GCCCD Microscopy Activity Determination of Specimen Size Questions
Exercise 3: The Unseen World, Part 1: Introduction to MicroscopyMost of us have been conditioned throughout our life to believe that what we see with our eyes represents all that exists and that our eyes give us a valid picture of an item or an event. But in Exercise 1 you learned that just because you can’t see something, doesn’t mean it isn’t there (remember the sugar in the soda bottle and the differences in candle observations between you and your lab partner?).The reality is that our eyes are only capable of seeing a small percentage of the life that exists on Earth. Take a drop of water from a pond, look at it under a microscope and you will enter a whole new universe that you probably never suspected existed. At an even smaller scale, the individual molecules that make up living organisms cannot be seen at all, but must be measured by some indirect means. In today’s lab exercise you will learn to use some of the tools that will allow you to investigate part of that invisible realm next week. In a few weeks you will learn how to measure the presence of molecules that cannot be seen at all. Remember to use the information in the pre-lab to think about the questions posed here.The ScenarioYou are a scientist who is studying the ecosystem of a small pond near your home. You have decided to examine the pond over the next year to find out how the composition of organisms living in the pond changes over the year. This will be your initial set of observations about the pond. But before you can do your pond study, you will need to be sure that you know how to use the new microscope that was purchased for your study. The first four activities will help you learn to work with the microscope. Next week you will put what you learn here to work to investigate a small ecosystem.The first thing that you should do is go through the following video that goes through the basic operation of the compound microscope. Listen to each of the things that she says very carefully as the time will come when you will need to know how to use one of these microscopes. The microscope in this video is very similar to the ones that you will be using in future biology courses at Cuyamaca. Now go ahead and watch the following video: Activity 1: The Compound MicroscopeFor this activity, you will be looking at a video () that will walk you through the steps below looking at the letter e. ...you will probably need to go through the video several times to listen to all of the information and find the answers to the questions below. Everything is there in the video for you to answer the following questions. 1. Following the directions in the pre-lab for setting up the microscope, obtain a letter “e” slide and place it onto the mechanical stage of the microscope so that it is set as if you were going to read it. Using the lowest power objective (4X) bring the letter into focus.Question 1: When you look at the letter “e” under the microscope, is the letter oriented in the same direction as when you look at the slide? If it is oriented differently, why do you think that might be the case (see the optics diagram in the pre-lab to help you out)2. Once you have made your observations at 4X, change the magnification to 10X by rotating the 10X objective into position on the nosepiece. Be careful that the objective is not close to the slide andPage 2Ex 3: The Unseen World Part 1: Introduction to Microscopydoes not bump into it in any way. You may need to slightly refocus using the fine focus adjustment, but should not have to change the coarse focus adjustment.Question 2: How is what you see now different from what you saw under the 4X objective? Explain what that difference is.3. Now look at the same slide under the 40X objective. Again, it may be necessary to slightly refocus with the fine focus adjustment.Question 3: How is this view different from what you saw at 10X? Write a short statement that describes what is happening in what you see as you change from the 10X to 40X objectives.4. While you are looking through the microscope, use the control knobs for the mechanical stage to move the stage holding the slide from left to right. Question 4: When you move the stage from left to right, which direction does the image of the letter “e” move? Why do you suspect this is the case?5. Now, you will need to look at a different video that talks about looking at a slide with 3 threads, one in blue, one in red, and one in yellow. Carefully look at the slide in the video and answer the following questions. Question 5: Do all of the strands on the slide appear to be completely in focus at the same time at this lowest magnification?6. Change to 10X, then to 40X and look at the same slide. Question 6: Why do the strands appear to be in focus at some magnifications and not others? (Hint: are the threads really flat, or is there depth to them?)Activity 2In this section you will be looking at some living cells, including a human epithelial (skin) cell and a plant cell (Elodea). Although you will not be preparing the slides, and will looking at photos that are on the skill check worksheet, make sure you go through the steps below so that you know how these slides would have been prepared. 1. Make a slide of an epithelial (cheek) cell. First, add a very small drop of water (one drop from a dropper) to the center of a clean microscope slide. This will work better if you wash the slide with soap and water first, and then thoroughly rinse it with tap water and then deionized water. 2. Take a toothpick and gently scrape it on the side of your cheek inside of your mouth.3. Rub the material on the toothpick in the small drop of water on the slide and spread it around into a thin layer. Allow the water to dry for a few minutes, until the slide is dry. If you have too much water on the slide, you will not get a thin layer and the slide will not dry.4. Stain with methylene blue. To do this, add a few drops of methylene blue onto the surface of the now dry slide where the sample was spread. Allow the stain to sit for 30 seconds, then gently rinse off the Page 3Ex 3: The Unseen World Part 1: Introduction to Microscopymethylene blue with water. Very gently blot the slide dry with a paper towel. Place a clean cover slip over your sample.5. Observe the cells on the slide at 10X and 40X power. Find the cells at 10X first, and then switch to 40X. Draw the cell you see at the 10X & 40X magnification in the space provided on the Skill Check worksheet, and label under the drawing with the name of the specimen, the magnification and your estimate of the specimen’s size (go back to the pre-lab (page 45/46) if you don’t remember how to estimate the size). Label any structures you can see in the cell. It is preferable to draw one or two cells showing a lot of detail, rather than a lot of cells drawn with little detail.Question 7: What structures can you see in these cells (nucleus, cytoplasm, cell membrane)? Estimate the size of these cells using the procedure you learned in the pre-lab.6. Take a small Elodea leaf, tear off the very tip using forceps, and gently place on a slide. Add a small drop of water onto the leaf, and then cover with a cover slip. Observe the structure of the cells in the leaf tip first at 10X and then at 40X. Draw a sample of one or two of the cells you see at the 10X and then the 40X magnification on the Skill Check worksheet and label under the drawing with the name of the specimen, the magnification, and your estimate of its size. Label any structures you can see in the cell.Question 8: What do the cells in the tip of the Elodea leaf look like? What structures can you see in the cells (cell wall, cell membrane, cytoplasm, chloroplasts, nucleus, vacuole)?Activity 3In this activity you will be using the compound microscope to look at two different organisms from the Kingdom Protista, Euglena, and Paramecium. These are relatively fast moving organisms that are found in water in many different places. To look at these organisms you will need to take a sample from the container and place a small drop on the center of a clean glass slide. These organisms move very quickly, and one way to slow them down is to add a drop of Protoslo to the original drop of water. Then, add a glass cover slip over the drop of water. If the cover slip seems to float on the water drop, you have added too much water, and should remove some of the liquid. The water should never be in danger of dripping over the edge of the slide onto the microscope. You should make a slide of one of the organisms, and your partner should make a slide of the other. Again, once you are done observing the slide you made, switch with your partner and look at his/her slide.1) Observe the drop of water under 10X to scan and find the organisms. The higher power objectives can be used to examine details of organisms.2) Use the higher power objective (40X) to look at more detail of the organisms you find. Locate and draw at least one organism of each type in the space provided on the Skill Check worksheet. Draw the organism under whichever magnification you think gives you the best picture of the organism. Label the organism name, magnification and estimated size under the drawing. Label any cell structures that you can find in these organisms. a) Euglena: flagellum, eyespot, nucleus, chloroplasts, others?b) Paramecium: Cilia, oral groove, contractile vacuole, others?Activity 4: The Stereo MicroscopePage 4Ex 3: The Unseen World Part 1: Introduction to MicroscopyIn this activity you will learn to use the stereo microscope. To begin, you will look at a common object that you would find on daily basis; this will help you become familiar with the microscope. Then you will look at some biological specimens to gain a better understanding of the ways in which you can use this microscope.1) Select an object such as a pen, pencil, or coin and place it on the base of the microscope. Spend some time looking at it, changing the magnification and experimenting with the different lighting capabilities of the microscope. 2) When you have completed your investigation of this microscope, go to the side bench and select two different biological specimens to investigate. Ideally, you should look at two different types of specimens that will represent different sizes and shapes. Find an interesting area of each of the specimens, and examine it using the variable magnification available on the microscope. (Photos are already on the Skill Check Worksheet for you to look at with all necessary information) Remember to think about how big these items are in the real world. How big is a penny in diameter? How big is an ant? Don’t just do a random calculation of size without thinking whether the answer you get makes