For example, if you know the diameter of fov at 100x magnification, the diameter of the fov
at 1000x magnification = 1.78mm x 100 divided by 1000 = 0.178 mm or 178 micrometers.

1. The discovery of a virus called "mimivirus" in 1992 complicates the placement of viruses in the overall classification scheme for living organisms. Prior to this discovery, viruses were generally considered nonliving until they hijack a living cell. Officially, this virus got its name because it mimics bacteria (microbes) in size and complexity. It was placed in a new family of viruses, the Mimiviridae. Mimivirus was found inside an amoeba within a cooling tower in Bradford, UK. [The cooling tower was being investigated as the source of an influenza outbreak.] Mimivirus is the largest known virus, about 0.8 micrometers (800 nanometers) across. In fact it is larger than the bacterium causing gonorrhea.

Diameter of an Individual Mimivirus

metric unit	abbreviation**	decimal value
meter	m	0.000000800
millimeter	mm	0.000800
micrometer	µ	0.800
nanometer	nm	800
Angström	Å	8000

**html code for abbreviations may not show on all browsers.

With the exception of a some bacteriophages, viruses fall into two main morphological groups, those with cubical symmetry and those with helical symmetry. Until 1960, the only known examples of viruses with helical symmetry were those of plant viruses. The best studied example being the tobacco mosaic virus. The capsid denotes the protein shell that encloses the nucleic acid. It is composed of numerous repeating structural units. "Linear" viral capsids have RNA genomes that are encased in a helix of identical protein subunits. The length of the helical viral nucleocapsid is determined by the length of the nucleic acid.

Cubical viruses have the general molecular symmetry of an icosahedron. Although most viruses are not visible under an ordinary light microscope, mimivirus appears like a minute spheroid object under a compound microscope using an oil immersion objective (1000x magnification). An icosahedron has 20 identical equilateral triangles (facets), each subdivided into more equilateral triagular facets. There are electron micrographs of mimivirus available on the Internet. Simply do a search for mimivirus using one of the excellent search engines, such as google.com.

The mimivirus genome contains 1.2 million bases, more than many bacteria. The bases make up 1,260 genes, which makes it as complex as some bacteria. Most viruses use either DNA or RNA to carry their genetic information, but mimivirus has both of these nucleic acids. In addition, mimivirus can make about 150 of its own proteins, and can even repair its own DNA if it gets damaged. Normal viruses are not capable of protein synthesis or DNA repair on their own, they must rely on the organelles of their host cells for these activities. Whether mimivirus should be placed in an existing domain (superkingdom), or in its own domain, remains to be seen. For more information, see D. Raoult, et al. "The 1.2-Mb Genome Sequence of Mimivirus." Science Published On-line, DOI: 10.1126/Science.1101485 (2004); B. La Scola et al. "A Giant Virus in Amoebae." Science 299 (5615): 2033 (2003).

See The Three Domains Of Life

Some scientists have speculated that the evolution of eucaryotic cells involved the merging of two or more genomes, a phenomenon called symbiogenesis. Eukaryotic cells are characterized by the presence of membrane-bound organelles, including chloroplasts, mitochondria and nuclei. The origin of a complex cell has intrigued scientists for decades, and has been a strongly debated topic between evolutionists and creationists. According to the endosymbiont hypothesis, bacteria may be the progenitors of cellular organelles such as chloroplasts and mitochondria. A primitive nucleus (protonucleus) may have evolved from an intracellular virus; however, one weakness of this hypothesis is that viruses generally lack some of the key genes found in eukaryotes. The complex genome of mimivirus includes these genes, lending support to the evolution of a protonucleus from a virus.

See Symbiogenesis & The Endosymbiont Hypothesis

Typical viruses are not placed in the three major domains of life. They are much smaller and much less complex than cells. They are macromolecular units composed of DNA or RNA surrounded by an outer protein shell. They have no membrane-bound organelles, no ribosomes (organelle of protein synthesis), no cytoplasm (living contents of a cell), and no source of energy production of their own. They do not exhibit autopoiesis--i.e. they do not have the self-maintenance metabolic reactions of living systems. Viruses lack cellular respiration, ATP-production, gas exchange, etc. However, they do reproduce, but at the expense of the host cell. Like obligate parasites, they are only capable of reproduction within living cells. In a sense, viruses hijack the host cell and force it to produce more viruses through DNA replication and protein synthesis. Outside of their host cells, viruses can survive as minute macromolecular particles. Viruses may attack animals and plants. Infectious human viruses can be dispersed though the air (airborne viruses) or body fluids (HIV virus). Epidemic viruses (such as HIV) that are passed from person to person via sexual conjugation are remarkably similar to computer viruses. Unfortunately in humans there is no resident antivirus program to alert you of a potential infection, or to quickly scan your body and delete the invader once it has entered your system. Humans must rely on their amazing antibody and cell-mediated immune responses, some of the most complex and remarkable achievements in the evolution of living systems.

See The Five Major Kingdoms Of Life Biological Viruses vs. Computer Viruses See The WAYNE'S WORD Virus Article

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1a. The following information and image is from Wikipedia (accessed 2 March 2020): Coronavirus is the common name for the virus family Coronaviridae. Coronaviruses cause diseases in mammals and birds. In humans, the viruses cause respiratory infections, including the common cold, which are typically mild, though rarer forms such as SARS, MERS and COVID-19 can be lethal. Symptoms vary in other species: in chickens, they cause an upper respiratory disease, while in cows and pigs coronaviruses cause diarrhea. There are no vaccines or antiviral drugs to prevent or treat human coronavirus infections. They are enveloped viruses with a single-stranded RNA genome and a nucleocapsid of helical symmetry.

The name "coronavirus" is derived from the Latin corona, meaning crown or halo. The name refers to the characteristic appearance of virions (the infective form of the virus outside a host cell) by electron microscopy, which have a fringe of large, bulbous surface projections creating an image reminiscent of a crown or solar corona. In this illustration of a coronavirus virion, the club-shaped viral spike peplomers, coloured red, create the look of a corona surrounding the virion, when viewed with electron microscope. For health care workers in contact with coronavirus patients, the CDC recommends a more specialized type of face mask called N95--one that is individually fitted to a person's face to create a seal and that filters out 95 percent of particles that are at least 0.3 microns in diameter. This is diameter of a coronavirus virion. [A micron (micrometer) is 1/1,000th of a millimeter or 0.001 mm]

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2. This is the width of an oval (elliptical) spore. Spores of this size can easily escape from a folded (closed) paper envelope that is not airtight. Anthrax (Bacillus anthracis) is one of the microorganisms used in biological warfare because strains have been developed that are extremely infectious through the skin and through inhalation. In addition, it forms highly resistant spores that can survive for long periods. Approximately one teaspoon or two grams of anthrax may contain up to 20 billion spores. With an average infection rate of 10,000 spores per person, this is theoretically enough spores to infect 2 million people with inhalation anthrax.

Left: Highly magnified view (2000x) of human pus showing white blood cells (called neutrophils) with deeply-lobed purple nuclei. The minute paired dots (red arrow) are diplococcus gonorrhea bacteria (Neisseria gonorrhoeae). Each dot (coccus bacterium) is only about 0.5 micrometers in diameter. Some of the neutrophils have ingested the bacteria through phagocytosis. Right: A culture of rod-shaped anthrax bacteria (Bacillus anthracis). Some of the bacteria have divided by fission (red arrow). [Both images came from old (circa 1960) prepared microscope slides enhanced with Adobe PhotoShop by W.P. Armstrong.]

Successive Orders Of Magnitude: Galaxy To A Proton

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3. One human nucleus contains 46 chromosomes (single chromosomes during interphase). These 46 chromosomes comprise about 6 feet of DNA (2 meters). This amount of DNA was previously thought to contain about 100,000 functional genes, but that number has now been reduced to about 30,000 genes (one percent of the total DNA in the nucleus). In terms of information storage, the genetic information in a cell is roughly equivalent to 500 printed volumes of Encyclopedia Brittanica (12 characters per inch).

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4. Mature sperm (spermatozoa) are composed of three distinct parts: a head, a middle piece (midpiece), and a tail (flagellum). The middle piece and tail contain microtubules in the characteristic 9 + 2 pattern of cilia and flagella (see animal cell illustration). In the middle piece, mitochondria are packed around the microtubules and provide the energy for movement. The journey of a single sperm in the female reproductive tract is analogous to a salmon swimming ten miles upstream to spawn. The head contains a nucleus covered by an outer cap called the acrosome which stores enzymes needed to penetrate the cellular and glycoprotein layers surrounding the egg.

Surgical sterilization of a man is called a vasectomy. Each of the two vas deferentia (sperm ducts) from the left and right testicles are cut and tied in two places, and the portion between the ties removed. Residual sperm may be present in the vas deferentia for up to a month following a vasectomy; therefore, periodic microscopic examinations are recommended until sperm are no longer visible in semen samples.

Microscope image of human sperm in semen (1000x). The illustration insert shows the acrosome, head and middle piece of a human spermatozoan.

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5. A baseball-sized puffball (Calvatia gigantea) in San Diego County, California. The inside is filled with a dark mass of spores intermingled with threadlike hyphae (capillitium). The close-up view of spores (right) was taken at 1,000x. Each spherical spore has a diameter of about 1/200 mm (5 µm), slightly smaller than a human red blood cell (7.5 µm). Depending on the species, puffballs range in size from a baseball to a basketball. When they are mature, the puffball releases millions of spores into the air in a cloud of black dust. This can easily be demonstrated if you accidentally kick one. According to David Arora (Mushrooms Demystified, 1986), a large puffball may contain 7 trillion spores. Lined up single file, this number of spores would extend around the earth's equator. If each spore produced a puffball the size of a basketball, the resulting puffballs would extend from the earth to the sun and back!

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6. Lichens are a symbiotic relationship between algae and fungi. The main body of a lichen is composed of fungal tissue (usually class Ascomycota) with photosynthetic algal cells (usually division Chlorophyta) embedded within this fungal mass (mycelium). The spores are produced by the fungal component or mycobiont, usually in a cup-shaped body called an ascocarp. Lichen spores can be 1-2 micrometers in Acarospora chlorophana, or up to 40 micrometers long in Diploschistes scruposus (left). The size, color and shape of spores are useful traits in separating different species of lichens. Spores up to 40 micrometers or longer are considered large.

Muriform Spore Of Diploschistes muscorum Muriform Spores Of Rhizocarpon disporum Two-Celled Spores Of Dimaelaena radiata

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7. The width (diameter) of a human hair ranges from very fine (0.017 mm) to very coarse (0.181 mm). The right image shows a fine human hair at 1,000 x magnification. The hair width is 0.070 mm or 70 micrometers. With the unaided eye the single hair shaft is visible when placed on a sheet of white paper.

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8A. A simple test for the resolving power of the unaided human eye:

A. Two fine human hairs are placed 70 micrometers apart. Each hair is approximately 70 micrometers in width (diameter). With 20-20 vision you should be able to differentiate between the two hairs at the proper focal distance. B. When placed closer to each other (about 15 micrometers apart), the two hairs appear to blend together and cannot be differentiated with the naked eye. A hand lens or magnifying glass is necessary to differentiate between the two hairs. Although the hairs can be seen on a white background, they cannot be resolved if they are placed close together. The minimum resolution for a computer monitor is 72 dots per square inch (dpi), otherwise the image becomes pixelated. Printed photos are also composed of dot patterns. Above 150 dpi, the dots generally blend together and cannot be resolved. Under a hand lens or microscope the dots can easily be observed. 8B: "Floaters in the Eye" by Harvey E. White and Paul Levatin. Scientific American June 1962: "The diameter of the cone cells decreases progressively toward the center of the fovea [Where visual acuity is highest.] In the most closely packed area of this center of visual acuity the average center-to-center distance between cone cells is one and a half to two microns. When the diffraction pattern of a floater falls on a patch of the central fovea, it illuminates some of the cones in the mosaic and leaves others dark. The four-micron space between the outer rings of the pattern that is resolved by the fovea is approximately equal to two cone widths. it would appear that two lines in a pattern must be two cone widths apart if they are to be seen as separate. This anatomical requirement would specifically limit the resolution of which the eye is capable."

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9. Certain epiphytic orchids of the tropical rain forest produce the world's smallest seeds weighing only one 35 millionths of an ounce (1/35,000,000) or 0.81 micrograms. Some seeds are only about 1/300th of an inch long (85 micrometers). One seed capsule from a single flower may contain up to four million seeds. They are dispersed into the air like minute dust particles or single-celled spores, eventually coming to rest in the upper canopy of rain forest trees.

See The Minute Seed Of A Coral-Root Orchid

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10. This minute one-seeded fruit is approximately 1/100 of an inch long and weighs about 70 micrograms or 1/400,000 of an ounce. Compare this tiny fruit with the most massive pumpkin that weighs over 1000 pounds (over 450,000 grams).

Wolffia: The World's Smallest Fruit

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11. The plant body of the Australian species Wolffia angusta is only 0.6 mm long (1/42 of an inch). It weighs about 150 micrograms or 1/190,000 of an ounce. This is the world's smallest flowering plant, rivaled in minuteness by the Asian species W. globosa.

Wolffia: The World's Smallest Flowering Plant Strange Duckweeds From Far Away Lands

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12. The Australian tree (Eucalyptus regnans) is the world's tallest flowering plant. Some of the largest trees are over 300 feet tall, rivaling in size the California coast redwood (Sequoia sempervirens).

See Botanical Record-Breakers

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13. The planet earth has a diameter of about 8,000 miles (13,000 kilometers) or 13 billion (13,000,000,000) millimeters. It has a volume of about one nonillion (1 X 10³⁰) cubic millimeters. This astonishing volume is roughly equivalent to the volume of one nonillion wolffia plants packed together after 4 months of asexual budding!

If a water molecule is represented by 100, then a wolffia plant is about 1020 power larger than the water molecule. The earth is about 1020 power larger than a wolffia plant, or 1040 power larger than the water molecule.

Successive Orders Of Magnitude: Galaxy To A Proton

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14. A hair follicle mite (Demodex brevus) in your nose!

Hair follicle mites of the genus Demodex are among the smallest multicellular animals. They were first described in humans in 1841 by Frederick Henle who reported this minute parasite from "miliary glands" of the ear canal. He was uncertain about the parasite's taxonomic position in the animal kingdom. [Henle is also known for the Henle's loop in the vertebrate nephron.] Another scientist from this time period by the name of Berger (1845) thought it was a member of the phylum Tardigrada. Tardigrades are minute animals often found on lichens and mosses. According to Desch and Nutting (The Journal of Parasitology 58 (1): 169-177, 1972), there are two species of follicle mites on humans. Demodex folliculorum measures 0.3 to 0.4 mm in length and typically occupies hair follicles. It also called an "eyelash mite" because it commonly occurs in follicles at the base of eyelashes. Demodex brevis is about half that size (0.15 to 0.2 mm) and typically lives in sebaceous glands adjacent to hair follicles. The latter mite is only about the size of a unicellular Paramecium and appears to be the species I found in my nose. Illustration (left) modified from T. Ross and photographs of dorsal side of D. brevus by W.P. Armstrong.

Demodex brevis (184 micrometers in length) compared in size with a freshwater protozoan Paramecium bursaria. Magnification 400x.

More Information & Images Of The Follicle Mite Demodex brevus

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15. The blue whale (Balaenoptera musculus) is the largest animal to have ever existed on Earth. At 100 feet in length and weighing almost 200 tons, it is larger than the largest herbivorous dinosaurs. Fossil evidence fom Patagonia indicates that 70 ton titanosaurs were the largest animals to have ever walked on land.

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16. California coast redwood (Sequoia sempervirens) is the tallest documented living tree at 379 feet (116 m).

World's Tallest Tree

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17. Diameter of corn silk (Zea mays) through which each pollen tube travels.

In 1978, a Bulgarian dissident, Georgi Markov, was assassinated in London after being pricked by a ricin-tipped umbrella. Ricin causes a slow and painful death through blood poisoning and a breakdown of the circulatory system. There is no known antidote for ricin poisoning. Even before the tragic terrorist plane crashes into the Trade Center Twin Towers in New York, some airports hand-inspected umbrellas packed in carry-on luggage. Following the Gulf War, UN investigator teams (UNSCOM) discovered that Iraq was purifying ricin for possible use in biological warfare, along with anthrax (Bacillus anthracis), botulism toxin (Clostridium botulinum), gas gangrene (C. perfringens), and aflatoxin (Aspergillus parasiticus). From: Facts on File News Services (23 January and 13 February 1998).

According to The Washington Post Online (16 November 2001), Osama bin Ladens's al-Qaida network also had working plans for making ricin. Instructions for preparing the poison were found in the cellar of an abandoned house once used as a terrorist training center. According to the article, the ricin may be ingested, injected and inhaled. The article also states that the laxative effect of castor oil is due to ricin, but this is doubtful. Castor oil is derived from the seeds of the castor bean. It contains 87 percent ricinoleic acid, a fatty acid with many industrial uses, along with small amounts of several other fatty acids including oleic (7%), linoleic (3%), palmitic (2%) and stearic (1%). The deadly protein ricin is not a component of purified castor oil.

2. Plasmolysis: Shrinkage of the protoplast or cell contents due to water loss when a drop of salt water (NaCl) is added to the Elodea slide. Because of all the salt ions (Na+ and Cl- ions) outside the cell membrane of each Elodea cell, water molecules move out of the cell membrane causing the cell membrane and it contents to shrink into a blob in the center of the cell wall. The porous, cellulose wall does not shrink because the salt ions easily pass through the wall but cannot pass through the membrane. Therefore, the cell membrane (not the cell wall) loses water molecules and shrinks.

1. Visit the restroom during the latter part of the half-hour commercial/preview period, just before the movie starts.

2. Do not drink diuretics, such as coffee or tea, three hours prior to the movie, and definitely not during the movie.

3. Do not maintain your urine at a low specific gravity by drinking large quantities of water before or during the movie. In fact, it is wise to reduce your intake of all beverages during the movie.

4. Eat salty popcorn during the movie. If it makes you thirsty, suck on some candy mints. As the salt content of extracellular fluids in the blood and kidneys goes up, so does the osmotic concentration and specific gravity of these fluids. Special sensors in the brain sense this change in salt concentration and stimulate the pituitary to secrete antidiuretic hormone (ADH). ADH is carried to the kidneys in the blood where it stimulates cells in the posterior convoluted tubules and the collecting ducts to reabsorb more water. In addition to returning more water to the blood, ADH also reduces sweating and causes constriction of arterioles. ADH is also referred to as vasopressin because it increases the blood pressure. These homeostatic actions of ADH result in decreased water loss and more concentrated urine. Consequently, your bladder does not fill as rapidly.

   Note: If you are concerned about consuming large quantities of unhealthy theatre popcorn, try carrying a small Himalayan rock salt plate and lick it during the movie. You might even get some valuable trace elements in this slab of halite mined in Pakistan. See image of salt plate below.

5. As a last resort, wear waterproof undergarments.

Another hands-on demonstration for depth of field utilizes the wing of a common house fly (Musca domestica). These were plentiful in the windows of old biology lab rooms at Palomar College. Students are asked to determine whether there are hairs on both sides of the wing. This requires careful focusing up and down because depth of field is limited to one layer of hairs when using the compound microscope. [Fly image from Wikipedia.]

2. Plasmolysis: Shrinkage of the protoplast or cell contents due to water loss when a drop of salt water (NaCl) is added to the Elodea slide. Because of all the salt ions (Na+ and Cl- ions) outside the cell membrane of each Elodea cell, water molecules move out of the cell membrane causing the cell membrane and it contents to shrink into a blob in the center of the cell wall. The porous, cellulose wall does not shrink because the salt ions easily pass through the wall but cannot pass through the membrane. Therefore, the cell membrane (not the cell wall) loses water molecules and shrinks.

3. Hypertonic and Hypotonic: When comparing two solutions, such as the inside of a red blood cell (RBC) with the solution they are placed in, the solution with the greater salt concentration is hypertonic, while the solution with the lower salt concentration is hypotonic. Compared with the RBCs, a 10% NaCl solution is hypertonic while a 0.1 % NaCl is hypotonic. Since the latter solution is almost pure water, the blood cells are actually hypertonic by comparison.

4. Osmosis: Movement of water molecules from a region of high concentration to a region of lower concentration through a differentially permeable cell membrane. In biology, this definition should include water molecules and cell membrane.

5. Diffusion: Movement of molecules or ions (charged atoms) from a region of high concentration to a region of lower concentration. This definition does not include a cell membrane and refers to molecules of any substance, not specifically water. Examples of diffusion include perfume molecules in the air, ether molecules in a classroom, sugar molecules in a cup of coffee, methylene blue molecules in a bowl of clear gelatin, etc.

6. Active Transport: Movement of molecules and ions through a cell membrane against a diffusion gradient (i.e. from a low to a higher concentration). This movement involves carrier proteins (channels) in the cell membrane and requires energy in the form of ATP (adenosine triphosphate). Active transport occurs during a nerve impulse or action potential (wave of depolarization) when a nerve cell membrane suddenly becomes permeable to sodium ions. The inflow of sodium ions moves quickly along the nerve cell axon, activating an adjacent nerve cell or muscle. As sodium ions rapidly move across the membrane to the inside of the axon, the polarity of the membrane changes. This reversal in polarity causes the sodium channels to close and the potassium channels to open. Now potassium ions move from inside the axon to the outside of the axon in a wave of repolarization.

During a lethal injection, a fatal dosage of potassium chloride is administered intravenously. The large influx of potassium ions interrupts the wave of depolarization (action potential) to the heart muscle resulting in cardiac arrest. A paralyzing agent, such as pancuronium bromide or tubocurarine chloride, plus a lethal dosage of a general anesthetic, such as sodium thiopental (sodium pentothal) are usually given before the potassium chloride is administered. Tubocurarine is the active ingredient of curare, an extract from the bark and stems of the South American vine (Chondodendron tomentosum). Amazonian Indians use the gummy extract to coat the poison darts of their blowguns. The alkaloid D-tubocurarine blocks acetylcholine receptor sites at neuromuscular junctions, causing relaxation and paralysis of muscles, including respiratory organs and the heart.

6. Halophyte: A plant adapted to soil or water containing a high salt concentration. The root cells contain a salt concentration higher than the water they are growing in. Since they are hypertonic compared with the water or soil, the root cells can take in water molecules and do not become plasmolyzed. Good examples of halophytes are the seagrasses (see link below), red and black mangroves (Rhizophora and Avicennia), salt grass (Distichlis) and salt bush (Atriplex). There are also species of bacteria and algae that are extremely halophilic (salt-loving), living in saturated brine and salt crust (see link below).

7. Imbibition: The movement of water molecules into a porous, colloidal substance causing it to swell. Enormous pressures can be produced by imbibition, sufficient to split boulders apart.

8. Light Reactions of photosynthesis: The production of ATP and NADPH₂ within the grana region (thylakoid membranes) of a chloroplast using light energy.

9. Dark Reactions of photosynthesis (also known as the Calvin Cycle): The conversion of carbon dioxide into glucose within the stroma region of a chloroplast. This complex series of reactions requires ATP and NADPH₂ from the light reactions.

10. Fluorescence: The emission of a reddish glow when a beam of light is directed on a chlorophyll solution.

11. Bioluminescence: The emission of light by an organism or population of organisms. This phenomenon involves the oxidation of luciferin in the presence of ATP and the enzyme luciferase. Examples of bioluminesence include dinoflagellates causing "red tide," lightning "bugs" (beetles), glow worms (beetle larvae), comb jellies (phylum Ctenophora), the deep sea angler fish, and a remarkable fungus called the jack-o-lantern mushroom.

2. To calculate the specific gravity of a block of wood, divide the numerical value for its weight by the numerical value for its volume. Specific gravity is expressed as a number, without any units of measurements. For more information about this subject, refer to the Wayne's Word article about hardwoods.

2. Three obvious characteristics of plant cells that are not found in typical animal cells are: a cellulose cell wall, a large central vacuole, and chloroplasts (site of photosynthesis).

3. The cells within an organism are basically similar. They differ in their size, shape and function. Cells are organized into tissues (nerve, muscle, adipose, epithelial, etc.) and tissues are organized into organs (heart, liver, brain, kidneys, etc.). Although they are not as anatomically complex, plants also have organs (leaf, root, flower, etc.). Plants probably equal or exceed the complexity of animals when it comes to their incredible number of diverse biochemical reactions and products.

Unlike other cells in the filaments of cyanobacteria, the heterocyst is nonphotosynthetic. As the heterocyst matures, the photosynthetic membranes (thylakoid membranes) become contorted or reticulate compared to regular photosynthetic cells of cyanobacteria, and they become non-photosynthetic (and do not produce oxygen). This fact is especially noteworthy because nitrogen fixation requires the essential enzyme nitrogenase, and the activity of nitrogenase is greatly inhibited by the presence of oxygen.

The fowing explanation is from Jim Deacon of the Institute of Cell and Molecular Biology, The University of Edinburgh.

Two molecules of ammonia are produced from one molecule of nitrogen gas. The reaction requires 16 molecules of ATP and a supply of electrons and protons (hydrogen ions) plus the enzyme nitrogenase. Nitrogenase consists of two proteins, an iron protein and a molybdenum-iron protein. The reaction occurs while N2 is bound to the nitogenase enzyme complex. The Fe protein is first reduced by electrons donated by ferredoxin. Then the reduced Fe protein binds ATP and reduces the molybdenum-iron protein, which donates electrons to N2, producing HN=NH. In two futher cycles of this process (each requiring electrons donated by ferredoxin) HN=NH is reduced to H2N-NH2, and this in turn is reduced to 2 NH3. Depending on the type of microorganism, the reduced ferredoxin which supplies electrons for this process in generated by photosynthesis, respiration or fermentation.

2. Nitrification: A prokaryotic skill in which the ammonia from nitrogen fixation is converted into nitrites (NO₂-) and nitrates (NO₃-).

3. Ammonification: A prokaryotic skill in which ammonia is formed from the decay of protein.

Although our atmosphere is almost 80% nitrogen gas (N₂), the element nitrogen is unavailable to plants in the inert gaseous state. Nitrogen fixation, nitrification, and ammonification make nitrogen available to autotrophic plants and ultimately to all members of the ecosystem. Symbiotic relationships such as the water fern (Azolla) are especially interesting because this little aquatic fern obtains a rich supply of nitrogen in the form of ammonia from the cyanobacteria (Anabaena) living within cavities in its leaves.

4. Denitrification: A prokaryotic skill in which nitrites and nitrates are converted back into unusable, inert, nitrogen gas by bacteria in the soil and water. Luckily for plants and animals on the earth, natural nitrogen fixation exceeds denitrification. However, the serious problem today is that humans have greatly accelerated nitrogen fixation by the tremendous production of chemical fertilizers. These fertilizers eventually get into lakes and ponds resulting in excessive growth (blooms) of filamentous algae which form scummy masses on the water surface. Although algae produce oxygen through photosynthesis, the decay (oxidation) of these massive algal blooms actually depletes the oxygen supply in the water, resulting in massive fish kills and putrefaction of lakes and ponds. The biological term for this process is called eutrophication. Although eutrophication is a natural process it has been accelerated by humans to an alarming rate. It is even beginning to be noticeable in clear mountain lakes, such as Lake Tahoe, where the water is not quite as clear.

5. The three major types of archaebacteria are: (1) Methanogens (methane-producers) which are responsible for swamp gas; (2) Extreme Thermophiles that live in hot springs and black smokers (heat vents) at the bottom of the ocean; and (3) Extreme Halophiles (halobacteria) that live in saturated brine and salt crust.

6. The archaebacteria have some characteristics that are very different from the true bacteria (eubacteria) and cyanobacteria in the kingdom Monera. Lipids of archaebacterial cell membranes differ considerably from those of both prokaryotic and eukaryotic cells, as do the composition of their cell walls and the sequence of their ribosomal RNA subunits. In addition, recent studies have shown that archaebacterial RNA polymerases resemble the eukaryotic enzymes, not the eubacterial RNA polymerase. Some authorities hypothesize that eukaryotic organisms may have evolved from ancient archaebacteria (archae = ancient) rather than from the common and cosmopolitan eubacteria. The archaebacteria could have flourished more than 3 billion years ago under conditions previously thought to be uninhabitable to all known life forms. Although many conservative references place the archaebacteria in a separate division within the kingdom Monera, some authorities now recognize them as a new 6th kingdom--The kingdom Archaebacteria. [Some references state that the genes of archaebacteria are edited before they are translated into protein, a complex pathway known to occur in eukaryotic cells; however, more scholarly references do not mention this DNA similarity with eukaryotic cells, so it will not be postulated here.]

The vacuoles of some members of the duckweed family (Lemnaceae) contain calcium oxalate crystals that are visible under 400x magnification. Crystals of calcium oxalate may be needle-like (raphide crystals) or many faceted like a glistening diamond (druse crystals). The raphide crystals in the plant body of Lemna species appear like minute microscopic needles. Needlelike raphide crystals are also found in members of the arum family (Araceae), including the common house plant called Dieffenbachia. The crystals may cause irritation and swelling of the tongue if you chew on the leaves of this plant. Comparative DNA studies have shown that arums are closely related to the duckweed family. For more information about this remarkable family of flowering plants, refer to the following link: