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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

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  • The intellectual processusing all available mental and physical resources to better understand, explain, quantitate, and predict normal as well as unusual natural phenomena
  • The goal of scienceis 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
Scientific Method
  • Observation
  • Measurement
  • Accumulation and analysis of verifiable data
scientific method1
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 method2
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.”
  • 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
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
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 hypothesesusing 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
Test Hypothesis
  • Scientific hypotheses must be proposed in a waythat 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
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
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?
  • 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
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
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
setting up a controlled experiment1
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.
redi s experiment1
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 experiment3
Redi’s Experiment
  • The manipulated variablewas the presence or absence of the gauze covering
  • The results of this experiment helped:
    • Disprove the hypothesis of spontaneous generation
recording and analyzing results
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
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
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
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?????)
needham s test of redi s findings
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
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
spallanzani s experiment1
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
  • 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
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
the impact of pasteur s work
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
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”
  • 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
  • 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
  • The word biology means the study of life
    • The Greek word bios means “life,” and -logy means “study of”
    • Biologyis 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
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
made up of cells
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
made up of cells1
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
  • 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
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
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
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 energy1
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
    • 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 energy2
Need for Materials and Energy
  • Most other organisms rely on the energy stored during photosynthesis
    • 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
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 stimulicome 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
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
  • 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
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 biology1
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
biology in everyday 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
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
  • 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
  • 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
  • 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.
  • To perform dimensional analysis, you must use a conversion factor
  • A conversion factor is afraction 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
  • 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:
  • 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.
  • 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 theconversion 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:
  • 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
  • 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)
  • 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)
  • 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) 
  • 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
  • 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 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
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
electron microscopes
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 microscopesuse 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 microscopes1
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
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
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 cellfractionation 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.