Laboratory Resource Guide to accompany Biology Laboratory Manual Twelfth Edition
Sylvia S. Mader
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Mader: Biology 12/e Lab Resource Guide Part I The Cell 1 Scientific Method 2 Metric Measurement and Microscopy 3 Chemical Composition of Cells 4 Cell Structure and Function 5 How Enzymes Function 6 Photosynthesis 7 Cellular Respiration Part II The Genetic Basis of Life 8 Mitosis 9 Meiosis 10 Mendelian Genetics 11 Human Genetics 12 DNA Biology and Technology 13 Evidence of Evolution 14 Natural Selection Part III Microbiology and Evolution 15 Bacteria and Protists 16 Fungi Part IV Plant Evolution and Biology 17 Nonvascular Plants and Seedless Vascular Plants 18 Seed Plants 19 Organization of Flowering Plants 20 Water Absorption and Transport in Plants 21 Control of Plant Growth and Responses 22 Reproduction in Flowering Plants Part V Animal Evolution and Diversity 23 Introduction to Invertebrates 24 Invertebrate Coelomates 25 The Vertebrates Part VI Comparative Animal Biology 26 Animal Organization 27 Basic Mammalian Anatomy I 28 Chemical Aspects of Digestion 29 Basic Mammalian Anatomy II 30 Homeostasis 31 Nervous System and Senses 32 Musculoskeletal System 33 Animal Development Part VII Ecology 34 Sampling Ecosystems 35 Effects of Pollution on Ecosystems
Page 3 9 17 24 33 40 47 51 55 58 66 72 77 83 87 93 99 104 110 116 122 129 134 140 146 151 160 167 171 178 183 188 192 194
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Laboratory
1
Scientific Method (LM pages 1–8)
MATERIALS AND PREPARATIONS Instructions are grouped by procedure. Some materials may be used in more than one procedure. Special Requirements Living material. Live pillbugs, Armadillidium vulgare, for all sections of lab. Earthworm alternative. See appendix below if you wish to use earthworms instead of pillbugs in all sections of lab. Fresh material. Substances for instructor to feed pillbugs and substances for students to test pillbug behavior (see Section 1.4 below). 1.2
Observing the Pillbug (LM pages 4–5) _____ pillbugs, Armadillidium vulgare, live (Carolina 14-3082) _____ pen, white (or correction fluid, white) or tape tags _____ magnifying lenses or stereomicroscopes _____ small glass or plastic dishes, such as disposable petri dishes _____ graduated cylinders or small beakers for observing pillbug movement _____ rulers, metric, 30 cm plastic _____ stopwatch
Live pillbugs (LM pages 1–7). Obtain 50 pillbugs for a class of 20 to 35 or more students. Order pillbugs so that they arrive as close as possible to the date they will be needed. Use one container of fresh pillbugs for each lab. Care and feeding of pillbugs: Follow care and feeding instructions provided with the pillbug order. Withdraw food 1–2 days prior to the experiment. Use white correction fluid or tape tabs to number the pillbugs for identification. Collecting pillbugs (LM pages 1–7) Pillbugs like moisture, and avoid sunlight. They can be found next to brick buildings along the grass line or next to sidewalks, or under logs and planks of wood. They are attracted to wet grass covered with a cardboard box or plastic tarp. Encourage students to collect their own pillbugs and give them lab participation points. Collect pillbugs in the spring, summer, and fall as they are hard to find in the winter. Maintaining pillbugs in the lab (LM pages 1–7) After collecting, pillbugs can be easily maintained in a terrarium to keep a fresh supply all year long. They feed primarily on decaying organic matter; they like moisture and avoid sunlight. They like carrots and cucumbers. Change the food daily to prevent mold growth. 1.3
Formulating Hypotheses (LM page 6)
1.4
Performing the Experiment and Coming to a Conclusion (LM pages 6–7) _____ pillbugs, Armadillidium vulgare, live
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_____ small beakers, 35-mm film cans, watch glasses, or small petri dishes for distributing test substances _____ petri dishes, preferably 150 mm (or else 100 mm) for testing the pillbugs _____ small plastic bottle for spritzing _____ distilled water _____ cotton balls Suggested test substances: _____ flour _____ cornstarch or bran flakes _____ coffee creamer _____ baking soda _____ fine sand (control) _____ milk _____ orange juice or apple juice _____ ketchup _____ applesauce _____ carbonated beverage _____ water (control) Do not use salt, vinegar, or honey, as these substances are harmful to pillbugs. Plain water is used as a control for liquids. Fine sand is used as a control for powders. Experimental design (LM pages 6–7) These methods are recommended: For a dry substance, make a circle of the test substance in a petri dish and put the pillbug in the center of the circle. For a liquid, put a cotton ball soaked with the test substance in the pillbug's path. Rinse pillbugs between testing procedures by spritzing with distilled water and then placing them on a paper towel to dry. Cleanup (LM pages 6–7). Cleanup is easier and the experiment goes well if there is a limited number of test substances and each student chooses only two dry and two liquid test substances. Substances can be distributed to several stations in small beakers, 35-mm film cans, watch glasses, or small petri dishes. Testing pillbugs in 150 mm petri dishes works well.
EXERCISE QUESTIONS 1.1 Using the Scientific Method (LM pages 2–3) Why does the scientific method begin with observations? To study the natural world, scientists have to observe natural phenomena. What is the benefit of formulating a hypothesis? The hypothesis tells what is to be tested by experiment or further observations. Why must a scientist keep complete records of an experiment? So others can repeat the experiment and can check that the data are valid. What is the purpose of the conclusion? The conclusion tells what has been learned from the experiment (or further observations). How is a scientific theory different from a conclusion? Each experiment has a conclusion. A scientific theory is based on many conclusions from various experiments in related fields. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
1.2 Observing the Pillbug (LM pages 4–5) Observation: Pillbug’s External Anatomy (LM page 4) 1. Examine the exterior of a pillbug. • How can you recognize the head of a pillbug? The head bears antennae and eyes. • How many segments and pairs of walking legs are in the thorax? There are 7 segments and 7 pairs of legs. Observation: Pillbug’s Motion (LM page 5) 1. Watch a pillbug's underside. a. Describe the action of the feet and any other motion you see. The seven pairs of legs move with the front pair leading, and each pair moves in succession thereafter. b. Allow a pillbug to crawl on your hand. Describe how it feels. It tickles the skin as it moves. c. Does a pillbug have the ability to move directly forward? Yes d. Do you see evidence of mouthparts on the underside of the pillbug? A pillbug has four pairs of mouthparts. 2. As you watch the pillbug, identify a. the anatomical parts that allow a pillbug to identify and take in food. Antennae, eyes, and mouthparts b. behaviors that will allow a pillbug to acquire food. For example, is the ability of a pillbug to move directly forward a help in acquiring food? Explain. Yes because it is the most efficient way to reach food. What other behaviors allow a pillbug to acquire food? A pillbug has the ability to eat food. c. a behavior that helps a pillbug avoid dangerous situations The pillbug rolls into a ball when it is threatened. 3. Measure the speed of three pillbugs. See Table 1.1 Pillbug Speed Table 1.1 Pillbug Speed* Pillbug Millimeters Traveled (mm) 1 71 2 132 3 64
Time Speed (sec) (mm/sec) 30 2.36 60 2.20 30 2.13 Average speed 2.23 mm/sec *Answers will vary. The answers provided here are examples. 1.3 Formulating Hypotheses (LM page 6) 2. Hypothesize in Table 1.2 how you expect the pillbug to respond, and offer an explanation for your reasoning. The following is an example of three possible student hypotheses regarding flour. Students uses "0" for no response, "—" for moves away from the substance and "+" for moving toward the substance and eating it.
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Table 1.2 Hypotheses About Pillbug’s Response to Potential Foods Substance Hypothesis Reason for Hypothesis Flour 0 Flour is a bland substance. Flour — Flour is a dry substance. Flour + Flour is a food substance. 1.4 Performing the Experiment and Coming to a Conclusion (LM pages 6–7) Experimental Procedure: Pillbug’s Response to Potential Foods (LM pages 6–7) 5. Do your results support your hypotheses? Table 1.3 Pillbug’s Response to Potential Foods Substance Pillbug’s Response Hypothesis supported? Flour + Depends on hypotheses Cornstarch + Coffee creamer + Baking soda — Fine sand 0* Milk + Orange juice — Ketchup — Applesauce + Carbonated beverage + Water 0* *pillbugs may move toward these substances but do not eat them. 6. Are there any hypotheses that were not supported by the experimental results (data)? Answer depends on student hypotheses. What do they tell you about pillbug behavior? Pillbugs prefer moist substances. 7. Compare your results with those of other students who tested the same substances. Complete Table 1.4. Table 1.4 Pillbug's Response to Potential Foods: Class Results Answers will vary depending on class data. 8. On the basis of the class data do you need to revise your conclusion for any particular pillbug response? Depends on class data 9. Did the pillbugs respond as expected to the controls, i.e., did not eat them? If they did not, the controls are suitable to use as controls.
LABORATORY REVIEW 1 (LM page 8) 1. What are the essential steps of the scientific method? The scientific method usually includes: new observations, formulating a hypothesis, testing the hypothesis through experimentation and further observations, and reaching a conclusion. 2. What is a hypothesis? A hypothesis is a tentative explanation of observed phenomena. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
3. Is it sufficient to do a single experiment to test a hypothesis—why or why not? No, multiple experiments are needed to assure accuracy of the results. 4. What do you call a sample that goes through all the steps of an experiment but does not contain the factor being tested? A control 5. What part of a pillbug is for protection, and what does it do to protect itself? The exoskeleton is for protection; it rolls into a ball to protect itself. 6. Name one observation that you used to formulate your hypotheses regarding pillbug reactions toward various substances. Personal experience with the test substances 7. Why is it important to test one substance at a time when doing an experiment? Allows a response of attraction or avoidance to be recorded accurately per substance Indicate whether statements 8 and 9 are hypotheses, conclusions, or scientific theories. 8. The data show that various vaccines protect people from disease. Conclusion 9. All living things are made of cells. Scientific theory 10. How should an affirmative conclusion always be worded? The results of this study support the hypothesis that … (hypothesis should be restated).
Earthworm Alternative Earthworms can be used instead of pillbugs for all of the exercises in this laboratory. Place earthworms in large rectangular plastic storage containers and let them roam around for approximately 15 min. (can also be used to keep earthworms between experiments). Plexiglass is also needed to place test substances on while holding earthworms above to see behavior towards substances. Earthworms want to move rapidly to escape. They are inclined to move away from light, move under things, and seem to want to move downward. They are expected to move away from heat source. They also move toward each other and pile up on each other. They can move up and down on glass at a 45 degree angle. With regard to what students already know about earthworm activity, they might predict certain behaviors. Earthworms live (or hide) in the soil, so they would move down and through soil. Soil prevents desiccation and keeps them cool and moist. By moving under things, they could stay cooler, stay moist, and stay hidden in the dark. Perhaps light bothers them also. Earthworms can move backward and forward from both ends. When they are investigating a substance, they make a long, skinny point out of the end they are investigating with, and if they are repelled by a substance, they pull back and the end becomes thick and round. When testing with liquids, if earthworm gets even close to the substance, the substance will be pulled along the earthworm’s body without the earthworm doing anything. Is this capillary action or cohesion tension? To prevent this, hold the earthworm above the substance, in case the substance (especially lemon juice) might harm the earthworm. Just let the worm move its pointed end into or near the substance. You can tell when it is repelled as it will pull away. Rinse the earthworm right away if it touches a substance (especially lemon juice).
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WHEN FINISHED WITH EARTHWORMS, mix damp potting soil with some oatmeal, potato peels, lettuce, or other organic matter from the test—not too much, just enough to give the earthworms something to eat. Add earthworms. Cover container with newspaper. Keep soil damp. When completely finished, release earthworms into garden or greenhouse soil.
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Laboratory
2
Metric Measurement and Microscopy (LM pages 9–27)
MATERIALS AND PREPARATIONS Instructions are grouped by procedure. Some materials may be used in more than one procedure. Special Requirements Living material. Euglena. Fresh material. Onion, pond water (order if not available locally).
2.1 The Metric System (LM pages 10–14) Length _____ rulers, plastic millimeter _____ meterstick, metric and English _____ long bones from disarticulated human skeleton _____ cardboard (10 cm x 30 cm), two pieces Weight _____ balance scale _____ wooden block, small enough to hold in hand _____ object, such as a penny, a piece of granite, or a trilobite fossil, small enough to fit through the opening of a small graduated cylinder Volume _____ _____ _____ _____ _____ _____ _____
wooden block and object from above graduated cylinders, 50 ml or 100 ml test tubes (large enough to hold 20 ml of water) dropper bottles containing water index card, blank white (20 cm or 30 cm) beaker, 50 ml graduated pipet (for demonstration)
Temperature _____ thermometer, Celsius _____ cold water, hot water, ice water (conveniently available for temperature measurement) 2.2
Microscopy (LM pages 15-16) _____ paper and pencil
2.3
Stereomicroscope (Dissecting Microscope) (LM pages 17–18) _____ microscope, stereomicroscope with illuminator _____ lens paper
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_____ an assortment of objects for viewing (e.g., coins, plastomount) 2.4
Use of the Compound Light Microscope (LM pages 19–23) _____ microscopes, compound light _____ lens paper _____ slide, prepared: letter e ; or newspaper, scissors, slides and coverslips _____ rulers, clear plastic millimeter from above _____ slide, prepared: colored threads; or to prepare your own, you will need slides and coverslips, three or four colors of sewing thread (or hairs), scissors, and a dropper bottle of water
2.5
Microscopic Observations (LM pages 24–26) All exercises: _____ microscope slides (glass or plastic) _____ coverslips _____ lens paper _____ microscopes, compound light _____ methylene blue solution, or iodine-potassium-iodide (IKI) solution (premade) in dropper bottle Onion Epidermal Cells _____ onion, fresh _____ scalpel Human Epithelial Cells _____ toothpicks, prepackaged flat for student to obtain cells from mouth _____ ethyl alcohol (ethanol), 70% ; or alcohol swabs (if toothpicks are not individually prepackaged) _____ biohazard waste container for toothpicks _____ container of 10% bleach solution for slides and coverslips (to be washed directly or autoclaved and washed at lab technician’s discretion) or _____ prepared slide: human stratified squamous epithelium, cheek Euglena _____ Protoslo® or methyl cellulose solution _____ Live Euglena culture (from a biological supply house) and/or _____ pond water, obtain locally or order from supply house _____ pictorial guides Microscope supplies. Set aside an area in the laboratory for storage of clean microscope slides, coverslips, and lens paper. Post a notice in this area, outlining the established procedures for handling dirty slides. Possible procedures include: 1. Wash, rinse, and dry all slides, and return them to their boxes; discard plastic coverslips. 2. Wash and rinse all slides, and place them in the drying rack. 3. Place dirty slides in the detergent solution provided; discard plastic coverslips. Some laboratories prefer that the laboratory assistant wash all slides in an ultrasonic cleaner, rinse the slides in distilled water, and allow the slides to drain dry. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
4. Discard plastic coverslips. Glass coverslips should be placed in detergent solution in a beaker. 5. To eliminate the possibility of contact with pathogens, the epithelial slide exercise (page 25) can be done as a demonstration using a flexscope or videoscope for students to view from their seats. Otherwise, use a biohazardous waste container for toothpick disposal, and wash slides and coverslips in a 10% bleach solution. Microscopes should also be wiped with a disinfecting solution. Solutions/Reagents. Order solutions/reagents or prepare your own. Methylene blue solution (LM page 25) Make up a 1.5% stock solution, using 1.5 g methylene blue stain (dye powder) in 100 ml of 95% ethyl alcohol. Dilute one part stock solution with nine parts water for laboratory use, or use iodine (IKI) solution. Methylene blue staining solution can also be purchased premade. Iodine (IKI) solution (LM page 25) Iodine-potassium-iodide (IKI) solution can be purchased premade, or the ingredients can be purchased separately as potassium iodide (KI) and iodine (I). These dry ingredients have a long shelf life and can be mixed as needed according to the following recipe: To make a liter of stock solution, add 20 g of potassium iodide (KI) to 1 liter of distilled water, and stir to dissolve. Then add 4 g of iodine crystals, and stir on a stir plate; dissolution will take a few hours or more. Keep the stock reagent in dark, stoppered bottles. For student use, place in dropper bottles. Label as “iodine (IKI) solution.” Iodine solution stored in clear bottles loses potency over time. If the solution lightens significantly, replace it. Small dropper bottles can be stored for about a month, and they are used in other exercises. A screw-capped, brown bottle of stock iodine can be stored for about six months. Dispose of it if the solution turns light in color. Protoslo® (or methyl cellulose solution) (LM page 25) You can also use glycerol and water as a substitute for Protoslo®. Note: Thickened Protoslo® can be reconstituted with distilled water. Pond water (LM page 26) A good culture of pond water can be maintained to provide algae and protozoans during any season. Collect pond water during an active growing season from any local pond or stream. Include some algae and a small amount of organic debris and living aquatic (aquarium) plants, such as Elodea. Place the collected pond water and other items in a transparent container with a large surface area. Both container and lid should be transparent. A large culture dish covered with another culture dish or a small aquarium is suitable as a container. If kept in diffuse window light or under artificial illumination, the culture will grow and provide material for future labs, even in the middle of winter. If live cultures of pond water organisms or Euglena are purchased for a particular laboratory, they can be added to the maintained culture once they are no longer in use.
EXERCISE QUESTIONS 2.1 The Metric System (LM pages 10–14) Length (LM pages 10–11) 1. How many centimeters are represented? Usually 15 One centimeter equals how many millimeters? 10 According to Table 2.1, 1 µm = 0.001 mm, and 1 nm = 0.000001 mm. Therefore, 1 mm = 1,000 µm = 1,000,000 nm. 2. Measure the diameter of the circle shown to the nearest millimeter. This circle is 38 mm = 38,000 µm = 38,000,000 nm. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
For example because there are 1,000 µm in one mm, 38 mm = 38,000 µm 3. How many centimeters are in a meter? 100 How many millimeters are in a meter? 1,000 The prefix milli- means thousandth. 4. For example, if the bone measures from the 22 cm mark to the 50 cm mark, the length of the bone is 28 cm. If the bone measures from the 22 cm mark to midway between the 50 cm and 51 cm marks, its length 28.5 cm = 285 mm. 5. Record the length of two bones. Recorded lengths will vary. Weight (LM page 11) 2g = 2,000 mg; 0.2 g = 200 mg; and 2 mg = 0.002 g Experimental Procedure: Weight (LM page 11) 2. Measure the weight of the block to the tenth of a gram. Answers will vary. 3. Measure the weight of an item small enough to fit inside the opening of a 50 ml graduated cylinder. Answers will vary. Volume (LM pages 12–13) 1. For example, use a millimeter ruler to measure the wooden block used in the previous Experimental Procedure to get its length, width, and depth. Answers will vary according to the size of the block used. Computations of volume will also vary. 3. Hypothesize how you could find the total volume of the test tube. Fill the test tube with water, and pour the water into the graduated cylinder. Read the volume in milliliters. What is the test tube’s total volume? Answers will vary. 4. Hypothesize how you could use this setup to calculate the volume of an object. Fill the cylinder with water to the 20 ml mark. Drop the object into the cylinder, and read the new elevated volume. The difference between the two readings is the volume of the object alone. Now perform the operation you suggested. Answers will vary. 5. Hypothesize how you could determine how many drops from the pipet of the dropper bottle equal 1 ml. Using a 10 ml graduated cylinder, count the number of drops it takes to get to 1 ml. How many drops from the pipet of the dropper bottle equal 1 ml? Approximately 10 (Answers will vary with student’s technique and with the type of pipet.) 6. Are pipets customarily used to measure large or small volumes? Small Temperature (LM page 14) 1a. Water freezes at 32°F = 0°C. 1b. Water boils at 212°F =100°C. 2. Human body temperature of 98°F is what temperature on the Celsius scale? 37°C 3. Record any two of the following temperatures in your lab environment. Answers will vary. 2.2 Microscopy (LM pages 15–16) Electron Microscopes (LM page 16) Conclusions: Microscopy (LM page 16) • Which two types of microscopes view the surface of an object? (1) stereomicroscope; (2) scanning electron microscope • Which two types of microscopes view objects that have been sliced and treated to improve contrast? Compound light microscope and transmission electron microscope • Of the microscopes just mentioned, which one resolves the greater amount of detail? Transmission electron microscope Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
2.3 Stereomicroscope (Dissecting Microscope) (LM pages 17–18) Identifying the Parts (LM page 17) 2. What is the magnification of your eyepieces? 10x or 20x Locate each of these parts on your stereomicroscope, and label them on Figure 2.7. Figure 2.7, top to bottom: Eyepiece lens, magnification changing knob, binocular head; illuminator, focusing knob Focusing the Stereomicroscope (LM page 18) 4. Does your microscope have an independent focusing eyepiece? Yes (most likely) Is the image inverted? No 5. What kind of mechanism is on your stereomicroscope? Answers will vary. 2.4 Use of the Compound Light Microscope (LM pages 19–23) Identifying the Parts (LM pages 19–20) 1. What is the magnifying power of the ocular lenses on your microscope? The magnifying power of the ocular lenses is marked on the lens barrel (usually 4x, 10x and 40x). 5. Objectives (objective lenses) a. What is the magnifying power of the scanning objective lens on your microscope? (usually 4x). b. What is the magnifying power of the low-power objective lens on your microscope? The magnifying power of the low-power objective lens is marked on the lens barrel (usually 10x). c. What is the magnifying power of the high-power objective lens on your microscope? The magnifying power of the high-power objective lens is marked on the lens barrel (usually 40x). d. Does your microscope have an oil immersion objective? Depends on microscope 6. Does your microscope have a mechanical stage? Depends on microscope Figure 2.8. Left side, top to bottom: ocular lens or lenses, viewing head, nosepiece, objective lens or lenses, condenser, diaphragm/diaphragm control lever, light source Right side, top to bottom: arm, stage clips, stage, coarse-adjustment knob, fineadjustment knob, base Inversion (LM page 21) Observation: Inversion (LM page 21) 1. Draw the letter e as it appears on the slide (with the unaided eye, not looking through the eyepiece). The letter should be in the normal position. 2. Draw the letter e as it appears when you look through the eyepiece. The letter should be upside down and reversed. 3. What differences do you notice? The letter is inverted—that is, it appears to be upside down and reversed compared to its appearance when viewed by the unaided eye. 4. Move the slide to the right. Which way does the image appear to move? The image appears to move to the left. 5. Move the slide toward you. Which way does the image appear to move? The image appears to move away from you. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Focusing the Compound Light Microscope—Higher Powers (LM page 21) 5. On a drawing of the letter e, draw a circle around the portion of the letter that you are now seeing with high-power magnification. A small portion will be circled. Total Magnification (LM pages 22) Observation: Total Magnification (LM page 22) Calculate total magnification figures for your microscope, and record your findings in Table 2.3. Table 2.3 Total Magnification* Objective Scanning power (if present) Low power High power Oil immersion (if present) *Answers may vary with equipment.
Ocular Lens 10x 10x 10x 10x
Objective Lens 4x 10x 40x 100x
Total Magnification 40x 100x 400x 1,000x
Field of View (LM pages 22–23) Observation: Field of View (LM pages 22–23) Low-power (10x) Diameter of Field (LM page 22) 2. Estimate the number of millimeters, to tenths, that you see along the field: Approximately 1.6 mm. Convert the figure to micrometers: Approximately 1,600 µm. High-power (40x) Diameter of Field (LM page 22) 1. To compute the high-power diameter of field (HPD), substitute these data into the formula given: a. LPD = low-power diameter of field (in micrometers) = 1,600 µm b. LPM = low-power total magnification (from Table 2.3) = 100x c. HPM = high-power total magnification (from Table 2.3) = 400x HPD = (1,600 µm) x (100x) = 400µm (400x) Conclusions: Total Magnification and Field of View (LM page 23) • Does low power or high power have a larger field of view (one that allows you to see more of the object)? Low power • Which has a smaller field but magnifies to a greater extent? High power • To locate small objects on a slide, first find them under low power; then place them in the center of the field before rotating to high power. Depth of Field (LM page 23) Observation: Depth of Field (LM page 23) 2. Determine the order of the threads or hairs, and complete Table 2.4.
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Table 2.4 Order of Threads (or Hairs)* Depth Thread (or Hair) Color Top Red Middle Blue Bottom Yellow * The order of threads given is that of Carolina Biological Supply Company slide 29-1418. The order of threads in other slides may be different. 2.5 Microscopic Observations (LM pages 24–26) Observation: Onion Epidermal Cells (LM page 24) Label Figure 2.11. 1. nucleus; 2. cell wall 5. Count the number of onion cells that line up end to end in a single line across the diameter of the high-power (40x) field. For example, five cells What is your high-power diameter of field (HPD) in micrometers? 400 µm. Calculate the length of each onion cell (HPD / number of cells): For example, 80 µm. Observation: Human Epithelial Cells (LM page 25) 3. Label Figure 2.12. 1. plasma membrane; 2. nucleus; 3. cytoplasm Table 2.5 Differences Between Onion Epidermal and Human Epithelial Cells Differences Onion Epidermal Cells Human Epithelial Cells (Cheek) Shape Square or rectangular Rounded Orientation Regular (in rows) Random Boundary Thick Thin Observation: Euglena (LM page 25) 5. Compare your Euglena specimens with Figure 2.13. List the labeled features that you can actually see: Answers will vary. Observation: Pond Water (LM page 26) Use Figure 2.13 to help you identify organisms you see in Pond Water.
LABORATORY REVIEW 2 (LM page 27) 1.
Make the following conversions: a. 1 mm = 1,000 µm = 0.1 cm b. 15 mm = 1.5 cm = 15,000 µm c. 50 ml = 0.05 liter d. 5g = 5,000 mg 2. Explain the designation “compound light” microscope: a. compound There are two sets of lenses—objective and ocular. b. light Light is used to view the object. 3. What function is performed by the diaphragm of a microscope? The diaphragm regulates the amount of light coming through the lenses. 4. Why is it helpful for a microscope to be parfocal? Little, if any, adjustment is needed when switching from low to high power.
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5. Why is locating an object more difficult if you start with the high-power objective than with the low-power objective? The diameter of field is smaller in high power than in low power. 6. How much larger than actual size does an object appear with a low-power objective lens? 100x 7. A virus is 50 nm in size. a. Would you recommend using a stereomicroscope, compound light microscope, or an electron microscope to see it? Electron microscope Why? Only an electron microscope has the capability of observing an object this small because it magnifies more and has greater resolving power. b. How many micrometers is the virus? 0.05 µm 8. If the diameter of a field is 1.6 mm, and you count 40 consecutive cells from one end of the field to the other, how wide is each cell of micrometers? 40 µm 9. What type of microscope, aside from the compound light microscope, might you use to observe the organisms found in pond water? Stereomicroscope 10. Briefly describe the necessary steps for observing a slide at low power under the compound light microscope. Center the slide on the stage. Looking from the side, decrease the distance between the slide and the objective lens until the lens comes to a stop. Looking through the ocular lens(es), use the coarse-adjustment knob to increase the distance between the slide and the lens until the object comes into view.
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