SCIENCE

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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

2
Scientific Method

• Observation
• Measurement
• Accumulation and analysis of verifiable data

3
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

4
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.

5
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

6
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

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Explaining and Interpreting EvidenceHYPOTHESIS

• 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

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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

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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.

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Stating the ProblemObservation

• 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?

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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
  matterspontaneous generation
• In today's terms, the idea of spontaneous
  generation can be considered a hypothesis

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Redis 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 hypothesisflies
  produce maggots
• Redi's next step was to test his hypothesis

13
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
• Equipment used
• Type of material
• Amount of material
• Temperature
• Light
• Time

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Setting Up a Controlled Experiment

• 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
• All other variables should be kept unchanged, or
  controlled
• This type of experiment is called a controlled
  experiment
• 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.

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Redis 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.

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Redis Experiment
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Redis 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

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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

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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

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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.

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Microscope Discovery

• About the time Redi was carrying out his
  experiment, Anton van Leeuwenhoek (LAY-vun-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?????)

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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)

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Spallanzani's Test of Redi's Findings 

• 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
• 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

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Spallanzanis Experiment
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Spallanzanis 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

28
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

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Pasteur's Test of Spontaneous Generation

• 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
• 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

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Pasteurs Experiment
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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.

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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

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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
  well-tested explanation that unifies a broad
  range of observations
• A theory enables scientists to make accurate
  predictions about new situations

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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

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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

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Characteristics of Life

• Living things share the following
  characteristics
• 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

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Made Up of Cells 

• Living things, or organisms, are made up of
  small, self-contained 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 single-celled
• Many of the microorganisms involved in
  Spallanzani's and Pasteur's experiments were
  unicellular organisms

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Made Up of Cells

• The organisms you are most familiar withfor
  example, animals and plantsare 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

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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 organismsfrom
  maple trees to birds and humansreproduce
  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

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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

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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!

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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

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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

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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

47
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

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Maintaining Internal Balance 

• 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-oh-STAY-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
• Often internal stimuli help maintain homeostasis
• For example, when your body needs more water to
  maintain homeostasis, internal stimuli make you
  feel thirsty

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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

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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

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Branches of Biology

• 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

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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

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A Common Measurement System

• Because researchers need to replicate each
  other's experiments and most experiments involve
  measurements, scientists need a common system of
  measurement
• 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
• A revised version of the original metric system
  is called the International System of Units, or
  SI
• 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

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Metric

• POWER DECIMAL
• OF TEN EQUIVALENT PREFIX SUFFIX SYMBOL
•  
• 1012 1,000,000,000,000 tera
  T
• 109 1,000,000,000 giga
  G
• 106 1,000,000 mega M
  
• 103 1,000
  kilo k
• 102 100 hecto h
• 10 10 deka da
• 1
  meter/liter/gram m/l/g

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Metric

• POWER DECIMAL PREFIX SUFFIX SYMBOL
• OF TEN EQUIVALENT
• 1 meter/liter/gram
  m/l/g
• 10-1 0.1 deci d
• 10-2 0.01 centi
  c
• 10-3 0.001 milli
  m
• 10-6 0.000 001 micro
  u
• 10-9 0.000 000 001 nano
  n
• 10-12 0.000 000 000 001
  pico p
• 10-15 0.000 000 000 000 001 femto f
• 10-18 0.000 000 000 000 000 001 atto
  a
• to express the units you combine the prefix
  and suffix

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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.

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Metric

• To perform dimensional analysis, you must use a
  conversion factor
• A conversion factor is a fraction that equal 1.
• Example
• 1 kilometer equals 1000 meters
• So the fraction 1 kilometer / 1000 meters equals
  1
• 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

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Metric

• Lets 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
  
• 1000 grams / 1 kilogram 1
• or
• 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.

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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

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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
•   2500 kilograms / 1000 2.5 kilograms

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Metric

• 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)

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Metric

• 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)

65
Metric

• 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) 

66
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

67
Metric

• 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

68
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
  magnificationthat 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?

69
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
  three-dimensional images of processes such as
  cell movement

70
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
  one-fiftieth 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

71
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

72
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

73
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.