Handbook : Representing and Applying Data
As you read a science textbook, you will see many drawings, diagrams, and photographs.
Illustrations help you to understand what you read. Some illustrations are included
to help you understand an idea that you can't see easily by yourself. For instance,
we can't see atoms, but we can look at a diagram of an atom that helps us to understand
some things about atoms.
something often helps you remember more easily. Illustrations also provide examples
that clarify difficult concepts or give additional information about the topic
you are studying. Maps, for example, help you to locate places that may be described
in the text.
have captions. A caption identifies or explains the illustration. Some captions
are short; others are longer and more descriptive. Diagrams often have labels
that identify parts of the organism or the order of steps in a process, such as
the labels in Figure 19.
An illustration of an organism shows that organism from a particular side.
In order to understand the illustration,
you may need to identify the front (anterior) end, the tail (posterior) end, the
underside (ventral), and the back (dorsal) side, as shown in Figure 20.
Have you ever worked on a model car, plane, or rocket? Models look, and sometimes
work, much like the real thing, but they are often smaller or larger. In science,
models are used to help simplify processes or structures that otherwise would
be difficult to see and understand.
make a model, you first have to get a basic idea about the structure or process
involved. For example, make a model to show the differences in size of arteries,
veins, and capillaries. First, read about these structures. All three are hollow
tubes. Arteries are round and thick. Veins are flat and have thinner walls than
arteries. Capillaries are small.
what you can use for your model. Common materials are often best and cheapest
to work with when making models. The different kinds and sizes of pasta shown
in Figure 21 might work for these models. Different sizes of rubber tubing
might do just as well. Cut and glue the different noodles or tubing onto thick
paper so the openings can be seen. Then label each. Now you have a simple, easy-to-understand
model showing the differences in size of arteries, veins, and capillaries.
scientific ideas might a model help you to understand? A model of a molecule can
be made from gumdrops (using different colors for the different elements present)
and toothpicks (to show different chemical bonds). A working model of a volcano
can be made from clay, a small amount of baking soda, vinegar, and a bottle cap.
Other models can be devised on a computer.
The International System (SI) of Measurement is accepted as the standard for measurement
throughout most of the world. Four of the base units in SI are the meter, liter,
kilogram, and second.
of the unit can be determined from the prefix used with the base unit name. Look
at Figure 22 for some common metric prefixes and their meanings. The prefix
kilo- attached to the unit gram is kilogram, or 1000 grams. The prefix deci- attached
to the unit meter is decimeter, or one-tenth (0.1) of a meter. The metric system
is convenient because its unit sizes vary by multiples of 10. When changing from
smaller units to larger units, divide by 10. When changing from larger units to
smaller units, multiply by 10. For example, to convert millimeters to centimeters,
divide the millimeters by 10. To convert 30 millimeters to centimeters, divide
30 by 10 (30 millimeters equal 3 centimeters).
is the SI unit used to measure length. A baseball bat is about one meter long.
When measuring smaller lengths, the meter is divided into smaller units called
centimeters and millimeters. A centimeter is one- hundredth (0.01) of a meter.
A millimeter is one-thousandth of a meter (0.001).
rulers have lines indicating centimeters and millimeters. The centimeter lines
are the longer, numbered lines; the shorter lines are millimeter lines. When using
a metric ruler, line up the 0-centimeter mark with the end of the object being
measured and read the number of the unit where the object ends.
Units of length are also used to measure surface area. The standard unit of area
is the square meter (m2). A square that's one meter long on each side
has a surface area of one square meter. A square centimeter, (cm2),
shown in Figure 24, is one centimeter long on each side. The surface area
of an object is determined by multiplying the length times the width.
The volume of a rectangular solid is also calculated using units of length. The
cubic meter (m3) is the standard SI unit of volume. A cubic meter is
a cube one meter on each side. You can determine the volume of rectangular solids
by multiplying length times width times height.
During science activities, you will measure liquids using beakers and graduated
cylinders marked in milliliters, as illustrated in Figure 25. A graduated
cylinder is a cylindrical container marked with lines from bottom to top. Liquid
volume is measured using a unit called a liter. A liter has the volume of 1000
cubic centimeters. Because the prefix milli- means thousandth (0.001), a milliliter
equals one cubic centimeter. One milliliter of liquid would completely fill a
cube measuring one centimeter on each side.
Scientists use balances to find the mass of objects in grams. You will use a triple
beam balance similar to the one shown in Figure 26. Notice that on one
side of the balance is a pan and on the other side is a set of beams. Each beam
has an object of a known mass, called a rider, that slides along the beam.
you find the mass of an object, set the balance to zero by sliding all the riders
back to the zero point. Check the pointer on the right to make sure it swings
an equal distance above and below the zero point on the scale. If the swing is
unequal, find and turn the adjusting screw until you have an equal swing.
object on the pan. Slide the rider with the largest mass along its beam until
the pointer drops below zero. Then move it back one notch. Repeat the process
on each beam until the pointer swings an equal distance above and below the zero
point. Add the masses on each beam to find the mass of the object.
never place a hot object or pour chemicals directly onto the pan. Instead, find
the mass of a clean beaker or a glass jar. Place the dry or liquid chemicals in
the container. Then find the combined mass of the container and the chemicals.
Calculate the mass of the chemicals by subtracting the mass of the empty container
from the combined mass.
When you apply a hypothesis, or general explanation, to a specific situation,
you predict something about that situation.
must identify which hypothesis fits the situation you are considering. People
use prediction to make decisions every day. Based on previous observations and
experiences, you may form a hypothesis that if it is wintertime, then temperatures
will be low. From weather data in your area, temperatures are lowest in February.
You may then use this hypothesis to predict specific temperatures and weather
for the month of February. Someone could use these predictions to plan to set
aside more money for heating bills during that month.
When working with large populations of organisms, scientists usually cannot observe
or study every organism in the population. Instead, they use a sample or a portion
of the population. To sample is to take a small number of organisms of a population
for research. Information discovered with the small sample may then be applied
to the whole population. For example, scientists may take a small number of mice
from a field to study the effects of day length on reproductive rate. This information
could be applied to the population as a whole.
Scientific work also involves estimating. To estimate is to make a judgment about
the size of something or the number of something without actually measuring or
counting every member of a population. Here is a familiar example. Have you ever tried to guess how many kernels
of popcorn were in a sealed jar? If you did, you were estimating. What if you
knew the jar of popcorn held one liter (1000 mL)? If you knew that 60 popcorn
kernels would fit in a 100-milliliter jar, how many kernels would you estimate
to be in the one-liter jar? If you said about 600 kernels, your estimate would
be close to the actual number of popcorn kernels.
use a similar process to estimate populations of organisms from bacteria to buffalo.
Scientists count the actual number of organisms in a small sample and then estimate
the number of organisms in a larger area. For example, if a scientist wanted to
count the number of black-eyed Susans, the field could be marked off in a large
grid of 1-meter squares. To determine the total population of the field, the number
of organisms in one square-meter sample can be multiplied by the total number
of square centimeters in the field.