7.11: Immune Defenses Against Infectious Diseases
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Natural barriers against pathogens
The physical and chemical barriers that prevent pathogens from getting into our body tissues in the first place are often overlooked. As Figure 6 shows, the most comprehensive barrier is the waterproof layer of skin that covers the body’s surface. Human skin keeps most pathogens out as long as it remains intact. The speed with which a cut or graze can become infected is a reminder of the protection we normally get from our skin.
Figure \(\PageIndex{1}\). Physical and chemical barriers against infection
Vector-borne infections (e.g. malaria) are transmitted by biting invertebrates (e.g. mosquitoes) penetrating the skin when taking a blood meal. Humans are also vulnerable to invasion by pathogens in the air, food, water and soil, or during physical contact with infected people, some animals (e.g. pigs, dogs, poultry) or their feces. As Figure \(\PageIndex{1}\) illustrates, the inner surface of the respiratory system (nose, throat, airways and lungs), stomach, intestines, bladder and reproductive tract are lined with membranes that secrete jelly-like mucus, presenting a barrier against pathogens entering our tissues via these routes. Microscopic hairs called cilia [sill-ee-ah] line the respiratory system and ‘beat’ in unison to shunt mucus containing trapped pathogens towards the nose and mouth, where they can be expelled by coughing and sneezing, or swallowed into the stomach where acid destroys them.
Chemical barriers against infection include enzymes in tears, saliva and mucus that break down the surface of bacteria. The acid in sweat and in the stomach kills cellular pathogens and there are anti-bacterial proteins in semen (the fluid that contains male sperm). The more complex mechanisms of the immune system are only needed if pathogens breach these physical and chemical barriers.
The immune response to infection
The human immune system is an extremely complex network of interacting cells and biological molecules. The aim here is simply to give you an overview of how an immune response to infection develops, without going into too much detail. It occurs in three overlapping stages, the first of which is triggered when body cells are damaged. When tissues are injured, the damaged cells release chemicals that trigger the sequence of events described as inflammation. It occurs in response to any type of injury, such as a blow or a cut, an insect bite, or damage caused by pathogens multiplying in body tissues. Inflammation has four characteristic effects at the site of an injury, the first two of which are visible around the splinter shown in Figure \(\PageIndex{2}\):
- swelling
- redness
- heat
- pain
Figure \(\PageIndex{2}\). Inflammation of the tissues around a splinter
The inflamed area shows these signs because the local blood vessels dilate (get wider), increasing blood flow into the injury site, so it looks red as well as feeling warmer than the surrounding tissue. The walls of the blood vessels near the injury become leaky, allowing fluid, defensive proteins and immune system cells (described shortly) to flood into the area, which becomes swollen as a result. One of the proteins released during the inflammatory response also makes the area more sensitive to painful stimuli, so inflamed tissue is sore to touch.
Sites of tissue injury are vulnerable to invasion by pathogens so the benefits of inflammation generally outweigh the discomfort it causes. Flooding the area with fluid dilutes any pathogens that are already present, and the local concentration of immune system cells and defensive proteins enables an immune response to begin more quickly.
Leukocytes: the cells of the immune system
Once the barriers to infection have been breached and inflammation has begun, the active agents of the immune system, the leukocytes [loo-koh-sites], get to work. Leukocytes are often described as ‘white blood cells’ to distinguish them from the red blood cells that transport oxygen around the body; however, calling them ‘blood’ cells is misleading because leukocytes roam throughout the body tissues and only spend part of their lives in the bloodstream. In fact, they spend more time in the lymphatic system (Figure \(\PageIndex{3}\)), the network of fine tubules that collect tissue fluid from all over the body and return it to the bloodstream.
Figure \(\PageIndex{3}\). The human lymphatic system
The lymphatic system includes specialized organs and tissues where leukocytes develop. During an immune response to pathogens, we may become aware of swollen lymph nodes (popularly called ‘glands’) in the neck, armpits or groin, which enlarge when the leukocytes they contain are multiplying near a site of infection.
Leukocytes can distinguish between ‘self’, the cells and proteins generated by the organism whose body they patrol, and ‘non-self’ (or ‘foreign’) material such as pathogens that originated outside the host’s body. Leukocytes are self-tolerant , i.e. they do not normally attack the host’s own cells or body proteins, but direct their actions only against non-self material that may pose a threat.
Although we have referred to ‘the’ immune response, as if it was just one thing, in fact, there are two types of immune response, distinguished as innate and adaptive immunity.
Innate immunity
All animals, even those with much simpler bodies than our own (e.g. parasitic worms) respond to tissue damage in ways that resemble inflammation in humans. They have cells similar to leukocytes and defensive proteins that flood into areas of tissue damage or infection. These leukocytes and proteins can defend the organism from pathogens because they recognize common patterns of molecules that occur in the structures of many different types of pathogens. These pathogen ‘signature’ molecules are known as PAMPs, or pathogen-associated molecular patterns .
The fact that PAMPs are commonly found in unrelated pathogens means that the leukocytes that recognize them cannot tell one type of pathogen from another. This non-specific immune response against pathogens is so widespread among animals that it is described as innate immunity (‘innate’ means ‘inborn’). Some texts use the alternative term ‘natural’ immunity.
The leukocytes involved in innate immunity are of two general types, each with a different action against pathogens:
- Cytotoxic [sigh-toh-tox-ik] leukocytes, which simply means ‘cell poisoning’ (the prefix ‘cyto’ denotes a cell). These leukocytes have various methods of attaching to the outside of a pathogen and releasing destructive chemicals onto its surface. Worm larvae, bacteria and protists can all be killed this way.
- Phagocytic [fag-oh-sit-ik] leukocytes (the prefix ‘phago’ comes from a Greek word meaning ‘to eat’), often abbreviated to phagocytes [fag-oh-sigh-tz]. These leukocytes engulf small pathogens such as bacteria, drawing them into the cytosol where destructive chemicals break them down. This action is termed phagocytosis [fag-ohsigh-toh-siss].
The anti-pathogen activities of certain specialized proteins are important contributors to the innate immune response. They include proteins that accelerate inflammation, target leukocytes onto pathogens or make host cells resistant to invasion by viruses. Their concentration increases rapidly in the bloodstream during an infection and this rise can be detected in blood tests as a diagnostic sign of infection.
In summary, all animals have innate immunity based on cells similar to human leukocytes and defensive proteins that defend the organism against pathogens ‘in general’ in a nonspecific way, i.e. these defenses cannot distinguish between one type of pathogen and another. Humans and other warm-blooded animals have an additional defensive capability called adaptive immunity, which differentiates specifically between pathogens, as the next section describes.
Adaptive Immunity
Adaptive immunity is due to the actions of two types of specialized leukocytes, known as T cells and B cells. (If you are interested, the letters denote ‘thymus’ and ‘bone marrow’, the tissues where each of these leukocytes mature.) We will describe their individual contributions to the adaptive immune response shortly, but first we focus on the most striking difference between innate and adaptive immunity. The clue lies in the word ‘adaptive’.
T cells and B cells have recognition methods that distinguish between different pathogens (e.g. different species of bacteria), and they adapt during their first encounter with a particular pathogen. The second time they meet it in the body, the adaptive response begins earlier, lasts longer and is more effective than it was on the first occasion.
So, there is a much faster and increased response to a subsequent encounter with a pathogen and this demonstrates the adaptability of the immune system. This response is due to the production of long-lived memory cells that circulate in the body after the primary adaptive immune response subsides. These memory cells are specifically programmed to recognize the same pathogens that triggered the primary response if they ever get into the body again.
Antigens and the specific recognition of pathogens
Every type of pathogen has at least one (often many more) unique molecules known as antigens in their structure. In addition to the PAMPs (pathogen-associated molecular patterns) shared by many different pathogens, each type of pathogen also has its own unique distinctive antigens. Each individual T cell and B cell (the leukocytes responsible for adaptive immunity) is programmed to recognize just one specific antigen, so it follows that each T or B cell can usually recognize only one type of pathogen, or at most two or three closely related pathogens that have very similar antigens. Recognition of an antigen by these adaptive leukocytes triggers an immune response against only those pathogens with that antigen in their structure. The political slogan ‘One person, one vote’ springs to mind as an analogy for ‘One adaptive leukocyte, one target’!
Antibodies and B cells
Antibodies are very large proteins that contribute to adaptive immunity. A distinguishing feature of antibodies is that their structure includes at least two binding sites for antigens. B cells produce antibodies and also use them as their antigen receptors. The B cells carry antibodies embedded by the ‘tail’ in their outer cell membrane, with the binding sites facing outwards. This enables the B cell to bind to antigens that fit the binding sites in the antibodies it carries on its surface. This binding event is essential (but not sufficient on its own) to activate B cells into making a lot more antibody molecules that recognize the same antigen. These antibodies are released by the B cells and circulate in the bloodstream, tissue fluids and the lymphatic system. Antibodies are also abundant in the mucus membranes lining the respiratory system, the gut and the reproductive system, i.e. the sites in the body in contact with substances such as air, food, drinking water and sexual fluids that could contain pathogens.
Antibodies are often portrayed in the media as if they were ‘magic bullets’ that attack pathogens, but in fact they are more like ‘waving flags’ with a message that reads ‘here is a pathogen – come and destroy it’. When antibodies bind to a pathogen, they simply label it for destruction by leukocytes with the innate ability to phagocytose (engulf) it, or cytotoxic (cell-killing) leukocytes and defensive proteins. You can think of them as recruiting the cells and defensive proteins of the innate immune system to join the attack. We conclude this tour of adaptive immunity by describing the T cells.
T cells in adaptive immunity
There are two types of T cells with different roles in adaptive immunity. The cytotoxic T cells release destructive chemicals onto their target’s outer surface in much the same way as the cytotoxic leukocytes do in an innate immune response. But there is one crucial difference. Cytotoxic T cells are programmed to kill the body’s own cells that have become infected by viruses or by the few types of bacteria and single-celled pathogens that can ‘hide’ inside the cells of their host ( Mycobacterium tuberculosis , the bacteria that cause TB, can do this). Without the cytotoxic T cells, we woud be particularly susceptible to infectious diseases caused by these pathogens.
The other T cell type is called the helper T cells . They send activation signals to all the other leukocytes involved in inflammation, phagocytosis, cytotoxicity or production of antibodies by B cells. Recognition of a pathogen by binding to it is only the first step. The other leukocytes cannot take action against the pathogens they encounter without activation signals from the helper T cells.
Figure \(\PageIndex{4}\). The Cell-Mediated Immune Response
Vaccination
Vaccination relies on the development of immunological memory for its protective effect. Vaccines contain killed pathogens, or extracts from pathogens, or modified strains of pathogens that are no longer harmful. For example, the MMR vaccine contains weakened (the technical term is ‘attenuated’) variants of the three viruses that cause measles, mumps and rubella (Figure \(\PageIndex{5}\)).
Figure \(\PageIndex{5}\). The MMR vaccine contains live attenuated strains of measles, mumps and rubella viruses.
Note that each of the memory cells and the T cells and B cells generated in an adaptive immune response are specifically directed against just one type of pathogen or a very closely related strain. Vaccination with MMR vaccine is only protective against measles, mumps and rubella infection.
Despite decades of effort, medical science has so far been unable to produce effective vaccines against a number of important infectious diseases, including HIV/AIDS and other sexually transmitted infections (although trials of several candidate vaccines are underway). Vaccines against malaria have shown some potential, but they only protected about half the vaccinated children in large-scale African trials. There are no effective vaccines against infections caused by any other single-celled or multicellular parasites.
Some vaccines are effective only for a relatively short time, e.g. cholera vaccines give protection for only around six months. Others, such as the tetanus vaccine, need repeated booster doses. Annual influenza vaccinations are offered to vulnerable groups in the population because influenza viruses alter their antigens over time.
Opposition to vaccination
Another major challenge is parental opposition to vaccination because of concerns about vaccine safety. Some parents are understandably anxious about taking a healthy child to be given a vaccine derived from infectious agents. Most vaccines are injected, which can be a frightening and painful experience for a child. Of even greater concern is that some children experience a negative reaction to a vaccine, most often inflammation around the injection site and/or a mild fever lasting a day or two, but rare instances of more severe reactions such as convulsions sometimes occur.
Hesitancy about vaccinating a child is increased if parents have no experience of the disease the vaccine prevents, because it has become rare in communities with high vaccine coverage. Some parents conclude that vaccination is unnecessary and might expose their children to an avoidable risk.
Negative rumors about a vaccine are another deterrent. For example, the myth that vaccination is a Western plot to sterilize Muslim children has deterred parents in northern Nigeria, Pakistan and Afghanistan from allowing their children to be vaccinated against polio (Figure \(\PageIndex{6}\)). Terrorist attacks have occurred against polio vaccination teams in all three countries – the only remaining locations where polio had not been eradicated by the WHO target of 2015.
Figure \(\PageIndex{6}\). Negative rumors about the oral polio vaccine did not deter this Nigerian child’s parents from bringing her for vaccination.
An inevitable consequence of falling vaccination rates in a community is an increase in infections, sometimes with fatal outcomes. In 2014, the WHO warned that progress on eliminating measles had stalled and the number of deaths had begun to rise – from 122 000 in 2012 to 145 700 in 2013.
Countries urgently need to prioritize maintaining and improving immunization coverage. Failure to reverse this alarming trend could jeopardize the momentum generated by a decade of achievements in reducing measles mortality.
Even in countries where over 90% of children are fully vaccinated, uptake rates can plummet under pressure from negative rumors. For example, false claims in 1998 that the MMR vaccine caused autism led to a sustained fall in vaccinations in the United States and United Kingdom, followed by a significant rise in measles cases and, to a lesser extent, mumps. The largest outbreak of measles around Wales in 2012–13 caused more than 1200 cases and one death (Public Health Wales, 2013). Once parents saw the reality of measles infection and the misery and discomfort it causes, a rapid increase in uptake of the MMR vaccine followed the outbreak. The memory of infection fades in well-protected communities, until an outbreak reminds everyone of how devastating infectious diseases can be.


21.7B: Nonrespiratory Air Movements
The lungs have a number of metabolic functions in addition to their functions in gas exchange.
LEARNING OBJECTIVE
Discuss the non-respiratory air movements of the respiratory system
Key Takeaways
Key Points
- The lungs have a number of metabolic functions, such as the secretion of ACE (angiotensin converting enzyme), which converts angiotensin I to angiotensin II to stimulate changes in the renal system.
- Higher levels of ACE lead to higher blood pressure. ACE inhibitors are used to treat hypertension by reducing ACE to reduce blood pressure.
- Airway epithelial cells can secrete a variety of molecules—immunoglobulins (IgA), proteases, reactive oxygen species, and antimicrobial peptides—that all help protect the lungs and body from pathogens.
- Non-respiratory air movements are mechanical functions that aren’t involved in gas exchange, such as voice production and coughing.
Key Terms
- ACE : Angiotensin converting enzyme, which is secreted in the lungs and helps to increase blood pressure in the body through renal system feedback loops.
- Airway epithelial cells : Airway epithelial cells can secrete a variety of molecules that aid in the immune system defense of lungs.
EXAMPLE
Non-respiratory air movements do not involve gas exchange. Examples are: sneezing, coughing, burping, laughing, singing, and talking.
While the primary function of the lungs is gas exchange, they have several other functions, which are both metabolic and mechanical. These include the secretion of many enzymes and proteins involved in other body systems and nonrespiratory air movements.
Metabolic Functions
The lungs secrete many enzymes and proteins that serve non-respiratory metabolic functions.
ACE (angiotensin converting enzyme) is an enzyme secreted by the endothelial cells of the capillaries in the lungs. ACE converts angiotensin I into angiotensin II, which are two important hormones in the renin-angiotensin feedback loop of the renal system.
The renin-angiotensin-aldosterone system: The renin-angiotensin-aldosterone system is dependent on ACE from the lungs to regulate blood pressure. ACE activity results in increased blood pressure.
This system works to regulate blood pressure and blood volume by changing the amount of water retained by the kidneys. In general, more ACE leads to more angiotensin II, which leads to more aldosterone, which leads to more retained water through sodium reabsorption in the kidney, which leads to increased blood volume and blood pressure.
ACE inhibitors are a common treatment for those with hypertension, as it will reduce the amount of ACE, which will cause the kidney to excrete more water, which lowers blood volume and blood pressure.
The epithelial cells and macrophages of the lungs secrete many molecules that have immune system functions. In general these molecules have anti-microbial functions.
- Immunoglobin A (IgA): An antibody that can attack pathogens and mark them for phagocytosis from macrophages and neutrophils.
- Protease: Secreted from lung macrophages and neutrophils during inflammatory response to damage pathogens. A fibrinolytic that can break up thrombosis (blood clots) in the lungs.
- Reactive oxygen species (ROS): Free radicals, which are any substance with an unpaired electron in the valence shell, can cause oxidative stress (damage) in cells. They are used to kill pathogens after being engulfed (phagocytized) by immune cells.
- Anti-microbial peptides: Various chemokines and proteins that are secreted by the mucus membranes of the airways. They can damage and inhibit pathogens and are considered a barrier component of the immune system.
Mechanical Functions
There are several types of non-respiratory air movements that have important functions that are not primarily related to gas exchange. One example is voice production for speaking and singing, which involves fine control over the direction and flow of the air as it passes into the upper respiratory tract.
Other mechanical functions include sneezing and coughing, which protect the lungs and airways from irritants that could potentially cause damage. Coughing is a result of constriction from nervous stimulation in the trachea and larynx and also serves to dislodge mucus trapped inside the lungs.
LICENSES AND ATTRIBUTIONS
CC LICENSED CONTENT, SHARED PREVIOUSLY
- Lung volume. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Lung_volume . License : CC BY-SA: Attribution-ShareAlike
- tidal volume. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/tidal_volume . License : CC BY-SA: Attribution-ShareAlike
- vital capacity. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/vital_capacity . License : CC BY-SA: Attribution-ShareAlike
- partial pressure. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/partial_pressure . License : CC BY-SA: Attribution-ShareAlike
- The respiratory system. Provided by : Wikibooks. Located at : en.wikibooks.org/wiki/Human_P...iratory_system . Project : Human Physiology. License : CC BY-SA: Attribution-ShareAlike
- Respiratory system. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Respiratory_system . License : CC BY-SA: Attribution-ShareAlike
- syrinx. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/syrinx . License : CC BY-SA: Attribution-ShareAlike
- surfactant. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/surfactant . License : CC BY-SA: Attribution-ShareAlike
- Renin angiotensin aldosterone system. Authored by : A. Rad. Located at : commons.wikimedia.org/wiki/F...one_system.png . License : CC BY-SA: Attribution-ShareAlike
- Curation and Revision. Authored by : Boundless.com. Provided by : Boundless.com. License : CC BY-SA: Attribution-ShareAlike


11.6: Population Genetics
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- Ying Liu
- City College of San Francisco
A population is a large group of individuals of the same species, who are capable of mating with each other. It is useful to know the frequency of particular alleles within a population, since this information can be used to calculate disease risks. Population genetics is also important in ecology and evolution, since changes in allele frequencies may be associated with migration or natural selection.
Allele frequencies may also be studied at the population level
The frequency of different alleles in a population can be determined from the frequency of the various phenotypes in the population. In the simplest system, with two alleles of the same locus (e.g. A , a ), we use the symbol p to represent the frequency of the dominant allele within the population, and q for the frequency of the recessive allele. Because there are only two possible alleles, we can say that the frequency of p and q together represent 100% of the alleles in the population ( p+q=1 ).
We can calculate the values of p and q, in a representative sample of individuals from a population, by simply counting the alleles and dividing by the total number of alleles examined. For a given allele, homozygotes will count for twice as much as heterozygotes.
For example:
| genotype | number of individuals |
|
AA Aa aa |
320 160 20 |
|
A (p) |
a (q) |
|
|
A (p) |
p 2 |
pq |
|
a (q) |
pq |
q 2 |
\[\begin{align} \mathbf{p} &= \mathbf{\dfrac{2(AA) + Aa}{total\: alleles\: counted}}\\ &= \dfrac{2(320) + 160}{2(320) + 2(160) + 2(20)} = 0.8 \end{align}\]
\[\begin{align} \mathbf{q} &= \mathbf{\dfrac{2(aa) + Aa}{total\: alleles\: counted}}\\ &= \dfrac{2(20) + 160}{2(320) + 2(160) + 2(20)} = 0.2 \end{align}\]
Hardy-Weinberg formula
With the allele frequencies of a population we can use an extension of the Punnett Square, and the product rule, to calculate the expected frequency of each genotype following random matings within the entire population. This is the basis of the Hardy-Weinberg formula:
\[p^2 + 2pq + q^2=1 \label{HW}\]
Here \(p^2\) is the frequency of homozygotes AA , \(2pq\) is the frequency of the heterozygotes, and \(q^2\) is the frequency of homozygotes aa . Notice that if we substitute the allele frequencies we calculated above (p=0.8, q=0.2) into the Equation \ref{HW} , we obtain expected probabilities for each of the genotypes that exactly match our original observations:
\[\begin{align} &\mathrm{p^2=0.8^2=0.64} &&0.64 \times 500 = 320 \\ &\mathrm{2pq= 2(0.8)(0.2)=0.32} &&0.32 \times 500 = 160 \\ &\mathrm{q^2=0.2^2=0.04} &&0.04 \times 500 = 20 \end{align}\]
This is a demonstration of the Hardy-Weinberg Equilibrium , where both the genotype frequencies and allele frequencies in a population remain unchanged following successive matings within a population, if certain conditions are met. These conditions are listed in Table \(\PageIndex{1}\). Few natural populations actually satisfy all of these conditions. Nevertheless, large populations of many species, including humans, appear to approach Hardy-Weinberg equilibrium for many loci. In these situations, deviations of a particular gene from Hardy-Weinberg equilibirum can be an indication that one of the alleles affects the reproductive success of organism, for example through natural selection or assortative mating .
Conditions for the Hardy-Weinberg equilibrium
- Random mating : Individuals of all genotypes mate together with equal frequency. Assortative mating, in which certain genotypes preferentially mate together, is a type of non-random mating.
- No natural selection : All genotypes have equal fitness.
- No migration : Individuals do not leave or enter the population.
- No mutation : The allele frequencies do not change due to mutation.
- Large population : Random sampling effects in mating (i.e. genetic drift) are insignificant in large populations.
The Hardy-Weinberg formula can also be used to estimate allele frequencies, when only the frequency of one of the genotypic classes is known. For example, if 0.04% of the population is affected by a particular genetic condition, and all of the affected individuals have the genotype aa, then we assume that q 2 = 0.0004 and we can calculate p, q, and 2pq as follows:
\[\mathrm{q^2 = 0.04\% = 0.0004}\]
\[\mathrm{q = \sqrt{0.0004} = 0.02}\]
\[\mathrm{p= 1-q = 0.98}\]
\[\mathrm{2pq = 2(0.98)(0.02) = 0.04}\]
Thus, approximately 4% of the population is expected to be heterozygous (i.e. a carrier) of this genetic condition. Note that while we recognize that the population is probably not exactly in Hardy-Weinberg equilibrium for this locus, application of the Hardy-Weinberg formula nevertheless can give a reasonable estimate of allele frequencies, in the absence of any other information.


11.2: Sexual Reproduction
Skills to Develop
- Explain that meiosis and sexual reproduction are evolved traits
- Identify variation among offspring as a potential evolutionary advantage to sexual reproduction
- Describe the three different life-cycle types among sexual multicellular organisms and their commonalities
Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. It appears to have been very successful because most eukaryotes are able to reproduce sexually, and in many animals, it is the only mode of reproduction.  On the surface, creating offspring that are genetic clones of the parent appears to be a better system. If the parent organism is successfully occupying a habitat, offspring with the same traits would be similarly successful. There is also the obvious benefit to an organism that can produce offspring whenever circumstances are favorable by asexual budding, fragmentation, or asexual eggs. These methods of reproduction do not require another organism of the opposite sex. Indeed, some organisms that lead a solitary lifestyle have retained the ability to reproduce asexually. In addition, in asexual populations, every individual is capable of reproduction. In sexual populations, the males are not producing the offspring themselves, so in theory an asexual population could grow twice as fast.
However, multicellular organisms that exclusively depend on asexual reproduction are exceedingly rare. Why is sexuality (and meiosis) so common? This is one of the important unanswered questions in biology and has been the focus of much research beginning in the latter half of the twentieth century. There are several possible explanations, one of which is that the variation that sexual reproduction creates among offspring is very important to the survival and reproduction of the population. Thus, on average, a sexually reproducing population will leave more descendants than an otherwise similar asexually reproducing population. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms, but in addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes and the genes are mixed into different combinations by crossovers during prophase I and random assortment at metaphase I.
Evolution Connection: The Red Queen Hypothesis
It is not in dispute that sexual reproduction provides evolutionary advantages to organisms that employ this mechanism to produce offspring.  Variation is the outcome of sexual reproduction, but why are ongoing variations necessary? Enter the Red Queen hypothesis, first proposed by Leigh Van Valen in 1973. 1 The concept was named in reference to the Red Queen's race in Lewis Carroll's book, Through the Looking-Glass .
All species co-evolve with other organisms; for example predators evolve with their prey, and parasites evolve with their hosts. Each tiny advantage gained by favorable variation gives a species an edge over close competitors, predators, parasites, or even prey. The only method that will allow a co-evolving species to maintain its own share of the resources is to also continually improve its fitness. As one species gains an advantage, this increases selection on the other species; they must also develop an advantage or they will be outcompeted. No single species progresses too far ahead because genetic variation among the progeny of sexual reproduction provides all species with a mechanism to improve rapidly. Species that cannot keep up become extinct. The Red Queen’s catchphrase was, “It takes all the running you can do to stay in the same place.” This is an apt description of co-evolution between competing species.
Life Cycles of Sexually Reproducing Organisms
Fertilization and meiosis alternate in sexual life cycles . What happens between these two events depends on the organism. The process of meiosis reduces the chromosome number by half. Fertilization, the joining of two haploid gametes, restores the diploid condition. There are three main categories of life cycles in multicellular organisms: diploid-dominant , in which the multicellular diploid stage is the most obvious life stage, such as with most animals including humans; haploid-dominant , in which the multicellular haploid stage is the most obvious life stage, such as with all fungi and some algae; and alternation of generations , in which the two stages are apparent to different degrees depending on the group, as with plants and some algae.
Diploid-Dominant Life Cycle
Nearly all animals employ a diploid-dominant life-cycle strategy in which the only haploid cells produced by the organism are the gametes. Early in the development of the embryo, specialized diploid cells, called germ cells , are produced within the gonads, such as the testes and ovaries. Germ cells are capable of mitosis to perpetuate the cell line and meiosis to produce gametes. Once the haploid gametes are formed, they lose the ability to divide again. There is no multicellular haploid life stage. Fertilization occurs with the fusion of two gametes, usually from different individuals, restoring the diploid state (Figure \(\PageIndex{1}\)).
Haploid-Dominant Life Cycle
Most fungi and algae employ a life-cycle type in which the “body” of the organism—the ecologically important part of the life cycle—is haploid. The haploid cells that make up the tissues of the dominant multicellular stage are formed by mitosis. During sexual reproduction, specialized haploid cells from two individuals, designated the (+) and (−) mating types, join to form a diploid zygote. The zygote immediately undergoes meiosis to form four haploid cells called spores. Although haploid like the “parents,” these spores contain a new genetic combination from two parents. The spores can remain dormant for various time periods. Eventually, when conditions are conducive, the spores form multicellular haploid structures by many rounds of mitosis (Figure \(\PageIndex{2}\)).
Art Connection
If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce?
Alternation of Generations
The third life-cycle type, employed by some algae and all plants, is a blend of the haploid-dominant and diploid-dominant extremes. Species with alternation of generations have both haploid and diploid multicellular organisms as part of their life cycle. The haploid multicellular plants are called gametophytes , because they produce gametes from specialized cells. Meiosis is not directly involved in the production of gametes in this case, because the organism that produces the gametes is already a haploid. Fertilization between the gametes forms a diploid zygote. The zygote will undergo many rounds of mitosis and give rise to a diploid multicellular plant called a sporophyte . Specialized cells of the sporophyte will undergo meiosis and produce haploid spores. The spores will subsequently develop into the gametophytes (Figure \(\PageIndex{3}\)).
Although all plants utilize some version of the alternation of generations, the relative size of the sporophyte and the gametophyte and the relationship between them vary greatly. In plants such as moss, the gametophyte organism is the free-living plant, and the sporophyte is physically dependent on the gametophyte. In other plants, such as ferns, both the gametophyte and sporophyte plants are free-living; however, the sporophyte is much larger. In seed plants, such as magnolia trees and daisies, the gametophyte is composed of only a few cells and, in the case of the female gametophyte, is completely retained within the sporophyte.
Sexual reproduction takes many forms in multicellular organisms. However, at some point in each type of life cycle, meiosis produces haploid cells that will fuse with the haploid cell of another organism. The mechanisms of variation—crossover, random assortment of homologous chromosomes, and random fertilization—are present in all versions of sexual reproduction. The fact that nearly every multicellular organism on Earth employs sexual reproduction is strong evidence for the benefits of producing offspring with unique gene combinations, though there are other possible benefits as well.
 The variation introduced into the reproductive cells by meiosis appears to be one of the advantages of sexual reproduction that has made it so successful. Meiosis and fertilization alternate in sexual life cycles. The process of meiosis produces unique reproductive cells called gametes, which have half the number of chromosomes as the parent cell. Fertilization, the fusion of haploid gametes from two individuals, restores the diploid condition. Thus, sexually reproducing organisms alternate between haploid and diploid stages. However, the ways in which reproductive cells are produced and the timing between meiosis and fertilization vary greatly. There are three main categories of life cycles: diploid-dominant, demonstrated by most animals; haploid-dominant, demonstrated by all fungi and some algae; and the alternation of generations, demonstrated by plants and some algae.
Art Connections
Figure \(\PageIndex{2}\): If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce?
- Answer
-
Yes, it will be able to reproduce asexually.
Footnotes
- 1 Leigh Van Valen, “A New Evolutionary Law,” Evolutionary Theory 1 (1973): 1–30
Glossary
- alternation of generations
- life-cycle type in which the diploid and haploid stages alternate
- diploid-dominant
- life-cycle type in which the multicellular diploid stage is prevalent
- haploid-dominant
- life-cycle type in which the multicellular haploid stage is prevalent
- gametophyte
- a multicellular haploid life-cycle stage that produces gametes
- germ cells
- specialized cell line that produces gametes, such as eggs or sperm
- life cycle
- the sequence of events in the development of an organism and the production of cells that produce offspring
- sporophyte
- a multicellular diploid life-cycle stage that produces haploid spores by meiosis


18.1: The Undiscovered Statistics
First, I’m going to talk a bit about some of the content that I wish I’d had the chance to cram into this version of the book, just so that you can get a sense of what other ideas are out there in the world of statistics. I think this would be important even if this book were getting close to a final product: one thing that students often fail to realise is that their introductory statistics classes are just that: an introduction. If you want to go out into the wider world and do real data analysis, you have to learn a whole lot of new tools that extend the content of your undergraduate lectures in all sorts of different ways. Don’t assume that something can’t be done just because it wasn’t covered in undergrad. Don’t assume that something is the right thing to do just because it {} covered in an undergrad class. To stop you from falling victim to that trap, I think it’s useful to give a bit of an overview of some of the other ideas out there.
Omissions within the topics covered
Even within the topics that I have covered in the book, there are a lot of omissions that I’d like to redress in future version of the book. Just sticking to things that are purely about statistics (rather than things associated with R), the following is a representative but not exhaustive list of topics that I’d like to expand on in later versions:
- Other types of correlations In Chapter 5 I talked about two types of correlation: Pearson and Spearman. Both of these methods of assessing correlation are applicable to the case where you have two continuous variables and want to assess the relationship between them. What about the case where your variables are both nominal scale? Or when one is nominal scale and the other is continuous? There are actually methods for computing correlations in such cases (e.g., polychoric correlation), but I just haven’t had time to write about them yet.
- More detail on effect sizes In general, I think the treatment of effect sizes throughout the book is a little more cursory than it should be. In almost every instance, I’ve tended just to pick one measure of effect size (usually the most popular one) and describe that. However, for almost all tests and models there are multiple ways of thinking about effect size, and I’d like to go into more detail in the future.
- Dealing with violated assumptions In a number of places in the book I’ve talked about some things you can do when you find that the assumptions of your test (or model) are violated, but I think that I ought to say more about this. In particular, I think it would have been nice to talk in a lot more detail about how you can tranform variables to fix problems. I talked a bit about this in Sections 7.2, 7.3 and 15.9.4, but the discussion isn’t detailed enough I think.
- Interaction terms for regression In Chapter 16 I talked about the fact that you can have interaction terms in an ANOVA, and I also pointed out that ANOVA can be interpreted as a kind of linear regression model. Yet, when talking about regression in Chapter 15 I made no mention of interactions at all. However, there’s nothing stopping you from including interaction terms in a regression model. It’s just a little more complicated to figure out what an “interaction” actually means when you’re talking about the interaction between two continuous predictors, and it can be done in more than one way. Even so, I would have liked to talk a little about this.
- Method of planned comparison As I mentioned this in Chapter 16, it’s not always appropriate to be using post hoc correction like Tukey’s HSD when doing an ANOVA, especially when you had a very clear (and limited) set of comparisons that you cared about ahead of time. I would like to talk more about this in a future version of book.
- Multiple comparison methods Even within the context of talking about post hoc tests and multiple comparisons, I would have liked to talk about the methods in more detail, and talk about what other methods exist besides the few options I mentioned.


25.7: Discharge Planning
By the end of this section, you will be able to:
- Describe the process of discharge preparation for an infant at high risk
- Discuss education provided to caregivers preparing for discharge with a newborn at high risk
- Delineate the differences and additional needs of the high-risk infant who is discharged under hospice care
All new parents have concerns and anxieties as they prepare to take their newborn home. But these concerns are multiplied when the newborn is at high risk. All families caring for infants who are born premature or with a congenital and/or genetic disorder have an increased risk for family dysfunction.  They may also require psychosocial and financial support to function at their best.
Discharge Planning
A high-risk infant is determined to be ready for discharge on the basis of their medical status. Considerations include the readiness of the family to take the infant home, what care the infant needs, and what can be logistically provided at home. In addition, the ongoing cost of the infant’s hospital stay must be considered (American Academy of Pediatrics Committee on Fetus and Newborn, 2008).
Medical readiness for discharge means that the infant is physiologically stable. This consists of the following:
- The infant demonstrates that they can maintain an axillary temperature between 36.5° C and 37.5° C without external warming.
- The infant maintains a mature respiratory pattern without episodes of apnea or bradycardia .
- The infant demonstrates mature oral feeding skills, allowing enough caloric intake for appropriate growth, with weight gain paralleling a normal growth curve.
- The infant has the ability to sleep in a flat, supine position.
Multiple routine screenings are completed before discharge. Some, like the newborn screen, are completed for every newborn within the first couple days of life; others are more specific to the high-risk infant. A hearing screen is performed using auditory brainstem responses for all discharging newborns. However, a follow-up hearing evaluation is scheduled between 1 and 3 months of age after discharge for the high-risk infant because of the increased risk for hearing loss (Smith & Stewart, 2021). A head ultrasound (HUS) or magnetic resonance imaging (MRI) of the head for follow-up from earlier findings may be required. Infants born at less than 30 weeks’ gestational age are at risk for developing retinopathy of prematurity (ROP) . They will require routine ophthalmologic screening serially until their retinal vessels are mature and a pediatric ophthalmologic exam by 1 year of age (Smith & Stewart, 2021). Vaccinations are given prior to discharge, according to the Centers for Disease Control and Prevention’s (CDC) vaccination schedule.
The Centers for Disease Control and Prevention (CDC) provides vaccination schedules for all ages.
All infants require a car seat for safe travel. For infants at risk for cardiorespiratory compromise , defined as apnea, bradycardia, or oxygen desaturation (Smith & Stewart, 2021), the nurse will observe the infant in their car seat prior to discharge. The observation lasts for 90 to 120 minutes or the length of their travel time home, whichever is longer. A failure of the car seat screening occurs if the infant drops their saturations for more than 10 seconds, has apnea greater than 20 seconds, or experiences bradycardia less than or equal to 80 beats per minute (Smith & Stewart, 2021).
Infants with Dependence on Technology
Some high-risk infant s discharged to home will require gavage feedings, supplemental oxygen , mechanical ventilation , and continuous or nighttime cardiorespiratory monitoring. In gavage , medications and/or liquids, including formula or breast milk, are administered through a small tube placed through the nose or mouth to the stomach or small intestine. Parents and other caregivers require education about each piece of equipment, how to determine if it is working correctly, and what to do if it is not. It is recommended that two home caregivers receive all discharge education so that one person is not tackling this challenge alone. A case manager will connect a durable medical equipment (DME) company to the family early on to deliver necessary equipment to their home. Further, the home environment must be able to safely house the at-risk infant and should meet the following criteria:
- Working electricity that is compatible with the equipment needed for care
- Entryways wide enough to allow equipment, including the patient’s bed, to be delivered and moved if needed
- Local EMS informed of patient’s requirements and care needs (Smith & Stewart, 2021)
A high-risk infant who relies on gavage feedings requires a tube. A nasogastric (NG) tube or an orogastric (OG) tube is a feeding tube placed in the infant’s nostril or mouth down to their stomach. This is not a permanent device. When an infant is discharged home with gavage feeding, the NG or OG tube is cared for and replaced by the parent. Feeds—breast milk or formula—are then delivered directly to the stomach as bolus gavaged feeds 7 to 8 times a day. Even though this tube was placed by the nurse in the hospital, the care provider will be the person to determine if the tube is placed correctly, if the infant is receiving their feeds, and if the tube needs to be replaced. A gastric tube (G-tube) is a more stable tube for feedings and is placed surgically or via interventional radiology. The G-tube is used when the infant is likely to require gavage feeding for a lengthy period of time or the NG or OG tubes are not considered safe for home nutritional support (Figure 25.18). Some feeding tubes, such as a J-tube or NJ-tube, reach beyond the gastric sphincter to the duodenum or jejunum of the small intestine to provide continuous feeds when the infant cannot tolerate gastric feedings. These small-intestinal tubes are threaded through the G-tube and if dislodged require replacement in the hospital with imaging to confirm correct placement.
A high-risk infant may be discharged home with a tracheostomy in place and/or a ventilator to support their oxygenation and ventilation (Figure 25.19). Discharge parameters at each medical facility may differ slightly, but a minimum oxygen requirement is the goal. Typically, 40 percent FiO2 is the maximum for home-going purposes. The family will need to have a tracheostomy tube (trach) of the same size the infant has in place and one a size smaller available at the bedside. This is for replacement if the trach becomes dislodged or clogged.
Respiratory care equipment requires an inspection of the infant’s home prior to discharge. A respiratory therapist will evaluate the electrical outlets in the home, door opening size, and electrical panel location and capacity to ensure that the home is safe with the addition of oxygen and/or a ventilator (Smith & Stewart, 2021).
Parent Education
Before the high-risk infant can be discharged home, the home caregivers must demonstrate competency in all the care their newborn requires. Each task the home caregiver must complete before discharge is a point of education for the nurse. All home-going medications are listed and described, and administration is shown by the nurse prior to the caregiver completing the medication administration. The home feeding pump is set up by the nurse first, and then the caregiver does the same preparation under the watchful eyes of the nurse. Placement of the feeding tube, if required for feeding, is first done by the nurse, and then the caregiver is asked to demonstrate their comfort in placing the gavage tube, administering the feeding on a pump, and identifying if the tube has been dislodged. The care provider must be able to administer and store the infant's medications safely. They must verbalize that they can identify signs and symptoms of illness, that they know when to contact the primary care provider, and that they can recognize when urgent care is needed. Infant cardiopulmonary resuscitation (CPR) training instruction is provided to most caregivers of premature infants prior to discharge. Education surrounding all the infant’s care begins early during the admission and continues throughout the hospital stay with consistent and realistic, but hopeful, information. Tools to prepare the home caregiver may include checklists showing care successfully demonstrated, pictographs, visual aids, or recorded information. Inviting the family to participate in rounds, particularly prior to discharge, allows them to direct questions to the primary care team.
Families with limited English proficiency or immigrant families are at increased risk for difficulties in understanding discharge and home care instructions. Discharge instructions in their primary language are essential. Appropriately trained medical interpreters are utilized throughout the parent education and training process to decrease the risk of misunderstanding. Allowing home caregivers to practice care with direct supervision and return demonstration decreases chances for error at home (Smith & Stewart, 2021). This practice is particularly well done with rooming-in practices where the caregivers stay with the newborn for one or two nights prior to discharge, providing the maximum amount of care that they can as a practice run for home. This is not always an option at all facilities, depending on space and room availability, but it can be a helpful practice for new parents and an efficient way to complete and evaluate discharge teaching.
Immigrant Families of High-Risk Newborns
Families who are immigrants to the United States, whether proficient in English or not, require culturally competent care along with discharge planning specific to their home life. “Cultural values, historical trends, parents' level of education, and the process of immigration blend in intricate ways to determine how immigrant parents in the United States enact the role of parenting” (Bradley et al., 2014). How the family tackles their child's health-care needs and what materials they need to assist their children in growing and developing is different for each family (McGowan et al., 2019).
A psychosocial assessment , an assessment to determine a family's mental health and social well-being, is performed by a social worker prior to discharge to identify and support any social or financial needs for the family. Families with high-risk infants are at higher risk for child abuse or neglect (Puls et al., 2019). Both preterm birth and prolonged hospitalization are known family stressors and risk factors for family dysfunction and child abuse (American Academy of Pediatrics Committee on Fetus and Newborn, 2008). Family risk factors identified at discharge require close follow-up and support. Risk factors for families that lead to closer follow-up are financial difficulties, history of or current substance use disorder, inadequate prenatal care, domestic violence, marital instability, and parental mental health diagnosis of anxiety or depression.
The Center for Healthy Families provides support to teen, foster, and adoptive parents through community- and school-based services.
Discharge to home may not be possible if the infant is medically unready or the home environment is inadequate for the needs of the infant. In these instances, transfer to a less acute hospital for care or to a foster care placement that can provide adequate care may be an appropriate interim home until is it determined that the family can safely care for and house the infant (Smith & Stewart, 2021).
WIC provides financial support for supplemental food and nutritional education for low-income families with infants and children.
Infant Hospice Care
When an infant is nearing the end of life, they may need specialized medical care, called hospice care . It includes multidisciplinary care as a consulted service for high-risk infants who have an incurable terminal disorder. Any infant who has been found to have a disorder or disease state that has made it so that surgical and medical interventions will not significantly improve their health or well-being and who will experience a shortened lifespan because of those diagnosed disorders or diseases qualifies for hospice care. The hospice organization provides medical home visits, home nursing visits, respite care for the care providers, pain and comfort measures, and bereavement support for the whole family (Smith & Stewart, 2021). Part of the hospice team’s work is to provide a letter stating the infant’s do not resuscitate status and to share that information with local emergency medical services.


1.1: Diversity
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- Krischa Esquivel, Emily Elam, Jennifer Paris, & Maricela Tafoya
- College of the Canyons
Diversity
Let’s begin by defining diversity and exploring its significance to working with children. The concept of diversity means understanding that each individual is unique, and recognizing our individual differences.  It is the exploration of these differences in a safe, positive, and nurturing environment. It is about understanding each other and moving beyond simple tolerance to embracing and celebrating the rich dimensions of diversity contained within each individual.
Diversity is a reality created by individuals and groups from a broad spectrum of demographic and philosophical differences. It is extremely important to support and protect diversity, to value individuals and groups without prejudice, and foster a climate where equity and mutual respect are intrinsic.
According to Queensborough Community College, “‘Diversity’ means more than just acknowledging and/or tolerating difference. Diversity is a set of conscious practices that involve:
- Understanding and appreciating interdependence of humanity, cultures, and the natural environment.
- Practicing mutual respect for qualities and experiences that are different from our own.
- Understanding that diversity includes not only ways of being but also ways of knowing;
- Recognizing that personal, cultural and institutionalized discrimination creates and sustains privileges for some while creating and sustaining disadvantages for others;
- Building alliances across differences so that we can work together to eradicate all forms of discrimination.
Diversity includes, therefore, knowing how to relate to those qualities and conditions that are different from our own and outside the groups to which we belong, yet are present in other individuals and groups. These include but are not limited to age, ethnicity, class, gender, physical abilities/qualities, race, sexual orientation, as well as religious status, gender expression, educational background, geographical location, income, marital status, parental status, and work experiences. Finally, we acknowledge that categories of difference are not always fixed but also can be fluid, we respect individual rights to self-identification, and we recognize that no one culture is intrinsically superior to another”. [4]
Cultural and Linguistic Diversity in the U.S. and California
There is a rich array of ethnic and social groups found in many early childhood programs in California. Much of this cultural diversity is due to high levels of immigration. Foreign-born persons represented 12 percent (32.5 million) of the U.S. population in 2002, with almost 50 percent of that group coming from Latin America, 25 percent from Asia, and 20 percent from Europe (Schmidley 2003). In 2010, of the more than 2.5 million children under the age of five living in California, about half of these children were Latino (U.S. Census Bureau 2010). It is important to note that Latinos may be of any race, according to the U.S. Census Bureau. White non-Latino children make up 30 percent of children under five in California, Asian-Pacific Islanders make up 10 percent, Black or African Americans make up 6 percent, and the remaining 4 percent represent a wide range of ethnic groups (Whitebook, Kipnis, and Bellm 2008). [5]
Significance of Diversity
A growing body of research shows that diversity in schools and communities can be a powerful lever leading to positive outcomes in school and in life. Racial and socioeconomic diversity benefits communities, schools, and children from all backgrounds. Today's students need to be prepared to succeed with a more diverse and more global workforce than ever before. Research has shown that more diverse organizations make better decisions with better results. The effects of socioeconomic diversity can be especially powerful for students from low-income families, who, historically, often have not had equal access to the resources they need to succeed. [6]


14: Quantitative Analysis- Descriptive Statistics
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Numeric data collected in a research project can be analysed quantitatively using statistical tools in two different ways. Descriptive analysis refers to statistically describing, aggregating, and presenting the constructs of interest or associations between these constructs. Inferential analysis refers to the statistical testing of hypotheses (theory testing). In this chapter, we will examine statistical techniques used for descriptive analysis, and the next chapter will examine statistical techniques for inferential analysis. Much of today’s quantitative data analysis is conducted using software programs such as SPSS or SAS. Readers are advised to familiarise themselves with one of these programs for understanding the concepts described in this chapter.


1.6: Assignment- Communicating in Business
Part 1
Your task is to read the statements below and rate your perception of your communication skills.
| How often does this describe me during a conversation/communication? | Usually | Sometimes | Seldom | |
|---|---|---|---|---|
| Writing Skills | I know the parts of a proper email, memo, and business letter formatting. | |||
| I know the basic parts of formal or informal reports. | ||||
| I can evaluate a document to determine if it might be successful. | ||||
| Reading Skills | I am familiar with specialized vocabulary in my field of work. | |||
| I am willing to look up the meanings of words or concepts I don’t fully understand. | ||||
| I can get the basic meaning of words I am unfamiliar with by using context clues in the text | ||||
| I am comfortable reading a text in a variety of mediums (paper, tablet, computer screen, etc) | ||||
| Listening Skills | I do not react to distractions (phone, etc). | |||
| I listen to half of the conversation without taking it over. | ||||
| I can provide proper verbal and nonverbal feedback (nodding). | ||||
| I can summarize the speaker’s ideas by paraphrasing and asking questions. | ||||
| Speaking Skills | I find it easy and comfortable to talk with friends. | |||
| I find it easy and comfortable to talk with coworkers | ||||
| I am confident when giving a presentation to different audiences | ||||
| I am confident in pronouncing and using words correctly |
After rating your skills, write a short response to the following questions (max 500 words)
- What are your strongest and weakest skills?
- How do you think this class will help you improve or build upon your current communication skill set?
Part 2
Your task is to write an email to your instructor to introduce yourself. Put your first and last name and the assignment title in the subject line. For example: Maria Ruiz Assignment 1
Your message should address the following:
- Reasons for taking this class
- Your career goals (short term/long term)
- Familiarity with computer technology
- A brief discussion of how you view your current communication skill levels. Were there any parts of the quiz that surprised you? What are your strongest and weakest skills?
- Is there anything in the class/syllabus that worries you? Any topic you are excited about or have extensive experience with?
Grading Rubric
| Criteria | Not Evident | Developing | Proficient | Exemplary | Points |
|---|---|---|---|---|---|
| Organization and format |
2 pts
Writing lacks logical organization. It may show some coherence but ideas lack unity. Serious errors and generally is an unorganized format and information. |
3 pts
Writing is coherent and logically organized, using a format suitable for the material presented. Some points may be contextually misplaced and/or stray from the topic. Transitions may be evident but not used throughout the essay. Organization and format used may detract from understanding the material presented. |
4 pts
Writing is coherent and logically organized, using a format suitable for the material presented. Transitions between ideas and paragraphs create coherence. Overall unity of ideas is supported by the format and organization of the material presented. |
5 pts
Writing shows high degree of attention to details and presentation of points. Format used enhances understanding of material presented. Unity clearly leads the reader to the writer’s conclusion and the format and information could be used independently. |
5 pts |
| Content |
2 pts
Some but not all required questions are addressed. Content and/or terminology is not properly used or referenced. Little or no original thought is present in the writing. Concepts presented are merely restated from the source, or ideas presented do not follow the logic and reasoning presented throughout the writing. |
3 pts
All required questions are addressed but may not be addressed with thoughtful consideration and/or may not reflect proper use of content terminology or additional original thought. Additional concepts may not be present and/or may not be properly cited sources. |
4 pts
All required questions are addressed with thoughtful consideration reflecting both proper use of content terminology and additional original thought. Some additional concepts may be presented from other properly cited sources, or originated by the author following logic and reasoning they’ve clearly presented throughout the writing. |
5 pts
All required questions are addressed with thoughtful in-depth consideration reflecting both proper use of content terminology and additional original thought. Additional concepts are clearly presented from properly cited sources, or originated by the author following logic and reasoning they’ve clearly presented throughout the writing. |
5 pts |
| Development – Critical Thinking |
4 pts
Shows some thinking and reasoning but most ideas are underdeveloped, unoriginal, and/or do not address the questions asked. Conclusions drawn may be unsupported, illogical or merely the author’s opinion with no supporting evidence presented. |
6 pts
Content indicates thinking and reasoning applied with original thought on a few ideas, but may repeat information provided and/ or does not address all of the questions asked. The author presents no original ideas, or ideas do not follow clear logic and reasoning. The evidence presented may not support conclusions drawn. |
8 pts
Content indicates original thinking, cohesive conclusions, and developed ideas with sufficient and firm evidence. Clearly addresses all of the questions or requirements asked. The evidence presented supports conclusions drawn. |
10 pts
Content indicates synthesis of ideas, in-depth analysis and evidence beyond the questions or requirements asked. Original thought supports the topic, and is clearly a well-constructed response to the questions asked. The evidence presented makes a compelling case for any conclusions drawn. |
10 pts |
| Grammar, Mechanics, Style |
2 pts
Writing contains many spelling, punctuation, and grammatical errors, making it difficult for the reader to follow ideas clearly. There may be sentence fragments and run-ons. The style of writing, tone, and use of rhetorical devices disrupts the content. Additional information may be presented but in an unsuitable style, detracting from its understanding. |
3 pts
Some spelling, punctuation, and grammatical errors are present, interrupting the reader from following the ideas presented clearly. There may be sentence fragments and run-ons. The style of writing, tone, and use of rhetorical devices may detract from the content. Additional information may be presented, but in a style of writing that does not support understanding of the content. |
4 pts
Writing is free of most spelling, punctuation, and grammatical errors, allowing the reader to follow ideas clearly. There are no sentence fragments and run-ons. The style of writing, tone, and use of rhetorical devices enhance the content. Additional information is presented in a cohesive style that supports understanding of the content. |
5 pts
Writing is free of all spelling, punctuation, and grammatical errors and written in a style that enhances the reader’s ability to follow ideas clearly. There are no sentence fragments and run-ons. The style of writing, tone, and use of rhetorical devices enhance the content. Additional information is presented to encourage and enhance understanding of the content. |
5 pts |
| Total: | 25 pts |
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- Assignment: Communicating in Business. Provided by : Lumen Learning. License : CC BY: Attribution


45.6E: Mating Systems and Sexual Selection
- Differentiate among monogamous, polygynous, and polyandrous mating systems, and distinguish between intersexual and intrasexual mate selection
Finding Sexual Partners
Not all animals reproduce sexually, but many that do have the same challenge: they need to find a suitable mate and often have to compete with other individuals to obtain one. Significant energy is spent in the process of locating, attracting, and mating with a sex partner.
Types of Mate Selection
Two types of selection that occur during the process of choosing a mate may be involved in the evolution of reproductive traits called secondary sexual characteristics. These types are: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex). Intersexual selection is often complex because choosing a mate may be based on a variety of visual, aural, tactile, and chemical cues. An example of intersexual selection is when female peacocks choose to mate with the male with the brightest plumage. This type of selection often leads to traits in the chosen sex that do not enhance survival, but are those traits most attractive to the opposite sex (often at the expense of survival). Intrasexual selection involves mating displays and aggressive mating rituals such as rams butting heads; the winner of these battles is the one that is able to mate. Many of these rituals use up considerable energy, but result in the selection of the healthiest, strongest, and/or most dominant individuals for mating.
Mating Systems
Three general mating systems, all involving innate as opposed to learned behaviors, are seen in animal populations: monogamous (monogamy), polygynous (polygyny), and polyandrous (polyandry).
In monogamous systems, one male and one female are paired for at least one breeding season. In some animals, such as the gray wolf, these associations can last much longer, even a lifetime. Several explanations have been proposed for this type of mating system. The “mate-guarding hypothesis” states that males stay with the female to prevent other males from mating with her. This behavior is advantageous in such situations where mates are scarce and difficult to find. Another explanation is the “male-assistance hypothesis,” where males that remain with a female to help guard and rear their young will have more and healthier offspring. Monogamy is observed in many bird populations where, in addition to the parental care from the female, the male is also a major provider of parental care for the chicks. A third explanation for the evolutionary advantages of monogamy is the “female-enforcement hypothesis.” In this scenario, the female ensures that the male does not have other offspring that might compete with her own, so she actively interferes with the male’s signaling to attract other mates.
Polygynous mating refers to one male mating with multiple females. In these situations, the female must be responsible for most of the parental care as the single male is not capable of providing care to that many offspring. In resourced-based polygyny, males compete for territories with the best resources. They then mate with females that enter the territory, drawn to its resource richness. The female benefits by mating with a dominant, genetically-fit male; however, it is at the cost of having no male help in caring for the offspring. An example is seen in the yellow-rumped honeyguide, a bird whose males defend beehives because the females feed on the wax. As the females approach, the male defending the nest will mate with them. Harem mating structures are a type of polygynous system where certain males dominate mating while controlling a territory with resources. Elephant seals, where the alpha male dominates the mating within the group, are an example. A third type of polygyny is a lek system. Here there is a communal courting area where several males perform elaborate displays for females; the females choose their mate from this group. This behavior is observed in several bird species.
In polyandrous mating systems, one female mates with many males. These types of systems are much rarer than monogamous and polygynous mating systems. In pipefishes and seahorses, males receive the eggs from the female, fertilize them, protect them within a pouch, and give birth to the offspring. Therefore, the female is able to provide eggs to several males without the burden of carrying the fertilized eggs.
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- OpenStax College, Behavioral Biology: Proximate and Ultimate Causes of Behavior. October 17, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44879/latest...e_45_07_02.jpg . License : CC BY: Attribution
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- polygyny. Provided by : Wiktionary. Located at : http://en.wiktionary.org/wiki/polygyny . License : CC BY-SA: Attribution-ShareAlike
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Key Points
- Two types of mate selection occur: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex).
- Three general mating systems, all involving innate as opposed to learned behaviors, are seen in animal populations: monogamous ( monogamy ), polygynous ( polygyny ), and polyandrous (polyandry).
- In monogamous systems, one male and one female are paired for at least one breeding season; although in some animals, these partnerships can last even longer, sometimes an entire lifetime; males provide substantial parental care.
- Polygynous mating refers to one male mating with multiple females; in these situations, the female must be responsible for most of the parental care as the single male is not capable of providing care to that many offspring.
- In polyandrous mating systems, one female mates with many males; these types of systems are much rarer than monogamous and polygynous mating systems.
Key Terms
- polyandry : the mating pattern whereby a female copulates with several males
- polygyny : the mating patterns whereby a male copulates with several females
- monogamy : a form of sexual bonding involving an exclusive pair bond between two individuals


7.2: Divisions of the Skeletal System
By the end of this section, you will be able to:
- Discuss the functions of the skeletal system
- Distinguish between the axial skeleton and appendicular skeleton
- Define the axial skeleton and its components
- Define the appendicular skeleton and its components
The skeletal system includes all of the bones, cartilages, and ligaments of the body that support and give shape to the body and body structures. The skeleton consists of the bones of the body. For adults, there are 206 bones in the skeleton. Younger individuals have higher numbers of bones because some bones fuse together during childhood and adolescence to form an adult bone. The primary functions of the skeleton are to provide a rigid, internal structure that can support the weight of the body against the force of gravity, and to provide a structure upon which muscles can act to produce movements of the body. The lower portion of the skeleton is specialized for stability during walking or running. In contrast, the upper skeleton has greater mobility and ranges of motion, features that allow you to lift and carry objects or turn your head and trunk.
In addition to providing for support and movements of the body, the skeleton has protective and storage functions. It protects the internal organs, including the brain, spinal cord, heart, lungs, and pelvic organs. The bones of the skeleton serve as the primary storage site for important minerals such as calcium and phosphate. The bone marrow found within bones stores fat and houses the blood-cell producing tissue of the body.
The skeleton is subdivided into two major divisions—the axial and appendicular.
The Axial Skeleton
The skeleton is subdivided into two major divisions—the axial and appendicular. The axial skeleton forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back (Figure 7.2). It serves to protect the brain, spinal cord, heart, and lungs. It also serves as the attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs.
The axial skeleton of the adult consists of 80 bones, including the skull , the vertebral column , and the thoracic cage . The skull is formed by 22 bones. Also associated with the head are an additional seven bones, including the hyoid bone and the ear ossicles (three small bones found in each middle ear). The vertebral column consists of 24 bones, each called a vertebra , plus the sacrum and coccyx . The thoracic cage includes the 12 pairs of ribs , and the sternum , the flattened bone of the anterior chest.
The Appendicular Skeleton
The appendicular skeleton includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton. There are 126 bones in the appendicular skeleton of an adult. The bones of the appendicular skeleton are covered in a separate chapter.


11.4: Water Absorption
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- Tom Buckley
- University of California, Davis
Learning Objectives
- Explain the function of root hairs.
- Define root pressure and explain its mechanism.
- Contrast the three pathways of water movement through the roots and identify each cell type or tissue involved.
Most plants secure the water and minerals they need from their roots. Water moves from the soil to the roots, stems, and ultimately the leaves, where transpiration occurs. The roots absorb enough water to compensate for water lost to transpiration. Rapid absorption is aided by root hairs , which extend from epidermal cells, increasing surface area (Figure \(\PageIndex{1}\)). As discussed earlier in this chapter, roots draw water from the soil because they have lower water potential than the soil. Much of this difference in water potential is an indirect result of transpiration, but roots can also water potential by decreasing solute potential.
Root Pressure
When a tomato plant is carefully severed close to the base of the stem, sap oozes from the stump (Figure \(\PageIndex{2}\)). The fluid comes out because roots are constantly absorbing water, drawing it into the vascular cylinder, and pushing it up the xylem. This is called ro ot pressure , and it is created by the osmotic pressure of solutes trapped in the vascular cylinder by the Casparian strip .
Although root pressure plays a small role in the transport of water in the xylem in some plants and in some seasons, it does not account for most water transport. As evidence, few plants develop root pressures greater than ~0.2 kPa, and some develop no root pressure at all. Additionally, the volume of fluid transported by root pressure is not enough to account for the measured movement of water in the xylem of most trees and vines. Furthermore, the highest root pressures occur in the spring, but water moves through the xylem most rapidly in the summer (when transpiration is high).
As discussed in the Cohesion-Tension Theory section , transpiration, rather than root pressure, is typically the driving force for upward water movement in a plant. However, when transpiration rates are very low, such as in cool and humid weather, root pressure pushes water up the xylem faster than water is lost through the stomata. As a result water droplets are forced out of openings on the leaf margin, a phenomenon called guttation (Figure \(\PageIndex{3}\)). Droplets resulting from guttation are not to be confused with dew droplets, which result from the condensation of water vapor when the air becomes colder and has less capacity to hold water. In other words, guttation results from water that was inside of the plant, but dew droplets form from water vapor that was in the surrounding air.
Pathways of Water Movement
Water can move through the roots by three separate pathways: apoplast, symplast, and transmembrane (transcellular). In the apoplast pathway (apoplastic route), water moves through the spaces between the cells and in the cells walls themselves. In the symplast pathway (symplastic route), water passes from cytoplasm to cytoplasm through plasmodesmata (Figure \(\PageIndex{4}\)). In the transmembrane pathway , water crosses plasma membranes, entering and exiting each cell. Water moving through the transmembrane pathway thus moves through both the symplast (interconnected cytoplasms) and apoplast (cell walls and spaces in between cells). Water may also cross the tonoplast, entering the central vacuole as part of the transmembrane pathway.
Water from the soil is absorbed by the root hairs of the epidermis and then moves through the cortex through one of the three pathways. However, the inner boundary of the cortex, the endodermis , is impervious to water due to the Casparian strip. Regardless of how the water moved up to this point (apoplast, symplast, transmembrane), it must enter the cytoplasms of the endodermal cells. From here it can pass via plasmodesmata into the cells of the vascular cylinder (stele). Once inside, water is again free to move through the apolast, the symplast, or both (transmembrane).
Once in the xylem, water with the minerals that have been deposited in it (as well as occasional organic molecules supplied by the root tissue) move up in the vessel elements and tracheids. At any level, the water can leave the xylem and pass laterally to supply the needs of other tissues. At the leaves, the xylem passes into the petiole and then into the veins of the leaf. Water leaves the finest veins and enters the cells of the spongy and palisade layers. Here some of the water may be used in metabolism, but most is lost in transpiration.
Figure \(\PageIndex{4}\) illustrates minerals moving through the apoplast or symplast, but minerals typically move through the symplast. Minerals enter the root by active transport into the symplast of epidermal cells and move toward and into the vascular cylinder through the plasmodesmata connecting the cells. They enter the conducting cells of the xylem from the pericycle and other parenchyma cells via active transport through specialized transmembrane channels.
Attributions
Curated and authored by Melissa Ha using the following sources:
- 16.2A Xylem from Biology by John. W. Kimball (licensed CC-BY )
- 30.5 Transport of Water and Solutes in Plants from Biology 2e by OpenStax (licensed CC-BY ). Access for free at openstax.org .