Title: SCIENCE
1SCIENCE
- 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
2Scientific Method
- Observation
- Measurement
- Accumulation and analysis of verifiable data
3Scientific 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
4Scientific 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.
5Inference
- 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
6Explaining 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
7Explaining 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
8Test 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
9Designing 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.
10Stating 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?
11Hypothesis
- 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
12Redis 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
13Setting 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
14Setting 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.
15Redis 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.
16Redis Experiment
17Redis 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
18Recording 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
19Drawing 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
20Publishing 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.
21Microscope 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?????)
22Needham'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)
23(No Transcript)
24Spallanzani'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
25Spallanzanis Experiment
26(No Transcript)
27Spallanzanis 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
28Challenge
- 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
29Pasteur'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
30Pasteurs Experiment
31(No Transcript)
32(No Transcript)
33The 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.
34How 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
35Theory
- 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
36Theory
- 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
37BIOLOGY
- 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
38Characteristics 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
39Made 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
40Made 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
41Reproduction
- 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
42Based 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
43Growth 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!
44Need 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
45Need 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
46Need 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
47Response 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
48Maintaining 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
49Evolution
- 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
50Branches 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
51Branches 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
52(No Transcript)
53Biology 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
54A 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
55(No Transcript)
56Metric
- 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
57Metric
- 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
58Metric
- 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.
59Metric
- 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
60Metric
- 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.
61Metric
- 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
62Metric
- 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
63Metric
- 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)
64Metric
- 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)
65Metric
- 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)
66Metric
- 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
67Metric
- 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
68Microscopes
- 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?
69Light 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
70Electron 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
71Electron 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
72Cell 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
73Cell 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.