Chapter 2: Biology as a Science
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Characteristics of Living
Things
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Characteristics of Living
Things
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We can state that all living things
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Are made up of one or more units
called cells
Reproduce
Grow and develop
Obtain and use energy
Respond to their environment
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Living Things Are Made Up of
Cells
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Each cell is a collection of living matter enclosed by a
barrier that separates the cell from its surroundings
Most cells can perform all the functions we associate
with life
Organisms consisting of only a single cell are called
unicellular
Most of the organisms you are familiar with are
multicellular
 Contain hundreds, thousands, even trillions of cells
or more
Cells are not found in nonliving matter unless that
matter was once alive
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 Wood
Living Things Reproduce
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Living things can produce new organisms of the
same type
Because all individual organisms eventually die,
reproduction is necessary if a group of similar
organisms is to survive
Two basic kinds of reproduction
 Sexual reproduction requires that two cells
from different individuals unite to produce the
first cell of a new organism
 Asexual reproduction occurs when a single
organism reproduces without the aid of
another
 Some single-celled organisms divide in two
to form two organisms
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Living Things Grow and Develop
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All living things are capable of growth
During growth, most living things go through a cycle of
change called development
The single cell that starts an organism’s life divides
and changes again and again to form the many varied
cells of an adult organism
As development continues, organisms experience a
process called aging
During aging, an organism becomes less efficient at
the process of life
 The ability to reproduce comes to an end
 For virtually all organisms, death is the inevitable
end of the life span of every individual
 Death is a process of change that separates living 5
and nonliving things
Living Things Obtain and Use
Energy
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Living things obtain energy from their environment and
use it to grow, develop, and reproduce
All organisms require energy to build substances that
make up their cells
Any process in a living thing that involves putting
together complex substances from simpler
substances is called anabolism
The final breakdown of complex substances into
simpler ones, usually resulting in the release of
energy, is called catabolism
Living things must practice both of these at the same
time
The total sum of all chemical reactions in the body –
the balance of anabolism and catabolism – is called
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metabolism
Living Things Respond to Their
Environment
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Anything in the environment that causes an
organism to react is called a stimulus
 Light, temperature, odor, sound, gravity, heat,
water, and pressure
The ability of living things to react to stimuli is
known as irritability
In general, living things respond to stimuli in ways
that improve their chances for survival
The process by which organisms respond to
stimuli in ways that keep conditions in their
body suitable for life is called homeostasis
Homeostasis refers to an organism’s ability to
maintain constant or stable conditions that are
necessary for life
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Chapter 2: Biology as a Science
2-2
Biology: The Study of Life
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Biology: The Study of Life
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Biology is the science that seeks to
understand, explain, and even control the
living world
Biology advances by observing the world,
asking questions, and forming
hypotheses that can be tested by
experiment
A biologist is anyone who uses the
scientific method to study living
things
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Branches of Biology
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Contains many branches, or divisions
 Examples:
 Zoology
 Microbiology
 Botany
 Paleontology
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Questions at the Molecular Level
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Molecular biologists may study the basic
chemical units of life
Molecular geneticists investigate the
workings of DNA, the molecule that
controls heredity and directs all the
activities of the cell
Other researchers might study the effects
of drugs on molecules in cells in order to
understand why entire organisms react to
those drugs as they do
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Questions at the Cellular Level
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Cell biologists might study the way
normal cells become cancer cells
when exposed to radiation or to the
chemicals found in cigarette smoke
Might try to explain how a single cell
divides and changes to form all the
cell types in an adult organism
Other cell biologists might study how
cells communicate with nearby cells
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Questions at the Multicellular
Level
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Goes beyond individual cells
Study changes in animals,
evolution, etc.
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Questions at the Population Level
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Interested in groups of organisms
that make up populations and how
these populations interact with
their environment
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Questions at the Global Level
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Takes a more worldwide view of
biology and are concerned with
organisms and their environment on a
global scale
Biologists are both studying and trying
to preserve the wonderful things that
are alive on planet Earth – not just for
their own use, but for the use of those
who will live on this planet after us
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Tools of a Biologist
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Use a wide variety of tools
 Graduated cylinders
 Balances
 Computers
To study small organisms, researchers
have developed several kinds of
microscopes
Microscopes are instruments that
produce larger-than-life images, pictures,
or even videotapes
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The Compound Light Microscope
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Most commonly used microscope
Make it possible to observe many kinds of cells and
small organisms while they are still alive
To view –
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Object is placed on a microscope slide and covered
with a cover slip
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It is then placed on the stage of the microscope so
that light passes through it into the lenses of the
microscope
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Lens at the bottom = objective lens
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Lens at the top = ocular lens
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Because both lenses are used to form an image, it is
properly known as a compound light microscope 17
Limits of Resolution
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There are limits to what can be seen with
the compound light microscope
As the magnification is increased, more
and more detail can be seen – up to a
certain point
Beyond this point, called the limit of
resolution, objects get blurry and detail
is lost
For standard light microscopes, the limit
of resolution is about 0.2 micrometers
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Using a Compound Light
Microscope
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Many specimens are stained before they are
observed under a microscope
Stains are used to color cells or parts of cells
to make them clearly visible
Because many stains kill living cells, special
types of light microscopes that do not require
staining are used to observe living specimens
Each uses a different property of light rays to
improve the clarity of the image
 Phase contrast microscope
 Dark field microscope
 Nomarski microscope
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Electron Microscopes
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In the 1920s physicists in Germany realized that
electromagnets could bend streams of electrons
They used these electromagnets to build electron
microscopes
The limit of resolution of electron microscopes is
about 1000 times finer than the light microscope
Transmission electron microscopes (TEMs) –
shine a beam of electrons at a sample and then
magnify the image onto a fluorescent screen and the
bottom of the microscope
Scanning electron microscopes (SEMs) – beam of
electrons scans back and forth across the surface of a
specimen; electrons that bounce off the specimen are
picked up by detectors that provide the information to
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form an image on a television screen
Limitations of Electron
Microscopes
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Extremely useful but do have serious
drawbacks
Specimens must be placed inside a
vacuum and cut into very thin slices
Specimens must be completely dried
out before they are placed in the
vacuum
Living cells cannot be observed in the
electron microscope – they are killed
by the sample-preparation processes
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Probe Microscopes
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Developed in the 1980s
Do not use lenses to produce images
Trace the surfaces of a sample with a
fine tip known as a probe
Have revolutionized the study of
surfaces and have even made it
possible to observe single atoms
Specimens do NOT need to be
placed in a vacuum
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Laboratory Techniques of a
Biologist
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In addition to staining, the following
techniques are also used in the
laboratory
 Centrifugation
 Micromanipulation
 Cell cultures
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Centrifugation
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Involves placing cells in a blender to break them
apart
 Cell fractionation
The broken bits of cells are then placed in a liquid
in a tube
The tube is inserted into a centrifuge, which is a
device that can spin the tube up to 20,000 times per
minute
While spinning, the cell parts begin to separate –
with the heaviest parts setting near the bottom of
the tube
A scientist can then remove the specific part of the
cell to be studied by selecting the appropriate layer
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Micromanipulation
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Another technique to remove parts
of a cell is called micro-dissection,
which is a form of micromanipulation
 Special tools that are so small
they can be used only by looking
through a microscope are used to
dissect, remove, insert, or
otherwise manipulate specific
parts of a cell
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Cell Cultures
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Sometimes scientists want to study
a particular kind of cell but to do so
they need large numbers of that
exact cell
To obtain a cell culture, a single cell
is placed in a dish that contains the
nutrients the cell needs
The cell is allowed to reproduce so
that in time an entire population is
grown from that single original cell
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