Chapter 16. Media and Popular Culture
16.1 Media and Society
William Little and Ron McGivern
The Bias of Communication
Forms of communication and media have a powerful role in the way societies are structured. Oral cultures that pass stories and history down by way of mouth produce different societal structures than cultures which communicate through symbols and languages imprinted in stone or clay. Both types of culture differ from societies that communicate through writing on paper. The dominant media used to communicate in a society is profoundly linked to its material foundations of life, time, and space.
In his 1951 book, The Bias of Communication, the Canadian historian Harold Innis (1894–1952) argued that forms of communication bias societies towards two types of configurations: time-binding societies or space-binding societies. The bias of communication in this sense refers to how a form of communication orients the institutional framework of a society toward either the control of time or the control of space (Innis, 1951).
Time-biased media were forms of communication that sought to transcend or “bind” time. They were imprinted into durable materials like clay or stone which had long lifespans and were difficult to transport, such as Sumerian cuneiforms, Egyptian hieroglyphics, or Indigenous rock paintings (pictographs) and rock carvings (petroglyphs). Or they took the form of speech and story telling in oral culture, passing down ancestral memories, values, and traditional knowledges from generation to generation. In both cases, Innis argued, time-biased media bound the past in a continuous line to the present and future. In purely oral story telling cultures this encouraged dialogue and equality, but durable media (clay, stone, etc.) favoured hierarchical societies. The power of elite groups like the Egyptian or Babylonian priests, or the Catholic clergy of the Middle Ages, was based on their exclusive access to sacred knowledge. But both oral and durable media supported civilizations that were rooted in specific locales and based on historical continuity of local customs, rather than centralized civilizations that controlled large expanses of territory.
Space-biased media were forms of communication more suited to transmission over distances. They made it possible to transcend geographical boundaries to bind space. Historically they were printed on paper or papyrus, which were impermanent media but easily transportable, making them ideal for administrating large empires or conducting long distance trade. Innis (1950) argued for example that “the conquest of Egypt by Rome gave access to supplies of papyrus, which became the basis of a large administrative empire.” It gave the Romans and eventually modern colonial empires the ability to pass instructions along lengthy chains of communication. Writing, and later radio, television, and mass circulation newspapers, are ephemeral media that facilitate the transmission of practical administrative information (as opposed to sacred values and experiences) and the expansion of political and economic empires. They thereby supported less hierarchical, (in the sense that access to paper media was more widespread), but administratively centralized societies that extended over vast spaces.
Mass Media
The development of modern mass media such as television, radio, newspapers, and books, has different implications for the structure of societies. The term media means that the communication is not direct, or face-to-face, but mediated through the intervention of an agency or sender that produces messages and distributes them though different technologies. The term mass means that the communication is received by many people. Mass media are forms of communication that pass from a centralized location to the masses. They are one of many forms of communication.
The mass media therefore have three characteristics. First, they tend to be one way and hierarchical, (i.e., messages go from the TV studio or newspaper publisher to the audience, but not back again). Second, their messages are undifferentiated; everyone in the audience receives the same message, program, or story regardless of their location, social background, or specific interests. Finally, they are media that address a mass: a large and disperse group, lacking self-awareness and self-identity, whose members are largely unknown to one another, and who are incapable of acting together in a concerted way to achieve objectives. The masses addressed by mass media are characterized by anonymity and passivity.
This lead 20th century critics, like Horkheimer and Adorno (2002/1947), to be concerned about mass media products — TV, Hollywood movies, pop music, pulp fiction, sensationalist newspapers, etc. — that were pitched to the lowest common denominator to have the widest commercial appeal. The commercial mass media produced standardized products like the TV sitcom or the three-chord pop song that could be consumed without thought or critical reflection. They distracted audiences from real problems and created a mass culture of conformity by integrating audiences into the commercial circuit of media production and consumption. As Lowenthal (1961) put it, culture industry products are characterized by “standardization, stereotype, conservativism, mendacity [and] manipulated consumer goods.” As a result, they affirmed the power structures of society and depoliticized the audience while providing them with easy to consume pleasures, wish-fulfillments, and diversions.
But others, like C. W. Mills (1956) argued that the mass media play an important function in democracy and modern citizenship. The mass media not only address a public, but construct it in crucial respects. They extend the reach of information in large populations where people do not have direct access to sources and provide facts and opinions necessary for rational debate. A healthy functioning democracy is predicated on the electorate making informed choices and this in turn rests on the quality of information that they receive (Mwengenmeir, 2014). In this regard, modern professional news media have been described as society’s fourth estate, a watchdog that monitors the government of society by exposing excesses and corruption, and holding those in power accountable. This role in creating a public or citizenry extends to other media of popular culture like film, fashion, celebrity, and popular music where people gain access to trends, images, ideas, values, and identities.
The debate centers on whether society is like a mass or a public. Whereas communication to a mass tends to be one way and top down, like a broadcast that delivers a message to potentially millions of separate listeners, in a public there is the expectation that people will engage with and respond to information. They can and will “answer back” (Mills, 1956). This is the foundation of Habermas’ concept of the public sphere, the open “space” of public debate and deliberation in democratic societies where public opinion can be formed (See Chapter 17, Government and Politics). As Habermas puts it, “a portion of the public sphere comes into being in every conversation in which private individuals assemble to form a public body” (Habermas, 1974). The mass media provide a common framework for people in large societies to recognize and debate common issues. Is this a form of manipulation, or is this the basis of public engagement and citizenship?
Information Society
Manuel Castells (2010/1996) describes an information society as one in which the sources of economic productivity and political power are based on new information technologies (e.g., micro-electronic computers, digital communications technologies, gene editing) and the generation, processing and transformation of information. Exchange of information has always been important but in an information society technological development and information itself become fundamental drivers of social processes, productivity, and profits.
Information society is the condition for the formation of global society as a unit operating in simultaneous real time (see Chapter 10. Global Society) and the realignment of social organization towards fluid and flexible network structures. Increasingly tasks are not accomplished through bureaucratic organization but through loose networks of actors: a “specific set of linkages [are] organized ad hoc for a specific project, and dissolve/reform after the task is completed” (Castells, 1997). It is supported by the development of digital media or computer mediated communication networks. “Digital” means that messages, images or pieces of information are translated into series of digits in a computer code, which can be transmitted instantaneously through global cable, wireless and satellite networks, and reconstituted as consumable, machine-readable media (social media, email, streams, gaming, 3D printing, word/image/sound processing, etc.). This also enables communications to be stored, processed, and manipulated by mathematical operations like algorithms, encryption, and artificial intelligence.
The communication system of information societies is not characterized by the hierarchical, one-way, undifferentiated messages of the mass media, but rather “targeted messages to specific segments of audience” (Castells, 1997). For example, advertising or suggested content can be catered to the specific history of an audience member’s browses, searches, “likes” and views. Whereas the mass media communicate from the one to the many, digital media can communicate one-to-one, one-to-many and many-to-many. They are interactive media, enabling dialogues through two-way or many-way messages.
A product of this is a medium of communication or a mediascape of virtuality. The framework for local and global interaction is digitally simulated reality. If virtuality is the quality of having the attributes of something without sharing its real or imagined physical form, it is nevertheless as real as physical reality in its consequences for the conduct of everyday social life. The emotions experienced and the hours spent playing a video game or responding to trolls on social media are as real as in other activities, even if the virtual stimulus is never actualized or tangible.
Castells sums up the effects of digital media on societies:
Media are extraordinarily diverse, and send targeted messages to specific segments of audiences and to specific moods of the audiences…. Instead of a global village we are moving towards mass production of customized cottages. While there is oligopolistic concentration of multimedia groups around the world, there is at the same time, market segmentation, and increasing interaction by and among the individuals that break up the uniformity of a mass audience. These processes induce the formation of what I call the culture of real virtuality. It is so, and not virtual reality, because when our symbolic environment is, by and large, structured in this inclusive, flexible, diversified hypertext, in which we navigate every day, the virtuality of this text is in fact our reality, the symbols from which we live and communicate (Castells, 1997).
At the same time, Castells notes that digital technology is not equally distributed around the world, nor within societies. This is the aspect of the digital divide, the uneven access to the new technologies along race, class, and geographic lines. The Organisation for Economic Co-operation and Development (OECD) defines the digital divide as “the gap between individuals, households, businesses and geographic areas at different socio-economic levels with regard to both their opportunities to access information and communication technology (ICTs) and to their use of the Internet for a wide variety of activities” (OECD, 2001). As with any technological development in human society, not everyone has equal access. Technology, in particular, often creates changes that lead to ever greater inequalities. In short, the gap gets wider faster leading to not only unequal access to the dominant forms of digital communication but also a knowledge gap, an ongoing and increasing gap in information for those who have less access to technology. This process of technological stratification has led to a complicated set of questions about how to ensure better access for all.
Making Connections: Big Picture
Bias of Communication: Timeless Time and the Spaces of Flows
To return to the bias of communication theme, Innis (1951) showed how media of communication affect the meaning of time and space and how these meanings manifest in social practice and the formation of societies. Castells (1997) argues that digital media create a different relationship to time and space than the other types of historical media: they are the source of “timeless time” and “spaces of flows.”
Although Castells notes that the effect of digital media does not spread evenly and leads to new types of social exclusion, the relationship to time in information societies has fundamentally altered as processes become instantaneous, while space is reorganized on a global basis through digitally mediated linkages between distant locales.
In the era of digital media, the biological time of human life and seasonal cycles, and the measured clock time of the industrial age and mass media scheduling, collapse into the instantaneous time of nanoseconds. Digital media create the experience of time as a perpetual present or “now.” The barriers of time — the length of time it takes to do something, for example — are continually eliminated as communication becomes instant and tasks can be done in a moment through computation and artificial intelligence. The 24-hour news cycle, microblogging feeds, and streaming television are examples of how people’s media consumption has shifted away from the “morning newspaper” and competition between TV shows in “prime time” to a situation where everything is available in the “now” all of the time.
In this regard, Castells (1997) argues that time becomes “timeless” to the degree that the ordinary sequencing of time — the division of past, present, and future, or the succession of things that define time — is eliminated. Like a film in which the scenes have been shot out of order and then reassembled into a sequence or story line in the editing studio, the time of everyday procedures and processes can also be reassembled through digital technologies. In the information society, all dominant processes are reorganized around timeless time: the accumulation of capital through instantaneous financial transactions, the blurring of the lifecycle through new reproductive techniques, the restructuring of work tasks and schedules through a global division of labour and production processes, and so on.
As with time, space is also altered through digital media. The concept of a space of flows captures the way in which dominant processes like market transactions, circulation of global media, the production of knowledge, technological processes, etc. operate through electronic networks and information systems that link distant locations, bypass boundaries, and establish a pattern of uninterrupted flows information exchange. The way the world was divided up into discrete, distinct geographical locations and independent institutional units is surpassed by digitally mediated linkages of circuits and continuous flows of information. This reconfigures the space of everyday life by removing the physical dimension of space. For example, people and things still share “real time,” in the sense of interacting at the same time. They just do not have to be physically together in the same location to do so because information can flow freely between them at a distance. Thus the “space of flows is the material organization of time-sharing social practices that work through flows” (Castells, 1997).
Both timeless time and the space of flows are unevenly distributed throughout the world, leading to some characteristic sources of conflict in the information society. This is an aspect of the digital divide in access to technology. Timeless time describes the dominant economic processes and the privileged social groups who benefit from them, while most people in the world are still subject to seasonal time, biological time, and clock time. Similarly, people still live in specific places, bounded by geographical, physical, and cultural borders. However, the logic of the space of flows dominates, structures, and shapes the space of these places. Shifts in global investment can suddenly make a local industry redundant or put the price of housing beyond the means of locals to afford. Electronic networks that allow people to be employed in a central business district while working from home or in suburban satellite offices can mean that poor urban neighbourhoods or entire regions and countries are bypassed and further impoverished.
Types of Media and Technology
Technology and the media are interwoven, and neither can be separated from contemporary society. From the time the printing press was created (and even before), technology has influenced how and where information is shared. Today, it is impossible to discuss media and the ways that societies communicate without addressing the fast-moving pace of technology. Thirty years ago, if a person wanted to share news of their baby’s birth or a job promotion, they phoned or wrote letters. They might tell a handful of people, but would not call up several hundred, including their old high school chemistry teacher, to let them know. Now, by posting their big news, the circle of communication is wider than ever.
Technology creates media. The comic book a parent bought their daughter at the drugstore is a form of media, as is the movie they streamed for family night, the app they used to order dinner online, the billboard they saw on the way to get that dinner, and the news feed they read while waiting to pick up your order. Without technology, modern media would not exist.
Media and technology have evolved hand in hand, from early print to modern publications, from radio to television to social media. New media emerge constantly, changing the media landscape people move through and the mediated ways in which they are connected with others.
Print Newspaper
Early forms of print media, found in ancient Rome, were hand-copied onto boards and carried around to keep the citizenry informed. With the invention of the printing press, the way that people shared ideas changed, as information could be mass produced and stored. For the first time, there was a way to spread knowledge and information more efficiently. Many credit this development as leading to the Renaissance, the Protestant Reformation and ultimately the formation of a unique public sphere during the Age of Enlightenment. This is not to say that newspapers of old were more trustworthy than the Weekly World News and National Enquirer are today. Sensationalism abounded, as did censorship that forbade any subjects that would incite the populace.
The invention of the telegraph, in the mid-1800s, changed print media almost as much as the printing press. Suddenly information could be transmitted in minutes. As the 19th century became the 20th, American publishers such as Hearst redefined the world of print media and wielded an enormous amount of power to socially construct national and world events. Of course, even as the Canadian media empires of Max Aitken (Lord Beaverbrook) and Roy Thomson or the U.S. empires of William Randolph Hearst and Joseph Pulitzer were growing, print media also allowed for the dissemination of counter-cultural or revolutionary materials. Internationally, Vladimir Lenin’s Irksa (The Spark) newspaper was published in 1900 and played a role in Russia’s growing communist movement (World Association of Newspapers, 2004). Nevertheless, the flourishing working class press in Britain in the early 19th century was eliminated by the industrialization of the press and the rise of the new daily local newspaper, which required massive capital investments and profits to sustain new technology, machinery, and mass circulation (Herman and Chomsky, 2008).
With the invention and widespread use of television in the mid-20th century, newspaper circulation steadily dropped off, and in the 21st century with the advent of social media, circulation has dropped further as more people turn to internet news sites and other forms of digital media to stay informed. This shift away from newspapers as a source of information has profound effects on societies. When the news is given to a large diverse conglomerate of people, it must maintain some level of broad-based reporting and balance to appeal to them and keep them subscribing. As newspapers decline, news sources become more fractured, so that the audience can choose specifically what it wants to hear and what it wants to avoid. This creates the problem of silos and the spread of non-fact checked misinformation, which undermines the role of the public sphere in democratic decision making.
But the real challenge to print newspapers is that revenue sources are declining much faster than circulation is dropping. “Revenue from all sources, and inclusive of both “daily” and “community” papers, peaked between 2006 and 2008 at just a little over $4.8 billion. It has plunged ever since, except for … 2020 and 2021 … when a bottom of sorts seems to have been reached at $1.9 billion — forty per cent of what it was a decade-and-a-half earlier” (Winseck, 2022). Unable to compete with digital media, large and small newspapers are closing their doors across the country. Digital media has downloaded much of the costs of producing and distributing printed newspapers onto the consumer through personal technology purchases.
Television and Radio
Radio programming obviously preceded television, but both shaped people’s lives in a similar way. In both cases, information (and entertainment) could be enjoyed at home, with a kind of immediacy and community that newspapers could not offer. Prime Minister Mackenzie King broadcast the first network radio message out to the entire country in 1927 using telegraph and telephone lines to hook up the 57 private radio stations that were in operation at that time. He later used radio to promote economic cooperation in response to the international crisis of capitalism in the 1930s (McGivern, 1990).
Radio was the first “live” mass medium. People heard about the Japanese attack on Pearl Harbor as it was happening. Hockey Night in Canada was first broadcast live in 1932. Even though people were in their own homes, media allowed them to share these moments in real time. Unlike newspapers, radio has unique qualities that have allowed it to survive the disruptions of the digital media era. As O’Reilly asserts, radio survives “because it is such a ‘personal’ medium. Radio is a voice in your ear. It is a highly personal activity.” He also points out that “radio is local. It broadcasts news and programming that is mostly local in nature. And through all the technological changes happening around radio, and in radio, be it AM moving to FM moving to satellite radio and internet radio, basic terrestrial radio survives into another day” (O’Reilly, 2014).
The introduction of Canadian television in the 1940s and 1950s has always reflected a struggle with the influence of U.S. television dominance, the language divide, and strong federal government intervention into the industry for political purposes. There were thousands of televisions in Canada receiving U.S. broadcasting a decade before the first two Canadian stations began broadcasting in 1952 (Filion, 1996). Public television, in contrast, offered an educational nonprofit alternative to the sensationalization of news spurred by the network competition for viewers and advertising dollars. Those sources — the CBC (Canadian Broadcasting Corporation), PBS (Public Broadcasting Service) in the United States, and the BBC (British Broadcasting Corporation) — which straddled the boundaries of public and private, garnered a worldwide reputation for quality programming and a global perspective. Al Jazeera, the publicly owned Arabic-language international news network of Qatar, has joined this group as a similar media force that broadcasts to people worldwide.
The impact of television on North American society is hard to overstate. By the late 1990s, 98% of homes had at least one television set. As of May 2022, TV reached around 85.3% of Canadians aged 2 and older every week (Stoll, 2022). All this television has a powerful socializing effect, with these forms of visual media providing reference groups while reinforcing social norms, values, and beliefs.
Film
The film industry took off in the 1930s, when colour and sound were first integrated into feature films. Unlike the private consumption of television from the home, film involves a directly communal experience: As people gathered in theatres to watch new releases, they would laugh, cry, and be scared together. Movies also act as time capsules or cultural touchstones for society. From tough-talking Clint Eastwood to the biopic of Facebook founder and Harvard dropout Mark Zuckerberg, movies illustrate society’s dreams, fears, and experiences. The film industry in Canada has struggled to maintain its identity while at the same time embracing the North American industry by actively competing for U.S. film production in Canada. Today, a considerable number of the recognized trades occupations requiring apprenticeship and training are in the film industry. While many North Americans consider Hollywood the epicentre of moviemaking, India’s Bollywood actually produces more films per year, speaking to the cultural aspirations and norms of Indian society.
Digital Media
Digital media encompass all forms of computer mediated interaction and information exchange. This usually takes place on online platforms, where one-to-one, one-to-many and many-to-many forms of mediated communication prevail. These include browsers, search engines, online shopping, social networking sites, blogs, podcasts, wikis, and virtual worlds. The list grows almost daily.
On one hand, digital media tend to break down the hierarchical structure of the mass media and level the playing field in terms of who is producing and receiving messages (i.e., creating, publishing, distributing, and accessing information) (Lievrouw and Livingstone, 2006). Digital media also offer alternative forums to groups unable to gain access to traditional political platforms, such as the groups associated with the Arab Spring protests or conspiracy theorists (van de Donk et al., 2004). On the other hand, new media are dominated by a handful of media platforms like Google, Facebook, Instagram, YouTube, and TikTok, which generate profits through selling targeted advertising space based on surveillance of users. There is also no guarantee of the accuracy of the information offered. In fact, the instantaneous communication of digital media coupled with lack of oversight and anonymity of sources means that people must be more careful than ever to ensure their news and information is coming from accurate sources.
Making Connections: Sociological Research
Just “Friend” Me: Students and Social Networking
The phenomenon known as Facebook was designed specifically for students. Whereas earlier generations wrote notes in each other’s printed yearbooks at the end of the academic year, modern technology, smart phones and the internet ushered in dynamic new ways for people to interact socially. Instead of having to meet up on campus, students could post, text, and video chat from their dorm rooms or off campus rentals. Instead of a study group gathering weekly in the library, online collaborative software and chat rooms help learners connect virtually. The availability and immediacy of computer technology has forever changed the ways students engage with each other.
Now, after several social networks have vied for primacy, a few have established their place in the market, and some have attracted niche audiences. While Facebook launched the social networking trend geared toward teens and young adults, today it is often seen as the older generation’s social media. In Canada, over 80% of Facebook users were older than aged 25 in 2022 (Dixon, 2023), whereas 43% of TikTok users were between 18 and 30 (Ceci, 2022a). The dominant social networks in Canada are Facebook (79% of social media users), YouTube (68%), Instagram (54%), TikTok (32%), and Twitter (31%) (Kunst, 2023).
These new modes of social interaction have also spawned questionable consequences, such as cyberbullying and what some call FAD, or Facebook addiction disorder (Andreassen et al., 2012). In an international study of smartphone users aged 18 to 30, 60% say they are “compulsive” about checking their smartphones and 42% admit to feeling “anxious” when disconnected; 75% check their smartphones in bed; more than 33% check them in the bathroom and 46% email and check social media while eating (Cisco, 2012). Similarly, Canadians reported spending 4.22 hours per day engaging with mobile apps in 2021 and 45% said they could not live without their smart phone (Ceci, 2022b). The most popular online activities via mobile device for Canadians were social media (42% of users), email (40%) and instant messaging (29%).
An International Data Corporation (IDC, 2012) study of 7,446 smartphone users aged 18 to 44 in the United States in 2012 found that:
- Half of the U.S. population have smartphones and of those 70% use Facebook. Using Facebook is the third most common smartphone activity, behind email (78%) and web browsing (73%).
- 61% of smartphone users check Facebook every day.
- 62% of smartphone users check their device first thing on waking up in the morning, and 79% check within 15 minutes. Among 18- to 24-year-olds the figures are 74% and 89%, respectively.
- Smartphone users check Facebook approximately 14 times a day.
- 84% of the time using smartphones is spent on texting, emailing, and using social media like Facebook, whereas only 16% of the time is spent on phone calls. People spend an average of 132 minutes a day on their smart phones including 33 minutes on Facebook.
- People use Facebook throughout the day, even in places where they are not supposed to: 46% use Facebook while doing errands and shopping; 47% when they are eating out; 48% while working out; 46% in meetings or class; and 50% while at the movies.
The study noted that the dominant feeling the survey group reported was “a sense of feeling connected” (IDC, 2012). Yet, in the international study cited above, two-thirds of 18- to 30-year-old smartphone users said they spend more time with friends online than they do in person.
All these social networks demonstrate emerging ways that people interact, whether positive or negative. Sociologists ask whether there might be long-term effects of replacing face-to-face interaction with social media. In an interview on the Conan O’Brian Show that ironically circulated widely through social media, the comedian Louis CK described the use of smartphones as “toxic.” They do not allow for children who use them to build skills of empathy, because children do not interact face-to-face or see the effects their comments have on others. Moreover, he argues, they do not allow people to be alone with their feelings. “The thing is, you need to build an ability to just be yourself and not be doing something. That’s what the phones are taking away” (NewsComAu, 2013). This is still an open question. How do social media like Facebook and TikTok and communication technologies like smartphones change the way we communicate? How could this question be studied?
Media Attributions
- Figure 16.3 Writing-on-Stone/Áísínai’pi new World Heritage Site by the Government of Alberta, via Flickr, is used under a CC BY-NC-ND 2.0 licence.
- Figure 16.4 A newspaper printing press by Newspaper Club, via Flickr, is used under a CC BY-NC-ND 2.0 licence.
- Figure 16.5 Manuel Castells in La Paz Bolivia by is used under a licence.
- Figure 16.6 Time zone map of Canada by MapGrid, via Wikimedia Commons, is used under a CC BY-SA 4.0 licence.
- Figure 16.7 The Yellow Press, 1910 by L.M. Glackens from the Library of Congress’s Prints and Photographs division, digital ID ppmsca.27675, via Wikimedia Commons, is in the public domain.
- Figure 16.8 Facebook by Gustavo da Cunha Pimenta, via Flickr, is used under a CC BY-SA 2.0 licence.


Chapter 3: Boundaries
Significance of boundaries
We have defined an organism as living material that is discrete (i.e., bounded) in space and time. Being distinct in space requires a boundary that separates the organism from the ‘outside’. For single-celled organisms the boundary is the outermost component of that cell, and for most of the single celled organisms studied in this course that outermost component is a cell wall, but the chemical and physical nature of the wall varies considerably. For some unicellular organisms there is no cell wall and the outermost layer is a structure called a cell membrane. For multicellular organisms, the boundary is the collective of all the (generally specialized) cells on the organism’s perimeter, its dermal tissues. For most of the organisms studied here the dermal cells have a cell wall and also a specialized coating on the outside. This chapter examines the physical and chemical nature of organism boundaries and also considers the significant functions of the boundary, starting with its influence on something called flux, the movement of materials in and out of the organism.
TOPICS
- Boundaries and flux
- Structural, chemical and physical nature of boundaries
- Membrane
- Walls
- Polysaccharide cell walls
- plants, fungi, bacteria, archaebacteria
- Inorganic cell walls
- Internal cell walls
- Polysaccharide cell walls
- Dermal tissue
- Coatings
- Boundaries and structure
- Boundaries and movement
- Boundaries and communication
Boundaries and flux
One reason the boundary is significant because it represents a barrier to movement into and out of the organism. This movement can be described as a ‘flux’ and flux can be modeled as being a function of three parameters present in the following formula (which is actually a model of what causes materials to move):
Flux = (driving force * surface area) / resistance
While in many ways this equation is a simplification, it does point out the three fundamental properties that determine the flow of materials into and out of the cell:
- Driving force—this is generally approximated by the difference in the concentration of something on the inside vs. the outside, but in the case of heat flow the driving force is the difference in temperature; considering the movement of fluids (e.g., air, water) the driving force can be pressure differences. In all these situations, the bigger the driving force, the more flux there is.
- Resistance—the resistance can be described as the difficulty with which materials can move from the outside to the inside, or vice versa. Some materials readily allow the movement of molecules (or heat) through them, i.e., they have a low resistance. Other materials only reluctantly allow materials (or heat) to move through them, i.e., they have a high resistance. It is important to appreciate that resistance depends on the substance/ molecule one is keeping track off; a boundary may have a very high resistance to some molecules and a very low resistance to others. (related terms are conductance and permeability, which, for our purposes, are the reciprocal of resistance)
- Surface area — the more surface area through which materials can flow, the more flux.
As will be discussed in the next chapter, the surface area is determined by the shape and size of the organism. The driving force is determined by where the organism is and what is going on inside and outside of the organism. Organisms can manipulate fluxes by manipulating the driving force. Most of the discussion of these mechanisms is beyond the scope of this book but we will mention some in Chapter 22. In the case of the flow of materials or heat into and out of cells, the resistance to flux is determined by the chemical and physical characteristics of the boundary between the organism and its environment.
Besides being important in influencing the flux of materials into and out of organisms, boundaries serve other important functions that will be discussed after describing different types of boundaries.
Structural, chemical and physical nature of boundaries
Cell membrane
The chemical nature of the cell membrane should be familiar to biology students: a phospholipid bilayer with proteins imbedded in and through it. The two sides of this membrane are ‘w et’ (i.e., hydrophilic) due to the attraction of polar water molecules to the charged phosphate groups of the membrane. The interior of the membrane is dry (i.e., hydrophobic) because lipid molecules carry no charges and have no regions that are even partially charged and to which a polar (= partially charged) water molecule might be attracted. However, there are tubular proteins passing through cell membranes. These tubular proteins may have a ‘wet’ in interior, providing for water filled channels running from the outside to the inside. Some of these channels allow selective passage of ions and many of these can be manipulated (opened or closed). Although the chemical nature of the hydrophobic layer is different in the Archaea, the basic structure of membranes is fundamentally the same for all organisms. Significant to organism function is that the membrane is quite permeable (low resistance) to small, uncharged molecules (significantly O2, CO2 and H2 O) but not very permeable (high resistance) to charged molecules (ions) and to larger molecules, especially if they are not soluble in lipids. The cell membrane generally has little strength and readily yields to internal and external forces, that can cause the cell to change shape. Organisms lacking a cell wall in terrestrial environments cannot be very tall because the force of gravity flattens them. This can be overcome with an internal skeleton (vertebrates) or an external one (exoskeleton), which is a rigid boundary.
Cell walls
In contrast to the consistent presence and composition of the cell membrane in the cells of organisms, cell walls show much greater variability. Many organisms (e.g., almost all animals) have no cell wall. For the organisms that possess walls, its composition is quite variable (Table 1), although some of its structural features are more consistent.
Polysaccharide cell walls
The cell walls of plants, fungi, water molds, brown algae, red algae and (most) green algae have a similar structure and chemistry. These cell walls are composite structures, and can be considered to be gels. They consist of fibers made of elongate carbohydrate polymers that resist being stretched. These are imbedded in a matrix of different carbohydrate polymers that are highly hygroscopic (water absorbing) (Fig. 4).
Two common fiber materials are cellulose (found in plants, water molds and green algae) and chitin (found in fungi). Cellulose is a polymer made up of glucose monomers, as is the more familiar polysaccharide, starch, but the two have very different roles, one structural and one energy storage. Chitin is also a polysaccharide polymer but the subunits (N-acetylglucosamine) are hexoses with a nitrogen attached (Fig. 5).
The fibers of cellulose and chitin are consist of multiple (20-100) individual polymer molecules that interact with neighboring molecules to form a crystalline structure of the fiber. These fibers are significant in multiple ways: (1) because there are multiple molecules and they are bound to each other, the fibers, and the wall they are present in, are considerably ‘stronger’ (see below) than would be the case if the individual molecules did not interact to form fibers; (2) the fiber is difficult to digest because the component polymer molecules are not very accessible to enzymes and the fiber itself is not soluble in water, in spite of the fact that the monomers units, e.g. glucose, are very soluble in water.
The fibers of chitin and cellulose are deposited in a matrix of other polysaccharide polymers whose composition is much more variable. This is because the polymer ‘chain’ consists of several subunits, not just one, and also because the linkages between subunits are more variable, not always the same one, and not always ‘end to end’ but with branching (one subunit connected to three other subunits, not just to the ones ‘in front and behind’ it). While these polymers are given names (hemicellulose, pectin, agaropectin), the names refer to groups of chemicals and not to a specific chemical structure and composition. Some of these chemicals bind to cellulose or chitin fibers, connecting them to each other and providing more structure to the cell wall and also allowing the cell walls of adjacent cells to be bound to each other.
Although they are made primarily of polysaccharides, these cell walls contain some protein molecules. The function(s) of the proteins are not known with certainty. They are probably not particularly significant structurally in the way that the chitin and cellulose are and the way that the intracellular proteins tubulin and actin are. The protein component of the cell wall is probably significant in being able to change, through enzymatic action, the structure of the rest of the wall, e.g., during cellular growth when the wall ‘relaxes’ and allows the internal pressure of the cell to bring about growth (Chapter 25). Wall proteins are probably also significant in allowing material to get through the cell wall (both inward or outward).
Generally, carbohydrate cell walls readily absorb water and can be considered to be a hydro gel. The absorption of water comes from the adhesion of water molecules to the carbohydrate components of the cell wall, in particular the ‘matrix’ polymers (e.g., pectins, hemicellulose) plus the cohesion of water to itself. The hydrophilic nature of the cell wall makes it highly permeable (low resistance) to the movement of water (as a result of either diffusion or as a result of pressure differences, i.e., mass flow (m ore discussion on this when discussing material movement, Chapter 24). Small water-soluble molecules also move readily through the wall both as a result of their individual diffusion and as a result of being dissolved in water that may be moving via mass flow. However, dissolved ions may be slowed by becoming bound to charged components of the polysaccharides.
Under some circumstances, the cell wall of plants can shift from being hydrophilic to being hydrophobic as the result of the deposition in the cell wall of ‘water-proofing’ materials called cutin and suberin. These materials are found in cell walls of certain plant tissues and their ability to retard the movement of water is significant. Both suberin and cutin are mixtures of multiple compounds including polymers with hydrophobic subunits and wax molecules. Like the lipid portion the cell membrane, these chemicals are ‘dry’ (hydrophobic) and water movement through walls with these materials is much retarded. While there are some chemical differences between the two, the primary distinction between cutin and suberin is location. Cutin is deposited in a coating called cuticle, present on the external walls of cells located on the outside of the aerial portions of plants. Suberin is deposited in the walls of certain cells as they are produced. Suberin is found in the above-ground portion of the plant in places where growth or mechanical damage has eliminated the cuticle. Suberin is also found in the below-ground portion of most vascular plants in a cylindrical tissue called the endodermis, whose significance will be discussed later.
A final component found in some polysaccharide cell walls is lignin, a material absent in non-vascular plants (e.g., mosses) but found in the cell walls of most vascular plants, and a material that is highly significant to their evolutionary success, i.e., their prevalence in today’s flora. Structurally, lignin is similar to pectins and hemicellulose, i.e., a matrix that surrounds cellulose fibrils. Lignin is produced in what is described as the secondary cell wall, a component of the cell wall present only in certain cells. The secondary cell wall is laid down after cells have stopped growing, necessarily so because lignin is a rigid material that will not yield readily, therefore preventing the cellular expansion needed for growth. Lignin is the material that makes wood tissues woody. It is stiff and rigid and allows plants to be tall by resisting the compressive force of gravity. Like hemicellulose and pectin, lignin is a complex polymer with subunits that are not all the same and are not always connected the same way. Moreover, the subunits of lignin are not sugars, they are phenolic molecules chemically quite different from sugars. Lignin polymers extend in three dimensions, forming a solid material. Lignin is hard to digest and its breakdown products are phenols, chemicals that are poisonous to many organisms. Hence, lignin is resistant to degradation. The secondary cell wall is deposited inside of the primary cell wall and it necessarily shrinks the space available to the membrane bounded cytosol, sometimes eliminating it almost completely. Most cells with secondary cell walls are short-lived and are structural, providing function to the plant when they are dead.
Bacterial cell walls
Not all bacteria possess cell walls but the ones that do possess a wall material unique to bacteria called peptidoglycan. As the name implies, peptidoglycan has components that are peptides (sequences of amino acids) and components that are sugars (carbohydrates). Unlike the polysaccharide wall materials described above that are chains of monomers, peptidoglycan polymers form a mesh, a three-dimensional molecule (like lignin) with units linked not just end-to-end but also above-and-below and side-to-side. Also significant is the fact that many bacteria, including ‘gram-negative’ bacteria and cyanobacteria, have an ‘outer membrane’, a second phospholipid membrane that occurs outside of a thin peptidoglycan cell wall. Some bacteria possess one additional layer, an ‘S-layer’, a protein layer on the very outside of the cell, outside the outer membrane of gram-negative bacteria and the peptidoglycan cell wall layer of gram-positive bacteria.
Archaea cell walls
Recall that Archaea and Bacteria are prokaryotes and used to be considered a single group. One of the several features that distinguish Archaea is a distinct cell wall structure one that lacks peptidoglycan. The chemical composition of Archaeal cell walls is diverse and some have a cell wall composed of a carbohydrate/peptide material similar to peptidoglycan. Like some Bacteria, most Archaea are bounded on the outside by an S-layer, a self-assembling structure composed of globular proteins or glycoproteins.
‘Inorganic’ cell walls’
All of the cell wall materials discussed so far would be considered ‘organic’, a flexible term whose exact meaning wanders considerably. In this context it refers to ‘biological materials’, molecules found in living things, as opposed to inorganic molecules, those generally found in non-living things, e.g. rocks/minerals. Two important cell wall materials, calcium carbonate and silica dioxide, are most commonly found as minerals in rocks. However, these minerals are in some sense ‘organic’ because they can be produced by biological processes, cells produce conditions whereby calcium carbonate or silicon dioxide is precipitated out of solutions. In fact, their presence in some rocks is completely due to their manufacture by marine organisms whose remains became deposits at the bottoms of oceans and eventually in rocks. The ‘White Cliffs of Dover’ (Fig. 6) are formed from a massive deposit of coccolithophores, a type of marine algae that produces distinctive looking calcium carbonate plates as its outside boundary (Fig. 2). Although not as common or extensive as calcium carbonate cliffs, there are similar deposits of ‘diatomite’, a sedimentary rock formed from deposits of diatoms, another unicellular photosynthetic organism that produces an external skeleton, i.e., a cell wall, made of silica dioxide (Fig. 1). Exactly how the material is precipitated in such a precise, and often ornate, manner is not known with certainty.
‘Internal’ cell walls
A few organisms have an unusual structure where wall-like materials (i.e., structural components) occur just inside the membrane. One example is gram negative bacteria where there is a wall inside a membrane, but these bacteria also have a second membrane in its normal location, inside the cell wall. In contrast, dinoflagellates have plates of cellulose enclosed in membranes that occur inside of the plasma membrane. Cryptomonads have wall-like glycoprotein plates both inside and outside of the plasma membrane, forming a structure called the periplast that is unique to this group of organisms.
Dermal tissues of multicellular organisms
Most multicellular organisms have groups of cells, called dermal tissues, that form a ‘skin’ to an organism. These cells / tissues will be considered anatomically in a later chapter but they generally are cells tightly bound to each other (no spaces between them) so that they collectively form a boundary to the organism. Often these cells have different components in their cell wall (e.g., cutin, suberin, lignin) and/or produce a secretion on the outside (cuticle, see below) that is important to their functioning. Additionally, many multicellular organisms produce structures, organs, that have specialized boundaries that are significant to their role. In inanimate life the most common of these are organs associated with reproduction, e.g., spore cases (sporangia), fruits and seeds. The ‘skin’ of these structures may be important in protecting the structures inside, e.g., the sporangium of mosses, the outside of an acorn (a fruit wall), the seed coat of apple seeds (in the latter two cases it is lignin depositions in the cell walls of dermal cells that are particularly important). The ‘skin’ of reproductive structures must eventually open up and allow the dispersal/release of its contents and sometimes features of the ‘skin’ actively participate in dispersing its contents (see discussion below on ‘explosive’ movements). In other situations, the permeability of the coating, in particular how much water/oxygen enters, can significantly influence the behavior of the enclosed structures.
Specialized coatings
Some organisms /colonies of organisms cover themselves or part of themselves with some sort of coating. A number of algae and bacteria coat themselves in a polysaccharide gel outside of the cell wall. A striking example of this is with some species of Nostoc, a colonial, filamentous cyanobacterium that sometimes forms gelatinous sheets or spheres that may be several centimeters across (Fig. 7). The bulk of the sphere is a polysaccharide secretion deposited outside the cell walls of individual cells. Coatings may be significant to the organism for a variety of reasons including: retention of water, protection, adhesion to substrates, keeping a colony of cells together, buoyancy. Similar coatings are sometimes important in producing biofilms, communities of one to several organisms including bacteria, archaea, fungi and others, that coat surfaces (e.g., dental plaque) and are sometimes important ecologically and to human disease).
Fig. 7 Nostoc, a cyanobacterium, can form spherical structures up to several centimeters in extent (left photo), the result of polysaccharide secretions. The photo on the right shows the filaments of the algae, the spaces in between the filaments are filled with polysaccharide hydrogel secretions.
Cuticle
Most plants, who are terrestrial organisms exposed to a drying atmosphere, have a coating on the outside called a cuticle (Figure 8) that lessens water loss. The cuticle is a complex mix of chemicals including cutin (mentioned above as a component of some cell walls) and other similar (hydrophobic) constituents. The cuticle is much more impermeable to water (it has a high resistance to water movement) than the membrane because it is substantially thicker and also because proteins do not span across it. The cuticle’s high resistance to water movement is significant because it lessens water loss from plants to the atmosphere. However, the cuticle is also impermeable to gases, in particular carbon dioxide, and this feature has important consequences for photosynthesizing plants. The cuticle is produced by the cells on the outside of the plant, and the outer part of the cell walls of these cells have extensive deposits of cutin. In addition, hydrophobic materials are deposited completely outs ide of the cell wall (outside the area where cellulose microfibrils are present). The mechanism whereby materials can be deposited outside of the cell walls is not completely understood.
In addition to reducing water loss, the cuticle is a physical barrier to the entrance of organisms into plants, and it also serves to absorb and reflect UV radiation, thereby protecting tissues within. Also, the dryness of the cuticle, along with other specific chemical features, makes it a very inhospitable place for the growth of other organisms, adding to its protective function. The cuticle of many plants may be ruptured by growth from within (discussed later). In these cases, the protection of the cuticle is replaced by a new layer or layers of cells that are produced with suberin in their cell walls, forming the outside portion of what we know as bark.
Spropollenin
Pollen grains (of seed plants) and the spores of a variety of organisms are coated with sporopollenin, a chemical that is particularly resistant to degradation and is thought to be significant in protecting against desiccation, oxidation and enzymatic degradation. It is the resistance of sporopollenin to breakdown that allows pollen buried several hundred million years ago in sediments to be preserved and recognized. Its exact chemical nature has not been determined (partly because it is so hard to breakdown!) but it has some similarities to cutin in having hydrocarbon components as well as phenolic components.
Boundary diversity
The following table summarizes boundary materials for organisms that we cover (plus a few others) grouped grouped by whether they are unicellular or multicellular and whether or not they possess a cell wall.
| Boundary and organism type | Organisms | Features | |
| Unicellular organisms with no walls | Some bacterial groups | Mostly parasites | |
| Cellular slime molds | For parts of their life cycle they do have walls | ||
| Plasmodial slime molds | Like a giant amoeba | ||
| Euglenoids | No wall, but the membrane is reinforced with protein filaments forming a structure called a pellicle, often exhibiting parallel striations on the outside | ||
| Cryptomonads | Wall-like materials (glycoproteins) both inside and outside of the plasma membrane, forming a structure called a periplast. | ||
| Dinoflagellates | Often possess multiple ‘plates’ of cellulose that lie interior to the cell membrane | ||
| Multicellular organisms with cells with no walls | Animals | Many do have coatings (‘skin’) that are groups of cells | |
| Unicellular organisms with cell walls of some sort | Bacteria (most), including all Cyanobacteria | Wall contains a peptidoglycan polymer with polysaccharide and amino acid components. Some bacteria have a second, ‘outer membrane’ outside the peptidoglycan layer | |
| Archaea | Wall contains a polymer similar to peptidoglycan with polysaccharide and amino acid components | ||
| Diatoms | Wall is made of silica (SiO2) — Silicon (Si) is an element that most organisms do not accumulate. The wall is also distinctive because it is not organic (i.e. carbon based), does not absorb water and is very rigid | ||
| (some) Green algae (Chlorophyta) | A variety of wall materials (and sometimes none at all) many green algae have walls containing cellulose, a polymer of glucose | ||
| Haptophytes (Coccolithophores) | Wall consists of round plates of calcium carbonate outside the cell membrane | ||
| Bread molds (Zygomycota) | Cell walls are composed of chitin, a polymer of acetyl glucosamine units (essentially sugar units with a nitrogen attached). The same material is found in the exoskeleton of insects and mollusks. | ||
| Water molds (Oomycota) | Cell walls are contains cellulose, a polymer of glucose units. | ||
| Multicellular organisms with cell walls | Club fungi (Basidiomycota) | As is the case in all fungi and in the bread molds, the cell wall is composed of chitin, a polymer of acetyl glucosamine units (essentially sugar units with a nitrogen attached). | |
| Sac fungi (Ascomycota) | Same as Club fungi | ||
| Red algae (Rhodophyta) | Wall contains cellulose and sulfated polysaccharides. | ||
| Brown algae (Phaeophyta) | Wall has small amounts of cellulose with large amounts of alginate, a polysaccharide polymer composed of uronic (sugar-acid) units | ||
| Green algae (Chlorophyta) | Wall varies but some with cellulose as the main constituent; other green algae have mannans (polymers of mannose), xylans (polymers of xylose), glycoprotein polymers and some have no wall at all | ||
| Plants (mosses, conifers, flowering plants) | Cell wall contains filaments of crystalline cellulose connected by hemicellulose polymers and imbedded in pectin polymers. Many plant cells develop an inner secondary cell wall containing cellulose and lignin, a complex, phenolic polymer. |
Cell walls, cell membranes and structural integrity
One reason that an organism’s boundary is significant is because the boundary resists physical forces that are acting on the organism. These forces can come from the outside (e.g., wind, gravity) or from the inside (internal pressure). For unicellular organisms it is the strength of the boundary that prevents (or allows) deformation that would come about as a result of these forces. For multicellular organisms it is the boundaries of individual cells and also their linkages to each other that determine how the organism will respond to external forces.
Osmotic forces
A common factor that might cause a cell to change shape is ‘osmotic disruption’, brought about by osmosis, the diffusion of water. All other things being equal (more in Chapter 22) water moves by diffusion from areas where it is purer (i.e. has less solutes) to areas where it is less pure (has more solutes). Since living things acquire and manufacture solutes and the impermeability of the cell membrane allows these solutes to be concentrated inside cells, cells are often are in situations where water is going to spontaneously move into them. The cell membrane offers little resistance to expansion and is not able to be stretched. Consequently cells/organisms with only a membrane will burst if exposed to pure water, or any water that is purer than that inside the organism, unless they have mechanisms to eliminate the water. The presence of a cell wall outside the membrane solves this problem because it resists expansion. This allows the cell to pressurize, and this pressure prevents the entry of more water (note that diffusion is NOT just dependent upon differences in purity, as it is often described. It is also dependent upon pressure, more in Chapter 24). It is important to note that the strength required to resist expansion is ‘tensile’ strength. The cell ‘resists’ water absorption because components of the wall (e.g., cellulose or chitin microfibrils) are resistant to being stretched.
If the cell with a cell wall were in an environment causing it to lose water, e.g., an aquatic habitat high in solutes or in a terrestrial habitat where organisms are losing water to a drying atmosphere, water would diffuse outward and the presence of a wall would not prevent the cytosol from collapsing unless the membrane were somehow glued to the cell wall to prevent it. This is not thought to be the case. Moreover, for plant cells with only primary cell walls (no lignin reinforcement) or fungal cells, the wall is not strongly resistant to compression and if water leaves the cell the cell will shrink in size (collapse). Note that although cellulose fibers have a high tensile strength, they are not very resistant to compression, i.e., have little compressive strength. Consider a string (which often times is actually a collection of cellulose microfibrils): you can pull on the string and it resists stretching but it is very easy to collapse the string, it has very little compressive strength.
Walls and ‘structural integrity’
Cells and organisms do need compressive strength to: (1) provide protection from certain predators who would like to crack them open to get to the goodies inside, and (2) allow the organism/cell to resist various forces in the environment, e.g., gravity. Resisting forces becomes more significant if organisms are bigger, especially for organisms in terrestrial environments where the surrounding medium (air) provides little support. In terrestrial environments, organisms will be collapsed by gravity if they are more than a few centimeters in height unless they have structural strength to resist it. Three-dimensional wall materials (e.g., peptidoglycan, calcium carbonate, silica dioxide), can resist compression but these wall materials are only present in very small organisms. Plants are ‘big’ and terrestrial, how do they resist gravity? Walls with lignin, another 3-dimensional material, will resist compression, but not all plant cells have lignin. Plant cells lacking lignin have structural integrity against gravity because of the combination of water, a membrane that ‘holds’ solutes but allows water movement, and a cell wall that has tensile strength. Water is very difficult to compress as long as it is contained in something that doesn’t allow water to escape. It might seem that water should be able to be ‘squeezed out’ of cells by the force of gravity but this doesn’t happen because water movement out, as a cell is squeezed and pressurized by gravity, is balanced by water movement in due to purity (the low water purity inside is because of solutes, Chapter 24). To summarize: plant cells without lignin resist the force of gravity because is incompressible (high compressive strength) and is located within a selectively permeable membrane surrounded by a cell wall with tensile strength.
This structural feature is demonstrated in wilting plants. Deprived of a supply of water, many plants are unable to resist the force of gravity and to maintain their structure. The cells, mostly with only primary cell walls (no lignin) in and of themselves cannot resist compression, they need water, and if re-watered a wilted plant will once again stand up against gravity Fig. 9). Woody plants, at least the woody parts of woody plants as well as some herbaceous plants do not wilt because they have cells with secondary walls containing lignin that provides the compressive strength to resist the forces of gravity.
Although most cell walls resist expansion, the resistance is not absolute and cells can yield (i.e., expand) to some extent when pressures increase inside them. The yielding of cell wall is both elastic (the wall yields, but returns to its original form when the force, internal pressure, is eliminated) and also plastic (the wall yields but does not return to its original shape if the internal pressure is reduced). Because cell walls are present even in newly created cells, plastic deformation is essential for cellular growth.
Considering a tree trunk being pushed by the wind, the windward side needs tensile strength, the lee side needs compressive strength. Woody stems are almost entirely composed of lignified cells that have both tensile strength from the cellulose and compressive strength from the lignin. Such a composite material is comparable to ‘reinforced’ concrete (concrete poured around wire/steel rods) or fiberglass (resin poured around glass fibers), where the matrix of concrete/resin provides compressive strength and the fibers of wire/glass provides the tensile strength. Moreover, the lignin in plant cells was deposited while the cellulose was under tension, because the cell was pressurized when the lignin was deposited in the secondary cell wall. This produces a composite material like pre-stressed concrete, a concrete made by pouring concrete around steel cables that are under tension. Pre-stressed concrete has superior strength when compared to regular reinforced concrete. Finally, a tree trunk blown by the wind not only has to have structurally strong cells, the cells need also to stick to each other because separations between cells will cause structural failure, and indeed when stems break or lumber fails it is both because of separations between individual cells and also failures within individual cells.
Boundaries and organism movement
Organisms move by manipulating their boundaries relative to the environment. For familiar organisms (lions and tigers and bears) this is done with appendages (legs, fins, tentacles) whose positions are manipulated internally. This is comparable to the movement brought about by flagellae and cilia, which are extensions of the boundary of cells that often provide motility to unicellular organisms, including most of the groups covered here: most archaea (e.g. Halobacterium), most bacteria (e.g. Agrobacterium, Rhizobium), euglenoids (e.g. Euglena), dinoflagellates (e.g. Gonyaulax), cryptomonads, some of the green algae (e.g. Chlamydomonas). Flagellae and flagellar motility is commonly found in the reproductive cells (e.g. sperm, zoospores) of most multicellular organisms, and, as considered in Chapter 2, these cells might be considered organisms. Thus flagellated mobility is near ubiquitous, lacking only in a few groups, all of them ‘inanimate’, being absent in all red algae, all flowering plants (and almost all seed plants), almost all fungi (except in some Chytrids), and almost all diatoms.
But there are other means of movement and the diversity of organisms that we cover illustrate a diversity of movement mechanisms, all of which, like flagellar movement, are related to manipulation of boundaries. Some examples are given below:
Flagellar motility
Cytoplasmic streaming
Like amoebae, the amoeboid cells of cellular slime molds move by pushing and pulling on their boundary by means of microtubules, keeping the volume of the beast constant while changing its form. This allows them to move through their environment or to flow around a particular food item. Plasmodial slime molds, though much bigger and multi nucleate, are able to move in a similar manner. Their cytosol is seen to stream back and forth but more so in one direction, propelling the organism in the direction of greater flow.
Euglena motion
Organisms in the Euglena group can move by both flagellar movement and by a movement that involves reshaping their form, comparable to an amoeba or slime mold.
Growth
Fungi and plants move by growing, which requires the extension of boundaries into new territory. This process will be covered later but it requires the extension of individual cells, accomplished by the pressure inside these cells exceeding the tensile strength of the cell wall and also exceeding the resistance to movement provided by the medium that they are moving through (e.g., soil).
Stomatal movement
Vascular plants and a few non-vascular plants have the ability to change the shape of pairs of cells (guard cells) in the skin tissue of (generally) leaves, thereby opening pores (stomata) in the leaf surface. This is accomplished by means of changing hydration levels of cells, thereby changing their pressure and shape and in turn opening a hole in between them. Stomatal movement ties into two topics of this chapter: (1) the change in shape in guard cells is a consequence of asymmetric deposition cellulose microfibrils in the cell walls, (2) the opening of stomates dramatically changes the dermal permeability to carbon dioxide and water, allowing water to escape the leaf and carbon dioxide to enter.
Leaflet/organ movement
In addition to moving by growing, a number of plants are able to move appendages, usually leaves. This is accomplished in a manner similar to the operation of stomates: by changing hydration levels of specific cells and groups of cells, thereby changing their pressure and volume and in turn changing their shape. In flowering plants, the changes in cellular shape happen in special cells at pivot points that allow leaves to move. In mosses, changes in cellular shape happen in all the cells of the ‘leaves’ (microphylls) , sometimes causing them to twist and curl up next to the main axis of the moss. Most mosses also possess appendages called peristome teeth at the end of the spore-producing capsule. Changes in the hydration of the cells in these teeth change their shape, which allows the capsule to close in times of high humidity, when spores are less likely to be dispersed, and open in times of low humidity, when spores are more likely to be dispersed. Although not a boundary movement, a similar mechanism and motion happens with groups of cells called elaters that are present in the sporangia (containers where spores are produced) of horsetails and liverworts and whose movement aids in the dispersal of spores.
‘Explosive’ movements
Mentioned earlier was the fact that as cells absorb water and expand, the change in size may be elastic, in which case energy is being stored in the wall; this energy can be utilized to cause movement. Such an energy storage and a resultant movement is significant in spore and seed dispersal. A container, which may be a cell (e.g. the basidium of club fungi (Basidiomycota) or may be a container with a wall of dermal cells (the fruit of dwarf mistletoe or squirting cucumber, both flowering plants) becomes pressurized and stores energy in the wall(s). Then a part of the wall(s) breaks open and the pressure is rapidly released, expelling the contents (spores or seeds). A similar phenomenon occurs in Pilobolus, a bread mold (Zygomycota) except that what is expelled is the whole spore container (sporangium), occasionally with other organisms hitching a ride. Dehydration can also result in movement. Cells in the fruit wall of some fruits (e.g., witch-hazel) and also in the spore containers (sporangia) of many ferns dehydrate as the fruits/sporangia mature. Dehydration results in shrinkage that is resisted by the cohesive strength of water bound to cell wall materials. More and more force builds up as more and more water is lost. Eventually the force exceeds the cohesive strength of the water in the walls of the cells, again causing the structure to rupture. This is often accompanied with an extremely rapid change in the form of the fruit/ spore capsule that can result in the forceful release of seeds/ spores, like a catapult.
Boundaries and communication/sensation
A final point about boundaries is that they play a role in the sensation of the environment and communication between organisms. Organisms need to sense their environment, which means that either signals need to get through the boundary or alternatively that there exists a sensor molecule that extends through the boundary and allows a molecular interaction outside to cause a response inside. Both of these things happen. It is also the case that important signals are actively transported out of organisms and that some signals are components of the boundaries (e.g. cell wall compounds, or derivatives of enzymatic action on cell wall compounds). A great example of this is the communication between Rhizobium, a nitrogen fixing bacteria and the plants they associate with.
Further Reading and Viewing
- “Squirting Cucumber: The Plant That Explodes” by Animalogic. Exploding fruits.
- “Exploding Cucumbers! | Slo Mo #36 | Earth Unplugged” by BBC Earth Unplugged
- “Exploding myths about seed dispersal” by Stuart Gillespie
- “See the Plant Kingdom’s Hidden Microscopic Wonders” by Michael Greshko. Nice images of plants, see in particular the first image showing the cuticle coating on part of a moss and images 3 and 11 that show the interlocking nature of a plant epidermis (“skin”) cells as well as the stomates. And images 17 and 18 show the “glass houses” of diatoms.
- “The Formation and Function of Plant Cuticles” by Trevor H. Yeats, Jocelyn K.C. Rose. Good technical discussion of the plant cuticle.
- General Microbiology by Linda Bruslind. Good discussion on the membranes of archaea.
Media Attributions
- Diatoms © Mary Ann Tiffany, San Diego State University is licensed under a CC BY (Attribution) license
- Coccolithus pelagicus © Richard Lampitt, Jeremy Young, The Natural History Museum, London is licensed under a CC BY (Attribution) license
- Cell membrane detailed diagram © LadyofHats Mariana Ruiz is licensed under a Public Domain license
- Chitin, glucose, and cellulose © Arion422 is licensed under a CC BY-SA (Attribution ShareAlike) license
- Plant cell wall diagram © LadyofHats is licensed under a Public Domain license
- White Cliffs of Dover © Immanuel Giel is licensed under a CC BY-SA (Attribution ShareAlike) license


1.8 Types of Medications
There are a variety of drugs and substances that clients may utilize for symptom management or to enhance their wellness. Nurses document clients’ use of prescription medications, over-the-counter medications, herbal substances, and other supplements in the medical record. Some substances have a long half-life and have the potential to interact with new medications, so accuracy is vital. Ensuring an accurate medical record and knowledge of the different types of substances a client is taking is important for an effective nursing plan of care.
Prescription Medications
Drugs are prescribed by a licensed prescriber for a specific person’s use and regulated through the United States Food and Drug Administration (FDA). More information about FDA approval of medications is described in the “Legal/Ethical” chapter. Prescription medications include brand-name medications and generic medications.[1]
Common Prefixes, Suffixes, And Roots For Classes Of Medication
Table 1.8 provides prefixes, suffixes, and roots associated with common prescription medications. As a nurse, familiarizing yourself with the content in the table can help you to quickly organize medications based on their name and recall their mechanism of action and identify potential interactions or side effects. This knowledge can improve your ability to safely administer medications and provide health teaching. Ultimately, this knowledge can lead to improved client outcomes, increased satisfaction, and a reduced risk of adverse events and medication errors.
Table 1.8 Common Classes of Medications, Examples, Suffixes, and Roots
| Class of Medication | Example | Common Suffixes | Common Roots |
|---|---|---|---|
| Analgesics | lidocaine | -caine | -morph, -morphe, -morphic |
| Antacids | omeprazole | -azole | -tidine |
| Antibiotics | levofloxacin | -mycin, -floxacin | bacter-, vir-, -cidal |
| Anticoagulants | warfarin | -arin | coagul- |
| Antidepressants | fluoxetine | -oxetine, -ipramine | serotonin, norepinephrine |
| Antihistamines | diphenhydramine | -dine, -mine | hist- |
| Anti-inflammatory | cortisone | -one | -corti-, -flam-, -prost- |
| Antipsychotics | olanzapine | -azine, -apine | dopa-, sero-, -plegia |
| Beta-blockers | metoprolol | -olol | adrenergic, beta- |
| Bronchodilators | albuterol | -terol | bronch-, -pnea |
| Corticosteroids | prednisone | -sone or -solone | |
| Diuretics | furosemide | -semide, -thiazide | -uret-, -osm- |
| Hypoglycemics | glipizide | -ide | gluc-, insulin- |
| Statins | atorvastatin | -statin | cholesterol, lipid- |
Generic Medications
Generic medications can be safe and effective alternatives to their brand-name counterparts at a significantly reduced cost. By law, generic medications must have the same chemically active ingredient in the same dose as the brand name (i.e., they must be “bio-equivalent”). However, the excipients (the base substance that holds the active chemical ingredient into a pill form (such as talc) or the flavoring can be different. Some clients do not tolerate these differences in excipients very well. When prescribing a medication, the provider must indicate that a generic substitution is acceptable. Nurses are often pivotal in completing insurance paperwork on the client’s behalf if the brand-name medication is more effective or better tolerated by that particular client.[2]
When studying medications in nursing school and preparing for the NCLEX, it is important to know medications by their generic name because the NCLEX does not include brand names in their questions.
Over-the-Counter Medications
Over-the-counter (OTC) medications do not require a prescription. They can be bought at a store and may be used by multiple individuals. OTC medications are also regulated through the FDA. Some prescription medications are available for purchase as OTC in smaller doses. For example, diphenhydramine (Benadryl) is commonly prescribed as 50 mg every 6 hours, and the prescription strength is 50 mg. However, it can also be purchased OTC in 25 mg doses (or less for children.)[3]
Herbals and Supplements
Herbs and supplements may include a wide variety of substances including vitamins, minerals, enzymes, and botanicals. Supplements such as “protein powders” are marketed to build muscle mass and can contain a variety of substances that may not be appropriate for all individuals. Herbals and supplements are often considered complementary and alternative medications (CAM). Complementary and alternative medications (CAM) are types of therapies that are commonly used in conjunction with or as an alternate to traditional medical therapies. These herbal and supplement substances are not regulated by the FDA, and most have not undergone rigorous scientific testing for safety for the public. While clients may be tempted to try these herbals and supplements, there is no guarantee that they contain the ingredients listed on the label. It is also important to remember that there is a potential for adverse effects or even overdose if the herbal or supplement contains some of the same drug that was also prescribed to a client.[4] By understanding the use of CAM therapies, nurses can help their clients make informed decisions and take a holistic approach to their care. Additionally, being knowledgeable about CAM therapies can help nurses to better educate their clients on the potential benefits and risks associated with these therapies, which can help improve client outcomes and satisfaction.
Read additional information on complementary and alternative medicine at the National Center for Complementary and Integrative Health (NCCIH) Database.
- U.S. Food & Drug Administration. (2017, Nov. 13). Prescription drug and over the counter drugs: Questions and answers. https://www.fda.gov/drugs/questions-answers/prescription-drugs-and-over-counter-otc-drugs-questions-and-answers ↵
- U.S. Food & Drug Administration. (2018, June 19). Patient education. https://www.fda.gov/drugs/generic-drugs/patient-education ↵
- U.S. Food & Drug Administration. (2017, Nov. 13). Prescription drug and over the counter drugs: Questions and answers. https://www.fda.gov/drugs/questions-answers/prescription-drugs-and-over-counter-otc-drugs-questions-and-answers ↵
- U.S. Food & Drug Administration. (2017, Nov. 13). What are dietary supplements? https://www.fda.gov/food/information-consumers-using-dietary-supplements/tips-older-dietary-supplement-users#what ↵
Therapies that are commonly used in conjunction with or as an alternate to traditional medical therapies.