Any object has its own shape, size and dimension. In biology, it is very important to know the overall physical and chemical status of any living organism. There are specific units to describe various characteristic features that come with proper symbols. Fundamental Units: These units are the units of fundamental quantities. The fundamental units are followed throughout the world. Whereas USA has its own U.S. Customary units for almost all physical quantities. Some of the fundamental units are listed below: Physical Quantity Units in Metric System Symbol U.S. Customary Units Symbol Mass Kilogram Kg Pound lb Length Meter M Feet ft Time Second S Second S Temperature Centigrade C Fahrenheit F Volume Liter L Gallon gal Derived Units: There are units that are obtained from fundamental units. For example, velocity. Velocity is derived from length and time and its unit is m/s. Units of Length in Metric System: Length is generally measured in meters. In Metric system, units of length are micrometers (µm), millimeters (mm), centimeters (cm), meters (m) and kilometers (km). In biological science, since the size of microorganisms and molecules present in the body are very minute, smaller units of length are also used such as nanometer (nm) and Angstrong (Å). Feet and inch are also units of length in U.S. Customary Units. 1 meter = 100 centimeters 1 centimeter = 0.01 meter 1 meter = 1,000 millimeters 1 kilometer = 1,000 meters 1 inch (in) = 2.54 centimeters 1 feet = 12 inches 1 feet = 0.3048 meter Copyright iteachly.com 1
Size of Various Molecules and Cells Units of Mass in Metric System: The mass is measured in grams. Like length, mass also has different units within the Metric system and these are micrograms (µg), milligrams (mg), grams (gm) and kilograms (kg). In U.S. Customary units, another unit of mass is ounce and pound. A slice of bread is considered to have a mass of 1 ounce. A Slice of Bread 1 kg = 2.21 pounds Units of Volume in Metric System: Volume is generally measured in milliliter (ml). Volume also has different units within the metric system such as microliters (µl), milliliters (ml) and liters (l). 1 cc = 1 ml 1 liter = 1 dm 3 1 gallon = 3.8 liters 1 ounce = 30 ml Copyright iteachly.com 2
One drop of a liquid is approximately 1 milliliter of liquid. A Drop of Water Length Weight Volume 1 km = 1,000 m 1 kg = 1,000 gm 1 l = 1,000 ml 1 cm = 0.01 m 1 mg = 0.001 gm 1 cl = 0.01 ml 1 mm = 0.001 m 1 µg = 0.00001 gm 1 µl = 0.00001 ml 1 µm = 0.00001 m 1 ng = 0.00000001 gm 1 nl = 0.00000001 ml 1 nm = 0.00000001 m 1 gm = 1,000 mg 1 kl = 1,000 l 1 Å = 0.000000001 m 1 gm = 0.001 kg 1 ml = 0.001 l Units of Temperature in Metric System: Temperature is generally measured in degree centigrade ( C). In U.S. Customary unit temperature is measured in degree Fahrenheit ( F). In biology, generally C is used. These two units of temperatures are easily interconvertible. Converting Fahrenheit to Celsius: Following are the steps for this conversion: 1. Subtract 32 from the Fahrenheit value. 2. Multiply the obtained value by 5. 3. Then divide the resultant by 9. Conversion from Celsius to Fahrenheit: Following are the steps for this conversion: 1. Multiply the temperature in ( C) by 9. 2. Divide the obtained number by 5. 3. At last, add 32 in it. Copyright iteachly.com 3
Conversion of Units Within Metric System: The units of length, mass, time and temperature can be converted within the metric system. Let s take an example. You can calculate the length of any object using a scale. Here scale is acting as a tool for measuring the length of an object such as a paper. You can calculate the length of that paper in meter, centimeter, millimeter, etc or even convert it into various units of length. A Scale If the length of a paper comes to 10 cm, it can be converted to mm. As you known that 1 cm = 0.01 m therefore, 10 cm will be equal to 10 X 0.01 m = 0.1 m. Now you have to convert 0.1 m to mm. As you know that 1 m = 0.001 mm, therefore 0.1 m will be equal to 0.1 X 0.001 mm = 0.0001 mm or 10-4 mm. In similar way, other units can also be converted to each other as per requirement. Laboratory Equipments A biology laboratory generally consists of some common equipments and glasswares that a student should be aware of. Every equipment and glassware have their own function in the laboratory. Some of the common glasswares and equipments are listed below: Measuring Cylinder It is also known as graduated cylinder. It is used to measure the volume of a liquid in ml. The measuring cylinder has marking on it so that the correct amount of liquid can be measured with it. While measuring any liquid two meniscuses are observed, lower meniscus and upper meniscus due to surface tension. It should be noted that during measuring a liquid, the lower meniscus is considered, and the reading is noted. Measuring Cylinders Lower Meniscus Copyright iteachly.com 4
Beaker It is used to store the measured amount of liquid in it. It is also used to hold solids and to mix materials. It comes in various capacity such as 50 ml, 250 ml, 500 ml, 1000 ml, etc. It has very poor accuracy with the volume of liquid, so it should not be used to measure the volume of liquid. Different Sizes of Beaker Erlenmeyer Flask This is also known as conical flask due to its conical shape. Like a beaker, the flask is also used to hold certain amount of solids or liquids. It is generally used to heat any liquid and solid and also stirring as it can avoid spilling due to its shape. Erlenmeyer Flask Bunser Burner It is used for burning or heating things such as liquids and solids. It is commonly used in biology and chemistry laboratory. Bunsen Burner Copyright iteachly.com 5
Spirit Lamp It is also used for the same purpose as the Bunsen burner. It has a container filled with spirit or alcohol and a wick inside. Spirit Lamp Burette It is used to measure very accurate amount of liquid. It is also used in titration process to hold certain amount of dye in it. It is basically used in biological and chemical experiments. Burette Copyright iteachly.com 6
Dropper It is used to transfer one drop of liquid at a time. It can be made up of plastic or glass. The disposable droppers are made up of plastic. Droppers Pipette It is also used to get the accurate amount of liquid in very small amount that cannot be measured by a graduated cylinder. It can measure volume of liquid in millimeters also. The liquid should never be sucked with mouth. A dispenser or a pipette bulb can be used to dispense the liquid. There are two types of pipettes- glass pipette and micropipette. A glass pipette is most commonly used in the laboratory whereas a micropipette is used in research studies for measuring minute amount of liquid. The glass pipette is also known as graduated pipette. Micropipettes Copyright iteachly.com 7
Graduated Pipette Wire Gauge It is a mesh like structure made up of iron that is used to hold a beaker or a flask while heating. It is square in shape with a round asbestos sheet in the center of the square. Wire Gauges Test tube It is the most common glassware used in a biological laboratory. It also comes in various sizes. It is used to mix liquids, solids with liquid, heat the chemical, grow cultures, etc. Test Tube Copyright iteachly.com 8
Test Tube Rack This is like a stand that is used to hold 5-10 test tubes in a laboratory. Test Tube Rack Spatula It is used to pick small quantity of solid or chemical and for transferring it to any container. It is generally used as a spoon in a biological laboratory. Mortar Pestle Spatula It is made up of porcelain and used to crush and grind solids into fine powder or mixture. Mortar Pestle Copyright iteachly.com 9
Watch Glass It is a small glassware used to hold small amount of solid and liquid chemicals. It can also be used as a cover for a beaker. Watch Glasses Petri Dish A petri dish is a shallow glass or plastic dish that comes with a cover. It is named after its inventor Julius Richard Petri. It is used by the biologists to grow microbiological cultures. Petri Dishes Digital Balance It is also known as analytical balance. It is used to measure the weight of any solid. The chemical to be weighed is not directly placed on the weighing pan. After switching on the machine, the weighing boat or a white paper is kept on the weighing pan and then tare button is pressed. This makes the reading again to zero. Then, the chemical to be weighed is kept on the paper or weighing boat. The reading that comes on the scale is the weight of that chemical. Copyright iteachly.com 10
A Digital Balance ph Meter A ph meter is an instrument most commonly used in a science laboratory to determine the acidity and alkalinity of a sample liquid. It measures the hydrogen ion concentration in the given solution. A solution that has more hydrogen ion concentration is more acidic while those having more hydroxyl ion concentration is more alkaline. ph is measured on a scale from 1-14. 7 is considered as neutral, below 7 is acidic and above 7 is alkaline. A ph meter consists of a glass probe that has two glass electrodes- a sensor electrode and a reference electrode. The sensor electrode is made up of permeable glass membrane which is coated with silica and metal salts. It also contains a silver chloride coated wire immersed in the ph buffer solution. The reference electrode consists of potassium chloride solution in which a wire coated with silver chloride is immersed. When the glass ph probe is placed in the sample solution, the hydrogen ions accumulate around the bulb that replaces the metal ions. This exchange of ions leads to electric flow which is measured in the form of ph of that solution. Copyright iteachly.com 11
A Digital ph Meter A Pen ph Meter Copyright iteachly.com 12
Compound Microscope A compound microscope is also known as student microscope that is most commonly used in a biology laboratory. It uses two lenses one close to the object and one close to the observer s eye. Eye piece lens is close to the observer s eye while the objective lens is close to the object to be observed. A compound microscope can be of two types: monocular microscope and binocular microscope. Monocular microscope has a single tube with a single eyepiece while a binocular microscope has two tubes each with one eye piece. It may or may not consist of a light source. The modern compound microscope consists of a light source which is a bulb. It also has a condenser lens that condenses and focuses the beam of light falling on the object. The beam of light falling on the object passes through the objective lens and the magnified image is formed that again passes through the eye piece to again magnify the image. This magnified image is then viewed by the observer s eye. Compound Microscope Copyright iteachly.com 13