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User:Drewbie/Macromolecules/Origins

Abiogenesis
In the physical sciences, abiogenesis, the question of the origin of life, is the study of how life on Earth might have evolved from non-life sometime between 3.9 and 3.5 billion years ago. This topic also includes theories and ideas regarding possible extra-planetary or extra-terrestrial origin of life hypotheses, thought to have possibly occurred over the last 13.7 billion years in the evolution of the known universe since the big bang.

Origin of life studies is a limited field of research despite its profound impact on biology and human understanding of the natural world. Progress in this field is generally slow and sporadic, though it still draws the attention of many due to the eminence of the question being investigated. A few facts give insight into the conditions in which life may have emerged, but the mechanisms by which non-life became life are still elusive.

For the observed evolution of life on earth, see the timeline of life.

History of the concept
In a letter to Joseph Dalton Hooker of February 1 1871, Charles Darwin made the suggestion that the original spark of life may have begun in a "warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. present, [so] that a protein compound was chemically formed ready to undergo still more complex changes". He went on to explain that "at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed." In other words, the presence of life itself prevents the spontaneous generation of simple organic compounds from occurring on Earth today – a circumstance which makes the search for the origin of life dependent on the sterile conditions of the laboratory.

An experimental approach to the question was beyond the scope of laboratory science in Darwin's day, and no real progress was made until 1936 when Aleksandr Ivanovich Oparin demonstrated that it was the presence of atmospheric oxygen and other more sophisticated life-forms that prevented the chain of events that would lead to the evolution of life. In his The Origin of Life on Earth, Oparin argued that a "primeval soup" of organic molecules could be created in an oxygen-less atmosphere through the action of sunlight. These would combine in ever-more complex fashion until they dissolved into a coacervate droplet. These droplets would "grow" by fusion with other droplets, and "reproduce" through fission into daughter droplets, and so have a primitive metabolism in which those factors which promote "cell integrity" survive, those that don't become extinct. All modern theories of the origin of life take Oparin's ideas as a starting point.

Current models
There is no truly "standard" model of the origin of life. But most currently accepted models build in one way or another upon a number of discoveries about the origin of molecular and cellular components for life, which are listed in a rough order of postulated emergence:

 * 1) Plausible pre-biotic conditions result in the creation of certain basic small molecules (monomers) of life, such as amino acids. This was demonstrated in the Miller-Urey experiment by Stanley L. Miller and Harold C. Urey in 1953.
 * 2) Phospholipids (of an appropriate length) can spontaneously form lipid bilayers, a basic component of the cell membrane.
 * 3) The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes (RNA world hypothesis).
 * 4) Selection pressures for catalytic efficiency and diversity result in ribozymes which catalyse peptidyl transfer (hence formation of small proteins), since oligopeptides complex with RNA to form better catalysts. Thus the first ribosome is born, and protein synthesis becomes more prevalent.
 * 5) Proteins outcompete ribozymes in catalytic ability, and therefore become the dominant biopolymer. Nucleic acids are restricted to predominantly genomic use.

The origin of the basic biomolecules, while not settled, is less controversial than the significance and order of steps 2 and 3. The basic inorganic chemicals from which life was thought to have formed are methane (CH4), ammonia (NH3), water (H2O), hydrogen sulfide (H2S), carbon dioxide (CO2), and phosphate (PO43-).

As of 2006, no one has yet synthesized a "protocell" using basic components which would have the necessary properties of life (the so-called "bottom-up-approach"). Without such a proof-of-principle, explanations have tended to be short on specifics. However, some researchers are working in this field, notably Steen Rasmussen at Los Alamos National Laboratory and Jack Szostak at Harvard University. Others have argued that a "top-down approach" is more feasible. One such approach, attempted by Craig Venter and others at The Institute for Genomic Research, involves engineering existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life were reached. The biologist John Desmond Bernal, coined the term Biopoesis for this process, and suggested that there were a number of clearly defined "stages" that could be recognised in explaining the origin of life.

Stage 1: The origin of biological monomers Stage 2: The origin of biological polymers Stage 3: The evolution from molecules to cell

Bernal suggested that Darwinian evolution may have commenced early, some time between Stage 1 and 2.

Miller's experiments
Experiments were performed by Stanley Miller starting in 1953, under simulated conditions resembling those then thought to have existed shortly after Earth first accreted from the primordial solar nebula. The experiments are called the "Miller experiments". The original experiment in 1953 was done by Miller as a graduate student and his professor Harold Urey. The experiment used a highly reduced mixture of gases (methane, ammonia and hydrogen). However, the composition of the prebiotic atmosphere of Earth is currently controversial. Other less reducing gases produce a lower yield and variety. It was once thought that appreciable amounts of molecular oxygen were present in the prebiotic atmosphere, which would have essentially prevented the formation of organic molecules; however, the current scientific consensus is that such was not the case.

The experiment showed that some of the basic organic monomers (such as amino acids) that form the polymeric building blocks of modern life can be formed spontaneously. Simple organic molecules are of course a long way from a fully functional self-replicating life form. But in an environment with no pre-existing life these molecules may have accumulated and provided a rich environment for chemical evolution ("soup theory"). On the other hand, the spontaneous formation of complex polymers from abiotically generated monomers under these conditions is not at all a straightforward process. Besides the necessary basic organic monomers, also compounds that would have prohibited the formation of polymers were formed in high concentration during the experiments.

Other sources of complex molecules have been postulated, including sources of extra-terrestrial stellar or interstellar origin. For example, from spectral analyses, organic molecules are known to be present in comets and meteorites. In 2004, a team detected traces of polycyclic aromatic hydrocarbons (PAH's) in a nebula, the most complex molecule, to that date, found in space. The use of PAH's has also been proposed as a precursor to the RNA world in the PAH world hypothesis.

It can be argued that the most crucial challenge unanswered by this theory is how the relatively simple organic building blocks polymerise and form more complex structures, interacting in consistent ways to form a protocell. For example, in an aqueous environment hydrolysis of oligomers/polymers into their constituent monomers would be favored over the condensation of individual monomers into polymers. Also, the Miller experiment produces many substances that would undergo cross-reactions with the amino acids or terminate the peptide chain.

Eigen's hypothesis
In the early 1970s a major attack on the problem of the origin of life was organised by a team of scientists gathered around Manfred Eigen of the Max Planck Institute. They tried to examine the transient stages between the molecular chaos in a prebiotic soup and the transient stages of a self replicating hypercycle, between the molecular chaos in a prebiotic soup and simple macromolecular self-reproducing systems.

In a hypercycle, the information storing system (possibly RNA) produces an enzyme, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery that RNA, in certain circumstances forms itself into ribozymes, a form of RNA enzyme.

Wächtershäuser's hypothesis
Another possible answer to this polymerization conundrum was provided in 1980s by Günter Wächtershäuser, in his iron-sulfur world theory. In this theory, he postulated the evolution of (bio)chemical pathways as fundamentals of the evolution of life. Moreover, he presented a consistent system of tracing today's biochemistry back to ancestral reactions that provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds.

In contrast to the classical Miller experiments, which depend on external sources of energy (such as simulated lightning or UV irradiation), "Wächtershäuser systems" come with a built-in source of energy, sulfides of iron and other minerals (e.g. pyrite). The energy released from redox reactions of these metal sulfides is not only available for the synthesis of organic molecules, but also for the formation of oligomers and polymers. It is therefore hypothesized that such systems may be able to evolve into autocatalytic sets of self-replicating, metabolically active entities that would predate the life forms known today.

The experiment as performed, produced a relatively small yield of dipeptides (0.4% to 12.4%) and a smaller yield of tripeptides (0.003%) and the authors note that: "under these same conditions dipeptides hydrolysed rapidly." Another criticism of the result is that the experiment did not include any organomolecules that would most likely cross-react or chain-terminate (Huber and Wächtershäuser, 1998).

The latest modification of the iron-sulfur-hypothesis was provided by William Martin and Michael Russell in 2002. According to their scenario, the first cellular life forms may have evolved inside so-called black smokers at seafloor spreading zones in the deep sea. These structures consist of microscale caverns that are coated by thin membraneous metal sulfide walls. Therefore, these structures would solve several critical points of the "pure" Wächtershäuser systems at once:

 * 1) The micro-caverns provide a means of concentrating newly synthesised molecules, thereby increasing the chance of forming oligomers;
 * 2) The steep temperature gradients inside a black smoker allow for establishing "optimum zones" of partial reactions in different regions of the black smoker (e.g. monomer synthesis in the hotter, oligomerisation in the colder parts);
 * 3) The flow of hydrothermal water through the structure provides a constant source of building blocks and energy (freshly precipitated metal sulfides);
 * 4) The model allows for a succession of different steps of cellular evolution (prebiotic chemistry, monomer and oligomer synthesis, peptide and protein synthesis, RNA world, ribonucleoprotein assembly and DNA world) in a single structure, facilitating exchange between all developmental stages;
 * 5) Synthesis of lipids as a means of "closing" the cells against the environment is not necessary, until basically all cellular functions are developed.

This model locates the "last universal common ancestor" (LUCA) inside a black smoker, rather than assuming the existence of a free-living form of LUCA. The last evolutionary step would be the synthesis of a lipid membrane that finally allows the organisms to leave the microcavern system of the black smokers and start their independent lives. This postulated late acquisition of lipids is consistent with the presence of completely different types of membrane lipids in archaebacteria and eubacteria (plus eukaryotes) with highly similar cellular physiology of all life forms in most other aspects.

Another unsolved issue in chemical evolution is the origin of homochirality, i.e. all monomers having the same "handedness" (amino acids being left handed, and nucleic acid sugars being right handed). Homochirality is essential for the formation of functional ribozymes (and probably proteins too). The origin of homochirality might simply be explained by an initial asymmetry by chance followed by common descent. Work performed in 2003 by scientists at Purdue identified the amino acid serine as being a probable root cause of organic molecules' homochirality. Serine forms particularly strong bonds with amino acids of the same chirality, resulting in a cluster of eight molecules that must be all right-handed or left-handed. This property stands in contrast with other amino acids which are able to form weak bonds with amino acids of opposite chirality. Although the mystery of why left-handed serine became dominant is still unsolved, this result suggests an answer to the question of chiral transmission: how organic molecules of one chirality maintain dominance once asymmetry is established.

From organic molecules to protocells
The question "How do simple organic molecules form a protocell?" is largely unanswered but there are many hypotheses. Some of these postulate the early appearance of nucleic acids ("genes-first") whereas others postulate the evolution of biochemical reactions and pathways first ("metabolism-first"). Recently, trends are emerging to create hybrid models that combine aspects of both.

"Genes first" models: the RNA world
The RNA world hypothesis suggests that relatively short RNA molecules could have spontaneously formed that were capable of catalyzing their own continuing replication. It is difficult to gauge the probability of this formation. A number of theories of modes of formation have been put forward. Early cell membranes could have formed spontaneously from proteinoids, protein-like molecules that are produced when amino acid solutions are heated - when present at the correct concentration in aqueous solution, these form microspheres which are observed to behave similarly to membrane-enclosed compartments. Other possibilities include systems of chemical reactions taking place within clay substrates or on the surface of pyrite rocks. Factors supportive of an important role for RNA in early life include its ability to replicate (see Spiegelman Monster); its ability to act both to store information and catalyse chemical reactions (as a ribozyme); its many important roles as an intermediate in the expression and maintenance of the genetic information (in the form of DNA) in modern organisms; and the ease of chemical synthesis of at least the components of the molecule under conditions approximating the early Earth.

A number of problems with the RNA world hypothesis remain, particularly the instability of RNA when exposed to ultraviolet light, the difficulty of activating and ligating nucleotides and the lack of available phosphate in solution required to constitute the backbone, and the instability of the base cytosine (which is prone to hydrolysis). Recent experiments also suggest that the original estimates of the size of an RNA molecule capable of self-replication were most probably vast underestimates. More-modern forms of the RNA World theory propose that a simpler molecule was capable of self-replication (that other "World" then evolved over time to produce the RNA World). At this time however, the various hypotheses have incomplete evidence supporting them. Many of them can be simulated and tested in the lab, but a lack of undisturbed sedimentary rock from that early in Earth's history leaves few opportunities to test this hypothesis robustly.

"Metabolism first" models: iron-sulfur world and others
Several models reject the idea of the self-replication of a "naked-gene" and postulate the emergence of a primitive metabolism which could provide an environment for the later emergence of RNA replication.

One of the earliest incarnations of this idea was put forward in 1924 with Alexander Oparin's notion of primitive self-replicating vesicles which predated the discovery of the structure of DNA. More recent variants in the 1980s and 1990s include Günter Wächtershäuser's iron-sulfur world theory and models introduced by Christian de Duve based on the chemistry of thioesters. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by Freeman Dyson in the early 1980s and Stuart Kauffman's notion of collectively autocatalytic sets, discussed later in that decade.

However, the idea that a closed metabolic cycle, such as the reductive citric acid cycle, could form spontaneously (proposed by Günter Wächtershäuser) remains unsupported. According to Leslie Orgel, a leader in origin-of-life studies for the past several decades, there is reason to believe the assertion will remain so. In an article entitled "Self-Organizing Biochemical Cycles" (PNAS, vol. 97, no. 23, November 7, 2000, p12503-12507), Orgel summarizes his analysis of the proposal by stating, "There is at present no reason to expect that multistep cycles such as the reductive citric acid cycle will self-organize on the surface of FeS/FeS2 or some other mineral." It is possible that another type of metabolic pathway was used at the beginning of life. For example, instead of the reductive citric acid cycle, the "open" acetyl-CoA pathway (another one of the four recognised ways of carbon dioxide fixation in nature today) would be even more compatible with the idea of self-organisation on a metal sulfide surface. The key enzyme of this pathway, carbon monoxide dehydrogenase/acetyl-CoA synthase harbours mixed nickel-iron-sulfur clusters in its reaction centers and catalyses the formation of acetyl-CoA (which may be regarded as a modern form of acetyl-thiol) in a single step.

Bubble Theory
Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles comprised of mostly water burst quickly, oily bubbles happen to be much more stable, lending more time to the particular bubble to perform these crucial experiments.

The phospholipid is a good example of an oily compound believed to have been prevalent in the prebiotic seas. Because phospholipids contain a hydrophilic head on one end, and a hydrophobic tail on the other, they have the tendency to spontaneously form lipid membranes in water. A lipid monolayer bubble can only contain oil, and is therefore not conducive to harbouring water-soluble organic molecules. On the other hand, a lipid bilayer bubble can contain water, and was a likely precursor to the modern cell membrane. If a protein came along that increased the integrity of its parent bubble, then that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the experiment into the surrounding medium. Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multicellular organisms could be achieved. This theory is expanded upon in the book, "The Cell: Evolution of the First Organism" by Joseph Panno Ph.D.

Similarly, bubbles formed entirely out of protein-like molecules, called microspheres, will form spontaneously under the right conditions. But they are not a likely precursor to the modern cell membrane, as cell membranes are composed primarily of lipid compounds rather than amino-acid compounds.

Hybrid models
A growing realization of the inadequacy of either pure "genes-first" or "metabolism-first" models is leading the trend towards models that incorporate aspects of each.

Autocatalysis
British ethologist Richard Dawkins wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book The Ancestor's Tale. Autocatalysts are substances which catalyze the production of themselves, and therefore have the property of being a simple molecular replicator. In his book, Dawkins cites experiments performed by Julius Rebek and his colleagues at the Scripps Research Institute in California in which they combined amino adenosine and pentafluorophenyl ester with the autocatalyst amino adenosine triacid ester (AATE). One system from the experiment contained variants of AATE which catalysed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.

Clay theory
A hypothesis for the origin of life based on clay was forwarded by Dr A. Graham Cairns-Smith of the University of Glasgow in 1985 and adopted as a plausible illustration by just a handful of other scientists (including Richard Dawkins). Clay theory postulates that complex organic molecules arose gradually on a pre-existing, non-organic replication platform -- silicate crystals in solution. Complexity in companion molecules developed as a function of selection pressures on types of clay crystal is then exapted to serve the replication of organic molecules independently of their silicate "launch stage". It is, truly, "life from a rock."

Cairns-Smith is a staunch critic of other models of chemical evolution (see Genetic Takeover: And the Mineral Origins of Life ISBN 0-521-23312-7). However, he admits, that like many models of the origin of life, his own also has its shortcomings (Horgan 1991).

Peggy Rigou of the National Institute of Agronomic Research (INRA), in Jouy-en-Josas, France reports in the February 11, 2006 edition of Science News that prions are capable of binding to clay particles and migrate off the particles when the clay becomes negatively charged. While no reference is made in the report to implications for origin-of-life theories, this research may suggest prions as a likely pathway to early reproducing molecules.

"Deep-hot biosphere" model of Gold
The discovery of nanobes (filamental structures smaller than bacteria containing DNA) in deep rocks, led to a controversial theory put forward by Thomas Gold in the 1990s that life first developed not on the surface of the Earth, but several kilometers below the surface. It is now known that microbial life is plentiful up to five kilometers below the earth's surface in the form of archaea, which are generally considered to have originated either before or around the same time as eubacteria, most of which live on the surface including the oceans. It is claimed that discovery of microbial life below the surface of another body in our solar system would lend significant credence to this theory. He also noted that a trickle of food from a deep, unreachable, source promotes survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct.

"Primitive" extraterrestrial life
An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially, either in space or on a nearby planet (Mars). (Note that exogenesis is related to, but not the same as, the notion of panspermia).

Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating. Comets are encrusted by outer layers of dark material, thought to be a tar-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation by ultraviolet light. It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth.

An alternative but related hypothesis, proposed to explain the presence of life on Earth so soon after the planet had cooled down, with apparently very little time for prebiotic evolution, is that life formed first on early Mars. Due to its smaller size Mars cooled before Earth(a difference of hundred of millions of years), allowing prebiotic processes there while Earth was still too hot. Life was then transported to the cooled Earth when crustal material was blasted off Mars by asteroid and comet impacts. Mars continued to cool faster and eventually became hostile to the continued evolution or even existence of life (it lost its atmosphere due to low volcanism), Earth is following the same fate as Mars, but at a slower rate.

Neither hypothesis actually answers the question of how life first originated, but merely shifts it to another planet or a comet. However, the advantage of an extraterrestrial origin of primitive life is that life is not required to have evolved on each planet it occurs on, but rather in a single location, and then spread about the galaxy to other star systems via cometary and/or meteorite impact. Evidence to support the plausibility of the concept is scant, but it finds support in recent study of Martian meteorites found in Antartica and in studies of extremophile microbes.[2] Additional support comes from a recent discovery of a bacterial ecosytem whose energy source is radioactivity.[3]

RNA world hypothesis
The RNA world hypothesis proposes that RNA was the first life-form on earth, later developing a cell membrane around itself and becoming the first prokaryotic cell.

Support
The RNA World hypothesis is supported by the RNA's ability to store, transmit, and duplicate genetic information, just like DNA does. RNA can also act as a ribozyme (an enzyme made of ribonucleic acid). Because it can reproduce on its own, performing the tasks of both DNA and proteins (enzymes), RNA is believed to have once been capable of independent life. Further, while nucleotides were not found in Miller-Urey's experiments, they were found by others' simulations, notably those of Joan Oro. Experiments with basic ribozymes, like the viral RNA Q-beta, have shown that simple self-replicating RNA structures can withstand even strong selective pressures (e.g., opposite-chirality chain terminators) (The Basics of Selection (London: Springer, 1997)).

The phrase "RNA World" was first used by Walter Gilbert in 1986. However, the idea of independent RNA life is older and can be found in Carl Woese's book The Genetic Code (New York: Harper and Row, 1967). Five years earlier, the molecular biologist Alexander Rich, of the Massachusetts Institute of Technology, had posited much the same idea in an article he contributed to a volume issued in honor of Nobel-laureate physiologist Albert Szent-Györgyi.

Base pairing
RNA and DNA are made of long stretches of specific nucleotides, often called "bases", attached to a sugar-phosphate backbone. The RNA world hypothesis holds that in the primordial soup / primordial sandwich there existed free-floating nucleotides. These nucleotides regularly formed bonds with one another which often broke because the change in energy was so low. However, certain sequences of base pairs have catalytic properties that lower the energy of their chain being created, causing them to stay together for longer periods of time. As each chain grew longer it attracted more matching nucleotides faster, causing chains to now form faster than they were breaking down.

These chains are proposed as the first, primitive forms of life. In an RNA world, different forms of RNA compete with each other for free nucleotides and are subject to natural selection. The most efficient molecules of RNA, the ones able to efficiently catalyze their own reproduction, survived and evolved, forming modern RNA.

Competition between RNA may have favored the emergence of cooperation between different RNA chains, opening the way for the formation of the first proto-cell. Eventually, RNA chains randomly developed with catalytic properties that help amino acids bind together (peptide-bonding). These amino acids could then assist with RNA synthesis, giving those RNA chains that could serve as ribozymes the selective advantage. Eventually DNA, lipids, carbohydrates, and all sorts of other chemicals were recruited into life. This led to the first prokaryotic cells, and eventually to life as we know it.

Nucleic acid fragility
At first glance, the RNA world hypothesis seems implausible because, in today's world, large RNA molecules are inherently fragile and can easily be broken down into their constituent nucleotides through hydrolysis. The aromatic bases comprising RNA also absorb strongly in the ultraviolet region, and would have been liable to damage and breakdown by background radiation. (Pääbo 1993, Lindahl 1993).

Carl Zimmer has been working on a controversial hypothesis that viruses were instrumental in the transition from RNA to DNA and the evolution of Bacteria, Archae, and Eukarya. He believes the last common ancestor was RNA-based and evolved RNA viruses. Some of the viruses evolved into DNA viruses to protect their genes from attack. Through the process of viral infection into hosts the three domains of life evolved. [1]

A proposed alternative to RNA in an "RNA World" is the peptide nucleic acid, PNA. PNA is more stable than RNA and appears to be more readily synthesised in prebiotic conditions, especially where the synthesis of ribose and adding phosphate groups are problematic. Threose nucleic acid (TNA) has also been proposed as a starting point, as has Glycol nucleic acid GNA.

A different alternative to the assembly of RNA is proposed in the PAH world hypothesis.

Additionally, in the past a given RNA molecule might have survived longer than it can today. Ultraviolet light can cause RNA to polymerize while at the same time breaking down other types of organic molecules that could have the potential of catalyzing the break down of RNA (ribonucleases), suggesting that RNA may have been a relatively common substance on early Earth. This aspect of the theory is still untested and is based on a constant concentration of sugar-phosphate molecules.

Implications
The RNA world hypothesis, if true, has important implications for the very definition of life. For the majority of the time following the elucidation of the structure of DNA by Watson and Crick, life was considered as being largely defined in terms of DNA and proteins: DNA and proteins seemed to be the dominant macromolecules in the living cell, with RNA serving only to aid in creating proteins from the DNA blueprint.

The RNA world hypothesis places RNA at center-stage when life originated. This has been accompanied by many studies in the last ten years demonstrating important aspects of RNA function that were not previously known, and support the idea of a critical role for RNA in the functionality of life. In 2001, the RNA world hypothesis was given a major boost with the deciphering of the 3-dimensional structure of the ribosome, which revealed the key catalytic sites of ribosomes to be composed of RNA and for the proteins to hold no major structural role, and be of peripheral functional importance. Specifically, the formation of the peptide bond, the reaction that binds amino acids together into proteins, is now known to be catalyzed by an adenine residue in the rRNA: the ribosome is a ribozyme. This finding suggests that RNA molecules were most likely capable of generating the first proteins. Other interesting discoveries demonstrating a role for RNA beyond a simple message or transfer molecule include the importance of small nuclear ribonucleoproteins (SnRNPs) in the processing of pre-mRNA and RNA editing and reverse transcription from RNA in the maintenance of telomeres in the telomerase reaction.

Difficulties
The base cytosine does not have a plausible prebiotic simulation method because it easily undergoes hydrolysis.

Prebiotic simulations making nucleotides have conditions incompatible with those for making sugars (lots of formaldehyde). So they must somehow be synthesized, then brought together. However, they do not react in water. Anhydrous reactions bind with purines, but only 8% of them bind with the correct carbon atom on the sugar bound to the correct nitrogen atom on the base. Pyrimidines, however, do not react with ribose, even anhydrously.

Then phosphate must be introduced, but in nature phosphate in solution is extremely rare because it is so readily precipitated. After being introduced, the phosphate must combine with the nucleoside and the correct hydroxyl must be phosphorylated.

For the nucleotides to form RNA, they must be activated themselves. Activated purine nucleotides form small chains on a pre-existing template of all-pyrimidine RNA. However, this does not happen in reverse because the pyrimidine nucleotides do not stack well.

Additionally, the ribose must all be the same enantiomer, because any nucleotides of the wrong chirality act as chain terminators. [1]

A.G. Cairns-Smith in 1982 criticized writers for exaggerating the implications of the Miller-Urey experiment. He argued that the experiment showed, not the possibility that nucleic acids preceded life, but its implausibility. He claimed that the process of constructing nucleic acids would require 18 distinct conditions and events that would have to occur continually over millions of years in order to build up the required quantities.

One of the leading researchers into RNA world models, wrote: "The most reasonable assumption is that life did not start with RNA .... The transition to an RNA world, like the origins of life in general, is fraught with uncertainty and is plagued by a lack of experimental data.

— Gerald Joyce, 1989

Miller-Urey experiment
The Miller-Urey experiment (or Urey-Miller experiment) was an experiment that simulated hypothetical conditions present on the early Earth and tested for the occurrence of chemical evolution (the Oparin and Haldane hypothesis stated that conditions on the primitive Earth favored chemical reactions that synthesized organic compounds from inorganic precursors; the Miller-Urey tested this hypothesis). The experiment is considered to be the classic experiment on the origin of life. It was conducted in 1953 by Stanley L. Miller and Harold C. Urey at the University of Chicago.

Experiment and interpretation
The experiment used water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2). The chemicals were all sealed inside a sterile array of glass tubes and flasks connected together in a loop, with one flask half-full of liquid water and another flask containing a pair of electrodes. The liquid water was heated to induce evaporation, sparks were fired between the electrodes to simulate lightning through the atmosphere and water vapor, and then the atmosphere was cooled again so that the water could condense and trickle back into the first flask in a continuous cycle.

At the end of one week of continuous operation, Miller and Urey observed that as much as 10-15% of the carbon within the system was now in the form of organic compounds. Two percent of the carbon had formed amino acids, including 13 of the 22 that are used to make proteins in living cells, with glycine as the most abundant. As observed in all consequent experiments, both left-handed (L) and right-handed (D) optical isomers were created in a racemic mixture.

The molecules produced were simple organic molecules, far from a complete living biochemical system, but the experiment established that the hypothetical processes could produce some building blocks of life without requiring life to synthesize them first.

Other experiments
This experiment inspired many experiments in a similar vein. In 1961, Joan Oró found that amino acids could be made from hydrogen cyanide (HCN) and ammonia in a water solution. He also found that his experiment produced a large amount of the nucleotide base adenine. Experiments conducted later showed that the other RNA and DNA bases could be obtained through simulated prebiotic chemistry with a reducing atmosphere.

There were similar (electric discharge) experiments on the origin of life prior to or contemporaneous with Miller-Urey:

An article in The New York Times, March 8, 1953, page E9, titled "Looking Back Two Billion Years" describes the work of Wollman [sic] (William) M. MacNevin at Ohio State University. (The Miller Science paper was not published until May 1953.) MacNevin was passing 100,000 volt sparks through methane and water vapor and produced "resinous solids" that were "too complex for analysis." The article describes other early earth experiments being done by MacNevin. It is not clear if he ever published any of these results in the primary scientific literature.

K. A. Wilde submitted a paper to Science on December 15, 1952 (which was prior to the Miller submission date of February 14, 1953) that was published on July 10, 1953 (Science, 1953, 118(3054), 43-44). Wilde only used voltages up to 600 V on a binary mixture of CO2 and water in a flow system. He only observed small amounts of CO2 reduction to CO and no other significant reduction products or newly formed carbon compounds.

Earth's early atmosphere
There have been a number of objections to the implications derived from these experiments. Scientists believe that Earth's original atmosphere might contain less of the reducing molecules as was thought at the time of Miller-Urey experiment:

Originally it was thought that the primitive secondary atmosphere contained mostly NH3 and CH4. However, it is likely that most of the atmospheric carbon was CO2 with perhaps some CO and the nitrogen mostly N2. The reasons for this are (a) volcanic gas has more CO2, CO and N2 than CH4 and NH3 and (b) UV radiation destroys NH3 and CH4 so that these molecules would have been short-lived. UV light photolyses H2O to H· and ·OH radicals. These then attack methane, giving eventually CO2 and releasing H2 which would be lost into space.

In practice gas mixtures containing CO, CO2, N2, etc. give much the same products as those containing CH4 and NH3 so long as there is no O2. The H atoms come mostly from water vapor. In fact, in order to generate aromatic amino acids under primitive earth conditions it is necessary to use less hydrogen-rich gaseous mixtures. Most of the natural amino acids, hydroxyacids, purines, pyrimidines, and sugars have been produced in variants of the Miller experiment.[1]

More recent results may question these conclusions. The University of Waterloo and University of Colorado conducted simulations in 2005 that indicated that the early atmosphere of Earth could have contained up to 40 percent hydrogen---implying a much more hospitable environment for the formation of prebiotic organic molecules. The escape of hydrogen from Earth's atmosphere into space may have occurred at only one percent of the rate previously believed based on revised estimates of the upper atmosphere's temperature.[2] One of the authors, Prof. Owen Toon notes: "In this new scenario, organics can be produced efficiently in the early atmosphere, leading us back to the organic-rich soup-in-the-ocean concept... I think this study makes the experiments by Miller and others relevant again." Outgassing calculations using a chondritic model for the early earth, (Washington University, September 2005) complement the Waterloo/Colorado results in re-establishing the importance of the Miller-Urey experiment.[3]

Although lightning storms are thought to have been very common in the primordial atmosphere, they are not thought to have been as common as the amount of electricity used by the Miller-Urey experiment implied. These factors suggest that much lower concentrations of biochemicals would have been produced on Earth than was originally predicted (although the time scale would be 100 million years instead of a week). Similar experiments, both with different sources of energy and with different mixtures of gases, have resulted in amino and hydroxy acids being produced; it is likely that at least some organic compounds would have been generated on the early Earth.

However, when oxygen gas is added to this mixture, no organic molecules are formed. Opponents of Miller-Urey hypothesis seized upon recent research that shows the presence of uranium in sediments dated to 3.7 Ga and indicates it was transported in solution by oxygenated water (otherwise it would have precipitated out) (Rosing & Frei 2004). These opponents argue that this presence of oxygen precludes the formation of prebiotic molecules via a Miller-Urey-like scenario, attempting to invalidate the hypothesis of abiogenesis. However, the authors of the paper are arguing that this presence of oxygen merely evidences the existence of photosynthetic organisms 3.7 Ga ago (a value about 200 Ma earlier than current values[4]), a conclusion which while pushing back the time frame in which Miller-Urey reactions and abiogenesis could potentially have occurred, would not preclude them. Though there is somewhat controversial evidence for very small (less than 0.1%) amounts of oxygen in the atmosphere almost as old as Earth's oldest rocks the authors are not in any way arguing for the existence of a strongly oxygen containing atmosphere occurring any earlier than previously thought, and they state: ". . . In fact most evidence suggests that oxygenic photosynthesis was present during time periods from which there is evidence for a non-oxygenic atmosphere".

Conditions similar to those of the Miller-Urey experiments are present in other regions of the solar system, often substituting ultraviolet light for lightning as the driving force for chemical reactions. On September 28, 1969, the Murchison meteorite that fell near Murchison, Victoria, Australia was found to contain over 90 different amino acids, nineteen of which are found in Earth life. Comets and other icy outer-solar-system bodies are thought to contain large amounts of complex carbon compounds (such as tholins) formed by these processes, in some cases so much so that the surfaces of these bodies are turned dark red or as black as asphalt. The early Earth was bombarded heavily by comets, possibly providing a large supply of complex organic molecules along with the water and other volatiles they contributed. (This could also imply an origin of life outside of Earth, which then migrated here. See: Panspermia)

Recent related studies
During recent years, studies have been made of the amino acid composition of the products of "old" areas in "old" genes, defined as those that are found to be common to organisms from several widely separated species, assumed to share only the last universal ancestor (LUA) of all extant species. These studies found that the products of these areas are enriched in those amino acids that are also most readily produced in the Miller-Urey experiment. This suggests that the original genetic code was based on a smaller number of amino acids -- only those available in prebiotic nature -- than the current one (Brooks et al. 2002).

title: User:Drewbie/Macromolecules/Origins


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Horticulture/Screens

Screens are plantings used to block wind, sunlight, or views, and are an important feature in both landscapes and agriculture.

Screens planted to block wind are in most cases large trees, with large conifers being the most common plants used.

Screens used to block views (called "privacy screens" when the objective is to prevent views from the outside) are usually evergreens, often maintained as high hedges.

/Design

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Horticulture/Screens


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Wikibooks:Requests for deletion/Movie Making Manual/Film Academy Training

Movie Making Manual-Film_Academy Training
Another person nominated this page for speedy deletion due to it being an advertisement. It does look a bit like an advertisement to me, however its part of a book that was Book of the Month for August 2006, and this page has existed this way since before Augist 2006 from what I can tell, so am not sure if it is actually a problem or not. Figured better to bring it here and let others vote on it first. --darklama 00:33, 8 November 2006 (UTC)

 * I dont know enough about this page either, and I think it would be in our best interests to ask the authors of that book about the status of this page. If they want it gone, it should go. If they want it to stay, it will stay. --Whiteknight (talk) (projects) 02:06, 8 November 2006 (UTC)

*Keep - There are at least 2 commercial references and I doubt there are free movie classes, the problem seems to be the lack of alternatives but one may not impose that people contribute the missing info and write the books, the best way I see to fix this is to ask the active contributors to add more references to keep it NPV (but the actual 2 that are there, may just cover this point), as for the information it seems of relevance to a person interested in the book subject and in line with similar references to web sites on other books as there's, as previous discussed, a lack for a policy on this subject I don't see a reason covered by any other that makes this page a candidate for deletion. --Panic 04:23, 8 November 2006 (UTC)
 * Strong delete - Herbythyme "It was one of the editors of that who speedy'd it in the first place" - --Panic 15:39, 8 November 2006 (UTC)

 * Strong delete - I know you folk are amazingly tolerant but this is not a book. It is an advertisement.  Before you know it people will use WB rather than WP -- Herby  talk thyme 07:58, 8 November 2006 (UTC)

 * Delete - If there was more information about this topic rather than the links to external sites then I might agree that it's a book but as it stands at the moments it's an advertisement. Xania 11:04, 8 November 2006 (UTC)
 * Comment - bad naming convention, which I'm fixing now. Has anyone from MMM been asked about it yet? -- SB_Johnny | talk 11:28, 8 November 2006 (UTC)
 * Comment - for Xania - there is an entire (& good) book on theis Movie Making Manual. There are some pages that have taken advantage of this by spamming us.  To Johnny - yep on here and WP.  It was one of the editors of that who speedy'd it in the first place -- Herby  talk thyme 11:31, 8 November 2006 (UTC)
 * In that case, delete. -- SB_Johnny | talk 11:34, 8 November 2006 (UTC)
 * Comment - I asked about it at Talk:Movie Making Manual after what Whiteknight said. --darklama 11:59, 8 November 2006 (UTC)


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The Computer Revolution/Artificial Intelligence/Weak VS Strong AI

Weak Artificial Intelligence
Weak AI gives computers elements of human cognition--the ability to think like a human. A good example of Weak AI is computer software which uses an approach known as "brute force" to calculate probabilities. The case of chess master Garry Kasparov vs IBM's Deep Blue program is a good illustration. Although Kasparov had the advantage of human intuition, Deep Blue had the ability to calculate 200 million probabilities per second. In the end Kasparov was overcome by Deep Blue's super-efficient ability to calculate those probabilities. Another example of Weak AI is spell-checking software, which--like Deep Blue--uses probabilities to make determinations. When a writer spells a word incorrectly, the software does not check the spelling like a grade school teacher does, but compares the incorrectly spelled word against a dictionary of correctly spelled terms with similar characters. It then determines which word was probably intended by the author using a set of programmed heuristics. The efficiency of Weak AI is determined by the speed at which such comparisons can be made and the depth of the database which it draws upon.

Strong Artificial Intelligence
Strong AI claims that a computer can be given the ability to think on a level with humans, possibly becoming "aware" of itself at some point. Strong AI is still in its infancy and has yet to develop to a credible level among scholars. At Stanford University, professor Douglas Lenat and a team of programmers, linguists, theologians, mathematicians, and philosophers have recorded 1.4 million basic truths and generalities into a database in an attempt to give a computer the intelligence of a 12-year-old. They have also given the computer the ability to ask questions and form assumptions. Strong AI uses two approaches. Cyc which loads the database with facts and rules and Co.

Conclusion
The efforts of Douglas Lent and other teams of scholars who have attempted to impart a database with the distinctly human quality of intuition are admirable. However, the author does not see how this approach differs from Weak AI. Although the type of information differs, both methods require the building of databases and, at the core, use probabilities or high-speed comparisons to draw conclusions. Computers, though capable of performing tasks far beyond the ability of humans, are not (at this point) able to mimic human intuition, because intuition is a unique and individual possession of each person. It cannot be created or quantified by facts, figures, basic truths or generalities. It is not downloadable, regardless of the size of the data base.


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Adventist Youth Honors Answer Book/First aid/Firemans carry

If there are no indications of injury to the spine or an extremity and the victim cannot walk, he can be carried by the Fireman’s  Carry  The figure here shows the steps of this procedure.

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Adventist Youth Honors Answer Book/First aid/Pack strap carry

With the pack-strap carry, it is possible to carry a heavy person for some distance. Use the following procedure:
 * 1) Place the casualty in a supine position.
 * 2) Lie down on your side along the casualty’s uninjured or less injured side.  Your shoulder should be next to the casualty’s armpit.
 * 3) Pull the casualty’s far leg over your own, holding it there if necessary.
 * 4) Grasp the casualty’s far arm at the wrist and bring it over your upper shoulder as you roll and pull the casualty onto your back.
 * 5) Raise up your knees, holding your free arm for balance and support.  Hold both the casualty’s wrists close against your chest with your other hand.
 * 6) Lean forward as you rise to your feet, and keep both of your shoulders under the casualty’s armpits.  Do not attempt to carry a seriously injured person by means of the pack-strap carry,  especially if the arms, spine, neck, or ribs are fractured.

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User:AverieZen

User
Wikibooks user ID created November 24, 2006.

Contributions

 * Blender 3D: Noob to Pro

title: User:AverieZen


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Adventist Youth Honors Answer Book/First aid/Support carry

In the support carry, the casualty must be able to walk or at least hop on one leg, using the bearer as a crutch. This carry can be used to assist him as far as he is able to walk or hop.

/Transcluded Modules


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Adventist Youth Honors Answer Book/Camping/Choosing a campsite

To help remember the things that are important to camp site selection, remember the six W’s:

 * Wind- Find areas that are protected from the wind. This requires knowing or guessing at the normal wind direction (hint look at the direction trees are leaning and the current wind direction)
 * Water- Fresh water should be available for drinking, beware of drainage areas, flooding and other water related hazards. Marshy areas can have a high mosquito population that can make camping miserable.
 * Weather- Knowledge of the weather patterns of an area can help you decide the best location for the camp site.
 * Wild things- Beware of signs of large mammals such as bear, wolves, and mountain lions. Also watch out for the small wild things such as snakes, spiders, ticks, biting flies and mosquitoes.
 * Wood- Adequate wood should be available for a campfire, and no dead wood above sleeping area. Survey the trees to make sure that they will not fall on you in strong winds.
 * Willingness- Make sure the owner of the property is willing for you to camp on it. Make sure you have the proper permits for camping areas.


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Klingon/My first Klingon

You may find Learning Klingon difficult due to the alien nature of the language. When Mark Okrand developed tlhIngan Hol, he specifically designed it to violate typical human language rules; Klingon uses a word order rarely found among human languages, and combines sounds in atypical ways. Beginners may have more luck familiarizing themselves with basic words and phrases to get the phonetic pronunciation, than trying to memorize pronunciation rules.

Klingon cursing ranks among the most difficult linguistic activity; the most offensive words and phrases in tlhIngan Hol utilize difficult to produce sounds such as tlh or Q, as well as difficult sequences of phonemes such as toDSaH. Mastering Klingon cursing gives practical experience with pronunciation and sound formation.

Bastard
The word petaQ (pronounced) serves well as an introductory Klingon word; this word functions as an epithet, similar to "bastard" or "asshole" in context. This will undoubtedly provide an enriching addition to your skeletal Klingon vocabulary.

The word petaQ present difficulty at first due to the tlhIngon Hol Q sound; you pronounce this sound somewhat like the q but harder and louder, and the difference may not be clear at first. To form the Q sound, put the back of your tongue as far back into your mouth as you can; then force the air up as if you're trying to cough something up. Pronounce the Q forcefully. You may find this similar to producing a strong English 'k' sound, but with the back of your tongue pressed to your uvula.

Qu'vatlh ghuy'cha' baQa'
In the Star Trek episode, The Mind's Eye, Governor Vagh was convinced the federation was supplying weapons to Kriosian rebels. Picard replied with the phrase, "Qu'vatlh ghuy'cha' baQa'," at which point Vagh complimented him on his mastery of Klingon cursing.

Qu'  (task) and vatlh (hundred) make up the basis of the word Qu'vatlh ([[Media:Tlh-Qu'vatlh.oga|pronounced]]); thus, "a hundred tasks," frustration with an excessive workload and a lack of appropriate resources. ghuy'cha' , a general invective similar to "Damn it," consists of ghuy'  (an invective; "damn") and cha'  (two). Finally, baQa'  or b'aka (invective) indicates a frustration with one's own inability to accomplish a task.

Qu'vatlh uses the Klingon Q; you should pronounce this sound as in petaQ. It also uses the tlh sound; you may find producing this sound extremely difficult. You can produce the Klingon tlh sound by saying an English t while breathing a whispered l; you may have trouble doing this with any level of force at first. tlh may sound similar to an English th interrupted by an l, hence the notation.

The sound cuts abruptly after  Qu' ; you must pronounce the word Qu'vatlh properly. Many words in Klingon sound similar to other words except for the abrupt termination; Klingon places more emphasis on the enunciation of sounds than English.

title: Klingon/My first Klingon


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Adventist Youth Honors Answer Book/Nature/Amphibians - Advanced

Note: Must have completed all requirements for the Amphibians Honor prior to working on this next level.
==2. Design and carry out a study project based on natural or captive observation of a selected amphibian(s) and write a paper on the conclusions arrived at during the study. The parameters of the study should involve a minimum of 25 hours of actual observation time and no more than a maximum total duration of one season. Intentional harm/death of the study target is not permitted.== '''Note: Most amphibian species have had very little research carried out on them. It is a field wide open for study of even some of the simplest elements. For example,very little data exists on the seasonal activities of frogs and the climatic factors that influence them. When does chorusing begin and stop, when does it reach its highest volume, what are the atmospheric conditions and variations associated with these? What are the dates for egg laying, hatching, transformation? What are the growth rates, age of sexual maturity, average and maximum longevity, duration of breeding behavior, courtship behavior, rate of dispersal, location of brumation or estivation sites? Little is known about homing ability, territorial maintenance, interaction during breeding and non-breeding times, and many other issues. It is indeed a field wide open to the curious and fascinated.'''

There are a number of amphibian monitoring programs in the United States at both the federal and state levels. These programs rely on volunteer help to conduct their research. Plug "amphibian monitoring program" into the search engine of your choice to find one near you. You can also check with your state or province's Department of Fish and Game - they are often responsible for non-game wildlife as well. Even if you do not work on one of these projects, it would be good to check with your Fish and Game Department anyway - in some localities it is illegal to collect or harass amphibians (see the notes under requirement 11 of the Amphibians honor for more information.

Here is a list of known programs:

 * United States
 * USGS Amphibian Research and Monitoring Initiative (ARMI)
 * Arkansas Amphibian Monitoring Program (AAMP)
 * Indiana's North American Amphibian Monitoring Program
 * Southwest Florida Amphibian Monitoring Network
 * Kansas Anuran Monitoring Program (KAMP)
 * Maine Amphibian Monitoring Program (MAMP)
 * New Hampshire Reptile and Amphibian Reporting Program (RAARP)
 * Oregon - Amphibian monitoring program
 * Tennessee Amphibian Monitoring Program (TAMP)

 * Canada
 * Alberta Amphibian Monitoring Program (AAMP)

| /Nature /Completed Honors


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Adventist Youth Honors Answer Book/Nature/Animal Tracking

Basic Casting Techniques
To do this, you will need to bring dry plaster of Paris, water, a mixing container, a mixing stick (a paint stirrer will do nicely), and something to make rings out of. Plaster of Paris can be bought either dry, or ready-mixed. It is probably better to get the dry type so that you can mix it on site. It will need to be soupy to make a detailed cast. When you find a suitable track, place a ring around it. The ring can be made from almost anything - a large tin can with the bottom cut out, a paper cup with the bottom removed, a strip of poster board wide and taped together at the ends to form a circle, etc. You can also cut one from a water bottle (for small tracks), a two-liter soda bottle, or a milk jug (the ring does not have to be round). Make sure the ring is larger than the track, and note that some tracks are long or more. What a pity it would be to find a huge bear or moose track and not have a large enough ring to cast it! You can also make the cast without a ring, but it is much better if you use one. Once the ring is in place, mix just enough plaster and water to fill the ring up to deep. It sets quickly, so you will not want to mix up too much at a time. Mix water with the dry plaster and stir it until it is smooth. It should be about the same consistency as pancake batter or apple sauce. Pour it into the ring. Once this is done, you can set out in search of more tracks, or you can wait until the plaster sets. If you set out for more, be sure to come back to collect your cast.

One good way to complete this requirement is by heading to a river right after flooding has receded. There will likely be plenty of easily identifiable kinds of tracks, and the smooth mud makes for excellent casting.

Casting Tracks in Snow
Snow is difficult to cast because it is not nearly as firm as mud. Furthermore, plaster generates heat when it is mixed, and this can easily melt the snow surrounding the track. However, tracks are a lot easier to find in the snow, and casting can be done if you are careful.

If the snow is powdery, spray water on it with a plant mister. Don't overdo it though. Allow the water to freeze, making a much harder surface than the untreated, powdery snow. Then place the ring around the track. To counteract the heat generated by the plaster, store the powdered plaster outside so that it can be cold when you mix it. Use cold water when mixing it, and make it even colder by tossing in a few fists full of snow. Stir the snow around until the water is really cold, but if it does not all melt, scoop it out. Leaving snow in the plaster will cause air bubbles in the final cast. Once the plaster is mixed, carefully pour it in the ring, but do not pour it directly in the track. Pour it next to the track and let it flow gently into the track itself. The spot where the plaster is poured will very likely leave an impression in the snow, and you do not want that to overlap the track. The mix may take well over an hour to cure, so you might want to leave it for a day. With any luck, you should have a nice cast of your track, though it is not likely to be a nice as the ones you can cast in mud.

If you find these results unsatisfactory, you can purchase a product called Snow Print Wax. This product is marketed to the law enforcement community for forensic track casting (of human foot prints and tire tracks). It is far more expensive than plaster, but is nearly certain to yield superior results. You can also try using joint compound. Joint compound is similar to plaster with two exceptions: it does not generate heat when setting, and it is not nearly as durable once it sets. If you use joint compound, you may wish to pour plaster over the finished cast to get a positive cast. The positive cast made from plaster will be far more durable than the negative original made from joint compound.

Identification
Figuring out what kind of animal left the tracks you have found can be difficult for the beginner. Besides just knowing what its tracks look like, it helps to know something of the animal's habits, where it lives, what time of day (or year) it is active, etc.

This track guide is an invaluable resource for identifying tracks. If you find some tracks that have you stumped, take several detailed photographs of them, and post them to an online forum. The Bear-Tracker site (see references section) has an excellent and active forum. When taking pictures, it helps to disable flash, as that tends to fill in and eliminate the shadows - the resulting photo may end up looking like a featureless patch of dirt). Many cameras will automatically lengthen the exposure time to compensate for the lack of flash, and that means you will have to hold the camera impossibly still.  A tripod really helps in this situation.

We now present information on several animals found in North America, including their habits, tracks, and other sign they may leave for the observant tracker to find.

2. Name at least three things that tracks tell us.
Animal tracks can tell us many things about the animal that made them, including:
 * 1) The species
 * 2) Its direction of travel
 * 3) How fast it was going
 * 4) How large it was
 * 5) How long ago the animal made the tracks.
 * 6) Sometimes tracks can tell the gender of the animal
 * 7) Sometimes tracks can tell us the animal's age.

Trailing and Identifying
This is a perfect activity for an afternoon hike during a campout. Bring a tape measure so that you can measure the tracks. Bring some powdered plaster of Paris, and a mixing bowl so that you can make casts. You can also bring water, though it is better to keep that for drinking rather than mixing with plaster. You can probably find some water along the way, but just to make sure, you should bring some water for the plaster. You can refill a bottle for plaster making without treating it as long as you make it obvious that it is not fit for drinking (mud is a good indicator).

Instruct your Pathfinders that they are to look for animal tracks along the way. When they find some (or when you do), try to figure out the species by comparing the track to those in a field guide or those depicted in the answers to requirement one. See if you can find more tracks nearby. Which way was the animal moving? How far can you track it?

Walking vs Running
If the tracks are far apart relative to the size of the animal, it was most likely running. Another indicator of running is that the tracks are deeper than those made by a walking creature (running makes the feet strike the ground with greater force).

Measuring Tracks
There is nothing in this requirement to suggest that the tracks of one animal made while running and walking has to be a wild animal, or even that you have to find a set of tracks like these pre-made. If you or a person in your group, or a person you know has a dog, take it to a sandy area and have it walk and run. Then get a tape measure and determine the distance between the tracks.

You can also do this in a parking lot, but in order for the dog to leave tracks, you will need to dip its feet in tempera paint (which is non-toxic and water-soluble). It is best to pour some paint in a paper plate. Use two colors - one for the front feet, and one for the back. This will make it a lot easier to tell the front prints from the hind. Lift the dog, and have a helper wet the dog's pads. Then put the dog down and walk it (use a leash). Re-apply the paint, and then allow the dog to run. You should now have two sets of prints from a single animal. Get out a tape measure, and take the measurements.

The standard way to do this is to measure the distance between tracks made by the same foot. The distance between the left rear and the right front is almost meaningless.

a. Select a flat open space in some quiet place near your camp or home.
Do not select a space too close to your campsite, because you do not want to attract them into your camp. Animals need water, so a really good place to select is around a source of fresh water. River banks, stream banks, near ponds, and the shores of lakes are all good places to find animal tracks. However, the place you select must be quiet. Avoid places that are frequented by people.

b. Smooth out ground, mud, sand, etc.
There may already be some tracks in the area, but you are interested in fresh tracks. Smoothing the ground erases them and allows for fresh prints. A mason's trowel works very well for this in mud. You can also use a trowel on sand, but be careful not to pack it down. The smoother you can make the surface, the finer tracks you will be able to see.

For dirt, it helps if you can sift it onto a flat surface and then lightly wet it. If your garden hose has a "mist" setting, use that after sifting the dirt onto a flat surface.

c. Place food out for wildlife.
Another option is to use a salt or mineral block. The type of food you place will affect the type of animals you attract, as will the season. If there is plenty of food available without your "bait," the animals will be suspicious and stay away. However, if they are hungry (as in winter) or if the food you select is irresistible, they will be more likely to come. Sliced apples out of season will attract many types of animals.

The type of food you set out will have some effect on the type of animals you attract. Popcorn kernels or sunflower seeds are likely to attract squirrels. Cold cuts may attract predators such as raccoons or coyotes. Fresh dirt will attract worm-seeking birds. Fresh fruit will attract many types of animals.

d. Check each day for tracks and replenish food when necessary.
When camping, remember to store your food in a place where the animals cannot get to it. Seal it tightly and place it out of the reach of raccoons and bears (both of which are very clever at getting food). Under no circumstances should you store food in a tent - especially in one that people will be sleeping in. A tent poses no barrier to a hungry skunk.

The morning is the best time to check for tracks. Most forest creatures are nocturnal, so in the morning the tracks will be freshest. Also, human visitors are less likely to trample the tracks before you get a chance to observe and if necessary, cast them.

If you wish to photograph your tracks, it's best to do that in the early morning when the sunlight comes in at an angle. If you wait until the sun is high overhead, the track will not cast a shadow and it will be difficult to see. Turn off your camera's flash or it will completely wash out the shadows and the track will not show up in the photo. If you want to experiment with artificial light, use a flashlight to illuminate the track from the side. Place a coin or a ruler (for scale) next to the track before taking the picture. Take lots of photos (digital cameras are great for this) and hope that at least one of them turns out. It takes a lot of practice!

5. Name two animals for each tracking group.

 * a. Flatfoots: Flatfoots include bears, raccoons, porcupines, and skunks. The scientific term for flatfoot is plantigrade.
 * b. Toe walkers: Toe walkers include dogs, cats, lynxes, wolves, and coyotes. The scientific term for toe walker is digitigrade.
 * c. Toenail walkers: Toenail walkers include deer, antelope, moose, pigs, cattle, and horses. Basically, any hoofed animal is a toe walker.  The scientific term for toenail walker is Unguligrade.
 * d. Bounders or long hindleggers: These include rabbits, squirrels, mice, and rats.

6. Name four signs of the presence of mammals.
Animals leave many indications that they were present. These are collectively called sign. Sign includes:
 * Tracks: Not only footprints, but marks left on the ground by the tail or by other body parts. Beavers, muskrats, mice, and rats all leave tail marks on the ground.
 * Scat: Scat is another word for animal droppings or manure.
 * Fur and antlers: Animals may leave bits of fur behind if it gets caught in a tree's bark, or in thorns. In the fall deer drop antlers.
 * Cuttings: Cuttings are things such as acorn shells which have been nibbled on. Deer and squirrel often leave them behind.
 * Scratches on trees: Bears, members of the cat family, and other predators will sharpen their claws on tree trunks. Sometimes they will do this to mark their territory.  Porcupines will eat the bark all the way around the trunk of a conifer, often killing it.
 * Scent Posts: Many animals mark their territory by urinating on trees or other prominent items. If you are walking through the woods and smell a strong musky odor, look around — you may find other sign.
 * Carcasses: Once a predator has had its fill of a kill, it will leave the carcass. Some animals will guard their carcasses though so they can feed on them again after they've digested some of the previous meal, so be careful if you find one.

Rabbit vs Squirrel Tracks
Rabbits leave a distinctive pattern when they bound along. The front feet are thrown between the hind feet, but one of them is almost invariably thrown farther back, and the two forefeet often print one behind the other (though sometimes they print side-by-side). A rabbit's hind feet leave larger oval-shaped prints about the size of a man's thumbprint. Since they use the hind feet rather than their forefeet to leap forward, they will push out some material behind them. It may be difficult to make out individual toes in a rabbit print.

Squirrels are also bounders, and like the rabbit, they throw both forefeet between their hind feet. But unlike the rabbit, the squirrel's forefeet generally print side-by-side. The hind feet should print five toes (four finger-like and one thumb-like) and no claws. The forefeet should print only four toes.

In general, a rabbit's pads are shaped like an oval while a squirrel's pads are shaped like a human hand.

If you're lucky enough to find a large set of tracks in the snow, and they lead to the base of a tree, it is almost certainly a squirrel, as rabbits cannot climb trees. The only way a rabbit could leave such a trail is if it had been abducted by aliens (or by an owl!)

Dog vs Cat Tracks
Unlike dogs, cats can retract their claws, and they do so when walking. Therefore, you should expect to find claw marks present in dog tracks, but absent in cat tracks. In general dogs tracks are larger than cat tracks, but you cannot rely on this alone, as there are some very small dogs and some very large cats.

Try using this "door foldable" to teach this honor: http://www.youtube.com/watch?v=Ymk6Di-WUM8

8. Name two groups of animals (mammals, birds, insects, etc.) that leave tracks or scent trails that another of their kind can follow.
Some species of mammal and some species of insect leave scent trails to communicate with others of their species. Canines, cats, deer, moose, and others will mark their territory with urine.

Ants lay down pheromone trails that lead to food sources. If you have ever seen a column of ants scurrying about in single file, you can be sure they are following a scent trail.

a. Hopping
Most perching birds (passerines) hop, though many can both hop and walk (such as ravens, blackbirds, and robins). Jays, sparrows, cardinals, titmice, nuthatches, finches, and many others hop. The tracks of hopping birds often print side-by-side as they tend to keep their feet together as they hop.

b. Walking
Walking birds include crows, most waterfowl and shore birds (sandpipers, egrets, herons, etc.), and most game birds (wild turkeys, geese, ducks, grouse, doves, pigeons, etc.). The tracks of walking birds typically alternate left to right as they lift their feet one at a time.

10. Besides tracks, give two other signs of the presence of birds.

 * Feathers
 * Droppings
 * Nests
 * Birdsongs (if you can hear them, they must be present!)
 * Eggs or eggshells
 * Pellets: Birds of prey regurgitate the indigestible portions of their meals. Birds have no teeth so they rip their prey apart with their beaks and swallow large chunks at a time.  Then they digest the soft portions (such as meat) leaving the hair and bones behind to collect into pellets.  They cough up these pellets which can be found by the astute observer.

a. Toad or frog b. Snake c. Turtle
Tracks for these animals are described in an earlier requirement. Perhaps the easiest of these three to find are the tracks of the frog. Find a pond where frogs live, and smooth the mud as described in requirement 4. Another technique is to visit a frog pond and watch as they leap into the water at your approach. Look carefully at the spot from which they leap, and you may be able to see the track. If you have any Pathfinders brave enough, have one capture a frog, and then gently transport it to a muddy area where it can leave tracks. Put it in the center of this area and observe the tracks it makes. Recapture the frog and return it to its home when you are finished.

d. Mollusk
When most people think of mollusks, they think of clams and mussels. For this honor, it is beneficial to remember that snails and slugs are also members of the mollusk family, especially since they leave easily followed trails.

The best time to find snail or slug tracks is in the early morning. Look on the sidewalk near flower beds for the tell-tale slimy trails these creatures leave as they slip along. As these slime trails dry, they turn white and flaky, often curling at the edges.

That said, it is also possible to find the tracks of clams and mussels. The photo on the right shows the tracks left by a mussel in shallow water (about deep) at the edge of a fresh water pond.

e. Earthworm
Find a place where you have seen earthworms in the past, preferably where the dirt is bare (i.e., no grass). Soak the area with water to drive the worms out of the ground. Worms need air, so when it rains (or when a Pathfinder soaks the ground with a hose), they will come to the surface. They might not come out immediately, so you should plan to return a day later to look for tracks in the mud you've made.

f. Mole
Moles are burrowing rodents, and if you have them in your yard, it is not difficult to see where they have been. As they tunnel along, they raise the earth above their tunnels. At the end of the tunnel you may find a hole surrounded by a "mole hill".


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Adventist Youth Honors Answer Book/Nature/Bird Pets

1. Keep one or a pair of birds for at least six months.
Consider what you are doing carefully before becoming a pet bird keeper. Most of the birds commonly kept as pets live for decades. Parrots have the potential to outlive their keepers, with a lifespan that routinely reaches 50 years. Think about what you will be doing for the next 50 years and whether you expect you can care for another creature for that length of time. Pet birds that are given a lot of attention early in life get used to it. When the family situation changes and the bird no longer receives that amount of attention, it may begin to engage in self-mutilation.

Birds are incredibly intelligent and have a deep capacity for love. They also have a deep capacity for sorrow. You need to be mindful of this before you take on the responsibility of bird ownership.

==2. Show you have completed one of the following: a. If you have a cage bird, keep a record of its care for at least one month. Include food habits, water needs, cage cleaning, etc. b. If you do not have a cage bird now but completed requirement #1 in the past, take care of some one else's bird for at least one week while they are on vacation, etc., and maintain a record of the required care.==

a. Give the names of three varieties of canaries.
Canaries are generally divided into three main groups, with each group having several varieties:
 * 1) Colorbred Canaries (bred for their many color mutations - Ino, Eumo, Satinette, Bronze, Ivory, Onyx, Mosaic, Brown, etc.)
 * 2) Type Canaries (bred for their shape and conformation - Border, Fife, Gloster, Gibber Italicus, Raza Española, Berner, Lancashire, Yorkshire, Norwich, etc.)
 * 3) Song Canaries (bred for their unique and specific song patterns - Spanish Timbrado, Roller, Waterslager (also known as "Malinois"), American Singer, Russian Singer, Persian Singer).

b. Give a brief history of the origin and development of canaries.
The canary is a domesticated form of the Wild Canary, (Serinus canaria) a small songbird in the finch family originating from Madeira and the Canary Islands.

Canaries were first bred in captivity in the 1600s. They were brought over by Spanish sailors to Europe. Monks started breeding them and only sold the males (which sing). This kept the birds in short supply and drove the price up. Eventually Italians obtained hens and were able to breed the birds themselves. This made them very popular and resulted in many breeds arising and the birds being bred all over Europe.

The same occurred in England. First the birds were only owned by the rich but eventually the local citizens started to breed them and, again, they became very popular. Many breeds arose through selective breeding.

d. Describe briefly the general care of canaries.

 * Cage: Do not keep a canary in a round cage, or it will develop psychological problems. A square cage will avoid this problem.
 * Drafts: Keep the canary away from drafts.
 * Water: Make sure the canary always has fresh water. A canary will die in as little as 15 hours without water.
 * Food: Use a high quality, fresh seed mix. If the seeds can germinate, they are fresh.  You can test for this by wrapping some seed in a wet paper towel, placing them in a plastic bag, and storing in a warm place for about a week.  If the seeds have not sprouted by then, they were not fresh.  Give your canary a serving of greens every day.  A healthy canary can consume half its body weight per day in greens.  Use broccoli, romaine lettuce, collards, or even dandelion greens.
 * Sanitation: Replace the paper on the cage floor every day and clean the cage and perch weekly. Do not use perfumes or air fresheners around a canary.  These birds are highly sensitive to airborne toxins, which is why they were used in mines - to detect deadly gases.  Unfortunately, the gases were detected by the death of the canary, but it often gave the miners time to escape before succumbing themselves.

a. To what country are parakeets or love birds native?
Parakeets originally come from Africa and Australia. Love birds originally come from Africa.

b. Describe briefly their habits of feeding, nesting, and general behavior.
Parakeets: They don’t like to live together in colonies. The most that a large cage should accommodate is 2. They can however be kept with pigeons, pheasants or finches. They eat mixed varieties of seed such as budgie seed and oats. They also like their green feed such as spinach, cabbage and lettuce. Boiled egg can be added during the breeding season. They also need grass and palm leaves to build their nests.

Love Birds: They sleep in nests throughout the year and therefore should be provided with such or should be provided with the materials to weave their own. This includes palm leaves, papyrus, reeds, and grass. They eat a variety of seed such as sunflower seed, oats, canary seed and white, yellow, or red millet. They too can have boiled egg during the breeding season and are also very fond of green feed such as spinach, lettuce, etc.

6. What are the laws in your state or country regarding the capture, breeding, role and/or export of cage birds? Be sure you are abiding by them while fulfilling the requirements of this Honor.
In the United States:
 * It is illegal to export any wild-caught, native birds.
 * It is illegal to import any bird belonging to a threatened species, unless the bird was bred at a captive breeding facility approved by the U.S. government (the U.S. government periodically publishes a list of qualifying facilities).
 * If the importation of a species of bird causes excessive mortality, importation shall cease.
 * It is illegal to import birds into the United States from countries where their export is forbidden.


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Adventist Youth Honors Answer Book/Nature/Cacti

1. Name the chief characteristics of a cactus.

 * Areoles - Flowers, branches, spines sprout from these- no other plant has this feature.

 * Spines -  Perhaps the most familiar feature of cacti, spines can vary greatly in appearance, shape, size, and color. Spines are not thorns.

 * Flowers - Flowers are not unique to cacti, but cacti flowers are unique. Cacti flowers are typically quite spectacular and very complex. Unfortunately this field mark is only helpful, of course, if the plant happens to be blooming.

 * Leaves - Most cacti do not have leaves, however, some do. Pay special attention to the presence or absence of leaves.

 * Origin -   All cacti are native to the America's and surrounding islands. With one exception - Rhipsalis baccifera. Although, world wide cultivation has made this less helpful for identification.

2. Name four uses of cacti.

 * Cacti are used for:

 * 1. Decorating - as houseplants, in dry gardens, or, even as a fence.

 * 2. Edible Fruit Producing - such as Prickly Pear, Hylocereus, Dragon fruit.

 * 3. Psychoactive uses - the Peyote, Lophophora williamsii, is a well-known psychoactive agent used by Native Americans in southwestern United States.

 * 4. Host for bugs - the Opuntia is also used as a host for cochineal bugs for the Cochineal dye industry.

3. In what places are cacti the most plentiful? Why?

 * Most cactus species, there are some 2500 of them altogether, are not really suited to live in a true desert. Then mainly occur around the Tropics of Cancer and Capricorn, 23 degrees N and S, these zones have the largest diversity. In Mexico alone, you can find several hundred species of cactus.

 * But some indeed do live in the desert. In North America, the deserts are further north, about from the Tropic of Capricorn north to around 40 degrees N. The harshest conditions are found between 28 degrees N and 32 degrees N, approximately.

 * WHY? Because they can, what makes them survive is their adaptation to the environment. When it rains, they take advantage of it and store as much water as they can. Their roots are on the surface, which enables them to collect the water and store it in the stems quickly. Note that if over watered root rot can accrue.

4. Know and identify from life or pictures 15 species of cacti.
Hey! This is your part. Enjoy!

I took a photo of this cactus. Can you identify it?

Now go and identify more...

5. Photograph, observe or sketch at least 10 species of cacti and classify them or grow at least 3 different species of cacti.
There are different tribes of cacti:


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Adventist Youth Honors Answer Book/Nature/Cacti - Advanced

1. What are succulents?
Succulent plants, also known as succulents or fat plants are water-retaining plants adapted to xerophilic climatic or soil conditions. Succulent plants store water in their leaves, stems and/or roots. The storage of water often gives succulent plants a more swollen or fleshy appearance than other plants, also known as succulence. In addition to succulence, succulent plants variously have other water-saving features.

Agave
Agave is the name of a succulent plant of a large botanical genus of the same name, belonging to the family Agavaceae. Chiefly Mexican, they occur also in the southern and western United States and in central and tropical South America. The plants have a large rosette of thick fleshy leaves generally ending in a sharp point and with a spiny margin; the stout stem is usually short, the leaves apparently springing from the root. Along with plants from the related genus Yucca, various Agave species are popular ornamental plants. Each rosette is monocarpic and grows slowly to flower only once. During flowering a tall stem or "mast" grows from the center of the leaf rosette and bears a large number of shortly tubular flowers. After development of fruit the original plant dies, but suckers are frequently produced from the base of the stem which become new plants.

Aloe
Aloe, also written Aloë, is a genus containing about four hundred species of flowering succulent plants, the most well known of which is Aloe vera.

The genus is native to Africa and is common in South Africa's Cape Province and the mountains of tropical Africa, and neighbouring areas such as Madagascar, the Arabian peninsula and the islands off Africa.

Sedum
Sedum is the large stonecrop genus of the Crassulaceae, representing about 400 species of leaf succulents, found throughout the northern hemisphere, varying from annual groundcovers to shrubs. The plants have water-storing leaves and a typical form of blossom with five petals, seldom four or six. There are typically twice as many stamens as petals.

Many sedums are extensively cultivated as garden plants, due to their interesting and attractive appearance and hardiness. The various species differ in their requirements; some are cold-hardy but do not tolerate heat, some require heat but do not tolerate cold. They are preferred to grass for green roofs, popular in Germany and some other countries.

Ice Plant
The common name Ice Plant refers to Carpobrotus edulis, a creeping, mat-forming succulent species, and member of the Stone Plant family Aizoaceae, one of about 30 species in the genus Carpobrotus. It is also known as the Highway Ice Plant, Pigface or Hottentot Fig and in South Africa as the Sour Fig, on account of its edible fruit. It was previously classified in genus Mesembryanthemum and is sometimes referred to by this name.

The Ice Plant is a native of South Africa. In the early 1900s C. edulis was brought to California from South Africa to stabilize soil along railroad tracks and was later put to use by Caltrans for similar purposes. Thousands of acres were planted in California until the 1970s. It easily spreads by seed (hundreds per fruit) and from segmentation (any shoot segment can produce roots). Its succulent foliage, bright magenta or yellow flowers, and resistance to some harsh coastal climatic conditions (salt) have also made it a favoured garden plant. The Ice Plant was for several decades widely promoted as an ornamental plant, and it is still available at some nurseries. Ice Plant foliage can turn a vibrant red to yellow in color.

Jade Plant
Commonly known as jade plant or friendship tree, Crassula ovata is a succulent plant that sometimes has small pink or white flowers. Jade Plants are evergreen succulents native to South Africa where the environmental conditions are dry with little rainfall.

The plant itself can be identified with thick branches and smooth, rounded and fleshy leaves that grow in opposing pairs along the branches. The species has a jade green color to the leaves, and some species can also develop a red tinge on the edges of leaves when exposed to high levels of sunlight. The growth pattern and structure of the succulent is evenly distributed. Dependent on the environment in which it is in, the plant produces small white or pink star like flowers that adorn the ends of new stalks in the Spring.

Jade plants are popularly used as houseplants around the world. They are propagated by stem or leaf cuttings. As succulents, they require a normal watering when the soil is dry in the summer, and very little watering in the winter. Overwatering will cause them to lose their leaves and eventually the stem will rot away. They will grow in full sun to light shade. However, they do not tolerate extreme heat or overexposure to direct sun very well, showing damage ranging from scorched leaves to loss of foliage and rotting stems. Most of the common species will tolerate a limited degree of frost but overexposure to cold weather will kill them.

How are they different from cacti
None of the plants listed above have spines as cacti do.

3. Know the definitions of the following terms within a cacti/succulents frame of reference.

 * a. Areole: Areoles are the distinctive feature of cacti, and identify them as a separate family from other succulent plants.

 * b. Cephalium: Cephalium is a frequently brightly colored, structure of wool and bristle at the growing tip of certain cacti. It is most commonly found on cacti of the genus Melocactus and can take a number of colors, forms and shapes.

 * c. Coalesce: Coalesce is when two objects grow together.

 * d. Corymb: A corymb is similar to a panicle with the same branching structure, but with the lower flowers having longer stems, thus giving a flattish top superficially resembling an umbel.

 * e. Diurnal: A plant or animal that is active in the daytime

 * f. Epiphyte: An epiphyte is an organism that grows upon or attached to a living plant.

 * g. Glochid: Glochids are tiny, almost invisible barbed hairs found on the areoles of some cacti and other plants.

 * h. Nocturnal: Primarily active during the night.

 * i. Offshoot: Offshoots are lateral shoots that are produced on the main stem of a plant.

 * j. Panicle: A panicle is a compound raceme, a loose, much-branched indeterminate inflorescence with pedicellate flowers (and fruit) attached along the secondary branches (in other words, a branched cluster of flowers in which the branches are racemes).

 * k. Scale: Scale are small insects of the order Hemiptera, most of which are parasites of plants, feeding on sap drawn directly from the plant's vascular system.

 * l. Stolon: A stolon, commonly referred to as a runner, is an aerial shoot from a plant with the ability to produce adventitious roots and new clones of the same plant.

 * m. Zygomorphic: Having bilateral symmetry

4. When raising succulents — including cacti — they may be attacked by maladies. What are the most common and how can you prevent or cure the problems?
The most common cactus malady is mold, usually caused by overwatering. If mold is detected on a cactus, the affected part should be cut off as soon as possible, using a sharp knife. Then the wound should be sprinkled with sulphur or a fungicide. If the roots are affected, the core of the cacti is probably also affected and the plant will almost certainly die.

The only two pests that bother cacti are a type of scale insect of the family Coccoidea, and nematodes. Scale insects may be killed by squirting the plant with a mixture of rubbing alcohol and nicotine. If nematodes are detected, the roots of the cactus must be cut off with a sharp knife and the plant repotted in sterile soil until it grows new roots. The old soil should be sterilized and the removed roots should be burned.

5. Propagate at least one plant by using one of the following methods: from seed, by cuttings, or grafting.

 * The link under 'References' has good material for this activity that you need to do. Enjoy!