Protists

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Protists

• Protists are single celled eukaryotes. A few
  forms are multi-cellular.
• Protists often have a very complicated internal
  structure a single cell must do all the
  functions that we have many different cell types
  to do.
• Protists can be divided into plant-like,
  fungus-like, and animal-like forms. This
  division probably has little to do with their
  evolutionary history.

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Protist Phylogeny

• Protists are very diverse, and probably represent
  several different evolutionary lineages, more
  distinct from each other than plants, animals,
  and fungi are.

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Fungus-like Protists

• Water molds and slime molds
• Like fungi, they are heterotrophs they get food
  and energy from other organisms. Many are
  decomposers of dead organisms.
• Unlike fungi, the fungus-like protists produce
  motile (moving) cells during part of their like
  cycle. Also, these protists surround and engulf
  bacteria as food.
• Slime molds live as separate cells most of their
  lives, feeding on bacteria. When conditions get
  harsh, they aggregate into a multicellular slug,
  which migrates to a new location. The slug then
  forms a fruiting body that generates spores. The
  spores from the fruiting body are very hardy.

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Slime Molds

• Slime molds can be rather large and colorful.

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More Fungus-like Protists

• The water molds include some of the worst plant
  diseases.
• Phytphthora infestans causes rot in plants. In
  the 1840s, Phytophthora caused the potato blight
  in Ireland. The Irish were poor and overcrowded,
  and lived mostly on potatoes. The blight caused
  crop failures in several years, resulting in the
  deaths of of the population. Many Irish came to
  the US at that time.

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Animal-like Protists

• The animal-like protists are classified according
  to how they move amoeba-like, ciliated, or
  flagellated.
• Amoeba-like protists move by extending
  pseudopods, part of their cytoplasm, then pulling
  the rest of the cell along behind. The can
  surround and engulf their food this way.
• Some amoeba-like protists have hard shells. The
  foraminiferans are covered in calcium
  carbonatechalk, which we use on chalk boards.

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Amoebas in Action
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Ciliated Protists

• Cilia are small hairs surrounding the protists
  body. The cilia beat in a synchronized pattern
  to cause movement.
• Paramecium is a typical ciliate. It has a gullet
  to swallow food, and a contractile vacuole to get
  rid of excess water.
• Genetics the DNA used for sexual reproduction is
  stored in the small micronucleus. A copy of this
  information is used to run the cell the copy is
  kept in the much larger macronucleus.

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Flagellates

• Flagellates have a small number of long
  flagella, long whiplike hairs that beats to
  propel the cell.
• Some nasty parasites are flagellates, including
  Giardia lamblia, which causes diarrhea and which
  is found in most of the surface waters of the US.
  Another is Trypanosoma brucei, which causes
  sleeping sickness in Africa. Also Trichmonas
  vaginalis, a sexually transmitted disease.

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Sporozoans

• Sporozoans are animal-like protists that have
  part of their life cycle inside the cells of
  their hosts.
• The most important example is Plasmodium, the
  parasite that causes malaria. Malaria kills 1-2
  million people each year.
• Mosquitoes are part of the life cycle. They suck
  blood from infected humans, ingesting the
  sporozoans. The sporozoans undergo sexual
  reproduction in the mosquitos gut.
• When the mosquito bites another person, the
  sporozoans infect the blood and liver of the
  host. The parasites multiply asexually inside
  the red blood cells, destroying them as they
  leave.

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Algae

• The plant-like protists are called algae. Most
  are single-celled, but a few form large
  multicellular seaweed.
• The plant-like protists have chloroplasts. Some,
  like the Euglena, also have flagella for
  movement.
• Some, such as the diatoms, have calcium carbonate
  (chalk) or silica shells.

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Algae Blooms

• Algae blooms are the sudden growth of a large
  population of single celled algae. They occur
  near the coastlines, with the algae feed on
  fertilizer runoff and sewage. Algae blooms
  deplete the oxygen in the water, killing fish and
  other organisms. Some of the algae also secrete
  toxins. Red tide and Pfiesteria are examples of
  this.

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Multicellular Algae

• The multicellular algae are commonly called
  seaweed. They can be classified into red, brown,
  and green algae. All have chloroplasts, but the
  pigments in the chloroplasts vary, giving the
  different colors.
• Some, like kelp, are very large and contain
  several different types of cells and tissues to
  do specialized work. These include leaves for
  photosynthesis, gas-filled bladders for buoyancy,
  the root-like holdfast, and tubes to transport
  nutrients throughout the body.
• Algae contain the polysaccharide agar, which is
  tasteless and is used to thicken foods such as
  soft ice cream.

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Green Algae

• The green algae are the ancestors of plants. The
  term plant implies living on the land or
  derived from plants living on the land. Green
  algae and plants have very similar chloroplasts.
• Green algae have some unicellular species (such
  as Chlamydomonas), some simple colonies (such as
  Volvox), and some relatively complex
  multicellular organisms (such as Acetabularia).
• Green algae are haploid most of their live cycle,
  with only a very short diploid phase.