AP Lab 02 - Biology Lab Skills

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Name: ______________________________ AP Biology – Lab 02 ‣ Do no operate any laboratory equipment until you have been instructed in its use. ‣ Do not perform unauthorized experiments. ‣ Keep your work area neat, clean, and organized. ‣ Read and understand the experiments you will be doing before coming to the laboratory. Follow the procedures set forth by the laboratory manual. ‣ Know the location of emergency equipment: first aid kit eyewash bottle fire extinguisher showers fire blanket ‣ Report all accidents to your laboratory instructor immediately. ‣ Discard cracked or broken glass only in the broken glass containers. ‣ Report all unsafe conditions to your instructor. ‣ Clean your work area and glassware and wash your hands before leaving the laboratory. PART I – Measurement, Accuracy, Precision, and Graphical Analysis Measurement plays a particularly large role in science. In their studies, scientists gather data, and to do this they use measurements. Scientists measure the concentration of gases in the atmosphere, the growth of organisms under varying conditions, the rate of biochemical reactions, the distance of stars from the earth, and an innumerable number of other things. As measurements form the basis of scientific inquiry, they are deserving of in-depth analysis in lab. Biology students, as part of their laboratory experience, will be asked to make measurements or observations during the course of their investigations. These may be either qualitative or quantitative. A qualitative measurement/observation describes a characteristic and is not numerical; a quantitative measurement/observation is numerical. Scientific observations are usually made as quantitative as possible so that they are easier to evaluate. For example, if you were trying to find the insect with the world's largest wingspan, quantitative observations are needed. An insect's wingspan may be qualitatively described as huge, but a quantitative description of an insect‘s wing span as 20 centimeters would be much more useful for this project. In a scientific experiment, the investigator examines the effects of variations in the independent variable on the dependent variable through measurements. For example, let's assume a biologist is studying the effect of temperature on plant growth. She sets up several different temperature conditions, and grows groups of plants from seedlings in each condition. When the experiment ends, she must compare plant growth in the plants from different temperatures. But how should she do this? Should she just look at the plants and decide which grew the best? Should she pick up the plants and "feel" which ones have the greatest mass? Of course not… She would use some sort of quantitative measurement, such as measuring the height of each plant's stem in centimeters or determining the total plant biomass in grams. Whichever measurement she chooses, she would need to utilize an instrument to make it. Take a minute and look around you at the variety of objects surrounding you. There are probably a few pens or pencils, a notebook or two, and maybe assorted glassware. While you may be able to easily distinguish the differences between some objects (e.g., your notebook is longer than your pen), other differences are more difficult to discern. You may not be able to easily determine, for example, whether your computer keyboard or your course textbook has greater mass. Even when we can distinguish differences, it is not always easy to determine the Page 2 of 40
Name: ______________________________ AP Biology – Lab 02 extent of those differences. You may have noted that your computer monitor is heavier than your notebook, but is it twice as heavy or three times as heavy? Using only our senses, we cannot be certain about the answer, so we must take measurements. To take measurements we need instruments. Instruments include simple things like rulers and graduated cylinders, and complicated electronics like pH sensors and mass spectrometers. All of these instruments provide us what our senses cannot – a quantified measure of the properties of an object. As all scientific measurements utilize the metric system, we must first say a few things about it before proceeding on. The metric system is universally used in science because it is a decimal system of measurement and is easy to convert from one unit of related measurement to another (e.g ., volume to mass). The metric reference units are the meter (m) for length, the liter (l) for volume, and the gram (g) for mass. Prefixes are used as part of a unit to indicate a portion of or a multiple of a reference unit. For example, the prefix milli (m) indicates .001 ( 1 / 1000 ). A millimeter (mm) is 0.001 ( 1 / 1000 ) of a meter. A milliliter (ml) is 0.001 ( 1 / 1000 ) of a liter. A milligram (mg) is 0.001 ( 1 / 1000 ) of a gram. Note that the same prefixes are used throughout the metric system, regardless of whether we‘re discussing length, volume or mass. See Appendix A in your binder to see many of the metric prefixes that we will be using this year. Volumetrics Typical volumetric containers used in biology labs include beakers, flasks, cylinders, and pipettes. In most cases, these are made of glass and calibrated at a specific temperature. However, for very small volume measurements, micropipettes, constructed out of plastic, with disposable tips, are used. A beaker is a simple container for liquids, very commonly used in laboratories. Beakers are generally cylindrical in shape, with a flat bottom. Beakers are available in a wide range of sizes, from 10 mL up to several liters. They may be made of glass (typically Pyrex ® ) or of plastic. Beakers may be covered, perhaps by a watch glass, to prevent contamination or loss of the contents. Beakers are often graduated, or marked on the side with lines indicating the volume contained. For instance, a 250 mL beaker might be marked with lines to indicate 50, 100, 150, 200, and 250 mL volumes. The accuracy of these marks can vary from one beaker to another. A beaker is distinguished from a flask by having sides which are vertical rather than sloping. In the lab, beakers are used more often than flasks. A graduated cylinder is used to accurately measure out volumes of liquid chemicals. They are more accurate and precise for this purpose than beakers or flasks. Often, the largest graduated cylinders are made of polyethylene or other rigid plastic, making them lighter and less fragile than glass. Laboratory flasks come in a number of shapes and a wide range of sizes, but a common distinguishing aspect is a wider vessel "body" and one (or sometimes more) narrower tubular sections at the top called necks which have an opening at the top. Like beakers, laboratory flask sizes are specified by the volume they can hold. Laboratory flasks have traditionally been made of glass, but can also be made of plastic. Volumetric flasks come with a stopper or cap for capping the opening at the top of the neck. Stoppers can be made of glass, plastic, or rubber. In general, flasks can be used for making, holding, containing, collecting, or volumetrically measuring solutions. Page 3 of 40
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AP Lab 02 - Biology Lab Skills

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