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UNCG Biology 105 Study Guide, Part I

This outline of topics is designed to help students in Dr. O’Hara’s section of Biology 105 follow the main points made in the class. It is not a comprehensive presentation of all the course material; instead it is an outline that will help you keep the course structure and main points in mind. In studying for exams you should study your lecture notes, the syllabus, the poems-of-the-week, the assigned parts of the texts (including the Peabody Park website), and the species particularly described in class. The material in this section of the study guide (Part I) covers the first third of the course and includes all the main topics up to the first exam.


Natural History

The focus of this section of BIO 105 is natural history. “Natural history” is an old term that simply refers to the study of the earth and its diverse forms of life in a broad sense. In this sense, it was a term used 2000 years ago by the ancient Romans. The modern term “biology” for the study of living things was not coined until about 1800, and didn’t become popular until the late 1800s. A person who studies natural history is a “naturalist.” Many famous scientists of the past (like Charles Darwin) referred to themselves as naturalists, not biologists.

The Greek writer Aristotle (300s BC) wrote many works on animals and nature. The most famous ancient writer on natural history, though, was the Roman author Pliny (killed in AD 79 in the same eruption of Mt. Vesuvius that buried Pompeii and Herculaneum). Pliny’s multi-volume work Historia Naturalis (Natural History) was the basis for nearly all medieval writings on natural history. Most of these medieval works fall into two broad categories: the bestiaries (catalogs of animals, often describing their moral qualities) and the herbals (catalogs of plants, often describing their medicinal qualities).

Modern natural history got under way in the 1600s with authors such as John Ray who did new research into the types of plants and animals found in Europe. In the 1700s this work was continued in greater detail by researchers such as the Swedish naturalist Carl von Linné (known also by the Latin form of his name, Carolus Linnaeus). Linnaeus studied and taught at the University of Uppsala, and his important work, which went through several editions in the 1700s, was Systema Naturae (The System of Nature). In it he tried to describe and give names to all the animals, plants, and minerals (the three “kingdoms” of nature) that were then known.

The 1800s were a period of extensive research into the history of the earth and its life. Geology begins as a modern field of study in the early 1800s, and the major figure in the middle of the century is Charles Darwin. The first edition (1859) of his book On the Origin of Species presents an argument for how organisms have changed through time.

In the 1900s many specialties developed out of natural history (this had already begun in the 1800s), including modern ecology, systematics, geology, genetics, etc.

Peabody Park

Peabody Park is UNCG’s educational park, established in 1901 by George Foster Peabody. The park now comprises 34 acres, half of it native woodland and half open fields. The Park has been reduced substantially over the years by university construction, and the university plans to destroy even more of it. The Park woods are a fragment of the type of oak-hickory forest that covered this entire region centuries ago, and the Park fields are typical of the suburban/agricultural environment that is widespread here today. These two habitats are very different biological worlds. Most the species of plants found in the Park woods are native to North Carolina. Many of the plants in the fields, however, are introduced (or exotic, or alien; these are all synonyms). Thomas Gilbert Pearson, founder of the North Carolina Audubon Society and a president of the National Audubon Society, began his professional career on our campus and took students into Peabody Park soon after it was established.

You should visit the Peabody Park website for more information about the Park.

Where Are We?

The earth is the third planet from the sun (in order, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto). The earth is about 8000 miles in diameter, whereas the sun is about 800,000 miles in diameter. If the earth were a one-inch ball, the sun would be a ball about eight feet in diameter. (All these numbers are approximate; if you want exact numbers you can easily look them up in any reference book; what I want you to get is a general feeling for the magnitudes involved.)

The earth is 93 million miles from the sun. If the earth were a one-inch ball, the sun would be an eight-foot ball about a mile and a half away. That’s a long distance and a lot of empty space. By comparison, the distance on our campus from the Weatherspoon Art Gallery to Tower Village is a little less than a mile (about 0.9 miles). Imagine holding a one-inch ball at the Weatherspoon Gallery and looking at an eight-foot ball half again as far away as Tower Village; that’s how far the sun is from the earth.

The earth spins on its own axis, and at the same time it orbits the sun. The amount of time it takes for the earth to spin once on its axis is what we call a day; if you are standing on the earth you are facing the sun about half the time (daylight) and facing away from the sun (nighttime) the other half the time as the earth spins. Which way does it spin? From the point of view of a person on earth, the sun rises in the east and sets in the west, so: if you were to look down on the north pole from space you would see the earth spinning counter-clockwise. It takes 365 spins (days) for the earth to complete one orbit around the sun (actually 365 1/4, which is why we add an extra day to the calendar every four years). The amount of time for the earth to go once around the sun is what we call a year.

The moon orbits the earth while the earth orbits the sun. If the earth were a one-inch ball, the moon would be a 1/4-inch ball about 2.5 feet away. It takes about 27 days for the moon to make one orbit around the earth; that is the origin of the month as a unit of time, although in our modern calendars we have detached the notion of a month from the orbit of the moon and make our months 30–31 days long (and 28 for February).

What about surface irregularities on the earth? The highest mountains (the Himalayas) are about 6 miles above sea level, and the deepest ocean trenches (in the western Pacific) are about 7 miles below sea level. If the earth were a one-inch ball, 7 miles would be less than 1/1000 of an inch. So even though in human terms these surface features are enormous, the earth as a whole is very smooth and round.

The earth’s atmosphere is a very thin skin of gases that surrounds the earth, held in place by gravity (just like the water in the oceans). The atmosphere is mostly nitrogen (almost 80%), and the rest is oxygen (about 20%). (There’s another one or two percent of rarer gases mixed in.) Every breath you take is about 80% nitrogen: you breathe it in and out again and it does nothing. Only the oxygen in the air interacts with you physiologically.

The atmosphere has several layers, but you only need to remember two main ones: the troposphere, which goes from the surface up to about 7 miles in height, and the stratosphere, which goes from 7 to 30 miles in height. All weather phenomena (storms, clouds, hurricanes, etc.) take place within the troposphere. The highest cirrus clouds you can see are just about 7 miles up. Long airplane flights usually go up into the very bottom of the stratosphere in order to avoid the weather. Meteors (shooting stars) that you can see at night are tiny particles (most no bigger than a grain of sand) that usually burn up in the very thin outer layers of the atmosphere just above the stratosphere. Larger ones that survive the whole trip through the atmosphere are called meteorites once they are on the ground (“-ite” is a common suffix you will see in the names of many rocks and minerals).

We describe locations on the surface of the earth in terms of latitude and longitude. Let’s start with latitude, which measures angles north and south from the equator. The earth spins around an imaginary axis that runs from the north pole to the south pole. The equator runs around the middle. Imagine yourself as a point floating right at the center of the earth. The north pole would be above you, the south pole below you, and the equator right in your line of sight all around. Latitude is measured as an angle from the equator up (or down) toward the poles. The equator itself has a latitude of 0°; the north pole is 90° north latitude (usually written 90°N); the south pole is 90°S. (Now you can understand the title of Jarrell’s poem.) Our latitude in Greensboro, North Carolina, is about 36°N.

Longitude measures angles east and west, but east and west of what? There isn’t any naturally fixed line (like the equator) from which to measure east-west angles, so one was just chosen: the line that passes from the north pole south through Greenwich, England, at the site of the Royal Observatory (which is where many of these early calculations were performed). That line, called “the prime meridian,” represents 0° longitude, and every other point on earth described as being either west of Greenwich or east of Greenwich. We in Greensboro are about 80°W longitude. Our complete latitude and longitude, then, would be written 36°N 80°W. (The prime meridian crosses the equator in the Gulf of Guinea off the west-central coast of Africa; that spot is 0° longitude and 0° latitude.)

The parallels of latitude are concentric rings that get smaller and smaller as you go toward the poles. The meridians of longitude, by contrast, are not parallel: they all converge at the poles. Each meridian of longitude is a “great circle” (a full circumference of the earth), whereas the equator is the only parallel of latitude that is a great circle.

Your USGS (United States Geological Survey) topographic map is packed full of information about our local environment. You should be sure you know how to read most of the features on the map. The entire United States (actually the lower 48 states) have been mapped in this way; about 57,000 maps cover the country. This series of maps has a scale of 1:24,000, meaning one inch (or foot or centimeter) on the map represents 24,000 inches (or feet or centimeters) on the ground.

Each map in the series is named for some prominent locality or feature in the area covered; ours is called (not surprisingly) the Greensboro Quadrangle, and it was last revised in 1997. These maps show woods in green, open spaces in white, man-made features in black, water in blue, and contours in brown. The man-made features represented by black symbols include houses, schools, roads, churches, mines, and so on. The water features in blue include streams, lakes, and swamps. The contour lines in brown represent elevation above sea level, and at the bottom of the map you will see that the contour interval is 10 feet: that means that the lines are 10 feet apart in elevation on the ground. Some of the lines are marked with an elevation (they can’t all be just because there isn’t enough room on the map). If you look carefully at our campus you will see that its elevation is about 800 feet above sea level (about 850 at the water tower and about 750 along Market Street).

Why Is It So Cold Outside?

The existence of the seasons (spring, summer, fall, winter) is one of the most distinctive features of our environmental experience on earth. In the northern hemisphere (“half-globe”), June–August are hot and December–February are cold. The seasons are reversed in the southern hemisphere: in Australia, for example, June–August are the coldest months of the year, and December–February are hot beach weather.

The seasons are not caused by any variation in the distance of the earth from the sun during its annual orbit. The earth’s orbit is very nearly circular. The seasons are in fact caused by the tilt of the earth’s axis with respect to the plane of its orbit around the sun. The earth’s axis is not perfectly upright: it is tilted at an angle of 23°. At one point in the orbit the north pole is maximally pointed toward the sun (by 23°), and then six months later, at the other side of the orbit, it is maximally pointed away from the sun (by 23°). The single day when the northern hemisphere is most directly pointed toward the sun is called the summer (June) solstice, and it occurs every year about June 22. The single day when the northern hemisphere is most directly pointed away is the winter solstice (about December 22).

The different temperature averages between winter and summer are caused by differential heating that results from the earth’s tilt. In our summer, when the northern hemisphere is tilted toward the sun, the sun’s rays strike the earth from a higher angle and so are more “concentrated” (in a loose sense). During our winter, when the northern hemisphere is tilted away from the sun, the sun’s rays strike the earth at a lower angle and so their energy is spread over a larger area (in a loose sense).

At the summer (June) solstice, the sun illuminates not just the north pole, but the whole area around the pole all day long because the pole is tilted toward the sun. This illuminated area, which extends down from the pole 23°, is the arctic circle. There is a corresponding antarctic circle around the south pole that is fully illuminated on the December solstice.

From the point of view of an observer in North Carolina, the sun rises in the east, follows an arc across the sky reaching its highest point at noon, and then descends to set in the west. On the summer solstice, this arc is highest: the elevation of the sun at noon on the summer solstice is as high as it ever gets. Conversely, on the day of the winter solstice, the sun at noon is as low as the noon sun will get; the next day its noon elevation begins to climb higher and higher until six months later it has once again reached the high point on the summer solstice.

Here’s a thought experiment: suppose the earth was upright, and not tilted 23°. Would there be seasons? No, because the seasons are caused by the poles being tilted toward the sun at one time of the year and then tilted away from the sun six months later. The poles would still be cold and the equator warm, but there would be no seasonal variation.

Our tour of Tierra del Fuego and the Antarctic Peninsula illustrated a number of these principles, as well as other ones we will talk about later. (And be sure to remember a little geography: the southern end of South America includes parts of Chile and Argentina, and the very tip is called Cape Horn, not to be confused with the Cape of Good Hope which is the southern tip of Africa.) The photos I showed you were taken in December and January, the southern hemisphere summer, and the daylight period was about 22–23 hrs long each day (latitude 55–65°S). Much of what we know about the earth’s climate comes from data collected at research stations around the world like those shown on the tour. We also saw some of the impact that humans have had on this area (sealing in the 1800s, whaling in the 1900s, and habitat damage around the stations now). Parts of the Antarctic (like Deception Island) are geologically active, and illustrate the forces that have changed the earth’s surface over millions of years. We also saw many examples of biological adaptation: the fit of organisms to their environments (the black/white pattern of many seabirds, the ability of the “tubenose” birds to drink sea water and excrete excess salt, the glider-shaped bodies of many soaring birds that ride ocean winds for hours without ever flapping). We also saw individual variation within species, something that will be important later when we talk about natural selection.

What Time Is It?

In this section we are going to consider the age of the earth, and the history of ideas about the age of the earth. Our modern scientific understanding of this topic is the result of several hundred years of complex and fascinating debate. If you find the subject interesting, I recommend The Discovery of Time by Toulmin and Goodfield for more information.

First let’s look at our modern understanding. The universe as a whole is about 15 billion years old, and the earth is about 4.6 billion years old. “Billion” is such a huge number it’s almost impossible to grasp: a billion seconds is about 35 years. To get a feeling for these time spans, let’s suppose the whole history of the universe from big bang to present were compressed into a single year. If that were the case, the following dates and events (a “cosmic calendar” as Carl Sagan called it) will give you a feeling for the time spans we are dealing with.

  1 January         Origin of the universe
 14 September       Earth forms
 30 September       First life appears (known from microscopic fossils)
  1 December        Oxygen becomes common in the atmosphere
                     (it is a waste product of microbes and later plants)
 17 December        Multicellular animals diversify
                     (“the Cambrian explosion”)
 19 December        Land plants become common
                     (the land was essentially barren before this)
 25 December        First dinosaurs
 31 December, 10pm  First human-like fossils
 last 6 seconds     Human history from ancient Greece to the present

This understanding has developed over several centuries. In the ancient world, some people held a “steady-state view” of the universe, under which the earth and everything else has always been as it now is, eternal and unchanging. Others held what I call a “historical view” under which the earth and the universe originated at some particular point in the past, before which they didn’t exist. (The origin in this case might have been divinely caused, or it might have happened through some natural process.) But until the modern period (1600s onward) there was little real evidence to support either of these views.

When modern science gets underway in the 1600s we have a number of lines of evidence and argument developed concerning the history of the earth. The scriptural account found in the Hebrew Bible suggests that the earth is about 6000 years old. The nebular hypothesis, based on astronomical observations of what appeared to be other solar systems forming in the sky, proposed that the earth and the other planets condensed out of swirling gases. Rene Descartes, the French philosopher, was an advocate of this view in the 1600s. Immanuel Kant, the German philosopher of the 1700s, also held a version of the nebular hypothesis, and thought that “Millions and whole myriads of millions of centuries will flow on, during which always new worlds and systems of worlds will be formed.” This was an extraordinary view for his time (mid-1700s), and far beyond the common picture which saw the world as a few thousand years old.

Another line of evidence debated from the 1600s through the 1800s concerned “figured stones” that seemed to bear the designs or impressions of animals and plants. It wasn’t at all clear that these were in fact the remains of organisms; perhaps they grew in the rock like crystals. Many authors saw extinction as a theological impossibility. It took more than 100 years for people to agree that these “fossils” (“things dug up”) were in fact the remains of organisms, and that some of them were indeed permanently extinct.

The French naturalist Buffon conducted experiments on the question of the age of the earth in the 1700s. He heated iron spheres and recorded how long it took for them to cool down. Assuming the earth began in a molten state, he estimated the age of the earth to be 96,000 years. Not the billions of years of today, but far from the 6000-year account of scripture.

By the late 1700s two schools of thought had hardened. The catastrophists saw the earth as relatively young, and the earth’s features as having been caused by catastrophic events in the past that no longer occur today. The gradualists–also called actualists–saw the earth as much older, and the earth’s features as the product of ordinary (actual) causes added up gradually over a very long period of time. (And some people, like our poet William Cowper, thought they were all wasting their time.)

By the 1830s gradualism/actualism had won, and the Scottish geologist Charles Lyell’s Principles of Geology was the last nail in the catastrophists’ coffin. The rise of geology was greatly supported (coincidentally) by the industrial revolution, which increased the amount of mining going on in Europe, and which exposed the interior of the earth on an unprecedented scale thanks to all the excavation and blasting done to lay railroad lines. For the first time, scientists could study the interior structure of the earth over large areas of countryside.

The study of the interior of the earth revealed that it had a layered (stratified) structure. These strata were not random, but were arranged in recognizable sequences, often over many miles of territory. The study of these strata (stratigraphy) became the principal tool for the reconstruction of earth history. Particular fossils were often found in particular layers, and this allowed geologists to establish a series of relative dates (but not absolute dates) for many past events. Often strata were found tilted at an angle, demonstrating not only that a long period of time had been involved in depositing these sedimentary rocks, but that another long period of time had been involved in lifting them up from their original horizontal position. (Sedimentary rocks are formed horizontally when loose material such as sand or mud hardens. Limestone, sandstone, mudstone, and slate are all examples of sedimentary rocks. You can see some nice layered pieces in the stone-and-masonry wall around the Graham Building on campus.)

Geologists also discovered unconformities: locations where one set of strata overlay another set with a different orientation. One of the most famous examples was at Siccar Point in Scotland, where the enormous extent of earth history could be seen: one set of strata was formed, it was then tilted up, and then another layer was formed on top of it.

Absolute dating—attaching an actual year to a geological event—was rarely possible until the mid-20th century with the advent of radiometric dating. This technique is based on the rates of decay of radioactive substances: by measuring how much of a radioactive deposit has decayed, it is possible to estimate the date at which the deposit was formed. Radiometric dating is the basis for all our estimates of the major events in earth history today (for example, that the earth is about 4.6 billion years old).

The last great revolution in geology was the acceptance of the idea of continental drift in the 1960s. The idea had been worked out in some detail early in the century by Alfred Wegener on the basis of the shape of the continents (they seem to fit together like pieces of a jigsaw puzzle), but few people accepted it. Data collected from the Atlantic Ocean floor in the 1960s turned opinion around very quickly. The ocean floors were not ancient, as everyone had assumed, but were very young. The youngest rocks were along the mid-Atlantic ridge, and the rocks got older as you moved toward the continental margins. Further, the magnetic characteristics of the rocks on the east side of the ridge match those on the west side: they are mirror images of each other. The sea floor is in fact spreading apart, and the continents are being pushed away from each other. By putting all these data together it is possible to reconstruct a time when all the continents were united in a single land mass.

Our Neighbors

You should learn to identify the several species of plants around the Eberhart Building that will be pointed out in class. Some of them are listed at the end of this webpage. You should also know how to write or type the scientific name of an organism properly, and know the difference between native and introduced (also called exotic or alien) species, and between wild-growing individuals and those individuals planted as ornamentals. (Ornamentals may be native species or they may be introduced, but they have been individually planted by people where you see them.)

Naturalists have studied the diversity of animals and plants around the world for almost 300 years, but much is still unknown. Much of our knowledge comes from carefully collected and preserved specimens which can last for hundreds of years if well cared for in a research museum. You may have visited natural history museums and seen public exhibits there; what you have probably not seen are the many preserved research specimens behind the scenes that are used by scientists studying natural history. In Tort’s volume (p. 20) you can see some insect specimens collected more than 150 years ago that are still useful for research today.

Species You Should Know (and how scientific names work)

You don’t need to learn the scientific names of these species, only the English names, but you should recognize that the scientific names represent the formal names of species, and that when handwritten or typed they are conventionally underlined and when set in type they are italicized. The first part of the formal two-part scientific name of a species is the name of the genus to which the species belongs, and the second part is the name of the species itself. The name of the genus is always capitalized and the name of the species never is. For example: Cedrus deodara and Quercus phellos are both correct, whereas Cedrus Deodara and quercus phellos are both incorrect. If you are writing something that uses scientific names, once you have used the full form of the name once you may abbreviate the genus the second time (C. deodara), but it is never correct to use the species name alone (deodara) without the name of the genus. These rules are just conventions, but they are universally followed in good writing. If you don’t follow them your writing will look as funny as if you had written a person’s name as “george Bush” or “George bush” (in other words, it will look like you don’t know basic rules of writing).

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