Sometimes a practice or belief claims to be science but does not follow the scientific method or cannot be proven reliable through experimentation. These practices are examples of pseudoscience, which literally means “fake science. ” Charms, astrology = stars, and phrenology’= reading the bump on skull 1. 03 * In the mid asses in the Netherlands, the scientist Antonio van Leeuwenhoek developed the first known microscope using a single magnifying lens. He was the first person to observe microscopic cells that we now know to be bacteria and blood cells.
Leeuwenhoek shared the designs of his microscope, as well as his observations, with the scientific community. * Around 1655 the English scientist Robert Hooked used van Leeuwenhoek ideas and made the first compound light microscope, which used more than one lens to magnify an object. He examined thin slices of cork, a dead plant material, and saw that the cork was made up of thousands of empty chambers. Hooked named these small chambers “cells” after the rows of small rooms found in a monastery. * With each advance in microscope technology, biologists are better able to examine the microscopic cells that make up living organisms.
Let’s explore some of the microscopes commonly used today. * Light microscopes were the first invented and are still the most commonly used in biology laboratories today. In these microscopes, light travels through the specimen or bounces off the surface of the specimen and then passes through glass lenses. The lenses bend the beam of light to magnify the image viewed through an eyepiece. * A dissecting microscope is one type of light microscope. It is used for examining organisms at relatively low power, magnifying the image up to 40 times the size of the specimen.
A beam of light is reduced above the stage and reflects off of the specimen’s surface, passing through the glass lenses that magnify the image. * The dissecting microscope is useful for examining organs and tissue during a dissection. You can also use it to view the surfaces and details of leaves, stems, mold, spores, or other small objects that can be seen with the naked eye but require magnification in order to be examined closely. * Compound light microscopes are the most commonly used light microscope. They can be found in most science classrooms and biology laboratories.
The light source is low the stage, and the light shines up through the thin specimen and then through the magnification lenses. You can prepare the specimen for viewing by placing it on a rectangular glass slide. It can be stained with a dye that adds contrast to nearly transparent cells. Compound light microscopes usually have more than one magnification power, ranging from 40 times up to 400 or even 1,000 times the true size of the specimen. * Compound light microscopes can be used to view tissue samples, blood, microorganisms in pond water, microscopic cells, and some of the larger details within the cells.
Two important factors in microscopy are magnification and resolution. Magnification is how much larger an object appears compared to its real size. Resolving power is a measure tot the clarity tot the object. We can design light microscopes to magnify to very high powers, but the properties of light limit the resolving power. * There is decreased clarity with increased magnification. This is why light microscopes usually do not magnify beyond 1,500 times the true size of the specimen. They cannot resolve detail finer than about 0. 2 micrometers, which is the size of a small bacterium cell.
Because light microscopes re limited in resolve and magnification, biologists were not able to study the small details and complex structures inside cells until the development of electron microscopes. * Electron microscopes use beams of electrons, instead of light, to view specimens. The shorter wavelengths of electrons give these microscopes a much higher resolving power, up to 0. 2 manometers. This is 1,000 times greater than the best resolving power of a light microscope. A disadvantage of electron microscopes is that they cannot be used to view living specimens because the methods used to prepare them for viewing kills cells.
These microscopes use electromagnets instead of glass lenses to magnify the image of the specimen because electrons cannot pass through glass. The electromagnets magnify the image by bending the electron beams and then projecting it onto a screen or photographic film for viewing. Transmission electron microscopes and scanning electron microscopes are two types of electron microscopes. * Transmission electron microscopes (TEM) pass a beam of electrons through a thin specimen similar to how a compound light microscope transmits light. Scientists can apply stain to the specimen to increase contrast in the image.
Transmission electron microscopes are mainly used for studying the internal structures of cells that cannot be viewed under light microscopes. * Notice that the magnified images of the specimen are produced in black and white. Scientists can use computers to add artificial color to enhance visibility when needed. * Scanning electron microscopes (SEEM) are useful for studying the details of a specimen’s surface. The electron beam scans the specimen’s surface, which is coated with a thin layer of gold metal. The electrons that scatter off of the gold-coated surface are focused onto a screen, forming a detailed image of the specimen surface.
The image is three- dimensional and black and white. * Microbiologists study living organisms that are invisible to the naked eye, such as bacteria and fungi. They can also study viruses, which are not living. * There are many different types of microbiology: medical microbiology, environmental microbiology, veterinary microbiology, food microbiology and pharmaceutical microbiology. These fields investigate the ways microbes affect our health, the environment, animals, and our food supply. 1. 04 * Two main types of chemical bonds are ionic and covalent bonds.
An ionic bond is the attraction of a positively charged ion to a negatively charged ion. Atoms can gain or lose electrons to become charged ions. Positive ions and negative ions are attracted to each other because of their opposite charges. Because of this opposite attraction, ionic bonds are very strong. Atoms that are atomically bonded together form an ionic compound. Table salt, also known as sodium chloride (Nasal), is an example tot an ionic compound. The attraction between the positive sodium ion (An+) and the negative chloride ion (CLC-) is an ionic bond. A covalent bond forms hen two atoms overlap their outer energy levels in order to share pairs of valence electrons. The shared electrons are attracted to the nuclei of both atoms. Atoms that are covalently bonded together form a covalent compound, which can also be called a molecule. * Cohesion * Water is a polar molecule with a partially positive end and a partially negative end. The negative end of one water molecule attracts the positive ends of other water molecules surrounding it. Because of this attraction, the water molecules act like tiny magnets and cling to each other.
This attraction between the molecules is why water dads up on surfaces like a tabletop or the hood of a car. * Adhesion * Just as cohesion is the clinging of something to itself, adhesion is the clinging of one substance to another. The polarity of water attracts many other substances. This is especially noticeable when you fill a narrow tube, such as a graduated cylinder or straw, with water. Notice that the edges of the water’s surface are higher than the center, because the water adheres to the surface of the tube. * Surface Tension * Surface tension is a measure of how difficult it is to stretch or break the surface of a liquid.
The hydrogen bonding between water molecules gives water a stronger surface tension than many other liquids. The surface molecules form hydrogen bonds to the molecules around them and below them but do not have attractions pulling them from above. This uneven hydrogen bonding pulls surface molecules down and closer together. The surface tension almost forms a thin invisible film over the water’s surface. * You can observe surface tension by slightly overfilling a water glass. The water will stand over the rim. Surface tension allows some insects to walk on water without breaking the surface. Capillary Action In a plant, water moves up the roots and through the leaves through microscopic vessels. The water molecule at the surface of the leaf is attracted to the water molecule below it by hydrogen bonding. As that top molecule begins to evaporate and leave the leaf, it pulls on the molecule below. The new surface water molecules will pull the same way on the water molecule below it. The water molecules that are being pulled up the vessel by cohesion will also adhere to the sides of the vessel to prevent backfill.
This teamwork of adhesion and cohesion is called capillary action and allows water transport in even the tallest of trees. Water is one of a few substances that expand when they freeze. When water freezes, the hydrogen bonding between the molecules causes them to form rigid structures resembling six- sided hexagons. This specific arrangement requires more space than the arrangement of water molecules in liquid water. This makes frozen water, also known as ice, less dense than liquid water, allowing it to float. Density is a ratio of mass to volume.
One liter of liquid water weighs more than one liter of frozen water, because there are fewer water molecules present in the liter of ice. * If ice was not able to load in liquid water, lakes and ponds would freeze from the bottom up. This would kill the marine life in these bodies of water, destroying those ecosystems. Instead, the floating ice helps insulate the water below. This prevents the rest of the water from freezing and allows life to continue to live under the surface during the winter. * Universal Solvent * Water is oaten called the universal solvent because many deterrent substances dissolve well in water.
Ionic compounds, such as salt, can dissolve in water, as can most polar molecules such as sugar. Both of these types of compounds mix well with eater because they have positive and negative charges that are attracted to the negative and positive ends of the water molecules. * Examine the animation below to see an example of how the charged ions in table salt are attracted to the partially charged ends of the water molecule. Notice that as the concentration of hydration ions increases, the pH value decreases (becomes more acidic). It can be easy to confuse this, so be careful when you use the pH scale or compare pH values.
Type I [HUH+] I pH I Example I Acids | 1 x 100 | 1 x 10-1 II | 1 x 10-2 12 | 1 x 10-3 13 II x 10-4 14 laxly-5 15 | 1 x 10-6 16 Neutral II x 10-7 Bases | 1 | 1 x 10-9 19 | 1 x 10-10 110 | 1 x 10-11 Ill | 1 x 10-12 112 | 1 x 10-13 113 II x 10-14 114 I o I Battery Acid I I Stomach acid I Lemon Juice or Vinegar I I Grapefruit, Oranges, or Soda I Tomatoes I I Coffee I Milk or Saliva I 7 | Pure Water I 8 | Sea Water Baking soda (NACHOS solution) Milk of Magnesia or Great Salt Lake I Household Ammonia (NH) I Soapy Water Household Bleach or Oven Cleaner Liquid Drain Cleaner I * Pure water is a neutral substance with a pH of 7.
Substances with pH values below 7 are acids. The higher the concentration of H+ ions in the solution, the more acidic it is and the lower its pH value. Substances with pH values above 7 are bases. The closer to 14 a solution is on the scale, the lower the concentration of H+ ions. * Specific heat is the amount of energy needed to change the temperature of 1 gram of a substance by 1 degree Celsius. Water has a high specific heat compared to other covalent compounds. This means it can absorb or release a relatively large amount of heat with only a small change in its temperature. Heat of vaporization is the amount of heat energy needed to convert 1 gram of a liquid into a gas. Water as a high specific heat, so it also has a high heat of vaporization. Molecules must overcome the hydrogen bonds between them before they can separate and vaporize. This means it takes a lot of energy to change liquid water into a gas. Some water molecules in the sample of liquid can escape as a vapor at any temperature; this is called evaporation. However, water has a higher boiling point than many other small covalent compounds because of the hydrogen bonding that holds the molecules together. One of the reasons life can exist on Earth is water’s ability to absorb hear energy and moderate temperatures. . 05 * The transition trot inorganic molecules to organic molecules begins on Early Earth four billion years ago. There are multiple theories to consider. * The first theory is that organic molecules were the result of introducing inorganic molecules into the unique conditions on Earth. The inorganic molecules were nucleotides and amino asides. The conditions were low oxygen, high IV radiation, high heat, and large amounts of energy. * Another theory is that organic molecules were introduced to Earth by meteorites. Either way, organic molecules began to change the Earth. * Small organic compounds formed larger organic compounds, which is the basis of the RNA World hypothesis. * Organic compounds changed the environment of the Earth. Organic compounds also produced oxygen, which inhibits certain chemical reactions. Oxygen also produced the ozone layer, which reduced I-JP radiation. The addition of oxygen and reduction of IV radiation inhibits the creation of new organic compounds. * Astronomical and geological evidence suggests that active volcanoes covered early Earth.
In addition, with no protective atmosphere, Earth was probably very hot and constantly bombarded with comets and asteroids. Around 4. 2 billion years ago, Earth cooled enough for the surface to solidify and for water vapor to condense and fall as rain. This allowed permanent oceans to form. * This ancient planet was very different from Earth today. Theories suggest its atmosphere was similar to the gases released from volcanoes. This means there was little to no oxygen, and the atmosphere was made up primarily of carbon dioxide, water vapor, and nitrogen.
There may have also been small amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanide. * Carbon-based molecules are called organic molecules. Some are small, simple molecules, while others are long branching molecules containing hundreds of atoms. Organic molecules are important to life on Earth, so scientists are very interested in the origin of the very first organic molecules. * Some scientists have formed and tested hypotheses regarding the origin of the first organic molecules on Earth. In the asses, A. L. Ovarian, a Russian scientist, and J.
B. S. Holland, an English scientist, independently proposed ideas that the conditions of early Earth favored chemical reactions that were able to build small organic molecules from inorganic molecules in the atmosphere. The limited amount of oxygen in that early atmosphere, as well as the large amounts of energy provided by I-JP radiation and lightning, were thought to allow these reactions to occur spontaneously. * They argued that the reason we do not observe these reactions occurring today is the atmosphere now has a greater amount of oxygen gas.
Oxygen interferes with the reactions that would form carbon-based organic molecules. * Theories suggest that some of the first organic molecules formed on Earth may have been amino acids and nucleotides. Amino acids are the small organic molecules that bond together to form proteins. Nucleotides, another type of small organic molecule, bond together to form RNA and DNA molecules. The spontaneous formation of these small organic molecules from inorganic molecules can no longer happen in today’s oxygen-rich atmosphere.
Many scientists have attempted to re- create Earth’s early atmosphere to determine if these organic molecules could have formed from inorganic molecules present at Earth’s beginning. * Miller – Urea Experiment * Miller and Urea filled a sterile flask with water to simulate the ocean. They heated this water to a boil, producing water vapor. * To simulate art E en’s early atmosphere, they added methane, ammonia, and hydrogen gases to the water vapor. * The gases passed through highly charged electrodes to simulate the energy provided by lightning and other energy sources. * Cold water cooled the gases, forming liquid drops.
This liquid continued to cycle through the experimental apparatus for a week. * At the end of the weakling experiment, Miller and Urea observed 21 amino acids and other organic molecules present in the liquid. This experiment demonstrates how some of the organic molecules necessary for life could have formed from simpler molecules. Scientists now believe that the Miller-Urea experiment was not an accurate depiction of the conditions on early Earth. However, this experiment is still an important basis for demonstrating that small organic molecules can form from inorganic molecules. Many laboratories have conducted similar experiments using different mixtures of gases, such as the gases given off by active volcanoes (CO, CA, and NO) and possibly even low levels of oxygen gas. These experiments produced some organic compounds but in lesser amounts than the original experiment done by Miller and Urea. One of the most important heartsickness shared by all of these experiments is the limited amount of oxygen present. * The results of experiments, such as the one conducted by Miller and Urea, demonstrate that amino acids and other small organic molecules could have formed spontaneously in Earth’s early atmosphere.
These reactions would have required large amounts of energy. Ovarian and Holland proposed that lightning and the intense radiation that penetrated the thin primitive atmosphere provided the energy needed for these reactions. Other scientists propose that deep-sea vents may have provided the energy and chemical molecules needed to form the first organic impounds. * The ozone layer in our atmosphere today protects us from a lot of ultraviolet radiation. The oxygen gas in the atmosphere produces that ozone, so the ozone layer would not have been present to protect early Earth.
It is also possible that a younger sun may have given off greater amounts of ultraviolet radiation than what it gives off today. These ideas of early Earth indicate that there may have been high amounts of energy available for these reactions to occur. However, some scientists propose that even these energy sources may not have been able to provide s steady a flow of energy as the energy source used in the Miller-Urea experiment. * Thomas Czech and his coworkers at the University of Colorado, Boulder discovered that RNA is an important catalyst in modern cells. This means that RNA helps to speed up reactions. One important reaction that RNA helps to catalyst is the building of new RNA molecules. Before this discovery was made, the long-held view was that only proteins could serve as biological catalysts. If RNA is able to self- catalyst, this means that early RNA molecules may have been able to self-replicate without the help of other molecules. If early RNA molecules were able to copy themselves to build new RNA molecules, this helps to explain why all organisms share the same genetic code. * When RNA molecules are added to a test-tube solution of the nucleotides that make up RNA, small chains of nucleotides form.
These short organic molecules are not true RNA molecules, but this evidence gives some support to the RNA world hypothesis. However, some scientists challenge this hypothesis because no one has been able to get full RNA molecules to self-replicate. Alternative hypotheses include ideas tot simpler sell-replicating organic molecules receding modern DNA and RNA molecules. * All living organisms contain genetic information, stored in DNA and RNA molecules, which directs the functions of cells. The general coding and structure of these molecules is universally shared by all organisms.
Questions about the origin of these molecules are fundamental to our understanding of the origin of life on Earth. * Experiments like the one conducted by Miller and Urea demonstrated that organic molecules could have formed spontaneously in Earth’s early atmosphere, and smaller molecules could bond together to build large organic molecules. Some scientists hypothesize that some of the first large organic molecules to form and self-replicate were RNA molecules, with DNA molecules forming much later. This is called the RNA world hypothesis. These early RNA molecules were probably smaller than the RNA molecules in our cells today. They would have contained the codes for building specific protein molecules from the amino acids present on Earth at that time. Proteins are necessary components of all living cells. * Groups of molecules called mesospheric may have preceded the living cells of today. Mesospheric are tiny bubbles filled with groups of argue organic molecules; they can form under very specific conditions. These mesospheric may be a lot like the vesicles formed from the organic compounds taken off of the modern meteorites.
Mesospheric are not cells, but they do share some characteristics with cells. These bundles of molecules are able to maintain an internal environment different from the surroundings outside the bubble. They also have a simple way of storing and releasing energy. * These bundles of molecules expand by absorbing additional molecules until they reach an unstable size, and then they split into smaller mesospheric. This division is not true reproduction or cell division, but it may be a precursor to it. * The hypothesis of mesospheric builds off of the RNA world hypothesis.
If RNA molecules could self-replicate, it would mean that whenever a microscopes split, the early genetic coding in the RNA would pass to the newly formed mesospheric. This could be a predecessor to how cells pass on their genetic information today and may help explain why all organisms share a universal genetic code. * Evolution of true cells was made possible when genetic information could be passed from one microscopes to another. Scientists have found fossils of microscopic bacterial cells in rocks that are more than 3. 5 billion years old.
They believe that Earth’s atmosphere contained very little oxygen at the time, so these bacterial cells were probably able to survive without it. * By 2. 2 billion years ago, photosynthetic bacterial cells became common. These cells used energy from sunlight to produce food, giving off oxygen gas in the process. As oxygen accumulated in the atmosphere, the ozone layer also began to form. Over time, the oxygen levels rose until they reached the levels present today. As the conditions of he atmosphere changed, different types of organisms developed to live in the now oxygen-rich environment. The covalent bonds in water involve an uneven sharing of electrons. The oxygen atom’s nucleus attracts the shared electrons more strongly than the hydrogen nuclei. This difference in attraction causes the electrons to spend more time near the oxygen atom than they do near the hydrogen atoms. Because electrons are negatively charged particles, this uneven sharing of electrons gives the oxygen portion of the molecule a partial negative charge and the hydrogen portion a partial positive charge. The water molecule NAS no overall charge but NAS a positive end and a negative end. The charged ends of one water molecule are attracted to the oppositely charged regions of its neighboring water molecules. This attraction between water molecules forms a hydrogen bonding. * Hydrogen bonding is a weak attraction between the oxygen atom of one water molecule and a hydrogen atom of another water molecule. This attraction that occurs between molecules is not as strong as the covalent bonds that occur within the molecules, but many of the unique and important properties of water are a result of this attraction.