Introduction to the Microscope Investigation 2 Contrasting Cases Part 1 – Compare microscopes and telescopes

Introduction to magnification What are some tools used to magnify images? Have you ever used these any of these tools? When can it be useful to magnify an image? Introduction (5 minutes) Lead a discussion of these questions with the entire class or encourage students to discuss in pairs. Some students may have used a magnifying glass, binoculars, or even a telescope or microscope. Most students will be familiar with telescopes and microscopes, but they should understand that these tools help people – often scientists – to study details on an object that might be too small to see (or see well) with the naked eye.

Introduction to magnification What do these two things have in common? How are they different from each other? After asking this question, proceed to the next slide and give students a few minutes to copy the Venn diagram in their notebooks and write down the similarities and differences between microscopes and telescopes.

Telescope and microscope Both Microscope Students should draw this Venn diagram in their notebooks and put the qualities that describe telescopes, microscopes or both in the appropriate places. Allow students to work in pairs or groups, but at this point do not give them answers. Students can debate ideas within their pairs or groups for a few minutes. Once they have written down some ideas, tell them that we will look a little more closely at both tools to better understand how they are similar and different.

Telescopes What are some living things that might be viewed through a telescope? What are some non-living things that might be viewed through a telescope? Students will probably have an easier time thinking of non-living things viewed through a telescope, such as planets and stars. Pointing out that binoculars are actually a weak telescope might help them think of more living things viewed through a telescope, such as birds in trees or actors on a stage.

Nearby telescopic images Allow the students to suggest answers. Guide them toward the idea that the boat appears tiny because it is far away, but the telescope magnifies the image and makes it large enough to see details. Students may suggest specific details, like seeing people in the boat. How does a telescope change the image of this boat on a lake?

Compare telescope images The image on the left shows the moon as it might normally appear to an observer. Students may not notice the three small dots to the right of the moon; point them out to the students, telling them that they are (from top to bottom) Mercury, Mars and Jupiter. The images on the right the moon (top) and Jupiter (bottom), seen through a telescope. Allow students to suggest ways that the telescope changes the images. Again, guide them toward the idea that the telescope magnifies the images and allows the viewer to see greater detail of the images. For example, you can see the craters on the moon and the strips of color on Jupiter in the magnified images, but not with the naked eye. How does a telescope change the image of the moon (top) and Jupiter (bottom)?

Give the students time to suggest and debate ideas, then help direct them toward the concept that all both the moon and Jupiter and the boat appear very small because they’re far away. From a closer perspective, both the boat and the moon and Jupiter would be easily visible to the naked eye; thus the telescope is magnifying something that appears small because it’s so far away, even though it’s actually large enough to see from a closer point of view. Regarding differences, the moon and Jupiter are very big relative to the boat; while a boat might be 10 or 15 feet long, the moon and Jupiter are millions of feet wide. Use this comparison to point out that the size of things viewed through a telescope varies greatly, even though the magnified images might look like they’re about the same size. This point will be important when you compare the scale of different things magnified under the microscope and explain that, for example, a brine shrimp is much larger than a red blood cell even though they’re both “tiny.” Compare the things being magnified by the telescope. How are they similar? How are they different?

Microscopes What are some living things that might be viewed through a microscope? What are some non-living things that might be viewed through a microscope? Point out to students that “larger” and “smaller” objects are all on a microscopic scale. A “large” object might be the size of a pencil dot, while a “small” object could be a hundredth or many thousandths of that. To illustrate this idea, explain that you could line up about 1000 red blood cells across the width of a pencil dot. By comparison, the pencil dot is quite large.

Compare images Students should again notice that the magnified image shows them details that they could not see looking just at the cup. In this case, they can see the individual shapes of the brine shrimp in the magnified image. Point out that if they look carefully at the image of the cup, they can see that there are individual dots inside the cup, though it’s not possible to see what those dots are. How does a microscope change the appearance of the mixture of water and brine shrimp inside the cup?

Compare images Students should again notice that they can see greater detail in the magnified image of the blood. Point out that as with the brine shrimp, you can see individual blood cells in the magnified image; unlike the brine shrimp, you cannot detect the individual dots making up the blood in the image on the left. How does a microscope change the appearance of the blood on the slide?

Compare images Allow students to suggest and debate ideas, but guide them to the idea that the brine shrimp and the blood cells are very different sizes. Compare the things being magnified by the microscope. How are they similar? How are they different?

You may allow students to speak with their partners or in the same groups from early in the lesson, then ask students to share their ideas with the class. Once everyone has a chance to discuss, you can post the list on the next slide. Regarding differences, the moon and Jupiter are very big relative to the boat; while a boat might be 10 or 15 feet long, the moon and Jupiter are millions of feet wide. Use this comparison to point out that the size of things viewed through a telescope varies greatly, even though the magnified images might look like they’re about the same size. This point will be important when you compare the scale of different things magnified under the microscope and explain that, for example, a brine shrimp is much larger than a red blood cell even though they’re both “tiny.” Compare the types of things telescopes and microscopes magnify. Can you add to your comparison list?

Telescope and microscope Both Microscope - For things that are visible size but far away - Magnify images - For living and non-living - Come in different types, strengths - Scale of objects observed varies greatly - Image created shows more detail than object - For things that are tiny or invisible size but nearby Discuss any additional ideas students might have generated or questions they might have about these differences. Allow students to explain any points they might have suggested that aren’t on this list; if they are misconceptions, help them to recognize the error in their thinking through their explanation attempt.

Compare images Now compare a few more images. Can you tell which of these images are from microscopes and which are from telescopes? The top left image (the Milky Way) and the bottom right image (a bird on a telephone wire) are seen through kinds of telescopes. The top right image (end of a human hair) and the bottom left image (a newsprint letter “e”) are seen through kinds of microscopes. You may point out to the students that the image of the bird looks like a “normal” image they might see looking up at a telephone wire from the ground below; the person who took this image, however, was standing far away, so that the bird would have looked just like a small dot without the telescope. On the other hand, no one could see the planet Jupiter the way it appears here unless they were in space. Likewise, the image of the “e” looks a lot like a normal newsprint letter, except larger, while the image of a human hair does not look anything like a human hair viewed with the naked eye.

Levels of magnification An optical microscope, like the ones used in a science classroom, has different levels of magnification. Below are four images of human blood at different magnifications. Which image has been magnified the least? The most? Explain that the image on the left has an optical magnification level of 40x, meaning the image is 40 times larger than it would appear to the naked eye. Going across from the left, magnification levels are 40x, 100x, 400x and 1000x. Point out to the students that the increasing magnification shows a larger and more detailed image, but eventually the image becomes increasingly blurry as the magnification level increases. Explain that if you tried to increase the magnification level beyond 1000x with this microscope, the image would be larger but also even more blurry and would offer no more detail than shown here. This creates an upward limit on the magnification power of a microscope. Images from http://classic.sidwell.edu/us/science/vlb5/Labs/Microscope_lab/microscope_lab.html

Levels of magnification 40x 100x 400x 1000x Use this slide to visually demonstrate the different levels of magnification. You might reinforce what you said when explaining the last slide by asking the class, “What does 40x mean?” If someone says, “It means it’s magnified 40 times,” as them, “Times what?” It’s important that students understand magnification level means the image is magnified that many times the appearance to the naked eye.

Compare field of view By placing a clear ruler under a microscope, you can measure the field of view. Which image has been magnified the least? The most? Explain that the image on the left has been magnified at 40x, the image in the middle has been magnified at 100x, and the image on the right has been magnified at 400x. Remind students that the space between the bars is actually one millimeter – the smallest unit of measurement on a classroom ruler. You may also wish to note that while the ruler lines in the image appear in pink, the rulers they will use in class have black lines (or whatever color your classroom set is). Point out that the ruler lines become more details and less crisp as magnification increases. Ask students why the lines on the right have dots near them. Allow students to suggest answers and guide them to understand that at high levels of magnification, they can see that the lines are not perfectly straight and even; instead, the ink used in printing the rulers has some irregularities and tiny spots out of line, all of which is invisible to the naked eye. If students have trouble understanding this idea, use the analogy of coloring inside lines. When they color a picture it might look like they have colored perfectly inside the lines, but if they looked at the picture through a microscope they would see tiny errors where the color either crossed the line or did not quite make it to the line. This is a similar principle. It is important that the students understand why the highly magnified line looks imperfect before you proceed to the next slide.

Compare field of view By placing a clear ruler under a microscope, you can measure the field of view. 40x 100x 400x Which image has been magnified the least? The most? Explain that the image on the left has been magnified at 40x, the image in the middle has been magnified at 100x, and the image on the right has been magnified at 400x. Remind students that the space between the bars is actually one millimeter – the smallest unit of measurement on a classroom ruler. You may also wish to note that while the ruler lines in the image appear in pink, the rulers they will use in class have black lines (or whatever color your classroom set is). Point out that the ruler lines become more details and less crisp as magnification increases. Ask students why the lines on the right have dots near them. Allow students to suggest answers and guide them to understand that at high levels of magnification, they can see that the lines are not perfectly straight and even; instead, the ink used in printing the rulers has some irregularities and tiny spots out of line, all of which is invisible to the naked eye. If students have trouble understanding this idea, use the analogy of coloring inside lines. When they color a picture it might look like they have colored perfectly inside the lines, but if they looked at the picture through a microscope they would see tiny errors where the color either crossed the line or did not quite make it to the line. This is a similar principle. It is important that the students understand why the highly magnified line looks imperfect before you proceed to the next slide.

Compare blood and field of view Compare the ruler and blood, which are both magnified to the same level. 400x 400x How big do you think a red blood cell is? Students will struggle to accurately estimate how many blood cells would fit across one millimeter, but they should understand that it’s a large number. Encourage students to discuss how many blood cells they think would fit in the width of one millimeter (the space between two of the lines). A red blood cell is 6 to 8 microns wide – or 6 to 8 thousandths of a millimeter. That means you could fit about 150 blood cells across the width of one millimeter.

Compare optical and electron Compare the images of blood below. What are the differences? 1000x 11,000x Discuss how the optical microscope image, left, shows individual blood cells but they look flat and very small. It is not possible to see any details on the blood cells through the optical microscope. The electron microscope image on the right, however, shows the shape and texture of individual blood cells. The tan material attached to the blood cells is called fibrin, which helps with the clotting process. Point out to the students that the optical microscope image is magnified at 1,000x – very strong for an optical microscope, and stronger than they will be able to magnify things using the classroom microscopes. The electron microscope image is magnified at 11,000 – more than ten times the power of the optical microscope. Students do not need to understand how the electron microscope works, but you can offer a simple explanation that electron microscopes use electrons, instead of light, to illuminate images. Students should understand that they are able to magnify images much more than optical microscopes can.

Compare levels of magnification Like optical microscopes, electron microscopes can be used to study non-living objects and well as living cells and organisms. In your notebook, draw what you think sugar looks like when magnified through an optical microscope. Now draw what you think it looks like at a higher magnification through an electron microscope. Give students a moment or two to sketch what they imagine sugar looks like using an optical and an electron microscope. It is OK if their predictions are not correct – this is meant to give them a chance to reflect on the contrast between optical microscope magnification and electron microscope magnification.

Compare levels of magnification Which image is more magnified? How can you tell? Point out to the students that the image from the electron microscope (left) is more detailed than the image from the optical microscope (right). You might ask students if they can see any of these shapes when they look at sugar without any magnification. They should recognize that they can see individual grains of sugar but that can not see the individual shape of each crystal. Electron microscope Optical microscope

Compare levels of magnification Now compare a microscopic organism, a brine shrimp, at different levels of magnification. Encourage students to notice which details become visible with each increase in magnification. Optical Microscope Electron Microscope

Discussion Why might an early scientist using a weak optical microscope have believed that nothing could be smaller than a cell? When might the higher levels of magnification produced by an electron microscope be helpful to scientists? How do scientists today know that there are many smaller levels beyond the cell? Discuss how early, weak microscopes could not focus on things much smaller than a cell, but modern electron microscopes allow us to see some of the smaller parts that make up cells. Point out that cells can be many different sizes, and that microscopes are useful for studying living things (blood cells, brine shrimp) and non-living things (sugar).