Pre-Lab Homework for Lab 3: The Microscope

Transcription

1 Pre-Lab Homework for Lab 3: The Microscope Lab Section: Name: To be completed and turned in at the beginning of the lab! 1. What are the goals of this lab? (Hint: Read Lab number 3 to find this answer!) 2. In this week's lab you will be trying to identify living organisms on your slides, but there may also be non-living material on your slide. What are two different properties of life you could see under the microscope that will help you determine if what you are looking at is alive or not? (Hint: Look in chapter 1 of your textbook!) 3. In this lab you will hypothesize about the role an organism plays in an ecosystem. Using your textbook, lecture notes, or any other source, briefly define these terms: heterotroph: autotroph: producer: herbivore: carnivore: decomposer: 4. On the back of this page, explain the role in an ecosystem played by any two organisms you have seen or thought about in the last week using these terms (and any others you like ). 1

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3 Name Lab 3: Introduction to the Microscope GOALS: After successfully completing this lab a student will be able to: Use and care for compound microscopes and dissection scopes. Prepare a wet mount of a provided specimen. Make detailed observations of microscopic slides. Use observations to infer the ecological roles of organisms. Overview: Microscopes have been used by biologists for many years to help us to see organisms, or details of organisms, that would otherwise be invisible. During this lab, you will be introduced to this exciting microscopic world! To investigate this world we will need to spend some time learning the proper use and care of microscopes and the care and preparation of specimens for viewing. By the end of the lab you will have gone a long way toward becoming proficient with this very useful tool. This laboratory has three parts: An introduction to the use and care of the microscopes. An introduction to the preparation and care of specimens. An introduction to microscopic observations. Part I: The Microscope A. Before you get your scope, listen to your instructor and answer the following questions. 1. What are a few things you should do to take care of your microscope as you take it to your desk and as you put it away? 2. What are two things that you can do to make sure your scope's lenses are properly cared for? 3

4 B. Now get a compound microscope from the cabinet, sign the microscope check out sheet, and carry it carefully to your laboratory bench. When carrying a microscope, always use both hands! Grasp the stand firmly with one hand while supporting the base with the other hand. Special consideration must be shown to the microscope lenses; they must be kept clean and free from scratches. Dust should be removed by blowing it off with compressed air or brushing lightly (not by rubbing) with a piece of lens paper (not just any paper or rag that s handy!). As your instructor goes over the basic parts of the microscope fill out the following table of microscope parts and their role. Name LAMP Use: Provides light to view the specimen STAGE MECHANICAL STAGE CONTROLS Magnifies the specimen either 4x, 10x or 40x Eyepiece that magnifies the specimen 10X Raises and lowers the stage quickly Raises and lowers the stage slightly IRIS DIAPHGRAM Answer this question before you go on. 1. What are two things you can do to get the best image possible? 4

5 C. Remember: you are responsible for caring for your slide box and slides - taking good care of these will help all of the labs work smoothly! Please wait and go through the steps for care and use of slides with the class!!! 1. Using a blank slide and a photocopied ruler, measure the width of the field of view, in millimeters (mm), on each of the three different powers. To calculate total magnification you need to multiply the magnification from the ocular and the objective lenses. To calculate the field width in µm you will need to multiply the number of mm by 1000 since 1mm = 1000µm POWER TOTAL FIELD WIDTH IN estimated size of SCANNING MAGNIFICATION mm & µm the e in µm LOW HIGH Now starting with the lowest power objective, place the letter 'e' slide (#2 in your box) on your stage. Center the letter 'e' over the hole of light on the stage using the mechanical slide controls. While looking through the ocular, bring the 'e' into focus using the coarse focus knob. After focusing on the lowest power you should not need to use the coarse focus knob on the higher powers! 5

6 2. Draw and label a sketch of the letter 'e' at 100x. Now, using your knowledge of the width of the field of view, estimate the size of the letter 'e' at each of the powers and fill out the last column of the table. Letter 'e' at 100x 3. Using the prepared slide of the letter 'e' you have just focused on, compare the orientation of the letter through the scope and just by looking at it. What does this tell you about the effect of the lenses on what you are viewing? AN IMPORTANT PART! If you are chasing a fast moving Paramecium (a microscopic protist) and it moves out of your field of view to the right, which way should you move the slide to catch it? 6

7 4. Making sure you are on low, power replace the e slide with the crossed threads. On low power find a region of the slide where several fibers cross one another. Now move to the next higher power. (Remember these are parfocal microscopes, this means you will be nearly in focus at higher powers if you were in focus at the lower - you don't need to lower the stage to change lenses!) What does this slide tell you about the depth of field of the different powers? [Hint: Are more or less of the threads in focus on the higher power?) On the highest power, how can you draw a sketch of the threads as they would appear from the side? (You need to be able to tell which thread is on top, which is next and so on. How could you do that?) AN IMPORTANT PART! If you have a thick slide (many cells thick) how can you see all the layers? Part II: Preparing Slides A. You will be observing specimens on both prepared slides and slides that you make. So far you have been using prepared slides (prepared by someone else!) Now we will go over how to prepare a slide of your own by placing a sample onto a slide. Because we will be using water as a base for our specimen these slides are generally called 'wet mounts'. Steps to prepare wet mounts: 1. Get a slide and a cover slip from your drawer. You may want to take the box of slides and the box of coverslips to your table, but be sure to return them to your drawer at the end of the lab period. 2. Place a drop of pond water on your slide. If you are using a specimen that is not suspended in water (like a piece of mushroom or a hair or ) you would need to add a drop of water to your slide before you add your specimen. 7

8 3. Place one edge of the coverslip on the slide and slowly lower the other side. 4. You have now made your first slide. Congratulations! 5. When you are finished with the slide rinse the organisms back into the pond, rinse the slide off in the sink and clean your slide with a kimwipe - you can reuse the same slide for most of the lab! 6. If you find that the organisms on the slide move too quickly for you to sketch them you can add Protoslo to your slide. To do this, add a drop to the edge of your drop of pond water before you put on the coverslip. You do not need to mix these two - just make your observations in the area of the drop near the Protoslo. Part III: The Pond Water! A. Your goal while viewing your pond water slides is to try to develop an understanding of the differences and similarities between the types of organisms you see in the ponds. On your sketches be sure to include the region of the pond where the sample was taken (floating on top, down in the muck at the bottom?) Then make careful observations of the organisms that you see. As you observe the organisms on your slides, think about how they might compare with other organisms you are more familiar with (trees, raccoons, cougars, deer, grasses ). B. Your sketches need to include: Where the cell came from. The total magnification. An estimation of the size in µm. Any internal structure you can see. Notes on your observations. 8

9 1. Sample location: Power: Sketch of the cell: Notes: 2. Sample location: Power: Sketch of the cell: Notes:. Sample location: Power: Sketch of the cell: Notes: 9

10 4. Sample location: Power: Sketch of the cell: Notes: 5. Sample location: Power: Sketch of the cell: Notes: 6. Sample location: Power: Sketch of the cell: Notes: 10

11 Part IV: Ecological Roles: A. All of the organisms that you have been observing have specific roles in the ecosystem of the pond. These roles are not always clear, though, and it is up to you to decide what role you think these organisms are playing. While looking at these organisms think about their role in the pond. It may help to think about these questions: What color are photoautotrophic organisms usually? How does an organism's movement relate to its role? Does an organism's role relate to its location in the pond? Are some of these organisms more "animal like" or more "plant like"? B. Pick two of the organisms that you have sketched and, using your observations, hypothesize about the role of these organisms in the pond ecosystem. You need to use words like producer, primary and secondary consumer, decomposer, etc. [Hint: For full credit support the hypothesis with observations.] ORGANISM #1: Sketch # Hypothesis of Ecological Role: Evidence What additional information would support your hypothesis? ORGANISM #2: Sketch # Hypothesis of Ecological Role: Evidence: What additional information would support your hypothesis? 11

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