What is Life?

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What is Life?

• Because there is no one universal definition for
  all life, it is therefore defined by the common
  characteristics that it shares.

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1. Organization Cells DNA

• Living things are made up of one or more units
  called cells, the smallest units considered fully
  alive.
• Organisms consisting of only a single cell are
  called unicellular.
• Larger organisms, which contain many cells, are
  called multicellular
• Cells contain a universal genetic code called
  DNA.

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2. Reproduction

• Because all individual organisms eventually
  die, reproduction is necessary for a species (a
  group of similar organisms) to survive.
• There are two basic kinds of reproduction
• (A) sexual reproduction -- two cells from
  different individuals unite to produce the
  first cell of a new organism.
• (B) asexual reproduction -- a single
• organism produces offspring identical to itself.

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3. Growth and Development

• During growth an organism goes through a cycle of
  change called development. As development
  continues organisms experience a process called
  aging.
• Aging causes organisms to become less efficient
  at the process of life.
• Eventually, the ability to reproduce ends and is
  followed by the end of the life span called death.

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4. Obtaining and Using Material and Energy

• Living things obtain energy and materials from
  their environment to build the substances that
  make up their cells.
• They practice both anabolism (the process of
  synthesizing complex substances from simpler
  ones) and catabolism (the break down of complex
  substances into simpler ones) 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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5. Responding to the Environment

• These responses can be rapid (e.g., a behavioral
  change) or slow (e.g., growth).
• Anything in the environment that causes an
  organism to react is called a stimulus. Examples
  of stimuli include light, temperature, odor,
  sound, gravity, heat, etc.
• The ability of organisms to react to stimuli is
  called irritability.

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6. Homeostasis

• The process by which organisms respond to stimuli
  in ways that keep conditions in their body
  suitable for life is called homeostasis.
• In other words, homeostasis is the process by
  which organisms keep internal conditions constant
  despite changes in their external environments.

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7. Taken as a group, living things evolve.

• Over generations, groups of organisms evolve, or
  change over time.
• Evolutionary change links all forms of life to a
  common origin more than 3.5 billion years ago.

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Branches of Biology

• Biology is the study of life. A biologist is
• anyone who uses science to study life.
• Biology includes many different branches.
• The following is a small sample
• Anatomy - The study of an animals structure
  (morphology).
• Botany - The study of plants.
• Cytology - The study of cells.

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Branches of Biology

• Ecology - The study of the interactions of
  organisms with one another and their
  surroundings.Entomology - The study of insects.
  Ethology The study of animal behavior.
• Herpetology - The study of reptiles and
  amphibians. Mycology - The study of
  fungi.

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Branches of Biology

• Paleontology - The study of extinct organisms.
• Pathology - The study of diseases and
  disorders.
• Physiology - The study of the functions of
  living things.
• Virology - The study of viruses.
• Zoology - The study of animals.

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Different types of biologists ask different types
of questions.

• QUESTIONS AT THE MOLECULAR LEVEL
• A molecular biologist, for example, may study
  the basic chemical units of life.
• Or, they might study the effects of drugs on
  molecules in cells in order to understand why
  organisms react to those drugs as they do.

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Different types of biologists ask different types
of questions.

• QUESTIONS AT THE CELLULAR LEVEL
• A Cell biologist, for example, might study
• The way normal cells become cancer cells.
• How a single cell divides and changes to
  form the different cell types in an adult.

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Different types of biologists ask different types
of questions.

• QUESTIONS AT THE MULTICELLULAR LEVEL
• For example
• A Zoologist might study the changes within
  animals that tell them when to sleep,
  eat, or mate.
• A Paleontologist might try to explain how
  certain animals changed, or evolved, over time.

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Different types of biologists ask different types
of questions.

• QUESTIONS AT THE POPULATION LEVEL
• An ecologist might want to know how the following
  will affect nearby plant and animal life.
• The construction of a new road.
• The cutting down of forests.
• The use of pesticides.

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Different types of biologists ask different types
of questions.

• QUESTIONS AT THE GLOBAL LEVEL
• Some biologists take a worldwide view of biology
  and are concerned with organisms and their
  environment on a global scale.
• For example, Global ecologists, might try to
  estimate the effects on the Earth's climate
  of burning coal and oil.

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Tools of a Biologist

• MICROSCOPY
• Two factors play an important role in microscopy
  
• 1. Magnification is the comparison of the
  real size of a specimen with that of the
  one viewed under the microscope.
• 2. Resolution (resolving power) refers to the
  clarity of the specimen viewed under the
  microscope.

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Tools of a Biologist

• COMPOUND LIGHT MICROSCOPE
• The most commonly used microscope.
• Cells and small organisms can be observed
  while they are still alive.
• Light microscopes are limited to about 1000
  times magnification due to the limit of
  resolution.

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Tools of a Biologist

• COMPOUND LIGHT MICROSCOPE
• Limit of resolution is the point of
  magnification beyond which images
  become blurry and lose detail.
• This occurs because light passing through a lens
  is scattered, making it hard to form a clear
  image.

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Tools of a Biologist

• COMPOUND LIGHT MICROSCOPE
• For standard light microscopes, the limit of
  resolution is about 0.2 micrometers.
• A typical cell is about 10 micrometers
  across.

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Tools of a Biologist

• ELECTRON MICROSCOPES
• These microscopes use a beam of electrons and
  magnets instead of light and lenses.
• They have a shorter wave length
• (0.2 nanometers) than a light microscope.
• Because of the high-energy particles
  involved, these microscopes cannot
  view living specimens.

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Tools of a Biologist

• Transmission Electron Microscope (TEM)
• TEM transmits a beam of electrons through a
  very thinly sliced specimen.
• TEM can magnify objects up to 1,000,000
  times.
• The electron beam can also be used to
  expose photographic film to produce a
  permanent image of the specimen.

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Tools of a Biologist

• Scanning Electron Microscope (SEM)
• SEM get their name from a pencil like beam of
  electrons that scans back and forth
  across the surface of a specimen.
• Electrons that bounce off the specimen are
  picked up by detectors that provide
  information to form a
  three-dimensional picture.
• SEM can magnify objects up to 300,000
  times.

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Tools of a Biologist

• PROBE MICROSCOPES
• A new class of microscopes developed in the
  1980s.
• They do not use lenses to produce images.
• These instruments trace the surfaces of a
  sample with a fine tip known as a probe.
• They are called scanning probe microscopes.

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Tools of a Biologist

• PROBE MICROSCOPES
• Scanning probe microscopes have
  revolutionized the study of
  surfaces and
• have even made it possible to observe
• single atoms.
• Unlike electron microscopes, scanning
  probe microscopes do not require that
  specimens be placed in a vacuum.

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Laboratory Techniques

• CENTRIFUGATION
• Used to study specific parts of a cell.
• 1st, cells are broken apart in a blender.
• 2nd, they are placed in a liquid in a tube.
• 3rd, the tube is inserted into a centrifuge.

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Laboratory Techniques

• CENTRIFUGATION
• The centrifuge spins the tube up to 20,000
  times per minute.
• This causes the cell parts to separate with the
  heaviest parts settling near the bottom and
  the lightest parts rising toward the top.
• A scientist can then remove the specific part of
  the cell to be studied by selecting the
  appropriate layer.

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Laboratory Techniques

• MICROMANIPULATION
• With these techniques, special tools, that are
  so small they can be used only by looking
  through a microscope, are used to dissect,
  remove, insert, or manipulate specific
  parts of a cell.
• When parts are removed from the cell, it is
  also referred to as microdissection.

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Laboratory Techniques

• CELL CULTURES
• They are used to obtain many identical
  copies of a particular type of cell.
• In this technique, 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.