Protists

The Origin of Eukaryotes

  • Protists were the first eukaryotes

  • It is believed that the nucleus was formed because the ancestral prokaryotic developed folds in its cell membrane, increasing surface area. Eventually it folded so much that it formed a membrane around the genetic material

Endosymbiosis - Origins of Mitochondria and Chloroplast

  • Endosymbiosis is the theory that a single celled organism lives within the cell of another organism

  • This theory is used to explain how chloroplast and mitochondria are found in cells (remember they each contain their own DNA)

  • It is believed they both were prokaryotic cells that were engulfed by eukaryotic cells and incorporated into them


Protists:Classification

• Is the most diverse kingdom

• More than 200,000 known species

• Difficult to classify

• No "typical" protist

• Species that do not fit into the other kingdoms are usually placed here

• Once other kingdoms are ruled out, they are usually classified based on how they obtain nutrition and how they move

Some Characteristics of Single-Celled Protist

  • 1) eukaryotes - membranes around their organelles (nucleus), > 2mm

  • 2) unicellular - one celled

  • 3) reproduce asexually by binary fission

  • 4) must live in moist surrounding


Plant-like Protists

  • Mainly autotrophs

  • Contain chloroplasts which contain a green pigment (chlorophyll) to absorb sunlight for photosynthesis

  • Most are single celled, but some live-in colonies or are multicellular, making up red, brown and green algae

  • They are responsible for producing most of the Earth's oxygen

  • Can reproduce asexually and sexually (when conditions become less favourable)


Animal-like Protists

• Called protozoans (means "first animal")

  • Most are unicellular, no cell wall and are motile (are able to move)

  • They are heterotrophic and consume prokaryotes, other protists, or organic wastes

  • Some are parasitic and consume nutrients from the organism they live in

Fungus-like Protists

  • Decomposers, they absorb nutrients from living organisms, dead organisms, and wastes and are thus considered heterotrophic

  • They are similar to fungi in that they produce spores, but the structure of their cell wall is different from those of fungi

  • Prefer cool, damp habitats

  • Start as unicellular, but eventually combine with others to become multicellular

  • They are classified generally into two categories: slime moulds and water moulds.

Plant-like Protist: Multicellular algae

  • They all contain chlorophyll

  • Supplies 80% of the world's oxygen

  • Red and brown algae are called seaweed

  • Brown algae do not have true roots or leaves, they do have specialized tissues

  • Red algae contains extra pigments than green algae, to be able to absorb more of the suns light

  • Green algae resembles land plants the most, has a cell wall made of cellulose