Transcript SCIENCE

SCIENCE
• The intellectual process using all available mental
and physical resources to better understand, explain,
quantitate, and predict normal as well as unusual
natural phenomena
• The goal of science is to investigate and understand
the natural world, to explain events in the natural
world, and to use those explanations to make useful
predictions
• Organized way of using evidence to learn about the
natural world
– Body of knowledge that has been built up over the
years
Scientific Method
• Observation
• Measurement
• Accumulation and analysis of verifiable
data
Scientific Method
• Observation:
– Process of gathering information about
events or processes in a careful, orderly
way
– Generally involves using the senses,
particularly sight, hearing, touch, smell, and
taste
Scientific Method
• The information gathered from observations
is called data
– Observations and measurements that are made in an
experiment
– There are two main categories of data:
• Quantitative data are expressed as numbers, obtained by
counting or measuring
• Qualitative data are descriptive and involve characteristics
that can't usually be counted:
– The researcher might make the qualitative observations
that “the scar appears old” and “the animal seems healthy
and alert.”
Inference
• Scientists may use data to make
inferences
• Inference is a logical interpretation based
on prior knowledge or experience
– Example:
• Researcher might be testing water in a reservoir
Because he/she cannot test all the water, he/she
collects water samples from several different
parts of the reservoir
– If all the samples are clean enough to drink, she may
infer that all the water is safe to drink
Explaining and Interpreting
Evidence
• Scientists try to explain events in the
natural world by interpreting evidence
logically and analytically:
– Suppose:
• That many people contract an unknown disease
after attending a public event
• Public health researchers will use scientific
methods to try to determine how those people
became ill
Explaining and Interpreting Evidence
HYPOTHESIS
• After initial observations:
– Researchers will propose one or more hypotheses
– A hypothesis is a proposed scientific explanation for
a set of observations (educated guess)
– Scientists generate hypotheses using prior
knowledge, or what they already know; logical
inference; and informed, creative imagination
– For the unknown disease, there might be several
competing hypotheses, such as these:
• (1) The disease was spread from person to person by
contact
• (2) The disease was spread through insect bites
• (3) The disease was spread through air, water, or food
Test Hypothesis
• Scientific hypotheses must be proposed in a way
that enables them to be tested
• Some hypotheses are tested by performing
controlled experiments, as you will learn in the next
section
• Other hypotheses are tested by gathering more data:
– In the case of the mystery illness, data would be collected by
studying the location of the event; by examining air, water, and
food people were exposed to; and by questioning people about
their actions before falling ill
• Some hypotheses would be ruled out
• Others might be supported and eventually confirmed
Designing an Experiment
• People's ideas about where some living
things come from have changed over
the centuries
– Exploring this change can help show how
science works
– Remember that what might seem obvious
today was not so obvious thousands of years
ago.
Stating the Problem
Observation
• For many years, observations seemed to
indicate that some living things could just
suddenly appear:
– Maggots showed up on meat; mice were found on
grain; and beetles turned up on cow dung
– People wondered how these events happened. They
were, in their own everyday way, identifying a problem
to be solved by asking a question: How do new
living things, or organisms, come into being?
Hypothesis
• For centuries, people accepted the prevailing
explanation for the sudden appearance of
some organisms, that some life somehow
“arose” from nonliving matter:
– The maggots arose from the meat
– Mice from the grain
– Beetles from the dung
• Scholars of the day even gave a name to the
idea that life could arise from nonliving
matter—spontaneous generation
– In today's terms, the idea of spontaneous generation
can be considered a hypothesis
Redi’s Experiment
• In 1668, Francesco Redi, an Italian physician,
proposed a different hypothesis for the
appearance of maggots:
– Redi had observed that these organisms
appeared on meat a few days after flies were
present
– He considered it likely that the flies laid eggs too
small for people to see
• Thus, Redi was proposing a new hypothesis—flies
produce maggots
• Redi's next step was to test his hypothesis
Setting Up a Controlled Experiment
• In science, testing a hypothesis often
involves designing an experiment
• The factors in an experiment that can change
are called variables
– Examples of variables include:
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Equipment used
Type of material
Amount of material
Temperature
Light
Time
Setting Up a Controlled Experiment
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Suppose you want to know whether
an increase in water, light, or
fertilizer can speed up plant growth
If you change all three variables at
once, you will not be able to tell which
variable is responsible for the
observed results
Whenever possible, a hypothesis
should be tested by an experiment
in which only one variable is
changed at a time
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All other variables should be kept
unchanged, or controlled
This type of experiment is called a
controlled experiment
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The variable that is deliberately
changed is called the manipulated
variable
The variable that is observed and that
changes in response to the manipulated
variable is called the responding
variable.
Redi’s Experiment
• Based on his hypothesis, Redi
made a prediction that keeping
flies away from meat would
prevent the appearance of
maggots
• To test this hypothesis, he
planned the experiment
shown at right
• Notice that Redi controlled
all variables except one:
– Whether or not there was
gauze over each jar
– The gauze was important
because it kept flies off the
meat.
Redi’s Experiment
Redi’s Experiment
• The manipulated variable was the
presence or absence of the gauze
covering
• The results of this experiment helped:
– Disprove the hypothesis of spontaneous
generation
Recording and Analyzing Results
• Scientists usually keep written records of their observations, or
data
– In the past, data were usually recorded by hand, often in notebooks or
personal journals
– Sometimes, drawings recorded certain kinds of observations more
completely and accurately than a verbal description could
– Today, researchers may record their work on computers. Online storage
often makes it easier for researchers to review the data at any time and,
if necessary, offer a new explanation for the data
• Scientists know that Redi recorded his data because copies of
his work were available to later generations of scientists
– His investigation showed that maggots appeared on the meat in
the control jars
– No maggots appeared in the jars covered with gauze
Drawing a Conclusion
• Scientists use the data from an experiment to
evaluate the hypothesis and draw a valid conclusion
– That is, they use the evidence to determine whether the
hypothesis was supported or refuted
• Redi's results supported his hypothesis:
– He therefore concluded that the maggots were indeed
produced by flies
• As scientists look for explanations for specific
observations, they assume that the patterns in nature
are consistent
– Thus, Redi's results could be viewed not only as an
explanation about maggots and flies but also as a refutation
of the hypothesis of spontaneous generation
Publishing and Repeating Investigations
• A key assumption in science is that experimental results can be
reproduced because nature behaves in a consistent manner:
– When one particular variable is manipulated in a given set of variables,
the result should always be the same
– In keeping with this assumption, scientists expect to test one
another's investigations
– Thus, communicating a description of an experiment is an
essential part of science
• Today's researchers often publish a report of their work in a
scientific journal:
– Other scientists review the experimental procedures to make sure
that the design was without flaws
– They often repeat experiments to be sure that the results match
those already obtained
• In Redi's day, scientific journals were not common, but he
communicated his conclusion in a book that included a description
of his investigation and its results.
Microscope Discovery
• About the time Redi was carrying out his
experiment, Anton van Leeuwenhoek (LAYvun-hook) of the Netherlands discovered a
world of tiny moving objects in rainwater,
pond water, and dust:
– Inferring that these objects were alive, he called them
“animalcules,” or tiny animals
– He made drawings of his observations and shared
them with other scientists
– For the next 200 years or so, scientists could not
agree on whether the animalcules were alive or
how they came to exist (Spontaneous
Generation?????)
Needham's Test of Redi's Findings
• In the mid-1700s, John Needham, an English
scientist, used an experiment involving animalcules
to attack Redi's work
• Needham claimed that spontaneous generation
could occur under the right conditions:
– To prove his claim, he sealed a bottle of gravy and heated it
– He claimed that the heat had killed any living things that
might be in the gravy
– After several days, he examined the contents of the bottle
and found it swarming with activity
• “These little animals,” he inferred, “can only have
come from juice of the gravy.” (SPONTANEOUS
GENERATION)
Spallanzani's Test of Redi's Findings
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An Italian scholar, Lazzaro
Spallanzani, read about Redi's and
Needham's work
Spallanzani thought that Needham
had not heated his samples enough
and decided to improve upon
Needham's experiment
The figure shown at right illustrates
that Spallanzani boiled two
containers of gravy, assuming that
the boiling would kill any tiny living
things, or microorganisms, that
were present:
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He sealed one jar immediately and
left the other jar open
After a few days, the gravy in the
open jar was teeming with
microorganisms
The sealed jar remained free of
microorganisms
Spallanzani’s Experiment
Spallanzani’s Experiment
• Spallanzani concluded that nonliving
gravy did not produce living things:
– The microorganisms in the unsealed jar
were off-spring of microorganisms that
had entered the jar through the air
– This experiment and Redi's work
supported the hypothesis that new
organisms are produced only by existing
organisms
Challenge
• Well into the 1800s, some scientists continued
to support the spontaneous generation
hypothesis
• Some of them argued that air was a
necessary factor in the process of generating
life because air contained the “life force”
needed to produce new life
• They pointed out that Spallanzani's
experiment was not a fair test because air
had been excluded from the sealed jar
Pasteur's Test of Spontaneous Generation
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In 1864, an ingenious French scientist,
Louis Pasteur, found a way to settle the
argument
He designed a flask that had a long
curved neck, as shown in the figure at
right
The flask remained open to the air, but
microorganisms from the air did not make
their way through the neck into the flask
Pasteur showed that as long as the broth
was protected from microorganisms, it
remained free of living things
About a year after the experiment began,
Pasteur broke the neck of the flask, and the
broth quickly became filled with
microorganisms
His work convinced other scientists that
the hypothesis of spontaneous
generation was not correct:
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In other words, Pasteur showed that all
living things come from other living things
This change in thinking represented a
major shift in the way scientists viewed
living things
Pasteur’s Experiment
The Impact of Pasteur's Work
• During his lifetime, Pasteur made many discoveries
related to microorganisms
• His research had an impact on society as well as on
scientific thought
• He saved the French wine industry, which was troubled
by unexplained souring of wine, and the silk industry,
which was endangered by a silkworm disease
• Moreover, he began to uncover the very nature of
infectious diseases, showing that they were the result of
microorganisms entering the bodies of the victims
• Pasteur is considered one of biology's most remarkable
problem solvers.
How a Theory Develops
• As evidence from numerous investigations
builds up, a particular hypothesis may become
so well supported that scientists consider it a
theory
• That is what happened with the hypothesis
that new organisms come from existing
organisms
• This idea is now considered one of the major
ideas in science
– It is called biogenesis, meaning “generating from
life”
Theory
• You may have heard the word theory used in
everyday conversations as people discuss ideas
– Someone might say, “Oh, that's just a theory,” to
criticize an idea that is not supported by evidence
• In science, the word theory applies to a welltested explanation that unifies a broad range
of observations:
– A theory enables scientists to make accurate
predictions about new situations
Theory
• A useful theory may become the dominant view among
the majority of scientists, but no theory is considered
absolute truth
• Scientists analyze, review, and critique the strengths
and weaknesses of theories
• As new evidence is uncovered, a theory may be
revised or replaced by a more useful explanation:
– Sometimes, scientists resist a new way of looking at
nature, but over time new evidence determines which
ideas survive and which are replaced
– Thus, science is characterized by both continuity and
change
BIOLOGY
• The word biology means the study of life
– The Greek word bios means “life,” and -logy
means “study of”
– Biology is the science that seeks to understand
the living world
• A biologist is someone who uses scientific
methods to study living things
– The work of biologists can be quite varied, because
organisms are complex and vary so greatly
Characteristics of Life
• Living things share the following
characteristics:
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Living things are made up of units called cells
Living things reproduce
Living things are based on a universal genetic code
Living things grow and develop
Living things obtain and use materials and energy
Living things respond to their environment
Living things maintain a stable internal
environment
• Taken as a group, living things change over
time
Made Up of Cells
• Living things, or organisms, are made up of small, selfcontained units called cells
– A cell is a collection of living matter enclosed by a barrier
that separates the cell from its surroundings
• Cells are the smallest units of an organism that can be considered
alive
• Cells can grow, respond to their surroundings, and reproduce
• Despite their small size, cells are complex and highly organized
• Many living things consist of only a single cell and are therefore
called unicellular organisms
– The Latin prefix uni- means “one,” so unicellular means “singlecelled”
• Many of the microorganisms involved in Spallanzani's and Pasteur's
experiments were unicellular organisms
Made Up of Cells
• The organisms you are most familiar with—for example,
animals and plants—are multicellular
• The Latin prefix multi- means “many”
– Thus, multicellular means “many-celled”
• Multicellular organisms contain hundreds, thousands, or
even trillions of cells
• The cells in these organisms are often remarkably
diverse, existing in a variety of sizes and shapes
• In some multicellular organisms, each type of cell is
specialized to perform a different function
• The human body alone is made up of at least 85
different cell types
Reproduction
• All organisms produce new organisms through a
process called reproduction
• There are two basic kinds of reproduction: sexual
and asexual
• The vast majority of multicellular organisms—from maple
trees to birds and humans—reproduce sexually
• In sexual reproduction, cells from two different parents
unite to produce the first cell of the new organism
• In asexual reproduction, the new organism has a
single parent
• In some forms of asexual reproduction, a single-celled
organism divides in half to form two new organisms
• In another type of asexual reproduction known as
budding, a portion of an organism splits off to form a new
organism
Based on a Genetic Code
• Offspring usually resemble their parents:
– With asexual reproduction, offspring and their parents have
the same traits
– With sexual reproduction, offspring differ from their parents in
some ways
• However, there are limits to these differences:
– Flies produce flies, dogs produce dogs, and seeds from maple
trees produce maple trees
• Explaining how organisms inherit traits is one of the
greatest achievements of modern biology:
– Biologists now know that the directions for inheritance are
carried by a molecule called deoxyribonucleic acid, or DNA
– This genetic code, with a few minor variations, determines the
inherited traits of every organism on Earth
Growth and Development
• All living things grow during at least part of their lives:
– For some single-celled organisms, such as bacteria, growth is
mostly a simple increase in size
– Multicellular organisms, however, typically go through a
process called development:
• During development, a single fertilized egg cell divides again and
again to produce the many cells of mature organisms
• As those cells divide, they change in shape and structure to form
cells such as liver cells, brain cells, and muscle cells
• This process is called differentiation, because it forms cells that
look different from one another and perform different functions
• For many organisms, development includes periods of
rapid and dramatic change:
– In fact, although you will not sprout wings, your body is currently
experiencing one of the most intense spurts of growth and
development of your entire life!
Need for Materials and Energy
• Think of what an organism needs as it grows
and develops:
– Just as a building grows taller because workers use
energy to assemble new materials, an organism
uses energy and a constant supply of materials to
grow, develop, and reproduce
– Organisms also need materials and energy just to
stay alive:
• The combination of chemical reactions through which an
organism builds up or breaks down materials as it
carries out its life processes is called metabolism
Need for Materials and Energy
• All organisms take in selected materials that
they need from their surroundings, or
environment, but the way they obtain energy
varies
• Plants, some bacteria, and most algae obtain
their energy directly from sunlight
• AUTOTROPHS:
– Through a process called photosynthesis, these
organisms convert light into a form of energy that
is stored in certain molecules
– That stored energy is ready to be used when needed
Need for Materials and Energy
• Most other organisms rely on the energy
stored during photosynthesis
• HETEROTROPHS:
– Some organisms, such as grasshoppers and sheep,
obtain their energy by eating plants and other
photosynthesizing organisms (Herbivore)
– Other organisms, such as birds and wolves, get
energy by eating the grasshoppers or sheep
(Carnivore)
– And some organisms, called decomposers, obtain
energy from the remains of organisms that have
died
Response to the Environment
• Organisms detect and respond to stimuli from their
environment
– A stimulus is a signal to which an organism responds
• External stimuli, which come from the environment outside an
organism, include factors such as light and temperature
– For example, when there is sufficient water and the ground is
warm enough, a plant seed responds by germinating
– The roots respond to gravity and grow down into the soil
– The new leaves and stems grow toward light
• Internal stimuli come from within an organism
– The level of the sugar glucose in your blood is an example of an
internal stimulus
– If this level becomes low enough, your body responds by making
you feel hungry
Maintaining Internal Balance
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Even though conditions in the external environment may vary widely,
most organisms must keep internal conditions, such as temperature
and water content, fairly constant to survive
The process by which they do this is called homeostasis (hoh-mee-ohSTAY-sis)
– Homeostasis often involves internal feedback mechanisms that work in much the
same way as a thermostat
– Just as a thermostat in your home turns on the heat when room temperature
drops below a certain point, you have an internal “thermostat” that makes your
body shiver if your internal temperature drops too low
– The muscle action involved in shivering produces heat, thus warming your body
– In contrast, if you get too hot, your biological thermostat turns on “air
conditioning” by causing you to sweat.
– Sweating helps to remove excess heat from your skin
– When birds get cold, they hunch down and adjust their feathers to provide
maximum insulation
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Often internal stimuli help maintain homeostasis
For example, when your body needs more water to maintain
homeostasis, internal stimuli make you feel thirsty
Evolution
• Although individual organisms experience many changes
during their lives, the basic traits they inherited from their
parents usually do not change
• As a group, however, any given kind of organism can evolve, or
change over time
• Over a few generations, the changes in a group may not seem
significant
– But over hundreds of thousands or even millions of years, the
changes can be dramatic
• Scientists study deposits containing the remains of animals that
lived long ago to learn about the evolution of organisms
– From the study of very early deposits, scientists know that at one time
there were no fishes in Earth's waters
– Yet, in more recent deposits, the remains of fishes and other animals
with backbones are abundant
• The ability of a group of organisms to change over time is
invaluable for survival in a world that is always changing
Branches of Biology
• Living things come in an astonishing variety of shapes,
sizes, and habits
• Living systems also range in size from groups of
molecules that make up structures inside cells to the
collections of organisms that make up the biosphere
• No single biologist could study all this diversity, so
biology is divided into different fields
• Some fields are based on the types of organisms being
studied:
– Zoologists study animals
– Botanists study plants
– Other fields study life from a particular perspective
• Example:
– Paleontologists study ancient life
Branches of Biology
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Some fields focus on the study of
living systems at different levels of
organization, as shown in the table
at right
Some of the levels at which life can
be studied include molecules, cells,
organisms, populations of a single
kind of organism, communities of
different organisms in an area, and
the biosphere
– At all these levels, smaller
living systems are found within
larger systems
Molecular biologists and cell biologists
study some of the smallest living
systems
Population biologists and ecologists
study some of the largest systems in
nature
Studies at all these levels make
important contributions to the quality of
human life
Biology in Everyday Life
• Biologists do not make the decisions about most matters affecting
human society or the natural world; citizens and governments do
• In just a few years, you will be able to exercise the rights of a voting
citizen, influencing public policy by the ballots you cast and the
messages you send public officials:
– With others, you will make decisions based on many factors,
including customs, values, ethical standards, and scientific
knowledge
• Biology can provide decision makers with useful information
and analytical skills:
– It can help them envision the possible effects of their
decisions
• Biology can help people understand that humans are capable
of predicting and trying to control their future and that of the
planet
A Common Measurement System
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Because researchers need to replicate
each other's experiments and most
experiments involve measurements,
scientists need a common system of
measurement:
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Most scientists use the metric system
when collecting data and performing
experiments
The metric system is a decimal system of
measurement whose units are based on
certain physical standards and are
scaled on multiples of 10
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A revised version of the original metric system
is called the International System of Units, or
SI
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The abbreviation SI comes from the French Le
Système International d'Unités.
Because the metric system is based on
multiples of 10, it is easy to use
Notice in the table at right how the basic unit
of length, the meter, can be multiplied or
divided to measure objects and distances
much larger or smaller than a meter. The
same process can be used when measuring
volume and mass
Metric
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POWER
OF TEN
1012
109
106
103
102
10
DECIMAL
EQUIVALENT PREFIX
1,000,000,000,000
1,000,000,000
1,000,000
1,000
100
10
1
SUFFIX
SYMBOL
tera
giga
mega
kilo
hecto
deka
meter/liter/gram
T
G
M
k
h
da
m/l/g
Metric
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POWER
OF TEN
DECIMAL
PREFIX
SUFFIX
SYMBOL
EQUIVALENT
1
meter/liter/gram m/l/g
10-1
0.1
deci
d
10-2
0.01
centi
10-3
0.001
milli
10-6
0.000 001
micro
u
10-9
0.000 000 001 nano
n
10-12
0.000 000 000 001
pico
10-15 0.000 000 000 000 001
femto
10-18 0.000 000 000 000 000 001 atto
** to express the units you combine the prefix and suffix
c
m
p
f
a
Metric
• DIMENSIONAL ANALYSIS
• Now that you know the basic units of the
metric/SI system, it is important that you
understand how to go from one unit to another.
The skill of converting one unit to another is
called dimensional analysis
• Dimensional analysis involves determining in
what units a problem is given, in what units
the answer should be, and the factor to be
used to make the conversion from one unit
to another.
Metric
• To perform dimensional analysis, you must
use a conversion factor
• A conversion factor is a fraction that equal 1.
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Example:
• 1 kilometer equals 1000 meters
• So the fraction 1 kilometer / 1000 meters equals 1
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So does the fraction 1000 meters / 1 kilometer
The top number in a fraction is called the numerator
The bottom number in a fraction is called the denominator
In a conversion fraction the numerator always equals the
denominator so that the fraction always equals 1
Metric
• Let’s see how dimensional analysis works. Suppose you are told to
convert 2500 grams to kilograms. This means that grams are your
given unit and you must express your answer in kilograms. The
conversion factor you choose must contain a relationship
between grams and kilograms that has a value of 1. You have
two possible choices:
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1000 grams / 1 kilogram = 1
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1 kilogram / 1000 grams = 1
• To convert one metric unit to another, you must multiply the
given value times the conversion factor. Remember that
multiplying a number by 1 does not change the value of the number.
So multiplying by a conversion factor does not change the
value, just the units.
Metric
• Now, which conversion factor should you use to
change 2500 grams into kilograms? Since you are
going to multiply by the conversion factor, you want the
unit to be converted to cancel out during the
multiplication. This is just what will happen if the
denominator of the conversion factor has the same
units as the value you wish to convert. Since you are
converting grams into kilograms, the denominator of
the conversion factor must be in grams and the
numerator in kilograms. The first step in dimensional
analysis, then, is to write out the value given, the
correct conversion factor, and a multiplication
symbol between them:
Metric
• 2500 grams X 1 kilogram / 1000 grams =
• The next step is to cancel out the same
units:
• 2500 X 1 kilogram / 1000 =
• The last step is to multiply:
• 2500 kilograms / 1000
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2500 kilograms / 1000 = 2.5 kilograms
Metric
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MASS VALUES:
1 kilogram (kg) = 1,000 grams (g)
1 hectogram (hg) = 100 grams (g)
1 dekagram (dag) = 10 grams (g)
1 gram (g) = 1 gram (g)
1 decigram (dg) = 0.1 gram (g)
1 gram (g) = 10 decigram (dg)
1 centigram (cg) = 0.01 gram (g)
1 gram (g) = 100 centigram (cg)
1 milligram (mg) = 0.001 gram (g)
1 gram (g) = 1000 milligram (mg)
1 microgram (ug) = 0.000001 gram (g)
1 gram (g) = 1,000,000 microgram (ug)
1 nanogram (ng) = 0.000000001 gram (g)
1 gram (g) = 1,000,000,000 nanogram (ng)
Metric
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LIQUID VALUES:
1 kiloliter (kl) = 1,000 liters (l)
1 hectoliter (hl) = 100 liters (l)
1 dekaliter (dal) = 10 liters (l)
1 liter (l) = 1 liter (l)
1 deciliter (dl) = 0.1 liter (l)
– 1 liter (l) = 10 deciliter (dl)
• 1 centiliter (cl) = 0.01 liter (l)
– 1 liter (l) = 100 centiliter (cl)
• 1 milliliter (ml) = 0.001 liter (l)
– 1 liter (l) = 1000 milliliter (ml)
• 1 microliter (ul) = 0.000001 (l)
– 1 liter (l) = 1,000,000 microliter (ul)
• 1 nanoliter (nl) = 0.000000001 (l)
– 1 liter (l) = 1,000,000,000 nanoliter (nl)
Metric
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LENGTH VALUES:
1kilometer (km) = 1,000 meters (m)
1hectometer (hm) = 100 meters (m)
1dekameter (dam) = 10 meters (m)
1meter(m) = 1 meter (m)
1decimeter (dm) = 0.1 meter (m)
1meter (m) = 10 decimeter (dm)
1centimeter (cm) = 0.01 meter (m)
1meter (m) = 100 centimeter (cm)
1millimeter (mm) = 0.001 meter (m)
1meter (m) = 1000 millimeter (mm)
1micrometer (um) = 0.000001 meter (m)
1meter (m) = 1,000,000 micrometer (um)
1nanometer (nm) = 0.000000001 meter (m)
1meter (m) = 1,000,000,000 nanometer (nm)
Metric
• Do the following conversions for
homework. All work and individual steps
MUST be shown !
• *** as you will see later the volume
measurement of 1 ml is equivalent to 1
cubic centimeter or 1 cc or 1 cm 3
Metric
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CONVERSIONS:
3 m = _______ cm
3 m x 100 cm / 1 m = _________ cm
1,500 ml = ______ l
1,500 ml x 1 l / 1000 ml = ________ l
0.015 g = _______ mg
0.015 g x 1000 mg / 1 g = _________ mg
0.25 km = _______ m
0.25 km x 1000 m / 1 km = ________ m
2.5 l = __________ ml
2.5 l x 1000 ml / 1 l = _________ ml
2,750 mg = _______ g
2,750 mg x 1 g / 1000 mg = ________ g
2 mm = _________ um
2 mm x 1000 um / 1 mm = __________ um
2 mm = _________ nm
2 mm x 1,000,000 nm / 1mm = ____________ nm
Microscopes
• Microscopes are devices that produce magnified
images of structures that are too small to see with the
unaided eye
– Light microscopes produce magnified images by focusing
visible light rays
– Electron microscopes produce magnified images by
focusing beams of electrons
•
Since the first microscope was invented, microscope
manufacturers have had to deal with two problems: What
is the instrument's magnification—that is, how much
larger can it make an object appear compared to the
object's real size? And how sharp an image can the
instrument produce?
Light Microscopes
• The most commonly used microscope is the light microscope
• Light microscopes can produce clear images of objects at a
magnification of about 1000 times
• Compound light microscopes allow light to pass through the
specimen and use two lenses to form an image
– Light microscopes make it possible to study dead organisms
and their parts, and to observe some tiny organisms and
cells while they are still alive
– Biologists have developed techniques and procedures to
make light microscopes more useful:
• Chemical stains, also called dyes, can show specific
structures in the cell
• Fluorescent dyes have been combined with video cameras
and computer processing to produce moving threedimensional images of processes such as cell movement
Electron Microscopes
• All microscopes are limited in what they reveal, and light
microscopes cannot produce clear images of
objects smaller than 0.2 micrometers, or about onefiftieth the diameter of a typical cell
• To study even smaller objects, scientists use electron
microscopes
• Electron microscopes use beams of electrons, rather
than light, to produce images
• The best electron microscopes can produce images
almost 1000 times more detailed than light microscopes
can
Electron Microscopes
• Biologists use two main types of electron
microscopes:
– Transmission electron microscopes (TEMs) shine a beam of
electrons through a thin specimen
• TEMs can reveal a wealth of detail inside the cell
– Scanning electron microscopes (SEMs) scan a narrow beam
of electrons back and forth across the surface of a specimen
• SEMs produce realistic, and often dramatic, three-dimensional
images of the surfaces of objects
• Because electron microscopes require a vacuum to
operate, samples for both TEM and SEM work must be
preserved and dehydrated before they are placed inside
the microscope
– This means that living cells cannot be observed with
electron microscopes, only with the light microscope
Cell Cultures
• To obtain enough material to study, biologists
sometimes place a single cell into a dish
containing a nutrient solution
• The cell is able to reproduce so that a group
of cells, called a cell culture, develops from
the single original cell
– Cell cultures can be used to test cell responses under
controlled conditions, to study interactions between
cells, and to select specific cells for further study
Cell Fractionation
• Suppose you want to study just one part of a cell
• How could you separate that one part from the rest
of the cell?
• Biologists often use a technique known as cell
fractionation to separate the different cell parts:
– First, the cells are broken into pieces in a special blender
– Then, the broken cell bits are added to a liquid and placed in a
tube
– The tube is inserted into a centrifuge, which is an instrument that
can spin the tube
– Spinning causes the cell parts to separate, with the most dense
parts settling near the bottom of the tube
– A biologist can then remove the specific part of the cell to be
studied by selecting the appropriate layer.