronchioles branch into bronchi.
- Alveolar ducts connect to alveolar sacs.
- Gas exchange between the lung and blood takes place in the alveolus.
- Answer
-
B
Glossary
- alveolar duct
- duct that extends from the terminal bronchiole to the alveolar sac
- alveolar sac
- structure consisting of two or more alveoli that share a common opening
- alveolus
- (plural: alveoli) (also, air sac) terminal region of the lung where gas exchange occurs
- bronchus
- (plural: bronchi) smaller branch of cartilaginous tissue that stems off of the trachea; air is funneled through the bronchi to the region where gas exchange occurs in alveoli
- bronchiole
- airway that extends from the main tertiary bronchi to the alveolar sac
- diaphragm
- domed-shaped skeletal muscle located under lungs that separates the thoracic cavity from the abdominal cavity
- larynx
- voice box, a short passageway connecting the pharynx and the trachea
- mucin
- complex glycoprotein found in mucus
- mucus
- sticky protein-containing fluid secretion in the lung that traps particulate matter to be expelled from the body
- nasal cavity
- opening of the respiratory system to the outside environment
- particulate matter
- small particle such as dust, dirt, viral particles, and bacteria that are in the air
- pharynx
- throat; a tube that starts in the internal nares and runs partway down the neck, where it opens into the esophagus and the larynx
- primary bronchus
- (also, main bronchus) region of the airway within the lung that attaches to the trachea and bifurcates to each lung where it branches into secondary bronchi
- respiratory bronchiole
- terminal portion of the bronchiole tree that is attached to the terminal bronchioles and alveoli ducts, alveolar sacs, and alveoli
- terminal bronchiole
- region of bronchiole that attaches to the respiratory bronchioles
- trachea
- cartilaginous tube that transports air from the larynx to the primary bronchi


14.1B: Modern Applications of DNA
- Explain why DNA is a practical tool in various fields, such as forensics and medicine
The acronym “DNA” has become synonymous with solving crimes, testing for paternity, identifying human remains, and genetic testing. DNA can be retrieved from hair, blood, or saliva. Each person’s DNA sequences are unique, and it is possible to detect differences between individuals within a species on the basis of these unique features. DNA testing can also be used to identify pathogens, identify biological remains in archaeological digs, trace disease outbreaks, and study human migration patterns. In the medical field, DNA is used in diagnostics, new vaccine development, and cancer therapy. It is now also possible to determine predispositions to some diseases by looking at genes.
Cloning
Reproductive cloning is a method used to make a clone or an identical copy of an entire multicellular organism.
In cloning both the original organism and the clone have identical DNA. Identical twins are, in one sense, clones of each other; they have identical DNA, having developed from the same fertilized egg.
Cloning became an issue in scientific ethics when a sheep became the first mammal cloned from an adult cell in 1996.
Since then several animals such as horses, bulls, and goats have been successfully cloned, although these individuals often exhibit facial, limb, and cardiac abnormalities.
There have been attempts at producing cloned human embryos as sources of embryonic stem cells, sometimes referred to as ‘cloning for therapeutic purposes’. Therapeutic cloning produces stem cells to attempt to remedy detrimental diseases or defects (unlike reproductive cloning, which aims to reproduce an organism). Still, therapeutic cloning efforts have met with resistance because of bioethical considerations.
CRISPR
CRISPR (Clustered, Regularly-Interspaced Short Palindromic Repeats) allows scientists to edit genomes, far better than older techniques for gene splicing and editing. The CRISPR technique has enormous potential application, including altering the germline of humans, animals and other organisms, and modifying the genes of food crops.
Ethical concerns have surfaced about this biotechnology and the prospect of editing the human germline and making so-called ‘designer babies’.
CRISPR Technique : This movie goes through the process of CRISPR.
Genetically Modified Organisms
A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques. GMOs are a source of medicines and genetically modified foods and are also widely used in scientific research, along with the production of other goods.
Genetic modification involves the mutation, insertion, or deletion of genes. Inserted genes usually come from a different species in a form of horizontal gene-transfer.
Bacteria, plants, and animals have been genetically modified since the early 1970s for academic, medical, agricultural, and industrial purposes. In the US, GMOs such as Roundup-Ready soybeans and borer-resistant corn are part of many common processed foods. As in many of these biotechnology areas there is considerable controversy in the use of GMOs.
Contributions and Attributions
- Erwin Chargaff. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Erwin_Chargaff . License : CC BY-SA: Attribution-ShareAlike
- DNA. Provided by : OpenStax CNX. Located at : http://cnx.org/contents/GFy_h8cu@9.87:Q01G1mzh@2/Introduction . License : CC BY-SA: Attribution-ShareAlike
- DNA. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/DNA . License : CC BY-SA: Attribution-ShareAlike
- DNA Structure. Provided by : OpenStax CNX. Located at : http://cnx.org/contents/GFy_h8cu@9.87:U7tPDRxK@7/DNA-Structure-and-Sequencing . License : CC BY-SA: Attribution-ShareAlike
- figure2.jpg. Provided by : OpenStax CNX. Located at<EMAIL_ADDRESS>. License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44484/latest/?collection=col11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. October 22, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44485/latest/?collection=col11448/latest . License : CC BY: Attribution
- phenotype. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/phenotype . License : CC BY-SA: Attribution-ShareAlike
- genotype. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/genotype . License : CC BY-SA: Attribution-ShareAlike
- gene. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/gene . License : CC BY-SA: Attribution-ShareAlike
- GMO. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Genetically_modified_organism . License : CC BY-SA: Attribution-ShareAlike
- Biotechnology. Provided by : OpenStax CNX. Located at : http://cnx.org/contents/GFy_h8cu@9.87:exg4e4AU@7/Biotechnology . License : CC BY-SA: Attribution-ShareAlike
- CRISPR. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/CRISPR . License : CC BY-SA: Attribution-ShareAlike
- figure2.jpg. Provided by : OpenStax CNX. Located at<EMAIL_ADDRESS>. License : CC BY-SA: Attribution-ShareAlike
- CRISPR Technique. Located at : http://www.youtube.com/watch?v=2pp17E4E-O8 . License : Public Domain: No Known Copyright . License Terms : Standard YouTube license
- GloFish.jpg. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Genetically_modified_organism%23/media/File:GloFish.jpg . License : CC BY-SA: Attribution-ShareAlike
- data-attribution-url=cnx.org/content/m44484/latest...e_14_00_01.jpg. Provided by : Connexions. License : CC BY: Attribution
Key Points
- DNA is unique to each individual, and therefore can be used for identification purposes.
- The human genome consists of about 3 billion base pairs, corresponding to about 20,000 to 25,000 functional genes.
- Each person’s DNA is inherited from their parents: 23 chromosomes from the mother, and 23 chromosomes from the father.
Key Terms
- genotype : The combination of alleles, situated on corresponding chromosomes, that determines a specific trait of an individual.
- zygote : The single cell that arises from the union of two gametes; in animals, the cell that arises from the union of sperm and ovum.
- gene : A unit of heredity; the functional units of chromosomes that determine specific characteristics by coding for specific RNAs or proteins.
- phenotype : The appearance of an organism based on a multifactorial combination of genetic traits and environmental factors.


2.4: Evaluate, Simplify, and Translate Expressions (Part 2)
Translate Words to Algebraic Expressions
In the previous section, we listed many operation symbols that are used in algebra, and then we translated expressions and equations into word phrases and sentences. Now we’ll reverse the process and translate word phrases into algebraic expressions. The symbols and variables we’ve talked about will help us do that. They are summarized in Table \(\PageIndex{3}\) .
| Operation | Phrase | Expression |
|---|---|---|
| Addition |
a plus b the sum of a and b a increased by b b more than a the total of a and b b added to a |
a + b |
| Subtraction |
a minus b the difference of a and b b subtracted from a a decreased by b b less than a |
a - b |
| Multiplication |
a times b the product of a and b |
a • b, ab, a(b), (a)(b) |
| Division |
a divided by b the quotient of a and b the ratio of a and b b divided into a |
a ÷ b, a / b, \(\dfrac{a}{b}\), \(b \overline{) a}\) |
Look closely at these phrases using the four operations:
- the sum of \(a\) and \(b\)
- the difference of \(a\) and \(b\)
- the product of \(a\) and \(b\)
- the quotient of \(a\) and \(b\)
Each phrase tells you to operate on two numbers. Look for the words of and and to find the numbers.
Translate each word phrase into an algebraic expression:
- the difference of \(20\) and \(4\)
- the quotient of \(10x\) and \(3\)
Solution
- The key word is difference , which tells us the operation is subtraction. Look for the words of and and to find the numbers to subtract.
the difference of \(20\) and \(4\)
\(20\) minus \(4\)
\(20 − 4\)
- The key word is quotient , which tells us the operation is division.
the quotient of \(10x\) and \(3\)
divide \(10x\) by \(3\)
\(10x ÷ 3\)
This can also be written as 1\(0x / 3\) or \(\dfrac{10x}{3}\)
Translate the given word phrase into an algebraic expression:
- the difference of \(47\) and \(41\)
- the quotient of \(5x\) and \(2\)
- Answer a
-
\(47-41\)
- Answer b
-
\(5x\div 2\)
Translate the given word phrase into an algebraic expression:
- the sum of \(17\) and \(19\)
- the product of \(7\) and \(x\)
- Answer a
-
\(17+19\)
- Answer b
-
\(7x\)
How old will you be in eight years? What age is eight more years than your age now? Did you add \(8\) to your present age? Eight more than means eight added to your present age.
How old were you seven years ago? This is seven years less than your age now. You subtract \(7\) from your present age. Seven less than means seven subtracted from your present age.
Translate each word phrase into an algebraic expression:
- Eight more than \(y\)
- Seven less than \(9z\)
Solution
- The key words are more than. They tell us the operation is addition. More than means “added to”.
Eight more than \(y\)
Eight added to \(y\)
\(y + 8\)
- The key words are less than. They tell us the operation is subtraction. Less than means “subtracted from”.
Seven less than \(9z\)
Seven subtracted from \(9z\)
\(9z − 7\)
Translate each word phrase into an algebraic expression:
- Eleven more than \(x\)
- Fourteen less than \(11a\)
- Answer a
-
\(x+11\)
- Answer b
-
\(11a-14\)
Translate each word phrase into an algebraic expression:
- \(19\) more than \(j\)
- \(21\) less than \(2x\)
- Answer a
-
\(j+19\)
- Answer b
-
\(2x-21\)
Translate each word phrase into an algebraic expression:
- five times the sum of \(m\) and \(n\)
- the sum of five times \(m\) and \(n\)
Solution
- There are two operation words: times tells us to multiply and sum tells us to add. Because we are multiplying \(5\) times the sum, we need parentheses around the sum of \(m\) and \(n\).
five times the sum of \(m\) and \(n\)
\(5(m + n)\)
- To take a sum, we look for the words of and and to see what is being added. Here we are taking the sum of five times \(m\) and \(n\).
the sum of five times \(m\) and \(n\)
\(5m + n\)
Notice how the use of parentheses changes the result. In part (a), we add first and in part (b), we multiply first.
Translate the word phrase into an algebraic expression:
- four times the sum of \(p\) and \(q\)
- the sum of four times \(p\) and \(q\)
- Answer a
-
\(4(p+q)\)
- Answer b
-
\(4p+q\)
Translate the word phrase into an algebraic expression:
- the difference of two times \(x\) and \(8\)
- two times the difference of \(x\) and \(8\)
- Answer a
-
\(2x-8\)
- Answer b
-
\(2(x-8)\)
Later in this course, we’ll apply our skills in algebra to solving equations. We’ll usually start by translating a word phrase to an algebraic expression. We’ll need to be clear about what the expression will represent. We’ll see how to do this in the next two examples.
The height of a rectangular window is 6 inches less than the width. Let w represent the width of the window. Write an expression for the height of the window.
Solution
| Write a phrase about the height. | 6 less than the width |
| Substitute w for the width. | 6 less than w |
| Rewrite 'less than' as 'subtracted from'. | 6 subtracted from w |
| Translate the phrase into algebra. | w - 6 |
The length of a rectangle is \(5\) inches less than the width. Let \(w\) represent the width of the rectangle. Write an expression for the length of the rectangle.
- Answer
-
\(w-5\)
The width of a rectangle is \(2\) meters greater than the length. Let \(l\) represent the length of the rectangle. Write an expression for the width of the rectangle.
- Answer
-
\(l+2\)
Blanca has dimes and quarters in her purse. The number of dimes is \(2\) less than \(5\) times the number of quarters. Let \(q\) represent the number of quarters. Write an expression for the number of dimes.
Solution
| Write a phrase about the number of dimes. | two less than five times the number of quarters |
| Substitute q for the number of quarters. | 2 less than five times q |
| Translate 5 times q. | 2 less than 5q |
| Translate the phrase into algebra. | 5q - 2 |
Geoffrey has dimes and quarters in his pocket. The number of dimes is seven less than six times the number of quarters. Let \(q\) represent the number of quarters. Write an expression for the number of dimes.
- Answer
-
\(6q-7\)
Lauren has dimes and nickels in her purse. The number of dimes is eight more than four times the number of nickels. Let \(n\) represent the number of nickels. Write an expression for the number of dimes.
- Answer
-
\(4n+8\)
Key Concepts
-
Combine like terms.
- Identify like terms.
- Rearrange the expression so like terms are together.
- Add the coefficients of the like terms
Glossary
- term
-
A term is a constant or the product of a constant and one or more variables.
- coefficient
-
The constant that multiplies the variable(s) in a term is called the coefficient.
- like terms
-
Terms that are either constants or have the same variables with the same exponents are like terms.
- evaluate
-
To evaluate an algebraic expression means to find the value of the expression when the variable is replaced by a given number.
Practice Makes Perfect
Evaluate Algebraic Expressions
In the following exercises, evaluate the expression for the given value.
- 7x + 8 when x = 2
- 9x + 7 when x = 3
- 5x − 4 when x = 6
- 8x − 6 when x = 7
- x 2 when x = 12
- x 3 when x = 5
- x 5 when x = 2
- x 4 when x = 3
- 3 x when x = 3
- 4 x when x = 2
- x 2 + 3x − 7 when x = 4
- x 2 + 5x − 8 when x = 6
- 2x + 4y − 5 when x = 7, y = 8
- 6x + 3y − 9 when x = 6, y = 9
- (x − y) 2 when x = 10, y = 7
- (x + y) 2 when x = 6, y = 9
- a 2 + b 2 when a = 3, b = 8
- r 2 − s 2 when r = 12, s = 5
- 2l + 2w when l = 15, w = 12
- 2l + 2w when l = 18, w = 14
Identify Terms, Coefficients, and Like Terms
In the following exercises, list the terms in the given expression.
- 15x 2 + 6x + 2
- 11x 2 + 8x + 5
- 10y 3 + y + 2
- 9y 3 + y + 5
In the following exercises, identify the coefficient of the given term.
- 8a
- 13m
- 5r 2
- 6x 3
In the following exercises, identify all sets of like terms.
- x 3 , 8x, 14, 8y, 5, 8x 3
- 6z, 3w 2 , 1, 6z 2 , 4z, w 2
- 9a, a 2 , 16ab, 16b 2 , 4ab, 9b 2
- 3, 25r 2 , 10s, 10r, 4r 2 , 3s
Simplify Expressions by Combining Like Terms
In the following exercises, simplify the given expression by combining like terms.
- 10x + 3x
- 15x + 4x
- 17a + 9a
- 18z + 9z
- 4c + 2c + c
- 6y + 4y + y
- 9x + 3x + 8
- 8a + 5a + 9
- 7u + 2 + 3u + 1
- 8d + 6 + 2d + 5
- 7p + 6 + 5p + 4
- 8x + 7 + 4x − 5
- 10a + 7 + 5a − 2 + 7a − 4
- 7c + 4 + 6c − 3 + 9c − 1
- 3x 2 + 12x + 11 + 14x 2 + 8x + 5
- 5b 2 + 9b + 10 + 2b 2 + 3b − 4
Translate English Phrases into Algebraic Expressions
In the following exercises, translate the given word phrase into an algebraic expression.
- The sum of 8 and 12
- The sum of 9 and 1
- The difference of 14 and 9
- 8 less than 19
- The product of 9 and 7
- The product of 8 and 7
- The quotient of 36 and 9
- The quotient of 42 and 7
- The difference of x and 4
- 3 less than x
- The product of 6 and y
- The product of 9 and y
- The sum of 8x and 3x
- The sum of 13x and 3x
- The quotient of y and 3
- The quotient of y and 8
- Eight times the difference of y and nine
- Seven times the difference of y and one
- Five times the sum of x and y
- Nine times five less than twice x
In the following exercises, write an algebraic expression.
- Adele bought a skirt and a blouse. The skirt cost $15 more than the blouse. Let b represent the cost of the blouse. Write an expression for the cost of the skirt.
- Eric has rock and classical CDs in his car. The number of rock CDs is 3 more than the number of classical CDs. Let c represent the number of classical CDs. Write an expression for the number of rock CDs.
- The number of girls in a second-grade class is 4 less than the number of boys. Let b represent the number of boys. Write an expression for the number of girls.
- Marcella has 6 fewer male cousins than female cousins. Let f represent the number of female cousins. Write an expression for the number of boy cousins.
- Greg has nickels and pennies in his pocket. The number of pennies is seven less than twice the number of nickels. Let n represent the number of nickels. Write an expression for the number of pennies.
- Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
Everyday Math
In the following exercises, use algebraic expressions to solve the problem.
- Car insurance Justin’s car insurance has a $750 deductible per incident. This means that he pays $750 and his insurance company will pay all costs beyond $750. If Justin files a claim for $2,100, how much will he pay, and how much will his insurance company pay?
- Home insurance Pam and Armando’s home insurance has a $2,500 deductible per incident. This means that they pay $2,500 and their insurance company will pay all costs beyond $2,500. If Pam and Armando file a claim for $19,400, how much will they pay, and how much will their insurance company pay?
Writing Exercises
- Explain why “the sum of x and y” is the same as “the sum of y and x,” but “the difference of x and y” is not the same as “the difference of y and x.” Try substituting two random numbers for x and y to help you explain. 146. Explain the difference between “4 times the sum of x and y” and “the sum of 4 times x and y.”
Self Check
(a) After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.
(b) After reviewing this checklist, what will you do to become confident for all objectives?
Contributors and Attributions
- Lynn Marecek (Santa Ana College) and MaryAnne Anthony-Smith (formerly of Santa Ana College). This content produced by OpenStax and is licensed under a Creative Commons Attribution License 4.0 license.


1.34: Galilean Relativity
We now extend our discussion of spatial geometry to spacetime geometry. We begin with Galilean relativity, which we will then generalize in the next section to Einstein (or Lorentz) relativity.
The notion of relativity of motion is not something new with Einstein. It's built into Newtonian mechanics as well. The idea is that the results of experiments done in any inertial frame will be the same; i.e., one will not be able to determine by some experimental means what frame is at "absolute rest" and which frames are moving -- all motion is relative. An inertial frame is one in which Newton's laws of motion are satisfied. These laws prescribe accelerations, not velocities, so a frame that is moving at constant relative velocity with respect to an inertial frame must itself be an inertial frame.
Let's begin by considering a labeling of all points in space, at all points in time, with \( t, x, y, z \). Further, let's assume the spatial part of this is a Cartesian coordinate system such that a ruler (at rest in this coordinate systems) with one end at \(t,x,y,z\) and the other at \(t,x+dx, y+dy, z+dz\) has length whose square is \( d\ell^2 = dx^2+dy^2+dz^2 \) and the time labeling is such that a clock that goes from \(t, x, y, z\) to \(t+dt,x,y,z\) will indicate that the time elapsed is \(dt\). Further, we will assume that this reference frame is inertial: Newton's laws of motion are satisfied in this frame.
An example of such a coordinate system, although with just one spatial dimension, is shown in the first two figures in this chapter. A ruler stretching from point A to point B in the figure with these points horizontally displaced from each other, if the units of the tick marks on the x axis are in cm, would measure 1 cm. A clock that moves from A to B in the second figure, if the units on the t axis are seconds, would show a time elapsed of one second.
Now imagine a ball as it travels at uniform velocity from a spacetime point A to a spacetime point B. Let's set this up so that point A is \(t = 2\) seconds and \(x = 4\) cm and point B is at \(t = 5\) seconds and \(x = 7\) cm as in the figure to the left. From this given information we can conclude that the ball is moving toward increasing values of \(x\) at constant speed \(v = 1\) cm/s. Let's define another reference frame, called the primed frame, which is coincident with the original unprimed frame at \(t=t'=0\) but relative to the unprimed frame is moving to the right at speed \(v = 1\) cm/s just like the ball. In the primed frame (see the figure to the right) the origin of the primed frame is not moving (by definition), the ball is not moving, and the origin of the unprimed frame is moving toward decreasing values of \(x'\) at speed \(v\). The principle of relativity assures us that we can construct this primed frame so that it also has the same nice properties of the unprimed frame; i.e., the Pythagorean theorem applies for lengths, and the readings of stationary clocks make sense; i.e., a clock that goes from \(t', x', y', z'\) to \(t'+dt',x',y',z'\) will indicate that the time elapsed is \(dt'\). The principle of relativity also leads us to the conclusion that if the unprimed frame is an inertial frame, the primed frame will be as well.
So far we have not mentioned Galileo. The above statements all follow from the principle of relativity, and our assumption that space is Euclidean. We specialize to Galilean relativity when we assume that the relationship between these two coordinate systems is:
\[\begin{equation}
\begin{aligned}
t' & = t, \\ x' &= x - vt, \\ y' &= y,\ {\rm and}\\ z' & = z
\end{aligned}
\end{equation}\]
Because the relationship is time dependent (and because we are anticipating the generalization to Lorentz transformations), we have explicitly included time in the transformation, even though time transforms trivially. We will call such a transformation a "Galilean Boost." In this case the above equations describe the relationship between a reference frame we denote without primes (the unprimed reference frame) and a reference frame that we denote with primes (the primed reference frame), where the primed reference frame is moving relative to the unprimed reference frame with speed \(v\) in the \(+x\) direction.
One can quickly verify that, if evaluated at the same time \(t\), the distance between two infinitesimally separated points is unchanged by this transformation. Further, the transformation is symmetric. That is, there is nothing special about the primed frame relative to the unprimed frame. The reverse transformation, found by solving the above for \(t\), \(x\), \(y\), and \(z\) is
\[\begin{equation}
\begin{aligned}
t & = t', \\ x &= x' + vt', \\ y &= y',\ {\rm and}\\ z & = z'
\end{aligned}
\end{equation}\]
which is the same equation as above except with the replacement of \(v\) with \(-v\). That is, it is exactly the same rule, with \(v \rightarrow -v\) because while the primed frame is moving relative to the unprimed frame toward higher \(x\), the unprimed frame is moving relative to the primed frame toward lower \(x'\).
Box \(\PageIndex{1}\)
Exercise 3.1.1: With the Galilean boost transformation, velocities add in a simple manner. If \(u' = dx'/dt'\) where \(x'(t')\) is the \(x'\) location of some particle at time \(t'\), find \(u = dx/dt\) as a function of \(u'\) and \(v\).
Box \(\PageIndex{2}\)
Exercise 3.2.1: Show that Newton's Law for a spring is invariant under a Galilean transformation. In particular, show that the equation \(m {\ddot x} = -k(x-x_c) \) is invariant under a Galilean transformation assuming the location of the force-free point of the spring, \(x_c\), is transformed as well. Here we have taken the spring equilibrium length to be zero and the spring constant to be \(k\).
Box \(\PageIndex{3}\)
Exercise 3.3.1: Discuss what this invariance means for applicability of Newton's laws in both the primed and unprimed frames, and the question: "is such a law consistent with the principal of Galilean relativity?"


9.1: Why It Matters- Volcanoes
Explain the origin of volcanic features and landforms; as well as the causes and hazards associated with volcanic activity.
Volcanoes are one of the most dynamic, powerful and destructive forces on the Earth. While they are majestic in appearance, they are often sleeping giants just waiting to wake up and make us take notice. Some of you may have seen volcanic eruptions in person or on TV. Volcanoes are the geologists’ window into the Earth’s interior. If you recall from the previous section, plate tectonics directly influences the location and types of volcanoes we find across the globe. Now we understand why the west coast of America as a chain of volcanoes in the Cascade Mountains and why Japan has so many active volcanoes.
Volcanologists have one of the most exciting yet dangerous jobs of all scientists. Please watch this video on the eruption of Mt. St. Helens in 1980 to learn more about volcanic eruptions, how scientists study the volcanoes and why volcanologists are important to society.
This video shows the most destructive eruption ever that happen to also be the loudest sound ever recorded on earth. This eruption actually blew the volcanoes out of existence, until recently as a new active volcano is currently forming in its place.
Learning Outcomes
- Describe and compare different volcano types.
- Describe the processes that form volcanoes.
- Classify and identify igneous features.
- Describe major volcanic hazards and their potential effects.
- Identify the various methods used to monitor volcanic activity
Contributors and Attributions
- Authored by : Kimberly Schulte and Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution
- Mount St. Helens May 18, 1980. Provided by : USGS. Located at : https://youtu.be/Ec30uU0G56U . License : All Rights Reserved . License Terms : Standard YouTube License
- THE LOUDEST SOUND IN HISTORY. Authored by : Second Thought. Located at : https://youtu.be/opWwfRS7HZU . License : All Rights Reserved . License Terms : Standard YouTube License


15.5: Thermodynamics of Mixing and Dilution
The free energy of a pure liquid or solid at 1 atm pressure is just its molar free energy of formation Δ G multiplied by the number of moles present. For gases and substances in solution, we have to take into account the concentration (which, in the case of gases, is normally expressed in terms of the pressure). We know that the lower the concentration, the greater the entropy, and thus the smaller the free energy. The following excerpt from this lesson serves as the starting point for the rest of the present lesson.
Entropy Depends on Concentration
As a substance becomes more dispersed in space, the thermal energy it carries is also spread over a larger volume, leading to an increase in its entropy. Because entropy, like energy, is an extensive property, a dilute solution of a given substance may well possess a smaller entropy than the same volume of a more concentrated solution, but the entropy per mole of solute (the molar entropy) will of course always increase as the solution becomes more dilute.
For gaseous substances, the volume and pressure are respectively direct and inverse measures of concentration. For an ideal gas that expands at a constant temperature (meaning that it absorbs heat from the surroundings to compensate for the work it does during the expansion), the increase in entropy is given by
\[\Delta S = R\ln \left( \dfrac{V_2}{V_1} \right) \label{2-4}\]
(If the gas is allowed to cool during the expansion, the relation becomes more complicated and will best be discussed in a more advanced course.)
Because the pressure of a gas is inversely proportional to its volume, we can easily alter the above relation to express the entropy change associated with a change in the pressure of a perfect gas:
\[\Delta S = R\ln \left( \dfrac{P_1}{P_2} \right) \label{2-5}\]
Expressing the entropy change directly in concentrations \(c\), we have the similar relation
\[\Delta S = R\ln \left( \dfrac{C_1}{C_2} \right) \label{2-6}\]
Although these equations strictly apply only to perfect gases and cannot be used at all for liquids and solids, it turns out that in a dilute solution, the solute can often be treated as a gas dispersed in the volume of the solution, so the last equation can actually give a fairly accurate value for the entropy of dilution of a solution. We will see later that this has important consequences in determining the equilibrium concentrations in a homogeneous reaction mixture.
The Gibbs energy of a Gas: standard states
The pressure of a perfect gas does not affect its enthalpy, but it does affect the entropy (box at left), and thus, through the –T Δ S term, the free energy. When the pressure of such a gas changes from \(P_1\) to \(P_2\), the Gibbs energy change is
\[ \Delta G = \Delta H - T \Delta S = 0 - RT \ln \left( \dfrac{P_1}{P_2} \right) \label{4.8}\]
How can we evaluate the free energy of a specific sample of a gas at some arbitrary pressure? First, recall that the standard molar free energy G ° that you would look up in a table refers to a pressure of 1 atm. The free energy per mole of our sample is just the sum of this value and any change in free energy that would occur if the pressure were changed from 1 atm to the pressure of interest
\[ G = G^o + RT \ln \left( \dfrac{P_1}{1\; atm} \right) \label{4.9}\]
which we normally write in abbreviated form
\[G = G^o + RT \ln P \label{4-10}\]
The term escaping tendency is not commonly used in traditional thermodynamics because it is essentially synonymous with the free energy, but it is worth knowing because it helps us appreciate the physical significance of free energy in certain contexts. The higher the pressure of a gas, the greater will be the tendency of its molecules to leave the confines of the container; we will call this the escaping tendency . The above equation tells us that the pressure of a gas is a directly observable measure of its free energy ( G , not G °!). Combining these two ideas, we can say that the free energy of a gas is also a measure of its escaping tendency .
From Gases to Solutions: Mixing and Dilution
All substances, given the opportunity to form a homogeneous mixture with other substances, will tend to become more dilute. This can be rationalized simply from elementary statistics; there are more equally probable ways of arranging one hundred black marbles and one hundred white marbles, than two hundred marbles of a single color. For massive objects like marbles this has nothing to do with entropy, of course. However, when we are dealing with huge numbers of molecules capable of storing, exchanging and spreading thermal energy, mixing and expansion are definitely entropy-driven processes.
It can be argued, in fact, that mixing and expansion are really very similar ; after all, when we mix two gases, each is expanding into the space formerly occupied exclusively by the other.
Suppose, for example, that we have a gas initially confined to one half of a box, and we then remove the barrier so that it can expand into the full volume of the container. We know that the entropy of the gas will increase as the thermal energy of its molecules spreads into the enlarged space; the actual increase, according to Equations \(\ref{2-4}\) and \(\ref{2-5}\) above, is \(R \ln 2\). And from Equation \(\ref{4-10}\), the change in \(G\) will be \(–RT \ln 2\).
Now let us repeat the experiment, but starting this time with "red" molecules in one half of the container and "blue" ones in the right half. Because we now have two gases expanding into twice their initial volumes, the changes in S and G will be twice as great:
\[ΔS = 2 R \ln 2\]
\[ΔG = –2 RT \ln 2\]
However, notice that although each gas underwent an expansion, the overall process in this case is equivalent to mixing .
What is true for gaseous molecules can, in principle, apply also to solute molecules dissolved in a solvent. An important qualification here is that the solution must be an ideal one, meaning that the strength of interactions between all type of molecules (solutes A and B, and the solvent) must be the same. Remember that the enthalpy associated with the expansion of a perfect gas is by definition zero. In contrast, the \(ΔH_{mixing}\) of two liquids or of dissolving a solute in a solvent have finite values which may limit the miscibility of liquids or the solubility of a solute.
Given this proviso, we can define the Gibbs energy of dilution or mixing by substituting this equation into the definition of Δ G :
\[ \Delta G_{dilution} = \Delta H_{dilution} - RT\ln \left( \dfrac{C_1}{C_2} \right) \label{4-11}\]
If the substance in question forms an ideal solution with the other components, then \(ΔH_{diution}\) is zero, and we can write
\[ \Delta G_{dilution} = RT\ln \left( \dfrac{C_2}{C_1} \right) \label{4-12}\]
These relations tell us that the dilution of a substance from an initial concentration \(C_1\) to a more dilute concentration \(C_2\) is accompanied by a decrease in the free energy , and thus will occur spontaneously. By the same token, the spontaneous “un-dilution” of a solution will not occur (we do not expect the tea to diffuse back into the tea bag!) However, un-dilution can be forced to occur if some means can be found to supply to the system an amount of energy (in the form of work) equal to \(\Delta G_{dilution} \).
An important practical example of this is the metabolic work performed by the kidneys in concentrating substances from the blood for excretion in the urine.
To find the Gibbs energy of a solute at some arbitrary concentration, we proceed in very much the same way as we did for a gas: we take the sum of the standard free energy plus any change in the free energy that would accompany a change in concentration from the standard state to the actual state of the solution. From Equation \(\ref{4-12}\) it is easy to derive an expression analogous to Equation \(\ref{4-10}\):
\[G = G^o + RT \ln C \label{4-13}\]
which gives the free energy of a solute at some arbitrary concentration \(C\) in terms of its value \(G^o\) in its standard state.
Although Equation \(\ref{4-13}\) has the same simple form as Equation \(\ref{4-10}\), its practical application is fraught with difficulties, the major one being that it does not usually give values of \(G\) that are consistent with experiment, especially for solutes that are ionic or are slightly soluble. This is because most solutions (especially those containing dissolved ions) are far from ideal ; intermolecular interactions between solute molecules and between solute and solvent bring back the enthalpy term that we left out in deriving Equation \(\ref{4-12}\). In addition, the structural organization of the solution becomes concentration dependent, so that the entropy depends on concentration in a more complicated way than is implied by the concentration analog of Equation \(\ref{4-12}\).
Chemical Reactions and Mixing
We characterize the tendency for a chemical reaction A → B to occur at constant temperature and pressure by the value of its standard Gibbs energy change Δ G °. If this quantity is negative, we know that the reaction will take place spontaneously. However, have you ever wondered why it is that substance A is not completely transformed into B if the latter is thermodynamically more stable? The answer is that if the reaction takes place in a single phase (gas or liquid), something else is going on: A and B are mixing together, and this process creates its own Gibbs energy change \(ΔG_{mixing}\). For a simple binary mixture of A and B (without any reaction), the changes in \(S\) and \(G\) can be represented by these simple plots:
We will not try to prove it here, but it turns out that no matter how much lower the Gibbs energy of the products compared to that of the reactants, the free energy of the system can always be reduced even more if some of the reactants remain in the solution to contribute a Δ G mixing term. This is the reason that a plot of G as a function of the composition of such a system has a minimum at some point short of complete conversion.
D iffusion refers to the transport of a substance across a concentration gradient. The direction is always toward the region of lower concentration. You should now see that from a thermodynamic standpoint, these processes are identical in that they both represent the spontaneous "escape" of molecules from a region of higher concentration (lower entropy, higher Gibbs energy) to a region of lower concentration.
Instead of complicating G° by trying to correct for all of these effects, chemists have chosen to retain its simple form by making a single small change in the form of \(\ref{4-13}\):
\[G = G^o + RT \ln a \label{4-14}\]
This equation is guaranteed to work, because a , the activity of the solute, is its thermodynamically effective concentration. The relation between the activity and the concentration is given by
\[a = \gamma c \label{4-15}\]
where \(\gamma\) is the activity coefficient . As the solution becomes more dilute, the activity coefficient approaches unity:
\[ \lim _{c \rightarrow 0} \gamma =1 \label{4.16}\]
The price we pay for this simplicity is that the relation between the concentration and the activity at higher concentrations can be quite complicated, and must be determined experimentally for every different solution.
The question of what standard state we choose for the solute (that is, at what concentration is G ° defined, and in what units is it expressed?) is one that you will wish you had never asked. We might be tempted to use a concentration of 1 molar, but a solution this concentrated would be subject to all kinds of intermolecular interaction effects, and would not make a very practical standard state. These effects could be eliminated by going to the opposite extreme of an “infinitely dilute” solution, but by Equation \(\ref{4-12}\) this would imply a free energy of minus infinity for the solute, which would be awkward. Chemists have therefore agreed to define the standard state of a solute as one in which the concentration is 1 molar, but all solute-solute interactions are magically switched off, so that \(\gamma\) is effectively unity. Since this is impossible, no solution corresponding to this standard state can actually exist, but this turns out to be only a small drawback, and seems to be the best compromise between convenience, utility, and reality.


29.17B: Erectile Dysfunction and the Blue Pill
Erectile dysfunction (ED) is the inability to develop or maintain an erection during sexual intercourse.
- Describe the causes of and treatments for erectile dysfunction
Key Points
- A penile erection is managed by a reflex erection (obtained by touching the penis ) and/or a psychogenic erection (achieved by erotic/emotional stimuli).
- There are many causes of ED, including neurogenic disorders, Parkinson’s disease, aging, drugs, and psychological factors.
- Treatment for ED includes drugs such as Viagra (Sildenafil), Cialis (Tadalifil), exercise, and vacuum therapy.
- Psychological impotence is where erection or penetration fails due to thoughts or feelings (psychological reasons) rather than physical impossibility; this is somewhat less frequent but can often be helped.
- As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply, or psychological problems.
Key Terms
- psychogenic erection : Erection achieved by erotic or emotional stimuli
- chronic periodontitis : Chronic periodontitis is a common disease of the oral cavity consisting of chronic inflammation of the periodontal tissues, often caused by accumulation of profuse amounts of dental plaque.

  The process is often initiated as a result of sexual arousal, when signals are transmitted from the brain to nerves in the penis. Erectile dysfunction is indicated when an erection is difficult to produce. There are various circulatory causes, including alteration of the voltage-gated potassium channel, as in arsenic poisoning from drinking water. The most significant organic causes are cardiovascular disease and diabetes, neurological problems (for example, trauma from prostatectomy surgery), hormonal insufficiencies (hypogonadism), and drug side effects. Psychological impotence is where erection or penetration fails due to thoughts or feelings (psychological reasons) rather than physical impossibility; this is somewhat less frequent but can often be helped. Notably, there is a strong response to placebo treatment in psychological impotence.

Penile erection is managed by two different mechanisms. The first one is the reflex erection, which is achieved by directly touching the penile shaft. The second is the psychogenic erection, which is achieved by erotic or emotional stimuli. The former uses the peripheral nerves and the lower parts of the spinal cord, whereas the latter uses the limbic system of the brain. In both circumstances, an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system leads to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply, or psychological problems. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease, but can also be caused by prolonged exposure to bright light.
There are several possible causes of ED, which include the following: drugs, neurogenic disorders (generalized anxiety disorder, personality disorders or traits), psychological problems, negative feelings, aging (making it four times higher in men in their 60s than in men in their 40s), kidney failure, diseases such as diabetes and multiple sclerosis (MS), and lifestyle.
Iatrogenic (Medical) Causes
Surgical intervention for a number of different conditions may remove anatomical structures necessary for erection, damage nerves, or impair blood supply. Complete removal of the prostate gland or external beam radiotherapy of the gland are common causes of impotence; both are treatments for prostate cancer. A study in 2002 found that ED can also be associated with bicycling. The number of hours on a bike and/or the pressure on the penis from the saddle of an upright bicycle is directly related to erectile dysfunction A recent study suggests an epidemiological association between chronic periodontitis (periodontal inflammation) and erectile dysfunction, similar to the association between periodontitis and coronary heart diseases, as well as cerebrovascular diseases. In all the three conditions (erectile dysfunction, coronary heart disease, and cerebrovascular diseases), despite the epidemiological association with periodontitis, no causative connection has yet been proven.
Treatments
Besides treating the major underlying causes such as potassium deficiency or arsenic contamination in drinking water, the primary treatment for erectile dysfunction consists of a trial of PDE5 inhibitor drugs (the first of which is sildenafil or Viagra).  Additional treatments for ED are varied and include a purpose-designed external vacuum pump used to attain erection, with a separate compression ring fitted to the penis to maintain it. These pumps should be distinguished from other penis pumps (supplied without compression rings) which, rather than being used for temporary treatment of impotence, are claimed to increase penis length if used frequently, or vibrate as an aid to masturbation. More drastically, inflatable or rigid penile implants may be fitted surgically. Medications carry risk of priapism.
The cyclic nucleotide phosphodiesterases constitutes a group of enzymes that catalyze the hydrolysis of the cyclic nucleotides cyclic AMP and cyclic GMP. They exist in different molecular forms and are unevenly distributed throughout the body. One of the forms of phosphodiesterase is termed PDE5. The prescription PDE5 inhibitors sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP to degrade.


1.2: Lab Safety Assignment
Lab Safety Assignment:
Name: ______________
1. Sketch the lab space and note the locations of the following:
fire extinguisher, slide disposal, incubator, fume hoods, biohazard trash, eye wash, shower
2. What could happen if you shake a liquid culture?
3. What is wrong with laying an empty tube on the bench top?
4. What could happen if you pick up a tube by the cap?
5. If you spill a culture, what should you do FIRST?
6. When no longer needed, where do you place an empty test tube rack? Describe where you put it. Please do not use a letter for the location.
7. What is the most dangerous item in the microbiology teaching lab? How should it be treated?
References:
OpenStax CNX. (2018, Mar 19). OpenStax Microbiology, Microbiology . Retrieved from<EMAIL_ADDRESS>U.S. Department of Health and Human Services. (2009). Biosafety in Microbioloical and Biomedical Laboratories, 5th Ed. Centers of Disease Control and Prevention, National Institutes of Health, Public Health Service. HHS Publication No. (CDC) 21-1112. Retrieved from https:// www.cdc.gov/biosafety/publications/bmbl5/index.htm
World Health Organization. (2004). Laboratory Biosafety Manual. (3). Geneva, Switzerland. Retrieved January 14, 2019, from https://www.who.int/csr/resources/pu...Biosafety7.pdf