Download Chapter 1: Single-celled Organisms and Viruses

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Characteristics of Living Things
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Most living things are too small to be seen.
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Even the tiniest organisms are made of cells.
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Very small organisms are called microorganisms. These are
mostly unicellular (made of one cell).
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Remember that all living organisms are divided into
kingdoms.
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Most microscopic kingdoms: archaea, bacteria, and
protists.
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Review: all living organisms have four characteristics in
common.
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Organization  all single celled organisms contain
everything they need to function in their one cell
Growth  unicellular organisms do not grow as large as
multicellular organisms.
Reproduction  binary fission.
Response to Stimuli (Environment)  light, temperature,
and touch.
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Review: all living organisms need three things.
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Energy  some transform sunlight, others depend on other
organisms for energy.
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Materials  water, carbon dioxide, oxygen.
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Living space
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A virus has genetic material in a protein shell.
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They share many of their characteristics with living
organisms, but they are not living.
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They are not as complex as cells.
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Once viruses form they do not grow, and they only
“reproduce” by taking over a cell.
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Bacteria and Archaea
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Bacteria are the simplest kind of life known on Earth.
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they are composes of just one cell without a nucleus (what
do we call cells without a nucleus?)
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Genetic material is contained in loops within the cell.
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Reproduce by binary fission.
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Bacterial cells are about 1/10 to 1/20 the size of a normal
cell.
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Most have a covering called a cell wall – surrounds and
protects the cell membrane.
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Contain many large molecules and structures not found in
viruses.
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Classified by their external shapes.
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Spiral bacteria: occurs in single strands.
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Rod bacteria: occurs singly or in chains.
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Round bacteria: occurs singly, in pairs, in chains, or in
clusters.
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Similar to bacteria but share more in common with more
complex organisms.
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Archaea: single-celled organisms that can survive in a range
of environments.
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They are grouped based upon where they live.
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Named for methane, the gas they produce.
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die if exposed to oxygen.
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Live in dense mud, swamps, marshes.
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Guts of animals (cows and termites).
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Live in very salty lakes and ponds.
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Some die if water is not salty enough.
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They can survive drying, and will begin dividing if water
returns to the pond.
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Halophiles – halite (salt)
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Thrive in extreme heat or cold.
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Hot springs, hot vents in the sea, or meters deep in ice.
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Bacteria and Archaea
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Some contain chlorophyll – what does this allow them to
do?
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They produce their own food, so they are an important food
source for ocean animals and release oxygen gas.
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They are called producers.
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Example: Cyanobacteria
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Other bacteria break down dead plants and animals to help
recycle matter.
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They are called decomposers.
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Some bacteria live either inside or on the surface of other
organisms.
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Sometimes, this relationship causes no effect. Other times,
there is a benefit to both organisms.
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When there is a negative relationship between the two, the
bacteria is called a parasite to the host.
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Example: Staphylococcus infects humans.
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Bacteria that breaks down organic matter are helpful.
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Cities use these bacteria in sewage treatment plants. They
help purify the water before it is released to bodies of water.
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Some bacteria changes nitrogen gas to nitrogen
compounds (fixation), which allows plants to use nitrogen to
make proteins.
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Animals that eat plants depend on archaea.
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Methanogens help break down cellulose in cell walls which
makes it easier for animals to digest.
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Many types of bacteria can harm humans: tuberculosis,
cholera, and infant diarrhea.
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They can invade parts of the body and multiply in
cells/tissues.
They can poison the body with chemicals they release.
They can poison the body with chemicals that are in the
bacteria itself.
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We try to prevent these infections by getting vaccinations.
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Viruses
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When scientists first discovered bacteria, they were able to
filter it out of liquids by using a sieve.
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When this process did not always work, they came to the
conclusion that there was something smaller than bacteria.
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These are now called viruses.
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Contain genetic material contained inside a protein coat
called a capsid.
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The capsid can be a simple tube or have several layers.
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They use living cells to get their DNA copied, so they are
able to reproduce.
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They do not grow or respond to their environment.
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A virus uses a cell’s material, energy, and processes to
thrive.
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Can cause serious diseases such as polio, smallpox,
diphtheria, or AIDS.
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Influenza (the flu) is a more common virus.
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Viruses can also affect plants.
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They can have stunted growth or die because of viruses.
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If they infect crops, it can destroy farmland, which impacts
the farmers, community, and economy.
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Reproduction of Viruses
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Viruses must use materials from living cells to make copies
of their DNA.
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The cells that become infected by viruses are called host
cells.
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One every common virus is called a bacteriophage because
it infects bacteria.
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Step 1: attachment.
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The virus attaches to the surface of the host cell.
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Step 2: Injection.
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The virus injects its DNA into the host cell.
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Step 3: Production.
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The host cell goes through its normal functions to produce
copies of the viral DNA.
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Step 4: Assembly.
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New viruses assemble from the copied DNA.
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Step 5: Release.
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The host cell bursts, and hundreds of new viruses can be
released.
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Protists