15.9: Mutation- Altered Genes
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In the living cell, DNA undergoes frequent chemical change, especially when it is being replicated (in S phase of the eukaryotic cell cycle). Most of these changes are quickly repaired. Those that are not result in a mutation. Thus, mutation is a failure of DNA repair .
Single-base substitutions
A single base, say an A, becomes replaced by another. Single base substitutions are also called point mutations . (If one purine [A or G] or pyrimidine [C or T] is replaced by the other, the substitution is called a transition . If a purine is replaced by a pyrimidine or vice-versa, the substitution is called a transversion .)
Missense mutations
With a missense mutation, the new nucleotide alters the codon so as to produce an altered amino acid in the protein product.
Deasese: Sickle Cell anemia
The replacement of A by T at the 17th nucleotide of the gene for the beta chain of hemoglobin changes the codon GAG (for glutamic acid) to GTG (which encodes valine). Thus the 6th amino acid in the chain becomes valine instead of glutamic acid.
Nonsense mutations
With a nonsense mutation, the new nucleotide changes a codon that specified an amino acid to one of the STOP codons ( TAA , TAG , or TGA ). Therefore, translation of the messenger RNA transcribed from this mutant gene will stop prematurely. The earlier in the gene that this occurs, the more truncated the protein product and the more likely that it will be unable to function.
Cystic Fibrosis
Here is a sampling of mutations that have been found in patients with cystic fibrosis . Each of these mutations occurs in a huge gene that encodes a protein (of 1480 amino acids) called the c ystic f ibrosis t ransmembrane conductance r egulator ( CFTR ). The protein is responsible for transporting chloride and bicarbonate ions through the plasma membrane. The gene encompasses over 188,000 base pairs on chromosome 7 embedded in which are 27 exons encoding the protein. The numbers in the mutation column represent the number of the nucleotides affected. Defects in the protein cause the various symptoms of the disease. Unlike sickle-cell disease, then, no single mutation is responsible for all cases of cystic fibrosis. People with cystic fibrosis inherit two mutant genes, but the mutations need not be the same.
In one patient with cystic fibrosis ( Patient B ), the substitution of a T for a C at nucleotide 1609 converted a glutamine codon ( CAG ) to a STOP codon ( TAG ). The protein produced by this patient had only the first 493 amino acids of the normal chain of 1480 and could not function.
Silent mutations
Most amino acids are encoded by several different codons. For example, if the third base in the TCT codon for serine is changed to any one of the other three bases, serine will still be encoded. Such mutations are said to be silent because they cause no change in their product and cannot be detected without sequencing the gene (or its mRNA).
Splice-site mutations
The removal of intron sequences, as pre-mRNA is being processed to form mRNA, must be done with great precision. Nucleotide signals at the splice sites guide the enzymatic machinery. If a mutation alters one of these signals, then the intron is not removed and remains as part of the final RNA molecule. The translation of its sequence alters the sequence of the protein product.
Insertions and Deletions (Indels)
Extra base pairs may be added ( insertions ) or removed ( deletions ) from the DNA of a gene. The number can range from one to thousands. Collectively, these mutations are called indels .
Indels involving one or two base pairs (or multiples of two) can have devastating consequences to the gene because translation of the gene is "frameshifted". This figure shows how by shifting the reading frame one nucleotide to the right, the same sequence of nucleotides encodes a different sequence of amino acids. The mRNA is translated in new groups of three nucleotides and the protein specified by these new codons will be worthless. Scroll up to see two other examples ( Patients C and D ).
Frameshifts often create new STOP codons and thus generate nonsense mutations. Perhaps that is just as well as the protein would probably be too garbled anyway to be useful to the cell.
Indels of three nucleotides or multiples of three may be less serious because they preserve the reading frame (see the above figure).
However, a number of inherited human disorders are caused by the insertion of many copies of the same triplet of nucleotides. Huntington's disease and the fragile X syndrome are examples of such trinucleotide repeat diseases.
Disease: Fragile X Syndrome
Several disorders in humans are caused by the inheritance of genes that have undergone insertions of a string of 3 or 4 nucleotides repeated over and over. A locus on the human X chromosome contains such a stretch of nucleotides in which the triplet CGG is repeated (CGGCGGCGGCGG, etc.). The number of CGGs may be as few as 5 or as many as 50 without causing a harmful phenotype (these repeated nucleotides are in a noncoding region of the gene). Even 100 repeats usually cause no harm. However, these longer repeats have a tendency to grow longer still from one generation to the next (to as many as 4000 repeats).
This causes a constriction in the X chromosome, which makes it quite fragile. Males who inherit such a chromosome (only from their mothers, of course) show a number of harmful phenotypic effects including mental retardation. Females who inherit a fragile X (also from their mothers; males with the syndrome seldom become fathers) are only mildly affected.
The above image shows the pattern of inheritance of the fragile X syndrome in one family. The number of times that the trinucleotide CGG is repeated is given under the symbols. The gene is on the X chromosome, so women (circles) have two copies of it; men (squares) have only one. People with a gene containing 80–90 repeats are normal (light red), but this gene is unstable, and the number of repeats can increase into the hundreds in their offspring. Males who inherit such an enlarged gene suffer from the syndrome (solid red squares). (Data from C. T. Caskey, et al.).
Polyglutamine Diseases
In these disorders, the repeated trinucleotide is CAG , which adds a string of glutamines (Gln) to the encoded protein. These have been implicated in a number of central nervous system disorders including
- Huntington's disease (where the protein called huntingtin carries the extra glutamines). The abnormal protein increases the level of the p53 protein in brain cells causing their death by apoptosis.
- some cases of Parkinson's disease where the extra glutamines are in the protein ataxin-2.
Muscular Dystrophy
Some forms of muscular dystrophy that appear in adults are caused by tri- or tetranucleotide, e.g. (CTG) n and (CCTG) n , repeats where n may run into the thousands. The huge RNA transcripts that result interfere with the alternative splicing of other transcripts in the nucleus.
Amyotrophic Lateral Sclerosis (ALS)
ALS is a neurodegenerative disorder leading to dementia and muscle weakness. (ALS is often called "Lou Gehrig's disease" after the baseball player who died from it.)
The most common mutation in ALS is an expansion of the number of repeats of the hexanucleotide GGGGCC in a gene on chromosome 9 from the normal two, or at least fewer than three dozen, to hundreds or even several thousand. Translation of both the sense and the antisense strands containing these repeats (and in all 3 reading frames; there is no ATG start codon) produces polymers with long strings of gly-ala, gly-pro, gly-arg (from the sense strand) as well as pro-ala, another pro-gly, and pro-arg from the antisense strand.
Duplications
Duplications are a doubling of a section of the genome. During meiosis, crossing over between sister chromatids that are out of alignment can produce one chromatid with a duplicated gene and the other (not shown) with the two genes with deletions. In the case shown here, unequal crossing over created a second copy of a gene needed for the synthesis of the steroid hormone aldosterone .
However, this new gene carries inappropriate promoters at its 5' end (acquired from the 11-beta hydroxylase gene) that cause it to be expressed more strongly than the normal gene. The mutant gene is dominant: all members of one family (through four generations) who inherited at least one chromosome carrying this duplication suffered from high blood pressure and were prone to early death from stroke.
Gene duplication has also been implicated in several human neurological disorders.
Gene duplication has occurred repeatedly during the evolution of eukaryotes. Genome analysis reveals many genes with similar sequences in a single organism. Presumably these paralogous genes have arisen by repeated duplication of an ancestral gene.
Such gene duplication can be beneficial.
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Over time, the duplicates can acquire different functions.
- The proteins they encode can take on different functions; for example, if the original gene product carried out two different functions (see "pleiotropy"), each duplicated gene can now specialize at one function and do a better job at it than the parental gene.
- But even if they do not, changes in the regulatory sequences of the genes (promoters and enhancers) may cause the same protein to be expressed at different times, at different levels, and/or in different tissues.
- But even while two paralogous genes are still similar in sequence and function, their existence provides redundancy ("belt and suspenders"). This may be a major reason why knocking out genes in yeast, "knockout mice", etc. so often has such a mild effect on the phenotype. The function of the knocked out gene can be taken over by a paralog.
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After gene duplication, random loss — or inactivation — of one of these genes at a later time in
- one group of descendants
- different from the loss in another group
Translocations
Translocations are the transfer of a piece of one chromosome to a nonhomologous chromosome . Translocations are often reciprocal; that is, the two nonhomologues swap segments.
Translocations can alter the phenotype is several ways:
- the break may occur within a gene destroying its function
- translocated genes may come under the influence of different promoters and enhancers so that their expression is altered. The t(8;14) translocation in Burkitt's lymphoma (figure) is an example.
- the breakpoint may occur within a gene creating a hybrid gene. This may be transcribed and translated into a protein with an N-terminal of one normal cell protein coupled to the C-terminal of another. The Philadelphia chromosome found so often in the leukemic cells of patients with chronic myelogenous leukemia ( CML ) is the result of a translocation which produces a compound gene ( bcr-abl ).
Frequency of Mutations
Mutations are rare events. This is surprising. Humans inherit 3 x 10 9 base pairs of DNA from each parent. Just considering single-base substitutions, this means that each cell has 6 billion (6 x 10 9 ) different base pairs that can be the target of a substitution. Single-base substitutions are most apt to occur when DNA is being copied; for eukaryotes that means during S phase of the cell cycle.
No process is 100% accurate. Even the most highly skilled typist will introduce errors when copying a manuscript. So it is with DNA replication. Like a conscientious typist, the cell does proofread the accuracy of its copy. But, even so, errors slip through. It has been estimated that in humans and other mammals, uncorrected errors (= mutations) occur at the rate of about 1 in every 50 million (5 x 10 7 ) nucleotides added to the chain. (Not bad — I wish that I could type so accurately.) But with 6 x 10 9 base pairs in a human cell, that means that each new cell contains some 120 new mutations.
Should we be worried? The evidence is not clear. Only 1.2% of our DNA encodes the exons of our proteome, and for a long time it was thought that much of the rest was "junk" DNA. Mutations in it would most likely be harmless. And even in coding regions, the existence of synonymous codons could result in the altered (mutated) gene still encoding the same amino acid in the protein. But it now appears that as much as 80% of our DNA seems to participate in regulating which genes are expressed, and how strongly, in each of the multitude of differentiated cell types in our body as each responds to the signals (nutrients, hormones, etc.) it receives. So mutations in these regions might well have harmful, if subtle, effects.
As more vertebrate genomes are sequenced, it turns out that some of these stretches of DNA that do not encode proteins none-the-less have been remarkably conserved during vertebrate evolution. Some of these regions have accumulated even fewer mutations than protein-encoding genes have. This suggests that these sequences are extremely important to the welfare of the organism. However, other regions of the genome seem able to sustain point mutations with no detectible harm.
Recent advances have enabled the coding portions of the genome of single cells to be sequenced. Preliminary results indicate that each normal cell in an adult has accumulated ~20 somatic mutations, and that its collection of mutations differs from cell to cell. Cancer cells accumulate many more mutations (often in the hundreds).
How can we measure the frequency at which phenotype-altering mutations occur? In humans, it is not easy.
- First we must be sure that the mutation is newly-arisen . (Some populations have high frequencies of a particular mutation, not because the gene is especially susceptible, but because it has been passed down through the generations from a early "founder".
- Recessive mutations (most of them are) will not be seen except on the rare occasions that both parents contribute a mutation at the same locus to their child.
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This leaves us with estimating mutation frequencies for genes that are inherited as
- autosomal dominants
- X-linked recessives ; that is, recessives on the X chromosome which will be expressed in males because they inherit only one X chromosome.
Examples
Frequency is expressed as the frequency of mutations occurring at that locus in the gametes
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Autosomal dominants
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Retinoblastoma
in the RB gene: about 8 per million (8 x 10 -6 ) -
Osteogenesis imperfecta
in one or the other of the two genes that encode Type I collagen : about 1 per 100,000 (10 -5 ) -
Inherited tendency to polyps (and later cancer) in the colon.
in a tumor suppressor gene ( APC ): ~10 -5
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Retinoblastoma
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X-linked recessives
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Hemophilia A
~3 x 10 -5 (the Factor VIII gene) -
Duchenne Muscular Dystrophy (DMD)
>8 x 10 -5 (the dystrophin gene)
Why should the mutation frequency in the dystrophin gene be so much larger than most of the others? It's probably a matter of size. The dystrophin gene stretches over 2.4 x 10 6 base pairs of DNA. This is almost 0.1% of the entire human genome! Such a huge gene offers many possibilities for damage.
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Hemophilia A
Measuring Mutation Rate
The frequency with which a given mutation is seen in a population (e.g., the mutation that causes cystic fibrosis) provides only a rough approximation of mutation rate — the rate at which fresh mutations occur — because of historical factors at work such as natural selection (positive or negative), drift , and founder effect . In addition, most methods for counting mutations require that the mutation have a visible effect on the phenotype. Thus
- many (but not all) mutations in noncoding DNA
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mutations that produce
- synonymous codons (encode the same amino acid)
- or, sometimes, new codons that encode a chemically-similar amino acid
- mutations which disrupt a gene whose functions are redundant; that is, can be compensated for by other genes
will not be seen. But now these problems have been largely solved. The story is told in a report by D. R. Denver, et al. in the 5 August 2004 issue of Nature .
C. elegans
The Procedure
- Their organism = C. elegans
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Its advantages
- compact genome
- hermaphroditic — it fertilizes its own eggs and any new germline mutation will soon be either lost or appear on both homologous chromosomes.
- rapid generation time (4 days)
- They created 198 different experimental lines of worms.
- They grew them under optimum conditions to minimize any effects of natural selection.
- Only one offspring was kept at each new generation.
- Each line was maintained for several hundred generations.
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At the end of this time, random stretches of DNA
- derived from multiple locations on each of the six C. elegans chromosomes and
- totalling an average of ~21 thousand base pairs for each line
Results
Examining the DNA sequences from their experimental animals (a total of over 4 million base pairs!), and comparing them with the controls, turned up a total of 30 mutations.
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17 of these were insertions or deletions ("indels')
- 7 in exons — all but 2 of which produced frameshifts and a premature STOP codon.
- 10 in introns or between genes
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13 of these were single base substitutions ("point" mutations)
- 3 in exons : one "silent" producing a synonymous codon; two that changed the encoded amino acid.
- 10 in introns or between genes
Calculating Mutation Rate
From these results I have pooled their data to calculate an approximate rate at which spontaneous mutations occur throughout the genome.
Mutation Rate = # of mutations observed [30] ÷ (# of experimental lines [198]) x (average # of generations [339]) x (average # of base pairs sequenced [~21,000])
yielding a rate of 2.1 x 10 -8 mutations per base pair per generation.
The total C. elegans genome contains some 10 8 base pairs so this tells us that two new germline mutations occur somewhere in each of C. elegans 's two haploid genomes in each generation.
A similar analysis for Drosophila (whose genome is about the same size as that of C. elegans ) showed a similar mutation rate: ~10 -8 mutations per base pair per generation. As for the green plant Arabidopsis thaliana , its spontaneous mutation rate is slightly lower: ~7 x 10 -9 mutations per base pair per generation.
In the 30 April 2010 issue of Science , Roach, J. C., et al ., reported that the rate for humans is in the same range: ~1.1 x 10 -8 mutations per base pair in the haploid genome. With a diploid genome of 6 x 10 9 base pairs, that works out to some 70 new mutations in each child. They derived these numbers from comparing the complete genome sequence of two children and their parents.
In the 20 July 2012 issue of Cell , Wang, J., et al . reported the results of sequencing 8 individual sperm cells from a 40-year-old man. They found a mutation rate ranging from 2.0 x 10 -8 to 3.8 x 10 -8 .
Should we be worried about such spontaneous mutation rates? Probably not too much. With our high proportion of noncoding DNA, many mutations will occur in regions that will have no effect on our phenotype. Evidence: out of a total of 251 mutations found in the 8 sperm cells, only 3 were missense mutations altering a gene product. However, even in noncoding DNA, point mutations may affect the expression of genes, so perhaps as many as 10% of the point mutations a child inherits may have harmful, if subtle, effects.
Males Contribute More Mutations Than Females
If most mutations occur during S phase of cell division, then males should be more at risk. This is because only two dozen (24) or so mitotic divisions occur from the fertilized egg that starts a little girl's embryonic development and the setting aside of her future eggs (which is done long before she is even born). Furthermore, the sperm of a 30-year old man, in contrast, are the descendants of at least 400 mitotic divisions since the fertilized egg that formed him.
So, fathers are more likely than mothers to transmit newly-formed mutations to their children. The sperm of a 25-year-old man might carry some 45 new mutations. This number rises at a rate of about 1 per year, so the sperm of a 40-year-old man may transmit some 60 new mutations to his children (about 20 of these in coding regions). No matter what the age of the mother, she transmits only about 15 new mutations to her offspring. (But chromosomal aberrations , like aneuploidy, are more apt to arise in eggs than in sperm, and the incidence of these increases with maternal age.) These data explain why the children of aged fathers suffer more genetic disorders than those of young fathers.
Somatic vs. Germline Mutations
The significance of mutations is profoundly influenced by the distinction between germline and soma. Mutations that occur in a somatic cell , in the bone marrow or liver for example, may
- damage the cell
- make the cell cancerous
- kill the cell
Whatever the effect, the ultimate fate of that somatic mutation is to disappear when the cell in which it occurred, or its owner, dies.
Germline mutations , in contrast, will be found in every cell descended from the zygote to which that mutant gamete contributed. If an adult is successfully produced, every one of its cells will contain the mutation. Included among these will be the next generation of gametes, so if the owner is able to become a parent, that mutation will pass down to yet another generation.


9.5: Synovial Joints
By the end of this section, you will be able to:
- Describe the structural features of a synovial joint
- Discuss the function of additional structures associated with synovial joints
- List the six types of synovial joints and give an example of each
Synovial joints are the most common type of joint in the body (Figure \(\PageIndex{1}\) ). A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity. This fluid-filled space is the site at which the articulating surfaces of the bones contact each other. Also unlike fibrous or cartilaginous joints, the articulating bone surfaces at a synovial joint are not directly connected to each other with fibrous connective tissue or cartilage. This gives the bones of a synovial joint the ability to move smoothly against each other, allowing for increased joint mobility.
Structural Features of Synovial Joints
Synovial joints are characterized by the presence of a joint cavity. The walls of this space are formed by the articular capsule , a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. The bones of the joint articulate with each other within the joint cavity.
Friction between the bones at a synovial joint is prevented by the presence of the articular cartilage , a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. However, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. Instead, the articular cartilage acts like a Teflon ® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. Lining the inner surface of the articular capsule is a thin synovial membrane . The cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. This fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. The ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.
Outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. These strengthen and support the joint by anchoring the bones together and preventing their separation. Ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. Ligaments are classified based on their relationship to the fibrous articular capsule. An extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.
At many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. A tendon is the dense connective tissue structure that attaches a muscle to bone. As forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. This type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.
Additional Structures Associated with Synovial Joints
A few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This is called an articular disc , which is generally small and oval-shaped, or a meniscus , which is larger and C-shaped. These structures can serve several functions, depending on the specific joint. In some places, an articular disc may act to strongly unite the bones of the joint to each other. Examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. At other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. Finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. Some synovial joints also have a fat pad, which can serve as a cushion between the bones.
Additional structures located outside of a synovial joint serve to prevent friction between the bones of the joint and the overlying muscle tendons or skin. A bursa (plural = bursae) is a thin connective tissue sac filled with lubricating liquid. They are located in regions where skin, ligaments, muscles, or muscle tendons can rub against each other, usually near a body joint (Figure \(\PageIndex{2}\)). Bursae reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other. Bursae are classified by their location. A subcutaneous bursa is located between the skin and an underlying bone. It allows skin to move smoothly over the bone. Examples include the prepatellar bursa located over the kneecap and the olecranon bursa at the tip of the elbow. A submuscular bursa is found between a muscle and an underlying bone, or between adjacent muscles. These prevent rubbing of the muscle during movements. A large submuscular bursa, the trochanteric bursa, is found at the lateral hip, between the greater trochanter of the femur and the overlying gluteus maximus muscle. A subtendinous bursa is found between a tendon and a bone. Examples include the subacromial bursa that protects the tendon of shoulder muscle as it passes under the acromion of the scapula, and the suprapatellar bursa that separates the tendon of the large anterior thigh muscle from the distal femur just above the knee.
A tendon sheath is similar in structure to a bursa, but smaller. It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements.
Homeostatic Imbalances
Bursitis
Bursitis is the inflammation of a bursa near a joint. This will cause pain, swelling, or tenderness of the bursa and surrounding area, and may also result in joint stiffness. Bursitis is most commonly associated with the bursae found at or near the shoulder, hip, knee, or elbow joints. At the shoulder, subacromial bursitis may occur in the bursa that separates the acromion of the scapula from the tendon of a shoulder muscle as it passes deep to the acromion. In the hip region, trochanteric bursitis can occur in the bursa that overlies the greater trochanter of the femur, just below the lateral side of the hip. Ischial bursitis occurs in the bursa that separates the skin from the ischial tuberosity of the pelvis, the bony structure that is weight bearing when sitting. At the knee, inflammation and swelling of the bursa located between the skin and patella bone is prepatellar bursitis (“housemaid’s knee”), a condition more commonly seen today in roofers or floor and carpet installers who do not use knee pads. At the elbow, olecranon bursitis is inflammation of the bursa between the skin and olecranon process of the ulna. The olecranon forms the bony tip of the elbow, and bursitis here is also known as “student’s elbow.”
Bursitis can be either acute (lasting only a few days) or chronic. It can arise from muscle overuse, trauma, excessive or prolonged pressure on the skin, rheumatoid arthritis, gout, or infection of the joint. Repeated acute episodes of bursitis can result in a chronic condition. Treatments for the disorder include antibiotics if the bursitis is caused by an infection, or anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids if the bursitis is due to trauma or overuse. Chronic bursitis may require that fluid be drained, but additional surgery is usually not required.
Types of Synovial Joints
Synovial joints are subdivided based on the shapes of the articulating surfaces of the bones that form each joint. The six types of synovial joints are pivot, hinge, condyloid, saddle, plane, and ball-and socket-joints (Figure 9. \(\PageIndex{3}\) ).
Pivot Joint
At a pivot joint , a rounded portion of a bone is enclosed within a ring formed partially by the articulation with another bone and partially by a ligament (see Figure \(\PageIndex{3}\) a ). The bone rotates within this ring. Since the rotation is around a single axis, pivot joints are functionally classified as a uniaxial diarthrosis type of joint. An example of a pivot joint is the atlantoaxial joint, found between the C1 (atlas) and C2 (axis) vertebrae. Here, the upward projecting dens of the axis articulates with the inner aspect of the atlas, where it is held in place by a ligament. Rotation at this joint allows you to turn your head from side to side. A second pivot joint is found at the proximal radioulnar joint . Here, the head of the radius is largely encircled by a ligament that holds it in place as it articulates with the radial notch of the ulna. Rotation of the radius allows for forearm movements.
Hinge Joint
In a hinge joint , the convex end of one bone articulates with the concave end of the adjoining bone (see Figure 9. \(\PageIndex{3}\) b ). This type of joint allows only for bending and straightening motions along a single axis, and thus hinge joints are functionally classified as uniaxial joints. A good example is the elbow joint, with the articulation between the trochlea of the humerus and the trochlear notch of the ulna. Other hinge joints of the body include the knee, ankle, and interphalangeal joints between the phalanx bones of the fingers and toes.
Condyloid Joint
At a condyloid joint (ellipsoid joint), the shallow depression at the end of one bone articulates with a rounded structure from an adjacent bone or bones (see Figure \(\PageIndex{3}\) e ). The knuckle (metacarpophalangeal) joints of the hand between the distal end of a metacarpal bone and the proximal phalanx bone are condyloid joints. Another example is the radiocarpal joint of the wrist, between the shallow depression at the distal end of the radius bone and the rounded scaphoid, lunate, and triquetrum carpal bones. In this case, the articulation area has a more oval (elliptical) shape. Functionally, condyloid joints are biaxial joints that allow for two planes of movement. One movement involves the bending and straightening of the fingers or the anterior-posterior movements of the hand. The second movement is a side-to-side movement, which allows you to spread your fingers apart and bring them together, or to move your hand in a medial-going or lateral-going direction.
Saddle Joint
At a saddle joint , both of the articulating surfaces for the bones have a saddle shape, which is concave in one direction and convex in the other (see Figure \(\PageIndex{3}\) c ). This allows the two bones to fit together like a rider sitting on a saddle. Saddle joints are functionally classified as biaxial joints. The primary example is the first carpometacarpal joint, between the trapezium (a carpal bone) and the first metacarpal bone at the base of the thumb. This joint provides the thumb the ability to move away from the palm of the hand along two planes. Thus, the thumb can move within the same plane as the palm of the hand, or it can jut out anteriorly, perpendicular to the palm. This movement of the first carpometacarpal joint is what gives humans their distinctive “opposable” thumbs. The sternoclavicular joint is also classified as a saddle joint.
Plane Joint
At a plane joint (gliding joint), the articulating surfaces of the bones are flat or slightly curved and of approximately the same size, which allows the bones to slide against each other (see Figure \(\PageIndex{3}\) d ). The motion at this type of joint is usually small and tightly constrained by surrounding ligaments. Based only on their shape, plane joints can allow multiple movements, including rotation. Thus plane joints can be functionally classified as a multiaxial joint. However, not all of these movements are available to every plane joint due to limitations placed on it by ligaments or neighboring bones. Thus, depending upon the specific joint of the body, a plane joint may exhibit only a single type of movement or several movements. Plane joints are found between the carpal bones (intercarpal joints) of the wrist or tarsal bones (intertarsal joints) of the foot, between the clavicle and acromion of the scapula (acromioclavicular joint), and between the superior and inferior articular processes of adjacent vertebrae (zygapophysial joints).
Ball-and-Socket Joint
The joint with the greatest range of motion is the ball-and-socket joint . At these joints, the rounded head of one bone (the ball) fits into the concave articulation (the socket) of the adjacent bone (see Figure \(\PageIndex{3}\) f ). The hip joint and the glenohumeral (shoulder) joint are the only ball-and-socket joints of the body. At the hip joint, the head of the femur articulates with the acetabulum of the hip bone, and at the shoulder joint, the head of the humerus articulates with the glenoid cavity of the scapula.
Ball-and-socket joints are classified functionally as multiaxial joints. The femur and the humerus are able to move in both anterior-posterior and medial-lateral directions and they can also rotate around their long axis. The shallow socket formed by the glenoid cavity allows the shoulder joint an extensive range of motion. In contrast, the deep socket of the acetabulum and the strong supporting ligaments of the hip joint serve to constrain movements of the femur, reflecting the need for stability and weight-bearing ability at the hip.
Interactive Link
Watch this video to see an animation of synovial joints in action. Synovial joints are places where bones articulate with each other inside of a joint cavity. The different types of synovial joints are the ball-and-socket joint (shoulder joint), hinge joint (knee), pivot joint (atlantoaxial joint, between C1 and C2 vertebrae of the neck), condyloid joint (radiocarpal joint of the wrist), saddle joint (first carpometacarpal joint, between the trapezium carpal bone and the first metacarpal bone, at the base of the thumb), and plane joint (facet joints of vertebral column, between superior and inferior articular processes). Which type of synovial joint allows for the widest range of motion?
Aging and the...
Joints
Arthritis is a common disorder of synovial joints that involves inflammation of the joint. This often results in significant joint pain, along with swelling, stiffness, and reduced joint mobility. There are more than 100 different forms of arthritis. Arthritis may arise from aging, damage to the articular cartilage, autoimmune diseases, bacterial or viral infections, or unknown (probably genetic) causes.
The most common type of arthritis is osteoarthritis, which is associated with aging and “wear and tear” of the articular cartilage (Figure \(\PageIndex{4}\)). Risk factors that may lead to osteoarthritis later in life include injury to a joint; jobs that involve physical labor; sports with running, twisting, or throwing actions; and being overweight. These factors put stress on the articular cartilage that covers the surfaces of bones at synovial joints, causing the cartilage to gradually become thinner. As the articular cartilage layer wears down, more pressure is placed on the bones. The joint responds by increasing production of the lubricating synovial fluid, but this can lead to swelling of the joint cavity, causing pain and joint stiffness as the articular capsule is stretched. The bone tissue underlying the damaged articular cartilage also responds by thickening, producing irregularities and causing the articulating surface of the bone to become rough or bumpy. Joint movement then results in pain and inflammation. In its early stages, symptoms of osteoarthritis may be reduced by mild activity that “warms up” the joint, but the symptoms may worsen following exercise. In individuals with more advanced osteoarthritis, the affected joints can become more painful and therefore are difficult to use effectively, resulting in increased immobility. There is no cure for osteoarthritis, but several treatments can help alleviate the pain. Treatments may include lifestyle changes, such as weight loss and low-impact exercise, and over-the-counter or prescription medications that help to alleviate the pain and inflammation. For severe cases, joint replacement surgery (arthroplasty) may be required.
Joint replacement is a very invasive procedure, so other treatments are always tried before surgery. However arthroplasty can provide relief from chronic pain and can enhance mobility within a few months following the surgery. This type of surgery involves replacing the articular surfaces of the bones with prosthesis (artificial components). For example, in hip arthroplasty, the worn or damaged parts of the hip joint, including the head and neck of the femur and the acetabulum of the pelvis, are removed and replaced with artificial joint components. The replacement head for the femur consists of a rounded ball attached to the end of a shaft that is inserted inside the diaphysis of the femur. The acetabulum of the pelvis is reshaped and a replacement socket is fitted into its place. The parts, which are always built in advance of the surgery, are sometimes custom made to produce the best possible fit for a patient.
Gout is a form of arthritis that results from the deposition of uric acid crystals within a body joint. Usually only one or a few joints are affected, such as the big toe, knee, or ankle. The attack may only last a few days, but may return to the same or another joint. Gout occurs when the body makes too much uric acid or the kidneys do not properly excrete it. A diet with excessive fructose has been implicated in raising the chances of a susceptible individual developing gout.
Other forms of arthritis are associated with various autoimmune diseases, bacterial infections of the joint, or unknown genetic causes. Autoimmune diseases, including rheumatoid arthritis, scleroderma, or systemic lupus erythematosus, produce arthritis because the immune system of the body attacks the body joints. In rheumatoid arthritis, the joint capsule and synovial membrane become inflamed. As the disease progresses, the articular cartilage is severely damaged or destroyed, resulting in joint deformation, loss of movement, and severe disability. The most commonly involved joints are the hands, feet, and cervical spine, with corresponding joints on both sides of the body usually affected, though not always to the same extent. Rheumatoid arthritis is also associated with lung fibrosis, vasculitis (inflammation of blood vessels), coronary heart disease, and premature mortality. With no known cure, treatments are aimed at alleviating symptoms. Exercise, anti-inflammatory and pain medications, various specific disease-modifying anti-rheumatic drugs, or surgery are used to treat rheumatoid arthritis.
Interactive Link
Watch this animation to observe hip replacement surgery (total hip arthroplasty), which can be used to alleviate the pain and loss of joint mobility associated with osteoarthritis of the hip joint. What is the most common cause of hip disability?
Interactive Link
Watch this video to learn about the symptoms and treatments for rheumatoid arthritis. Which system of the body malfunctions in rheumatoid arthritis and what does this cause?


17.1: Physical Defenses
- Describe the various physical barriers and mechanical defenses that protect the human body against infection and disease
- Describe the role of microbiota as a first-line defense against infection and disease
Angela, a 25-year-old female patient in the emergency department, is having some trouble communicating verbally because of shortness of breath. A nurse observes constriction and swelling of the airway and labored breathing. The nurse asks Angela if she has a history of asthma or allergies.  With some difficulty, she explains that her father died suddenly at age 27, when she was just a little girl, of a similar respiratory attack. The underlying cause had never been identified.
- What are some possible causes of constriction and swelling of the airway?
- What causes swelling of body tissues in general?
Nonspecific innate immunity can be characterized as a multifaceted system of defenses that targets invading pathogens in a nonspecific manner. In this chapter, we have divided the numerous defenses that make up this system into three categories: physical defenses, chemical defenses, and cellular defenses. However, it is important to keep in mind that these defenses do not function independently, and the categories often overlap. Table \(\PageIndex{1}\) provides an overview of the nonspecific defenses discussed in this chapter.
| Overview of Nonspecific Innate Immune Defenses | |
|---|---|
| Physical defenses | Physical barriers |
| Mechanical defenses | |
| Microbiome | |
| Chemical defenses | Chemicals and enzymes in body fluids |
| Antimicrobial peptides | |
| Plasma protein mediators | |
| Cytokines | |
| Inflammation-eliciting mediators | |
| Cellular defenses | Granulocytes |
| Agranulocytes |
Physical defenses provide the body’s most basic form of nonspecific defense. They include physical barriers to microbes, such as the skin and mucous membranes, as well as mechanical defenses that physically remove microbes and debris from areas of the body where they might cause harm or infection. In addition, the microbiome provides a measure of physical protection against disease, as microbes of the normal microbiota compete with pathogens for nutrients and cellular binding sites necessary to cause infection.
Physical Barriers
Physical barriers play an important role in preventing microbes from reaching tissues that are susceptible to infection. At the cellular level, barriers consist of cells that are tightly joined to prevent invaders from crossing through to deeper tissue. For example, the endothelial cells that line blood vessels have very tight cell-to-cell junctions, blocking microbes from gaining access to the bloodstream. Cell junctions are generally composed of cell membrane proteins that may connect with the extracellular matrix or with complementary proteins from neighboring cells. Tissues in various parts of the body have different types of cell junctions. These include tight junctions, desmosomes, and gap junctions, as illustrated in Figure \(\PageIndex{1}\). Invading microorganisms may attempt to break down these substances chemically, using enzymes such as proteases that can cause structural damage to create a point of entry for pathogens.
The Skin Barrier
One of the body’s most important physical barriers is the skin barrier, which is composed of three layers of closely packed cells. The thin upper layer is called the epidermis. A second, thicker layer, called the dermis, contains hair follicles, sweat glands, nerves, and blood vessels. A layer of fatty tissue called the hypodermis lies beneath the dermis and contains blood and lymph vessels (Figure \(\PageIndex{2}\)).
The topmost layer of skin, the epidermis, consists of cells that are packed with keratin. These dead cells remain as a tightly connected, dense layer of protein-filled cell husks on the surface of the skin. The keratin makes the skin’s surface mechanically tough and resistant to degradation by bacterial enzymes. Fatty acids on the skin’s surface create a dry, salty, and acidic environment that inhibits the growth of some microbes and is highly resistant to breakdown by bacterial enzymes. In addition, the dead cells of the epidermis are frequently shed, along with any microbes that may be clinging to them. Shed skin cells are continually replaced with new cells from below, providing a new barrier that will soon be shed in the same way.
Infections can occur when the skin barrier is compromised or broken. A wound can serve as a point of entry for opportunistic pathogens, which can infect the skin tissue surrounding the wound and possibly spread to deeper tissues.
Mike, a gardener from southern California, recently noticed a small red bump on his left forearm. Initially, he did not think much of it, but soon it grew larger and then ulcerated (opened up), becoming a painful lesion that extended across a large part of his forearm (Figure \(\PageIndex{3}\)). He went to an urgent care facility, where a physician asked about his occupation. When he said he was a landscaper, the physician immediately suspected a case of sporotrichosis, a type of fungal infection known as rose gardener’s disease because it often afflicts landscapers and gardening enthusiasts.
Under most conditions, fungi cannot produce skin infections in healthy individuals. Fungi grow filaments known as hyphae, which are not particularly invasive and can be easily kept at bay by the physical barriers of the skin and mucous membranes. However, small wounds in the skin, such as those caused by thorns, can provide an opening for opportunistic pathogens like Sporothrix schenkii , a soil-dwelling fungus and the causative agent of rose gardener’s disease. Once it breaches the skin barrier, S. schenkii can infect the skin and underlying tissues, producing ulcerated lesions like Mike’s. Compounding matters, other pathogens may enter the infected tissue, causing secondary bacterial infections.
Luckily, rose gardener’s disease is treatable. Mike’s physician wrote him a prescription for some antifungal drugs as well as a course of antibiotics to combat secondary bacterial infections. His lesions eventually healed, and Mike returned to work with a new appreciation for gloves and protective clothing.
Mucous Membranes
The mucous membranes lining the nose, mouth, lungs, and urinary and digestive tracts provide another nonspecific barrier against potential pathogens. Mucous membranes consist of a layer of epithelial cells bound by tight junctions. The epithelial cells secrete a moist, sticky substance called mucus, which covers and protects the more fragile cell layers beneath it and traps debris and particulate matter, including microbes. Mucus secretions also contain antimicrobial peptides.
In many regions of the body, mechanical actions serve to flush mucus (along with trapped or dead microbes) out of the body or away from potential sites of infection. For example, in the respiratory system, inhalation can bring microbes, dust, mold spores, and other small airborne debris into the body. This debris becomes trapped in the mucus lining the respiratory tract, a layer known as the mucociliary blanket. The epithelial cells lining the upper parts of the respiratory tract are called ciliated epithelial cells because they have hair-like appendages known as cilia. Movement of the cilia propels debris-laden mucus out and away from the lungs. The expelled mucus is then swallowed and destroyed in the stomach, or coughed up, or sneezed out (Figure \(\PageIndex{4}\)). This system of removal is often called the mucociliary escalator.
The mucociliary escalator is such an effective barrier to microbes that the lungs, the lowermost (and most sensitive) portion of the respiratory tract, were long considered to be a sterile environment in healthy individuals. Only recently has research suggested that healthy lungs may have a small normal microbiota. Disruption of the mucociliary escalator by the damaging effects of smoking or diseases such as cystic fibrosis can lead to increased colonization of bacteria in the lower respiratory tract and frequent infections, which highlights the importance of this physical barrier to host defenses.
Like the respiratory tract, the digestive tract is a portal of entry through which microbes enter the body, and the mucous membranes lining the digestive tract provide a nonspecific physical barrier against ingested microbes. The intestinal tract is lined with epithelial cells, interspersed with mucus-secreting goblet cells (Figure \(\PageIndex{5}\)). This mucus mixes with material received from the stomach, trapping foodborne microbes and debris. The mechanical action of peristalsis, a series of muscular contractions in the digestive tract, moves the sloughed mucus and other material through the intestines, rectum, and anus, excreting the material in feces.
Endothelia
The epithelial cells lining the urogenital tract, blood vessels, lymphatic vessels, and certain other tissues are known as endothelia. These tightly packed cells provide a particularly effective frontline barrier against invaders. The endothelia of the blood-brain barrier, for example, protect the central nervous system (CNS), which consists of the brain and the spinal cord. The CNS is one of the most sensitive and important areas of the body, as microbial infection of the CNS can quickly lead to serious and often fatal inflammation. The cell junctions in the blood vessels traveling through the CNS are some of the tightest and toughest in the body, preventing any transient microbes in the bloodstream from entering the CNS. This keeps the cerebrospinal fluid that surrounds and bathes the brain and spinal cord sterile under normal conditions.
- Describe how the mucociliary escalator functions.
- Name two places you would find endothelia.
Mechanical Defenses
In addition to physical barriers that keep microbes out, the body has a number of mechanical defenses that physically remove pathogens from the body, preventing them from taking up residence. We have already discussed several examples of mechanical defenses, including the shedding of skin cells, the expulsion of mucus via the mucociliary escalator, and the excretion of feces through intestinal peristalsis. Other important examples of mechanical defenses include the flushing action of urine and tears, which both serve to carry microbes away from the body. The flushing action of urine is largely responsible for the normally sterile environment of the urinary tract, which includes the kidneys, ureters, and urinary bladder. Urine passing out of the body washes out transient microorganisms, preventing them from taking up residence. The eyes also have physical barriers and mechanical mechanisms for preventing infections. The eyelashes and eyelids prevent dust and airborne microorganisms from reaching the surface of the eye. Any microbes or debris that make it past these physical barriers may be flushed out by the mechanical action of blinking, which bathes the eye in tears, washing debris away (Figure \(\PageIndex{6}\)).
Name two mechanical defenses that protect the eyes.
Microbiome
In various regions of the body, resident microbiota serve as an important first-line defense against invading pathogens. Through their occupation of cellular binding sites and competition for available nutrients, the resident microbiota prevent the critical early steps of pathogen attachment and proliferation required for the establishment of an infection. For example, in the vagina, members of the resident microbiota compete with opportunistic pathogens like the yeast Candida . This competition prevents infections by limiting the availability of nutrients, thus inhibiting the growth of Candida , keeping its population in check. Similar competitions occur between the microbiota and potential pathogens on the skin, in the upper respiratory tract, and in the gastrointestinal tract. As will be discussed later in this chapter, the resident microbiota also contribute to the chemical defenses of the innate nonspecific host defenses.
The importance of the normal microbiota in host defenses is highlighted by the increased susceptibility to infectious diseases when the microbiota is disrupted or eliminated. Treatment with antibiotics can significantly deplete the normal microbiota of the gastrointestinal tract, providing an advantage for pathogenic bacteria to colonize and cause diarrheal infection. In the case of diarrhea caused by Clostridium difficile , the infection can be severe and potentially lethal. One strategy for treating C. difficile infections is fecal transplantation, which involves the transfer of fecal material from a donor (screened for potential pathogens) into the intestines of the recipient patient as a method of restoring the normal microbiota and combating C. difficile infections.
Table \(\PageIndex{2}\) provides a summary of the physical defenses discussed in this section.
| Defense | Examples | Function |
|---|---|---|
| Cellular barriers | Skin, mucous membranes, endothelial cells | Deny entry to pathogens |
| Mechanical defenses | Shedding of skin cells, mucociliary sweeping, peristalsis, flushing action of urine and tears | Remove pathogens from potential sites of infection |
| Microbiome | Resident bacteria of the skin, upper respiratory tract, gastrointestinal tract, and genitourinary tract | Compete with pathogens for cellular binding sites and nutrients |
List two ways resident microbiota defend against pathogens.
Key Concepts and Summary
- Nonspecific innate immunity provides a first line of defense against infection by nonspecifically blocking entry of microbes and targeting them for destruction or removal from the body.
- The physical defenses of innate immunity include physical barriers, mechanical actions that remove microbes and debris, and the microbiome, which competes with and inhibits the growth of pathogens.
- The skin, mucous membranes, and endothelia throughout the body serve as physical barriers that prevent microbes from reaching potential sites of infection. Tight cell junctions in these tissues prevent microbes from passing through.
- Microbes trapped in dead skin cells or mucus are removed from the body by mechanical actions such as shedding of skin cells, mucociliary sweeping, coughing, peristalsis , and flushing of bodily fluids (e.g., urination, tears)
- The resident microbiota provide a physical defense by occupying available cellular binding sites and competing with pathogens for available nutrients.


10.8: End of Chapter Problems
Building Blocks of Nucleic Acids
1. Name the four bases that are present in DNA.
2. Name the four bases that are present in RNA.
3. Name the monosaccharide used to make DNA. Draw in the ß-furanose form.
4. Name the monosaccharide used to make RNA. Draw in the ß-furanose form.
5. Which three components go into making a nucleotide?
6. Shown below is the structure of ATP, a nucleotide triphosphate.
a. How many phosphoester bonds are present in the molecule?
b. How many phosphoanhydride bonds are present?
c. What is the name of the base?
d. What is the name of the monosaccharide?
e. Where is the base attached?
f. What type of bond connects the sugar and the base?
Polynucleotide
Shown below is the structure of a polynucleotide. Answer the following questions based on the structure.
a. Name the monosaccharide in this polynucleotide.
b. Name the bond that connects the heterocyclic amine to the monosaccharide.
c. Name the bond that connects one nucleotide to another.
d. Label the terminus on the polynucleotide with the appropriate nomenclature.
e. Is this polynucleotide a part of RNA or DNA?
f. Write the primary sequence of this nucleotide.
7. Name the two kinds of nucleic acids.
8. Which type of nucleic acid stores genetic information in the cell?
9. What is the primary structure of DNA?
10. What are complementary bases?
11. Why is it structurally important that a purine base always pair with a pyrimidine base in the DNA double helix?
12. Which nitrogenous base in DNA pairs with each nitrogenous base?
cytosine adenine guanine thymine
13. Describe the secondary structure of DNA?
14. What level of structure is disrupted when DNA is denatured?
15. What does it mean to renature DNA?
Information Flow
1. A segment of one strand from a DNA molecule has the sequence 3′‑TCCATGAGTTGA‑5′. What is the sequence of nucleotides in the opposite, or complementary, DNA chain?
2, A segment of one strand from a DNA molecule has the sequence 3′‑CCAGTGAATTGCCTAT‑5′. List the base sequence in a new DNA strand produced by DNA polymerase. What process is this called?
3. A portion of the template strand of a gene has the sequence 3′‑TCCATGAGTTGA‑5′. What is the sequence of nucleotides in the RNA that is formed from this template? What process is this called?
4. A portion of the template strand of a gene has the sequence 3′‑CCAGTGAATTGCCTAT‑5′. What is the sequence of nucleotides in the RNA that is formed from this template? What process is this called?
5. Name three types of RNA and describe their function.
6. A portion of an mRNA molecule has the sequence 5′‑AUGCCACGAGUUGAC‑3′. What amino acid sequence does this code for? What process is this called?
7. A portion of an RNA molecule has the sequence 5′‑AUGCUGAAUUGCGUAGGA‑3′. What amino acid sequence does this code for? What process is this called?
8. The sequence dTATCCT appears in a template strand of DNA.
a. Which base is at the 3'-terminus of this primary structure?
b. What is the sequence in the DNA strand that is complementary to this sequence? Label the terminus.
c. What is the sequence in the RNA strand that is synthesized from this sequence? Label the terminus.
d. What is the sequence of the dipeptide from this strand?
e. Draw the dipeptide in the line bond structure at physiological pH. Label the terminuses.
f. In an aqueous environment will this dipeptide that is part of a larger protein likely to be buried inside the tertiary structure or located on the surface? Explain.
Mutation
1. Define the term mutation.
2. Are all mutations harmful to an individual? Explain.
3. Are all mutations passed on to an offspring?
4. What level of protein structure is affected by a mutation?
5. A mutation produces a DNA polymerase with lower than normal effectiveness at proofreading and repair. Could an individuals health be impacted by this mutation?


3.1A: Microbe Size
- Recall the size of microbes in comparison to human cells and viruses
Microbiology is the study of microbes. The name of the field is driven by the tool that largely determines if something is a microbe. Basically, microbiology is the study of organisms that one needs to use a microscope to visualize. Of course, there are exceptions. There are types of microscopes that visualize to the atomic level, which is significantly smaller than microbes. Alternatively, there are single cell organisms, such as some types of green algae and some protozoans that are generally studied by microbiologists. These are macroscopic or view-able without a microscope.
The size of microbes can be hard to imagine because they are so small in comparison to what most people see day to day. Even in comparison to animal cells, microbes tend to be smaller. They are about 1/10th the size of a typical human cell. So, a microbe such as a bacteria cell would be the size of a cat or small dog in comparison to a human-sized animal-cell. Viruses are about 1/10th the size of other microbes such as bacteria. Therefore, if a bacteria is the size of cat, then a virus would be about the size of a mouse.
To put a numerical value on microbial size, most measurements of microbes are done with the unit of measure of micrometer, which is one millionth of a meter (one 2,500th of an inch). In relation to something more tangible a period or “. ” is about 0.5 millimeters or 0.5/1,000th of a meter. A typical microbe would be about 1/500th of a period.
Of course there are exceptions. Some unicellular organisms studied by microbiologists are macroscopic. This includes Valonia ventricosa, which can be up to 5 cm in length. It is a member of the Chlorophyta phylum which are a sub-group of green algae. Many types of green algae are not microscopic, but they are often studied by microbiologists.
Key Points
- Microbes are generally described as being microscopic in size. Therefore, they are smaller than a human eye can see.
- The size of microbes can be hard to imagine because they are so small. In comparison to animal cells, microbes tend to be smaller. They are about 1/10th the size of a typical human cell.
- Microbes are generally measured in the scale of one millionth of a meter, which is known as a micrometer.
Key Terms
- protozoan : Any of the diverse group of eukaryotes, of the phylum Protozoa, that are primarily unicellular, existing singly or aggregating into colonies, are usually nonphotosynthetic, and are often classified further into phyla according to their capacity for and means of motility, as by pseudopods, flagella, or cilia.
- macroscopic : Visible to the unassisted eye.


4.3.7: Group Decision-Making
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- Jamie Hammond and Western Technical College
- OpenStax
Learning Objectives
- Understand the advantages and disadvantages of group decision-making, and how managers can improve the quality of group decision-making
Involving more people in the decision-making process can greatly improve the quality of a manager's decisions and outcomes. However, involving more people can also increase conflict and generate other challenges. We turn now to the advantages and disadvantages of group decision-making.
Advantages of Group Decisions
An advantage to involving groups in decision-making is that you can incorporate different perspectives and ideas. For this advantage to be realized, however, you need a diverse group. In a diverse group, the different group members will each tend to have different preferences, opinions, biases, and stereotypes. Because a variety of viewpoints must be negotiated and worked through, group decision-making creates additional work for a manager, but (provided the group members reflect different perspectives) it also tends to reduce the effects of bias on the outcome. For example, a hiring committee made up of all men might end up hiring a larger proportion of male applicants (simply because they tend to prefer people who are more similar to themselves). But with a hiring committee made up of an equal number of men and women, the bias should be cancelled out, resulting in more applicants being hired based on their qualifications rather than their physical attributes.
Having more people involved in decision-making is also beneficial because each individual brings unique information or knowledge to the group, as well as different perspectives on the problem. Additionally, having the participation of multiple people will often lead to more options being generated and to greater intellectual stimulation as group members discuss the available options. Brainstorming is a process of generating as many solutions or options as possible and is a popular technique associated with group decision-making.
All of these factors can lead to superior outcomes when groups are involved in decision-making. Furthermore, involving people who will be affected by a decision in the decision-making process will allow those individuals to have a greater understanding of the issues or problems and a greater commitment to the solutions.
Disadvantages of Group Decisions
Group decision-making is not without challenges. Some groups get bogged down by conflict, while others go to the opposite extreme and push for agreement at the expense of quality discussions. Groupthink occurs when group members choose not to voice their concerns or objections because they would rather keep the peace and not annoy or antagonize others. Sometimes groupthink occurs because the group has a positive team spirit and camaraderie, and individual group members don’t want that to change by introducing conflict. It can also occur because past successes have made the team complacent.
Often, one individual in the group has more power or exerts more influence than others and discourages those with differing opinions from speaking up ( suppression of dissent ) to ensure that only their own ideas are implemented. If members of the group are not really contributing their ideas and perspectives, however, then the group is not getting the benefits of group decision-making.
How to Form a Quality Group
Effective managers will try to ensure quality group decision-making by forming groups with diverse members so that a variety of perspectives will contribute to the process. They will also encourage everyone to speak up and voice their opinions and thoughts prior to the group reaching a decision. Sometimes groups will also assign a member to play the devil’s advocate in order to reduce groupthink. The devil’s advocate intentionally takes on the role of critic. Their job is to point out flawed logic, to challenge the group’s evaluations of various alternatives, and to identify weaknesses in proposed solutions. This pushes the other group members to think more deeply about the advantages and disadvantages of proposed solutions before reaching a decision and implementing it.
The methods we’ve just described can all help ensure that groups reach good decisions, but what can a manager do when there is too much conflict within a group? In this situation, managers need to help group members reduce conflict by finding some common ground—areas in which they can agree, such as common interests, values, beliefs, experiences, or goals. Keeping a group focused on a common goal can be a very worthwhile tactic to keep group members working with rather than against one another.Table 2.3 summarizes the techniques to improve group decision-making.
| Type of Decision | Technique | Benefit |
| Group decisions | Have diverse members in the group. | Improves quality: generates more options, reduces bias |
| Assign a devil’s advocate. | Improves quality: reduces groupthink | |
| Encourage everyone to speak up and contribute. | Improves quality: generates more options, prevents suppression of dissent | |
| Help group members find common ground. | Improves quality: reduces personality conflict |
Table 2.3(Attribution: Copyright Rice University, OpenStax, under CC-BY 4.0 license)
Conclusion
Decision-making is a crucial daily activity for managers. Decisions range from small and simple, with straightforward answers, to big and complex, with little clarity about what the best choice will be. Being an effective manager requires learning how to successfully navigate all kinds of decisions. Expertise, which develops gradually through learning and experience, generally improves managerial decision-making, but managers rarely rely solely on their own expertise. They also conduct research and collect information from others; they pay attention to their own biases and to ethical implications; and they think critically about the information that they have received to make decisions that will benefit the organization and its stakeholders.
Concept Check
- Explain why group decision-making can be more effective than individual decision-making.
- What are some things that can prevent groups from making good decisions?
- As a manager, what can you do to enhance the quality of group decision-making?


10.9: Chapter Review - Review Questions
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Review Questions
1 .
What is one method to name data ranges?
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On the Page Layout tab, use options in the Sheet Options command group.
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Use the Formula Bar.
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Press Ctrl+Shift+Enter.
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On the Formulas tab, select Define Name in the Defined Names command group.
2 .
What is one example of a benefit of using Data Tables in your worksheet?
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renaming a cell reference
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reorganizing the values from large to small
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adding an extra column on your table with results
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autofilling and calculating multiple scenarios
3 .
Where is the Data Table tool?
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on the Home tab in the Sort & Filter command group
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on the Data tab under the What-If Analysis menu
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on the Insert tab in the Charts command group
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on the Formulas tab under Financial functions
4 .
What are the benefits of using data ranges in your worksheets?
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You can autofill and compute scenarios.
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You can simultaneously calculate different operations in different worksheets.
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You can save time by not going back to search for named cells.
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You can reorganize the data following different criteria.
5 .
Which comparison operator represents “not equal”?
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<>
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=/
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>=
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><
6 .
What is a mixed cell reference?
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when you combine cells together
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when either the row or the column is fixed
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an absolute cell reference
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a relative cell reference
7 .
Which function is used to total a range based on a certain criteria?
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COUNT
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SUM
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NPER
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SUMIF
8 .
Identify the correct order for the PV function.
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=pv(rate,nper,pmt,fv)
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=pv(rate,nper,pmt,pv)
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=pv(rate,nper,pv,fv)
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=pv(rate,pmt,pv,fv)
9 .
What is a PivotTable?
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a tool that derives information from raw data, which it processes in different arrangements depending on the variables the user chooses
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a tool that autoformats your workbook by automatically changing the background canvas, fonts, and data types
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a tool that defines the names of given ranges, so that you can use them for building formulas with certain cell references
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a tool that automatically makes simultaneous calculations in one cell, yet needs you to design and write the formulas
10 .
What does the Recommended PivotTable tool provide?
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The tool recommends and constructs a PivotTable with several variables based on your data.
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The tool creates both a PivotTable and a PivotChart from the selected data.
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The tool recommends PivotTable variables (i.e., headings) to be the leading data presented in one-dimensional tables.
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The tool recommends appropriate formulas to analyze the data in the PivotTable.
11 .
Where do you select the headers you want to use in a PivotTable?
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on the Insert tab in the Text command group
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on the Data tab under What-If Analysis
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in the PivotTable Field List after creating a PivotTable
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on the Insert tab using the Insert PivotTable command
12 .
What is one reason you might audit a formula?
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You would audit a formula if you get a negative number.
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You would audit a formula to copy it to another cell.
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You would audit a formula if your PivotTable is not formatting correctly.
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You would audit a formula if you have an error such as #NUM! on the spreadsheet.
13 .
How does a user inspect if the current cell has input and/or output problems?
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The user would use the Step In tool.
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The user would use the Inquire add-in.
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The user would use the Watch Window.
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The user can run the Trace Precedents and Dependents tools.
14 .
How would you create a custom color in a theme?
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A custom theme color is created using the Format Painter.
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Choose cell styles from the Home tab.
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On the Page Layout tab, choose Colors.
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The custom color can be created using the Effects menu.
15 .
Where would you go to reformat a phone number?
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the Format Cells tool in the Number command group on the Home tab
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in the Page Layout menu in the Themes command group
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using the Format Painter
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using Cell Styles from the Home tab


2.21: Engineering
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- Susan Rahman, Prateek Sunder, and Dahmitra Jackson
- CC ECHO
Engineering is the applied use of mathematics and sciences, including chemistry and physics, in order to complete tasks such as building structures, parts,infrastructures, and machines. In a society like the United States, where constant growth, innovation, and improvement is expected, Engineering is nearly always promoted to students, especially those with interest or aptitude in math and science classes.In large part, this has led to the “STEM or Starve” narrative, where majors included in the STEM fields (Science, Technology, Engineering,and Mathematics) are viewed as superior, as they are those fields with the most applicable and profitable value. This mindset is dangerous for several reasons, including its exclusion of other disciplines such as social sciences (which, despite being sciences, are not included in STEM), less applied forms of traditional sciences, and the arts.
Engineering design and build has a direct impact on the structure of the world. Like other disciplines, Engineering is also a predominantly white male driven industry and field of study,and there is little representation of women or a variety of ethnic minority groups. Over the last 30 years, the overall number of bachelor’s degrees awarded to Black scholars has increased. However, in engineering disciplines, the proportion of Black students who receive degrees has maintained a consistent rate of roughly 4% (Patel, 2021). An article by the Hechinger report provides additional information and statistics. The National Science Foundation, (NSF) found that from a 15 year window spanning from 2001 to 2016, Bachelor of Science (BS) degrees in engineering earned by Black students declined from 5% to 4%, and mathematics degrees earned by black students decreased from 7% to 4% (Newsome, 2021). Despite the supposed demand and need for massive increase in STEM educated students, the disciplines seem to be regressing in their mission for diverse inclusion.
Microaggressions also are a frequent occurrence for ethnic and racial minority STEM students. Amida Koroma entered the University of Maryland as a Bioengineering student, and was a regular recipient of honors such as the Dean’s list. She reported that often, white students would undermine her, and rather than allow her to take on hands-on roles, assign her to tasks such as typing and recording. This cycle eventually led her to become so frustrated that she decided to change her major to Psychology, thus turning away from Bioengineering.(Newsome, 2021) An article published in the International Journal of STEM Education further described these racial microaggressions (RMAs) within the disciplines. The research involved a survey of 4800 students of color, with a STEM subsect of 1688 students of color. The study found that on a campus, academic, and peer level, microaggressions were a significant factor in the lack of students of color within the STEM majors. Students in the survey also reported that being the only, or one of the only students of color within STEM classrooms led to feelings of isolation, loneliness, and invalidation. This creates a self-fulfilling prophecy, and because STEM students of color feel alone, they are less likely to enroll in and stay within the field, which leads to lower levels of representation and increased feelings of isolation and non representation (Lee, Collins, et. al, 2020). College enrollment as a whole for Black students was on the decline as well. As of Fall 2021, Black freshman enrollment was down 7.5%, and their decline in enrollment was greatest at two year, public colleges, or community colleges, which are often heralded as great equalizers due to their affordability and accessibility (Lee, Collins, et. al,2020).
Beyond bachelor degrees, advanced degrees in engineering are also riddled with inequity and environments of hostility. Brian Burt is an assistant professor at Iowa State in the School of Education, as well as the lead author of a research article which describes a graduate engineering degree for Black men as “riding out a storm” (Hunt, 2020). The metaphorical storm, as Brian Burt describes it, represents the tensions and struggles these young men face as a result of structural inequalities, and faculty who are largely either unwilling or unable to support these underrepresented students through the storm (Hunt, 2020). On a societal level,there is a belief that success and failure are representations of individual character, and so there is a belief that students who drop out of an engineering program do so because they are not smart enough or are otherwise incapable of success. However, that explanation relies on individual flaws, when actually and the main challenges that students faced were systemic and structural, not individual, and thus out of their control.
Marcus, a third year student in the program stated, “People are naturally going to want to be around people who look like them,” and that, “As a Black man in engineering, I don’t have that camaraderie. So, I am forced to immediately look outside of my comfort zone in order to find people who I can study with, talk with, and have overall support” (Hunt, 2020). This lack of camaraderie from peers with similar experiences can exacerbate feelings of isolation and feeling a lack of belonging. Some students even reported that they considered leaving their programs due to this feeling and a lack of support. Students further reported receiving discouraging messages from advisors, which ranged from passive aggressive slights to explicit challenges about the student’s ability to conduct doctoral level work and research.
The disparity in engineering does not end in the classrooms. From a salary perspective,pay inequality is rampant. On average, a white worker with a bachelor’s in engineering earns$90,000 a year, while Black workers with graduate degrees earn an average of $87,000 (Patel,2021). In order to improve equity in the discipline, there are several actions which can be taken.First, universities can improve recruitment by admitting more Black students, and take steps to improve retention. For example, establishing learning communities for underrepresented students provides a sense of belonging and support for underrepresented students. Universities and individual departments can also help students learn to be culturally sensitive and aware. Free college is also a fair and, given the value of education, realistic suggestion.
Underrepresented students, especially first generation students, do not have the familial and generational resources to attend college on their parents' dime. This forces students to combine working part time or even full time jobs in addition to being a full time student, while also trying to pursue personal and career experiences. This can create near insurmountable amounts of pressure, and make it more difficult to secure internships and career opportunities. Service learning and paid internships may also prove beneficial, as they would provide for cultural capital and financial relief for students. Engineering, like the larger entity of higher education, has a need to improve equity and opportunity for all students. The future of our nation and innovation may depend on it.


7.8: Activity-Based Costing
Learning Outcomes
- Describe situations in which activity-based absorption costing is used
Activity-based absorption costing assigns all manufacturing overhead costs to products based on the activities performed to make those products.
In this method, we look only at non-direct costs. Direct costs are easily traced to an activity, so we don’t need to do anything further with those costs. Non-direct costs are the overhead costs, such as rent, property taxes, accounting and administrative costs and all other costs not directly related to the production of our product.
Activity-based absorption costing (ABC) is much more complicated that traditional costing, but can give you a much better allocation picture. Let’s look at an example where ABC may produce a better picture for a company.
Example
You are a manager at a company that makes two kinds of kayaks: the basic model and the deluxe. Currently, you are using a traditional costing method and assigning manufacturing overhead based on direct labor hours. So all of the direct labor and materials are being charged to each of the models, and then the overhead is allocated. But what if the deluxe kayak is consuming three times as much machine time due to more frequent setups? Or what if there are more parts in the deluxe model requiring a great deal more time in the purchasing department? These activities could cause traditional costing to be “off” compared to costing based on each activity.
This is a situation, where ABC may be more reflective of the actual cost allocation. It is necessary to determine if the benefits of implementing the ABC method outweigh the costs. After doing an evaluation of your situation, then the decision can be made regarding which method to utilize.
Practice Questions


36.5: Proud to be an American, Where at Least I Know I’m… Part of an Industry?
In J. Hector St. John de Crèvecoeur’s Letters from an American Farmer , Crèvecoeur makes the claim that America is a nation built upon hard work, freedom, generosity, and that the American identity is one based on a variety of different experiences, both racial and religious, but is based more so upon a mutual respect for these differences. Crèvecoeur paints this positive identity within the minds of the readers when he explains, “Thus all sects are mixed as all nations; thus religious indifference is imperceptibly disseminated from one end of the continent to the other; which is… one of the strongest characteristics of the Americans.” (611). Essentially, Crèvecoeur is stating that the many differences existing among Americans as far as their demographic backgrounds are concerned does not matter in America, as it is a nation based upon diversity.
However, Crèvecoeur seems to contradict this positive image throughout his narrative, switching back and forth between claiming that America is a land of respected diversity, and claiming that America is a “chain of settlements” (605). While the author continues to create an extremely elaborate yet positive image of what it means to be an American, he continuously refers to America as an “industry”. While it can be considered general knowledge that America’s success as a nation can be accounted for by industrialization, by consistently referring back to America as an “industry”, it creates the image of America’s identity being more of a mass-produced product rather than something unique and original to each individual, and therefore, undermining America’s national identity.
In short, Crèvecoeur’s narrative makes the claim that America’s national identity is based upon the “American Dream”- that if you put your best effort forward and work hard enough, you can obtain anything you set your mind to, regardless of your race, religion, or financial standing. However, this same identity is attributed to ALL Americans, thus making it so that this same identity can be considered as a product that is mass-generated. Overall, Crèvecoeur’s narrative implies that American literature traditions are also based upon freedom and struggle, but also that we cannot view all American literature through this sense; we must give each piece its own unique scrutiny so that we can continue to learn and have a better understanding of what it means to be an American.


3.2: [a, b)
This section will study intervals in the form \([a,b)\). The interval begins with a left bracket and ends with a right parentheses. Starting the interval with a brackets means the right endpoint is included in the set and ending with the use of a parentheses means the left endpoint in not included.
\([2,5)\)
Solution
In the example above, the interval starts with a left bracket and ends with a parentheses. Hence,the interval includes the number 2 and does not include the number 5. By observing the corresponding number a closed bullet \(\bullet\) is used to demonstrate that the number 2 is included in the interval, on the other hand an open bullet \(\circ\) is on the number 5 to demonstrate that 5 in not in the interval. Some of the numbers in the set include 2, 2.5, 3.4, 4 and 4.99. Again, the number 5 is not in this set.
\([-4,10)\)
Solution
Similar to example 1, the endpoint on the left which corresponds to the number -4 is included in the interval, while the endpoint on the right is not included in the interval. Some numbers on the interval above are -4, -2, 0, 3.5, 8.5 and 9.9.
Draw a number line for the following intervals and list at least three numbers inside the set.
- \([-3,1)\)
- \([-12,-2)\)
- \([-233,-223)\)
- \([3.5,5)\)
- \([0,1)\)
- \([-1.4,2.8)\)


3.3: Patient's Bill of Rights
Th Patient’s Bill of Rights is an evolving document related to providing culturally competent care. In 1973 the American Hospital Association (AHA) adopted the Patient’s Bill of Rights. [1] See the following box to review the original Patient’s Bill of Rights. The bill has since been updated, revised, and adapted for use throughout the world in all health care settings. There are different versions of the bill, but, in general, it safeguards a patient’s right to accurate and complete information, fair treatment, and self-determination when making health care decisions. Patients should expect to be treated with sensitivity and dignity and with respect for their cultural values. While the Patient’s Bill of Rights extends beyond the scope of cultural considerations, its basic principles underscore the importance of cultural competency when caring for people.
- The patient has the right to considerate and respectful care.
- The patient has the right to and is encouraged to obtain from physicians and other direct caregivers relevant, current, and understandable information concerning diagnosis, treatment, and prognosis.
- Except in emergencies when the patient lacks decision-making capacity and the need for treatment is urgent, the patient is entitled to the opportunity to discuss and request information related to the specific procedures and/or treatments, the risks involved, the possible length of recuperation, and the medically reasonable alternatives and their accompanying risks and benefits.
- Patients have the right to know the identity of physicians, nurses, and others involved in their care, as well as when those involved are students, residents, or other trainees.
- The patient has the right to know the immediate and long-term financial implications of treatment choices, insofar as they are known.
- The patient has the right to make decisions about the plan of care prior to and during the course of treatment and to refuse a recommended treatment or plan of care to the extent permitted by law and hospital policy and to be informed of the medical consequences of this action. In case of such refusal, the patient is entitled to other appropriate care and services that the hospital provides or transfer to another hospital. The hospital should notify patients of any policy that might affect patient choice within the institution.
- The patient has the right to have an advance directive (such as a living will, health care proxy, or durable power of attorney for health care) concerning treatment or designating a surrogate decision-maker with the expectation that the hospital will honor the intent of that directive to the extent permitted by law and hospital policy. Health care institutions must advise patients of their rights under state law and hospital policy to make informed medical choices, ask if the patient has an advance directive, and include that information in patient records. The patient has the right to timely information about hospital policy that may limit its ability to implement fully a legally valid advance directive.
- The patient has the right to every consideration of privacy. Case discussion, consultation, examination, and treatment should be conducted so as to protect each patient’s privacy.
- The patient has the right to expect that all communications and records pertaining to his/her care will be treated as confidential by the hospital, except in cases such as suspected abuse and public health hazards when reporting is permitted or required by law. The patient has the right to expect that the hospital will emphasize the confidentiality of this information when it releases it to any other parties entitled to review information in these records.
- The patient has the right to review the records pertaining to his/her medical care and to have the information explained or interpreted as necessary, except when restricted by law.
- The patient has the right to expect that, within its capacity and policies, a hospital will make a reasonable response to the request of a patient for appropriate and medically indicated care and services. The hospital must provide evaluation, service, and/or referral as indicated by the urgency of the case. When medically appropriate and legally permissible, or when a patient has so requested, a patient may be transferred to another facility. The institution to which the patient is to be transferred must first have accepted the patient for transfer. The patient must also have the benefit of complete information and explanation concerning the need for, risks, benefits, and alternatives to such a transfer.
- The patient has the right to ask and be informed of the existence of business relationships among the hospital, educational institutions, other health care providers, or payers that may influence the patient’s treatment and care.
- The patient has the right to consent to or decline to participate in proposed research studies or human experimentation affecting care and treatment or requiring direct patient involvement and to have those studies fully explained prior to consent. A patient who declines to participate in research or experimentation is entitled to the most effective care that the hospital can otherwise provide.
- The patient has the right to expect reasonable continuity of care when appropriate and to be informed by physicians and other caregivers of available and realistic patient care options when hospital care is no longer appropriate.
- The patient has the right to be informed of hospital policies and practices that relate to patient care, treatment, and responsibilities. The patient has the right to be informed of available resources for resolving disputes, grievances, and conflicts, such as ethics committees, patient representatives, or other mechanisms available in the institution. The patient has the right to be informed of the hospital’s charges for services and available payment methods.
Read a current version of the “ Patient Care Partnership ” brochure from the American Hospital Association that has replaced the Patient’s Bill of Rights.
- American Hospital Association. (2003). The patient care partnership . https://www.aha.org/other-resources/patient-care-partnership ↵
- American Hospital Association. (2003). The patient care partnership . https://www.aha.org/other-resources/patient-care-partnership ↵


4.6: Scientific Notation in SPICE
The SPICE circuit simulation computer program uses scientific notation to display its output information, and can interpret both scientific notation and metric prefixes in the circuit description files. If you are going to be able to successfully interpret the SPICE analyses throughout this book, you must be able to understand the notation used to express variables of voltage, current, etc. in the program.
Let’s start with a very simple circuit composed of one voltage source (a battery) and one resistor:
To simulate this circuit using SPICE, we first have to designate node numbers for all the distinct points in the circuit, then list the components along with their respective node numbers so the computer knows which component is connected to which, and how. For a circuit of this simplicity, the use of SPICE seems like overkill, but it serves the purpose of demonstrating practical use of scientific notation:
Typing out a circuit description file, or netlist , for this circuit, we get this:
The line “ v1 1 0 dc 24 ” describes the battery, positioned between nodes 1 and 0, with a DC voltage of 24 volts. The line “ r1 1 0 5 ” describes the 5 Ω resistor placed between nodes 1 and 0.
Using a computer to run a SPICE analysis on this circuit description file, we get the following results:
SPICE tells us that the voltage “at” node number 1 (actually, this means the voltage between nodes 1 and 0, node 0 being the default reference point for all voltage measurements) is equal to 24 volts. The current through battery “v1” is displayed as -4.800E+00 amps. This is SPICE’s method of denoting scientific notation. What its really saying is “-4.800 x 10 0 amps,” or simply -4.800 amps. The negative value for current here is due to a quirk in SPICE and does not indicate anything significant about the circuit itself. The “total power dissipation” is given to us as 1.15E+02 watts, which means “1.15 x 10 2 watts,” or 115 watts.
Let’s modify our example circuit so that it has a 5 kΩ (5 kilo-ohm, or 5,000 ohm) resistor instead of a 5 Ω resistor and see what happens.
Once again is our circuit description file, or “netlist:”
The letter “k” following the number 5 on the resistor’s line tells SPICE that it is a figure of 5 kΩ, not 5 Ω. Let’s see what result we get when we run this through the computer:
The battery voltage, of course, hasn’t changed since the first simulation: its still at 24 volts. The circuit current, on the other hand, is much less this time because we’ve made the resistor a larger value, making it more difficult for electrons to flow. SPICE tells us that the current this time is equal to -4.800E-03 amps, or -4.800 x 10 -3 amps. This is equivalent to taking the number -4.8 and skipping the decimal point three places to the left.
Of course, if we recognize that 10 -3 is the same as the metric prefix “milli,” we could write the figure as -4.8 milliamps, or -4.8 mA.
Looking at the “total power dissipation” given to us by SPICE on this second simulation, we see that it is 1.15E-01 watts, or 1.15 x 10 -1 watts. The power of -1 corresponds to the metric prefix “deci,” but generally we limit our use of metric prefixes in electronics to those associated with powers of ten that are multiples of three (ten to the power of . . . -12, -9, -6, -3, 3, 6, 9, 12, etc.). So, if we want to follow this convention, we must express this power dissipation figure as 0.115 watts or 115 milliwatts (115 mW) rather than 1.15 deciwatts (1.15 dW).
Perhaps the easiest way to convert a figure from scientific notation to common metric prefixes is with a scientific calculator set to the “engineering” or “metric” display mode. Just set the calculator for that display mode, type any scientific notation figure into it using the proper keystrokes (see your owner’s manual), press the “equals” or “enter” key, and it should display the same figure in engineering/metric notation.
Again, I’ll be using SPICE as a method of demonstrating circuit concepts throughout this book. Consequently, it is in your best interest to understand scientific notation so you can easily comprehend its output data format.


9.5.4: Humid Subtropical Climate
Geographic Distribution
The humid subtropical climate is found on the east coast of continents between 20 o and 40 o N and S latitude. The humid subtropical climate can be found in the southeastern United States, southeastern South America; coastal southeast South Africa; eastern Australia; eastern Asia from northern India through south China to Japan.
Controlling Factors
The east coast location of the Humid Subtropical climate places it near the source region for maritime tropical air. Additionally, warm ocean currents paralleling these coasts further enhance the instability of the air. These factors combine to produce moderate amounts of precipitation in most months of the year. The humid subtropical climate is subject to cold temperatures during the winter as cP air masses embedded in cyclonic storms pass through this region.
|
Figure \(\PageIndex{2}\): Climograph for Memphis, TN
Latitude/Longitude = 35
o
N; 90
o
W
|
Distinguishing Characteristics
Temperature
The humid subtropical climate is noted for its warm summer months, and relatively mild winters. Summer temperatures average between 21 o (69.8 o F) to 26 o C (78.8 o F) and no winter month has an average temperature below 0 o C (32 o F). Many days the temperature can hit 32 o C (90 o F) or higher. Moving poleward through the various climates of the earth, one notices the distinct development of a seasonal cycle of temperature, especially toward the poleward limits of the climate. The high humidity experienced in the humid subtropical climate makes warm days feel oppressive. The daily temperature range tends to be very small as the evening does not cool down much during the summer. Winter temperatures will dip into the single digits with the relatively frequent invasions of cP air masses, especially on the poleward side of the climate.
Precipitation
The humid subtropical climate gets its name from the high humidity experienced in this environment. Dominance of the warm and moist maritime tropical air creates summers similar to the humid tropics. Precipitation is generally evenly distributed throughout the year. Annual precipitation varies from 254 cm (100 in) near the coast to 63.5 cm (25 in) inland. Frost is generally only a problem in winter when very cold cP air masses penetrate this region, a real hazard for fruit and vegetable growers in the southeastern United States. A monsoon influence is experienced in Asia.