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Chapter 2: Biology as a Science

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Characteristics of Living Things

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Characteristics of Living Things

We can state that all living things 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

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 Wood

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Living Things Reproduce

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

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 and

nonliving things

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Living Things Obtain and Use Energy

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 metabolism

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Living Things Respond to Their Environment

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

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Biology: The Study of Life

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Biology: The Study of Life

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

Contains many branches, or divisions Examples:

Zoology Microbiology Botany Paleontology

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Questions at the Molecular Level

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

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

Goes beyond individual cells Study changes in animals,

evolution, etc.

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Questions at the Population Level

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

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

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

Most commonly used microscope Make it possible to observe many kinds of cells and small

organisms while they are still alive To view –

Object is placed on a microscope slide and covered with a cover slip

It is then placed on the stage of the microscope so that light passes through it into the lenses of the microscope

Lens at the bottom = objective lens Lens at the top = ocular lens Because both lenses are used to form an image, it is

properly known as a compound light microscope

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Limits of Resolution

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

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

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 form an image on a television screen

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Limitations of Electron Microscopes

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

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

In addition to staining, the following techniques are also used in the laboratory Centrifugation Micromanipulation Cell cultures

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Centrifugation 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

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

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