9.8: The Solar Interior - Observations
Learning Objectives
By the end of this section, you will be able to:
- Explain how the Sun pulsates
- Explain what helioseismology is and what it can tell us about the solar interior
- Discuss how studying neutrinos from the Sun has helped understand neutrinos
Recall that when we observe the Sun’s photosphere (the surface layer we see from the outside), we are not seeing very deeply into our star, certainly not into the regions where energy is generated. That’s why the title of this section—observations of the solar interior—should seem very surprising. However, astronomers have indeed devised two types of measurements that can be used to obtain information about the inner parts of the Sun. One technique involves the analysis of tiny changes in the motion of small regions at the Sun’s surface. The other relies on the measurement of the neutrinos emitted by the Sun.
Solar Pulsations
Astronomers discovered that the Sun pulsates—that is, it alternately expands and contracts—just as your chest expands and contracts as you breathe. This pulsation is very slight, but it can be detected by measuring the radial velocity of the solar surface—the speed with which it moves toward or away from us. The velocities of small regions on the Sun are observed to change in a regular way, first toward Earth, then away, then toward, and so on. It is as if the Sun were “breathing” through thousands of individual lungs, each having a size in the range of 4000 to 15,000 kilometers, each fluctuating back and forth (Figure \(\PageIndex{1}\)).
The typical velocity of one of the oscillating regions on the Sun is only a few hundred meters per second, and it takes about 5 minutes to complete a full cycle from maximum to minimum velocity and back again. The change in the size of the Sun measured at any given point is no more than a few kilometers.
The remarkable thing is that these small velocity variations can be used to determine what the interior of the Sun is like. The motion of the Sun’s surface is caused by waves that reach it from deep in the interior. Study of the amplitude and cycle length of velocity changes provides information about the temperature, density, and composition of the layers through which the waves passed before they reached the surface. The situation is somewhat analogous to the use of seismic waves generated by earthquakes to infer the properties of Earth’s interior. For this reason, studies of solar oscillations (back-and-forth motions) are referred to as helioseismology .
It takes a little over an hour for waves to traverse the Sun from center to surface, so the waves, like neutrinos, provide information about what the solar interior is like at the present time. In contrast, remember that the sunlight we see today emerging from the Sun was actually generated in the core several hundred thousand years ago.
Helioseismology has shown that convection extends inward from the surface 30% of the way toward the center; we have used this information in drawing \(16.3.6\) in Section 16.3. Pulsation measurements also show that the differential rotation that we see at the Sun’s surface, with the fastest rotation occurring at the equator, persists down through the convection zone. Below the convection zone, however, the Sun, even though it is gaseous throughout, rotates as if it were a solid body like a bowling ball. Another finding from helioseismology is that the abundance of helium inside the Sun, except in the center where nuclear reactions have converted hydrogen into helium, is about the same as at its surface. That result is important to astronomers because it means we are correct when we use the abundance of the elements measured in the solar atmosphere to construct models of the solar interior.
Helioseismology also allows scientists to look beneath a sunspot and see how it works. Sunspots are cool because strong magnetic fields block the outward flow of energy. Figure \(\PageIndex{2}\) shows how gas moves around underneath a sunspot. Cool material from the sunspot flows downward, and material surrounding the sunspot is pulled inward, carrying magnetic field with it and thus maintaining the strong field that is necessary to form a sunspot. As the new material enters the sunspot region, it too cools, becomes denser, and sinks, thus setting up a self-perpetuating cycle that can last for weeks.
The downward-flowing cool material acts as a kind of plug that block the upward flow of hot material, which is then diverted sideways and eventually reaches the solar surface in the region around the sunspot. This outward flow of hot material accounts for the paradox that the Sun emits slightly more energy when more of its surface is covered by cool sunspots.
Helioseismology has become an important tool for predicting solar storms that might impact Earth. Active regions can appear and grow large in only a few days. The solar rotation period is about 28 days. Therefore, regions capable of producing solar flares and coronal mass ejections can develop on the far side of the Sun, where, for a long time, we couldn’t see them directly.
Fortunately, we now have space telescopes monitoring the Sun from all angles, so we know if there are sunspots forming on the opposite side of the Sun. Moreover, sound waves travel slightly faster in regions of high magnetic field, and waves generated in active regions traverse the Sun about 6 seconds faster than waves generated in quiet regions. By detecting this subtle difference, scientists can provide warnings of a week or more to operators of electric utilities and satellites about when a potentially dangerous active region might rotate into view. With this warning, it is possible to plan for disruptions, put key instruments into safe mode, or reschedule spacewalks in order to protect astronauts.
Solar Neutrinos
The second technique for obtaining information about the Sun’s interior involves the detection of a few of those elusive neutrinos created during nuclear fusion. Recall from our earlier discussion that neutrinos created in the center of the Sun make their way directly out of the Sun and travel to Earth at nearly the speed of light. As far as neutrinos are concerned, the Sun is transparent.
About 3% of the total energy generated by nuclear fusion in the Sun is carried away by neutrinos. So many protons react and form neutrinos inside the Sun’s core that, scientists calculate, 35 million billion (\(3.5 × 10^{16}\)) solar neutrinos pass through each square meter of Earth’s surface every second. If we can devise a way to detect even a few of these solar neutrinos, then we can obtain information directly about what is going on in the center of the Sun. Unfortunately for those trying to “catch” some neutrinos, Earth and everything on it are also nearly transparent to passing neutrinos, just like the Sun.
On very, very rare occasions, however, one of the billions and billions of solar neutrinos will interact with another atom. The first successful detection of solar neutrinos made use of cleaning fluid (\(\ce{C2Cl4}\)), which is the least expensive way to get a lot of chlorine atoms together. The nucleus of a chlorine (Cl) atom in the cleaning fluid can be turned into a radioactive argon nucleus by an interaction with a neutrino. Because the argon is radioactive, its presence can be detected. However, since the interaction of a neutrino with chlorine happens so rarely, a huge amount of chlorine is needed.
Raymond Davis, Jr. (Figure \(\PageIndex{3}\)) and his colleagues at Brookhaven National Laboratory, placed a tank containing nearly 400,000 liters of cleaning fluid 1.5 kilometers beneath Earth’s surface in a gold mine at Lead, South Dakota. A mine was chosen so that the surrounding material of Earth would keep cosmic rays (high-energy particles from space) from reaching the cleaning fluid and creating false signals. (Cosmic-ray particles are stopped by thick layers of Earth, but neutrinos find them of no significance.) Calculations show that solar neutrinos should produce about one atom of radioactive argon in the tank each day.
This was an amazing project: they counted argon atoms about once per month—and remember, they were looking for a tiny handful of argon atoms in a massive tank of chlorine atoms. When all was said and done, Davis’ experiment, begun in 1970, detected only about one-third as many neutrinos as predicted by solar models! This was a shocking result because astronomers thought they had a pretty good understanding of both neutrinos and the Sun’s interior. For many years, astronomers and physicists wrestled with Davis’ results, trying to find a way out of the dilemma of the “missing” neutrinos.
Eventually Davis’ result was explained by the surprising discovery that there are actually three types of neutrinos. Solar fusion produces only one type of neutrino, the so-called electron neutrino, and the initial experiments to detect solar neutrinos were designed to detect this one type. Subsequent experiments showed that these neutrinos change to a different type during their journey from the center of the Sun through space to Earth in a process called neutrino oscillation .
An experiment, conducted at the Sudbury Neutrino Observatory in Canada, was the first one designed to capture all three types of neutrinos (Figure \(\PageIndex{4}\) ). The experiment was located in a mine 2 kilometers underground. The neutrino detector consisted of a 12-meter-diameter transparent acrylic plastic sphere, which contained 1000 metric tons of heavy water. Remember that an ordinary water nucleus contains two hydrogen atoms and one oxygen atom. Heavy water instead contains two deuterium atoms and one oxygen atom, and incoming neutrinos can occasionally break up the loosely bound proton and neutron that make up the deuterium nucleus. The sphere of heavy water was surrounded by a shield of 1700 metric tons of very pure water, which in turn was surrounded by 9600 photomultipliers, devices that detect flashes of light produced after neutrinos interact with the heavy water.
To the enormous relief of astronomers who make models of the Sun, the Sudbury experiment detected about 1 neutrino per hour and has shown that the total number of neutrinos reaching the heavy water is just what solar models predict. Only one-third of these, however, are electron neutrinos. It appears that two-thirds of the electron neutrinos produced by the Sun transform themselves into one of the other types of neutrinos as they make their way from the core of the Sun to Earth. This is why the earlier experiments saw only one-third the number of neutrinos expected.
Although it is not intuitively obvious, such neutrino oscillations can happen only if the mass of the electron neutrino is not zero. Other experiments indicate that its mass is tiny (even compared to the electron). The 2015 Nobel Prize in physics was awarded to researchers Takaaki Kajita and Arthur B. McDonald for their work establishing the changeable nature of neutrinos. (Raymond Davis shared the 2002 Nobel Prize with Japan’s Masatoshi Koshiba for the experiments that led to our understanding of the neutrino problem in the first place.) But the fact that the neutrino has mass at all has deep implications for both physics and astronomy. For example, we will look at the role that neutrinos play in the inventory of the mass of the universe in The Big Bang.
The Borexino experiment, an international experiment conducted in Italy, detected neutrinos coming from the Sun that were identified as coming from different reactions. Whereas the p-p chain is the reaction producing most of the Sun’s energy, it is not the only nuclear reaction occurring in the Sun’s core. There are side reactions involving nuclei of such elements as beryllium and boron. By probing the number of neutrinos that come from each reaction, the Borexino experiment has helped us confirm in detail our understanding of nuclear fusion in the Sun. In 2014, the Borexino experiment also identified neutrinos that were produced by the first step in the p-p chain, confirming the models of solar astronomers.
It’s amazing that a series of experiments that began with enough cleaning fluid to fill a swimming pool brought down the shafts of an old gold mine is now teaching us about the energy source of the Sun and the properties of matter! This is a good example of how experiments in astronomy and physics, coupled with the best theoretical models we can devise, continue to lead to fundamental changes in our understanding of nature.
Key Concepts and Summary
Studies of solar oscillations (helioseismology) and neutrinos can provide observational data about the Sun’s interior. The technique of helioseismology has so far shown that the composition of the interior is much like that of the surface (except in the core, where some of the original hydrogen has been converted into helium), and that the convection zone extends about 30% of the way from the Sun’s surface to its center. Helioseismology can also detect active regions on the far side of the Sun and provide better predictions of solar storms that may affect Earth. Neutrinos from the Sun call tell us about what is happening in the solar interior. A recent experiment has shown that solar models do predict accurately the number of electron neutrinos produced by nuclear reactions in the core of the Sun. However, two-thirds of these neutrinos are converted into different types of neutrinos during their long journey from the Sun to Earth, a result that also indicates that neutrinos are not massless particles.
Glossary
- helioseismology
- study of pulsations or oscillations of the Sun in order to determine the characteristics of the solar interior
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 ).


1.3: Chapter 3 – Business Models
Learning Objectives
After completing this chapter, you will be able to
- Describe what a business model is
- Analyze existing and proposed businesses to determine what business models they are applying and what business models they plan to apply
- Develop and analyze alternative business models for new entrepreneurial ventures
Overview
In this chapter the concept of the business model is introduced. One concept of the business model in particular, the Business Model Canvas, is explored as a way to conceptualize and categorize elements of a business model.
Figure 5 – Business Model (Illustration by Lee A. Swanson)
What are Business Models?
Magretta (2002) described business models as “stories that explain how enterprises work” (p. 87) and Osterwalder, Pigneur, and Clark (2010) noted that they reveal “the rationale of how an organization creates, delivers, and captures value” (p. 14). Chatterjee (2013) said that “A business is about selling what you make for a profit. A business model is a configuration (activity systems) of what the business does (activities) and what it invests in (resources) based on the logic that drives the profits for a specific business” (p. 97).
Osterwalder et al. (2010) said that a start-up is something quite different than an ongoing venture. A start-up should not be viewed as a smaller version of a company because it requires very different skills to start up a company than it does to operate one. A start-up that is still a start-up after some time has passed—maybe after a couple of years for some kinds of start-ups—is actually a failed enterprise since it hasn’t converted into an ongoing venture. Entrepreneurs who develop a business model for their ventures that deliver value to the targeted customers and to the entrepreneur stand a better chance of converting their start-up into an ongoing venture.
The Business Model Canvas
The business model canvas is made up of nine parts that, together, describe the business model (see Figure 6).
Figure 6 – Business Model Canvas from https://strategyzer.com/ (Designed by: Strategyzer AG, strategyzer.com, Creative Commons Attribution-Share Alike 3.0 Unported License)
The following elements of the Business Model Canvas were taken, with permission, from http://www.businessmodelgeneration.com .
-
Key partners
- Who are our key partners?
- Who are our key suppliers?
- Which key resources are we acquiring from partners?
- Which key activities do partners perform?
- Motivations for partnerships: optimization and economy; reduction of risk and uncertainty; acquisition of particular resources and activities
-
Key activities
- What key activities do our value propositions require?
- Our distribution channels?
- Customer relationships?
- Revenue streams?
- Categories: production; problem solving; platform/network
-
Key resources
- What key resources do our value propositions require?
- Our distribution channels?
- Customer relationships?
- Revenue streams?
- Types of resources: physical; intellectual (brand patents, copyrights, data); human; financial
-
Value propositions
- What value do we deliver to the customer?
- Which one of our customer’s problems are we helping to solve?
- What bundles of products and services are we offering to each customer segment?
- Which customer needs are we satisfying?
- Characteristics: newness; performance; customization; “getting the job done”; design; brand/status; price; cost reduction; risk reduction; accessibility; convenience/usability
-
Customer relationships
- What type of relationship does each of our customer segments expect us to establish and maintain with them?
- Which ones have we established?
- How are they integrated with the rest of our business model?
- How costly are they?
- Examples: personal assistance; dedicated personal assistance; self-service; automated services; communities; co-creation
-
Customer segments
- For whom are we creating value?
- Who are our most important customers?
- Mass market; niche market; segmented; diversified; multi-sided platform
-
Channels
- Through which channels do our customer segments want to be reached?
- How are we reaching them now?
- How are our channels integrated?
- Which ones work best?
- Which ones are most cost-efficient?
- How are we integrating them with customer routines?
-
Channel phases:
- awareness – How do we raise awareness about our company’s products and services?
- evaluation – How do we help customers evaluate our organization’s value proposition?
- purchase – How do we allow customers to purchase specific products and services?
- delivery – How do we deliver a value proposition to customers?
- after sales – How do we provide post-purchase customer support?
-
Revenue streams
- For what value are our customers really willing to pay?
- For what do they currently pay?
- How are they currently paying?
- How would they prefer to pay?
- How much does each revenue stream contribute to overall revenues?
- Types: asset sale; usage fee; subscription fees; lending/renting/leasing; licensing; brokerage fees; advertising
- Fixed pricing: list price; product feature dependent; customer segment dependent; volume dependent
- Dynamic pricing: negotiation (bargaining); yield management; real-time-market
-
Cost structure
- What are the most important costs inherent in our business model?
- Which key resources are most expensive?
- Which key activities are most expensive?
- Is our business more cost driven (leanest cost structure, low price value proposition, maximum automation, extensive outsourcing) or value driven (focused on value creation, premium value proposition)?
- Sample characteristics: fixed costs (salaries, rents, utilities); variable costs; economies of scale; economies of scope
The idea is to keep adding descriptions or plans to the nine components to create the initial business model and then to actually do the start-up activities and replace the initial assumptions in each of the nine parts with newer and better information or plans and let the business model evolve. This model is partly based on the idea that the owner should be the one interacting with potential customers so they fully understands what these potential customers want. These interactions should not only be done by hired sales people, at least until the business model has evolved into one that works, because this evolution can only happen when the venture owner is completely engaged with the potential customers and the other business operations (Osterwalder et al., 2010).
A business plan shouldn’t be created until the above has been done because you need to know what your business model is before you can really create a business plan (Osterwalder et al., 2010). Thus, the Business Model Canvas is best suited to technology-based and other types of companies that can be started and operated in some way and later converted into an ongoing venture. By starting operations and making adjustments as you go along, you are actually doing a form of market research that can be compiled into a full business plan when one is needed.
According to Osterwalder et al. (2010), the things we typically teach people in business school are geared to helping people survive in larger, ongoing businesses. What is taught—including organizational structures, reporting lines, managing sales teams, advertising, and similar topics—is not designed to help students understand how a start-up works and how to deal with the volatile nature of new ventures. The Business Model Canvas tool is meant to help us understand start-ups better.
The Business Model Canvas tool is intended to be applied when business operations can be started on a small scale and adjustments can be made continually until the evolving business model works in real life. This contrasts the more traditional approach of pre-planning everything, going through the set-up and start-up processes, and ending up with a business venture that opens for business one day without having proven at all that the business model it is founded upon will even work. These traditional start-ups sometimes flounder along as the owners find that their plans are not quite working out and they try to make adjustments on the fly. It can be difficult to adjust, though, because the processes are already set up. For example, sales teams might be in the field trying to make sales and blaming the product developers for the difficulty they are having, and the product developers might be blaming the sales teams for not being able to sell the product properly. The real issue might be that the company simply isn’t meeting customers’ needs and they don’t have any good mechanism for detecting, understanding, and fixing this problem.


11.5B: Functions of the Cerebellum
Cerebellar function was once believed to be motor-specific, but newer findings suggest the cerebellum is also involved in higher-level brain processing.
- Describe the function of the cerebellum
Key Points
-
The cerebellum is essential for making fine adjustments to motor actions.
Cerebellar dysfunction primarily results in problems with motor control. - Four principles are important to cerebellar processing: feedforward processing, divergence and convergence, modularity, and plasticity.
- Signal processing in the cerebellum is almost entirely feedforward. Signals move through the system from input to output with very little internal transmission.
- The cerebellum both receives input and transmits output via a limited number of cells.
- The cerebellar system is divided into thousands of independent modules with similar structure.
Key Terms
- neural divergence : When a neuron fires and the signal is sent to many other neurons.
- neuroplasticity : Changes in neural pathways and synapses due to changes in behavior, environment, neural processes, or bodily injury.
- feedforward processing : A property of some neural circuits where signals move unidirectionally through the system from input to output with very little recurrent internal transmission.
Examining the consequences of damage to the the cerebellum provides the strongest clues to its function. Animals and humans with cerebellar dysfunction show problems with motor control. They can still generate motor activity, but lose precision and produce erratic, uncoordinated, or incorrectly timed movements. Functional imaging studies have also shown cerebellar activation in relation to language, attention, and mental imagery. Additionally, correlation studies have shown interactions between the cerebellum and non-motor areas of the cerebral cortex.
Principles of Cerebellar Function
The comparative simplicity and regularity of the cerebellar anatomy led to an early hope that a similar simplicity of computational function could be implied. This was expressed in one of the first books on cerebellar electrophysiology, The Cerebellum as a Neuronal Machine by John C. Eccles, Masao Ito, and Janos Szentágothai. Although a full understanding of cerebellar function has remained elusive, at least four principles have been identified as important: feedforward processing, divergence and convergence, modularity, and plasticity.
- Feedforward processing: The cerebellum differs from other parts of the brain (especially the cerebral cortex) in that the signal processing is almost entirely feedforward. This means signals move unidirectionally through the system from input to output with very little recurrent internal transmission. The small amount of recurrence that does exist consists of mutual inhibition. There are no mutually excitatory circuits. This feedforward mode of operation means that the cerebellum, in contrast to the cerebral cortex, cannot generate self-sustaining patterns of neural activity. Signals enter the circuit, are processed by each stage in sequential order, and then leave. This provides a quick, concise response to any combination of inputs.
- Divergence and convergence: In the human cerebellum, information from 200 million mossy fiber inputs is expanded to 40 billion granule cells. This neural divergence is followed by parallel fiber outputs that converge onto 15 million Purkinje cells. Due to their longitudinal alignment, the approximately 1000 Purkinje cells belonging to a microzone may receive input via neural convergence from as many as 100 million parallel fibers. The cells then focus their own output down to a group of less than 50 deep nuclear cells. Therefore, the cerebellar network only receives a modest number of inputs to process and send results via a limited number of output cells.
- Modularity: The cerebellar system is functionally divided into thousands of independent modules. All modules have a similar internal structure but different inputs and outputs. A module consists of a small cluster of neurons in the inferior olivary nucleus, a set of long narrow strips of Purkinje cells in the cerebellar cortex (microzones), and a small cluster of neurons in one of the deep cerebellar nuclei. Different modules share input, but also appear to function independently. The output of one module does not seem to significantly influence the activity of other modules.
- Plasticity: The synapses between parallel fibers and Purkinje cells and between mossy fibers and deep nuclear cells are both susceptible to modification of their strength. In a single cerebellar module, input from as many as a billion parallel fibers converge onto a group of less than 50 deep nuclear cells, and the influence of each parallel fiber on those nuclear cells is adjustable. This arrangement gives tremendous flexibility for fine-tuning the relationship between cerebellar inputs and outputs.
Role of the Cerebellum in Motor Learning
There is considerable evidence that the cerebellum plays an essential role in some types of motor learning, most clearly in tasks in which fine adjustments must be made to an action’s performance. There has been much dispute about whether learning takes place within the cerebellum itself, or whether it merely serves to provide signals that promote learning in other brain structures.
One of the most extensively studied cerebellar learning tasks is the eyeblink conditioning paradigm. A blink response is elicited when a neutral conditioned stimulus, such as a tone or a light, is repeatedly paired with an unconditioned stimulus, such as an air puff.
After many conditioned-unconditioned stimuli (CS-US) pairings, an association is formed whereby a learned blink, or conditioned response, occurs and precedes US onset. The magnitude of learning is measured by the percentage of all paired CS-US trials that result in a CR.
Experiments showed that lesions localized either to a specific part of the interpositus nucleus (one of the deep cerebellar nuclei), or to a few specific points in the cerebellar cortex, abolished learning of a correctly timed blink response. If cerebellar outputs are pharmacologically inactivated while leaving the inputs and intracellular circuits intact, learning takes place even while the animal fails to show any response. However, if intracerebellar circuits are disrupted, no learning takes place; these facts taken together make a strong case that learning occurs inside the cerebellum and that its cells exhibit neuroplasticity.
Clinical Relevance
Motor abnormalities are the primary symptoms of cerebellar dysfunction, and the nature of those depends on the part of the cerebellum affected.
EXAMPLE SYMPTOMS OF CEREBELLAR DYSFUNCTION
-
Damage to the flocculonodular lobe (vestibulocerebellum): loss of equilibrium causing an altered
walking gait -
Lateral zone damage: problems with skilled voluntary and planned movements leading to errors in intended movements (eg., dysdiadochokinesia, the inability to perform rapid
alternating movements). - Damage to the midline portion: disruption of whole-body movements
-
Damage to the upper part of the cerebellum: gait impairments and other problems with
leg coordination (ie, ataxia).
LICENSES AND ATTRIBUTIONS
CC LICENSED CONTENT, SHARED PREVIOUSLY
- Curation and Revision. Authored by : Boundless.com. Provided by : Boundless.com. License : CC BY-SA: Attribution-ShareAlike
CC LICENSED CONTENT, SPECIFIC ATTRIBUTION
- Cerebellum. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Cerebellum . License : CC BY-SA: Attribution-ShareAlike
- Purkinje cells. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Purkinje%20cells . License : CC BY-SA: Attribution-ShareAlike
- granule cells. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/granule%20cells . License : CC BY-SA: Attribution-ShareAlike
- cerebellum. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/cerebellum . License : CC BY-SA: Attribution-ShareAlike
- Gray706. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Gray706.png . License : Public Domain: No Known Copyright
- cerebellum.png. Provided by : Wikipedia commons. Located at : commons.wikimedia.org/wiki/File%3ASobo_1909_624.png . License : Public Domain: No Known Copyright
- CerebellumDiv. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:CerebellumDiv.png . License : Public Domain: No Known Copyright
- Eyeblink Conditioning. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Eyeblink_conditioning . License : CC BY-SA: Attribution-ShareAlike
- Cerebellum. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Cerebellum%23Function . License : CC BY-SA: Attribution-ShareAlike
- neural divergence. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/neural%20divergence . License : CC BY-SA: Attribution-ShareAlike
- neuroplasticity. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/neuroplasticity . License : CC BY-SA: Attribution-ShareAlike
- feedforward processing. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/feedforward%20processing . License : CC BY-SA: Attribution-ShareAlike
- Gray706. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Gray706.png . License : Public Domain: No Known Copyright
- cerebellum.png. Provided by : Wikipedia commons. Located at : commons.wikimedia.org/wiki/File%3ASobo_1909_624.png . License : Public Domain: No Known Copyright
- CerebellumDiv. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:CerebellumDiv.png . License : Public Domain: No Known Copyright


5.2: Acclimation and Adaptation
Species respond to environmental stressors through acclimation and adaptation. The distinction between the two is important; though they are linked, they operate at very different scales and with different short-term and long-term ramifications. Acclimation occurs when an individual organism experiences a change in its phenotype in response to an environmental stressor. This change is reversible and occurs very rapidly, sometimes in as little as a few minutes. Adaptation occurs when a population experiences a change in its genotype in response to an environmental stressor. This change occurs much more slowly, usually across many generations, and is a result of natural selection.
For example, imagine you set out to hike to the summit of Mt. Whitney in California’s Sequoia National Park . The peak is approximately 14,505 feet (~4420 meters) in elevation; high enough that the air is much thinner at the top (Fig 5.2.1) and therefore your lungs will struggle to obtain the oxygen necessary for you to breathe. As you hike higher and higher in elevation, your body will acclimate by producing more hemoglobin.  In this example, the concentration of hemoglobin in your blood is the phenotype that changes in response to the environmental stressor of reduced oxygen availability. When you hike down to lower elevations, the hemoglobin concentrations in your blood will return to normal.
Now consider the long-term impacts on a population of humans that live at very high elevations for many generations. The Tibetan Plateau, for example, has an average elevation of approximately 14,800 feet (~4500 meters) and has been inhabited by humans for possibly as long as 30,000 years. Genetic comparisons performed by Yi et al (2010) between Tibetan Plateau populations and their close relatives, the Han Chinese revealed differences between these groups in the frequency of different alleles for a gene called EPAS1. At this gene, both populations contained a particular allele that increases the production of cells called erythrocytes (which contain hemoglobin) in the blood; however, this allele was 78% more common in the high-elevation Tibetan population. In this case, differences in the frequency of EPAS1 alleles between these two populations represent an adaptation to long-term exposure to the environmental stressor of reduced oxygen availability. We will discuss alleles and their frequencies in different populations of organisms more in the inheritance sections.
In the following sections, we will discuss acclimational and adaptational responses to abiotic (temperature) and biotic (predator/prey interactions) stressors.


7.2.19: Essay (Usable with Best Practices)
Query \(\PageIndex{1}\)
Overall Usability
Usable with Best Practices:
- The activity requires minimal adjustments by content authors.
Important Reminders
Use best practices for content authoring, including:
- Provide a correctly structured heading at the beginning of the activity
- Provide users with instructions that describe the Show solution button and the Retry button icons for users who require magnification.
Visible Indication of Focus
The activity buttons and form fields have a visible indication of focus.
Color Contrast
The visible indication of focus does not have good contrast. The visible indication of focus is a thin black line. Users who require a visible indication of focus with more contrast may use assistive technology.
Keyboard Usability
The activity is usable with the keyboard.
No Keyboard Traps
There are no keyboard traps.
Magnification
Content magnifies up to 200% using browser settings without loss of content or functionality. The Feedback text is partially obscured when the activity is magnified up to 400%. The Show solution button and the Retry button text is not visible at 400% and the tooltip for the buttons do not magnify.
An alternative version of the activity may need to be included that supports magnification up to 400% without requiring horizontal scrolling to view content and interact with content.
Usability with Screen Reading Software
The activity is usable with screen reading software.


3.3: Objections
This is the final skill in argument mapping that we’ll discuss. It’s very important to be aware of because without it we can only ever map parts of a discussion which agree with one another. Meaning that if someone has an objection to an argument, we won’t be able to pinpoint where the disagreement is on our argument maps. Our argument maps are more expressive and powerful if we can diagram disagreements as well as agreements, so let’s discuss how to map disagreements!
We need to have a tool to map objections to an argument that we’ve already mapped so we can see where those objections are “putting pressure” or what exactly they’re trying to critique.
We use either hashed arrows or dotted arrows to signify relations of objection. They mean “objects to” or “rejects”.
These are the only arrows in our system which point up.
There are two kinds of objections:
1. Objections to a proposition
-
Analyst A: (1) Building this highway would threaten the existence of the species of fairy shrimp that inhabits the proposed route, so (2) we must reroute the highway.
Analyst B: I understand your concern for the fairy shrimp, but (3) the proposed route is not the only habitat for the fairy shrimp in this area, so it wouldn’t threaten their existence.
Note that the arrow is pointing to the Premise.
2. Objections to an inference
- Obama said that (1) people who were brought here illegally as children shouldn’t be punished for the choices of their parents, because (2) their parents made the decision and not them. But that doesn’t follow because (3) we’re not punishing them, instead we’re just enforcing our laws.
Note that the arrow is pointing to the other Arrow.
Could have also used a dotted arrow.
Diagramming Tip
Here’s a weird case, so that you can see what sorts of situations you might get into when trying to map objections:
Notice how objection 7 has to cross over an inference to point to the inference from 3 to 1. That’s okay. But it helps to keep your argument maps a bit larger and as clear as possible. You want to be able to clearly decipher what’s going on in the argument map as you go along.


4.2.3: The Environmental Protection Agency
The U.S. Environmental Protection Agency (EPA) plays a significant role in public health by addressing environmental issues and hazards that can impact the well-being of the American population. The EPA's responsibilities related to public health include:
- Regulating Air Quality: The EPA sets and enforces national air quality standards to reduce the levels of harmful pollutants, such as particulate matter, ground-level ozone, sulfur dioxide, and nitrogen oxides. By reducing air pollution, the EPA helps lower the risk of respiratory and cardiovascular diseases, asthma, and other health problems associated with poor air quality.
- Safe Drinking Water: The EPA establishes and enforces regulations for the safety of drinking water supplies in the United States. This includes setting standards for contaminants in drinking water and ensuring that public water systems comply with these standards, thereby reducing the risk of waterborne diseases and exposure to harmful chemicals.
- Toxic Substances Control: The EPA regulates and assesses the risks of toxic substances and hazardous chemicals in the environment. This includes evaluating the potential health risks associated with exposure to these substances and taking measures to reduce or mitigate these risks.
- Waste Management and Cleanup: The EPA oversees the management and cleanup of hazardous waste sites and chemical spills to protect public health from exposure to toxic materials. This work helps prevent contamination of soil, water, and air in affected areas.
- Lead Poisoning Prevention: The EPA is involved in lead poisoning prevention efforts, such as enforcing regulations related to lead-based paint in homes and public facilities. Reducing lead exposure is vital for preventing developmental and health problems, particularly in children.
- Environmental Justice: The EPA addresses environmental disparities and injustices by ensuring that all communities, regardless of their socioeconomic status or demographic makeup, have equal protection from environmental hazards. This promotes public health equity.
- Research and Data Collection: The EPA conducts research and collects data to better understand the health impacts of environmental factors. This research informs policy decisions and public health recommendations.
- Emergency Response: The EPA plays a role in responding to environmental emergencies, such as chemical spills, natural disasters, and acts of terrorism, to minimize public health risks associated with these incidents.
- Public Education and Outreach: The EPA conducts public education and outreach efforts to raise awareness of environmental health issues, inform the public about risks, and provide guidance on ways to reduce exposure to environmental hazards.
By addressing these and other environmental concerns, the EPA contributes to protecting public health, reducing the incidence of environmentally related diseases, and improving overall well-being. Its work is critical for safeguarding the health and safety of the American population and ensuring that people have access to clean air, safe drinking water, and a healthy environment.


10.4: Born-Haber Cycles for NaCl and Silver Halides
-
- Last updated
- Save as PDF
Now that we have an equation for the lattice energy of an ionic crystal, we can ask the question of how accurate it is. Remember, we made several approximations in arriving at this formula. We assumed that the lattice was completely ionic, we ignored the van der Waals attractive energy of the ions, and we assumed that there was no covalent contribution to the bonding.
Let's consider the lattice energy of table salt (NaCl)
\(\ce{Na^{+}_{(g)} + Cl^{-}_{(g)} -> NaCl_{(s)}}\)
To calculate the lattice energy, we lump together the physical constants:
\[E_{L} (\frac{kJ}{mol}) = (1389.3) \frac{Aq_{1}q_{2}}{r_{o}}(1-\frac{.345}{r_{o}})\]
where r o is expressed in Å. Now we can calculate the lattice energy for NaCl using r o = 2.814 Å, as:
\[E_{L} = -(1389.3) \frac{1.7476}{2.814} (1 -\frac{.345}{2.814}) = -766.5 \frac{kJ}{mol}\]
We can alternatively construct a Born-Haber cycle for the formation of NaCl from the elements and calculate the lattice energy as the "missing" term in the cycle.
S= Sublimation energy of Na(s)
IP= Ionization potential of Na(g)
D= Bond dissocation energy of Cl 2 (g)
EA= Electron affinity of Cl(g)
E L =Lattice energy of NaCl
R= Gas constant
T= Absolute temperature
From Hess' Law: \(\Delta H_{f} = s + \frac{1}{2}D + IP + EA + E_{L} -2RT = \mathbf{-396 \frac{kJ}{mol}}\)
Here we have to subtract 2RT to convert our cycle of energies to a cycle of enthalpies, because we are compressing two moles of gas in making NaCl(s) and PΔV = ΔnRT, where Δn = -2.
Experimentally ΔH f for NaCl is -411 kJ/mol
Because all the other numbers in the cycle are known accurately, the error in our calculation is only about 15 kJ (about 2% of E L ). The result is promising because we neglected the van der Waals term.
But....how did we get away with neglecting the van der Waals term?
This is because we used energy minimization to obtain the repulsion energy in the Born-Mayer equation. If we underestimate the attractive energy of the crystal lattice, the energy minimization criterion ensures that the repulsion energy is underestimated as well. The two errors partially compensate, so the overall error in the calculation is small.
We can do better by explicitly including the short-range van der Waals attractive energy between ions. The table below shows results of more detailed lattice energy calculations for ionic fluorides in which the van der Waals term is explicitly included. The errors in this case are only about 1% of E L .
| Compound | Calculated Lattice Energy (kJ/mol) | Experimental E L from Born-Haber Cycle |
|---|---|---|
| MgF 2 (rutile structure) | -2,920 | -2,908 |
| CaF 2 (fluorite structure) | -2,586 | -2,611 |
| BaF 2 (fluorite structure) | -2,326 | -2,368 |
Silver Halides
It is interesting to repeat this exercise for the silver halides, which have either the NaCl structure (AgF, AgCl, AgBr) or zincblende structure (AgI).
| Silver Halide | Calculated | Cycle | Difference (kJ/mol) |
|---|---|---|---|
| AgF | -920 | -954 | 34 |
| AgCl | -833 | -908 | 75 |
| AgBr | -816 | -900 | 84 |
| AgI | -778 | -883 | 105 |
Looking at the table, we see that the error is small for AgF and becomes progressively larger for the heavier silver halides. However we are still obtaining answers within about 12% error even for AgI. Should we interpret the good agreement with values calculated from the ionic model to mean that these compounds are ionic? Clearly, this description is inappropriate for AgI, where the electronegativity difference Δχ is only 0.6 (compare this value to 0.4 for a C-H bond, which we typically view as non-polar).
|
A drop of siver nitrate solution, when added to a dilute hydrochloric acid solution, results in the immediate formation of a white silver chloride precipitate. This reaction is used as a qualitative test for the presence of halide ions in solutions. The covalent bonding contribution to the lattice energies of AgCl, AgBr, and AgI makes these salts sparingly soluble in water. |
Again, we can interpret the fortuitous agreement between the calculated and experimentally obtained energies in terms of compensating errors. Our lattice energy calculation overestimates the ionic contribution in the case of the heavier silver halides, but underestimates the covalent contribution. Of these compounds, only AgF is soluble in water and should be thought of as an ionic compound. The others are progressively more insoluble in water (K sp is 10 -10 , 10 -13 , and 10 -16 for AgCl, AgBr, and AgI), reflecting increasing covalency as Δχ decreases.
The moral of the story is that simple lattice energy calculations based on the ionic model work well, but they do not necessarily imply that the compounds are ionic !


14.5: Learning Activities
Learning Activities
(Answers to “Learning Activities” can be found in the “Answer Key” at the end of the book. Answers to interactive activity elements will be provided within the element as immediate feedback.)
Scenario 1
Mr. Jones is a 67-year-old patient on the medical surgical floor who recently underwent a bowel resection. He is post-op Day 2 and has been NPO since surgery. He has been receiving IV fluids but has been asking about when he can resume eating.
- What assessments should be performed to determine if the patient’s diet can be progressed?
- What are the first steps during dietary transition from NPO status?
Scenario 2 [1]
Mrs. Casey is a 78 year-old widow who recently had a stroke and continues to experience mild right-sided weakness. See Figure 14.14 for an image of Mrs. Casey. [2] She is currently receiving physical therapy in a long-term care facility and ambulates with the assistance of a walker. Mrs. Casey confides, “I am looking forward to going home, but I will miss the three meals a day here.”
Her height is 5’2″ and she weighs 84 pounds. Her recent lab work results include the following:
Hgb: 8.8 g/dL, WBC 3500, Magnesium 1.4 mg/dL, Albumin 10 g/dL
- What is Mrs. Casey’s BMI and what does this number indicate?
- Analyze Mrs. Casey’s recent lab work and interpret the findings.
- Describe focused assessments the nurse should perform regarding Mrs. Casey’s nutritional status.
- Create a PES nursing diagnosis statement for Mrs. Casey based on her nutritional status.
- Create a SMART outcome statement for Mrs. Casey.
- Outline planned nutritional interventions for Mrs. Casey while she is at the facility, as well as when she returns home.
- How will you evaluate if your nursing care plan is successful for Mrs. Casey?
Query \(\PageIndex{2}\)
Query \(\PageIndex{3}\)
Query \(\PageIndex{4}\)
- " woman-1031000_960_720.jpg " by Free-Photos is licensed under CC0 ↵
- " woman-1031000_960_720.jpg " by Free-Photos is licensed under CC0 ↵


1.6: Mitosis and Meiosis II
Introduction to Mitosis
In eukaryotic cells, the time and phases from the beginning of one cell division until the beginning of the next cell division is called the cell cycle (Figure 1) . The first phase of the cell cycle is interphase. Interphase is the time during which the cell performs its normal functions and prepares for cell division. Cells spend most of their time in this phase. During interphase, chromosomes are not visible because they are decondensed (present only as a tangled mass of thin threads of DNA with associated proteins, called chromatin). The nuclear membrane is present, and visible, as is the nucleolus .
Figure 1. The cell cycle.
Interphase includes two gap phases, G1 and G2, where the cell increases in size and synthesizes new organelles, enzymes, and other proteins that are needed for cell division. In between the two gap phases, the DNA replicates in preparation for cell division. This stage is called the S phase . At the beginning of S phase, chromosomes are single and unreplicated. By the end of S phase, each chromosome has made an exact copy of itself and consists of two sister chromatids . At this point in the cell cycle the sister chromatids are held together tightly at the centromere . While the two sister chromatids are physically joined together they are still considered one replicated chromosome (Figure 2). When the sister chromatids physically separate, later during the cell cycle, they are then considered to be individual chromosomes.
In animal cells, interphase is also when the centrosome (consisting of two centrioles ) is replicated. Spindle fibers form from and radiate outward from the centrosomes to attach to and move chromosomes during cell division.
Figure 2. Chromosomes and sister chromatids.
Interphase is followed by mitosis (in the somatic cells) or meiosis (in reproductive cells), which is when replicated chromosomes and cytoplasm separate, during the process of karyokinesis and cytokinesis respectively.
Chromosomes that are the same length, have the same centromere location and the same gene sequences and positions are called homologous chromosomes. Human somatic cells contain pairs of homologous chromosomes. Each homologous pair consists of one maternal chromosome and one paternal chromosome. Cells that contain two copies of each chromosome are called diploid (2n, where n is the number of different chromosomes in a single set). Human sex cells (eggs and sperm) contain only one copy of each chromosome. Cells with only one copy of each chromosome are haploid (n). When the haploid sperm (n) and egg (n) combine during fertilization this forms a diploid zygote (2n).
MITOSIS
Mitosis is nuclear division that results in two cells containing the same number of chromosomes as the parent cell. Most human cells (skin, muscle, bone, etc.) divide by mitosis. This process is necessary for the normal growth and development of a multicellular eukaryotic organism from a zygote (fertilized egg), as well as growth and the repair and replacement of cells and tissues. At the end of mitosis, two daughter cells are formed that are identical to the original (parent) cell. Mitosis is also a form of asexual reproduction in unicellular eukaryotes.
Mitosis is a complex and highly regulated process. It occurs in the following 4 separate phases: prophase, metaphase, anaphase, and telophase. Telophase is quickly followed by cytokinesis.
Prophase: Cells prepare for division by coiling and condensing their chromatin into chromosomes. By late prophase, individual chromosomes can be seen, each consisting of two sister chromatids joined at a centromere. Spindle fibers begin to form from the centrosomes, which have begun to migrate to opposite “poles” of the cell. The nucleoli and the nuclear membrane degrade. (Figure 3)
Figure 3. Cell in prophase
Metaphase: Spindle fibers (called kinetochore microtubules or kinetochore spindle fibers) that emanate from the centromeres attach to the kinetochore (a proteinaceous area) on the sister chromatids. The fibers pull and otherwise manipulate the chromosomes to align them on the plane that passes through the center of the cell (metaphase plate) (Figure 4). This “plate” is not an actual structure; it merely signifies the location of replicated chromosomes prior to their impending separation.
Other non-kinetochore spindle fibers or tubules (aka polar microtubules), emanating from the two centrosomes, elongate and eventually overlap with each other near the metaphase plate.
Figure 4. Spindle fibers attaching to kinetochores in metaphase.
Anaphase: The centromeres divide, with the help of separase enzymes, and separate the sister chromatids (Figure 5). This happens simultaneously in all the chromosomes. The kinetochore spindles shorten and pull each chromatid to which they are attached toward the pole (and centrosome) from which they originate. This equally distributes exactly half the chromosomal material to each side of the cell. In late anaphase, the non-kinetochore spindles begin to elongate, lengthening the cell.
Figure 5. Cell in anaphase.
Telophase: The non-kinetochore microtubules continue to elongate, further elongating the cell in preparation for cytokinesis (splitting of the cytoplasm). The chromosomes reach their respective poles. The kinetochores disappear. The two nuclear membranes (one in each half of the cell) begin to form around the chromosomes. Nucleoli reappear and the chromosomes in each soon-to-be new cell begin to decondense back into chromatin. Mitosis is complete at the end of this stage.
Cytokinesis (splitting of the cytoplasm):
In animal cells and all other eukaryotes without a cell wall, cytokinesis is achieved by means of a constricting “belt” of protein fibers that slide past each other near the equator of the cell. As this occurs, the diameter of the belt decreases, pinching the cell to form a cleavage furrow around the cell’s circumference. As constriction proceeds, the furrow deepens until it eventually slices its way into the center of the cell. At this point, the cell is divided into two.
Plant cell walls are far too rigid to be split apart by contracting proteins. Instead, these cells assemble membrane proteins (in vesicles that bud off the Golgi apparatus) in their interior at right angles to the spindle apparatus. This expanding membrane partition, called a cell plate, continues to grow outward until it reaches the interior surface of the plasma membrane and fuses with it. This divides the cell in two.
The phases of Mitosis
Exercise 1: Modeling the Phases of Mitosis with Pop Beads
Materials:
- Chalk (can be used directly on lab bench to draw cellular structures and then washed off)
-
Chromosome modeling kits
- Commercially available pop bead kits (e.g Carolina Biological Supply Company, Item #171100)
- 40 pop beads of one color (red)
- 40 pop beads of another color (yellow)
- 8 magnetic centromeres
- 4 laminated pictures of centrosomes (each consisting of a pair of centrioles)
- Paper towels / Kimwipes
Procedure:
Using models is a great way to represent natural structures and processes that are too small, or too large, or too complex to observe directly. By building chromosomes from the pop beads and manipulating them to model cell division (mitosis and meiosis) you will enhance your understanding of the nature of chromosomes and the cellular structures needed to perform cell division. In this simulation, your cell will be a diploid (2n) cell with 4 chromosomes. It will contain 2 homologous pairs of chromosomes. In order to differentiate between the pairs of homologs, one pair of homologous chromosomes will be longer than the other. One chromosome of each pair is red and represents maternal DNA (genetic material contributed by a female’s egg). The other chromosome of each pair is yellow and represents paternal DNA (genetic material contributed by a father’s sperm). Thus, for each pair of homologous chromosomes, one should be red and one should be yellow. The strands of pop beads represent the DNA in the form of chromatin during the G1, S, and G2 phases. They then represent chromosomes as they enter the phases of mitosis.
This diploid cell with 2 homologous pairs of chromosomes will be modeled as it moves through the following phases of mitosis:
- Interphase (uncondensed DNA) Before Synthesis of DNA (G1)
- Interphase (uncondensed DNA) After Synthesis of DNA (G2)
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
- You will build 2 pairs of homologous chromosomes (2n = 4). The first homologous pair of single chromosomes should be constructed using 12 red beads for one member of the long pair and 12 yellow beads for the other member of the pair. You may place the magnetic centromere at any position along the chromosome, but it must be at the same position on both members of the homologous pair.
- The second homologous pair of single chromosomes should be constructed using 6 red beads for one member of the short pair and 6 yellow beads for the other member of the pair. You may place the magnetic centromere at any position along the chromosome, but it must be at the same position on both members of the homologous pair.
- Use the pop beads to model the G1 phase of interphase (before synthesis of the DNA). On your lab bench, use the chalk to draw the cell membrane, nucleus, and nucleolus. Place a laminated centrosome in the cytoplasm of your cell. Place the 4 assembled chromosomes in the nucleus of your cell drawing. Remember that these represent a mass of chromatin.
- DNA replication takes place during the S phase of interphase. Model the S phase of interphase by assembling a second strand that is identical to each of the 4 single chromosomes. The identical strands are considered sister chromatids, which are held together by their magnetic centromeres. (Note: In a living cell, the centromere is a single unit until it separates in anaphase. Therefore, consider the pair of magnets to be a single centromere.)
- Model the G2 phase of interphase by letting your 4 assembled replicated chromosomes rest in the nucleus of your cell. Duplicate the centrosomes by placing another laminated centrosome in the cytoplasm of your cell drawing. Begin to move them towards opposite poles of the cell drawing.
- To model the prophase stage of mitosis, leave the chromosomes where they are in your cell drawing. In this stage, the chromatin coils and condenses into chromosomes. Using the paper towel (or Kimwipe) start erasing some of the nuclear membrane on your cell drawing. This will simulate the breakdown of the nuclear membrane. Also erase the nucleolus, as the nucleolus disappears in this stage. Continue to move your centrosomes to opposite sides of the cell. Use the chalk to draw spindle fibers beginning to form and radiating outward toward the chromosomes.
- At prometaphase the centrosomes are at opposite poles of the cell. During this phase the chromosomes continue to condense, the nuclear membrane completely breaks down, and the spindle fibers start to attach to the kinetochores of the centromeres. These are called kinetochore microtubules . Other spindle fibers radiate outward from the centrosomes, but these do not attach to the kinetochores. These spindle fibers are called nonkinetochore microtubules.
- To model metaphase , move the centromeres of your chromosomes to lie on an imaginary plane midway between the centrosomes that are now positioned at opposite poles of the cell. Line up the individual chromosomes in the middle (equator) of the cell. Sister chromatids remain attached at the centromere during metaphase.
- To model anaphase , pull the magnetic centromeres apart and slide them towards opposite poles of the cell. Keep them attached to your drawn kinetochore microtubules, but use the paper towel to erase them, making them shorter. With the chalk, lengthen the nonkinetochore microtubules and have them overlap in the middle of your cell. After separation at the centromere, each sister chromatid is now referred to as an individual chromosome. Anaphase ends when the chromosomes reach the opposite ends of the cell.
- Model telophase by piling up your chromosomes at each pole. Erase your spindle fibers, as they disappear during this stage. Even though we can’t simulate it, the chromosomes will start to decondense and uncoil back into chromatin. Redraw a nuclear envelope around each pile of chromosomes. Also add nucleoli to your drawing. The formation of separate nuclear envelopes divide the nuclei and marks the end of telophase.
- The division of the cytoplasm, or cytokinesis, results in the formation of two separate cells. To model cytokinesis in animal cells, fungi, and slime molds, leave the piles of chromosomes at their separate poles. Draw indentations of the cell membrane inwards, towards the cytoplasm, on the sides of the cell where there are no centrosomes. This represents a cleavage furrow ,which eventually “pinches” the cell’s cytoplasm into two separate cells. The proteins actin and myosin contribute to the formation of the cleavage furrow. In plant cells, membrane-bound vesicles migrate to the center of the cell (the equatorial plane) and fuse together to form a cell plate . The cell plate eventually divides the cytoplasm into two separate cells. Materials needed to build the cell wall are released from the vesicles at the cell plate, forming a new cell wall.
- How do the daughter cells you formed compare to the original parent cell? _________________________________________________________________
Observe the phases of Mitosis in Plant Cells
Exercise 2: Observing the Phases of Mitosis in the Onion Root Tip
Materials:
- Prepared slide of the onion root tip
- Compound light microscope
Procedure:
- Examine a slide of a longitudinal section of an onion root tip. Adjust the slide to view the region just above the root cap, where there are likely to be dividing cells.
- Focus on the dividing cells using the 4x scanning objective lens, then switch to the 10x objective and then the 40x objective.
- Survey the slide to find a cell in each phase of mitosis. Draw a cell for each phase in the boxes provided.
Interphase
DNA is uncondensed and in the form of chromatin. Individual chromosomes are not visible. The nuclear membrane is intact. The nucleolus is visible.
Prophase
Chromatin begins to condense into distinguishable chromosomes. These “puffy” structures are seen throughout the nucleus. Nucleoli begin to disappear. In late prophase (often called prometaphase) the nuclear membrane is no longer visible.
Metaphase
The chromosomes line up in the middle of the cell. Spindle fibers attach to kinetochores at the centromere and extend to the poles of the cell.
Anaphase
Centromeres split, separating each former chromatid into two individual chromosomes. The chromosomes move toward opposite poles.
Telophase and Cytokinesis
Chromosomes reach the poles. The nuclear envelopes begin to reform. The formation of a cell plate forms between the two cells to carry out cytokinesis.
Observe the phases of Mitosis in Animal Cells
Exercise 3: Observing the Phases of Mitosis in the Whitefish Blastula
Materials:
- Prepared slide of whitefish blastula
- Compound light microscope
Procedure:
The blastula is an early embryonic stage where many of the cells are dividing at any one time.
- Focus on the dividing cells using the 4x scanning objective lens, then switch to the 10x objective and then the 40x objective.
- Survey the slide to find a cell in each phase of mitosis. Draw a cell for each phase in the boxes provided.
Interphase
The DNA is uncondensed and in the form of chromatin. Individual chromosomes are not visible. The nuclear membrane is intact. The nucleolus is visible.
Prophase
Chromatin begins to condense and chromosomes are distinguishable. These “puffy” structures are seen throughout the nucleus. The nucleoli begin to disappear. In late prophase (often called prometaphase) the nuclear membrane is no longer visible.
Metaphase
The chromosomes line up in the middle of the cell. Spindle fibers attach to kinetochores at the centromere and extend to the poles of the cell.
Anaphase
Centromeres split, separating each former chromatid into two individual chromosomes. The chromosomes move toward opposite poles.
Telophase and Cytokinesis
Chromosomes reach the poles. The nuclear envelopes begin to reform. A cleavage furrow forms between the two cells to carry out cytokinesis.
- Why would the method of cytokinesis in animal cells not work in plant cells? Explain. __________________________________________________________________
How Long Does a Cell Spend in Each Phase of the Cell Cycle?
Exercise 4: Determining Time Spent in Different Phases of the Cell Cycle (Optional)
Materials:
- Laptop
- Calculator
Procedure:
- Obtain a laptop.
- Open a web browser and go to the following site: http://www.biology.arizona.edu
- This site will provide an interactive test of your ability to identify the stages of mitosis. It will also allow you to calculate the duration of the stages identified in the laboratory exercise you just completed, but the website will give standard results for the entire class.
- Go to the Cell Biology section, and find the activity “ Online Onion Root Tips ”.
- Keep clicking on “Next” at the bottom of the page until you get to the screen: Determining Time Spent in Different Phases of the Cell Cycle
- Click on “Next” at the bottom of the page.
- Identify each stage shown to you by the program. When a picture of a cell pops up in a stage of mitosis, simply click on the phase in which the cell belongs. If you make a mistake, read the explanation for why you were mistaken before making a new selection.
- When you are finished, use the formula given below and record your results in the table.
- The duration of each stage of mitosis can be determined by using the following formula. Compute the length of time for each stage and place your calculations in the table below.
(Number of cells in a stage ÷ Total number of cells) x 1440 (min in a day) = minutes a cell spends
in each stage in one day
|
Number of cells in each stage |
Interphase ______ |
Prophase ______ |
Metaphase ______ |
Anaphase _______ |
Telophase _______ |
Total 36 |
|---|---|---|---|---|---|---|
|
Percent of cells (# of cells / Total) |
100% |
|||||
|
Time (in minutes) spent in Stage – use calculation above |
Practical Challenge Questions
- In the circle below, sketch a 2n=6 diploid cell in metaphase of mitosis. Be sure to label the centromere, centrioles, and spindle fibers.
References
Belwood, Jacqueline; Rogers, Brandy; and Christian, Jason, Foundations of Biology Lab Manual (Georgia Highlands College). “Lab 10: Mitosis & Meiosis,” (2019). Biological Sciences Open Textbooks . 18. CC-BY
https://oer.galileo.usg.edu/biology-textbooks/18
Meiosis
Introduction to Meiosis (aka “Reduction Division”)
Meiosis is a special type of cell division in which the daughter cells produced have half the number of chromosomes (n) as their parent cell. In animals, this division occurs in the reproductive organs (gonads -- testes of males or ovaries of females) of species that reproduce sexually, and results in the formation of gametes (eggs or sperm) that contain half the number of chromosomes as the original cell. Sexual reproduction involves the joining of gametes (fertilization) to form a zygote, which then has two copies of each chromosome (2n). Meiosis is a critical process, as it increases genetic diversity within a species.
Cells that divide by meiosis prepare for cellular division (during interphase) much like every other cell. Meiosis progresses through the same phases as mitosis (prophase, anaphase, metaphase, telophase, and cytokinesis). However, unlike mitosis, meiosis involves two rounds of cellular division (meiosis I and meiosis II). Meiosis involves only one round of DNA replication where each chromosome replicates to form sister chromatids. Therefore, when meiosis is completed, each daughter cell contains only half the number (n) of chromosomes as the original cell.
The stages of meiosis:
- Meiosis I
- Prophase l
- Metaphase l
- Anaphase l
- Telophase l
- Cytokinesis l
- Meiosis II
- Prophase ll
- Metaphase ll
- Anaphase ll
- Telophase ll
- Cytokinesis ll
Prophase I: During prophase of meiosis I, the chromosomes join in homologous pairs. Homologous chromosomes (aka homologs) are the same length, have their centromere in the same position, and carry genetic information (genes) for the same traits, but not necessarily the same versions (alleles) of the gene.
For example, human chromosome #19 contains a gene for eye color. In one person, one allele might code for blue eyes and the other allele codes for green eyes. Since every human inherits two copies of chromosome 19 (one from the mother’s egg and one from the father’s sperm) a person could have 2 blue alleles, 2 green alleles, or one of each.
Paired homologous chromosomes are called tetrads and are said to be in synapsis. During synapsis, equivalent pieces of homologous chromatids are exchanged between the chromosomes. This is called crossing-over and can occur several times along the length of the chromosomes. As occurs in the mitotic division, prophase of meiosis I also involves the degradation of the nuclear membrane, disassembly of the nucleolus, and formation of spindle fibers.
Metaphase I: Metaphase of meiosis I occurs when the joined homologous chromosome pairs are moved to the center of the cell by spindle fibers (Figure 6). The fibers arrange the pairs so that homologs are on opposite sides of the metaphase plate (aka equatorial plane).
Figure 6. Homologous pairs line up at the equatorial plate in Metaphase l.
Anaphase I follows, as homologs are pulled apart, toward opposite poles of the cell (Figure 7). [*Note: this is significantly different from the separation of sister chromatids that occurs during mitosis].
Figure 7. In Anaphase l mitotic spindles pull homologs to opposite poles of the cell.
Telophase I marks the end of meiosis I, as new nuclei form and cytokinesis separates the cytoplasm forming two daughter cells.
At the end of meiosis I, the two daughter cells have half the number of chromosomes as did their parent cell. Thus, the cells have been reduced from diploid (2n) to haploid (n) (Figure 8). [n refers to the number of chromosomes in a set that are characteristic for a species. Humans have one set (n) of 23 unique chromosomes (n = 23). A diploid human cell has 2 sets (2n) of 23 unique chromosomes (2n = 46).
Figure 8. Meiosis l results in two haploid cells.
*Meiosis II follows meiosis I, which proceeds very much like mitosis.
During Prophase II , chromosomes containing two sister chromatids are lined up on the equator of each daughter cell by the spindle fibers. This is completed by the end of Metaphase II (Figure 9).
Figure 9. Metaphase ll of Meiosis
The centromeres separate and sister chromatids are pulled to each pole of the cell during Anaphase ll (Figure 10) . Cytokinesis II occurs after Telophase II to complete cell division and ultimately the production of four (4) daughter cells (Figure 11). The cells produced (egg or sperm, in humans) are haploid (n rather than 2n) and will either unite (via fertilization) or die. They do not divide further on their own as meiosis is not a cycle.
Figure 10. Anaphase ll of Meiosis
Figure 11. Meiosis results in four haploid cells.
The Phases of Meiosis
Exercise 1: Modeling the Phases of Meiosis
Materials:
- Chalk (can be used directly on lab bench to draw cellular structures and then washed off)
-
Chromosome modeling kits
- Commercially available pop bead kits (e.g Carolina Biological Supply Company, Item #171100)
- 40 pop beads of one color (red)
- 40 pop beads of another color (yellow)
- 8 magnetic centromeres
- 8 laminated pictures of centrosomes (each consisting of a pair of centrioles)
- Paper towels / Kimwipes
- Fine point sharpie
- Small round stickers
Procedure:
A diploid cell with 2 homologous pairs of chromosomes (as in the previous modeling exercise) will be modeled as it moves through the meiosis. First, you will model meiosis l. Then, you will model meiosis ll as described below.
Model Meiosis l (1 diploid cell → 2 haploid cells)
-
tetrads form, crossing over occurs, homologues separate
- Interphase Before Synthesis of DNA (G1)
- Interphase After Synthesis of DNA (G2)
- Prophase l
- Metaphase l
- Anaphase l
- Telophase l
- Cytokinesis l
Model Meiosis ll (2 haploid cells → 4 haploid cells)
- sister chromatids separate
- Prophase ll
- Metaphase ll
- Anaphase ll
- Telophase ll
- Cytokinesis ll
Modeling Meiosis l
- You will build 2 pairs of homologous chromosomes (2n = 4). The first homologous pair of single chromosomes should be constructed using 12 red beads for one member of the long pair and 12 yellow beads for the other member of the long pair. You may place the magnetic centromere at any position along the chromosome, but it must be at the same position on both members of the homologous pair.
- The second pair of single chromosomes will represent the X and Y sex chromosomes in a male. The X chromosome should be constructed using 8 red beads. To make manipulation of the chromosomes easier, place the magnetic centromere in the middle of the X chromosome so that you have 4 red beads on one side of the centromere and 4 red beads on the other side. The Y chromosome should be constructed using 2 yellow beads with a magnetic centromere between them.
- Alternative forms of genes are called alleles. We will use the letter “B” or “b” to represent the gene for eye color. Labeled stickers will be used to represent alleles. With the Sharpie, label one small sticker with a “B” and another small sticker with a “b”. “B” will represent the dominant allele for brown eyes and “b” will represent the recessive allele for blue eyes. You may place the “B” sticker on any of the red beads of the long red chromosome. The “b” sticker must be placed at the same bead position of the “B” sticker, but on the long yellow chromosome.
- To model the G1 phase of interphase (before synthesis of the DNA). On your lab bench, use the chalk to draw the cell membrane, nucleus, and nucleolus. Place a laminated centrosome in the cytoplasm of your cell. Place the 4 assembled chromosomes in the nucleus of your cell drawing. Remember that these represent a mass of chromatin.
- DNA replication takes place during the S phase of interphase. Model the S phase of interphase by assembling a second strand that is identical to each of the 4 single chromosomes. The identical strands are considered sister chromatids, which are held together by their magnetic centromeres. (Note: In a living cell, the centromere is a single unit until it separates in anaphase. Therefore, consider the pair of magnets to be a single centromere.)
- Model the G2 phase of interphase by letting your 4 assembled replicated chromosomes rest in the nucleus of your cell. Duplicate the centrosomes by placing another laminated centrosome in the cytoplasm of your cell drawing. Begin to move them towards opposite poles of the cell drawing.
- To model the prophase I stage of meiosis, leave the chromosomes where they are in your cell drawing. In this stage, the chromatin coils and condenses into chromosomes. Using the paper towel (or Kimwipe) start erasing some of the nuclear membrane on your cell drawing. This will simulate the breakdown of the nuclear membrane. Also erase the nucleolus, as the nucleolus disappears in this stage. Continue to move your centrosomes to opposite sides of the cell. Use the chalk to draw spindle fibers beginning to form and radiating outward toward the chromosomes.
- Prophase l of meiosis has some notable differences compared to prophase of mitosis. To further model prophase l of meiosis, arrange the condensed chromosomes so that homologous chromosomes are paired. Put homologous chromosomes next to each other in your cell drawing to simulate this process of synapsis (homologs pairing). Homologous pairs of chromosomes paired in this way are called tetrads . When tetrads form, the inner non-sister chromatids of the tetrad pair can exchange DNA by a process known as crossing over . Pieces of equivalent segments of non-sister chromatids can be exchanged from one non-sister chromatid to the other. Crossing over can occur several times along the length of the chromosomes.
- How many tetrad complexes do you have in your cell, which is 2n = 4? ____________________________________________________________
- Exchange segments of the inner non-sister chromatids of the red and yellow beads that contain the two different alleles, “B” and “b”. Remember that the red beads represent DNA from the maternal chromatid and the yellow beads represent DNA from the paternal chromatid. You now have one crossover event for this tetrad.
- Metaphase l of meiosis is also notably different than metaphase of mitosis. To model metaphase l of meiosis, move your tetrads to the equator, midway between the two centrosomes, which should now be positioned at the two opposite poles of the cell. Draw spindle fibers radiating out from the centrosomes to the homologous pairs (tetrads) which are lined up along the equatorial plane of the cell. Homologs are paired together but the maternal and paternal chromosomes are on opposite sides of the equatorial plate along the middle of the cell. Every pair of chromosomes is arranged independent of another. The side of the equatorial plate where each chromosome is arranged is completely random and independent of the side of the equatorial plate on which other chromosomes are located. Therefore, there are several different arrangements that can occur (Figure 12).
Figure 12. Independent Assortment in a cell with 2 homologous pairs.
- In anaphase l of meiosis, homologous chromosomes separate toward opposite poles of the cell. Centromeres do not split as they do in mitosis. For each homologous pair, move the duplicated maternal chromosome and duplicated paternal chromosome to opposite poles of the cell. Remember that in our model, the two magnets (one of each of the two sister chromatids) represent one centromere. Erase the spindle fibers and redraw them shorter and shorter as each homologous pair moves away from one another towards opposite poles of the cell.
- How does the structure of chromosomes in anaphase I of meiosis differ from that in anaphase of mitosis? ____________________________________________________________
- Anaphase ends and telophase l begins when chromosomes reach opposite poles of the cell. Arrange the chromosomes in groups at opposite ends of the cell. You should have one long chromosome of 12 beads and either the X chromosome or the Y chromosome at each pole. Nuclear division happens in telophase. The formation of separate nuclear envelopes divide the nuclei and mark the end of telophase.
- Model cytokinesis l by drawing the formation of a cleavage furrow to divide the cytoplasm into two and form two separate cells. Redraw the nuclear membrane around the chromosomes and draw a nucleolus inside of each nucleus. These two cells will now enter meiosis ll. Note that each daughter cell has half the number of chromosomes as the parental cell. Thus, the cells have been reduced from diploid (2n) to haploid (n) . [n refers to the number of pairs of chromosomes that are characteristic for a species . Humans have a “n” of 23, so a diploid human cell has 2(23), or 46 chromosomes].
Meiosis ll
- There is no DNA replication before the second cell division stage of meiosis. The stages of meiosis ll proceed very much like mitosis. The two cells created in meiosis l will enter into prophase ll . The chromosomes in each cell contain two sister chromatids, which are condensed and distributed throughout the nucleus. Add another laminated centrosome. There should be two centrosomes in each new cell. In your drawing be sure to note that the nuclear envelope begins to break down, the nucleolus disappears, the centrosomes move towards opposite poles, and spindle fibers begin to form and radiate toward the chromosomes. Spindle fibers attach to kinetochore proteins at the centromeres of the chromosomes.
- To model metaphase ll , line up the individual chromosomes on the equator (middle) of each cell. Sister chromatids remain attached at the centromere during metaphase ll.
- Model anaphase ll by pulling the two magnetic centromeres of each duplicated chromosome apart. The sister chromatids should be separated and moved toward opposite poles of each cell. After separation at the centromere, the chromatids are now called chromosomes. In anaphase II single chromosomes move towards opposite poles.
- Anaphase ll ends and telophase ll begins when the chromosomes reach opposite poles of the cells. Nuclear division happens in telophase. The spindle fibers disassemble. Nuclear envelopes and nucleoli reappear. Condensed chromosomes begin to decondense and uncoil. The formation of separate nuclear envelopes divide the nuclei and marks the end of telophase.
- Model cytokinesis ll by drawing the formation of a cleavage furrow to divide the cytoplasm of each cell into two separate cells.
- What is the total number of nuclei and cells now present? ___________________
- How many cells were present when meiosis began? _______________________
- How many chromosomes were present in the original parental cell? ___________
- How many chromosomes are in each new daughter cell? ___________________
- Are the chromosomes in the new daughter cells identical to the chromosomes in the original parental cell? Explain your results in terms of independent assortment and crossing over. __________________________________________________
Questions for Review
- What is the meaning of diploid? What abbreviation do we use to represent diploid? Name 2 diploid cells in humans.
- What is the meaning of haploid? What abbreviation do we use to represent haploid? Name 2 haploid cells in humans.
- In what stage of the cell cycle does S phase occur? Explain why the DNA must be duplicated during the S phase of the cell cycle, prior to mitosis taking place.
- What specific feature of cytokinesis in animal cells can you use to distinguish this process from cytokinesis in plant cells?
Practical Challenge Questions
- In the circle below, sketch a 2n=6 haploid cell in metaphase l of meiosis.
- A monogenic gene gives rise to a trait from a single set of alleles. A polygenic gene gives rise to a trait from several sets of alleles. Give an example of a monogenic and polygenic trait.
References
Belwood, Jacqueline; Rogers, Brandy; and Christian, Jason, Foundations of Biology Lab Manual (Georgia Highlands College). “Lab 10: Mitosis & Meiosis,” (2019). Biological Sciences Open Textbooks . 18. CC-BY


3: Pulse and Respiration Last updated Save as PDF Page ID 16790 Lapum et al. Ryerson University (Daphne Cockwell School of Nursing) via Ryerson University Library 3.1: Respiration Technique 3.2: Finding the Error Activity- Radial Pulse 3.3: Finding the Error Activity- Radial Pulse – Feedback 3.4: Finding the Error Activity- Infant Apical Pulse 3.5: Finding the Error Activity- Infant Apical Pulse – Answer 3.6: Try it Out 3.7: Try it Out- Radial Pulse and Respiration 3.8: Try it Out- Apical Pulse 3.9: Test Yourself 3.10: Test Yourself- Answers 3.11: How Best to View this Chapter? 3.12: Test Yourself- List in the Correct Order 3.13: Test Yourself- List in the Correct Order – Answers 3.14: Chapter Summary 3.15: What is Pulse? 3.16: Why is Pulse Measured? 3.17: What Pulse Qualities are Assessed? 3.18: Radial Pulse 3.19: Carotid Pulse 3.20: Brachial Pulse 3.21: Apical Pulse 3.22: What is Respiration?


Skip to main content
16.9: Collaborative Group Activities
-
-
Last updated
-
-
Save as PDF
-
-
In this chapter, we learned that meteorites falling into the Sun could not be the source of the Sun’s energy because the necessary increase in the mass of the Sun would lengthen Earth’s orbital period by 2 seconds per year. Have your group discuss what effects this would cause for our planet and for us as the centuries went on.
-
Solar astronomers can learn more about the Sun’s interior if they can observe the Sun’s oscillations 24 hours each day. This means that they cannot have their observations interrupted by the day/night cycle. Such an experiment, called the GONG (Global Oscillation Network Group) project, was first set up in the 1990s. To save money, this experiment was designed to make use of the minimum possible number of telescopes. It turns out that if the sites are selected carefully, the Sun can be observed all but about 10% of the time with only six observing stations. What factors do you think have to be taken into consideration in selecting the observing sites? Can your group suggest six general geographic locations that would optimize the amount of time that the Sun can be observed? Check your answer by looking at the GONG website.
-
What would it be like if we actually manage to get controlled fusion on Earth to be economically feasible? If the hydrogen in
water
becomes the fuel for releasing enormous amounts of energy (instead of fossil fuels), have your group discuss how this affects the world economy and international politics. (Think of the role that oil and natural gas deposits now play on the world scene and in international politics.)
-
Your group is a delegation sent to the city council of a small mining town to explain why the government is putting a swimming-pool-sized vat of commercial cleaning fluid down one of the shafts of an old gold mine. How would you approach this meeting? Assuming that the members of the city council do not have much science background, how would you explain the importance of the project to them? Suggest some visual aids you could use.
-
When Raymond Davis first suggested his experiment in the underground gold mine, which had significant costs associated with it, some people said it wasn’t worth the expense since we already understood the conditions and reactions in the core of the Sun. Yet his experiment led to a major change in our understanding of neutrinos and the physics of subatomic particles. Can your group think of other “expensive” experiments in astronomy that led to fundamental improvements in our understanding of nature?