This Document Contains Experiments 27 to 30 Name____________________________________________________Section________________Date___________ Experiment 27: Motions of the Sun Background (Note: Experiment 26, “Celestial Coordinates” is a prerequisite for this exercise). The sun rises above the eastern horizon, traces an arched path across the sky, and then sinks below the western horizon. Midway between sunrise and sunset the sun climbs to its highest altitude over the horizon in the south. This daily event, the transit of the sun across the celestial meridian, defines noon, a fundamental reference in the measurement of time. The interval from one noon to the next sets the length of the solar day. Subdivisions of the day have had a long and sordid history, and not everyone welcomed the partitioning of the day into smaller units. As Platus lamented c. 200 B.C.: The gods confound the man who first found out how to distinguish hours! Confound him too, who in this place set up a sundial to cut and hack my days so wretchedly into small pieces. The Romans were the principal partitioners of the day. By the end of the fourth century B.C., they formally divided their day into two parts: before midday (ante meridiem, A.M., L. before the meridian) and after midday (post meridiem, P.M., L. after the meridian). An assistant to the Roman consul was assigned the task of noticing when the sun crossed the meridian and announcing it in the Forum, since lawyers had to appear in the courts before noon. By the beginning of the Common Era, the Romans eventually made finer subdivisions of the day. The “hours” of their daily lives were one-twelfth of the time of daylight or of darkness. These variant “hours”—equal subdivisions of the total time of daylight or of darkness—were quite elastic and not really chronometric hours at all. For example, at the time of the winter solstice, by our modern measures there would be only 8 hours, 54 minutes of daylight, leaving 15 hours, 6 minutes for darkness. Near the winter solstice, the Roman daylight “hour” corresponds to (8 54h m) = 45 minutes by modern measure. **Calculate the length (in modern time units) of a Roman “hour” at night at the time of the winter solstice. At the summer solstice the times were exactly reversed. One-twelfth of a changing interval of time was not a constant from day to day. These “hours” came to be called “temporary hours” or “temporal hours,” for they had meaning and length that was only temporary and did not equal an hour the next day. From the Romans’ point of view, both day and night always had precisely 12 hours year round. What a problem for the clockmaker! Sundials were common and were a universal measure of time. They were handy measuring devices since a simple sundial could be made anywhere by anybody without much in the way of special knowledge or equipment. But the cheery boast “I count only the sunny hours” inscribed on many modern sundials, also announces the obvious limitation of the sundial for measuring time. A sundial measures the position of the sun’s shadow; thus, no sun, no shadow. And what do you use at night? By the Roman era, water clocks became prevalent and served as a way to measure the shadowless and dark hours. Such clocks had a limited precision, at least by modern standards, but we must be amazed not that the Romans did not provide a more precise timepiece, but that under their reckoning of hours they were able to provide an instrument that served daily needs at all. It required a hefty amount of ingenuity, but the Romans made their water clocks indicate the shifting length of hours from month to month, rather than from day to day. (The day-to-day changes were too small to be of practical interest.) The equal hour did not arise until about the fourteenth century. Around 1330 the hour became our modern hour, one of twenty-four equal parts of a day. This new “day” included the night, and it was measured by the average time between one noon and the next, the average being over one year. For the first time in history, an “hour” took on a precise, year-round meaning everywhere. This movement from the seasonal or “temporary” hour to the equal hour is a subtle but profound revolution in human experience. Here was humanity’s declaration of independence from the sun, new proof of our growing mastery over ourselves and our surroundings. Only later would it be revealed that we had accomplished this mastery by putting ourselves under the dominion of a machine, with impervious demands all its own. Procedure Part A: The Solar and Sidereal Day Why does the sun appear to move in our sky at all? The earth is spinning about an axis once a day and revolving around the sun once a year. The rotation of the earth about its spin axis once a day has the effect that celestial objects seem to spin around the earth once a day—apart from any motion the celestial objects might have relative to the earth. If the earth did not revolve around the sun but simply spun on its axis, the sun would appear to go around the earth once a day—once a sidereal day. But the earth does revolve around the sun and this relative motion introduces a small complication: the time from one noon to the next (one solar day) is not the same as the time for the earth to spin once upon its axis (one sidereal day). This difference is so important that we will examine it in two different ways so that its origin is clear. First, we will adopt a geocentric perspective, that is, we will consider the earth to be motionless and the celestial sphere and the objects on it to revolve around us. For concreteness, let us pick a fixed point on the celestial sphere, say the vernal equinox (see Figure 27.1), the intersection of the celestial equator and the ecliptic where the sun goes from south of the equator to north of it. (The sun in its motion along the ecliptic is at the vernal equinox on or about March 21.) Let us further suppose that it is about noon on March 21 so that the sun as well as the vernal equinox are on the local celestial meridian as in Figure 27.1A. The celestial sphere rotates (due to, of course, the earth rotating about its spin axis). Sometime during the next day that fixed point on the celestial sphere—the intersection of the ecliptic and celestial equator, the vernal equinox—is again on the meridian. That interval of time is one sidereal day. A fixed point on the celestial sphere has gone around once. But in that time the sun has moved eastward along the ecliptic as shown in Figure 27.1B. In Figure 27.1B, it is not quite noon since the sun is not yet on the meridian. We have to wait a bit longer for the celestial sphere to continue to spin to bring the sun up to the meridian. l. The sun moves 360° around the ecliptic in 365 days, so the sun moves about 1° per day along the ecliptic. Therefore, the sun is about 1° east of the vernal equinox. Calculate how long you have to wait after the situation depicted in Figure 27.1b so that the sun is on the meridian. Express your answer in minutes. The earth rotates 360° in 24 hours (or 1440 minutes). The Earth needs to rotate only 1° so that the Sun is on the meridian. 1° = 1440 min/360 = 4 minutes. The Sun will be on the meridian in 4 minutes. We have described one way of showing that a solar day is a bit longer than a sidereal day. Now we shall examine the situation from a different perspective, a heliocentric one. In Figure 27.2, the earth is initially at position A in its orbit around the sun. It is noon for an observer at the foot of the dotted arrow. Consequently, it is midnight for an observer at the foot of the solid arrow at A. One sidereal day later, the earth is at B and the arrows have the same orientation as at A, but at B the daylight dotted arrow does not point to the sun and so it is not noon. A little later, the earth has turned more upon its axis and moved a bit in its orbit and now the dotted daylight arrow points toward the sun. The time from A to B constituted one sidereal day, while the time from A to C constituted one solar day. 2. Figure 27.3 depicts the sun’s apparent motion along the ecliptic (where the zodiacal constellations are found) in a heliocentric perspective. As the earth orbits the sun, the line of sight of the sun and toward the background stars also moves. For example, the diagram shows the sun in Leo. A month later the earth will have moved enough so that Virgo lies behind the sun. Figure 27.2 The difference between a sidereal day and a solar day arises from the rotation of the Earth about its axis and its revolution around the Sun. The illustration is a view of the Earth and Sun from far above the north pole of Earth. Figure 27.3 Part A: The Analemma—Details of the Sun’s Motion If the earth’s orbit were circular and if the earth’s spin axis were perpendicular to the plane of its orbit, the sun would always rise precisely in the east, move along the celestial equator at a constant rate and set precisely in the west. The sun would also appear to move eastward among the stars at a constant rate, completing one revolution in one year. In this idealized situation, the sun would be a perfect clock and would arrive on the observer’s meridian at exactly equal intervals. As you know, the earth’s orbit around the sun is elliptical and the earth’s spin axis is tilted 23 1/2° from the perpendicular. These circumstances, as you will see, will cause the time interval between successive meridian crossings of the sun to vary throughout the year. We can still refer to a fictitious mean sun that moves uniformly along the celestial equator and is on the meridian at noon and again precisely 24 hours later. The real sun, unfortunately, does not behave this way, but the corrections to the time kept by the real sun are not large. They can be represented on a threecoordinate plot called the analemma (L., sundial). The analemma is a closed curve resembling a flatbottomed figure 8 (see Figure 27.4). You may have seen the analemma on a terrestrial globe where it is usually placed in the empty part of the Pacific Ocean. Each point on the analemma presents a date in the year. The north-south coordinate at Figure 27.4 The analemma graphs the sun’s declination and the daily difference between clock noon and noon by the sundial (sun on meridian for every day of the year). Declination is the distance in degrees north or south of the celestial equator. Figure 27.5 Illustration of how the equator-ecliptic angle affects the sun’s timekeeping. At the equinox, E represents the solar motion along the ecliptic; its eastward component E’ on the equator is shorter. At the solstice, S (equal to E) runs due eastward and the hour circles are closer together, the component S’ is longer than both E’ and E. the point gives the sun’s declination on that date. The east-west coordinate indicates the number of degrees (or minutes of time) by which the sun is east or west of the observer’s meridian when the local mean solar time is noon. In the following, we shall examine the origin of the difference between the mean sun and the actual sun, and the information contained in the analemma. The spin axis of the earth is inclined 23 1/2° to the plane of its orbit around the sun. Because of this tilt, the yearly path of the sun eastward among the stars (the ecliptic) is tilted 23 1/2° with respect to the celestial equator. In late June the sun is 23 1/2° north of the equator and in late December 23 1/2° south of it. This annual north-south oscillation of the sun’s declination is responsible for the lengthwise extension of the analemma pattern. The ecliptic tilt has yet another effect on the sun’s motion. Since the sun moves along the ecliptic, which is tilted with respect to the celestial equator, the sun’s motion relative to the stars is due east only in late June and late December. Hence, the sun’s eastward advance per day is greatest at those times and least in March and September when the ecliptic crosses the equator at a slant (see Figure 27.5). Because the meridians of right ascension are more closely spaced at declinations of ±23 1/2° than at the equator, the actual sun’s effective eastward motion is faster than that of the mean sun’s. Twice a year, near the solstices, the sun arrives later and later on the local meridian because of its relatively fast eastward motion from day to day (look again at Figure 27.1A and B), and as a clock it runs slow. Twice a year near the equinoxes, the sun arrives on the observer’s meridian earlier and earlier each day, and as a clock it runs fast. Therefore, two times during the year the actual sun is ahead of clock time and two times during the year it is behind. This effect gives rise to the east-west spread to analemma and determines its general figure-8 shape. One further influence on the shape of the analemma arises because of the elliptical orbit of the earth around the sun. As Johannes Kepler discovered nearly four centuries ago, a planet moves fastest in its orbit near perihelion (point nearest the sun) and slowest at aphelion (point farthest from the sun). Since the earth reaches perihelion on January 3 and aphelion on July 7, the motion of the sun along the ecliptic is faster than average during the winter months and slower than average during the summer months. On January 3, the apparent rate of the sun along the ecliptic is 1.019 degrees per day, while on July 7 the sun moves at a rate of 0.953 degrees per day. The principal effect of this annual velocity variation of the sun is to broaden the southern loop of the analemma and compress the northern loop. In summary, the analemma graphs the sun’s declination, and daily difference between clock noon and noon by the sun (sun on meridian) for every day of the year. Looking at Figure 27.4 we see that the sun is west of the mean sun, that is, ahead of clock noon, from September 1 to December 26, falls behind from December 26 to April 15, then moves ahead again until June 15. It falls behind again until September 1, alternately speeding up and slowing down with respect to clock time. Briefly describe the effect on the shape of the analemma if the ecliptic-equator angle were to increase. Obtain from your instructor the latitude of your location and fill it in below. latitude of your location = ___________________________ Determine the altitude over the southern horizon of the intersection of the celestial equator and the local celestial meridian. Use the analemma in Figure 27.4 and your answer to step 4 to fill in Table 27.1. The latitude of Altengaard, Norway is +70°. Rip van Winkle awakens from his extended slumber and asks a passerby what year it is so he can determine how long he slept. The passerby quickly responds and then rapidly moves away. Realizing a twenty year snooze might be a world’s record, he thinks he should pin down the date as well as the year. He moves out from under the tree where he slept and measures the altitude of the sun when it crosses the meridian; he finds it is 44° over the southern horizon. He knows that the latitude of his chosen spot on the Hudson River in New York is 42°. On what two possible dates could Rip van Winkle have awakened? He notices that buds are appearing on the tree he slept under. What is the date of his awakening? As we saw previously, the analemma graphs the daily difference between clock noon and apparent noon when the sun crosses the meridian. As an example, check the analemma in Figure 27.4 to see that on October 15 the sun will cross the meridian 14 minutes before clock noon. For the dates given in the table below, use the analemma in Figure 27.4 to determine whether the actual sun will cross the meridian before or after clock noon and by how many minutes. Determine the altitude over the southern horizon of the actual sun and the time when it crosses your local meridian on the dates in the table below.
Name____________________________________________________Section________________Date___________ Experiment 28: Diffusion and Osmosis Invitation to Inquiry Diffusion occurs when there is a concentration gradient and molecules are in constant motion. This means that they will move from a place where they are in a higher concentration to a place where they are in lower concentration. Try this: Pick a quiet room for this work. It could be in a house, a lab, or a small room such as your dorm room. Be sure that no one will be moving about or coming in during your investigation. Pick a place in the room where you can locate a container of one of the following: an aromatic liquid such as household cleaner (ex. 409), perfume/aftershave, or a solid such as a spice or a scented candle. Be sure to have a stop watch or one which can measure seconds. On the first day: place the aromatic material in your selected spot. Open the top of the container and start timing your work. Quickly move to a pre-selected spot in the room as far from the open container as possible. Stay in that place until you sense the aroma of the material. Note this time. Repeat this procedure with other materials on different days under similar conditions. Record the time it takes for you to smell these materials. These are the diffusion rates of your various aromatic materials. Once you have gathered all your data, compare your results. What factors could contribute to differences in the diffusion rates? Consider such factors as: (1) the phase of the material (solid, liquid, gas), (2) molecular weight, (3) solubility, and (4) air currents. Why should you do this in several different days? Background Although you may not know what diffusion is, you have experienced the process. Can you remember walking into the front door of your home and smelling a pleasant aroma coming from the kitchen? It was diffusion of molecules from the kitchen to the front door of the house that allowed you to detect the odors. Diffusion is defined as the net movement of molecules from an area of greater concentration to an area of lesser concentration until the concentration everywhere is the same. The movement in one direction minus the movement in the opposite direction determines the direction of net movement. To better understand how diffusion works, let’s consider some information about molecular activity. The molecules in a gas, a liquid, or a solid are in constant motion because of their kinetic energy. Moving molecules are constantly colliding with each other. These collisions cause the molecules to move randomly. The higher the concentration of molecules in one region, the greater the number of collisions. Some molecules are propelled into the less concentrated area and others are propelled into the more concentrated area. Over time, however, there will be more collisions in the highly concentrated area, resulting in more molecules being propelled into the less concentrated area. Thus, the net movement of molecules is always from more tightly packed areas to less tightly packed areas. Diffusion occurs when there is a difference in concentration from one region to another or from one side of a membrane to another (Figure 28.1a). A difference in the concentration of molecules over a distance is called a concentration gradient. When the molecules become uniformly distributed, as in Figure 28.1b, that have reached dynamic equilibrium, in which the number of molecules moving in one direction is balanced by the number moving in the opposite direction. It is dynamic because molecules continue to move, but because motion is equal in all directions and there is no net change in concentration over time, equilibrium exists. The process of diffusion occurs in both living and nonliving systems. Biologically speaking, diffusion is responsible for the movement of a large number of substances, such as gases and small uncharged molecules, into and out of living cells. (a) (b) Figure 28.1 The direction of diffusion is always from where there were originally more molecules to where there are fewer. This is similar to the scattering of a crowd of people leaving a theater. Many of the individuals move from the theater to the outside, but some go back to retrieve their gloves or popcorn. The net movement, however, is the movement of the individuals leaving the theater minus the movement of those returning. Imagine that your instructor opens a bottle of ammonia in a corner of the room. The bottle would have the highest concentration of ammonia molecules in the room; the individual ammonia molecules would move from this area of highest concentration to where they are less concentrated (Figure 28.2). Figure 28.2 Although you could not actually see this happening, ammonia molecules would leave the bottle and move throughout the air in the room because of molecular movement. You could detect this by the odor of the ammonia. If you compare the relative number of ammonia molecules in the bottle to those dispersed in the room, you would be dealing with what is called relative concentration. Relative concentration compares the amount of a substance in two separate locations. Whenever there is a difference in concentrations of a substance, you can predict the direction that most of the molecules will move. You can predict that when the bottle is first opened, ammonia molecules will move from the area of higher concentration (the bottle) to the region of lower concentration (the air in the room). Soon, however, the molecules of ammonia will mix with the air molecules in the room. Because the ammonia molecules are moving randomly, some of them will move from the air back into the bottle. As long as there is a higher concentration of ammonia molecules in the bottle, more of them move out of the bottle than move in. One way of dealing with the direction of movement is to compare the number of molecules leaving the bottle with the number reentering the bottle. This is called the net amount of movement. The movement in one direction minus the movement in the opposite direction is the direction of net movement. If, for example, 100 molecules of ammonia leave the bottle and 10 reenter during that time, the net movement is 90 molecules leaving the bottle. Ultimately, the number of ammonia molecules moving out of the bottle will equal the number of ammonia molecules moving into it. When this point is reached, the ammonia molecules are said to have reached dynamic equilibrium. When several kinds of molecules are present, consider only one case of diffusion at a time even though several different types of molecules are moving. For example, consider the exchange of gases between the lungs and blood. In the lungs, there are a series of tubes that transport gases. These tubes divide into smaller and smaller branches and eventually end at a series of small alveolar sacs. Adjacent to these sacs are a number of capillaries containing blood. By the process of diffusion, there is an exchange of oxygen and carbon dioxide between the alveolar sacs and the blood in the capillaries (Figure 28.3). Figure 28.3 Is the direction of net movement of carbon dioxide molecules in Figure 28.3 from the blood to the lungs or from the lungs to the blood? Explain your answer. It is from the blood to the lungs because the concentration is higher in the blood. Is the direction of net movement of oxygen molecules in Figure 28.3 from the blood to the lungs or from the lungs to the blood? Explain your answer. It is from the lungs to the blood because the concentration is higher in the lungs. Another example of diffusion is sugar dissolving in water. When sugar molecules and water molecules mix, a solution is created. A solution is any mixture where two or more different types of molecules are evenly dispersed throughout the system. Draw an arrow on Figure 28.4 to show the net direction of sugar movement.The arrow goes from the sugar to the surrounding water. Figure 28.4 Figure 28.5 shows a differentially permeable membrane. A differentially permeable membrane is a thin sheet of material that selectively allows certain molecules to cross but prevents others from crossing. The membrane in this figure is permeable only to water molecules. Water molecules may freely diffuse across the membrane, but other types of molecules cannot. The diffusion of water across a differentially permeable membrane is called osmosis. On each side of the differentially permeable membrane in Figure 28.5 is a chloride solution. A solution is characterized by the dissolved substance called the solute. Chloride in this example is the solute. The substance in which the solute is dissolved is called the solvent. In Figure 28.5 and in biological systems, water is Figure 28.5 the solvent. 4. What is the percentage of solute in the left side of the container (Figure 28.5)? 30% What is the percentage of solvent in the left side of the container? 70% What is the percentage of solute in the right side of the container? 10% What is the percentage of solvent in the right side of the container? 90% Where is the water in higher concentration—the left or right side? Right Draw an arrow to indicate the net direction of movement of the water molecules. The arrow should go from the right to the left side. In each of the previous examples, the net movement was a result of diffusion of molecules from a place of higher concentration to a place of lower concentration. The rate at which diffusion occurs is related to the amount of energy the molecules have and the degree of difference between the areas of high and low concentration. Adding energy doesn’t change relative concentrations, nor does it influence the direction of diffusion. It merely affects the rate at which diffusion occurs. Molecules with greater kinetic energy move faster causing diffusion to happen quicker. The kinetic molecular theory states that all substances are made up of molecules that occupy space and are constantly in motion. This exercise helps you examine some phenomena related to this motion of molecules. During this lab exercise you will: Set up a demonstration of osmosis under a variety of temperature conditions and determine how temperature influences the rate of osmosis. Set up a demonstration of osmosis using a variety of concentration gradients and determine how concentration differences influence the rate of osmosis. Graph the results of the osmosis demonstrations. Procedure Part A: Osmosis and the Effect of Temperature Working in groups, prepare three sacs to demonstrate osmosis. Obtain three pieces of dialysis tubing (sausage casing) and soak them in tap water for about 1 minute. Form each of the pieces of tubing into a tubular bag. Shake off the excess water, fold over one end of the dialysis tubing, and securely tie it with a piece of string. Fill each tubular bag about half full with full-strength molasses. Leave room for a small pocket of air. Tie the open end of each bag. After rinsing each bag, pat it dry and cut off any excess string. Use a balance to obtain an initial weight for each bag. Record this data in Data Table 28.1 on page 213. a. Place one bag in a beaker of water at room temperature (approximately 20˚C). Place the second bag in a water bath heated to 40˚C. Place the third bag in a beaker of ice water (approximately 0˚C) (Figure 28.6A). Record the exact temperature of the water in each beaker. Make certain that each bag is completely covered with water. After 5 minutes, remove each bag and gently squeeze to assess any changes in firmness. Observethe size, shape, and firmness of each bag. Gently pat each bag dry and weigh. Record your results in Data Table 28.1. Return each bag to its appropriate container of water for another 5-minute interval. Repeat your observations and measurements every 5 minutes. (Measurements should be taken at 0, 5, 10, 15, and 20 minutes). To more easily visualize the effect of temperature on osmosis use the data collected in Data Table 28.1 to construct a graph of the effect of temperature on the rate of osmosis. Graph paper is provide on page 217. If you do not have three different colored pencils, use a solid line for the hot water, a dashed line for room-temperature water, and a dotted line for the ice water. Figure 28.6
Data Table 28.1 Effect of Temperature on the Rate of Osmosis
Temperature Initial weight 5 minutes 10 minutes 15 minutes 20 minutes
Warm
Tap
Ice
Part B: Osmosis and the Effect of Concentration Repeat the construction of the differentially permeable bags (see instructions under “Osmosis and the Effect of Temperature”). Prepare three bags but fill each with a different concentration of molasses according to the following specifications (Figure 28.7): Bag 1: one part molasses to three parts water (2.5 mL molasses; 7.5 mL water) Bag 2: one part molasses to one part water (5 mL molasses; 5 mL water) Bag 3: full-strength molasses (10 mL molasses) Rinse and gently pat the bags dry. Record the initial weight of each bag. Place each bag in a container of room-temperature tap water. Check their weight and firmness at 5-minute intervals for a period of 20 minutes. Record all data in Data Table 28.2, and graph your results on the graph provided on page 219. Results In a perfectly tied and unbroken bag, should we see evidence of sugar molecules passing through the “membrane?” Qualify your answer in terms of how differential permeability operates. No. A differentially permeable membrane will allow only certain molecules to pass. The molasses remains inside the bag; only the water is able to cross the membrane. From your graph of the influence of temperature on the rate of osmosis, what can you conclude about the effects of temperature on the rate of osmosis? The higher the temperature, the greater the kinetic energy; the greater the kinetic energy, the greater the molecular movement; therefore, the greater the rate of osmosis. Was dynamic equilibrium reached in any of the molasses demonstrations? Explain your answer. Answers will vary. Some of the bags may have reached dynamic equilibrium. This will be indicated by a lack of change in mass from one time period to the next. How do differences in concentration affect the rate of osmosis? The greater the concentration difference, the greater the rate of osmosis. Why does a good cook wait to put the salad dressing on a salad until just before serving? Answer by explaining what happens to the cells in a lettuce leaf when the dressing is added. When dressing is added, the concentration of water inside the lettuce cells is higher than that outside of the cell and water diffused out of the cells (actually osmosis), causing the lettuce to wilt. Human cells contain 0.9% solute (dissolved materials). Therefore, there is 99.1% water in these cells. The Pacific Ocean contains 3.56% salt. Although this seems like a silly question, how much (%) water is in the ocean? You are cast adrift on this ocean. What would happen to your cells if you were to drink the salt water? The ocean contains 96.44% water. Since your cells are 99.1% water and the salt water is 96.44% water, if you ingest the ocean water, water will move from the higher concentration in your cells to the lower concentration in your digestive system. As your cells lose water you will dehydrate and could eventually die. Your younger brother just put your favorite saltwater fish into his freshwater aquarium. Predict what will happen to the fish, its cells, and your younger brother. The cells of the saltwater fish would contain a lower concentration of water than that found inside the freshwater tank. The osmosis of water into the cells of the fish could kill it. If this happens, your little brother needs a biology lesson on the effects of osmosis. Was the purpose of this lab accomplished? Why or why not? (Your answer to this question should show thoughtful analysis and careful, thorough thinking.)
Time (minutes) Time (minutes) Name____________________________________________________Section________________Date___________ Experiment 29: The Microscope Invitation to Inquiry The jobs of a microscope are to magnify and resolve; i.e., it should enlarge and should show you the details of the component parts of the material you choose to observe. This lab exercise will provide you with the opportunity to use the most common microscope, the compound light microscope. There are many other kinds of microscopes that play vital roles in providing information about the microscopic world about you. Go to the internet and dig out information that will allow you to compare and contrast different kinds of microscopes including the polarizing, electron, and tunneling microscopes. Compare how each functions in relation to the compound light microscope. Background Because biological study includes the microscopic examination of one-celled organisms and the cells and tissues of multicellular organisms, it is important to learn the correct procedures for efficient operation of a light microscope. In addition to giving you an opportunity to learn proper microscope technique, this exercise also gives you a chance to practice using a microscope. During this lab exercise you will: Identify and name the parts of a light microscope, and describe the functions of the various parts. Determine the total magnification of a set of lenses in a compound microscope. Focus on a practice slide. Focus on crossed hairs in a temporary wet mount to determine the depth of field of a set of lenses. Procedure Take your assigned microscope to your work station. Refer to Figure 29.1 and Table 29.1 to familiarize yourself with the operation and function of each microscope part. Magnification The compound microscope is a device that uses two sets of lenses to increase the apparent size of objects. The two lenses are known as the ocular lens (the lens you look through) and the objective lens, which is near the stage. The magnifying power (how much it magnifies) of each lens
1. Table 29.1 Parts and Function of a Light Microscope Part Function Ocular lens (eyepiece with pointer) Lens through which you view magnified specimen. Pointer may appear as a needle or as a curved line. Revolving nosepiece Movable mount for selecting objective lens to provide the magnification desired. Objective lens Lens on revolving nosepiece, which accomplishes the initial magnification of the specimen. Stage Flat work surface upon which the slide is placed. Iris diaphragm Regulates the amount of light passing through the stage aperture and specimen. Lamp Constant light source beneath the iris diaphragm. Mechanical stage A microscope with a mechanical stage has a lever that is opened laterally (never lifted) to secure the slides to the stage and is used for precise movement of a slide by control knobs that move the stage. Coarse adjustment knob Gives initial focus on low power. Fine adjustment knob Gives refined focus on high power and oil immersion. is marked on its tubular housing. Simply multiply the magnifying power marked on the ocular lens housing times the value marked on the objective lens housing to determine how many times your specimen is enlarged. Notice that your ocular lens magnification is 10. If the low-power lens is also marked 10, the total low-power magnification is 10 × 10 = 100. Microscopes often have additional objective lenses, namely a scanning lens, which typically has a magnifying power of 4 and is used for initial viewing of the specimen, a high-power lens, which typically has a magnifying power of 45, and an oil-immersion lens, which typically has a magnifying power of 100. As the magnifying power increases the lenses get longer. Use of the oilimmersion lens requires special training, so do not use it unless instructed to do so by your instructor. Improper use could cause severe and costly damage to the oil-immersion lens. Calculate and record here the magnification of your microscope when the high-power objective lens is used: 45 × 10 = 450 Resolving Power Resolving power is a measure of lens quality. Quality lenses have a high resolving power, which is the capacity to deliver a clear image in fine detail. If a lens has a high magnifying power but a low resolving power, it is of little value. Although the image may be large, it is not clear enough to show fine detail. Another factor that influences resolving power is the cleanliness of the lenses. Dirt, water, or oil on the lens may scatter light and reduce the effective resolving power of the microscope. Therefore, lenses should always be kept clean. Use only lens paper to clean the lenses. Field of View You have already learned that lenses can have different magnifying powers, but it is also important to understand that each lens has a particular field of view. The field of view is the size of the area that the lens views. The larger the magnifying power of an objective lens, the smaller the area viewed. This is sometimes hard to appreciate because to you—the observer—the size of the circle of light you see through the ocular lens appears the same for all powers of the objective lenses. When you switch from low power to high power, you are actually looking at the central portion of what was visible under low power. Therefore, it is important to center the specimen on low power before making the switch to high power. Parfocal Capability A feature of a good quality microscope is its parfocal capability. This means that when a specimen is in focus under low-power magnification, you can switch to high-power magnification and have the specimen remain in reasonably good focus. Usually, just a slight touch to the fine adjustment knob is all that is needed to sharpen the focus. Of course, it is imperative that your specimen be accurately centered just before you switch over to high power. Viewing and Focusing Before you attempt to view any specimen through the microscope, you must learn the correct use of its parts. Always use the following procedures when viewing objects through the microscope. Carefully carry your assigned microscope to your work space using both hands. One hand should hold the microscope by the arm and the other hand should support the microscope base. Make sure the microscope is plugged in. Turn on the light. Rotate the low-power objective lens or scanning lens into position directly over the round opening in the flat stage of the microscope. Move it until it clicks into place. Rotate the coarse adjustment knob so that the distance between the objective lens and the stage is at its maximum. Center your specimen over the opening in the stage. Make sure that the slide is securely held in place by the clips or the fingers of the mechanical stage. Watch the stage and objective lens from alongside (not through) the microscope. Make the distance between the specimen and the low-power lens as small as possible. While looking through the ocular lens, turn the coarse adjustment knob to move the objective lens away from the specimen until a part of the specimen comes into focus. The iris diaphragm is located below the stage and regulates the amount of light passing through the specimen. Locate the lever that adjusts the iris diaphragm and move it so that you get a good image. While looking through the ocular lens, center the specimen in the field of view. Switch to high power and sharpen the focus with the fine adjustment knob only. If you are unable to find the specimen, switch back to low power and repeat steps 7, 8, and 9. Keep both eyes open even though only one is used in the monocular, compound microscope. After a short while, you can get accustomed to ignoring impressions coming from your free eye. If you have trouble at first simply cover your free eye with your hand. Squinting leads to muscle fatigue and headaches. Making a Wet Mount A wet-mount slide is made by placing the object in a drop of water on the slide and covering it with a thin glass coverslip. A coverslip must always be used. The use of a coverslip gives a flat surface to look through. If you don’t use a coverslip the water drop will form a curved surface and make viewing difficult. In addition, on high power, the heat from the lamp will cause water to evaporate and condense on the lens. A fogged lens is difficult to see through. Make a wet-mount slide by cutting out one of the words in Figure 29.3; your instructor may indicate a particular word. Place the word on the slide, put one or two drops of water on the paper, and place a coverslip overthe paper. If you place one edge of the coverslip against the glass slide and gently lower it into position, as shown in Figure 29.2, you will not trap air bubbles, which interfere with your ability to see the object. Figure 29.2 Place this slide on the microscope and examine it under low power. You should find that something comes into view with about a quarter of a turn of the coarse adjustment knob. Move the knob smoothly and slowly. If you cannot see anything, start over by returning the low-power lens to the position closest to the slide and trying again. If you still have trouble, ask your instructor for assistance. The first things you see are the fibers in the paper. You may also see the ink that forms the letters on the paper. If you do not see any letters, move your slide around until you do. Adjust the amount of light by moving the lever connected to the iris diaphragm. Notice that there is an optimal position for this lever that allows you to see the letters on the paper clearly. If you have any problems locating something to look at, call your instructor.
scope scope scope scope
Figure 29.3 Center a letter or portion of a letter in the center of the low-power field of view and switch to highpower. Focus using the fine adjustment knob. Use a pencil to sketch the word as seen with (1) the unaided eye, (2) the low-power objective and,(3) the high-power objective of the microscope. The letters in your drawings should be oriented as they actually appear when viewed through the microscope. Compare your three drawings. How are they different in regard to the number of visible letters? Answers will vary, but students should recognize that there are less letters visible as the magnification increases. Drawings of the word as seen with the microscope should have the letters reversed and inverted. As you move the slide slightly to the right, in which direction does the letter appear to move? The letter will move to the left. In what direction would you move the slide if a swimming specimen were leaving the field of view at the top of the slide and you wanted to continue looking at it? Move the slide down. Planes of Focus and Depth of Field Lenses have a plane of focus which is a position a specific distance from the lens where an object (or a portion of it) appears in sharp focus. You can actually move up and down through some specimens and focus on different levels of the specimen. The portion that is in focus at any given level is the portion in the plane of focus. This plane of focus has some depth to it. Therefore, it is a layer in space, a specific distance from the lens where objects are in sharp focus. The thickness of the layer that is in sharp focus is known as the depth of field. High-power lenses have a much shallower depth of field than do low-power lenses. To experience microscopic depth of field, prepare a wet mount of two human hairs. If possible, use two different types of hair—light hair and a dark hair, or a coarse hair and a fine hair. Place a drop of water on the center of a clean slide. Take a piece of hair (about 2 cm long) and place it lengthwise in the drop of water. Then take a second piece of hair (again, about 2 cm long) and lay it over the first so that they are crossed at right angles. Focus on the crossed hairs under low power. You will probably see both hairs clearly at the same time (Figure 29.4). They are both within the depth of field. Figure 29.4 Move the slide so that the point where the hairs cross is in the center of the field of view and switch to high power. Use the fine adjustment knob to bring the bottom hair into focus. Note that only one hair is in sharp focus. It is within the depth of field. The other is blurry. It is still distinguishable as a hair but is not clearly focused. Focus upward with the fine adjustment knob to see that the bottom hair goes out of focus as the top hair comes into focus. Is the high-power depth of field greater or less than the low-power depth of field? Less Further Practice Obtain a prepared slide. These slides have been stained with particular stains so that specific structures are highlighted. If the slide is of a large object, it has been sliced into thin sheets, which were then mounted on the slide and a coverslip was permanently affixed to the top surface. Remember, your purpose is to practice looking at microscopic structures. Use the iris diaphragm, low power, and high power, and move the slide around. Make drawings of your observations in the following space. Be sure to label all drawings with the name of the organism and the total magnification as demonstrated in the following example. Make your drawings large so that you can show details of the structure. Prepare wet mounts of the fresh specimens available. This variety of material could include such things as protozoa, cork, potato, algae, or microscopic animal life. Draw your observations here.
Title Total magnification = ________ Title Total magnification = ________
When finished, clean and dry your slides and return them to the slide box. Since coverslips are fragile, your instructor will inform you how to clean and return them. If you break any slides or coverslips do not put them in the wastepaper basket. Place broken glass in the container designated for the purpose. When you are finished using your microscope make sure you have removed any slides, clean any moisture from the stage or lenses, and position the nosepiece on low power before returning the instrument to its correct storage place. Results Part of learning how to use the microscope is learning how to troubleshoot. When you have difficulty, what should you do? In each of the following situations, list possible causes of the problem and indicate what you should do to resolve it. You have just set your microscope up for use and turned it on. You cannot see a field of view. Possible problem: Possible problem: The objective lens is not aligned. Solution: Align the objective lens with the body tube by clicking into place. Your slide is in focus on your microscope, but you do not see the specimen. Possibleproblem: Possible problem: Did not center specimen on low power before switching to high power. Solution: Return to low power and center specimen or part of slide that you are interested in. The specimen that you are examining is very thin and transparent. What can you do tomake it easier to see? Decrease the intensity of light by adjusting the diaphragm. You are looking at a specimen on low power and you cannot see the details that yourinstructor asked you to look at. What should you do? How is this done? Switch to high power by focusing in on the object using low power, centering object in the field of view, switching to the 45x objective, then using the fine adjustment knob. Complete the table, indicating the magnifying power of your microscope. The following diagrams illustrate the field of view if you were using low-power magnification. Circle the part of the slide (numbers) you would see when switching from low- to high-power magnification. The student should circle the center of the field -- numbers 9 and 10. If you were using low power and wanted to look at the number 3 on high power, what should you do before you switch to high power? Move the slide so that the number 3 is in the center of the field of view before switching to high power. Label the following structures on the microscope drawing on the next page: lamp, fine adjustment knob, coarse adjustment knob, mechanical stage knob, revolving nosepiece, stage, ocular lens, objective lens, iris diaphragm.) Was the purpose of this lab accomplished? Why or why not? (Your answer to this question should show thoughtful analysis and careful, thorough thinking.) (From Ruth Bernstein, et al., Biology Laboratory Manual. Copyright © 1996 The McGraw-Hill Companies, Inc., New York, NY. All rights reserved. Reprinted by permission.)
Name____________________________________________________Section________________Date___________ Experiment 30: Survey of Cell Types: Structure and Function Invitation to Inquiry Understanding the structure of the typical eukaryotic cell can be a real challenge. To help, you can construct a model using materials readily available to you. Based on the material present in the lab and the text, search out “ingredients” such as spaghetti, paper clips, ping-pong balls, and plastic wrap, and arrange them into a model of a typical eukaryotic cell. When finished take them to your instructor, explain your reasons for using the materials you have chosen to be sure that you on the right track. This might seem like a silly thing to do, but you may be very surprised to find just how much it helps in your learning of cell structure. Background The cell concept is basic to understanding the activities and characteristics of organisms. Cells are the smallest units of living things and are the units of structure and function of an organism. As functional units, they reflect the abilities of the organism as a whole. Some simple kinds of organisms consist of individual cells but many of the organisms with which we are most familiar are multicellular. Multicellular organisms usually are composed of several different kinds of cells, each having specific characteristics that relate to its function. The various kinds of living things have been subdivided into three domains: Eubacteria, Archaea, and Eucarya. The cells of the Eubacteria and Archaea are small and simple, and lack a nucleus. These cells are called prokaryotic cells. The cells of the Eucarya all have a nucleus and other kinds of structures called organelles within the cell. This type of cell is called a eukaryotic cell. Because the Archaea and Eubacteria are extremely small and difficult to see, in this exercise we will look only at Eubacteria as examples of a prokaryotic cell. We will spend the majority of our time looking at the various classifications of the Domain Eucarya, which is divided into the following kingdoms: Protista (algae and protozoa), Fungi, Plantae, and Animalia. Robert Hooke was the first person to use the word cell in reference to the units that make up organisms. He examined cork under a microscope and saw the cell walls of these plant cells. Hooke recounts his important observation. I took a good clear piece of cork, and with a Penknife sharpen’s as keen as a Razor, I cut a piece of it off . . . then examining it very diligently with a Microscope . . . I could exceeding plainly perceive it to be all perforated and porous, much like a Honey-Comb in these particulars . . . in that these pores, or cells, were not very deep, but consisted of a great many little Boxes. . . . For, as to the first, since our Microscope informs us that the substance of Cork is altogether fill’d with Air, and that Air is perfectly enclosed in little Boxes or Cells distinct from one another. Today we recognize that Hooke saw only the cell walls of plant cells. However, he did recognize that living material was made of many similar subunits which he called cells. We continue to use his terminology today. During this lab exercise you will prepare a temporary wet mount of sections of onion membrane, view the specimen througha microscope, identify common structures, and make a three-dimensional drawing of a typical onion cell. make a temporary wet mount of an Elodea leaf and view its cellular structure through a microscope, identify common structures, and make a three-dimensional drawing of a typical cell. make a temporary wet mount of Spirogyra, Euglena, and Paramecium, view the cells through a microscope, identify common structures, and make a three-dimensional drawing of a typical cell. observe cheek epithelial cells through a microscope, identify common structures, and make a three-dimensional drawing of a typical cell. observe slides of fungi, soil bacteria, and Anabaena and note their structures and characteristics. Procedure Kingdom Plantae We will begin with plant cells because they are relatively large and have several organelles that can be easily identified. Plants have many different kinds of cells organized into complex structures like leaves, fruits, and stems. We will look at two examples of plant cells: onion and Elodea. Onion An onion is composed of overlapping layers which form rings when the onion is sliced. Cut a small piece of an onion ring approximately 1 cm × 1 cm. On the concave surface of the piece of onion is a thin membrane that consists of many onion cells attached to one another. This membrane is one layer of cells thick. Peel this membrane from the rest of the piece of onion. Be careful to not wrinkle it and place it in a drop of water on a slide. Place a coverslip over the entire preparation and examine under a microscope. It should look something like figure 30.1. Begin viewing the onion cells with low power and proceed to high power to see detail. You should be able to see the following structures that are typical of plant cells; (1) cell wall, (2) nucleus, (3) one or more nucleoli in the nucleus, (4) a large central vacuole, and (5) cytoplasm. The cell wall is found on the outside of the cell and provides a “box” within which the rest of the cell is found. The cell walls of plant cells are composed of a complex carbohydrate known as cellulose. The nucleus will appear as a round or egg-shaped structure inside the cell and the small structures seen inside the nucleus are the nucleoli (singular nucleolus). The vacuole and cytoplasm will probably be the most difficult to recognize. The cytoplasm will appear as a granular material near the cell wall. This will be a very thin layer. There is an outer boundary to the cytoplasm known as the cell membrane which is located inside the cell wall and outside the cytoplasm. However, it is very thin and in plant cells it is pressed up against the cell wall making it difficult to see. Often in unstained cells, which are still alive, the cytoplasm may be seen to flow. Look closely at the granules or specks in the cytoplasm to see if they are moving. These granules are objects or cell structures too small to be seen clearly with the light microscope. The vacuole is a large water-filled space in the center of the cell. Because it does not have any particles in it, it appears to be empty but it is not. These cells are not flat but resemble a structure similar to a shoebox. The box itself represents the cell wall, the space in the center represents the vacuole, and all the other structures (nucleus and cytoplasm) are squeezed in between the cell wall and the vacuole. Figure 30.1 Staining After you have examined the wet mount of the living onion cells, you can stain the cells to make some of the structures easier to see. Biologists often use stains that bind to various macromolecules and structures in the cell to make the structures more visible. Living cells may be stained to show cilia, flagella, the nucleus, or other cell organelles. Some stains destroy cells immediately, whereas others, called “vital stains,” kill cells more slowly. The organisms absorb these stains and continue to carry on their life functions for some time. 1. Use caution when using all stains. Many will stain your hands and clothing. Use Lugol’s solution (composed of iodine and water) to stain your onion tissue, as demonstrated in figure 30.2. Lugol’s solution stains carbohydrates such as starches and glycogen. opposite side of coverslip. Figure 30.2 Microscopic Drawings The average student is not gifted with a “photographic mind” Many observations, including those done using a microscope, must therefore be recorded for later study and review. That means drawings must be made! Make drawings in pencil so that you can make modifications easily. Biological drawings should be simple but accurate representations of your observations. Make your drawings large enough so that you can show clear details. You are not expected to be an artist; such drawings are for your benefit. Drawings should be labeled with a title and the total magnification used. As you make sketches you will look more closely at the cells and this will help you remember what you saw. If you have seen an object well enough to reproduce it accurately in a drawing, then you have seen it well. 1. Sketch the three-dimensional shape of an onion cell in the outline in the space provided. Draw the cell structures in their proper relationships to one another as you viewed them, and label the following: cell wall, vacuole, cytoplasm, nucleus, nucleolus, and the position of the cell membrane. Onion cell Elodea The aquatic plant Elodea provides another good example of plant cells. Use forceps to pluck a young leaf from the tip of a sprig of Elodea and place it on a slide with a drop of water and a coverslip. Examine the leaf under the microscope. Begin with low power and switch to high power to see detail. The leaf is two layers of cells thick. Use the fine adjustment knob to focus up and down with your microscope so that you can see the two layers. Examine the cells under high power. You should be able to see the following structures; (1) cell wall, (2) vacuole, and many small green (3) chloroplasts in the (4) cytoplasm. There is also a nucleus but it is difficult to see among all the chloroplasts. You will also be able to see the cell membrane later. If you scan your slide you should be able to see some cells in which the chloroplasts are moving along the inside of the cell wall. It is actually the cytoplasm that is in motion, therefore, this phenomenon is known as cytoplasmic streaming. Draw and label the three-dimensional structure of an Elodea cell in the space provided. Label the cell wall, cytoplasm, cell membrane, chloroplasts, vacuole. Elodea cell Elodea cell with NaCl (label structures) (label structures) Total magnification = ________ Total magnification = ________ After you have examined the living cells of the Elodea leaf gently remove the coverslip, add a drop of 5% salt solution to the slide, and replace the coverslip. The salt solution will cause water to leave the large central vacuole and the cell will shrink and pull away from the cell wall. This will allow you to see the cell membrane, which is on the outside of the cytoplasm. In the space provided, draw and label an Elodea cell after salt water is added. Kingdom Protista The kingdom Protista contains many different kinds of organisms in which each cell functions as a separate unit. The many kinds of Protista are lumped together in one kingdom for convenience and are subdivided into two major types of organisms, algae and protozoa. Algae are either single cells or groups of similar cells that have cell walls and are capable of photosynthesis. Protozoa lack cell walls and with a few exceptions are not capable of photosynthesis. Spirogyra The freshwater organism, Spirogyra, is a good example of an alga. Spirogyra is composed of cells that are attached to one another end-to-end to form long hairlike strands. Use an eyedropper to obtain a few of these strands from the culture provided and prepare a slide for examination. In many ways a Spirogyra cell will appear similar to those of plants. It has a (1) cell wall, (2) cytoplasm (3) a large vacuole between the strands of cytoplasm and one or two spiral-shaped (4) chloroplasts. On the chloroplast you will be able to see dots. These are (5) pyrenoids which are places in the chloroplast where starch is manufactured. The cell also has a centrally located nucleus which is suspended in the center of the cell by strands of cytoplasm but this is difficult to see without special stains. The cell also has a different shape from that of the plants you looked at previously. These cells are cylindrical rather than boxlike. Draw and label a Spirogyra cell in the space below. Euglena Another member of the kingdom Protista is Euglena. Obtain a drop of the Euglena culture and place it on a slide with a coverslip. Examine it under the microscope. You should be able to see some organisms swimming around. Euglena has a long (1) flagellum at the anterior end that whips about and pulls the cell through the water. You will be able to see that they also have a red (2) eyespot at the base of the flagellum. Within the cytoplasm of the cell you will be able to see several green (3) chloroplasts. The eyespot allows the Euglena to swim toward a source of light and, therefore, position itself so that its chloroplasts receive sunlight. Euglena lacks a cell wall. Its outer covering is a flexible (4) cell membrane so it is able to bend as it swims. It has a nucleus but this is often difficult to see without special staining. Because it has chloroplasts it is able to carry on photosynthesis; however, it is also able to “eat” by taking up organic molecules from its surroundings. Because it has chloroplasts some people classify it with the algae. Because it swims, lacks a cell wall, and eats, some people prefer to classify it with the protozoa. Paramecium Paramecium is a large protozoan, which is just visible to the naked eye. Obtain a drop of culture medium containing Paramecium. They will have been fed yeast cells that were stained with the dye, congo red. You may need to place the organisms in a special syruplike, methyl cellulose solution to slow them down so that you can see them. Your instructor will provide the solution if needed. On their surface protruding through the (1) cell membrane are hundreds of tiny hairlike (2) cilia that they use for movement. On its surface you should be able to see a funnel-like structure through which the Paramecium feeds. Inside the organism you will see a number of spherical (3) food vacuoles containing yeast. Food vacuoles that were recently formed as the organism fed on the yeast will be red. Older food vacuoles in which digestion has begun will turn blue. Although Paramecium does not have a cell wall, it does have a stiff outer layer of its cytoplasm. At either end of the cell you should be able to see a (4) contractile vacuole which periodically fills with water and collapses expelling water from the cell. When the contractile vacuoles are empty they will appear star-shaped. They become large spherical clear areas as they fill with water. Paramecium has a large macronucleus and one or more smaller micronuclei but these are often difficult to see without staining. Draw and label cells of Euglena and Paramecium in the space below. Kingdom Animalia Animal cells are often difficult to study because they are small. They are also easily destroyed when making a slide because they do not have a protective cell wall. Cheek Epithelial Cells Whenever human tissue is used in lab we must follow special precautions. Therefore, the toothpick and the slides and coverslips you use must go in the special disposal container provided. One kind of animal cell that is relatively easy to study is the cheek epithelial cells from the inside of your mouth. Take a toothpick and scrape the inside of your cheek (figure 30.3). Gently scrape the inside of your cheek with the broad end of a toothpick. Figure 30.3 Smear the material from the toothpick onto a slide and add a drop of methylene blue stain and a coverslip. Use low power to locate some cells, then examine them under high power. You should be able to see flattened cells that have an irregular outline. (They will look like blue fried eggs.) The outside surface of the cell is the (1) cell membrane. You should also be able to see a football-shaped (2) nucleus in the (3) cytoplasm of the cell. On the surface of the cell you will be able to see a large number of tiny dots. These are (4) bacteria. Draw a cheek epithelial cell in the space at the top of the next page. Kingdom Fungi Fungi are composed of cells that are attached end-to-end to form long filaments known as (1) hyphae (singular, hypha). These hyphae may form masses with no particular shape or may be organized to form very specific shapes such as mushrooms. We will look at the cells of a common mold. Obtain a sample of the mold and transfer it to a slide with a toothpick. Add a drop of methylene blue stain and a coverslip. Examine it under the microscope. Although the cells are small you should be able to distinguish the following structures: (1) a cell wall surrounding the cell, (2) and large, clear vacuoles, within the (3) cytoplasm of the cells. Nuclei are present but are very small and difficult to see without extremely high magnification. Some fungi have the hyphae divided into individual cells and usually have one nucleus per cell. Other fungi may have two nuclei per cell. Still other fungi do not have cross walls separating the hyphae into individual cells and each hypha has several nuclei in it. You will probably see a large number of spherical structures. These are reproductive structures called spores. The large number of spores produced and their small size makes them ideal mechanisms for distributing the mold to new sources of food. Draw and label a fungal cell in the space below. Domain Eubacteria Most Eubacteria are extremely tiny and difficult to see. Because they lack a nucleus and most other kinds of organelles, it is difficult to see anything other than the general shape and size of the cells. You have already seen some bacteria on your cheek epithelial cells. Now you will view a mixture of bacteria cultured from soil and an example of cyanobacteria (blue-green algae), which is easily collected and viewed. Soil Bacteria Obtain a drop of the culture of soil bacteria, make a wet-mount slide and examine under low power. What you see will be a mixture of many different kinds of organisms: protozoa, worms, algae, etc. Use high power to look for the tiny bacteria. Some of the largest soil bacteria will be corkscrewshaped and will be swimming. These organisms do not have a nucleus and lack the other cellular structures typical of eukaryotic organisms. Therefore, it will be impossible to see any characteristics other than the general shape of the cells. Cyanobacteria Obtain a drop of the culture of Anabaena. It consists of strings of cells attached end-to-end like beads. These cells have a (1) cell wall. Often you will be able to see some larger cells that are specialized to withstand harsh environmental conditions. These specialized cells are called (2) heterocysts. They typically form when the algae begins to dry up from lack of water or when there is a significant change in the temperature. Few other structures are identifiable. Draw and label examples of the bacteria and Anabaena in the space below. Results List two structural differences between prokaryotic cells and eukaryotic cells. Prokaryotic cells are much smaller than eukaryotic cells. Prokaryotic cells lack a nucleus and other complex organelles such as chloroplasts, mitochondria, and so on. List two structural differences between plant and animal cells. How are these structural differences related to the ways the cells function? Plant cells have cell walls and chloroplasts, and generally have a large fluid-filled vacuole in the center. The cell walls provide support and the chloroplasts are responsible for photosynthesis. The large vacuole contains primarily water. In what ways do fungi resemble plant cells? In what ways are they different from plant cells? Fungi have cell walls and often have large vacuoles. Fungi lack chloroplasts and cell wall is not cellulose. Describe three ways in which algal cells and plant cells are similar. Algae have cellulose cell walls, a large vacuole, and chloroplasts. Why are algae and protozoa placed in the same kingdom, Protista? Primarily for convenience, however, they are simple, usually single-celled organisms. Describe the size and location of the vacuole in the onion cell. What does the vacuole contain? The vacuole is centrally located and fills the majority of the cell. It contains primarily water. Was the purpose of this lab accomplished? Why or why not? (Your answer to this question should show thoughtful analysis and careful, thorough thinking.) Solution Manual Experiment for Integrated Science Bill W. Tillery, Eldon D. Enger , Frederick C. Ross 9780073512259
Download
Close
Close
