Ch. 19 & 20

Evolution II


II. Connections


1. Sympatric Speciation & Microtubules: Sympatric speciation is when a species may form within a home range of an existing species, in the absence of a physical barrier.  Reproductive isolation is key for speciation to occur.  Reproductive isolation maight happen within a few generations through polyploidy.  Polyploids originate through spontaneous induced hybridization between closely related species or doubling of the chromosome number.  Homologous chromosomes failed to separate at meiosis, when the microtubule spindle fibers did not pull apart the chromosomes, and it produced fertile polyploids.


2. Endosymbiosis & Atmospheric Gases: Endosymbiosis is a theory that states a symbiont species lives out its life inside a host species, and the interaction benefits one or both of them.  By this theory, eukaryotic cells evolved after the noncyclic pathway of photosynthesis emerged and permanently changed the atmosphere.  BY 2.1 billion years ago, certain prokaryotic cells had adapted to the concentration of some atmospheric gases, such as oxygen, and were already engaged in aerobic respiration.  The ancestors of eukaryotic cells preyed upon some aerobic bacteria and were parasitized by others.  At that time, endsymbiotic interections began.


3. Adaptive Radiation & Character Displacement: An adaptive radiation is a urst of divergences from a single lineage that leads to many new species.  It requires adaptive zones, or a set of niches that come to be filled by a group of usually related species.  Either the lineage enters a vacant adaptive zone or it competes with the resident species will enough to displace them.  Sometimes as a result of this competition, a species will develop morphological differences  to reduce the competition.  This is known as character displacement.


4. Proto-cells & Uracil: Proto-cells were transitional forms between simple organic compounds and the first living cells.  These were no more than membrane-bound sacs that contained systems of enzymes and other agents of metabolism, and that were self-replicating. It all started with spontaneous formations of lipids, carbohydrates, amino acids, proteins, and nucleotides under abiotic conditions.  Then, the formation of lipid spheres and protein RNA systems appeared.  Because the one difference between RNA and DNA is a single -functional group of uracil, the RNA thus evolved into DNA, using RNA to create enzymes and proteins.  Proto-cells emerged and the living cells.


III. Few Essentials  


1. Prezygotic and Postzygotic Reproductive Isolation Mechanisms

• Mechanical Isolation: individuals can't make or pollinate because of physical incompatibilities
• Temporal Isolation: Individuals of different species reproduce at different times
• Behavioral isolation: Individuals of different species ignore or don't get the required cues for sex
• Ecological Isolation: Individuals of a different species live in different places and never meet up
• Gamete Mortality: Gametes of different species are incompatible, so no fertilization
• Hybrid Inviability: Hybrid embryos die early or the new individuals die before they can reproduce
• Hybrid Sterility: Hybrid individuals can't make functional gametes

2. The gradual model of speciation holds that species originate by slight morphological changes over time spans.  The model fits with many fossil sequences.  The sequence reflects gradual morphological change.  The punctuation model of speciation offers a different explanation for patterns of speciation.  Most morphological changes are said to evolve in a relatively brief geologic period, within the tens to hundreds of thousands of years when populations are starting to diverge.  Directional selection, genetic drift, the founder effect, bottlenecks, or some combination of them favor rapid speciation.

3. Stanley Miller was the first to test the hypothesis that the simple compounds that now serve as the building blocks of life can form by chemical processes.  He put water, methane, hydrogen, and ammonia in a reaction chamber.  He kept circulating the mixture and zapping it with sparks to stimulate lightning.  In less than a week, amino acids and other small organic compounds had formed in the chemical brew.

4. Evidence to support emdosymbiosis

• rod-shaped bacterium infected culture of amoeba discoides
• cells grew slowly and became vulnerable to starving to death
• five years later, infected amoebas were harboring many bacterial cells, yet all thriving
• infection-free cells got a nucles from an infected cell
• more than 90% survived when a few bacteria were included with transplant
• infected amoebas had lost their ability to synthesize an essential enzyme
• depended on bacterium to make it for them 
• mitochondria resemble bacteria in size and structure
• chloroplasts resemble cyanobacteria

5. on separate sheet of paper

Ch. 17 & 18

II. Connections


1. Prophase 1 & Allele Frequency: Allele frequency is the abundance of one allele relative to others at a gene locus among individuals of a population.  Alleles are different molecular forms of a gene at a given locus.  Alleles are a cause of genetic variation among individuals of a population.  The frequency of an allele in a population is determined by how often the gene is inherited.  An example of when an allele arises is during crossing over in meiosis 1.  When tetrads start forming in prophase 1, some alleles can switch between chromosomes causing an individual to inherit a different gene for a trait.


2. Analogous Structures & Natural Selection: Analogous structures are dissimilar body parts that have become similar in structure, function, or both in lineages that are not closely related but were subjected to similar pressures.  They are different responses of different body parts to similar challenges.  These similar challenges are results of environment changes that hindered the populations' survival.  The population needed to develop these changes in their body parts so that they can survive and reproduce.  These populations' experienced natural selection. 


3. Gene Pool & Bottleneck: A bottleneck is a drastic reduction in population size brought about by severe pressure, such as contagious disease, habitat loss, or hunting.  Even if a moderate number of individuals survive a bottleneck, a genetic drift will occur, changing the allele frequencies at random.  With different allele frequencies, the population will have a different gene pool because now their pool of genetic resources is altered.


4. Balanced Polymorphism & Search Image: Balanced polymorphism is an outcome of natural selection against homozygotes, so that two or more alleles for a trait are bring maintained in the population.  A search image is when a predator develops a knowledge of their prey type, including what the prey looks like, what it smells like, etc.  Both of these terms refer to ways that the environment limits the weak traits in a population and accentuates the strong traits in a population.


III. Few Essentials


1. Natural Selection

1. Natural populations have an inherent reproductive capacity to increase in size over time.
2. No population can indefinitely grow in size, because it individuals will run out of food, living space, and other resources.
3. Sooner or later, individuals will end up competing for dwindling resources.
4. Individuals share a pool of heritable information about traits, encoded in genes.
5. Variations in traits start with alleles, slightly different molecular forms of genes that arise through mutations.
6. Some forms of traits prove better than others at helping an individual compete for resources survive, and reproduce.  In time, alleles for adaptive forms become more frequent relative to others alleles in the population.  They lead to increased fitness- an increase in adaptation to the environment as measured by the genetic contribution to future generations.
7. Natural selection is the outcome of differences in reproduction among individuals of a population that vary in shared traits.  Environmental agents of selection act on the range of variation, and the population may evolve as a result.

2. Most Important Events

1. 4,600-3,800 million years ago: Chemical, molecular evolution leads to origin of life (from proto-cells to anaerobic prokaryotic cells)
2. 2,500-544 million of years ago: Oxygen accumulates in atmosphere; origin of anerobic metabolism; origin of eukaryotic cells.
3. 410-360 million of years ago: Origin of vascular plants
4. 99-65 million of years ago: Origin of angiosperms
5. 65 million years ago: Asteroid impact; mass extinction of all dinosaurs and many marine organisms
6. 1.8 million years ago-present: Modern humans evolve; most recent extinction crisis is under way

3. An individual organism does not evolve, or develop a mutation in their DNA causing them to have certain traits, on their own.  An individual's genes are determined during meiosis, where genetic variation occurs through mutations.  These mutations in individuals are either favored or hindered by the environment the individuals in the population are living in.  If the individuals have a favorable trait, those individuals will survive and reproduce, passing the genes of the favorable trait onto the their offspring.  If the individuals have the not-favorable trait, they will not survive, thus eliminating that trait.  A population of individuals can evolve from having one trait to another due to the environment favoring one trait over another.

4. Phenotypic variation most often comes from natural selection.  In natural selection, the environment decides specific genes that are the most favorable in a particular situation, and those organisms are the ones that are able to survive. The phenotypes that are not favorable in that particular environment die off and are eliminated from that population. Phenotypic variation also occurs in basic genetic variation. 

5. Hardy-Weinberg Principle 

• equation: p + q = 1.0 
• The dominant allele=A 
• The recessive=a
• Their frequencies=p and q 
• freq(A) = p; freq(a) = q; p + q = 1. 
• If the population is in equilibrium= 
• freq(AA) = p² 
• freq(aa) = q² 
• freq(Aa) = 2pq  
• 5 conditions: 
• there must be no mutation
• the population is infinitely large
• the population is isolated from all other populations of the species
• mating is random
• all individuals survive and produce the same number of offspring.

Ch. 15, 16 & 21

Molecular Biology II


II. Connections


1. Lysogenic & Binary Fission: When viruses attack host cells, the cells can divide and multiply in two different pathways.  A lysogenic pathway when a latent period extends the duration of the cycle because the virus does not kill the host right away.  Instead, a viral enzyme cleaves the host's chromosomal DNA, and integrates the viral genes into its base sequence.  This happens before prokaryotic fission, which is the cell reproduction mechanism for prokaryotic cells only.  Prokayotic fission can sometimes be confused with binary fission, but binary fission refers to the asexual reproductive mode among some animals where the body splits spontaneously, then both parts grow what is missing.


2. Conjugation & Bacterial Transformation: Conjugation is a mode of gene transfer that is possible when one of the cells has an F, or fertility, plasmid.  A plasmid is a small, self-replicating circle of DNA with a few genes.  Plasmids are only found in prokaryotic cells.  Bacteria are examples of prokaryotic cells.  Conjuction involves the transferring of replicated DNA from one prokaryotic cell to another.  The recipient cell receiving the replicated DNA can sometimes receive transferred DNA that has been transformed into infectious DNA.  This transformation is bacterial transformation.


3. Plasmid & Retrovirus: Plasmid is a small, self-replicating circle of DNA with a few genes.  Plasmids are used during cell reproduction in prokaryotic cells.  A virus cannnot reproduce on its own, which means it can only reproduce when its genetic material enters the host cell and becomes replicated.  Common animal viruses, such as retroviruses, have double or single stranded DNA or RNA that has been replicated with the virus gene in it.  HIV is a retrovirus, that leads to AIDS.  A virus that weakens the immune system by destroying white blood cells can cause the inability to fight infections such as HIV that may not otherwise be life threatening.


4. Operator & Hydrolysis: An operator is a binding site for a type of regulatory protein know as repressor, which stops transcription.  Operators can be found at the end of E. coli DNA, after three genes that code for lactose-metabolizing enzymes.  E. coli likes to consume glucose, but can settle for lactose when glucose is not present.  Lactose is a carbohydrate, and can be broken down with hydrolysis.  Hydrolysis is a cleavage reaction that uses enzymes to split molecules at specific groups.


5. Okazaki Fragments & Restriction Enzymes: Restriction enzymes cut double-stranded DNA at a specific base sequence between for and eight base pairs in length.  It makes staggered cuts that produce a sticky end on the DNA fragments.  The tail can base pair with a tail from another fragment cut by the same enzyme.  Restriction enzymes can cut base pairs form Okazaki fragments, which are the fragments of new DNA copied along with the parent strands.  Just like for the Okazaki fragments, DNA ligases seal the nicks of the base pairing between the cut fragments.


III. Few Essentials 


1. Promoters are short stretches of base sequences in DNA where regulatory proteins gather and control transcription of specific genes, often in response to hormonal signal.  Enhancers are binding sites where such proteins increase transcription rates.  Before transcription, acetylation can make histones loosen their grip so that the polymerases can access genes.  Some gene sequences can be rearranged or multiplied.  During transcript processing, exons for genes can be put together in different combinations in different types of cells.  Proteins attached to a nuclear envelope can move the transcript to the region where its supposed to be translated or stored.  Unfertilized eggs that stockpile maternal messages keep them silent with the help of controls called Y-box.  During translation, how long an mRNA lasts depends on the proteins that are attached to it and the length of its poly-A tail.  If translation is blocked, mRNA cannot attach to a ribosome when proteins bind to it, and initiation factors can be inactivated.  After translation, a new protein may be inactivated or activated.  Control of enzymes and other proteins influences many cell activities. 


2. look on notecard


3. DNA fragments can be separated by gel electrophoresis, a technique that sorts fragments as they move through a semisolid slab of polyacrylamide in response to an electric field.  DNA fingerprinting reveals differences in the tandem repeats among individuals.  Fragments are cut; the sizes of the fragments are unique to an individual.  The fragments can be subjected to gel electrophoresis to form distinct bands according to their length.  The banding patter of the fragments is the DNA fingerprint of the individual.


4. A prokaryotic cell nearly doubles in size, then divides in two.  Each daughter cell inherits a single bacterial chromosome, a circularized, double-stranded DNA molecule that has a few proteins associated with it.  This is different from  a eukaryotic cells genome because it is smaller, only having one chromosome where eukaryotic cells have 23 chromosomes.  DNA replication is simpler in prokaryotic cells.  After the DNA replicates, the parent molecule and the cope are both anchored to the plasma membrane at adjacent sites while the cell is growing.  The growing cell moves the molecules of DNA apart.  The cytoplasm splits in two, and the result is two genetically identical daughter cells.


5. In the lytic cycle, a virus particle injects genetic material into a suitable host cell after binding to its wall.  The viral DNA directs host cell to make viral proteins and replicate viral DNA.  The viral proteins are assembled into coats around viral DNA.  The coats get tail fibers.  Lysis of the host cell is induced and infectious particles escape.  The lysogenic cycle is different because the virus does not kill the host right away.  Instead, a viral enzyme cleaves the host's chromosomal DNA, then integrates the viral genes into its base sequence.  The viral DNA is excised from the chromosome.

Ch. 13 & 14

Molecular Biology 1


II. Connections


1. 5' & Electronegativity: The 5' carbon on a nucleotide is the highest carbon on the sugar component.  This carbon attaches to a phosphate group on the end.  A free nucleotide has a tail of three phosphate groups dangling from the 5' carbon.  A DNA polymerase detaches two of the phosphates.  The last phosphate is driven towards the -OH group dangling off from the 3' carbon, the carbon on the bottom of the sugar component, of another nucleotide.  Since the electronegativities of the phosphate group and the -OH are different, their energies connect and form a bond, linking two nucleotides together.


2. Start Codon & Incomplete Dominance: A codon is a base triplet of three nucleotides in mRNA.  There are 64 different codons, making up the genetic code for an organism.  One of these codons is called a start codon, that specifically codes as a start signal for translating three bases at a time.  The typical start codon is AUG, but one change in the nucleotide can alter the purpose of the codon.  This variation of codons cause genetic mutations in the codes for proteins.  Some of the mutations cause genetic variations of traits, including incomplete dominance, when a heterozygous gene codes for a new trait than a homozygous gene.


3. Semiconservative & Barr Body: Semiconservative replication is a mechanism by which a DNA molecule is duplicated.  For this to occur, the double helix unzips along its length, exposing the bases. The bases are used as a template, and a new strand is assembled.  The two stands are wound back up into a double helix.  Semiconservative replication can only occur if the chromosome decondenses into its chromatin form, so that the strands of DMA can be read and copied.  This form of replication cannot occur then in a Barr Body, a chromosome that does not decondense into its chromatin form, but stays condensed.


4. RNA Polymerase & Nucleolus: RNA polymerase is an enzyme that adds ribonucleotides one at a time to the end of a growing strand of RNA.  The enzyme is primarily used in transcription of RNA, resulting in mRNA.  To ensure the mRNA has no mistakes on it, the transcripts are modified of their mistakes before leaving the nucleolus, where the transcription is occuring.


5. DNA Polymerase & Glycosidic Linkage: DNA polymerase is an enzyme that catalyze the formation of two brand-new strands of DNA from free nucleotides.  These enzymes also catalyze the hydrogen bonding of each  new strand to the unwound region of one of the two parent DNA strands.  The nitrogen bases connect to each other based on pairing, A with T and C with G, by a glycosidic linkage.


6. Helicase & G2 Karyotype: DNA replication occurs during interphase in a cell's life cycle. Interphase starts with the G1 stage, when the DNA is unwinding and preparing to be replicated.  S phase is the phase of replication.  G2 stage is the when the replicated DNA is checked for mistakes in the replication.  To start this replication process, the DNA needs to be unwound into its chromatin form.  An enzyme called helicase unzips the DNA and breaks the hydrogen bonds between the nucleotides.  Helicases are primarily found in the S phase of a cell's life because that is when the replication occurs.  In G2, the DNA is already replicated, which is why in the karyotype, there will be twice as much DNA as before.


III. Few Essentials


1. For DNA replication, the DNA polymerases can only assemble new strands in a 5'-3' direction.  DNA in a double helix are formed by two strands of nucleotides that are anti-parallel, meaning they line up in different directions.  One strand in a 5'-3' direction is opposite of a strand in a 3'-5' direction.  Since DNA polymerases can only assemble in one direction, the nucleotides are assembled in short stretches.  DNA ligases are in charge of sealing the short stretches together into a continuous strand, so that it is complementary with the 3'-5' direction strand.


2. 3 structural differences between RNA and DNA:

1. RNA has 3 classes of molecules for protein synthesis, while DNA only has one.  mRNA is the outcome of of transcription, where the protein-building codes are carried.  rRNA becomes a component of ribosomes.  tRNA delivers amino acids one by one to ribosomes in the orders specified by mRNA.
2. RNA molecules have four kinda of ribonucleotides, like DNA.  Adenine, guanine, and cytosine are the same.  But, instead of thymine, RNA has uracil, a new nitrogen base. Uracil can bind with adenine.
3. Transcription results in one free RNA strand, not a hydrogen-bonded double helix like DNA. 

3. RNA has 3 classes of molecules for protein synthesis, while DNA only has one.  mRNA is the outcome of of transcription, where the protein-building codes are carried.  rRNA becomes a component of ribosomes.  tRNA delivers amino acids one by one to ribosomes in the orders specified by mRNA.

4. Protein Synthesis

    a. Transcription

        - 1st step in protein synthesis

        - sequence of nucleotide bases is exposed in an unwound region of DNA strand

        - sequence: template strand RNA is assembled from

        - RNA uses adenine, cytosine, guanine, and uracil

        - RNA polymerase adds nucleotides one at a time to end of growing strand of RNA

        - promoter: start signal that RNA polymerase binds to so it start adding nucleotides

        - when RNA polymerase reaches sequence that marks "the end": it stops

    b. RNA Splicing

        - occurs in the nucleus before being released

        - pre-mRNA is modified with a cap at the beginning and a poly-A tail at the end

        - all introns, noncoding sequences, are snipped from pre-mRNA strand

        - exons, protein-coding base sequences, are all kept

        - can be combined together to form a mature mRNA

    c. Translation

        - initiation stage: small ribosomal subunit and an initiator tRNA arrive at an mRNA transcript's start codon

        - large ribosomal subunit binds to them

        - anticodon and codon meet up here

        - elongation stage: tRNAs deliver amino acids to a ribosome in the order said by the sequence of mRNA codons

        - polypeptide chain lengthens as peptide bonds form between the amino acids

        - termination stage: stop codon triggers events that cause polypeptide chain and the mRNA to detach from ribosome   

Ch. 11 & 12

Inheritance


II. Connections


a. Gene Locus & Disulfide Bridge: A disulfide bridge is a bond between sulfur atoms in neighboring cysteine amino acids.  This bond occurs in protein folding to create different proteins.  DNA in the nucleus code for the making of proteins.  DNA strands are very long and can code for various genes.  A gene locus is the specific location of certain genes. 


b. Non-disjunction & 9-triplet Pattern: Non-disjunction is the failure of sister chromatids or homologous chromosomes to separate in meiosis or mitosis.  This results in daughter cells having too many or too few chromosomes.  The microtubules that form the spindle fibers that attach to the kinetochores of the chromosomes are made in a 9-triplet pattern.


c. Autosome & Steroid: Autosomes are the other chromosomes in body cells that are the same in both sexes.  This is similar to the steroids all people have in common, such as cholesterol.  Steroids, such as estrogen and testosterone, that are gender specific are similar to the sex chromosomes are specific chromosomes that determine gender.


d. Polygenic & Glycocalyx: Polygenic inheritance is the inheritance of multiple genes that affect the same trait.  This helps influence genetic variations in DNA, that leads to the evolution of cells, similar to the evolution of eukaryotic cells.  Because eukaryotic cells are more developed than prokaryotic cells, they do not have a glycocalyx, which is a ,eshlike capsul around the prokaryotic cell wall.      


III. Few Essentials


a. Mendel's law of segregation states that genes of homologous chromosomes are separated from each other during meiosis, so that one version of each ends up in different gametes.  Mendel's law of independent assortment states that genes are sorted individually from other genes during meiosis.  Both laws give rise to genetic variations of traits.  The law of segregation during meiosis, when the chromosomes are being pulled apart to opposite poles of the cell so that they end up in different gametes.  The law of independent assortment occurs after meiosis, when the chromosomes have already been sorted for distribution, and occur independently from other types of genes.  

Ch. 10

Cell Reproduction


II. Connections


1. Homologous chromosome & Duplicated chromosome


At the beginning of a cell's life cycle, a cell has 23 pairs of homologous chromosomes.  A homologous chromosome is one chromosome in a pair that have the same genes, but one version given from the mom and the other version given from the dad.  A duplicated chromosome is a pair of chromosomes that are completely identical to each other.  A cell has duplicated chromosomes after S-phase, when all the DNA in a cell is copied.  


2. Kinetochore & Microtubule Organizing Center (MTOC)


In an animal cell, the MTOC is a centrosome.  This is the place where microtubule spindle fibers develop and grow.  They connect to the kinetochores attached to the centromeres of the chromosomes during the prophase stage.  The spindle fibers shorten starting from the centrosomes, pulling the chromosomes apart. 


3. Haploid & Somatic


A somatic cell is any cell in the body that is not a germ cell.  The only cells in the body that are haploid are gametes, or reproductive cells.  Haploid cells only have half of the DNA a normal cell, or diploid cell, has.  This is because the reproductive cells from the mom and from the dad will come together during reproduction and fertilize a zygote, a diploid cell.


4. Nucleosome & Dehydration Reaction


A nucleosome is a small stretch of DNA wound twice around a spool of proteins called a histone.  Proteins are made up of amino acids linked together by peptide bonds.  They form in a dehydration reaction because the OH molecule on the carboxyl group and the H atom in the amino group bond together forming water, which is lost during this processs


III. Few Essentials


1. Chromosomes during Meiosis


A. Prophase 1: chromosomes are in thread-like form; homologous pairs are together; swap segments 
B. Metaphase 1: homologous chromosomes line up next to each other along the midway line of the cell
C. Anaphase 1: spindle fibers pull apart homologous chromosomes
D. Telophase 1: homologous chromosomes are now in different ends of the cell; all chromosomes are still duplicated
E. Prophase 2: no new DNA replication has occurred; spindle fibers attach to each chromosome
F. Metaphase 2: all chromosomes line up along the midway of the cell
G. Anaphase 2: attachment between sister chromatids of each chromosome breaks; one of each type of chromosome is moving towards the ends of the cell
H. Telophase 2: 4 cells result with a haploid number of chromosomes


2. Outline 10.4


I. Crossing Over in Prophase 1
   A. All chromosomes in a germ cell condense in the same way
       1. drawn close to its homologue
       2. chromatids of 1 become stitched to chromatids of another
           a. favors crossing over
       3. 2 "nonsister" chromatids swap genes
   B. Genes come in different forms- alleles
       1. crossing over: chance to swap slightly different versions of information on gene products
       2. crossing over leads to recombinations among genes of homologous chromosomes, and eventually to variation in traits among offspring
II. Metaphase 1 Alignments
    A. major shufflings of chromosomes: transition from prophase 1 to metaphase 1
       1. no particular pattern to the metaphase 1 positions of chromosomes
       2. either homologous partner can end up at either spindle pole
       3. 8,388,608 possible combinations of chromosomes


3. Similarities & Differences


Similarities

• starting cell is a diploid cell
• all chromosomes are duplicated from interphase
• both use spindles to sort and move chromosomes

Differences

• mitosis ends with 2 diploid cells; meiosis ends with 4 haploid cells
• mitosis happens in any part of the body; meiosis only occurs in the reproductive organs
• mitosis: basis of asexual reproduction and growth and tissue repair; meiosis: required step before the formation of gametes or sexual spores

Ch. 45 & 47 & 48

Ecology II


II. Connections


a. Carrying Capacity & Biotic Potential


The biotic potential, which is the maximum rate of increase per individual for nay population that is growing under ideal conditions, will eventually lead to the carry capacity of a population.  The carry capacity is the maximum number of individuals of a population that a given environment can sustain indefinitely.  If the biotic potential reaches 100%, it will fulfill the entire carrying capacity.


b. Biological Magnification & Trophic Level


Biological magnification occurs in trophic levels.  The concentration of a slowly degradable or non-degradable substance in body tissues increases as it passes along food chains.  If a primary producer has a concentration of x1 pollution, that number will consistently increase as it is eaten by a primary consumer, increasing to x2.  This increase remains constant as secondary and tertiary consumers eat their prey in the lower trophic level.


c. Detritivores & Autotrophs


Detritivores are organisms that obtain their energy by consuming dead plants and animals.  Autotrophs are primary producers who convert the sunlights energy into chemical energy.  The autotrophs are the first trophic level because they are the source of all chemical energy for other organisms to consume.  Detritivores are the last trophic level because they consume all the energy that was consumed by the other trophic levels.


d. Mitochondria & Greenhouse Gases


Wavelengths in rays from the sun warm the surface of the Earth.  The surface radiates heat, infrared wavelengths, to the atmosphere.  Greenhouse gases and water vapor absorb some infrared energy and radiate a portion of it toward back toward Earth.  Increased concentrations of greenhouse gases, for example, the increases concentration of carbon dioxide in the winter when photosynthesis rates decrease but aerobic respiration in the mitochondria still occurs, trap more heat near Earth's surface causing the temperature to rise.


III. Few Essentials


a. 45.4 Outline


I. Limits on the Growth of Populations
   A. Density-Dependent Limiting Factors
       1. environmental circumstances keep population from fulfilling biotic potential
       2. limiting factors affect population growth
   B. Carry Capacity and Logistic Growth
       1. sustainable supply of resources will determine population growth
       2. pattern of logistic growth can show the effects of carrying capacity
       3. when overcrowding occurs: density-dependent controls
   C. Density-Independent Limiting Factors
       1. can cause more deaths or fewer births
       2. regardless of population density


b. 3 Survivorship Curves


Type 1: reflect high survivorship until fairly later in life, then a large increase in deaths.
     ie: large mammals, such as elephants, have one or a few large-bodied offspring at a time, then engage in an extended parental care


Type 2: reflect a fairly constant death rate at all ages
     ie: organisms just as likely to be killed of die of disease at any age, such as lizards


Type 3: reflect a death rate that is highest early in life
     ie: species that produce many small offspring and do little parenting, such as sea stars


c. Age Structure Diagrams


1. A population undergoing negative growth: The base of the diagram representing pre-reproductive years is much smaller than the top of the diagram representing post-reproductive years.  The maximum population growth is at the early post-reproductive years, around age 45.


2. A population with nearly no growth: The base of the diagram stays almost the same width all the way up towards the start of the post-reproductive years.  It starts to decline after that showing a consistent death rate in those ages.


3. A population growing rapidly: The base of the diagram is way more than twice the size of the rest of the diagram.  It consistently decreases its width towards the top, resembling almost nothing at the highest ages.


4. A population growing slowly: It shows a steady decrease in width going from the base of the diagram to the top.  There is a very small difference between the number of pre-reproductive year people than post-reproductive year people.


d. The Nitrogen Cycle


Nitrogen in abundant in the atmosphere in its gaseous form of N2.  This form of nitrogen is useless to plants and animals, so it needs to be converted to a solid form.  Nitrogen fixing bacteria convert the N2 into NH4.  Nitrifying bacteria convert the NH4 to NO2, nitrites, and NO3, nitrates.  Plants can then absorb the NO3 and pass it to animals who consume the plants.  After the animals and plants die, detritivores break down their matter and release the nitrogen back to the soil through ammonification.