Name ____________________________

Period _____

AP / CP Biology

Scientific Processes – Tools and Measurements

Introduction:

The purpose of this activity is to identify some the common tools use in scientific investigation, and practice using the metric system. To conduct a scientific investigation, a researcher must be able to make accurate measurements. In today’s exercise you will become familiar with metric system units and converting between large and small metric units. In each of the sections that follow, you will familiarize yourself with the appropriate metric units that scientists commonly use, and then you will take the measurements of everyday objects.

Standard Metric Units

The metric system is based on standard units that can be easily converted by simply multiplying or dividing by ten. The standard metric unit for length is the meter (m). The Gram (g) is the standard unit of mass, and the liter (L) the standard unit of volume.

Metric Conversions

Conversions with the metric system can be made easily using a metric staircase. Each step of the staircase represents a ten-fold change in the value of the measure or a shift on the decimal point one place. For example, if you moved two steps down (10 X 10 = 100). If you moved three steps up (10 X 10 X 10 = 1000). Each step you move down the staircase represents multiplication by ten, or a movement of the decimal one place to the right. Each step up the staircase represents a division by ten, or the movement of the decimal point to the left.

Rules:

1. Always use decimals to express metric measurements. For example: write 2.25 cm, not 2 ¼ cm.

2. If a metric measurement is less than one, precede the decimal with a ZERO. For example, do not write .55, instead write 0.55.

Practice converting Metric Units

Use the staircase diagram to convert the following metric units into new metric units.

8 meters (m) = ________millimeters (mm)0.98 kilograms (kg) = ________g

22.1 milliliters (ml) = ________Liters (L)0.00003 m = ________mm

10,900 centimeters (cm) = ________m57 mm = ________cm

0.0034 milligrams (mg) = ________grams (g)0.98 kg = ________mg

0.0087 L = ________microliters (μL)349 mL = ________μL

660 g = ________mg4590 μL = ________mL

Length

Metric units of length measurement most commonly used in biology include the meter (m), centimeter (cm), millimeter (mm), micrometer (μm), and nanometer (nm).

Metric Units of Length Measurement

Unit

Meters(m)

Centimeters(cm)

Millimeters(mm)

Relative Size

Meter (m)

1 m

100 cm

1000 mm

largest

smallest

Centimeter (cm)

0.01 m

1 cm

10 mm

Millimeter (mm)

0.001 m

0.1 cm

1.0 mm

Micrometer (μm)

0.000001 m

0.0001 cm

0.001 mm

Nanometer (nm)

0.000000001 nm

0.0000001 cm

0.000001 mm

How many centimeters are in 1 meter? ________How many mm are in 1 centimeter? ________

How many μm are in 1 millimeter? ________How many nm are in 1 micrometer? ________

Obtain a meter stick. On the opposite side find the English measurement units of “inches.” How many inches are in a meter? ________ One meter is roughly equivalent to one yard.

Meter Stick

Turn the meter stick over and observe the metric subdivisions. How many centimeters are in a meter? ________.

The prefix centi- means 100. How many cents (pennies) are in a dollar? ________

How many millimeters are in 1 centimeter? ________. The prefix milli- means a thousand. How millimeters are in 1 meter? ________.

For measuring smaller objects, it is preferable to use a metric ruler, rather than a meter stick. Obtain a penny. Will it be easier to measure in centimeters or millimeters? Measure the diameter and include the units:________, then the width (thickness) and include the units: ________.

Why is it preferable to measure a penny in millimeters rather than centimeters or meters?

Use a meter stick or metric ruler, or tape measure to measure the following:

Width of classroom door opening (in meters): ________m, convert to cm: __________

Length of whiteboard (in meters): ________m, convert to cm: ________

Which of your fingernails is closest to 1 cm in width? _______________

Millimeter, Micrometer, and Nanometer

As you will discover in upcoming laboratory exercises (using microscopes), the units micrometer (μm) and nanometer (nm) are useful in microscopy for measuring very tiny objects like cells or even viruses.

Use a metric ruler marked in centimeters (cm) and millimeters (mm). Micrometers (μm) are not marked on the ruler, but remember that 1000 μm would fit in between each millimeter hashmark.

Measure the diameter of the circle ________mm

Now, calculate its diameter in micrometers ________μm

What is the diameter of the circle in nanometers? ________nm

Volume

The basic unit of volume in the metric system is the liter (symbol is L or l). The most common derived unit used for small amounts of liquids is the milliliter (mL – 1/1000 of a liter). A typical individual bottle of spring water might hold 500 mL (half a liter) of liquid.

In the biology laboratory, liquid volume is usually measured in milliliters, using

an appropriately sized graduated cylinder. The measurement marks etched on

the side of the cylinder are called “graduations.” When liquid is poured in, the top of the liquid

forms a slight curve, called a “meniscus”. The volume of the liquid should be

read at the graduation marks closest to the bottom of the meniscus.

For accuracy, you should read this on a flat surface, and at eye level. How many milliliters (mL) of liquid is in the graduated cylinder in this picture? ________

Volume Exercise 1: How many drops of water does it take to equal 1 mL?

To find out, fill a plastic transfer pipette with water and add one drop at time into a 10mL graduated cylinder. Count the number of drops it takes to fill the10 mL graduated cylinder to the 1 mL mark. Do not forget to read the meniscus at eye level. From this information, you should be able to calculate how many mL each drop is, too!

Repeat the process three times in order to calculate an average (mean). Use your average drops to answer how many drops of liquid will fill 1 mL.

Trial 1

Trial 2

Trial 3

Average (mean)

Drops per 1 mL = ________mL per drop = ________

Volume Exercise 2: Measuring the Volume of Solid Objects

Solid objects have a volume (the amount of space the object takes up). Volume can be measured in two ways. A first method, for regular objects, such as boxes, direct measurement of each side will provide a volume in cubic centimeters (cm3)

1. For symmetrical objects, volume is simply LENGTH (cm3) X WIDTH (cm3) X HEIGHT (cm3)

Use a tape measure to measure Box A and Box B to determine their volumes.

Volume Box A: ________Volume Box B: ________

Volume Exercise 3: Measuring Volume of Oddly Shaped Objects by Displacement.

2. A second method of measuring the volume of solid objects (like marbles, for example) can be obtained by using a water displacement technique. Find the volume of three (3) marbles by filling a 100 mL graduated cylinder to 30 mL. Drop the marbles into the graduated cylinder and observe how much the water rises. The difference in the volume of water is the volume of the marbles. Complete the table below.

A) Volume of water before adding marbles

B) Volume of water after adding marbles

Calculate total volume of all 3 marbles (B – A)

Now determine the volume of a single marble by dividing your total volume by 3: ________.

Volume Exercise 3 continued:

3. The volume of a marble can also be determined by direct measurement using the following formula:

Determine the radius of a marble and determine the volume

in the space below.

4. Refill the 100 mL graduated cylinder to 30 mL. Now drop a single marble into the graduated cylinder. What is its volume? ________. Is the volume of a single marble in the 100 mL cylinder the same as what you calculated after measuring three marbles at once? YES or NO (circle one) Is it the same or different from your direct measurement? YES or NO (circle one). Explain your answers:

MASS

The basic unit of mass in the metric system is the gram (g). A common derived unit used by biologists is the milligram (1mg = 1/1000 g).

How many grams (g) are in 2 kg? ________How many milligrams (mg) are in 0.2 g? ________

For measuring large masses, the kilogram (1kg = 1000 g) is often used (ex: body weight).

Convert the body weight of one person in your lab group to metric kilograms. To covert from pounds (lbs) to kilograms (kg) multiply by 0.4536 (rounded). To convert from kg to lbs, divide by 0.4536.

________ lbs X 0.4536 = ________kg

An object weighs 1,814.4 kg. How much does it weigh in pounds (lbs)? __________

Measuring Metric Mass Using an Electronic Digital Balance Scale

In measuring the mass of any material, you should ALWAYS weigh the mass two times to ensure accuracy. Ensure the balance is set to ZERO before weighing objects.

If you are weighing something in a container, first place the container on the scale, press the tare button to reset the scale to zero. Lastly, place the object in the container and read its mass.

Weigh your three (3) marbles. First place your container on the balance, zero the balance, then add the marbles. Weigh a second time.

Weight of three marbles: ________g

Tempurature

There are two temperature scales: Fahrenheit (F) and Celsius (C) scales.

The basic unit of temperature in the metric system used is the degree Celsius (°C).

Freezing point of water: 0°C

Boiling point of water: 100°C

Body temperature: 37°C

Useful conversion formulas:

To convert °C to °F Multiply by 9, then divide by 5, then add 32

To convert °F to °C Deduct 32, then multiply by 5, then divide by 9

Answer the following:

Water freezes at ________°F = ________°C

Water boils at ________°F = ________°C

Normal body temperature is ________°F, which is equivalent to ________°C

Temperature Exercise 1: Determining the temperature of heated water.

The hot plates are set to approximately 20°C. Check the temperature of the water in the beaker by checking the thermometer in the beaker to determine the exact temperature in °C, then convert the temperature in °F.

Water temperature: ________°C = ________°F

Common Glassware Used in Biology.

Erlenmeyer Flasks Beakers Test Tubes Graduated Cylinders