3.1: The Behavior of Light
Learning Objectives
By the end of this section, you will be able to:
- Explain the evidence for Maxwell’s electromagnetic model of light
- Describe the relationship between wavelength, frequency, and speed of light
- Discuss the particle model of light and the definition of photon
- Explain how and why the amount of light we see from an object depends upon its distance
Coded into the light and other kinds of radiation that reach us from objects in the universe is a wide range of information about what those objects are like and how they work. If we can decipher this code and read the messages it contains, we can learn an enormous amount about the cosmos without ever having to leave Earth or its immediate environment.
The visible light and other radiation we receive from the stars and planets is generated by processes at the atomic level—by changes in the way the parts of an atom interact and move. Thus, to appreciate how light is generated, we must explore how atoms work. There is a bit of irony in the fact that in order to understand some of the largest structures in the universe, we must become acquainted with some of the smallest.
Notice that we have twice used the phrase “light and other radiation.” One of the key ideas explored in this chapter is that visible light is not unique; it is merely the most familiar example of a much larger family of radiation that can carry information to us.
The word “radiation” will be used frequently in this book, so it is important to understand what it means. In everyday language, “radiation” is often used to describe certain kinds of energetic subatomic particles released by radioactive materials in our environment. (An example is the kind of radiation used to treat some cancers.) But this is not what we mean when we use the word “radiation” in an astronomy text. Radiation , as used in this book, is a general term for waves (including light waves) that radiate outward from a source.
As we saw in Orbits and Gravity, Newton’s theory of gravity accounts for the motions of planets as well as objects on Earth. Application of this theory to a variety of problems dominated the work of scientists for nearly two centuries. In the nineteenth century, many physicists turned to the study of electricity and magnetism, which are intimately connected with the production of light.
The scientist who played a role in this field comparable to Newton’s role in the study of gravity was physicist James Clerk Maxwell, born and educated in Scotland (Figure \(\PageIndex{1}\)). Inspired by a number of ingenious experiments that showed an intimate relationship between electricity and magnetism, Maxwell developed a theory that describes both electricity and magnetism with only a small number of elegant equations. It is this theory that gives us important insights into the nature and behavior of light.
Maxwell’s Theory of Electromagnetism
We will look at the structure of the atom in more detail later, but we begin by noting that the typical atom consists of several types of particles, a number of which have not only mass but an additional property called electric charge. In the nucleus (central part) of every atom are protons , which are positively charged; outside the nucleus are electrons, which have a negative charge.
Maxwell’s theory deals with these electric charges and their effects, especially when they are moving. In the vicinity of an electron charge, another charge feels a force of attraction or repulsion: opposite charges attract; like charges repel. When charges are not in motion, we observe only this electric attraction or repulsion. If charges are in motion, however (as they are inside every atom and in a wire carrying a current), then we measure another force called magnetism .
Magnetism was well known for much of recorded human history, but its cause was not understood until the nineteenth century. Experiments with electric charges demonstrated that magnetism was the result of moving charged particles. Sometimes, the motion is clear, as in the coils of heavy wire that make an industrial electromagnet. Other times, it is more subtle, as in the kind of magnet you buy in a hardware store, in which many of the electrons inside the atoms are spinning in roughly the same direction; it is the alignment of their motion that causes the material to become magnetic.
Physicists use the word field to describe the action of forces that one object exerts on other distant objects. For example, we say the Sun produces a gravitational field that controls Earth’s orbit, even though the Sun and Earth do not come directly into contact. Using this terminology, we can say that stationary electric charges produce electric fields , and moving electric charges also produce magnetic fields .
Actually, the relationship between electric and magnetic phenomena is even more profound. Experiments showed that changing magnetic fields could produce electric currents (and thus changing electric fields), and changing electric currents could in turn produce changing magnetic fields. So once begun, electric and magnetic field changes could continue to trigger each other.
Maxwell analyzed what would happen if electric charges were oscillating (moving constantly back and forth) and found that the resulting pattern of electric and magnetic fields would spread out and travel rapidly through space. Something similar happens when a raindrop strikes the surface of water or a frog jumps into a pond. The disturbance moves outward and creates a pattern we call a wave in the water (Figure \(\PageIndex{2}\)). You might, at first, think that there must be very few situations in nature where electric charges oscillate, but this is not at all the case. As we shall see, atoms and molecules (which consist of charged particles) oscillate back and forth all the time. The resulting electromagnetic disturbances are among the most common phenomena in the universe.
Maxwell was able to calculate the speed at which an electromagnetic disturbance moves through space; he found that it is equal to the speed of light, which had been measured experimentally. On that basis, he speculated that light was one form of a family of possible electromagnetic disturbances called electromagnetic radiation , a conclusion that was again confirmed in laboratory experiments. When light (reflected from the pages of an astronomy textbook, for example) enters a human eye, its changing electric and magnetic fields stimulate nerve endings, which then transmit the information contained in these changing fields to the brain. The science of astronomy is primarily about analyzing radiation from distant objects to understand what they are and how they work.
The Wave-Like Characteristics of Light
The changing electric and magnetic fields in light are similar to the waves that can be set up in a quiet pool of water. In both cases, the disturbance travels rapidly outward from the point of origin and can use its energy to disturb other things farther away. (For example, in water, the expanding ripples moving away from our frog could disturb the peace of a dragonfly resting on a leaf in the same pool.) In the case of electromagnetic waves, the radiation generated by a transmitting antenna full of charged particles and moving electrons at your local radio station can, sometime later, disturb a group of electrons in your car radio antenna and bring you the news and weather while you are driving to class or work in the morning.
The waves generated by charged particles differ from water waves in some profound ways, however. Water waves require water to travel in. The sound waves we hear, to give another example, are pressure disturbances that require air to travel though. But electromagnetic waves do not require water or air: the fields generate each other and so can move through a vacuum (such as outer space). This was such a disturbing idea to nineteenth-century scientists that they actually made up a substance to fill all of space—one for which there was not a single shred of evidence—just so light waves could have something to travel through: they called it the aether . Today, we know that there is no aether and that electromagnetic waves have no trouble at all moving through empty space (as all the starlight visible on a clear night must surely be doing).
The other difference is that all electromagnetic waves move at the same speed in empty space (the speed of light—approximately 300,000 kilometers per second, or 300,000,000 meters per second, which can also be written as \(3 × 10^8\) m/s, which turns out to be the fastest possible speed in the universe. No matter where electromagnetic waves are generated from and no matter what other properties they have, when they are moving (and not interacting with matter), they move at the speed of light. Yet you know from everyday experience that there are different kinds of light. For example, we perceive that light waves differ from one another in a property we call color. Let’s see how we can denote the differences among the whole broad family of electromagnetic waves.
The nice thing about a wave is that it is a repeating phenomenon. Whether it is the up-and-down motion of a water wave or the changing electric and magnetic fields in a wave of light, the pattern of disturbance repeats in a cyclical way. Thus, any wave motion can be characterized by a series of crests and troughs (Figure \(\PageIndex{3}\)). Moving from one crest through a trough to the next crest completes one cycle. The horizontal length covered by one cycle is called the wavelength . Ocean waves provide an analogy: the wavelength is the distance that separates successive wave crests.
For visible light, our eyes perceive different wavelengths as different colors: red, for example, is the longest visible wavelength, and violet is the shortest. The main colors of visible light from longest to shortest wavelength can be remembered using the mnemonic ROY G BIV—for R ed, O range, Y ellow, G reen, B lue, I ndigo, and V iolet. Other invisible forms of electromagnetic radiation have different wavelengths, as we will see in the next section.
We can also characterize different waves by their frequency , the number of wave cycles that pass by per second. If you count 10 crests moving by each second, for example, then the frequency is 10 cycles per second (cps). In honor of Heinrich Hertz, the physicist who—inspired by Maxwell’s work—discovered radio waves, a cps is also called a hertz (Hz). Take a look at your radio, for example, and you will see the channel assigned to each radio station is characterized by its frequency, usually in units of KHz (kilohertz, or thousands of hertz) or MHz (megahertz, or millions of hertz).
Wavelength (\(\lambda\)) and frequency (\(f\)) are related because all electromagnetic waves travel at the same speed. To see how this works, imagine a parade in which everyone is forced by prevailing traffic conditions to move at exactly the same speed. You stand on a corner and watch the waves of marchers come by. First you see row after row of miniature ponies. Because they are not very large and, therefore, have a shorter wavelength, a good number of the ponies can move past you each minute; we can say they have a high frequency. Next, however, come several rows of circus elephants. The elephants are large and marching at the same speed as the ponies, so far fewer of them can march past you per minute: Because they have a wider spacing (longer wavelength), they represent a lower frequency.
The formula for this relationship can be expressed as follows: for any wave motion, the speed at which a wave moves equals the frequency times the wavelength. Waves with longer wavelengths have lower frequencies. Mathematically, we can express this as
\[c=λf \nonumber\]
where the Greek letter for “l”—lambda, \(\lambda\)—is used to denote wavelength and c is the scientific symbol for the speed of light. Solving for the wavelength, this is expressed as:
\[λ=cf. \nonumber\]
Example \(\PageIndex{1}\): Deriving and Using the Wave Equation
The equation for the relationship between the speed and other characteristics of a wave can be derived from our basic understanding of motion. The average speed of anything that is moving is:
\[\text{average speed}= \text{distance} \times \text{time} \nonumber\]
(So, for example, a car on the highway traveling at a speed of 100 km/h covers 100 km during the time of 1 h.) For an electromagnetic wave to travel the distance of one of its wavelengths, \(\lambda\), at the speed of light, \(c\), we have \(c = \lambda /t\). The frequency of a wave is the number of cycles per second. If a wave has a frequency of a million cycles per second, then the time for each cycle to go by is a millionth of a second. So, in general, \(t = 1/f\). Substituting into our wave equation, we get \(c = \lambda \times f\). Now let’s use this to calculate an example. What is the wavelength of visible light that has a frequency of \(5.66 × 10^{14}\) Hz?
- Answer
-
Solving the wave equation for wavelength, we find:
\[λ=cf \nonumber\]
Substituting our values gives:
\[λ=3.00×10^8\, \text{ m/s} = 5.66×10^{14} \text{ Hz}=5.30×10^{–7}\, \text{ m} \nonumber\]
This answer can also be written as 530 nm, which is in the yellow-green part of the visible spectrum (nm stands for nanometers, where the term “nano” means “billionths”).
Exercise \(\PageIndex{1}\)
“Tidal waves,” or tsunamis, are waves caused by earthquakes that travel rapidly through the ocean. If a tsunami travels at the speed of 600 km/h and approaches a shore at a rate of one wave crest every 15 min (4 waves/h), what would be the distance between those wave crests at sea?
- Answer
-
\[ \lambda = \frac{600 \text{ km/h}}{4 \text{ waves/h}} =150 \text{ km} \nonumber\]
Light as a Photon
The electromagnetic wave model of light (as formulated by Maxwell) was one of the great triumphs of nineteenth-century science. In 1887, when Heinrich Hertz actually made invisible electromagnetic waves (what today are called radio waves) on one side of a room and detected them on the other side, it ushered in a new era that led to the modern age of telecommunications. His experiment ultimately led to the technologies of television, cell phones, and today’s wireless networks around the globe.
However, by the beginning of the twentieth century, more sophisticated experiments had revealed that light behaves in certain ways that cannot be explained by the wave model. Reluctantly, physicists had to accept that sometimes light behaves more like a “particle”—or at least a self-contained packet of energy—than a wave. We call such a packet of electromagnetic energy a photon .
The fact that light behaves like a wave in certain experiments and like a particle in others was a very surprising and unlikely idea. After all, our common sense says that waves and particles are opposite concepts. On one hand, a wave is a repeating disturbance that, by its very nature, is not in only one place, but spreads out. A particle, on the other hand, is something that can be in only one place at any given time. Strange as it sounds, though, countless experiments now confirm that electromagnetic radiation can sometimes behave like a wave and at other times like a particle.
Then, again, perhaps we shouldn’t be surprised that something that always travels at the “speed limit” of the universe and doesn’t need a medium to travel through might not obey our everyday common sense ideas. The confusion that this wave-particle duality of light caused in physics was eventually resolved by the introduction of a more complicated theory of waves and particles, now called quantum mechanics. (This is one of the most interesting fields of modern science, but it is mostly beyond the scope of our book. If you are interested in it, see some of the suggested resources at the end of this chapter.)
In any case, you should now be prepared when scientists (or the authors of this book) sometimes discuss electromagnetic radiation as if it consisted of waves and at other times refer to it as a stream of photons. A photon (being a packet of energy) carries a specific amount of energy. We can use the idea of energy to connect the photon and wave models. How much energy a photon has depends on its frequency when you think about it as a wave. A low-energy radio wave has a low frequency as a wave, while a high-energy X-ray at your dentist’s office is a high-frequency wave. Among the colors of visible light, violet-light photons have the highest energy and red-light photons have the lowest.
Test whether the connection between photons and waves is clear to you. In the above example, which photon would have the longer wavelength as a wave: the radio wave or the X-ray? If you answered the radio wave, you are correct. Radio waves have a lower frequency, so the wave cycles are longer (they are elephants, not miniature ponies).
Propagation of Light
Let’s think for a moment about how light from a lightbulb moves through space. As waves expand, they travel away from the bulb, not just toward your eyes but in all directions. They must therefore cover an ever-widening space. Yet the total amount of light available can’t change once the light has left the bulb. This means that, as the same expanding shell of light covers a larger and larger area, there must be less and less of it in any given place. Light (and all other electromagnetic radiation) gets weaker and weaker as it gets farther from its source.
The increase in the area that the light must cover is proportional to the square of the distance that the light has traveled (Figure \(\PageIndex{4}\)). If we stand twice as far from the source, our eyes will intercept two-squared (2 × 2), or four times less light. If we stand 10 times farther from the source, we get 10-squared, or 100 times less light. You can see how this weakening means trouble for sources of light at astronomical distances. One of the nearest stars, Alpha Centauri A, emits about the same total energy as the Sun. But it is about 270,000 times farther away, and so it appears about 73 billion times fainter. No wonder the stars, which close-up would look more or less like the Sun, look like faint pinpoints of light from far away.
This idea—that the apparent brightness of a source (how bright it looks to us) gets weaker with distance in the way we have described—is known as the inverse square law for light propagation. In this respect, the propagation of light is similar to the effects of gravity. Remember that the force of gravity between two attracting masses is also inversely proportional to the square of their separation.
Example \(\PageIndex{2}\): The inverse Square Law for Light
The intensity of a 120-W lightbulb observed from a distance 2 m away is 2.4 W/m 2 . What would be the intensity if this distance was doubled?
- Answer
-
If we move twice as far away, then the answer will change according to the inverse square of the distance, so the new intensity will be \((1/2)^2 = 1/4\) of the original intensity, or 0.6 W/m 2 .
Exercise \(\PageIndex{2}\)
How many times brighter or fainter would a star appear if it were moved to:
- twice its present distance?
- ten times its present distance?
- half its present distance?
- Answer
-
\[\text{a. } \left( \frac{1}{2} \right)^2= \frac{1}{4}; ~ \text{b. } \left( \frac{1}{10} \right)^2= \frac{1}{100} \left( \frac{1}{10} \right)^2= \frac{1}{100}; ~ \text{c. } \left( \frac{1}{1/2} \right)^2= 4 \nonumber\]
Key Concepts and Summary
James Clerk Maxwell showed that whenever charged particles change their motion, as they do in every atom and molecule, they give off waves of energy. Light is one form of this electromagnetic radiation. The wavelength of light determines the color of visible radiation. Wavelength (\(\lambda\)) is related to frequency (\(f\)) and the speed of light (\(c\)) by the equation \(c = \lambda f\). Electromagnetic radiation sometimes behaves like waves, but at other times, it behaves as if it were a particle—a little packet of energy, called a photon. The apparent brightness of a source of electromagnetic energy decreases with increasing distance from that source in proportion to the square of the distance—a relationship known as the inverse square law.
Glossary
- electromagnetic radiation
- radiation consisting of waves propagated through regularly varying electric and magnetic fields and traveling at the speed of light
- frequency
- the number of waves that cross a given point per unit time (in radiation)
- inverse square law
- (for light) the amount of energy (light) flowing through a given area in a given time decreases in proportion to the square of the distance from the source of energy or light
- photon
- a discrete unit (or “packet”) of electromagnetic energy
- wavelength
- the distance from crest to crest or trough to trough in a wave
Contributors and Attributions
-
Andrew Fraknoi (Foothill College), David Morrison (NASA Ames Research Center), Sidney C. Wolff (National Optical Astronomy Observatory) with many contributing authors. Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at https://openstax.org/details/books/astronomy ).


12.3: PDF
A PDF version of the primary textbook is available as a print only alternative. The pdf does not include interactive content such as simulations, videos, and quizzes and is not vetted for accessibility. For these reasons, we do not recommend using the textbook in the pdf form . The offline version should be used as a print backup rather than as the primary textbook.
You can download the PDF using the following link:
- PDF (42.3 MB)
To share these files with your students, copy and paste the text and download link above into a page or announcement in your learning management system (Blackboard, Canvas, etc.).
Contributors and Attributions
- PDF. Provided by : Lumen Learning. License : CC BY: Attribution
- Kindle Oasis. Authored by : Richard Slater. Located at : https://thenounproject.com/term/kindle-oasis/611350/ . License : CC BY: Attribution


16.3: Membrane Proteins
Clearly, membrane proteins themselves have domains that keep membranes in or attached to the membrane, provide catalytic surfaces and allow interactions inside, across and outside of cells and organelles. Membranes anchor proteins in several ways. As noted, membrane proteins, like phospholipids, are amphipathic, with hydrophobic domains that non-covalently interact strongly with the fatty acid interior of membranes. Some integral membrane proteins span the entire membrane, with hydrophilic domains facing the cytosol or cell exterior. Peripheral proteins bind to a membrane surface through non-covalent interactions. Examples of integral and peripheral membrane proteins, glycoproteins and lipoproteins are illustrated below.


14.4: Putting It All Together
Patient Scenario
Mr. Curtis is a 47-year-old patient admitted to the hospital with increased weakness, fatigue, and dehydration. His skin appears dry, and tenting occurs when skin turgor is evaluated. He is currently undergoing chemotherapy treatment for multiple myeloma and has experienced weight loss of 10 pounds within the last two weeks. He describes that “nothing tastes good,” and he feels as if there is “metal taste in his mouth.” When he does eat small meals, he reports that he is often nauseous. The patient’s serum protein level is 3.1 g/dL.
Applying the Nursing Process
Assessment: The nurse identifies that the patient is experiencing signs of imbalanced nutrition with the signs of increased weakness, fatigue, and signs of dehydration such as skin tenting and dryness. The patient has demonstrated a significant weight loss over the past two weeks and reports “nothing tastes good” and “a metal taste in the mouth.” The patient also reports nausea after eating. His serum protein level reflects signs of malnutrition.
Based on the assessment information that has been gathered, the following nursing care plan is created for Mr. Curtis:
Nursing Diagnosis: Imbalanced Nutrition: Less Than Body Requirements r/t insufficient dietary intake as manifested by weight loss of 10 pounds in the last two weeks, skin tenting and dryness, reports of “nothing tastes good,” and serum protein of 3.1 g/dL.
Overall Goal: The patient will demonstrate improvement in nutrition intake.
SMART Expected Outcome: Mr. Curtis will eat 50% of offered meals and demonstrate dietary tolerance within 24 hours.
Planning and Implementing Nursing Interventions:
The nurse will validate the patient’s feelings regarding his current symptoms and provide emotional support. The nurse will determine the time of day when the patient’s appetite is highest and offer the highest calorie meal at that time. The nurse will offer high-calorie protein shakes to the patient at frequent intervals. The nurse will assess the patient’s food preferences and ensure that small frequent meals are offered that incorporate those preferences. The nurse will also encourage the use of plastic utensils and encourage the patient to eat mints or chew gum to minimize the metallic taste in the mouth.
Sample Documentation:
Mr. Curtis demonstrates signs of imbalanced nutrition: less than body requirements. He reported a significant weight loss of 10 pounds over the past two weeks associated with chemotherapy. He reports feeling nauseous following small meals. He also reports “nothing tastes good” and having “a metal taste in the mouth.” He demonstrates signs of weakness, fatigue, and dehydration. Interventions have been implemented to increase the patient’s nutritional intake.
Evaluation:
Twenty-four hours later, the nurse evaluates Mr. Curtis and finds he is able to consume 50% of breakfast with his preferred dietary items. Planned interventions will continue and the nurse plan to reevaluate his progress the following day.


9.3: Direct Labor Budget
Learning Outcomes
- Create direct labor budget
Ok, so Hupana Running Company is getting all set for the new year. We have our sales budget, and know how many pairs of shoes we plan to sell. From that information we created our production budget, so we know how many pairs we need to produce each quarter, and how many we want in finished goods inventory at the end of each quarter. We also then figured out how much raw materials we need to bring in each quarter to keep our production facilities humming along.
So now we need to determine our direct labor needs. Direct labor includes all of the employees who are required to actually manufacture the shoes. These are the people working on the production floor. This information is important, so they don’t run into a labor shortage and can plan for potential adjustments in their labor needs. Another use for this budget is to schedule plant shutdowns for cleaning and maintenance. Without the completion of the other budgets we have done, we couldn’t fill in all the blanks in the direct labor budget!
So what new information might we need to complete this budget?  Then we need to know our cost per hour for our direct labor. This cost per hour includes wages, payroll taxes and fringe benefits for each of our production employees. Don’t forget those things, as they can make a huge impact on the cost of an employee per hour!
So let’s figure out our labor information.
One pair of shoes takes .5 labor hours @ $20/ hour average
We already know how many pairs we need to make each quarter, so let’s get started on our direct labor budget!
| Hupana Running Company Direct Labor Budget | |||||
|---|---|---|---|---|---|
| Quarter | Q1 | Q2 | Q3 | Q4 | Total |
| Required production in pairs | 450 | 500 | 500 | 600 | 2050 |
| Direct labor hours-pair | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 |
| Total direct labor hours needed | 225 | 250 | 250 | 300 | 1025 |
| Direct labor cost per hour | $20 | $20 | $20 | $20 | $20 |
| Total direct labor cost | $4,500 | $5,000 | $5,000 | $6,000 | $20,500 |
So we used the required production in pairs from our previous budgets. We noted above the time needed and the cost per hour for our manufacturing employees. With that information in hand, we can calculate our direct labor costs. We now know, how much we will spend each quarter on labor, and can staff properly!
Is all this budgeting fun starting to make sense? Let’s go over what we know so far.
We know our sales, production schedule, raw materials cost, direct labor cost and what we will have in finished goods and raw materials inventory at the end of the year! Are we having fun yet?
Practice Questions
On to manufacturing overhead!


8.15: Synthesis in Practice
- Demonstrate strategies for synthesis
Professors frequently expect you to interpret, make inferences, and otherwise synthesize—bring ideas together to make something new or find a new way of looking at something old. (It might help to think of synthesis as the opposite of analysis. To synthesize is to combine; to analyze is to break down.)
Getting Better at Synthesis
To get an A on essays and papers in many courses, such as literature and history, what you write in reaction to the work of others should use synthesis to create new meaning or to show a deeper understanding of what you learned.
To do so, it helps to look for connections and patterns. One way to synthesize when writing an argument essay, paper, or other project is to look for themes among your sources. So try categorizing ideas by topic rather than by source—making associations across and between sources.
Synthesis can seem difficult, particularly if you are used to analyzing others’ points but not used to making your own. Like most things, however, it gets easier with practice. So don’t be hard on yourself if it seems difficult at first.
Imagine that you have to write an argument essay about Woody Allen’s 2011 movie Midnight in Paris . Your topic is “nostalgia,” and the movie is the only source you can use.
In the movie, a successful young screenwriter named Gil is visiting Paris with his girlfriend and her parents, who are more politically conservative than he is. Inexplicably, every midnight he time-travels back to the 1920’s Paris, a time period he’s always found fascinating, especially because of the writers and painters—Hemingway, Fitzgerald, Picasso—with whom he’s now on a first-name basis. Gil is enchanted and always wants to stay in this fantastical past. But every morning, he’s back in the real present—feeling out of sync with his girlfriend and her parents.
For your essay, you’ve tried to come up with a narrower topic, but so far nothing seems right. Suddenly, you start paying more attention to the girlfriend’s parents’ dialogue about politics, which amount to such phrases as “we have to go back to…,” “it was a better time,” “Americans used to be able to…” and “the way it used to be.”
And then it clicks with you that the girlfriend’s parents are like Gil—longing for a different time, whether real or imagined. That kind of idea generation, where you find the connection and theme across related elements of the movie, is synthesis.
You decide to write your essay to answer the research question: How is the motivation of Gil’s girlfriend’s parents similar to Gil’s? Your thesis becomes “Despite seeming to be very different, Gil and his girlfriend’s parents are similarly motivated, and Woody Allen’s Midnight in Paris’s message about nostalgia can be applied to all of them.”
Of course, you’ll have to try to convince your readers that your thesis is valid, and you may or not be successful,—but that’s true with all theses. And your professor will be glad to see the synthesis.
Synthesizing From Multiple Sources
Below are some questions that highlight ways in which the act of synthesizing brings together ideas and generates new knowledge.
How do the sources speak to your specific argument or research question?
Your argument or research question is the main unifying element in your project. Keep this in the forefront of your mind when you write about your sources. Explain how, specifically, each source supports your central claim/s or suggests possible answers to your question. For example: Does the source provide essential background information or a definitional foundation for your argument or inquiry? Does it present numerical data that supports one of your points or helps you answer a question you have posed? Does it present a theory that might be applied to some aspect of your project? Does it present a recognized expert’s insights on your topic?
How do the sources speak to each other?
Sometimes you will find explicit dialogue between sources (for example, Source A refutes Source B by name), and sometimes you will need to bring your sources into dialogue (for example, Source A does not mention Source B, but you observe that the two are advancing similar or dissimilar arguments). Attending to interrelationships among sources is at the heart of the task of synthesis.
Begin by asking: What are the points of agreement? Where are there disagreements?
But be aware that you are unlikely to find your sources in pure positions of “for” vs. “against.” You are more likely to find agreement in some areas and disagreement in other areas. You may also find agreement but for different reasons—such as different underlying values and priorities, or different methods of inquiry.
Where are there, or aren’t there, information gaps?
Where is the available information unreliable (for example, it might be difficult to trace back to primary sources), or limited, (for example, based on just a few case studies, or on just one geographical area), or difficult for non-specialists to access (for example, written in specialist language, or tucked away in a physical archive)?
Does your inquiry contain sub-questions that may not at present be answerable, or that may not be answerable without additional primary research—for example, laboratory studies, direct observation, interviews with witnesses or participants, etc.?
Or, alternatively, is there a great deal of reliable, accessible information that addresses your question or speaks to your argument or inquiry?
In considering these questions, you are engaged in synthesis: you are conducting an overview assessment of the field of available information and in this way generating composite knowledge.
Remember, synthesis is about pulling together information from a range of sources in order to answer a question or construct an argument. It is something you will be called upon to do in a wide variety of academic, professional, and personal contexts. Being able to dive into an ocean of information and surface with meaningful conclusions is an essential skill.
One place synthesis is usually required is in literature reviews for honors’ theses, master’s theses, and Ph.D. dissertations. In all those cases, literature reviews are intended to contribute more than annotated bibliographies do and to be arguments for the research conducted for the theses or dissertations. If you are writing an honors thesis, master’s thesis, or Ph.D. dissertation, you will find more help with Susan Imel’s Writing a Literature Review .
Showing Synthesis
Some ways to demonstrate synthesis in your writing is to compare and contrast multiple sources. Below are some examples of sentence structures that demonstrate synthesis:
Synthesis that indicates agreement/support:
- Source A asserts that… Source B agrees when he or she states…
- According to both A & B…
- The combined conclusions of sources B & C seem to indicate that…
- The evidence shows that…
- Source B is correct that…
- Source C makes a convincing case when she argues…
- I agree with Source A’s conclusion that…
Synthesis that indicates disagreement/conflict:
- Source A asserts that…Yet Source B offers a different perspective by…
- Source C & B would likely disagree regarding…
- My view, however, contrary to what Source A has argued, is…
- I argue that X & Y are the best solution, though Source B offers a different option.
- In contrast, I would like to offer some objections to the opinions expressed by source C…
- While source A makes an intriguing argument, I would disagree…
What the above examples indicate is that synthesis is the careful weaving in of outside opinions in order to show your reader the many ideas and arguments on your topic and further assert your own. Notice, too, that the above examples are also signal phrases : language that introduces outside source material to be either quoted or paraphrased, i.e., “contrary to what Source A has argued, source B maintains ___________ .”
Here’s a technique to quickly assess whether there is enough of your original thought in your essay or paper, as opposed to information from your sources: Highlight what you have included as quotes, paraphrases, and summaries from your sources. Next, highlight in another color what you have written yourself. Then take a look at the pages and decide whether there is enough of your own thinking in them.
For the mocked-up pages below, assume that the yellow-highlighted lines were written by the writer and the pink-highlighted lines are quotes, paraphrases, and summaries she pulled from her sources.
Which page most demonstrates the writer’s own ideas?
Source: Joy McGregor. “A Visual Approach: Teaching Synthesis,” School Library Monthly, Volume XXVII, Number 8/May-June 2011.
[reveal-answer q=”149882″]Show Answer[/reveal-answer]
[hidden-answer a=”149882″]
Answer: The Middle Sample.
The yellow-highlighted sections in the middle sample shows more contributions from the author than from quotes, paraphrases, and summaries of other sources.
[/hidden-answer]
signal phrase : a phrase that introduces outside sources material that will be quoted or paraphrased
Contributors and Attributions
- Synthesizing Your Research Findings. Authored by : Christine Photinos. Project : Composing Ourselves and Our World . License : CC BY: Attribution
- Synthesizing. Authored by : Melanie Gagich. Located at : https://pressbooks.ulib.csuohio.edu/introduction-to-writing/chapter/8-1-synthesizing/ . Project : Introduction to Writing in College. License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike
- Synthesis of Your Own Ideas . Provided by : Ohio State University Libraries . Located at : https://ohiostate.pressbooks.pub/choosingsources/chapter/synthesis/ . Project : Choosing & Using Sources: A Guide to Academic Research by Teaching & Learning. License : CC BY: Attribution
- Image of a stack of books. Authored by : Ulrike Leone. Provided by : Pixabay. Located at : pixabay.com/photos/books-book-stack-isolated-1931195/. License : Other . License Terms : pixabay.com/service/terms/#license


17.3C: Energy Requirements
Cardiac cells contain numerous mitochondria, which enable continuous aerobic respiration and production of adenosine triphosphate (ATP) for cardiac function.
- Describe the energy requirements of cardiac muscle tissue
Key Points
- The myocardium requires significant energy to contract continually over the human lifetime.
- These energy needs are met through mitochondria, myoglobins, and rich blood supply from the coronary arteries.
- The mitochondria generate ATP for the contraction of cardiomyocytes.
- Myoglobins are oxygen-storing and oxygen-transferring pigments in cardiomyocytes.
- Aerobic metabolism occurs when oxygen is present, while anaerobic respiration occurs when tissue is deprived of oxygen. Aerobic metabolism accounts for nearly all of the metabolic function in the heart, but anerobic metabolism may contribute as well.
- Glucose reservoirs and lactate recycling allow the heart to function even during malnutrition.
Key Terms
- lactate : A molecule produced by anaerobic respiration that can be used to produce ATP without oxygen, albeit at lower levels.
- myoglobin : A small globular protein containing a heme group that carries oxygen to muscles from the blood and stores reserve oxygen.
The heart muscle pumps continuously throughout life and is adapted to be highly resistant to fatigue. Cardiomyocytes contain large numbers of mitochondria, the powerhouse of the cell, enabling continuous aerobic respiration and ATP production required for mechanical muscle contraction. Cardiac muscle tissue has among the highest energy requirements in the human body (along with the brain) and has a high level of mitochondria and a constant, rich, blood supply to support its metabolic activity.
Aerobic Metabolism
Aerobic metabolism is a necessary component to support the metabolic function of the heart. Oxygen is necessary, and if even a small part of the heart is oxygen-deprived for too long, a myocardial infarction (heart attack) will occur. Coronary circulation branches from the aorta soon after it leaves the heart, and supplies the heart with the nutrients and oxygen needed to sustain aerobic metabolism. Cardiac muscle cells contain larger amounts of mitochondria than other cells in the body, enabling higher ATP production.
The heart derives energy from aerobic metabolism via many different types of nutrients. Sixty percent of the energy to power the heart is derived from fat (free fatty acids and triglycerides), 35% from carbohydrates, and 5% from amino acids and ketone bodies from proteins. These proportions vary widely with available dietary nutrients. Malnutrition will not result in the death of heart tissue in the way that oxygen deficiency will, because the body has glucose reserves that sustain the vital organs of the body and the ability to recycle and use lactate aerobically.
Myoglobin : The heme component of myoglobin, shown in orange, binds oxygen. Myoglobin provides a back-up store of oxygen to muscle cells.
Heart muscle also contains large amounts of a pigment called myoglobin. Myoglobin is similar to hemoglobin in that it contains a heme group (an oxygen binding site). Myoglobin transfers oxygen from the blood to the muscle cell and stores reserve oxygen for aerobic metabolic function in the muscle cell.
Anaerobic Metabolism
While aerobic respiration supports normal heart activity, anaerobic respiration may provide additional energy during brief periods of oxygen deprivation. Lactate, created from lactic acid fermentation, accounts for the anaerobic component of cardiac metabolism. At normal metabolic rates, about 1% of energy is derived from lactate, and about 10% under moderately hypoxic (low oxygen) conditions. Under more severe hypoxic conditions, not enough energy can be liberated by lactate production to sustain ventricular contraction, and heart failure will occur.
Lactate can be recycled by the heart and provides additional support during nutrient deprivation. Recycling lactate is very energy-efficient in the nutrient-deprived myocardium, since one NAD+ is reduced to NADH and H+ (equal to 2.5 or 3 ATP) when lactate is oxidized to pyruvate. The produced pyruvate can then be burned aerobically in the citric acid cycle (also known as the tricarboxylic acid cycle or Krebs cycle), liberating a significant amount of energy.
LICENSES AND ATTRIBUTIONS
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- Curation and Revision. Authored by : Boundless.com. Provided by : Boundless.com. License : CC BY-SA: Attribution-ShareAlike
CC LICENSED CONTENT, SPECIFIC ATTRIBUTION
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- Myocardium. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Myocardium%23Appearance . License : CC BY-SA: Attribution-ShareAlike
- Sarcomeres. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Sarcomeres . License : CC BY-SA: Attribution-ShareAlike
- syncytium. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/syncytium . License : CC BY-SA: Attribution-ShareAlike
- sarcomere. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/sarcomere . License : CC BY-SA: Attribution-ShareAlike
- intercalated discs. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/intercalated%20discs . License : CC BY-SA: Attribution-ShareAlike
- Muskel-molekulartranslation. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Muskel-molekulartranslation.png . License : CC BY-SA: Attribution-ShareAlike
- Sarcomere. Provided by : Wikimedia. Located at : commons.wikimedia.org/wiki/File:Sarcomere.gif . License : CC BY-SA: Attribution-ShareAlike
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- Myocardium. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Myocardium%23Metabolism . License : CC BY-SA: Attribution-ShareAlike
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22.2: Types of Muscle Tissues
Introduction
Learning Objectives
- Explain the organization of muscle tissue
- Describe the function and structure of skeletal, cardiac muscle, and smooth muscle
- Explain how muscles work with tendons to move the body
- Describe how muscles contract and relax
- Define the process of muscle metabolism
- Explain how the nervous system controls muscle tension
- Relate the connections between exercise and muscle performance
- Explain the development and regeneration of muscle tissue
When most people think of muscles, they think of the muscles that are visible just under the skin, particularly of the limbs. These are skeletal muscles, so-named because most of them move the skeleton. But there are two other types of muscle in the body, with distinctly different jobs. Cardiac muscle, found in the heart, is concerned with pumping blood through the circulatory system. Smooth muscle is concerned with various involuntary movements, such as having one’s hair stand on end when cold or frightened, or moving food through the digestive system. This chapter will examine the structure and function of these three types of muscles.
Overview of Muscle Tissues
Learning Objectives
- Describe the different types of muscle
- Explain contractibility and extensibility
Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle ( Figure 10.2 ). All three muscle tissues have some properties in common; they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from polarized to depolarized) and send an electrical wave called an action potential along the entire length of the membrane. While the nervous system can influence the excitability of cardiac and smooth muscle to some degree, skeletal muscle completely depends on signaling from the nervous system to work properly. On the other hand, both cardiac muscle and smooth muscle can respond to other stimuli, such as hormones and local stimuli.
The body contains three types of muscle tissue: (a) skeletal muscle, (b) smooth muscle, and (c) cardiac muscle. From top, LM × 1600, LM × 1600, LM × 1600. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)
The muscles all begin the actual process of contracting (shortening) when a protein called actin is pulled by a protein called myosin. This occurs in striated muscle (skeletal and cardiac) after specific binding sites on the actin have been exposed in response to the interaction between calcium ions (Ca ++ ) and proteins (troponin and tropomyosin) that “shield” the actin-binding sites. Ca ++ also is required for the contraction of smooth muscle, although its role is different: here Ca ++ activates enzymes, which in turn activate myosin heads. All muscles require adenosine triphosphate (ATP) to continue the process of contracting, and they all relax when the Ca ++ is removed and the actin-binding sites are re-shielded.
A muscle can return to its original length when relaxed due to a quality of muscle tissue called elasticity . It can recoil back to its original length due to elastic fibers. Muscle tissue also has the quality of extensibility ; it can stretch or extend. Contractility allows muscle tissue to pull on its attachment points and shorten with force.
Differences among the three muscle types include the microscopic organization of their contractile proteins—actin and myosin. The actin and myosin proteins are arranged very regularly in the cytoplasm of individual muscle cells (referred to as fibers) in both skeletal muscle and cardiac muscle, which creates a pattern, or stripes, called striations. The striations are visible with a light microscope under high magnification (see Figure 10.2 ). Skeletal muscle fibers are multinucleated structures that compose the skeletal muscle. Cardiac muscle Home fibers each have one to two nuclei and are physically and electrically connected to each other so that the entire heart contracts as one unit (called a syncytium).
Because the actin and myosin are not arranged in such regular fashion in smooth muscle , the cytoplasm of a smooth muscle fiber (which has only a single nucleus) has a uniform, nonstriated appearance (resulting in the name smooth muscle). However, the less organized appearance of smooth muscle should not be interpreted as less efficient. Smooth muscle in the walls of arteries is a critical component that regulates blood pressure necessary to push blood through the circulatory system; and smooth muscle in the skin, visceral organs, and internal passageways is essential for moving all materials through the body.
- Chapter 10. Authored by : OpenStax College. Provided by : Rice University. Located at : http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22<EMAIL_ADDRESS>. Project : Anatomy & Physiology. License : CC BY: Attribution
- Lifetime Fitness and Wellness. Provided by : Extended Learning Institute of Northern Virginia Community College. Located at : https://eli.nvcc.edu/ . License : CC BY: Attribution


45.5B: Predation, Herbivory, and the Competitive Exclusion Principle
- Distinguish between predation and herbivory and describe defense mechanisms against each
Predation and Herbivory
Most animals fall into one of two major categories when it comes to obtaining the energy they need to survive in the environment: predation or herbivory. An animal that hunts, kills, and eats other animals is called a predator. Examples of predators include tigers, snakes, and hawks. Herbivory, on the other hand, refers to animals that eat plant matter. Deer, mice, and most song birds are examples. To protect themselves against these feeding mechanisms, many organisms have developed methods that keep them from being eaten.
Predation is the hunting of prey by its predator. Populations of predators and prey in a community are not constant over time; in most cases, they vary in cycles that appear to be related. The most-often-cited example of predator-prey dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), which is based on nearly 200-year-old trapping data from North American forests. This cycle of predator and prey lasts approximately 10 years, with the predator population lagging 1–2 years behind that of the prey population. As the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, they kill so many hares that the hare population begins to decline. This is followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, at least in part, to low predation pressure, starting the cycle anew.
Herbivory describes the consumption of plants by insects and other animals. Unlike animals, plants cannot outrun predators or use mimicry to hide from hungry animals. Some plants have developed mechanisms to defend against herbivory. Other species have developed mutualistic relationships; for example, herbivory provides a mechanism of seed distribution that aids in plant reproduction.
Defense Mechanisms against Predation and Herbivory
The study of communities must consider evolutionary forces that act on the members of the various populations contained within it. Species are not static, but slowly changing and adapting to their environment by natural selection and other evolutionary forces. Species have evolved numerous mechanisms to escape predation and herbivory. These defenses may be mechanical, chemical, physical, or behavioral.
Mechanical defenses, such as the presence of thorns on plants or the hard shell on turtles, discourage animal predation and herbivory by causing physical pain to the predator or by physically preventing the predator from being able to eat the prey. Chemical defenses are produced by many animals as well as plants, such as the foxglove which is extremely toxic when eaten.
Many species use their body shape and coloration to avoid being detected by predators. The tropical walking stick is an insect with the coloration and body shape of a twig, which makes it very hard to see when stationary against a background of real twigs. In another example, the chameleon can change its color to match its surroundings. Both of these are examples of camouflage: avoiding detection by blending in with the background.
Some species use coloration as a way of warning predators they are not good to eat. For example, the cinnabar moth caterpillar, the fire-bellied toad, and many species of beetle have bright colors that warn of a foul taste, the presence of toxic chemical, and/or the ability to sting or bite, respectively.  This type of defensive mechanism is called aposematic coloration, or warning coloration.
While some predators learn to avoid eating certain potential prey because of their coloration, other species have evolved mechanisms to mimic this coloration to avoid being eaten, even though they themselves may not be unpleasant to eat or contain toxic chemicals. In Batesian mimicry, a harmless species imitates the warning coloration of a harmful one. Assuming they share the same predators, this coloration then protects the harmless ones, even though they do not have the same level of physical or chemical defenses against predation as the organism they mimic. Many insect species mimic the coloration of wasps or bees, which are stinging, venomous insects, thereby discouraging predation.
Key Points
- Predation, the hunting and consuming of animals by other animals, often shows cyclical patterns of predator/prey population sizes; predators increase in numbers when prey species are plentiful.
- Herbivory is the eating of plant material for energy and can assist the plants with seed distribution.
- Plants have evolved spines and toxins to defend against being eaten by herbivores.
- Animals use bright colors to advertise that they are toxic; mimicry to hide from predators; or have spines, shells, and scales to protect themselves.
- Batesian mimicry is when a non-toxic species looks similar to a poisonous one, which deters predator attacks.
Key Terms
- camouflage : resemblance of an organism to its surroundings for avoiding detection
- herbivory : the consumption of living plant tissue by animals
- Batesian mimicry : the resemblance of one or more non-poisonous species to a poisonous species, for example, the scarlet king snake and the coral snake