Post lab biology questions

Who Invented the Microscope?

                        Long before an actual connection could be made between microbes and diseases, some historical figures theorized that there could be a relationship between invisible “living creatures” and illness.  This idea was suggested as far back as 98 – 55 BCE by a Roman philosopher named Lucretius.

[1]  Various microscopic lenses were utilized by Galileo (1564 – 1642) and later by Robert Hooke (1635 – 1703) who used a very basic microscope to sketch plants, insects, and fungus in his famous publication Micrographia.

[2]Although these sketches were intriguing, the scope was still very basic and the magnification power was still fairly weak compared to our modern light microscopes.  In other words, we may be able to see the many features of a fly’s eye, but those “invisible creatures” remained quite elusive.

Figure 1: Robert Hooke’s microscope.

            The first individual to actually hunt down and find a true microbe was not a full time scientist.  Antony van Leeuwenhoek (1632 – 1723) was a draper and a haberdasher living in the Netherlands.  He made his living by selling clothing to men and devised a method of working with glass to create convex lenses, or glass spheres.  He created a basic version of the single lens microscope that could magnify and object to 50 to 300 times its original size.  Two glass lenses were held between two silver plates, allowing the observer to see those elusive “invisible creatures” first theorized by Lucretius.[3]  Antony van Leeuwenhoek is therefore credited with being the Father of Microbiology and establishing this field of science.

Figure 2: Replica of Antony van Leeuwenhoek’s microscope.ByJeroenRouwkema, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3657142

What are Microorganisms (Microbes)?

Microorganisms are entities that are generally too small to be seen clearly with the naked eye.  Those that are “larger” are very simple forms of life that don’t have tissues and are rarely larger than 1 mm.[4]Special tools with magnifying power must be utilized on order to observe them.  These can include bacteria, viruses, fungi, and some parasites.  Today we know that some microorganisms can make us ill while others are necessary for us to remain healthy.  In fact, one cutting edge field of study is to understand the human “microbiome” and how it can change from moment to moment and from person to person.

Learn How To Use A Compound Light Microscope

Exercise 1–Review the parts of the compound light microscope with your Instructor or TA and summarize what each part does in your own words.

Procedure:

1. Pay attention as your Instructor or TA reviews the names and the function or each part of the compound light microscope. Summarize what each part does in your own words.

Exercise 2– Investigate Inversion

Procedure:

1. Obtain a slide with the letter “E” from your instructor. Hold the slide in your hands and look at the letter.  Is it right-side-up or up-side-down?

2. Place the slide carefully onto the stage keeping it in the same orientation. Use the metal arms on the stage to hold it in place. Turn the nosepiece so that the lowest-power lens is aligned over your slide. (Note:  This should be the shortest lens).

3. Use the course-adjustment knob to lift the stage slowly (Note: This should be the large outer knob).  See if you can spot the letter on your slide.  You may need to move the stage to the right or to the left.  If you are confused, ask for assistance from the instructor or TA.

4. When you spot the letter “E,” use the fine-adjustment knob to bring the image into better resolution (aka: sharpen the image). This will be the smaller or inner knob.  Record your observations below:

Exercise 3– Investigate Depth

Procedure:

1. Obtain a slide colored thread from your Instructor or TA.

2. Place the slide carefully onto the stage. Use the metal arms on the stage to hold it in place. Turn the nosepiece so that the lowest-power lens is aligned over your slide.  (Note:  This should be the shortest lens).

3. Use the course-adjustment knob to lift the stage slowly until you spot the area where the 3 colored threads meet (Note: This should be the large outer knob).  You may need to move the stage to the right or to the left.  If you are confused, ask for assistance from the instructor or TA.

4. As you change focus, note that only one thread color will be clear at a time. As the stage moves upward, objects on top should come into focus first.  See if you can determine which thread color is on top, which is in the middle, and which is on the bottom of the slide.

Exercise 3– Observe Slides and Sketch Observations

Procedure:

1. Obtain three slides from your Instructor or TA. These may include human cells, algae, fungi, or bacteria.  Be careful to read the label to know exactly what it is you are observing.

2. Using the techniques practiced in Exercise 2, observe each slide with your team members and discuss what exactly you see. Try to describe it in words and sketch your observations in the space provided below:

Slide #1

Slide #2

Slide #3

Apply the Knowledge

1. Are all microorganisms pathogenic? Defend your answer.

2. Describe the ‘ideal’ microscope.

3. Describe the difference between magnification and resolution.

4. What is the purpose of mechanical stage on a compound light microscope?

5. Why would an image be inverted when viewed through the lens?

6. To calculate the total magnification for the microorganism that you are viewing, you would need to multiply the magnification of the ocular lens by the objective lens. Use this knowledge to calculate the magnification for the letter “E” from lab.  Your ocular lens had a magnification of 10x.

7. The units appropriate for measuring an object under a microscope is either a micrometer (um) or a nanometer (nm). These are metric units that can be converted to and from millimeters and centimeters.  Use the conversion factors below to calculate the conversions:

1.0 millimeter (mm)= 1,000 micrometers (um) – 1,000,000 nanometers (nm)

3 mm = _________________________ nm

950,000 nm = _________________________ um

750 um = _____________________________ mm

8. Why would it be beneficial to view the same object at different levels of magnification?

[1]Joanne M. Willey, Linda M. Sherwood, and Christopher J. Woolverton (2008).The Evolution of Microorganisms and Microbiology.  Prescott’s Microbiology. 8^th Ed.  Pp 12 – 17

[2]Joanne M. Willey, Linda M. Sherwood, and Christopher J. Woolverton (2008).The Evolution of Microorganisms and Microbiology.  Prescott’s Microbiology. 8^th Ed.  Pp 12 – 17

[3]Joanne M. Willey, Linda M. Sherwood, and Christopher J. Woolverton (2008).The Evolution of Microorganisms and Microbiology.  Prescott’s Microbiology. 8^th Ed.  Pp 12 – 17

[4]Joanne M. Willey, Linda M. Sherwood, and Christopher J. Woolverton (2008).The Evolution of Microorganisms and Microbiology.  Prescott’s Microbiology. 8^th Ed.  Pp 2 – 3

BIOL-102 2019 Fall Post-lab 2

Name:

Exercise 1 – Review the parts of the compound light microscope with your Instructor or TA and summarize what each part does in your own words.

3. Microscopy: chapter-ending questions
4. Are all microorganisms pathogenic? Defend your answer.

2. Describe the ‘ideal’ microscope.

3. Describe the difference between magnification and resolution.

4. What is the purpose of mechanical stage on a compound light microscope?

5. Why would an image be inverted when viewed through the lens?

6. To calculate the total magnification for the microorganism that you are viewing, you would need to multiply the magnification of the ocular lens by the objective lens. Use this knowledge to calculate the magnification for the letter “E” from lab.  Your ocular lens had a magnification of 10x.

7. Why would it be beneficial to view the same object at different levels of magnification?

(summarize your microscopic observation [pictures] below; no page limit)

6. Cell structure and function: chapter-ending questions

1. What is a cell?

2. Would you expect a cell of a multicellular organism to be more complex than the cell of a unicellular organism? Less complex? Why?

3. What is the purpose of using a biological stain when microscopically examining cellular components?

4. How are eukaryotic cells different from prokaryotic cells? How are they similar?

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Last Updated on October 1, 2019