Biology Notes Chapter 20

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Biology Notes Chapter 20

• Multicellular Algae

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Chlamydomonas

• Chlamydomonas is a single celled green algae that
  grows in ponds, ditches, and wet soil.
• It is a small egg shaped cell that has two
  flagella.
• A flagella is a long whip like projection that
  aids in movement.
• Chlamydomonas has a light sensitive area known as
  an eyespot.
• An eyespot can not actually see it can sense
  whether the organism is in bright light or
  darkness.
• The cell wall does not contain cellulose, like
  land plants.

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Chlamydomonas Continued

• Chlamydomonas has a cup-shaped chloroplast that
  has a pyrenoid at one end that makes and stores
  starch.
• This form of algae contains two contractile
  vacuoles.
• Since Chlamydomonas has characteristics of both
  the algae grouped in the Protista kingdom and
  land plants, scientists believe that
  Chlamydomonas is a good example of one step in
  the evolution of multicellular plants from
  unicellular protists

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Colonial Green Algae

• Gonium is a colonial alga composed of between 4
  and 32 cells.
• In a colony many identical cells live together
  but still function independently.
• The cells do not form specialized tissues.
• If the colony is broken apart, each cell can live
  and grow into a new colony.

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Volvox

• Volvox is an alga that forms larger colonies.
• It can form colonies with between 500 cells and
  50,000 cells.
• The cells in a Volvox are connected by strands of
  cytoplasm.
• This allows the colonies cells to communicate
  with one another.
• Communication is necessary for the Volvox colony
  to swim.
• When the flagella on one side of the colony push
  its way through the water the flagella on the
  other side of the colony pull their way through
  the water.
• A few cells of the Volvox colony are specialized
  for reproduction.
• These cells, which produce gametes, are the first
  step in the development of specialized tissues
  that become more common in plants adapted to life
  on land.
• Because it shows some cell specialization, Volvox
  straddles the fence between colonial and
  multicellular life.

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Spirogyra and Oedogonium

• Spirogyra and Oedogonium are two common examples
  of freshwater filamentous green algae.
• Filamentous algae can grow and reproduce
  asexually.
• Oedogonium forms two different specialized
  reproductive cells or gametes.
• Each Oedogonium filament is attached to the
  bottom of a lake or pond by another kind of
  specialized cell called a holdfast cell.

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Ulva

• Ulva A Multicellular Green Alga
• Ulva or sea lettuce is a bright green
  multicellular marine alga that is commonly found
  along rocky seacoasts.
• They have a group of specialized cells at the
  base of the plant form holdfasts that attach it
  to the rocks.

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Phaeophyta The Brown Algae

• Brown algae are found in cool shallow costal
  waters of temperate or artic areas.
• They are not as well developed as land plants
• Most of what are referred to as sea weeds are
  species of brown algae.
• The largest algae in the world is a form of giant
  kelp that can grow m ore than 60 m long.
• Sargassum forms huge floating mats many
  kilometers long in an area of the Atlantic Ocean
  near Bermuda, know as the Sargasso Sea
• A very common brown algae is Fucus or rock weed,
  which lives along the rocky coast of the eastern
  U.S.

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Rhodophyta The Red Algae

• The Rhodophyta are another important group of
  marine algae that can be found in waters from the
  far north to the tropics.
• They can grow on the oceans surface or up to
  depths of 170 meters
• They can survive such extreme depths because of
  their ability to use energy found at other
  wavelengths than other algaes can use.
• Most species of red algae are multicellular.
• All species of red algae have complicated life
  cycles.

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Reproduction in Algae

• The lifecycles of most algae include both a
  diploid and haploid generation.
• Diploid cells have the normal number of
  chromosomes for a particular species.
• Haploid cells have half the normal number of
  chromosomes for a particular species.
• The switching back and fourth between the
  production of diploid and haploid cells is called
  alternation of generations.
• Most species of algae also shift back and forth
  between sexual reproduction that involves the
  production of gametes, and asexual reproduction
  that involves haploid cells called zoospores.

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Reproduction in Chlamydomonas

• Chlamydomonas spends most of its life in the
  haploid stage.
• As long as conditions are suitable this haploid
  cell reproduces asexually by mitosis.
• Each time it reproduces it produces identical
  haploid zoospores.
• If conditions are unfavorable it can switch to a
  stage that reproduces sexually.

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Reproduction in Chlamydomonas

• The haploid cells continue to undergo mitosis,
  but instead of releasing zoospores, the cells
  release gametes.
• These gametes are of 2 different types
• Scientist refer to these different gametes as ()
  and (-)
• These gametes appear to be identical.
• The condition in which gametes appear to be
  identical is called isogamy.
• During sexual reproduction, the gametes gather in
  large groups and the () and (-) gametes form
  pairs that soon move away from the group.
• The paired gametes join flagella and spin around
  in the water as they shed their cell membrane and
  fuse, forming a diploid zygote.
• The fusing of gametes is called syngamy.

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Reproduction in Chlamydomonas

• The zygote sinks to the bottom of the water that
  it is in and grows a thick protective wall.
• This protective wall allows the zygote to survive
  conditions that would kill the algae under normal
  conditions.
• When conditions become favorable again the zygote
  will grow.
• It divides by meiosis, to produce four
  flagellated haploid cells. These haploid cells
  can swim away, mature and reproduce asexually.

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Reproduction in Ulva

• The life cycle of the Ulva involves the
  alternation of generations in which both the
  diploid and the haploid stages are multicellular
  plants.
• The diploid plant is called the sporophyte, or
  spore producer because it produces spores.
• The haploid plant is called the gametophyte,
  because it produces gametes.
• Ulva have two different types of gametophytes.
• Each type produces a different kind of gamete,
  one of which is larger than the other.
• The production of two different kinds of gametes
  is called heterogamy.

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Reproduction in Ulva

• When two gametes fuse, the resulting diploid
  zygote begins to grow into a multicellular
  diploid sporophyte.
• Specialized cells in the sporophyte reproduce
  asexually by undergoing meiosis and releasing
  haploid zoospores.
• These zoospores then divide by mitosis to grow
  into two different types of gametophytes.

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Reproduction in Fucus

• The Fucus demonstrates both alternation of
  generation and heterogamy.
• The gametes are of two types that are very
  different than one another.
• The female gamete is large and cannot swim. (Egg)
• The male gamete is small and is has a flagella,
  and can swim. (Sperm)
• The Fucus resembles land plants in that the
  multicellular haploid gametophyte is missing

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Where Algae Fit into the World

• Algae provide food and shelter for many marine
  organisms.
• Life as we know it would not be possible without
  algae
• Algae produce much of the Earths free oxygen
  through photosynthesis.
• Scientists calculate that between 50 and 75 of
  all the photosynthesis that occurs on Earth is
  performed by algae.
• People use algae and the chemicals produced by
  algae in many different ways.
• Many species of algae are rich in vitamin C and
  iron.
• Chemicals in some algae are used to treat stomach
  ulcers, lung ailments, high blood pressure,
  arthritis, and other health problems.

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Where Algae Fit into the World

• Algae are also used in food products.
• Algae are used to make ice cream smooth and candy
  bars last longer.
• They are used in pickle relishes, salad
  dressings, chip dips, pancake syrup, eggnogs and
  canned chow mein.
• In Japan farmers raise red and brown algae to eat
  as a vegetable or used as flavorings in soups.
• Toothpastes, adhesives, hand lotions, and finger
  paints all contain algae.

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Where Algae Fit into the World

• Modern industry uses algae for many things as
  well.
• Chemicals from algae are used to make plastics,
  waxes, transistors, deodorants, paints,
  lubricants, and even artificial wood.
• Algae products are found in poultry feed, cake
  batters, pie fillers, bakery jellies and doughnut
  glazes.
• Scientists use algae products to grow bacteria in
  laboratories.
• The compound agar-agar, which is made from
  certain seaweeds, thickens the nutrient mixtures
  scientists use to grow bacteria and other
  microorganisms.