LAB 3A: GRAPHING, DENSITY, AND SPECIFIC GRAVITY;CLINICAL USE OF SPECIFIC GRAVITY MEASUREMENTSObjectives: By the end of today's lab session, you should:1. Understand the concepts of density, specific gravity, and a standard curve.2. Be able to perform calculations dealing with density and specific gravity.3. Have some practical experience in dealing with solutions, presenting data graphically, and determining unknown concentrations using standard curves.4. Be aware of the clinical usefulness of urine specific gravity measurements.A. PRESENTING DATA IN GRAPHS – GENERAL INFORMATIONLab reports often involve presentation of data in graphs. Graphical presentations are valuable because they present quantitative data in a manner that is easier to understand and interpret compared with a list of values in a table. In a graph, relationships between the two parameters being examined can be seen and appreciated visually. Each graph should be neat, well organized, and easy to understand. Your graphs should always have the following items:a) An informative title, usually outside the graph at the top but it may also be within the graph.b) A label on each axis, including the units in parentheses, and appropriate major and minor tick marks. c) Other information, if appropriate. This information can be inserted in any convenient blank spaceon the graph. You may want to draw a box around it. In some cases, the data table and/or relevant calculations can be included on the graph in this manner (see example below).Data points should be accurately placed and be large enough to be seen easily. If you know that the data points should theoretically fall on a straight line, draw the best straight line through all the points. If the origin (0,0) is a relevant data point, include this point when determining the best straight line. If the data lie on a clearly recognizable curved line, draw the best smooth curve through the points. If the data are irregularly situated, simply connect the individual data points. Think about what you want to show before you prepare your graph. Also, think about the type of line or curve expected (what is the likely relationship between the two parameters you are plotting) before you draw the best line through the points.Note: In this course, we would like to use a standardized format for graphing (particularly for linear plots). We suggest that you use the graphing functions in Microsoft Excel. Unfortunately, there are several versions of Excel and differences between PCs and Macs, thus, we can not easily supply instructions for all versions and computers. We will provide guidance in class, but you should consult the help menu in Excel to learn how to make graphs. Also, if you search on-line with the term “making graphs in excel,” you will find numerous tutorials.Remember that a well-prepared graph is one that a first-time reader can understand easily without additional information. The graph below is a best straight line plot; a straight line coming closest to the most points is best because a linear relationship between the two parameters, in this case DNA concentration and its Absorbance at 260 nm, is expected (Absorbance is a measure of how much light is absorbed by a sample). Grpahing programs like MS EXCEL have algorithms that calculate the best straight lines from the data. Note the additional information (slope data) added in the box.Biochem 107L3-2The graph below shows a curved function; the data points fall on a smooth curve, not a straight line. A curve means there is some mathematical relationship between the two parameters, but the relationship is not linear. Many biochemical (and biological) parameters show curved functions; the hyperbolic relationship shown below is probably the most common. Note that, in this case, a data table has been incorporated into the graph. Measurement of changes in a clinical parameter with time is an example of when you would simply connect the individual data points (see graph below). In this case, it is the changes in blood pressure with time that is examined; there is no expected mathematical relationship between the two parameters (blood pressure versus time ), so connecting the points is the only way to graphically present what is happening.Biochem 107L3-3BACKGROUND INFORMATION FOR TODAY’S EXERCISEDENSITY: Review the section on density and specific gravity in your textbook (8th ed., pp 30-35, 7th ed., pp 29-33). The density of an object describes the relationship between its mass and volume:Density = Mass VolumeIn the metric system, density is usually expressed as grams/cubic centimeter (g/cc or g/cm3) for solids and grams/milliliter (g/mL) for liquids. Because of their very low density, units of grams/liter (g/L) are usually used for gases.Because density is the ratio of a substance's mass to its volume, asubstance with a high density will have more mass per given volumethan a substance of lower density. For example, a 5 cm cube of lead ismuch heavier than a 5 cm cube of wood; therefore, lead has a higherdensity than wood. The table lists the densities of some commonsubstances. The density of asubstance usually decreases as the temperature increases because volume usually increases due to expansion. However, water is an important exception. Ice is less dense than water; thus, ice cubes will always float in your cola. This property also has enormous implications for climate and life on earth. If frozen seawater (ice) sunk to the bottom, northern oceans would freeze solid, deep ocean circulation would cease, and we’d have a permanent ice age! SPECIFIC GRAVITY: Specific gravity is a comparison of the density of a substance or solution with the density of a reference substance. Water at 4C is a convenient reference standard, and it is one that is used in clinical measurements.Specific gravity = density of solution (g/mL) density of water (g/mL)Note that specific gravity does not have units (the units cancel in the equation).Specific gravity can be measured by determining the weight (g) of an accurately measured volume (mL).However, it is easier and more reliable to use a hydrometer. A hydrometer is a sealed hollow glass tube that contains a weight on the bottom and has a slender neck that is calibrated to read units of specific gravity. When placed in a liquid, the hydrometer sinks in the liquid until it displaces an amount of liquid equal to the