LEARNING ABOUT THE NATURAL WORLD

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EXERCISE 1

LEARNING ABOUT THE NATURAL WORLD

Answers to Pre-lab Questions in Lab Manual Order 1.a 2.b 3.c 4.c 5.b 6.b 7.d 8.d 9.c 10.b Answers to Post-lab Questions 1.How does the modern scientific method differ from the natural philosophy of the ancient Greeks?The philosophy of the ancient Greeks was based on the belief that only natural forces govern living things and it accepted the concept of absolute truth which suppressed the testing of principles after they were formulated. Modern scientific method tests predictions of possible answers to questions in a manner that can be duplicated.

2.List the six steps of one full cycle of the scientific method. a. observation; b. question;

• hypothesis; d. prediction; e. experiment or pertinent observations; f. conclusion

3.What is tested by an experiment? The validity of the hypothesis is tested.

4.Within the framework of an experiment, describe the a. independent variable; b. dependent variable; c. controlled variables. a. The treatment or condition under study; b. The event or condition that is measured or observed when the results are gathered; c. All other factors which the investigator attempts to keep the same for all groups under study.

5.Is the statement, “In most biology experiments, the relationship between the independent and the dependent variable can best be described as cause and effect,” true or false? Explain your answer. True. Because the dependent variable is what is measured as a result of the varying of the independent variable.

6.Is a scientific principle taken as absolutely true? Explain your answer. A principle is accepted as absolutely true until new evidence arises to the contrary.

7.What is the function of research articles? To allow the scientific community to share their Knowledge in order to hasten the process of scientific discovery.

8.Identify three sources where research articles can be found. Primary research journals like Science, Nature, or The Lancet, the internet and government sponsored sites such as those from the NIH, CDC and others.

9.Describe how you have applied or could apply the scientific method to an everyday problem.This answer will vary from student to student but should include the basic steps of the scientific method such as observation, hypothesis formation, experimentation, data and conclusions.

10.Do you think the differences between religious and scientific knowledge make it difficult to debate points of perceived conflict between them? Explain your answer. Yes, because emotions will always become involved. However, in order to solve a problem, scientific Answers to Pre-lab Questions in Instructor’s Manual Order 1.a 2.b 3.c 4.c 5.b 6.b 7.d 8.d 9.c 10.b Laboratory Manual for Human Biology, 2e David Morton, Joy Perry, James Perry (Answer Key All Chapters) 1 / 4

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facts that may be proven by the scientific method must be separated from religious beliefs that are often based on faith alone. 2 / 4

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EXERCISE 2

OBSERVING MICROSCOPIC DETAILS OF THE NATURAL

WORLD Answers to Pre-lab Questions in Lab Manual Order

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Answers to Post-lab Questions

• What is the function of each of the following parts of a compound light microscope? a. condenser

lens—focuses the light on the specimen so that each of its points is evenly illuminated. b. iris diaphragm—limits the cone of light reaching the back of the objective lens; effectively controls contrast. c. objective—projects an image of the specimen to a point just beneath the ocular. d. ocular—magnifies the image produced by the objective, and, in conjunction with the eye lens, projects an image onto the retina.

• In order, list the lenses in the light path between a specimen viewed with the compound light

microscope and its image on the retina of the eye. Objective, ocular, lens of eye.

• What happens to contrast and resolving power when the aperture of the condenser (that is, the size

of the hole through which light passes before it reaches the specimen) of a compound light microscope is decreased? Contrast increases, resolving power (quality of image) decreases.

• What happens to the field of view in a compound light microscope when the total magnification is

increased? The field of view decreases.

• Describe the importance of the following concepts to microscopy. a. magnification—The lenses

of the compound light microscope project a magnified image of the specimen to a position where the eye lens can focus this image onto the retina. Magnification of this image results in a specimen detail covering a larger proportion of the retina than it would otherwise cover. b. resolving power—Magnification is useful only when adjacent points in a specimen are seen as separate. Magnification without adequate resolving power would be “empty’ in that specimen details would not be preserved. c. contrast—Contrast is necessary to see a specimen detail against the background of the image. That is, there must be sufficient intensity or color difference, or both, between a detail and the surrounding specimen for the detail to be seen.

• Which photomicrograph of unstained cotton fibers was taken with the iris diaphragm closed?

Photomicrograph a, which has the greatest contrast.

• Describe how you would care for and put away your compound light microscope at the end of the

laboratory period. Turn off light source. Rotate objective so that lowest-power objective is in light path. Remove slide from stage. Clean all lenses with lens tissue. Fold power cord onto itself and secure with rubber band or plastic strap. If supplied, place dust cover over microscope. Return to cabinet, holding on to the microscope arm with one hand while supporting the microscope base with the other.

Answers to Pre-lab Questions in Instructor’s Manual Order

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• Describe how to make a wet mount. Use a razor to cut a thin section of the material to be

observed. Place it on a glass microscope slide and add a drop of distilled water. Place a glass coverslip on one side of the specimen at a 45 degree angle and slowly lower it with a dissecting needle to avoid air bubbles.

• A camera mounted on a _____ microscope took this photo of a cut piece of cork. Transmission

Electron Microscope.

• Why were humans unaware of microorganisms for most of their history? Because the creatures

were too small to be seen with the naked eye.

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