Microscopic Measurement

Transcription

1 Microscopic Measurement Estimating Specimen Size : The area of the slide that you see when you look through a microscope is called the " field of view ". If you know the diameter of your field of view, you can estimate the size of things you see in the field of view. Figuring out the width of the field of view is easy --- all you need is a thin metric ruler. By carefully placing a thin transparent metric ruler on the stage (where a slide would usually go) and focusing under low power, we can measure the field of view in millimeters. Through the microscope it would look something like what you see here on the left. The total width of the field of view in this example is less than 1.5 mm. A fair estimate would be 1.3 or 1.4 mm. For example, if something we were looking at took up half of the field of view, its size would be approximately 1/2 x 1.3 centimeters =.65 centimeters (rounded to.7 centimeters). If something appeared to be 1/5 of the field of view, we would estimate its size to be 1/5 x 1.3 centimeters =.26 centimeters (rounded to.3 centimeters). In the following table, estimate the field of view for each circle in millimeters. Remember that each grid box is equal to 1 millimeter. **Always write your answer to the nearest decimal, even if it is.0** mm mm mm mm mm Draw in a single cell (oval) that would be 1.5mm large relative to the boxes field of view.

2 In the following examples, use the same principles as you did in the problems above, but this time, draw in the grid lines based on the information given. 2.0 mm 4.0 mm 5.0 mm 3.5mm 1.2 mm Calculating Specimen Size : This is something that requires some practice. So here you go. Example #1 : a) What is the diameter or field of view for this microscope? b) If 10 cells can fit end to end in the field of view, what is the approximate size of each cell? Example #2 : The diagram shows the edge of a millimeter ruler viewed under the microscope. a) What is the approximate width of the field of view in millimeters? b) If 5 cells fit across the field of view, what is the approximate size of each cell? Example #3 : The picture shows the low power field of view for a microscope with a field of view equal to 4 mm. a) What is the approximate size of the cell in millimeters? b) How many cells like the one in the picture could fit across the field of view? Density

3 Density is an important physical property, which can be used to help determine the identity of an unknown substance. While the mass or the volume of a substance will vary from sample to sample, the density will remain the same at a given temperature, even when the mass or volume is changed! The density of a substance is a measure of how much mass is present in a given unit of volume. The formula is shown below: Mass (grams) M (g) Density = or D = or Volume (cubic centimeters V (cm 3 or milliliters) or ml) Take a look at the two boxes below. Each box has the same volume (amount of space). If each molecule (ball) has the same mass, which box would weigh more? Why? Block I Block 2 Mass = 79.4 grams Mass = 25.4 grams Volume = 29.8 cubic centimeters Volume = 29.8 cubic centimeters The box that has more molecules has more mass per unit of volume. This property of matter is called density. The density of a material helps to distinguish it from other materials. Since mass is usually expressed in grams and volume in cubic centimeters, density is expressed in grams/cubic centimeter (g/cm 3 ). Calculate the following Density Equations Object Mass (g) Volume (cm 3 ) Density (g/cm 3 ) A B C D **Discuss the relationship between the changes in values** Which of the two objects above have the same density? & That tells you size does not matter when dealing with density, just proportions! We can calculate the mass and volume of density using the formula for Density even when it is density that we have and either need to determine the mass or volume. Using the triangle

4 formula determine if the object will float in water or not by circling either Yes or No. Hint: the density of water equal to 1.0 g/ cm 3 Cover the part of the equation you need to determine and then substitute in the formula. Block Mass (=Density x Volume) Volume (= Mass / Density) Density (=Mass / Volume) Will float in Water? A 20.0 grams 0.4 g/ cm 3 B g 1.25 g/ cm 3 C 15.0 cm g/ cm 3 D 74.3 ml 0.8 g/ ml E F G H I J K 17.0 grams 4.86 g/ml 34.0 grams 0.7 g/ cm grams 22.0 g/ cm g 8.67 cm g 35.9 cm cm g/ cm cm g/ cm 3 **Be sure to use the proper unit based on your knowledge of the information in the other parts**

5 Using the information you determined in the density table on the prior page, draw where each of the following blocks would rest if placed in a cup of water where: the density of water is equal to 1.0 g/ cm 3 Keep in mind, the amount of object below the surface of the water line for an object less dense than water is equal to its density value converted to a percentage. ex. an ice cube has a density of 0.9 g/ cm 3 therefore, the object will be 90% below the water line and 10% above A B C D

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7 Graphing What is a graph? Graphs help us see information better. When we have a lot of information, graphs put all the information in one place so that we can see it quickly and refer to it more easily. Since graphing depends upon putting information (*especially numbers) in the right place, you may want to draw your line graph on graph paper. Graph paper already has straight lines drawn on it, making it much easier to put information in the right place. It also ensures you have a constant interval between your numbers! Line Graphs A line graph is a way to summarize how two pieces of information are related and how they vary depending on one another. The numbers along a side of the line graph are called the scale or variables. How to Construct a Line Graph Step What To Do How To Do It 1 Identify the variables a. Independent Variable - ( controlled by the experimentor )--Goes on the X axis (horizontal) ex. year, mileage b. Dependent Variable - ( changes with the independent variable )--Goes on the Y axis (vertical) ex. weight, $ value Determine the variable range. Determine the scale of the graph. Number and label each axis. 5 Plot the data points. 6 Draw the graph 7 Title the graph. a. Subtract the lowest data value from the highest data value. b. Do each variable separately. a. Determine a scale, (the numerical value for each square), that best fits the range of each variable. b. Spread the graph to use MOST of the available space. Rectangular graph paper is turned so that the variable with the widest range is drawn along the widest side of the paper. This tells what data the lines on your graph represent. a. Plot each data value on the graph with a dot. b. If your point is not exactly on the cross of the two lines, estimate. a. Draw a curve or a line that best fits the data points. b. Most graphs of experimental data are not drawn as "connect-the-dots". a. Your title should clearly tell what the graph is about. b. If your graph has more than one set of data, provide a "key" to identify the different lines.

8 Graphing Living things occupy certain regions of the world called ecosystems. The plants and animals in one ecosystem live together and depend on each other for food and shelter. If certain factors change, such as weather or the introduction of predators, the ecosystem will not support the same number of organisms. In this exercise, the number of sunfish in a pond ecosystem are charted for a 12 year period. Graph the number of sunfish on the vertical axis and the year on the horizontal axis. Label both axes and give your graph a name. Then, answer the questions below using the graph. Year # of Sunfish Answer these questions using the graph. 1. During which year did the most rapid growth of sunfish take place? 2. During which year did the population decrease? 3. What kind of factors could have caused the decrease? 4. The number of organisms an ecosystem can support is its carrying capacity. Draw a dashed line on your graph at the carrying capacity for sunfish in this pond.

9 5. During years 2 and 3, the number of minnows doubled in the pond. Using the graph, this means that minnows are a. competitors of sunfish b. parasites of sunfish d. prey of sunfish c. predators of sunfish In the graphing exercise below you will graph the data, answer the questions, and determine values inclusive and exclusive of the data range. Sonia and Paul are working on a lab activity where they are tracking some leaves that are floating past them in a stream near their home. They want to measure how far the leaves travel in different amounts of time. They place a long tape measure along side of the stream to measure distance. They use a stopwatch to record the amount of time the leaf takes to travel. They plan to have time intervals that begin at two seconds, and increase by two seconds until they get to 20 seconds. The data they recorded is below. When plotting your points, round your numbers to the nearest whole number. Label the lines Leaf A and Leaf B on your graph. Distance leaf traveled Time (centimeters) (sec) Leaf A Leaf B

10 1. What was the total distance leaf A traveled according to the data above? 2. How far did the leaf B travel after 8 seconds according to the data above? 3. How far did the leaf A travel after 15 seconds according to the data above? 4. Approximate how far leaf A would have traveled after 22 seconds? 5. Determine how long would it take for the leaf B to travel about 18 centimeters based on the data above? Rounding Rounding to the Nearest... We always want to keep two things in mind when we round any number. The first is what we are rounding to. In your example we are rounding to tenths, so we should end up with one digit to the right of the decimal point, because that is the tenths place. Now immediately you can see that 451 is not an acceptable answer, but or could be. The second thing to keep in mind is the method we are using to round by. In your problem that is the nearest method. In the nearest method we look at the digit to the immediate right of the digit we will round to (so for this example we will look at the hundredths digit), and if it is a five or greater (5 through 9) we round up (add 1 to the digit we are rounding and drop all the digits to the right). If the digit to the right of our rounding digit is less than 5 (0 through 4) we round down (drop all digits to the right of digit we are rounding). So for our example: number to be rounded to nearest tenth number to the right of the tenths digit 5 since the number is a 5 we round up so our answer is What if we had instead? number to be rounded to nearest tenth number to the right of the tenths digit 4 since the number is a 4 we round down so our answer is 451.7

11 Practice rounding the following examples to the nearest tenth. Be sure if it is a whole number to include a decimal followed by a zero (.0).23 =.48 =.55 =.99 =.75 =.91 =.03 =.06 = = = = 2.34 = 3.45 = = = = = = 1.09 = =.87 =.76 =.65 =.54 =.43 =.32 =.21 =.10 = Measurement Measure the line to the nearest tenth of a centimeter and write your answer on the line using proper units (cm) Measure the area of the box to the nearest tenth of a centimeter and write your answer inside the box using proper units (cm 2 ) Use the formula: length x height or (l x h)

12 Measure the length and height (width is given) of the boxes and calculate their volume to the nearest tenth of a centimeter and write your answer inside the box using proper units (cm 3 ). Use the formula: length x width x height or (l x w x h)