Ap Human Geography Chapter 25 Summary

Chapter 25
Process of fossilization
· Moving water can suspend sediment – inorganic particles
· Moving water fills into still body of water o Sediment flats to the bottom o Forms a layer o More layers form with different compositions on the bottom of the lake or ocean
· Living things in the ocean die and get buried in the sediments in the ocean
· A lot of weight and pressure pushing down
· The organic material is replaced by rocks – mineralization resulting in fossils
· Fossils: representations of living things that used to exist
· Ocean is not the only possibility for fossils to form o Wind can move a lot of sediments as well o Water is ideal but not only possibility
· Places
that are dry land now may have been under water at some time
· Water dries, erosion occurs etc. exposing the different layers of rock and uncover fossils
· Mountains forming can uncover fossils as well
· Gives a relative picture of time (this is older than something above it)
25.1 Conditions on early Earth made the origin of life possible
· Origin of life o Oparin – Haldene Model
§ Steps
· Assemble simple molecules into building blocks for complex molecules – need to make DNA
· Assemble polymers that can store information and catalyze reactions
· Add membrane and an energy source to make a living organism o Miller-Urey experiment
§ Hypothesize what early earth would’ve been like
§ Put inorganic material in what you think early atmosphere is like and run electricity through it – to see spontaneous formation of life
§ Evidence that inorganic materials to amino acids is possible o Bacteria living in hostile environments
§ Extremophobes
§ Things living there were using a different environment that would normally be toxic o People have found amino acids inside meteorites
§ First amino acids could have come from outer space o In a water environment, the bonds of amino acids and nucleotides break as fast as they’re assembled
§ When in a clay and water environment, amino acids adhere to the clay and so the clay catalyzes their formation
§ Evidence for spontaneous assemble into macromolecules o Life?
§ Store info (genotype)
§ Express info (phenotype)
· The ribozyme o DNA needs protein, but protein needs DNA ???
§ Chicken and the egg o Ribozyme – piece of RNA that catalyzes a reaction – functions like a protein, can make another one of itself
§ May have been the first living things
§ RNA world hypothesis o Have not found a ribozyme that makes another copy of itself
§ Big piece of the puzzle o Life is cellular – ribozymes to cells o Lipids in a water environment form a sphere spontaneously o First kind of cellular life form – protobiont o A lot of evolutionary events had to happen before the first prokaryotic fossil 3.5 billion years ago o All prokaryotic fossils before 2 billion years ago o Prokaryotes
§ Bacteria
§ Archaea
· Heterotrophs
· Autotrophs → cyano bacteria →Oxygen
§ Oxygen levels increase 2.2 billion years ago o Eukaryotes
§ Mitochondria have their own DNA (and chloroplasts)
§ Endosymbiosis – living together
§ Figure 25.9
§ Heterotrophs, instead of one eating the others lived together
§ Compare DNA in mitochondria to bacteria and host nucleus, DNA in mitochondria looks closer to bacteria than host DNA
· Support endosymbiosis o Single cell to multicellular
§ Opens the door for cellular specialization
§ 600-700 million years ago
· Could be back as far as 1 billion
§ Large multi-cellular (3 billion years)? o “Cambrian Explosion”
§ Boom in diversity
· Chemical and physical processes on early earth, aided by the emerging force of natural selection, could have produced very simple cells through a sequence of four major stages: o The abiotic synthesis of small organic molecules such as amino acids and nucleotides o The joining of these small nucleotides into macromolecules o The packaging of these molecules into “protobionts,” droplets with membranes that maintained an internal chemistry different from that of their surroundings o The origin of self-replicating molecules that eventually made inheritance possible
· Synthesis of organic compounds on early earth o Solar system formed 4//6 billion years ago o Collisions ended 3.9 billion years ago o As earth cooled water vapor condensed to oceans and much of the hydrogen escaped to space o It is likely that small pockets of early atmosphere were reducing allowing organic compounds to form o Experiments show that abiotic synthesis of organic molecules are possible o Meteorites that land on earth also contain amino acids
· Abiotic synthesis of macromolecules o By dripping solutions of amino acids onto hot sand, clay or rock, researchers have been able to produce amino acid polymers
· Protobionts o Collections of abiotically produced molecules surrounded by a membrane-like structure o May exhibit some properties of life-simple reproduction and metabolism o Could have formed spontaneously from abiotically produced organic compounds
· Self-replicating RNA and the dawn of natural selection o The first genetic material was most likely RNA, not DNA o RNA can also carry out a number of enzyme catalytic functions
§ RNA catalysts are called ribozymes
§ Some can make complementary copies of short RNA o Natural selection on the molecular level has produced ribozymes capable of self-replication in the laboratory o The RNA molecule whose sequence is best suited to the surrounding environment and has the greatest ability to replicate itself will leave the most descendant molecules o RNA could have provided a template on which DNA nucleotides were assembled
25.2 The fossil record documents the history of life
· The fossil record o Based primarily on the sequence in which fossils have accumulated in sedimentary rock layers called strata o Shows that there have been great changes in the kinds of organisms that dominated life on earth at different points in time o Fossils also document how new groups of organisms arose from previously existing ones o There may be reasons why we see many of one type and not so many of another o Much more likely to see
§ Aquatic organisms (in ideal fossilization place)
§ Hard parts (skeletons and shells vs. soft bodies)
§ Larger organisms are more likely to be found
· Maybe not necessarily more ready to fossilize
§ Widespread organisms (vs. animals only in one lake)
§ Certain places are more explored than others
· This could change over time
§ Can start to construct a history
· Table 25.1 geologic time scale
· Fossils are the interface between geology (dating of the rocks) and biology (animals and names)
· Names come from abundance of these animals in that time
§ Debronian – fish life
§ Mesozoic – reptiles o The oldest fossil is about 3.5 billion years old
§ Cyano bacteria – single-celled, anaerobic, prokaryotic
§ Has to be something in between nothing and cyano bacteria
· How rocks and fossils are dated o Radiometric dating: based on the decay of radioactive isotopes
§ A “parent” radioactive isotope decays to a “daughter” radioactive isotopes at a constant rate expressed by the half-life
§ Half-life: time required for 50% of a parent isotope to decay
§ Each variety of radio isotope has a characteristic half-life which is not affected by the environment
§ Fossils contain radioactive isotopes that accumulated in them while they were still alive
§ Carbon-14 decays and carbon-12 does not
· Compare the amount of carbon-14 to the amount of carbon-12 to determine age
§ Hard to date since surrounding sediments have differing ages and long half-life radio isotopes do not build in skeletons of shells
§ Measure rock layers surround (top and bottom)
§ Decay of radioisotopes at a fixed rate to more stable form
§ C14 decays into N14 – half-life approximately 5730 years
· Can measure how fast this happens
§ Two half-lives, 25% of the sample has decayed
§ C12:C14 standard ratio in environment exists
§ Measure the amount of C12 compared to C14
§ C14 can only take us so far, approximately 75000 years ago
§ Cant date most things with C14
§ Can’t date most things with C14
§ Lots of elements that have half-lives
· U238
· K40 → Ar40 half-life 1.3 billion years o Found in lots of volcanic rock
· Can date different layers of rocks
· Can’t date fossil directly so date layers and find bracket o Between blank and blank o Magnetism of rocks can also be used to date
§ Iron particles in the rock align themselves with earth’s magnetic field and are frozen in time
§ Measurements of magnetism suggest that the earth’s magnetic poles have reversed repeatedly in the past
· The origin of new groups of organisms o Some fossils provide a detailed look at the origin of new groups of organisms
§ Illustrate how new feature of organisms arise and how long it takes for such changes to occur o Mammals have a number of unique anatomical feature that fossilize readily allowing scientists to trace o Fossil record shows that the unique features of mammalian jaws and teeth evolved as a series of gradual modifications [Figure 25.6]
25.3 Key events in life’s history include the origins of single-celled and multi-celled organisms and the colonization of land
· The study of fossils has helped geologists establish a geologic record of earth’s history o Divided into three eons: Achaean, Proterozoic, and the Phanerozoic o Phanerozoic encompasses most of the time animals have existed on Earth divided into three eras: Paleozoic, Mesozoic, and Cenozoic o Mesozoic – “age of reptiles”
§ Abundance of reptile fossils – including dinosaurs o Boundaries between the eras correspond to major extinction events
· The first single-celled organism o Stromatolites: layered rocks that form when certain prokaryotes bind thin films of sediments together
§ Earliest evidence of life o Photosynthesis and the oxygen revolution
§ Most atmospheric oxygen is produced during the water splitting step of photosynthesis
§ When oxygenic photosynthesis first evolved, the oxygen probably dissolved in the surrounding water until the concentration was high enough to react with iron creating iron oxide which accumulated as sediments
§ Oxygen continued to dissolve until the water was saturated and oxygen entered the atmosphere
§ The “oxygen revolution” has a great impact
· Oxygen attacks chemical bonds and inhibits enzymes – hurt many prokaryotic groups o The First Eukaryotes
§ Endosymbiosis: mitochondria and plastids were formerly small prokaryotes that began living within large cells
§ Scenario: heterotrophic host uses nutrients released from photosynthetic endosymbionts
§ All eukaryotes have mitochondria, but not all have plastids, so serial endosymbiosis supposes that mitochondria evolved before plastids
· The origin of multicellularity o The earliest multicellular eukaryotes
§ First fossils of algae from 1.2 billion years ago
§ Multicellular organisms limited in size and diversity until the late Proterozoic because of ice ages o The Cambrian explosion
§ Many phyla of living animals appear suddenly in fossils in the Cambrian period
§ Prior, all animals were soft-bodied and fossils reveal little evidence of predation
· Appear to be herbivores, filter feeders, or scavengers
§ Claws and defensive adaptations appeared
· The colonization of land o Gradual evolutionary venture out of aquatic environments was associated with adaptations that made it possible to reproduce on land and that helped prevent dehydration o Arthropods and tetrapods are the most widespread and diverse land animals
25.4 The rise and fall of dominant groups reflect continental drift, mass extinctions, and adaptive radiation
· Continental drift o Continents move over time o Continents are part of great plates of earth’s crust that essentially float on the hot, underlying portion of the mantle o Few cm per year o Can infer the past locations of the continents using the magnetic signal recorded in rocks at the time of their formation o Formation of mountains and islands occur at plate boundaries o Consequences of continental drift
§ Reshapes physical features and impacts life
§ Alters habitats – extinctions, new adaptations
§ Climate changes when it shifts north or south
§ Rerouted the ocean currents – causing the global climate to become cooler and the formation of polar ice caps
§ Promotes allopatric speciation
§ Explains geographic distribution of fossils
· Mass Extinctions o Overwhelming majority of species are now extinct o Mass extinction: where a certain disruptive global environmental change causes a dramatic increase in extinction o Extinction is forever o More than 60% of species going extinct in less than one million years o The “Big Five”
§ Represent a dramatic shift in the biodiversity
§ Ex. dinosaurs (65 million years ago)
§ End of Permian – 96% of species when extinct 450 million years ago
· Some evidence of massive volcanic eruptions – change atmosphere drastically
§ Permian extinction defines the boundary between Paleozoic and Mesozoic era
· 96% marine animals extinct
· 8 out of 27 insect species
· Enormous volcanic eruptions produced enough carbon dioxide to warm the climate o Slowed mixing of ocean water creating an oxygen deficit
§ Cretaceous
· Between Mesozoic and Cenozoic eras
· More than ½ marine life and many families of terrestrial plant and animals
· Including dinosaurs
§ Consequences of mass extinction
· When an evolutionary lineage disappears it cannot reappear – changes evolution forever
· Takes 5-10 million years for the diversity of life to recover after a mass extinction
· Alters ecological communities by changing the types of organisms found in them
· Pave the way for adaptive radiations
· Adaptive radiations o Periods of evolutionary change in which groups of organisms form many new species whose adaptation allow them to fill different ecological roles in their communities o Large scale adaptive radiations occurred after each of the big five extinctions o Instead of disappearance, large amount of biodiversity quickly o Cambrian explosion o Opposite of mass extinction o 65 million years ago (dinosaurs) – another example
§ Birds and mammals o Often after mass extinctions
25.5 Major changes in body form can result from changes in the sequences and regulation of developmental genes
· Evolutionary effects of developmental genes o Developmental genes influence the rate, timing, and spatial pattern of change in all organisms form o Evolutionary changes due to changes in rate and timing
§ Heterochromy: an evolutionary change in the rate or timing of developmental events
· Ex. slight changes in relative rates of growth can change the adult form substantially
· Can also alter timing of reproduction development relative to development of non-reproductive organs o Paedomorphosis o Changes in spatial pattern
§ Evolutionary changes due to alterations in genes that control the placement and spatial organization of body parts
· Homeolic genes
· The evolution of development o A set of genes sufficient to produce complex animals existed at least 30 million years before the Cambrian explosion o New genes (created by gene duplication events) may have taken on a wide range of new metabolic and structural function and may have contributed to the diversity found after the explosion o Changes in genes
§ New developmental genes arising after gene duplication very likely facilitated the origin of new morphological forms
§ Ex. Ubx gene o Changes in gene regulation
§ A change in the nucleotide sequence of a gene may affect its function wherever the gene is expressed
§ In contrast, changes in the regulation of gene expression can be limited to a single cell type – and therefore is less harmful
§ Thus, researchers suggest that changes in form in organisms often may be caused by mutations that affect the regulation of developmental genes – not their sequence
25.6 Evolution is not goal oriented
· Evolutionary novelties o Evolution of the human eye
§ Limpets have simple eyes – can only distinguish light from dark, cling more tightly to their rock when in shadows
§ Evolution took place through a series of incremental modifications that benefited the owner at every stage o Evolutionary novelties can also arise when structures that originally played one role gradually acquire a different one
§ Jaw hinge bones became part of the ear region and then transmitted sound
§ Called exaptation
· Evolutionary trends o Some lineages exhibit a trend toward large or smaller body size o Species undergo species selection
§ The species that endure the longest and generate the most new offspring species determine the direction of major evolutionary trends

Chapter 26
· Phylogeny: the evolutionary history of a species or a group of species
· Systematics: a discipline focused on classifying organisms and determining their evolutionary relationships
26.1 Phylogenies show evolutionary relationships
· Taxonomy: discipline of naming organisms o Allows for categorization o K, P, C, O, F, G, specific epithet
§ Kings play chess on fancy green stools
· Binomial nomenclature o Binomial: the two part format of the scientific, Latin name
§ First part is the genus (sing. Genera)
· Hierarchical classification o Species that appear to be closely related are grouped into the same genus o Hierarchy – related genera and placed in the same family, families into orders, orders into classes, classes into phyla, phyla into kingdoms, and kingdoms into domains o Taxon: the named taxonomic unit at any level of the hierarchy
· Linking classification and phylogeny o Phylogenetic tree: a branching diagram representing the evolutionary history of a group of organism o Branching pattern in some cases matches the hierarchical classification may not provide information on how the organism are evolutionarily related o PhyloCode: only names groups that include a common ancestry and all of its descendants
§ Species would no longer have ranks attached to them o Branch – points series of dichotomies showing evolutionary relationships
§ Each one represent the divergence of two evolutionary lineages from a common ancestry o Sister taxa: groups of organisms that share an immediate common ancestor and hence are each other’s close relatives o Rooted: a branch point within the tree that represents the ancestry for all the taxa in the tree o Polytomy: a branch point relationships from which more than two descendant groups emerge
· What we can and cannot learn from phylogenic trees o Sequence of branching in a tree does not necessarily indicate the actual ages of the particular species o Interpret the diagram solely in terms of patterns of descent o We cannot assume that a taxon on a phylogenetic tree evolved from the taxon next to it
· Applying Phylogenies o Gene identification
26.2 Phylogenies are inferred from morphological and molecular data
· Morphological and molecular homologies o Similarities due to shared ancestry are called homologies o Organisms that share very similar morphologies or similar DNA sequences are likely to be more closely related o Ex. morphological similarity:
§ Similar number and arrangement of bones in the forelimbs of mammals o Sometimes the morphological divergence between related species can be great and their genetic divergence small (or vice versa)
· Sorting homology from analogy o Analogy: similarity due to convergent evolution o Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages o Distinguishing between homology and analogy is critical to reconstructing phylogenies o Homoplasies: analogous structures that arose independently o To distinguish between consider the complexities of the characters being compared o The more points complex structures have in common the more likely they are related o Same concept applies for genetic material
· Evaluating Molecular Homologies o After sequencing the molecules, align comparable sequences from the species being studied o If species are closely related, the sequences probably differ at only one or a few sites o Important to distinguish homology from analogy o Molecular systematics is the discipline that uses DNA and other molecular data to determine evolutionary relationships
26.3 Shared characters are used to connect
· Cladistics o Common ancestry is the primary criterion used to classify organisms o Clades – groups that include an ancestral species and all of its descendants o Clades are nested within larger clades o Taxon is equivalent to a clade if it is monophyletic o Monophyletic: consists of an ancestral species and all its descendants
§ A group that share a common ancestry, with no descendants excluded
§ Paraphyletic group excludes some descendants o Paraphyletic: an ancestral species and some, but not all of its descendants o Polyphetic: includes taxa with different ancestors o Morphology is the main tool for identifying organisms o Can compare DNA – new information compared to morphology represents an inference given some data o These things can change o Showing us the sequence of evolutionary divergences
· Shared ancestral and shared derived characters o Shared ancestral character: a character that originates in all ancestor of the taxon
§ Ex. a mammal’s back bone o Shared derived character: an evolutionary novelty unique to a particular clade
§ Ex. hair in mammals
· Inferring phylogenies using derived characters o Make sure to compare the same thing in organisms – homologous characteristics (homology) o Expect similarity to express evolutionary history o Analogy: appears similar, but is not due to common ancestry
§ Birds and bats – wings
§ Evolved independently more than once
§ Convergent evolution o Shared derived characters – synapomorphy
§ Identify characteristics that are shared among some species and excludes other that has changed from early o Shared derived characters are unique to particular clades o Should be able to find the clade in which derived appeared and use it to infer evolutionary relationships o Outgroup: a species or group of species from an evolutionary lineage that includes the species we are studying (the ingroup) o Compare members of the ingroup to each other and to the outgroup we can determine which characters were derived at various branch points of vertebrate evolution o Outgroup allows us to understand which one is actually derived – gives the direction
§ Based on prior knowledge
· Phylogenetic trees with proportional branch lengths o In some tree diagrams, branch lengths are proportional to the amount of evolutionary change or to the time at which particular events occurred o Branch length can represent the number of changes that have taken place in a DNA sequence
· Maximum parsimony and maximum likelihood o Maximum parsimony: we should first investigate the simplest explanation that is consistent with the facts (Occam’s razor)
§ The most parsimonious tree requires the fewest evolutionary events (or if based on DNA fewest base changes
§ Minimize homoplasies (analogies) o Only allow evolutionary gains o Maximum likelihood
§ Given certain rules about how DNA changes over time a tree can be found that reflects the most likely sequence of evolutionary events o Many genes evolve at approximately equal rates in different lineages
· Phylogenetic trees as hypotheses o Hypothesis of ancestry and subject to change o Can make and test predictions based on phylogeny o Phylogenetic bracketing
§ Allows us to predict (by parsimony) the features shared by two groups of closely related organisms are present in their common ancestor and all of its descendants, unless independent data indicate otherwise
26.4 An organism’s evolutionary history is documented in its genome
· Molecular approach helps us understand phylogenetic relationships that are not apparent
· Helps uncover relationships that have little grounds for morphological comparison
· Allow us to reconstruct phylogenies among groups of present day prokaryotes and other microorganisms for which we have no fossil record
· Different genes evolve at different rates, even in the same lineage o Trees can represent short or long periods of time depending on what genes are used
· DNA that codes for rRNA evolves slowly so it is useful for older species
· Mitochondria DNA (mtDNA) evolves quickly so it can be used with more recent species
· Gene duplications and gene families o Gene duplication increases the number of genes in the genome, providing more opportunities for further evolutionary changes o Molecular techniques trace gene duplications and their evolutionary influences o Molecular phylogenies must account for repeated duplications that result in gene families o Gene families: groups of related genes within an organism’s genome o Orthologous genes: homologous genes that are found in different species because of speciation o Paralogous genes result from gene duplication so they are found in more than one copy in the same genome
§ Can diverge within a species
· Genome evolution o Orthologous genes are widespread and can extend over huge evolutionary distances
§ Demonstrates that all living organisms share many biochemical and developmental pathways o The number of genes seems not to have increased through duplication at the same rate as perceived phenotypic complexity
· Genetic data is being used more and more o Essentially the same process o Compare the same genes in all your organisms o Comparing genetic homologies o Can have homoplasies in genetic data too o Can look at nucleus DNA or mtDNA o Morphology vs. molecular
§ Molecular is not error proof, not as subjected
§ Can’t use genetic on fossils – they’re rock!
· Morphology is necessary
§ Maybe put them together
· Can use phylogenies to see convergent evolution
26.5 Molecular clocks help track evolutionary time
· Molecular clocks
o A yardstick for measuring the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve a constant rates o The number of nucleotide substitutions in orthologous genes is proportional to the time since the genes became duplicated o Rate of the clock may vary greatly between genes
· Neutral theory o Possible that many of the genetic changes result from genetic drift or are neutral (neither detrimental or adaptive) o Neutral theory: much evolutionary change in genes and proteins has no effect on fitness and therefore is not influences by Darwinian selection o If most are neutral, then the rate of molecular change should indeed be like a clock o Differences in a clock rate are a function of how important it is o More important = less neutral change, most harmful changes, change slowly o Less important = less harmful, more neutral, change quickly
· Difficulties with molecular clocks o Natural selection causes many irregularities o Have been used to date past the fossil record – highly uncertain o Problems may be avoided by using many genes
26.6 New information continues to revise our understanding of the tree of life
· Three domains are a level higher than the
kingdoms o Bacteria, archaea, eukarya
· Bacteria: most of the currently known prokaryotes
· Archaea: diverse group of prokaryotic organisms that inhabit a wide variety of environments
· Eukarya: organisms that have cells with true nuclei
· A simple tree of life o Horizontal gene transfer: a process in which genes are transferred from one genome to another through mechanisms such as exchange of transposable elements and plasmids, viral infection, and perhaps fusions of organisms

Chapter 22
22.1 The Darwinian revolution changed traditional views of a young Earth in habited by unchanging species
· Scala Naturae and classification of species o Scale of nature developed by Aristotle o Each form of life, perfect and permanent had an allotted rung on ladder of increasing complexity
· Ideas about change over time o Darwin drew his ideas from scientists studying fossils – the remaining of traces of organisms from the past
· Lamarck’s Hypothesis of Evolution o Less complex things are always being created o Chain of events lead to more complex things o Use and disuse, the idea that parts of the body that used extensively become larger and stronger while those that are not deteriorate o Inheritance of acquired characteristics, an organisms could pass these modification to its offspring o Thought evolution occurred because organisms have an innate drive to become more complex
· Cuvier o Strongly suggests that there is no way things could be changing o Says if you alter it, it won’t be able to function o Anatomist – prominent and respected o Its complexity must indicate it’s been designed
22.2 Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life
· The voyage of the Beagle o Darwin planned to chart poorly known stretches of the south American coastline o Collected South American plants and animal and noted the characteristics that made them well-suited to such diverse environments o Found fossils- physical evidence did not support the traditional view of a static Earth only a few thousand years old o Became interested in the geographic distribution of species
· Darwin’s research o Adaptations: characteristics of organisms that enhance their survival and reproduction in specific environments o Adaptations and origins of new species are closely related processes o His explanation of how adaptations arise centered on natural selection o Natural selection: a process in which individuals with certain inherited traits leave more offspring than individuals with other traits o Society is dominated by people like Cuvier
§ Hostile environment to some of his ideas
§ Spent a lot of time putting together evidence o Natural selection is the mechanisms that could cause descent with modification (evolution)
· Alfred Wallace o Contemporary of Darwin o Came up with natural selection as well o Sent his paper to Darwin o Darwin’s been working on this for 20 years o Darwin gets more attention because it seems that he was developing this idea before Wallace
· The Origin of Species o Descent with modification
§ Descent of all organisms from an ancestor that lived in the remote past
§ As the descendants of that ancestral organisms lived in various habitats over millions of years, they had accumulated diverse modifications, or adaptations, that fit them into specific ways of life
§ Over 99% of all species that ever lived are now extinct o Artificial selection, natural selection, and adaptation
§ Artificial selection: human modified species by selecting and breeding individuals that possess desired traits
§ Darwin’s observations of nature
· Members of a population often vary greatly in their traits
· Traits are inherited from parents to offspring
· All species are capable of producing more offspring than their environment can support
· Owing to lack of food or other resources many of these offspring do not survive
§ Inferences
· Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
· This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
§ Naturals selection, over time, imposed by factors such as predators, lack of food, or adverse physical conditions can increase the proportion of favorable traits in a population
· Refine the match between organisms an their environment o Natural selection: a summary
§ Natural selection is a process in which individuals that have certain heritable characteristics survive and reproduce at a higher rate than other individuals
§ Over time, natural selection can increase the match between organisms and their environment
§ If an environment changes, or if individuals move to a new environment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new species in the process
§ Individuals do not evolve, the population evolves over time
§ Natural selection can only amplify or diminish heritable traits
§ Four Postulates of Natural Selection
· Individuals within a population are variable o They’re not identical o Incorporating genetics: as a result of mutation creating new alleles and segregation and independent assortment shuffling those alleles into new combinations, individuals within populations are variable for many traits
· The variation among individuals are inherited from parents o Incorporating genetics: individuals pass their alleles to their offspring intact
· In each generation, some individuals are more successful at surviving and reproducing o Longer you survive, the more you reproduce
· The individuals with the most favorable variations are naturally selected o Incorporating genetics: individuals with the alleles and allelic combinations that best adapt them to their environment (i.e. offer higher fitness), will be naturally selected o Nonrandom survival and reproduction of individuals o Very specific reasons why certain characteristics result in survival
§ Fitness: the number of offspring you produce that survive to reproduce
22.3 Evolution is supported by an overwhelming amount of scientific evidence
· Direct observations of evolutionary change o Predation and coloration in guppies: scientific inquiry
§ [Figure 22.13] o Evolution of Drug Resistant HIV
§ 65 million infections, 25 million deaths – worldwide
· High death rate
§ Projected 50 million deaths by 2020
§ Virus progresses to AIDS – this is the stage in which death occurs
§ RNA genome
§ virus attaches to surface of host cell and inserts genome and proteins
· Reverse transcriptase makes HIV DNA from HIV RNA
· HIV DNA is spiced into host genome – leads to new HIV viruses
· Process of reproduction – population of virions is growing
§ HIV attacks immune cells – because of the proteins in their membrane
§ Number of immune cells decreases – not able to protect or fight other infections – AIDS
§ Natural selection
· Reverse transcriptase is sloppy at base pairing – mistakes don’t get fixed
· Get a lot of mutations in virions – means that some of the proteins won’t be the same
· Reverse transcriptase is not the same in all of them
· AZT triphosphate – as reverse transcriptase grabs the AZT it stops the growing DNA – get nonsense DNA
· AZT introduces an N3 bond that stops it
· Because of the mutation rates in RNA there are RNA transcriptase that will not accept the AZT molecules o Reverse transcriptase resistant to AZT
· Shift in the population from non-resistant to resistant
· The selection is the introduction of AZT
· Populations evolve not individuals o Darwin’s finches
§ 15 species
§ Different distributions on the island
§ Big difference in their bill shapes
§ Severe drought in 1977 – selective event
· 84% of medium ground finch died
· Certain plants were not able to survive
· Plants that did had larger seeds
· The size of the bill is correlated to size of seeds they eat
· Some were not able to adjust to the food source
§ Need to see that when they reproduce that a trait shifts to see evolution – do see this shift in the average bill depth
§ Variation is pre=existing (the bill depth existed before the selection event)
· Natural selection is a reactive process not a forward thinking process o The Fossil Record
§ Evidence for evolution-of how life on earth has changed over time
· Homology o Characteristics with an underlying similarity even though they may have very different function o Anatomical and molecular homologies
§ Homologous structures represent variation on a structural theme that was present in their common ancestor
§ Vestigial structures: remnants of features that served important function in the organism’s ancestor o Homologies and “tree thinking”
§ All life shares the deepest layer, and each successive smaller group adds their own homologies to those they share with larger groups o Convergent evolution
§ The independent evolution of similar features in different lineages
· Biogeography o The geographic distribution of species o To predict where fossils of different groups of organisms might be found

Chapter 23
23.1 Mutations and sexual reproduction produce the genetic variation that makes evolution possible
· Genetic variation o Acquired characteristics are not heritable o Variation within a population
§ Discrete characters can be classified on an either-or basis
· Many are determined by a single gene
§ Most heritable variation involves quantitative characters which vary along a continuum within a population – usually results from the influence of two or more genes
§ Gene variability can be quantified as the average heterozygosity, the average percent of loci that are heterozygous
· Often estimated by surveying the protein products of genes using gel electrophoresis (does not account for silent mutation so must use other methods)
§ Nucleotide variability is measured by comparing the DNA sequences of two individuals in a population and then averaging the data from many such comparisons
§ Gene variability tends to be greater than nucleotide variability o Variation between populations
§ Geographic variation: differences in the genetic composition of separate populations
§ Geographic variation – mice here compared to mice there
§ Cline: a graded change in a character along a geographic axis
· Some caused by a gradation in an environmental variable
§ Selection can only operate if multiple alleles exist for a given locus o Mutation
§ Ultimate source of new alleles
§ A change in the nucleotide sequence of an organism’s DNA
§ Only mutation in cell lines that produce gametes can be passed to offspring
§ Weak evolutionary force by itself
§ Mutation with selection is a potent evolutionary force
· A negative impact on fitness will drop off through selection
· Positives may spread
§ Point mutations
· A change in one base in a gene
· Point mutations in noncoding regions are often harmless
· Will have no effect if the amino acid composition is not changed
· On rare occasions, a mutant allele may actually make its bearer better suited to the environment, enhancing reproductive success
§ Mutations that alter gene number or sequences
· Chromosomal changes that delete, disrupt, or rearrange many loci at once are almost certain to be harmful
· But when large-scale mutation leave genes intact, their effects on organisms may be neutral o In rare cases may be beneficial
· An important source of variation beings when genes are duplicated due to errors in meiosis – unequal crossing over, slippage during DNA replication, or the activities of transposable elements
· Duplications of large chromosomal segments are often harmful, but smaller segments may not be
· Mutations can accumulate
· The result is an expanded genome with new loci that may take on new functions
· Major role in evolution
§ Mutation rates
· Low in plants and animals 1/100000 genes per generation
· Prokaryotes typically have short generation spans, so mutations can quickly generate genetic variation in populations of those organisms – same for viruses
· RNA genome has a much higher mutation rate because of the lack of RNA repair mechanisms in host cells
§ Sexual reproduction
· Most of the genetic variation in a population results from the unique combination of alleles that each individual receives
· At the nucleotide level, all the differences among these alleles have originated from past mutations
· The rearranging of alleles into fresh combinations each generation provides much of the genetic variation that makes evolution possible
23.2 The Hardy-Weinberg equation can be used to test whether a population is evolving
· Gene pools and allele frequencies o Population: a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
§ Don’t have to have strict boundaries
§ Can be isolated – ex. island o Can characterize a population’s genetic makeup by describing its gene pool, which consists of all the alleles for all the loci in all individuals of the population o If only one allele exists for a particular locus in a population that allele is said to be fixed in the gene pool, and all individuals are homozygous for that allele o But if there are two or more alleles for a particular locus in a population, individuals may be either homozygous or heterozygous o Each allele has a frequency in the population o Evolution: a change in allele frequencies over time
§ See this manifest in the shift of phenotypes o Population: a group of individuals that can mate
§ Life cycle of a population:
· Gametes to zygotes to juveniles to adults to gametes o Gene pool: all the eggs and sperm in the population
· The Hardy Weinberg principle o If in H.W. equilibrium you can predict genotype frequencies with allele frequencies and vice versa o One way to assess whether natural selection or other factors are causing evolution at a particular locus is to determine what the genetic makeup of a population would be if it were not evolving at that locus o Hardy-Weinberg equilibrium
§ The frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work – such a gene pool is said to be in Hardy-Weinberg equilibrium
§ p2+2pq+q2=1
· p2=expected frequency of pp
· 2pq=expected frequency of pq
· q2=expected frequency of qq
§ if in equilibrium and continues to mate randomly generation after generation, allele and genotype frequencies will remain constant o Conditions for Hardy-Weinberg equilibrium
§ No mutations. By altering alleles or deleting or duplication entire genes, mutation modify the gene pool
§ Random mating. If individuals mate preferentially within a subset of the population, such as their close relatives, random mixing of gametes does not occur and genotype frequencies change
§ No natural selection. Differences in the survival and reproductive success of individuals carrying different genotypes can alter allele frequencies
§ Extremely large population size. The smaller the population is, the more likely it is that allele frequencies will fluctuate by chance from one generation to the next (genetic drift)
§ No gene flow. By moving allele into or out of populations, gene flow can alter allele frequencies § Departure from any of these conditions usually results in evolutionary change
§ Can be evolving at some loci, but be in equilibrium at others
§ Unrealistic – these are the five mechanisms of evolutionary change
· The things that change allele frequencies
§ Under Mendelian genetics there would be no evolutionary change o Applying the Hardy-Weinberg principle
§ Can be used to estimate the percentage of a population carrying the allele for an inherited disease
23.2 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population
· Natural selection o Individuals in a population exhibit variations in their heritable traits, and those with traits that are better suited to their environment tend to produce more offspring than those with traits that are less well suited o Selection results in alleles being passed to the next generation in proportions different from their proportions in the present generation o By consistently favoring some alleles over others, natural selection can cause adaptive evolution – evolution that results in a better match between organisms and their environment
· Genetic drift o Chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next o Chance events can be associated with reproduction and survival o Chance events can also occur during fertilization o The Founder Effect
§ When a few individuals become isolated from a larger population, this smaller group may establish a new population whose new gene pool differs from the source population o The Bottleneck Effect
§ Caused by a severe drop in population size
§ By chance alone, certain alleles may be over represented among the survivors, others may be under represented, and some may be absent altogether
§ Ongoing genetic drift is likely to have substantial effects on the gene pool until the population becomes large enough that chance events have less effect
§ Human actions can sometimes create severe bottlenecks for other species o Genetic drift: from generation to generation we see small fluctuations in allele frequencies
§ No way to predict the impact of genetic drift o Always operating as long as there is a finite population o Effects of genetic drift: a summary
§ Genetic drift is significant in small populations
· Although chance events can occur in populations of all sizes, they alter allele frequencies substantially only in small populations
§ Genetic drift can cause allele frequencies to change at random
· Doesn’t favor some alleles over others like natural selection
§ Genetic drift can lead to a loss of genetic variation within populations
· Can influence ability to adapt
· Genetic drift can cause harmful alleles to become fixed o Survival can be threatened o Gene flow
§ Migration
§ New individuals moving into the population to do this repeatedly you would converge on the same allele frequencies
§ The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes
§ Because alleles are exchanged among populations, gene flow tends to reduce the genetic differences between populations
§ If it is extensive enough gene flow can result in two neighboring populations merging with a common gene pool
§ When neighboring populations live in different environments, alleles transferred by gene flow may prevent a population from fully adapting to its environment
§ Sometimes beneficial alleles are transferred widely
· Nonrandom mating o Inbreeding events o Preferential mating - causes some alleles to be more abundant o Inbreeding can expose deleterious alleles
§ Large negative impact on fitness
§ Another way that’ll cause allele frequencies to change o Sexual selection
§ A special case of natural selection
§ There are traits that function to attract a mate
· Could potentially outweigh the cost of natural selection
§ Different selective properties in men and women
· Eggs are energetically expensive
· Sperm are energetically inexpensive
· Predict females to be choosy – want to do their best to raise more eggs
· Predict males to be competitive- women are a limited resource o See exaggerated characteristics in males – beneficial in competing – sexual dimorphism, enhance their chances of mating
§ Inter and intra selection
· Most things are a combination of both
23.4 Natural selection is the only mechanism that consistently causes adaptive evolution
· A closer look at natural selection o Relative fitness
§ Adaptive advantage can lead to greater relative fitness
§ Relative fitness: the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
§ Selection acts more directly on the phenotype than on the genotype
§ Depends on the entire genetic and environmental context in which it is expressed
· Ex. a slightly disadvantageous allele may persist by being located close to a favorable allele o Directional, disruptive, and stabilizing selection
§ Three modes of selection
§ Directional selection occurs when conditions favor individuals exhibiting one extreme of a phenotypic range thereby shifting the frequency curve
· Common when environment changes
§ Disruptive selection occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
§ Stabilizing selection acts against both extreme phenotypes and favors intermediate variants
· Reduces variation
· Sexual selection o A form of natural selection in which individuals with certain inherited characteristics are more likely than others to obtain mates o Result in sexual dimorphism: marked differences between the two sexes in secondary sexual characteristics
§ Size, color, ornamentation, behavior o Intrasexual selection: selection within the same sex
§ Individuals of the same sex compete directly for mates of the opposite sex o Intersexual selection: individuals of one sex are choosy in selecting their mates from the other sex
Chapter 24
24.1 The biological species concept emphasizes reproductive isolation
· The biological species concept (BSC) o Species: a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring o Reproductive isolation
§ The formation of a new species depends on this
§ The existence of biological factors (barriers that impede members of two species from producing fertile, viable offspring
§ Barriers block gene flow and prevent hybrids
§ Hybrid: offspring that result from an interspecific mating
§ Prezygotic barriers block fertilization
· Impede members from attempting to mate
· Preventing an intended mating form being complete
· Hindering fertilization if successful
§ Postzygotic barriers
· Reduced survival due to developmental errors o limitations of the biological species concept
§ the number of species to which it can be applied is limited
§ no way to apply reproductive isolation to fossils
§ does not apply to asexual reproducing organisms
§ species are designated by the absence of gene glow
· yet gene flow occurs between species
· Other definitions of species o Morphological species concept characterizes a species by morphology – body shape etc.
§ Subjective but more applicable o Ecological species concept views a species in terms of its ecological niche, the sum of how members of the species interact with their environment o Phylogenetic species concept (PSC) defines a species as the smallest group of individuals that share a common ancestor o BSC and PSC are to the two most common ways to define a species o Both BSC and PSC agree that an interruption of gene flow needs to occur for differences to arise and that a species has to represent independent evolutionary units o But disagree on when we recognize a species as an independent evolutionary unit o Most of the time BSC and PSC agree – both have limitations o Recognizing independent species can affect thinking about conservation
§ Ex. elephants o Two lineages may have different shared derived characters but they may still retain their ability to mate o BSC and PSC don’t necessarily happen at the same time – PSC may evolve into BSC (picture)
24.2 Speciation can take place with or without geographic separation
· Speciation Process o An interruption to gene flow (migration) o Causes of divergence
§ Mutation
§ Natural selection
§ Non-random mating
§ Genetic drift
· Allopatric (“other country”) speciation o Gene flow is interrupted when a population is divided into geographically isolated subpopulations o The process of allopatric speciation
§ Once geographic separation has occurred, the separated gene pools may diverge through the mechanisms in chapter 23
§ Reproductive isolation may result from divergence
§ Separation itself is not a biological barrier to reproduction o Physical separation of geography o Dispersal over the barrier (unusual event) o Vicariance – splitting of population (i.e. barrier emerges that causes split populations
§ Ex. Hawaii
· Sympatric (“same country”) speciation o Speciation occurs in population that live in the same geographic area o Less common but can occur if gene flow is reduced by polyploidy, habitat differentiation, and sexual selection o No physical separation o Polyploidy
§ Extra set of chromosomes
§ Autopolyploid: an individual that has more than two chromosome sets that are all derived from a single species
· Ex. tetraploid plants can’t mate with triploid
§ Allopolyploid: fertile when mating with each other but cannot interbreed with either parent species
· Hybrid offspring
§ Far more common in plants
§ Can instantly isolate an individual from parent population o Habitat differentiation
§ Subpopulation exploits a habitat or resource that the parent population does not o Sexual selection
§ Difference in characteristics that enhance mating
§ Most common
§ Can act quickly
§ This process could happen with natural selection too o Isolation by distance
§ Further away, less gene flow – diverge
§ Relies on ability of individuals to move – if they can move, may not diverge as much
24.3 Hybrid zones provide opportunities to study factors that cause reproductive isolation
· Hybrid zone: a region in which members of different species meet and mate, producing at least some offspring of mixed ancestry
· Patterns within hybrid zones o Narrow bands or complicated spatial patterns
· Hybrid zones over time o Reinforcement: reproductive barriers may be strengthened (limiting the formation of hybrids)
§ May ignore each other
§ Mechanical isolation – physically cannot mate
§ Gametic isolation – games don’t join because genes don’t match
§ Habitat isolation – utilizing different habitats
§ Temporal isolation – separated in time
· Active at different times, don’t encounter
§ Behavioral isolation – behaviors mean they don’t mate
· Different display characteristics o Fusion: reproductive barriers may be weakened over time (causing the two species to fuse together) o Stability: hybrids may continue to be produced, creating a long term stable hybrid zone o In reinforcement barriers are stronger in sympatric than allopatric
24.4 Speciation can occur rapidly or slowly and can result from changes in few or many genes
· The time course of speciation o Patterns in the fossil record
§ Punctuated equilibrium: periods of apparent stasis punctuated by sudden change
§ Some change gradually some do the above o Speciation rates
§ Punctuated pattern suggests that once the process begins, speciation can be completed relatively rapidly
§ Total time of speciation is varied

Chapter 52
· Ecology: the stud of the interactions between organisms and the environment
52.1 Ecology integrates all areas of biological research and informs environmental decision making
· [Figure 52.2] Ecologists work at different levels of the biological hierarchy o Organismal ecology is concerned with how an organism’s structure, physiology, and behavior meet the challenges posed by its environment o Population ecology analyzes factors that affect population size and how and why it changes through time o Community ecology examines how interactions between species, such as predation and competition, affect community structure and organization o Ecosystem ecology emphasizes energy flow and chemical cycling between organisms and the environment o Landscape ecology focuses on the factors controlling exchanges of energy, materials, and organisms across multiple ecosystems o Global ecology examines how the regional exchange of energy and materials influences the functioning and distribution of organisms across the biosphere
· Linking ecology and evolutionary biology o The differential survival and reproduction of individuals that leads to evolution occurs in ecological time – minute to minute time frame
· Ecology and environmental issues o Ecology provides the scientific understanding needed to help us conserve and sustain life on earth
52.2 Interactions between organisms and the environment limit the distribution of species
· Ecologists ask where and why species occur – focus on biotic (living) and abiotic (non-living) factors
· Biotic and abiotic factors affect the distribution of species
· [Figure 52.6]
· Dispersal and distribution o Dispersal: the movement of individuals away from their area of origin or from center of high population density
§ Contributes to the global distribution of organisms o Natural range expansions
§ Importance of dispersal is more evident when organisms reach an area where they did not exist previously – natural range expansion o Species transplants
§ Observed transplanted species to see if dispersal is key factor limiting distribution – sometimes species haven’t dispersed as far as possible
· Behavior and habitat selection o When individuals seem to avoid certain habitats, even when the habitats are suitable, the organism’s distribution may be limited by habitat selection behaviors
· Biotic factors o Survival in a new area may be limited by predation, parasitism, competition o By the absence of other species on which is relies
· Abiotic factors o Temperature
§ Effects biological processes
§ Ex. proteins denaturing
§ Most organisms function best within a temperature range
§ Birds and mammals are exothermic – internally regulate temp
· Attempt to expand their niche
· Opposite: endothermic o Water
§ Distribution of terrestrial species reflect their ability to obtain and conserve water o Precipitation
§ Mitigating the loss of water o Salinity
§ Concentration of slat in water effects the water balance of organisms through osmosis o Sunlight
§ Energy
§ Too much light can limit the survival of organisms (so can not enough)
· Ex. temperature stress
§ Can regulate a lot of the biology – organisms are adapted to the sun o Rocks and soil
§ pH, mineral composition, and physical structure of rocks and soil limit the distribution of plants and thus of the animals that feed on them
· Climate o Temperature, precipitation, sunlight, and wind are the major components of climate o Climate: the long-term prevailing weather conditions in a particular area o Macroclimate: patterns on the global, regional, and local level o Microclimate: very fine patterns
§ ex. under a fallen log o Global climate patterns
§ Determined largely by the input of solar energy and the planet’s movement in space
52.3 Aquatic biomes are diverse and dynamic systems that cover most of Earth
· Biomes: major terrestrial or aquatic life zones, characterized by vegetation type in terrestrial biomes or the physical environment in aquatic

Chapter 54
54.1 Community interactions are classified by whether they help, harm, or have no effect on the species involved
· Interspecific interactions: interactions with individuals of other species in the community o Competition, predation, symbiosis, herbivory
· Competition o -/- interaction that occurs when individuals of different species compete for a resource that limits their growth and survival (interspecific competition) o Competitive exclusion
§ Two species competing for the same limiting resource cannot coexist in the same place
§ One uses the resource more efficiently and thus reproduces more rapidly
§ Eventually leads to the elimination of inferior competitor o Ecological niches
§ The sum of a species use of the biotic and abiotic resources in its environment
§ Ecological role (i.e. profession)
§ Two species cannot coexist permanently in a community if their niches are identical
§ Resource partitioning: the differentiation of niches that enables similar species to coexist in a community o Character displacement
§ Character displacement: the tendency for characteristics to diverge more in sympatric population of species
· Predation o +/- interaction between species in which one species, the predator, kills and eats the other, the prey o Predators have adaptations that help them catch and subdue prey o Prey animals possess adaptations that help them avoid being eaten o Cryptic coloration, or camouflage, makes prey difficult to spot o Aposematic coloration or warning coloration, appears on animals with effective chemical defenses o Batesian mimicry, a palatable or harmless species mimics and unpalatable or harmful model o Mullerian mimicry, two or more unpalatable species mimic one another o Predators use mimicry too
· Herbivory o +/- interaction in which an organisms eats parts of a plant or algae o Most are invertebrates o Plants may be protected by chemical toxins or physical structures such as spines and thorns
· Symbiosis o When individuals of two or more species live in direct and intimate contact with one another o Parasitism
§ +/- symbiotic interaction in which one organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process
§ Endoparasites feed inside
· Ex. tape worms
§ Ectoparasites feed outside
· Ex. ticks o Mutualism
§ An interspecific interaction that benefit both species +/+
§ Obligate mutualism: atleast one species has lost the ability to survive without its survivor
· Ex. bacteria in digestive tract
§ Facultative mutualism – both species can live alone o Commensalism
§ An interaction between species that benefits one of the species but neither harms nor helps the other
§ “hitchhiking” species
54.2 Dominant and keystone species exert strong control on community structure
· Species diversity o The variety of different kinds of organisms that make up the community o Two component – species richness and relative abundance o Species richness: the number of different species in the community o Relative abundance: the proportion each species represent of all individuals in the community o Shannon Diversity (H)
§ One widely used index of diversity based on species richness and relative abundance o Difficult to census entire community o Measuring species diversity is often challenging but essential for understanding community structure but for conserving biodiversity
· Trophic structure o Feeding relationships between organisms o Food webs
§ Food chains are not isolated units but are linked together in food webs o Limits on food chain length
§ Energetic hypothesis suggests that the length of a food chain in limited by the inefficiency of energy transfer along the chain
· Only 10% of energy stored in the organic matter of each trophic level is converted to organic matter at the next trophic level
· Biomass: the total mass of all individuals in a population
§ Dynamic stability hypothesis proposes that long food chains are less stable than short chains
· The longer a food chain is, the more slowly top predators can recover from environmental setbacks
§ Most data available supports energetic hypothesis
· Species with a large impact o Dominant species
§ Those species that re the most abundant or collectively have the highest biomass
§ Exert a powerful control over the occurrence and distribution of other species
§ Invasive species – organisms that take hold outside their native range
§ Loss of dominant species affects community o Keystone
§ Not necessarily abundant in a community
§ Impact community by their niche o Foundation species (ecosystem “engineers”)
§ Exert their influence by causing physical changes in the environment
§ Ex. beaver
§ Sometimes act as facilitators – they have positive effects on the survival and reproduction of other species
· Bottom-Up and Top-Down Controls o Bottom-Up
§ Postulates a unidirectional influence from lower to higher trophic levels
· Nutrients – vegetation – herbivory – predator o Direction of influence
§ Change community structure by altering the lower trophic levels o Top-Down
§ Opposite of bottom-up
§ Trophic cascade model
54.3 Disturbance influences species diversity and composition
· A disturbance is an event that changes a community by removing organisms from it or altering resource availability
· Nonequilibrium model describes most communities as constantly changing after being affected by disturbances
· Characterizing disturbance o A high level disturbance is generally the result of a high intensity and high frequency of disturbance o Intermediate disturbance hypothesis states that moderate levels of disturbance can create conditions that foster greater species diversity that low or high levels of disturbances
§ Open up habitats for occupation by less competitive
§ Rarely exceed environmental tolerance or rate of recovery by potential community members o Small scale disturbances can create patches of different habitats across a landscape
· Ecological Succession o A disturbed area colonized by a variety of species, which are gradually replaced by other species, which are in turn replaced by still other species o Primary succession – when this process begins in a virtually lifeless area where soil has not yet formed
§ Usually autotrophic prokaryotes and heterotrophic prokaryotes and protists o Secondary succession occurs when an existing community has been cleared by some disturbance that leaves the soil intact
§ Sometimes returned to something near its original state o Arrival of species either may facilitate, inhibit, or have no effect (tolerate) later arrivals
· Human Disturbance o Strongest agent of disturbance o Hinders species diversity in many communities
54.4 Biogeographic factors affect community biodiversity
· Latitudinal gradients o Plant and animal life is generally more diverse and abundant in the tropics o The two key factors in latitudinal gradients of species richness are evolutionary history and climate o Tropical communities are generally older than temperate or polar communities
§ The growing season is 5 times longer
§ So evolution events occur 5 times as fast o Tropical communities have a relatively high solar energy in input and water availability – correlated with biodiversity o Evapotranspiration: the evaporation of water from soil plus the transpiration of water from plants
§ Much higher in tropics
· Area effects o Species area curve: all other factors being equal, the larger the geographic area of a community, the more species it has o Larger areas offer a greater diversity of habitats and microhabitats o Can use it to predict the effect of a loss of a habitat
· Island Equilibrium Model o Islands provide excellent opportunities for studying the biogeographic feature that affect species diversity o Any patch of land surrounded by an environment not suitable for the “island” species o Immigration and extinction rates determine the number of species on an island o Size and distance from the mainland affect immigration and extinction rates
§ Small island generally have lower immigration
· Also higher extinction – fewer resources and less diverse habitats
§ Closer island has higher immigration
· Lower extinction – arrivals help sustain a species o Island equilibrium model – an equilibrium will eventually be reached where the rate of species immigration equals the rate of extinction o The number of species at this point is correlated with its size and distance from the mainland
54.5 Community ecology is useful for understanding
· Pathogens: disease-causing microorganisms, viruses, viroids, or prions
· Pathogens can alter community structure quickly and extensively
· Pathogens and community structure o Coral reef communities are increasingly susceptible to the influence of newly discovered pathogens o Human activities are transporting pathogens around the world and unprecedented rates
· Community ecology and zoonotic diseases o Zoonotic pathogens: those pathogens that are transferred from other animals to human, either through direct contact with an infected animal or by means of an intermediate species, called a vector
§ Ex. malaria, mad cow disease o Can help prevent by identifying key species interactions involving pathogens and their vectors and by tracking pathogen spread o Understanding parasite life cycles can allow us to control zoonotic diseases
Chapter 40
40.1 Animal form and function are correlated at all levels of organization
· Form affects the way an organism interacts with its environment o Organisms are designed to suit their environment o Not just at organismal level – molecular level also
· Physical constraints on animal size and shape o Properties of water limit
§ Ex. swimmer organisms have streamlined body contour
· Tapered on both ends o As body dimensions increase, thicker skeletons are required to maintain adequate strength o As body size increases, muscles required for locomotion must represent a larger fraction of body mass o Blood flow through vasculature o Lever action of skeletal muscle o Movement of substances across cell membranes o Body size
§ Delivering nutrients gets more difficult at larger sizes
· Exchange with the environment o Amount of material exchanged between internal and external environment is proportional to volume o Volume determines body needs o Surface area determines ability to transport o Rates of exchange for nutrients, waste, and gases are proportional to membrane surface area o The amount of material that must be exchanged to sustain life is proportional to volume o As cell number increases, the ratio of the outer surface area of the animal to its volume steadily decreases
§ When the ratio is less than one, needs can no longer be met by simple diffusion o Extensively branched or folded surfaces enable sufficient exchange with the environment
§ Ex. digestive tract o Exchange between the interstitial (between cells) and circulatory (ex. blood) fluid enables cells throughout the body to obtain nutrients and get rid of wastes o A cell with microvilli increases its surface area
§ Microvilli are an indication of secretion or absorption
· Hierarchical organization of body plans o Tissues: groups of cells of similar appearance and a common function
· Tissue structure and function o Epithelial, connective, muscle, and nervous tissue o Epithelial:
§ Occur as sheets of cell
§ Exposed to the environment
§ Very tightly packed together
§ Protects the body – from pathogens getting across
· Cuts split the barrier
§ Help limit water loss
· Burn patients lose epithelia
§ Modified epithelium forms
· Glands, hair/feathers, nails/claws/hooves o Keratinized epithelium
§ Covers the outside of the body and lines organs and cavities with the body
§ Often involve tight junctions
§ Barrier against mechanical injury, pathogens, and fluid loss
§ Cell shape can cuboidal (cube), columnar (columns), or squamous (flat)
§ Simple epithelium (single cell layer)
§ Stratified (multiple tiers of cells)
§ Pseudostratified – a single layer varying in heights
§ [Figure 40.5]
§ Epithelial junctions
· Tight junctions o Relatively impenetrable o Prevent movement between cells o Surround and attach cells
· Desmosomes o Structural reinforcement o Prevents the cells from being pulled apart o Spot welts
· Gap Junctions o Allow the two cells to communicate o Connective tissue
§ Cells are far apart which makes the extracellular matrix
§ Most varied of four types of tissue
§ May be a storage place, supports, protects, insulates
§ Bind and support other tissues
§ Six major types: loose connective tissue, cartilage, fibrous connective tissue, adipose tissue, blood, and bone
· Fibers inside determine function
§ Loose wraps around individual cells
· Insulating and protecting cells from each other
§ Cartilage: flexible, provides structure, support and protects the ends of bones at joints – absorbs shock – allows for mobility (ribs)
§ Adipose: storage place for fat (fuel)
· Important in insulation and protecting, supports
§ Blood: transports nutrients
· Protective (maintaining heat and carrying nutrients)
§ Bones: anchor site for movement, storage of calcium, protective (most bone around vital structures)
§ Fibrous: connects one type to another (tendons and ligaments)
§ Extracellular matrix:
· Fibers o Allows blood to clot o Determines rigidity of cartilage
· Fibers are mineralized in bone
§ Connective tissue fibers (made of protein) are of three kinds:
· Collagenous – strength combined with flexibility (collagen) o Do not tear easily, nonelastic
· Elastic – easily stretched but snap back (elastin)
· Reticular – very thin and branched, form a tightly woven fabric that joins connective tissue to adjacent tissue
§ Types of cells:
· Fibroblasts – secrete the protein ingredients of the extracellular fibers
· Macrophages – roam the maze of fibers engulfing foreign particles and debris o Muscle tissue
§ Responsible for nearly all types of movement
§ Consist of filaments contain actin and myosin allowing muscles to contract
§ Most abundant
§ Skeletal, cardiac, and smooth
§ Actin = thin filament myosin = thick filament
· All have actin and myosin that interact to produce force
§ Skeletal – attached to bone
· Voluntary (under conscious control_
· Has to be a way to get the signal from brain to muscle
· All skeletal muscle activated by motor neuron o Sever the neuron, no more contraction ever
§ Cardiac – only in the heart
· Involuntary
· Stimulant for contraction comes from the heart itself
§ Smooth
· Gut, wall of intestine/stomach, reproductive tract, urinary system, blood vessel walls, respiratory system
· involuntary o Nervous tissue
§ To sense stimuli and transmit signals in the form of nerve impulses from one part of the animal to another
§ Contains neurons (nerve cells) which have extensions called axons that are uniquely specialized to transmit nerve impulse
§ Also includes different forms of glial cells (glia) which help nourish, insulate, and replenish neurons
§ Neurons and glial cells
§ Signal transduction – take one form of signal and convert it into a signal the brain can understand (hearing/sight)
§ Specialized sensory structures receive information (stimulus_
§ Information is processed
§ Signal is sent
§ Action occurs
§ Fast, transient, specific
§ Uses labeled line (one pathway, one type of information)
· Coordination and control o Endocrine and nervous systems send signals to the body o Endocrine – hormones
§ Different hormones cause distinct effects and only cells that have receptors for a particular hormone respond
§ Relatively slow acting
§ Often long-lasting effects o Endocrine system
§ Specialized sensors detect changes (stimulus)
§ Cells release hormones into extracellular space
§ Hormone is carried in bloodstream to all cells of the body
§ Response is slower, longer-lasting
§ Only cells possessing specific receptors can respond
§ Target cells/organs – signal not just determined by receptor
· Age, stage of development, gender, season (ex. seasonal breeding) o Nervous system – nerve impulses
§ Not broadcast through entire body
§ Travel to a target cell along a dedicated communication line – consisting mainly of axons
§ Neurons, muscle cells, endocrine cells, and exocrine cells receive nerve impulses
§ Nervous system converges into by the pathway it takes
40.2 Feedback control loops maintain the internal environment in many animals
· Regulating and conforming o Regulators use internal control mechanisms to regulate internal change in the face of external fluctuation o Conformers allow its internal condition to conform to external change in the variable o An animal may regulate some internal conditions while allowing others to conform to the environment
· Homeostasis o “steady state” or internal balance o Achieving homeostasis, animals maintain a relatively constant internal environment even when the external environment changes significantly o Mechanisms of homeostasis
§ An animal achieves homeostasis by maintaining a variable at or near a particular value, or set point
§ Fluctuations above or below the set point serve as the stimulus
§ A receptor, or sensor, detects the stimulus and triggers a response, a physiological activity that helps return the variable to the set point o Feedback loops in homeostasis
§ Homeostasis relies largely on negative feedback
§ Homeostasis is a dynamic equilibrium
§ Physiological responses are not immediate
· So homeostasis reduces but doesn’t eliminate changes in the internal environment
§ Homeostasis is enhanced by mechanisms that reduce fluctuations – insulation, buffers
§ Positive feedback loops generally do not contribute to homeostasis o Alterations in homeostasis
§ Set points and normal ranges for homeostasis can change under various circumstances (regulated changes)
· Ex. temperature while sleeping
· Some are cyclic, or associated with a certain stage in life
§ May change through acclimatization: the process by which an animal adjusts to changes in its environment
Homeostatic processes for thermoregulation involve form, function and behavior
· Thermoregulation: the process by which animals maintain an internal temperature within a tolerable range
· Each species has an optimal temperature range
· Endothermy and ectothermy o Endothermic – warmed mostly by heat generated by metabolism o Ectothermic – gain most of their heat from external sources o Not mutually exclusive modes of thermoregulation
· Variation in body temperature o Animals can either have a constant or variable temperature o Poikilotherm – an animal whose temperature varies with its environment o Homeotherm – relatively constant temperature o There is no fixed relationship between the source of heat (endo/ectotherm) and the stability of body temperature (poikilo/homeotherm)
· Balancing heat loss and gain o Organism’s exchange heat by four physical processes
§ Conduction, convection, radiation, and evaporation o Essence of thermoregulation is maintaining rates of heat gain that equal rates of heat loss o In mammals, several of these mechanisms involve the integumentary system – the outer covering of the body o Insulation
§ Reduces the flow of heat between an animal and its environment
§ Many animals adjust their insulating layers to help thermoregulate
§ Secreting oily substances repels water and increases insulating capabilities o Circulatory adaptations
§ Circulatory systems provide a major route for heat flow between interior and exterior of the body
§ Adaptations that regulate the extent of blood flow near the surface or trap heat within the body core play a significant role in thermoregulation
§ Many animals alter the amount of blood flowing
· Expanding blood vessels/restricting blood vessels
§ In many birds and mammals, reduction of heat loss relies on countercurrent exchange: the flow of adjacent fluids in opposing directions that maximizes transfer rates of heat or solutes
§ Heat transfer involves an antiparallel arrangement of blood vessels (countercurrent heat exchanger)
· Arteries and veins are next to each other
· Warm blood passing through arteries warms cold blood in veins
§ By allowing blood to pass through the heat exchanger or diverting it to other blood vessels, these animals alter the rate of heat loss as their physiological state or environment changes o Cooling by evaporative heat loss
§ Evaporation is often the only way to keep the body temperature from rising rapidly
§ Terrestrial animals lose water by evaporation across the skin and when they breathe
§ The heat is carries away from the body when it evaporates
§ Panting
§ Sweating o Behavioral responses
§ Extreme migration and hibernation
§ Ectotherms regulate mostly by behavior
· Moving to solar heat/shade
· Expand the surface of their body exposed to the heat source
§ Certain postures maximize or minimize their absorption of heat o Adjusting metabolic heat production
§ Endotherms can vary heat production to match changing rates of heat loss
§ Ex. thermogenesis (heat production) is increased by muscle activity (shivering)
§ Some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP
· Acclimatization in thermoregulation o Includes adjusting the amount of insulation (endotherms) o Includes adjustments at the cellular level (ectotherms)
§ Producing variant of enzymes with the same function but differing optimal temperatures
§ Proportions of saturation and unsaturated lipids in membrane may change – unsaturated lipids keep membrane fluid at lower temperatures
§ Production of “antifreeze” compound
· Physiological thermostats and fever o The sensors for thermoregulation are concentrated in the hypothalamus
§ Contains nerves that function as a thermostat o Fever reflects an increase in the set point for the biological thermostat
§ Reduces fever in the rest of the body – heat flows to the surface
40.4 Energy requirements are related to animal size, activity, and environment
· Bioenergetics: the overall flow and transformation of energy in an animal o Determines nutritional needs and is related to size, activity, and environment
· Energy allocation and use o Food is dissolved by enzymatic hydrolysis and nutrients are absorbed by body cells
· Quantifying energy use o Metabolic rate: the sum of all the energy-requiring biochemical reactions over a given time o Can be measured by measuring amount of heat loss
· Minimum metabolic rate and thermoregulation o Basal metabolic rate (BMR): the minimum metabolic rate of a non-growing endotherm at rest
§ Measured at specific temperature o Standard metabolic rate: metabolic rate of an ectotherm at rest
· Influences on metabolic rate o Size and metabolic rate
§ Larger animals have larger body mass and therefore require more chemical energy
§ Metabolic rate proportional to (body mass)3/4 = m3/4
§ Hypothesized that for endotherms, the smaller the animal, the greater the energy cost of maintaining a stable temperature
· The smaller it is, the greater its surface area: volume ratio is – loses/gains heat faster from surroundings
§ Does not explain ectotherms inverse relationship between metabolic rate per gram and size
§ As body size decreases, energy cost per gram increases o Activity and metabolic rate
§ Increases BMR and SMR 2 – 4 times the amount
· Energy budgets
· Torpor and energy conservation o Torpor: a physiological state in which activity is low and metabolism decreases
§ Adaptations that allow animals to conserve energy o Hibernation is a long-term winter torpor
§ Estivation – summer torpor
Chapter 42
42.1 Circulatory systems link exchange surfaces with cells throughout the body
· The time it takes for a substance to diffuse from one place to another is proportional to the square of the distance
· Gastrovascular cavities o Animals that lack a distinct circulatory system o A singly opening maintains continuity between the fluid inside the cavity and the water outside o Nutrients only have to diffuse a short distance
· Open and closed circulatory systems o Minimizes distance of diffusion o Connects the aqueous environment of the body cells to the organs that exchange gases, absorb nutrients, and dispose of wastes o Three basic components
§ A circulatory fluid
§ A set of interconnecting tubes
§ A muscular pump, the heart o The heart powers circulation by using metabolic energy to elevate the hydrostatic pressure of the circulatory fluid, which then flows through a circuit of vessels and back to the heart o Open circulatory system – the circulatory fluid bathes the organs directly
§ The circulatory fluid – hemolymph – is also the interstitial fluid
§ Arthropods
§ Less costly than closed systems o Close circulatory system – blood is confined to vessels and is distinct form the interstitial fluid
§ One or more hearts pumps blood into large vessels that branch into smaller ones
§ Nutrients exchanged through the vessels and interstitial fluid
§ High blood pressure enables effective delivery of oxygen and other nutrients
· Organization of vertebrate circulatory systems o Cardiovascular system o Blood circulates to and from the heart o Three main types of blood vessels
§ Arteries: carry blood away from the heart to organs
· Branch into arterioles – small vessels that convey blood to the capillaries
§ Capillaries: microscopic vessels with very thin, porous walls
· Capillary beds – capillary networks
§ Veins: carry blood back to the heart o Portal veins vary blood between capillary beds o Atria receive the blood entering the heart o Ventricles pump blood out of the heart o Single circulation
§ Two chambers – atrium and ventricle
§ The blood passes through the heart once in each complete circuit
§ Blood that leaves the heart passes through two capillary beds before returning to the heart
· Blood pressure drops substantially when traveling through a bed o Double Circulation
§ Two distinct circuits
§ One pump, the right side delivers oxygen-poor blood to the capillary beds of the gas exchange tissues
· Pulmonary circuit
· Pulmocutaneous circuit if it includes capillaries in both the lungs and the skin
§ Blood from the lungs enter the left side, pump pumps blood to organs and tissues
§ Oxygen-poor blood returns to the heart completing the systemic circuit o o of double circulatory systems
§ Amphibians
· 3 chambers –two atria and the ventricle
· A ridge diverts most oxygen poor blood from the right atrium into the pulmocutaneous circuit and most oxygen rich blood from the left to eh systemic circuit
§ Reptiles
· Pulmonary and systemic circuits are connected where the arteries leave the heart
· Septum completely separates two atria
§ Mammals and birds
· Two atria, two ventricles
42.2 coordinated cycles of heart contraction drive double circulation in mammals
· Mammalian circulation o Contraction of the right ventricle pumps blood to the lungs via the pulmonary arteries
§ Blood loads oxygen and unloads carbon dioxide o Oxygen rich blood returns from the lungs via pulmonary veins to the left atrium o Oxygen rich blood flows into the right ventricle, which pumps it out to the body tissues through the systemic circuit o Blood leaves the left ventricle via the aorta, which conveys blood to arteries leading throughout the body
§ First branched are coronary arteries
§ The branches lead to head and arms
§ Then abdominal organs and legs o Oxygen poor blood is channeled into a large vein, the superior vena cave – head, neck, and forelimbs o Another large vein, the inferior vena cava, drains blood from the trunk and hind limbs o Two vena cavae empty oxygen poor blood into the right ventricle
· The mammalian heart: a closer look o Mostly cardiac muscle o Two atria have rather thin walls o Ventricle walls are thicker
§ Both pump the same amount of blood but left contracts more forcefully-more muscle in left o When the heart is relaxed blood flows into its chambers o Cardiac cycle: one complete sequence of pumping and filling o Systole: contraction phase o Diastole: relaxation phase o Cardiac output: the volume of blood each ventricle pumps per minute
§ Two factors determine:
· The rate of contraction – heart rate
· Stroke volume – the amount of blood pumped in a single contraction o Four valves in the heart prevent backflow and keep blood moving in the correct direction o Valves made of flaps of connective tissue o Open when pushed from one side, close when pushed from the other o Atrioventricular (AV) valve lies between each atrium and ventricle
§ Pressure by the contraction closes the AV valves, keeping blood from flowing back to the atria o Semilunar valves are located at the two exits of the heart: where the aorta leaves the left and pulmonary arteries leave the right
§ Pushed open by pressure of contraction o Heart murmur: an abnormal sound caused by blood squirting backward through a defective valve
· Maintaining the heart’s rhythmic beat o Some cardiac muscles are autorhythmic – contract and relax repeatedly without a signal o Sinoatrial (SA) node – a cluster of autorhythmic cells located in the wall of the right atrium that sets the rate and timing at which all cardiac muscles contract
§ Generates electrical impulses through gap junctions
§ Electrocardiogram (EKG) records the electrical currents in the heart through he skin o During atrial contraction, the SA impulse reach other autorhythmic cells between the left and right atria
§ These cells form a relay point called the atrioventricular (AV) node
§ Impulses are delayed .1s to let atria empty before signaling ventricles to contract via muscle fibers o Physiological cues alter heart tempo by regulating the SA node
§ Parasympathetic and sympathetic nerves responsible
42.3 Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels
· Blood vessel structure and function o Contain a central lumen (cavity) lined with an endothelium, a single layer of flattened epithelial cells o Smooth surface of endothelium minimizes resistance o Capillaries have thin walls consisting of just the endothelium and its basal lamina o Arteries and veins have two layers of tissue surrounding endothelium: an outer layer of connective tissue containing elastic fibers, which allow the vessel to stretch and recoil and a middle layer containing smooth muscle and more elastic fiber o Artery wall is three times as thick as a vein’s wall
§ Accommodates higher pressure o Signals from nervous system and homromes act on the smooth muscles in arteries, controlling blood flow to different parts of the body
· Blood flow velocity o Blood slows as it moves from arterires to arterioles to capillaires o Allows time for exchanges to occur o Speeds up as it enters the veins
· Blood pressure o Blood flows from higher to lower pressure o The force exerted against a wall of an artery stretches the wall and the recoil maintains blood pressure and thus blood flow o Changes in blood pressure during the cardiac cycle
§ Systolic pressure: pressure when the heart contracts – highest arterial blood pressure
§ Pulse – rhythmic bulging of the artery walls with each heart beat
· Surge partly due to arteriole resistance – blood enters faster than it can leave
§ Diastolic pressure – when ventricels are relazed
§ Blood continuously flows into arterioles and capillaries because blood remains pressurized o Regulation of blood pressure
§ Vasoconstriction: when smooth muscles in arteriole walls contract
· Can be caused by physical or emotional stress
· Increases blood pressure
§ Vasodilation: an increase in diameter that causes blood pressure in arteries to fall
· When smooth muscles relax
§ NO (g) serves as a major inducer of vasodilation
§ Endothelin for vasoconstriction o Blood pressure and gravity
§ Lowering head increases blood flow to brain
§ Rhythmic contractions of smooth muscles in the walls of venules and vbeins in the movement of blood
§ the contraction of skeletal muscles during exervise squeezes blood through the veins toward the heart
§ change in pressure in chest during inhalation causes the vena cavae and other large veins near the heart to expand and fill with blood
· Capillary Function o Every part of the body is supplied with blood at all times o Capillaries in brain, heart, kidneys, and liver are usually filled to capacity but other sites the blood supply varies over time o Contraction of smooth muscle in the wall of an arteriole reduces the vessles diameter and decreasese blood flow to capillaries o When smooth muscle relaxes, arterioles dilate, allowing blood to enter the capillaries o Precapillary sphincters, rings of smooth muscle located at the entrance to capillary beds
§ Nerve impulses and hormones regulate opening and closing o Some substances are exchanged by vesicles o Blood pressure drives fluids out but blood proteins pull back in – many are too large to pass readily o Creating an osmotic pressure difference and causing a net loss of fluid from capillaries
· Fluid return by the lymphatic system o Only about 85% of the fluid that leaves the capillaries reenters them o The lost fluid and proteins return to the blood via the lymphatic system o Lymphastic system includes a network of tiny vessels intermingled among capillaries of the vardiovascular system o After entering the lymphatic system, the fluid is called lymph o One system drains into large veins of the circulatory system at the base of the neck o Same mechanisms o Along a lymph vessel are organs called lymph nodes o By filtering the lymph and by housing cells that attack viruses and bacteria, lymph nodes play an important role in the body’s defense
42.4 Blood components function in exchange, transport, and defense
· Blood composition and function o Vertebrate blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma o Ions and proteins are dissolved in the plasma
· Plasma o 90% water o Dissolved salts in plasma are essential
§ Buffer the blood
§ Maintain osmotic balance of blood
§ Affects the composition of the interstitial fluid, where many of these ions have a vital role in muscle and nercve activity
§ Contribute to blood’s viscosity (thickness) o Immunoglobulins (antibodies) help combat viruses and other foreign agents that invade the body o Others excort lipids that can only travel when bound to proteins o Clotting factors o Much higher protein concentration than interstitial fluid
· Cellular elements o Suspended in blood plasma as red and white blood cells o Red blood cells which transport oxzygen o White blood cells function in defense o Also platelets – fragments of cells that are involved in the clotting process o Erythrocytes
§ Red blood cells, most numerous
§ Small disks that are biconcave – thinner in the center than at the edges
· Increases surface area, enhanving rate of diffusion of oxygen across their plasma membrane
§ Lack nuclei
· More space for hemoglobin, thie iron-containing protein that ransports oxygen
§ Lack mitochondria – generate ATP by anaearobic metabolism
§ One cell can transport about a billion oxygen molecules o Leukocytes
§ White blood cells, 5 major types
§ Phagocytic – engulfing and digesting microorganisms and debris
§ Found outside circulatory system o Platelets
§ Pinched-off cytoplasmic fragmentsw of specialized bgone marrow cells
§ No nuclei
§ Both structural and molecular functions in blood flotting o Blood clotting
§ The coagulant or sealant circulates in an inactive form, fibrin, which aggregates into threads that form the framework of the clot
§ Thrombus – clot within a blood vessel despite anticlotting factors o Stem cells and the replacement of cellular elements
§ Multipotent stem cells that are dedicated to replenishing the body’s blood cellpopulations
§ Located in the red marrow of bones
§ During division – one remains stem while the other takes on a specialized function
§ Replace cellular elements
§ Negative feedback sensitive to amount of oxygen controls erythrocyte production
§ Erythropoietin (EPO) – synthesized by the kidney if tissues do not receive enough oxygen to stimulate rythrocyte production
· Rises and falls depending on needs
· Cardiovascular disease o More than ½ deaths o Atherosclerosis
§ Hardening of the arteries by accumulation of fatty deposits o Heart attacks and stroke
§ Often result of arthersclerosis
§ Heart attack – the damage or death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
§ Stroke – the death of nervous tissue in the bran due to a lack of oxygen
§ Frequently result from thrombus that clogs an artery
42.7 adaptations for gas exchange include pigments that bind and transport gases
· Coordination of circulation and gas exchange o Partial pressure of oxygen and partial pressure of carbon dioxide differ at different points in the circulatory system o Gradients of partial pressure favor the diffusion of oxygen out of the blood and carbon dioxide into the blood in tissue capillaries o Gradients exist because mitochondria uses oxygen and forms carbon dioxide durinjg respiration
· Respiratory pigments o Low solubility of oxygen in water (and thus blood) poses a problem o Animals transport most of their oxygen bound to certain proteins called respiratory pigments o Circulate with blood and are often contained within specialized cells o Greatly increase amount of oxygen that can be carried in the circulatory fluid o Reduces cardiac output necessary o Have a distinctinve color o Protein bound to a metal o Hemoglobin
§ Almost all vertebrates and many invertebrates
§ Contained in erythrocytes
§ Four polypeptide chains, each with a heme group – has an iron atom at its center
· One iron per oxygen
· One molecule hemoglobin, four molecule oxygen
§ When oxygen binds to one subunit, the others change shape slightly, increasing their affinity for oxygen
§ Even a slight change in partical pressure of oxygen can force hemoglobin to load or unload
§ Borh shift: low pH dereases the affinity of hemoglobin for oxygen
§ Thus increased carbon dioxide prouuction, hemoglobin releases more oxygen for cellular respiration
· Carbon dioxide transport o Hemoglobin helps transport carbon dioxide and assists in buffering the blood o Carbon dioxide diffuses into blood plasma and then into erythrocytes o Carbon dioxide reacts with water and dissociates to H+ and HCO3- o Most of the H+ binds to hemoglobin and other proteins to minimize the change in pH o HCO3- diffuses into plasma o Diffusion of CO2 into alveoli stimulates HCO3- and H+ to form CO2 and H2O so more diffusion occurs
Chapter 48
48.1 Neuron organization and structure reflect function in information transfer
· Nervous system – communication system
· Glial cells – supporting cells o Don’t send signals
· Neurons are an example of form following function o Designed to relay information
· Introduction to information processing o 3 stages
§ Sensor input, integration, and motor output o Sensory neurons transmit information from eyes and other sensors that detect external stimuli or internal conditions
§ Sent to processing centers in the brain or ganglia o Interneurons in the brain integrate (analyze and interpret) the sensory input, taking into account the immediate context and the animal’s experience
§ Make only local connections o Motor neurons – neurons that extend out of the processing centers in bundles called nerves and generate output by triggering muscle or gland activity o Many animals, the neurons that carry out integration are organized in a central nervous system (CNS) which includes the brain and a longitudinal nerve cord o Peripheral nervous system: the neurons that carry information into and out of the CNS
· Neurons structure and function o Cell body: where most of a neuron’s organelles, including its nucleus are located
§ a.k.a. soma o A typical neuron has numerous dendrites – highly branched extensions that receive signals from other neurons
§ The more dendrites, the greater the ability to receive information o A neuron has a single axon – an extension that transmits signals to other cells
§ Often much longer than dendrites
§ Axon contains much fewer organelles o Axon hillock: the cone-shaped region of an axon where it joins the cell body
§ Typical region where signals that travel down the axon are generated o Each branched end of an axon transmits information to another cell at a junction called a synapse – the part of each branch that forms this specialized branch is a synaptic terminal (terminal bouton, or axon terminal) o Myelin sheath – surround axon – makes the signal sent go faster o Nodes of Ranvier – gaps in sheath o Electrical signal is converted to a chemical signal at the terminal o At most synapses, chemical messengers called neurotransmitters pass information from the transmitting neuron to the receiving cell
§ Neuron signals
· Long distance signals – electrical action potentials
· Short distance signals – chemical, synaptic release of neurotransmitters o Presynaptic cell: transmitting neuron o Postsynaptic cell receives the signal o To function normally, the neurons of vertebrates and most invertebrates require supporting cells called glial cells
§ May nourish, insulate, or regulate the extracellular fluid surrounding the neuron
48.2 Ion pumps and ion channels maintain the resting potential of a neuron
· Cells have a membrane potential: a voltage across their plasma membrane
· Resting potential at a resting neuron is about -70 mV
· Gradients o Pressure – hydrostatic, atmospheric o Chemical – concentration o Electrical – charge o Movement down the gradient is favored o Electrical
§ Caused by the separation of charge
§ PE: use of energy stored in the gradient to power work
§ Electrochemical gradients – ions distributed unequally
§ Cell uses a molecule of ATP to create a gradient each ion exhibits a concentration and an electrical gradient
§ Equilibrium potential – for each ion there is a point of theoretical equilibrium where the concentration gradient exactly balances the electrical gradient for that ion
· Everything wants to go to equilibrium
· Formation of the resting potential o K and Na ions are key o Concentration gradient of each maintain by sodium-potassium pumps o Represent a chemical form of potential energy o Ion channels: pores formed by clusters of specialized proteins that span the membrane
§ Involved in converting chemical PE to electrical PE
§ Allow ions to diffuse back and forth across the plasma membrane
§ The ions carry with them units of electrical charge
§ Any net movement generates a potential o Ion channels have selective permeability o Diffusion of K is critical for potential formation
§ K higher in the cell
§ Leads to diffusion out and an excess
· Charge inside
§ Na in cell o The separation of charge results in an electrical gradient that counteracts concentration gradient
48.3 Action potentials are the signals conducted by axons
· When neurons are active, membrane permeability and membrane potential increase o Occurs because neurons contain gated channels – ion channels that open or close in response to stimuli
· Hyperpolarization – increase in the magnitude of the membrane potential o Ex. opening K+ channels – cell becomes more negative
· Depolarization – reduction in the magnitude of the membrane potential o Often involves opening Na+ channels
· Graded potentials – the magnitude of the change varies with the strength of the stimulus
· Production of action potentials o Voltage-gated ion channels – open or close in response to a change in the membrane potential
§ Many of the gated ion channels in neurons o Action potential – massive change in membrane potential
§ The nerve impulses, or signals, that carry information along an axon
§ Occur whenever a depolarization increases membrane voltage to a particular value, called the threshold
§ Once initiated, the action potential has a magnitude that is independent of the strength of the triggering stimulus
§ All-or-none response to stimuli
· Generation of action potentials: a closer look o Lasts 1-2 msec o Neuron can produce hundreds/second
§ Frequency can vary with input
§ Frequency conveys information about signal strength o Membrane depolarization opens both types of channels (Na and K) but they respond independently and sequentially o Na first initiating action potential
§ Then a loop of the channel protein clocks flow through opening o Na channels remain inactive until after membrane reaches resting o K channels open more slowly but remain open and functional throughout the action potential

· A second stimulus during the falling phase will be unable to trigger an action potential – sodium channels are closed o Called the refractory period o Sets a limit on the maximum frequency at which action potentials can be generated o Also ensures that all signals in an axon travel in one direction, from the cell body to the axon terminals
· Conduction of action potentials o Regenerates itself as it travels from the cell body to the synaptic terminals o Shape and magnitude of the action potential remain constant o Refractory period causes the inward current that depolarizes the axon membrane ahead of the action potential to not be able to produce another action potential behind it – moves only toward terminals o Conduction speed
§ Several things affect speed
§ Axon diameter: wider axons conduct action potentials more rapidly than narrow ones
· Cross sectional area is inversely proportional to resistance
· Brings more distant regions of the membrane to the threshold sooner
§ Myelin sheath is an adaptation that allows quick transport in narrow axons
· A layer of electrical insulation that surrounds vertebrate axons
· Produced by two types of glia- oligodendrocytes in the CNS and the Schwann cells in the PNS
· Causes the depolarization to spread farther along the interior of the axon
· Space efficiency
§ Nodes of Ranvier
· Where voltage-gated sodium channels are restricted
· Gaps in myelin sheath
§ Salutatory conduction
48.4 Neurons communicate with other cells at synapses
· Some synapses contain gap junctions – electrical synapses o Allow electrical current to flow directly from one neuron to another
· Majority are chemical synapses o Involve the release of a chemical neuron synthesize the neurotransmitter and packages it in multiple membrane-bound compartments – synaptic vesicles
· Neurotransmitter diffuses across the synaptic cleft, the narrow gap that separates the presynaptic neuron from the postsynaptic cell
· Information transfer is much more readily modified at chemical synapses
· Variety of factors can affect the amount of neurotransmitter that is released or the responsiveness of the postsynaptic cell
· Generation of postsynaptic potentials o At many, ligand-gated ion channels capable of binding to the neurotransmitter are clustered in the membrane of the postsynaptic cell, directly opposite the synaptic terminal
§ Binding of an neurotransmitter (NT) to a particular part of the channel opens the channel and allows specific ions to diffuse across the postsynaptic membrane
§ Results in a change in membrane potential (Vm) – membrane depolarizes as Vm approaches value between EK and ENa
§ Depolarizations bring Vm near threshold so are called excitatory postsynaptic potentials (EPSPs) o Channels can open to allow Cl- to cross causing hyperpolarizations – inhibitory postsynaptic potentials (IPSP)
· Summation of postsynaptic potentials o Postsynaptic potentials are graded; their magnitude varies with a number of factors including the amount of NT released o Usually do not regenerate as they spread along the membrane of a cell; they become smaller with distance from the synapse o On some occasions, two EPSPs occur at a single synapse in such rapid succession that the postsynaptic cell's Vm has returned to resting yet, so the ESPS’s add together – temporal summation o Spatial summation – ESPSs produced nearly simultaneously by different synapses on the same postsynaptic neuron can also add together o In this way several ESPSs can depolarize the membrane at the axon hillock to the threshold – causing an action potential o Summation applies as well to IPSPs
§ Can also counter the effect of an ESPS
· Modulated synaptic transmission o There are also synapses in which the receptor for the NT is not part of the ion channel o Binding of the NT activates a signal transduction pathway involving a second messenger
§ Slower onset but last longer (minutes or hours) o Second messengers modulate the responsiveness of postsynaptic neurons to inputs in diverse ways – such as altering the number of open potassium channels
§ Can open or close many channels
· Neurotransmitters o Major classes are acetylcholine, biogenic amines, amino acids, neuropeptides, and gases o Acetylcholine
§ One of the most common in both vertebrates and invertebrates
§ Binds to receptors on ligand-gated channels in the muscle cell, producing an EPSP
§ Terminated by aceylcholinisterase o Biogenic amines
§ Derived from amino acids
§ Ex. serotonin, dopamine, epinephrine and norepinephrine
§ Norepinephrine generates EPSPs
· In the PNS
§ In the CNS, biogenic amines are often involved in modulating synaptic transmission o Amino acids
§ Major NTs in vertebrates CNS gamma-aminobutyric acid (GABA) and glutamate
§ GABA produces IPSPs – increase permeability to chloride
§ Glutamate is always excitatory o Neuropeptides
§ Relatively short chains of amino acids
§ Operate via signal transduction pathways
§ Substance pathway is a key excitatory neurotransmitter o Gases
§ Bone neurons release dissolved gases (ex. NO) that act as local regulators
Chapter 49
49.1 Nervous systems consist of circuits of neurons and supporting cells
· Most cnidarians have a series of interconnected nerve cells form a diffuse nerve net which controls the contraction and expansion of the gastrovascular cavity
· More complex animals, the axons of multiple nerve cells are often bundled together, forming nerves o Cephalization
· Nervous system organization often correlated with lifestyle
· Organization of the vertebrate nervous system o Spinal cord and CNS are tightly coordinated
§ cord conveys information to and from the brain and generates basic patterns of locomotion o Cord also acts independently also – reflexes
§ Reflex protects the body by triggering a rapid, involuntary response to a particular stimulus
§ Along dorsal side o central canal (cord) and the four ventricles (brain) are filled with cerebrospinal fluid
§ cerebrospinal fluid formed by filtration of arterial blood in the brain o brain and cord contain gray matter and white matter
§ gray matter: consists mainly of neuron cell bodies, dendrites, and unmyelinated axons
§ white matter: consists of bundled axons that have myelin sheaths (gives white color) o white matter on the outside – function: links CNS to sensory and motor neurons of PNS o glia in the CNS
§ ependymal cells line the ventricles and have cilia that promote circulation of the cerebrospinal fluid
§ microglia protect the nervous system from invading microorganisms
§ oligodendrocytes function in axon myelination
§ astrocytes appears to have the most diverse function
· provide structural support for neuron
· regulate the extracellular concentration of ions and neurotransmitters
· can facilitate information transfer
· When adjacent to active neurons cause nearby blood vessels to dilate. Increases blood flow and oxygen uptake
· induce cells that line capillaries in the CNS to form tight junctions resulting in the blood-brain barrier, which restricts the passage of most substances into the CNS o permits tight control of the extracellular chemical environment of the brain and spinal cord
§ radial glia play a critical role in development of the nervous system
· Peripheral nervous system o large role in regulation movement and internal environment o sensory information reaches the CNS along PNS neurons designated as afferent o following information processing within the CNS, instructions then travel to muscles, glands, and endocrine cells along PND neurons designated as efferent o vertebrate PNS consists of left-right pairs of cranial and spinal nerves and their associated ganglia o cranial nerves connect the brain with locations mostly in organs of the head and upper body o spinal nerves run between the spinal cord and parts of the body below the head o a few cranial are afferent only
§ ex. olfactory nerves o efferent branch: the motor and the autonomic nervous system
§ motor system consists of neurons that carry signals to skeletal muscles, mainly in response to external stimuli – general voluntary
§ autonomic nervous system regulates the internal environment by controlling smooth and cardiac muscles and the organs of the digestive, cardiovascular, excretory, and endocrine systems
· generally involuntary
· three division – sympathetic, parasympathetic, and enteric
· sympathetic division corresponds to arousal and energy generation
· parasympathetic division generally causes opposite responses that promote calming and a return to set-maintenance functions (“rest and digest”)
· enteric division consists of networks of neurons in the digestive tract, pancreas, and gallbladder o control secretion and the smooth muscle that produce peristalsis o can function independently but it is normally regulated by parasympathetic and sympathetic divisions
§ autonomic and motor systems often cooperation in maintaining homeostasis
49.2 The vertebrate brain is regionally specialized
· the brain stem o functions I homeostasis, coordination of movement, and conduction of information to and from higher brain centers o anterior end of spinal cord o consists of the midbrain, the pons, and the medulla oblongata o medulla and pons: transfer information between mid- and forebrain and also help coordinate large scale movements o midbrain contains centers for receiving and integrating several types of sensory information
§ also sends coded sensory information along neurons to specific region of the forebrain o signals from the brainstem affect attention, alertness, appetite, and motivation o Medulla contains centers that control several automatic, homeostatic functions, including breathing, heart and blood vessel activity etc.
§ pons also participates in some of these o arousal and sleep
§ arousal is a state of awareness of the external world
§ sleep is a state in which external stimuli are received but not consciously perceived
§ reticular formation – a diffuse network of neurons in the core of the brainstem that determine which incoming information reaches the cerebral cortex
§ the more information the cortex receives the more alert and aware a person is
§ the pons and medulla contain centers that cause sleep when stimulated and the midbrain has a center that causes arousal
§ melatonin, a hormone produced by the pineal gland, appears to play an important role in sleep/wake cycles
· peak secretion at night
· The cerebellum o Coordinates movement and balance o Monitors motor commands issued by the cerebrum o Integrates information as it carries out coordination and error checking during motor and perceptual functions
· The diencephalon o Develops into three adult brain regions the thalamus, hypothalamus and epithalamus o Thalamus and hypothalamus are major integrating centers that act as relay station for information flow in the body o Epithalamus includes the pineal gland, the source of melatonin and contain one of several clusters of capillaries that generates cerebrospinal fluid from blood o Thalamus is the main input cluster for sensory info going to the cerebrum
§ Information from the senses sorted here
§ Also receives input from the cerebrum and other part of the brain that regulate emotion and arousal o Hypothalamus is one of the most important brain regions for the control of homeostasis o Biological clock regulation by the hypothalamus
§ Specialized nerve cells regulate circadian rhythms, daily cycles of daily cycles of biological activity
§ Circadian rhythms in mammals rely on a biological clock. A molecular mechanism that directs periodic gene expression and cellular activity
§ In mammals, circadian rhythms coordinated by supra cliasmatic nucleus (SCN)
· The Cerebrum o Information processing center o Right and left cerebral hemispheres
§ Each consists of an outer covering of gray matter, the cerebral cortex; internal white matter; and groups of neurons collectively called basal nuclei that are located deep within the white matter
§ Basal nuclei are important centers for planning and learning movement sequences o Cerebral cortex is particularly extensive in mammals
§ Vitals for perception, voluntary movement, and learning
§ Divided into right and left – each half is responsible for the other half body
§ Corpus enables the right and left cerebral cortex to communicate
49.3 The cerebral cortex controls voluntary movement and cognitive functions
· Four lobes – frontal, temporal, occipital, and parietal
· Information processing in the cerebral cortex o Receives sensory input from two types of sources: dedicated sensory organs (eyes and nose) or somatic sensory receptors (hands, scalp etc.) o Most sensory information is directed via the thalamus to primary sensory areas within the brain lobes o Visual to occipital, auditory to temporal, and somatosensory information to parietal
§ Taste also to parietal but a different region
§ Smell eventually to frontal o In both to somatosensory and motor cortex, neurons are distributed in an orderly fashion according to the part of the body that generates the sensory input or receives the motor commands
· Language and speech o Broca’s area: small region in the frontal lobe in the front part of the primary motor cortex that controls muscles in the face – active in speech o Wenicke’s area – posterior portion of the temporal lobe comprehends speech
· Lateralization of cortical function o Left side of the cerebrum has a dominant role with regard to language
§ More adept at math and logical operations o Right hemisphere dominant in the recognition of faces and patterns, spatial relation, and nonverbal thinking o Lateralization: the establishment of these differences in hemisphere function in humans
· Emotions o Limbic system: a group of structure surrounding the brainstem in mammals
§ Includes amygdala, the hippocampus, and parts of the thalamus
§ Includes emotion, motivation, olfaction, behavior, and memory o Emotional experiences are often stored as memories that can be recalled by similar circumstances o Focus of emotional memory is the amygdala (temporal lobe) o Prefrontal cortex (frontal lobe) critical for emotional experience is also important in temperament and decision making
Chapter 50
50.5 The physical interaction of protein filaments is required for muscle function
· Vertebrate skeletal muscle o Consists of fibers running parallel to the length of the muscle – single cells with multiple nuclei o Muscle fiber contains a bundle of smaller myofibrils arranged longitudinally o Myofibrils are composed of thin and thick filaments o Thin filaments consist of two strands of actin and two strands of regulatory protein coiled around one another o Thick filaments are staggered arrays of myosin molecules o Skeletal muscle is called striated muscle because the regular arrangement of the filaments creates a pattern of light and dark bands o Each repeating unit is a sarcomere, the basic contractile unit of the muscle o The sliding-filament model of muscle contraction
§ Neither the thin or thick filaments change in length when the sarcomere shortens, rather the filaments slide past each other longitudinally increasing their overlap
§ Myosin head powers contraction; tail attaches to other myosin
§ Figure 50.29
§ The role of calcium and regulatory proteins
· Tropomyosin, a regulatory protein and the hoponin complex, a set of additional regulatory proteins, are bound to the actin strands of thin filament
· At rest, tropomysoin lowers the myosin-binding sites along the thin filaments – preventing interaction
· When calcium accumulates in the cytosol, it binds to the troponin complex, causing the proteins bound along the actin strands to shift position and expose the myosin-binding sites on the thin filaments
· Motor neurons cause muscle contraction by triggering release of calcium into the cytosol of muscle cells with which they form synapses
§ Nervous control of muscle tension
· Graded
· Two mechanisms by which the nervous system produces graded contractions of whole muscles o By varying the number of muscle fibers that contract o By varying the rate at which muscle fibers are stimulated
· Muscle fiber is controlled by one motor neuron, but each branched motor neuron may form synapses with many muscle fibers
· A motor unit consists of a single motor neuron and all the muscle fibers it controls
· When a motor neuron produces an action potential, all the muscle fibers in its motor unit contract as a group
· The strength at the resulting contraction depends on the number of fibers in its motor neuron controls
· The force (tension) developed by a muscle progressively increases as more and more of the motor neurons controlling the muscle are activated – recruitment
· Prolonged contraction can result in muscle fatigue due to depletion of ATP and dissipation of ion gradients required for normal electrical signaling
· A single action potential produces a twitch lasting about 100 msecs or less
· If a second potential arrives before the muscle fiber has completely released, the two add together resulting in greater tension
· When the rate is high enough that the fiber cannot relax at all between stimuli, the twitches fuse into one smooth, sustained contraction called tetanus
§ Types of skeletal muscle fibers
· Oxidative and glycolytic fibers o Rely mostly on aerobic respiration – oxidative
§ Many mitochondria, a rich blood supply and a large amount of an oxygen-storing protein called myoglobin
§ Myoglobin binds oxygen more tightly than hemoglobin
§ Makes use of a steady energy supply “dark meat” o Use glycolysis as primary source of ATP – glycolytic
§ Larger diameter and less myoglobin
§ Fatigue much more readily
§ “white meat”
· Fast twitch and slow-twitch fibers o Fast develop tension two to three times faster
§ Used for brief, rapid, powerful contraction o Slow fibers sustain long contraction
§ Ex. posture o Mainly because of the rate at which the myosin heads hydrolyze ATP
50.6 Skeletal systems transform muscle contraction into locomotion
· Types of skeletal systems o Hydrostatic skeletons
§ Consists of fluid held under pressure in a closed body compartment
§ Cnidarians, flatworms, nematodes, and annelids
§ Use muscle to change the shape of the fluid-filled compartments o Exoskeletons
§ A hard encasement deposited on an animal’s surface
§ Mollusks and arthropods o Endoskeleton
§ Hard supporting elements, such as bones, buried within the soft tissues of an animal
§ Mammalian skeleton >200 bones o Size and scale of skeletons
§ Body must support size
§ Size of leg bones directly proportion to the strain imposed by body weight
§ Posture – position of legs is more important in supporting body weight
· Types of locomotion o Active travel from place to place o Swimming
§ Friction is a large problem
§ A sleek, fusiform (torpedo-like) shape is common
§ Taking in water and spitting in bursts o Locomotion on land
§ Animal must be able to support itself, but air poses little resistance
§ Powerful muscle and strong skeletal shape
§ Maintaining balance o Flying
§ Gravity poses a major problem
§ Wings must develop enough lift to overcome gravity
§ Key is wing shape
§ Fusiform shape reduces drag
Chapter 45
45.1 Hormones and other signaling molecules bind to target receptors triggering specific response pathways
· Types of secreted signaling molecules o Hormones
§ Reach target cells via the bloodstream
§ Endocrine glands: endocrine cells grouped in ductless organs
§ Secrete hormones directly into the surrounding fluid
§ Exocrine glands have ducts that carry secreted substances onto body surfaces or into body cavities
§ Maintain homeostasis; mediate response to environmental stimuli; and regulate growth, development, and reproduction o Local regulators
§ Secreted molecules that act over short distances and reach their target cells solely by diffusion
§ Function in paracrine and autocrine signaling
§ Paracrine: target cells lie near the secreting cell
§ Autocrine: the secreting molecules act on the secreting cell itself
§ Some secreted molecules have paracrine and autocrine activity o Neurotransmitters and neurohormones
§ Neurosecretory cells: specialized neurons typically found in the brain
· Secrete molecules that diffuse from nerve cell endings into the bloodstream – neurohormones o Pheromones
§ Chemicals that are released into the external environment
§ Marking trails, defining territories, warning of predators and attracting potential mates
· Chemical classes of hormones o Polypeptides, amines, and steroids o Water soluble:
§ Polypeptide – insulin
§ Amine – epinephrine o Lipid soluble:
§ Steroid – cortisol
§ Amine – thyroxin
· Cellular receptors o Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and beyond to cell-surface signal receptors
§ Induces change in cytoplasmic molecules and sometimes alters gene transcription o Lipid-soluble hormones diffuse out across the membranes of endocrine cells and travel in the bloodstream bound to transport proteins
§ Diffuse into cells and bind to intracellular signal receptors and trigger change in gene transcription o Pathway for water-soluble hormones o Binding to signal receptors triggers events of the plasma membrane that result in a cellular response o Signal transduction: the series of changes in cellular proteins that convert the extracellular chemical signal to a specific intercellular response
§ Typically involves multiple steps o Pathway for lipid-soluble hormones
§ Usually perform the entire task of transducing a signal
§ Hormone activates the receptor which then directly triggers the cells response
§ In most cases the response to a lipid-soluble hormone is a change in gene expression
§ Steroid hormone receptors are in the cytosol
§ After binding, a hormone-receptor complex forms, which moves into the nucleus
§ Receptor portion interacts with DNA stimulating transcription of specific genes
· Multiple effects of hormones o Many hormones exhibit more than one type of response in the body o Effect can vary if target cells differ in the molecules that receive or produce the response to that hormone
§ Differing receptors or signal transduction pathways
· Signaling by local regulators o Act within seconds or milliseconds o Pathways are the same as hormones o Polypeptide local regulators: cytokines (immune responses), most growth factors (cell proliferation and differentiation) o NO is both neurotransmitter and local regulator o Prostaglandins – modified fatty acids
45.2 Negative feedback and antagonistic hormone pairs and common features of the endocrine system
· Simple hormone pathways o In response to an internal or external stimulus, endocrine cells secrete a particular hormone o Travels in bloodstream, interact with specific receptors o Signal transduction within target cells brings about a physiological response o Response leads to a reduction in the stimulus and the pathway shuts off o For many hormones, the response pathway involves negative feedback
45.3 The endocrine and nervous systems act individually and together in regulating animal physiology
· Coordination of endocrine and nervous systems in invertebrates o Reproduction and development
· Coordination of endocrine and nervous systems in vertebrates o Hypothalamus plays a central role
§ Receives information from nerve and initiates endocrine signaling appropriate to environmental conditions o Signals from hypothalamus travel to the pituitary gland
§ Anterior pituitary – hormones released by hypothalamus regulate secretion of hormone by anterior pituitary
§ Posterior pituitary – extension of the hypothalamus, stores and secretes two hormones made by the hypothalamus o Anterior pituitary hormones
§ Every anterior pituitary hormone is controlled by at least one releasing hormone – some have both a releasing and inhibiting hormone
§ Tropic hormones
· A hormone that regulates the function of endocrine cells or glands
45.4 Endocrine glands response to diverse stimuli in regulating metabolism, homeostasis, development, and behavior
· Thyroid hormone: control of metabolism and development
· Parathyroid hormone: control of blood calcium
· Adrenal hormones: response to stress
· Pancreatic hormones: regulate blood glucose o Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis o Islets of Langerhans
§ Clusters of cell in pancreas
§ Contain alpha and beta cells
§ Beta-insulin
§ Alpha-glucagon o Target tissues for insulin and glucagon
§ Insulin reduces blood glucose levels by:
· Promoting the cellular uptake of glucose – increasing glucose transporters in cell membrane (glucose enters)
· Slowing glycogen breakdown in the liver
· Promoting fat storage
· So we can use it later in between meals
§ Glycogon increases blood glucose levels by
· Stimulating conversion of glycogon to glucose in the liver
· Stimulating breakdown of fat and protein into glucose (last resort)
Chapter 44
· Not all animals osmoregulate – conformers
· Salt usually follows water o If solute can’t move, water will move o Osmotic pressure – solutes dissolved in fluid
§ Don’t care about hat, care about how many o More solutes – higher osmotic pressure
§ Osmotic pressure pulls water
§ Water moves from low to high pressure
· Osmoregulation o Regulates solute concentrations o Balances the gain and loss of water o Freshwater animals – reduce water intake, conserve solutes o Desert and marine animals – conserve water o Excretion – nitrogenous/other wastes removed
· Marine animals o Marine invertebrates – osmoconformers o Marin vertebrate and some invertebrates – osmoregulators o Marine bony fishes – hypoosmotic to environment
§ They lose water
§ They gain salt
§ Drink seawater
§ Sodium and chloride pumped out (active transport)
§ Gain water and salt ions from food
§ Osmotic water loss through gills and other parts of body surface
§ Gain of water and salt ions from drinking seawater
§ Excretion of salt ions and small amount of water in scanty urine from kidneys
· Freshwater animals o Hyperosmotic to environment o They lose salts o Excrete dilute urine o Uptake of water and some ions in food o Uptake of chloride ions by gills (sodium follows chloride) o Osmotic water gain through gills and other parts of body surfaces o Excretion of large amounts of water in dilute urine from kidneys
· Our osmoregulation is under hormonal control equal amounts of salt and water lost in waste
· Transport epithelia in osmoregulation o Animals regulate the composition of body fluid that bathes their cells o Transport epithelia o Arranged in complicated tubular network
§ Tubes containing blood
§ Tubes contain wastes – high salt concentration
§ Countercurrent exchanger o Nitrogenous waste
§ Breakdown products of proteins and nucleic acids
· Contain N
§ May be converted from toxic ammonia to less toxic compounds prior to excretion
§ Mots aquatic animals – ammonia diluted by water
§ Mammals, most amphibians, shark, some bony fishes – urea
· Mare expensive, less toxic
§ Many reptiles (including birds), insects, land snails – uric acid
· Most expensive, least toxic – can be highly concentrated
· Excretory processes o Excretory systems produce urine by refining filtrate derived from body fluid o Key function:
§ Filtration: pressure-driven, nonspecific, filtering of body fluids – blood vessels are leaky. – passive (difference in hydrostatic pressure
§ Reabsorption: reclaims valuable solutes
§ Secretion: adds toxins and solutes from body fluid to the filtrate – things that were too big to fit through in filtration
§ Excretion – removing the final filtrate o Protonephridia
§ Protonephridium – a network of dead-end tubules connected to external openings
§ Smallest branches are capped by a cellular unit call a flame bulb
§ Excrete a dilute fluid
§ Very little reabsorption or secretion – secrete though body wall o Metanephridia
§ Tubules that collect colonic fluid and produce dilute urine for excretion
§ Transport epithelium reabsorbs most solutes
§ Opening surrounded by cilia that beat, drawing fluid in o Malpighian tubules
§ Removes nitrogenous wastes from hemolymph in insects and other terrestrial and arthropods
§ No site of filtration o Kidneys
§ Principal site of water balance and salt regulation
§ Urine exits each kidney through ureter
§ Ureters drain into the urinary bladder and urine is expelled through urethra
§ About 25% of blood from heart goes to kidney
· 1600 L/day (only 5L of blood in body)
· 180L of filtrate o 1-1.5 L of urine o Nephron
§ Functional unit of the kidney, consists of a ball of capillaries (glomerulus) and a single long tubule
§ Glomerulus – leaky capillaries
§ Bowman’s capsule surrounds glomerulus and collects filtrate
§ Several nephrons empty into collecting duct o Plasma filtration
§ Hydrostatic pressure forces fluid from plasma into Bowman’s capsule
§ Filtration is nonselective – just needs to be small enough
§ Contains salts, glucose, amino acids, vitamins, nitrogenous wastes and other small molecules o Pathway of the filtrate
§ From Bowman’s capsule, the filtrate passes though:
· Proximal convoluted tubule
· Loop of Henle
· Distal convoluted tubule
· Fluid from several nephrons empties into collecting duct o Proximal convoluted tubule
§ Reabsorption of ions, water and nutrients
§ Some toxic material are secrete into filtrate (hydrogen ions and ammonia)
§ Overall filtrate volume decreases (2/3 reabsorbed)
§ All glucose and amino acids are reabsorbed o Loop of Henle
§ Descending limb – permeable to water
· Water reabsorption
· Driven by high osmolarity of the interstitial fluid
§ Ascending limb – permeable to sodium
§ Concentrated urine – save more water o Distal tubule
§ Regulates potassium and sodium chloride concentrations
§ pH regulation – controlled movement of hydrogen and bicarbonate ions o Collecting duct o Carries filtrate though the medulla o Water (and salt and urea) are lost o Antidiuretic hormone acts on collecting duct and distal tubule
§ Inserts water channels – reabsorbs it
§ Allow us to conserve water
§ From posterior pituitary