lab 2: Protists Flashcards
Explain why protists are considered a “junk drawer” or “catch-all group”.
The first protists probably evolved about two billion years ago from prokaryotic ancestors. All modern eukaryotic organisms subsequently arose from these early protists. The organisms formerly belonging to the kingdom Protista are extremely diverse in form and lifestyle and their taxonomy is in a state of change. Many protists are more closely related to plants, fungi or animals than they are to other protists. The group ‘protists’ is paraphyletic, meaning that these organisms represent some, but not all, of the descendants of a single common ancestor (see Fig 29.1 in your text). Although the kingdom Protista has been abandoned, the term protist is still used informally to refer to eukaryotic organisms that are not plants, animals, or fungi. In this lab you will investigate the stunning diversity of protists.
Describe the general characteristics of Protists
1) Their cells are eukaryotic and thus contain true nuclei as well as other membrane bound organelles such as chloroplasts and mitochondria.
2) Most are unicellular, but some colonial and multicellular forms also exist.
3) The cells are generally larger than those of the prokaryotes (although recently some very small protists have been discovered – see p. 578 in your text), and are the most complex in structure of the eukaryotes.
4) Most protists have a motile stage at some time in their life cycle. They may use flagella or cilia of the eukaryotic type containing microtubules, or other modes e.g. pseudopodia.
5) All protists can reproduce asexually using modified forms of mitosis. Some can also reproduce sexually when environmental conditions become unfavourable.
6) Most are aquatic, living in fresh or salt water or in moist places.
7) Nutrition is diverse in this group as members include photoautotrophs, chemoheterotrophs, and mixotrophs (combine photosynthesis and heterotrophic nutrition). Most protists are aerobic, requiring oxygen for cellular respiration.
8) The protists can be grouped informally into three groups according to their form and mode of nutrition:
Protozoa (animal-like protists) are mainly unicellular, motile, chemoheterotrophic organisms that actively seek and ingest their prey.
Algae (plant-like protists) are mainly photoautotrophs with chloroplasts containing chlorophyll a and a variety of accessory pigments. Many are microscopic unicellular or colonial forms, but there are also some larger multicellular species.
Fungus-like protists are all chemoheterotrophs and obtain their nutrition by absorption. Many are important decomposers, while others are parasites of plants and animals. Included in this group are the plasmodial and cellular slime moulds and the water moulds.
List 2 human diseases caused by protists and name the associated protist and state how it is transmitted to humans.
Malaria • Caused by the protist Plasmodium, a member of the Apicomplexan lineage of protists.
• Four different species of Plasmodium are capable of infecting humans and causing malaria.
• Plasmodium are probably the best studied protists, but yet we still face challenges in controlling malaria.
• Mosquitoes
– evolve resistance to insecticides.
• Plasmodium
– evolve resistance to drugs.
“Red tides”
• When unicellular species experience rapid population growth and reach high densities in aquatic environments, they are said to “bloom”.
• Dinoflagellates contain red pigments(carotenoids); also produce a toxin to protect themselves from predation
• During a bloom, high levels of toxins can build up in the water, which in turn builds up in the tissues of shellfish.
• Humans eat these shellfish —> poisoning.
• Example: Paralytic shellfish poisoning due
to saxitoxins.
• Tingling sensations in mouth, muscle weakness, paralysis.
• No antidote – biologists carefully monitor blooms
Euglena gracilis
Flagella
1/3 of species are photoautotrophic; most
also ingest bacteria or other small food particles
(are mixotrophs).
- Unicellular.
- Red eye spot used to guide the euglenoid towards
light for photosynthesis. - Paramecium and Euglena are often confused by
students because, when stained, they have the same color and shape; however, Euglena is much smaller than Paramecium, with a length that is about 1/10 – 1/6 of the field diameter at 400X
Volvox
Flagella
Photoautotrophic - Large, spherical colonies.
- Each cell in the colony has 2 flagella.
- Colony rotates through water as flagella beat.
- Daughter colonies develop within parent colony
(visible as spheres within the colony); parent colony
eventually splits open to release daughter colonies
and disintegrates.
Amoeba proteus
Cell crawling (pseudopodia)
Phagocytosis - Unicellular.
- Irregularly shaped.
- Pseudopodia.
- Contractile vacuole excretes excess water.
Paramecium caudatum
Cilia Ingestion – sweeps food particles through oral
groove (using cilia) into mouth opening, which
leads to a gullet.
- Unicellular.
- Large macronucleus and smaller micronucleus.
- Contractile vacuole excretes excess water.
- Paramecium and Euglena are often confused by
students because, when stained, they have the same color and shape; however, paramecium is much larger than Euglena, with a length that is about 1/3 – 2/3 of the field diameter at 400X.
Diatoms
- Generally free-floating or cling to surfaces.
- Limited movement in some species via mucilage propulsion or via vibrating fibrils.
Most are photoautotrophic.
- Unicellular or form chains of cells.
- May be round or elongate.
- Unique silica shells (i.e. “glass houses”) have a box-and-lid arrangement. - Plastids are brown or yellow (not green).
Spirogyra
Sessile
Photoautotrophic - Filamentous; form long straight filaments that are unbranched.
- Chloroplasts (green) are spiraled.
Dinoflagellates
Flagella (2); swim in a forward spinning
motion.
Most are photoautotrophic; many also ingest small bacteria or food particles.
- Most are unicellular; some live in colonies.
- Specimen viewed in lab was spined.
- Some photosynthetic species form symbiotic
relationships with coral. - Blooms (population explosion) lead to “red tides”,
which are harmful to other marine organisms (due
to neurotoxin produced by dfs.).
Trypanosoma
Undulating membrane and flagellum
Chemoheterotrophs; absorb nutrients through
their outer membrane from the body fluids of
their host.
- Unicellular, blood parasite.
- Thin, irregularly shaped membrane.
- Elongated shape, tapered at both ends.
Chlamydomonas
Two anterior flagella
Most are photoautotrophs; some mixotrophs
- Unicellular
- Eyespot senses light
- Note that image provided is at a higher magnification than viewed in lab.
Radiolaria
Coast in currents Some use needle-like pseudopodia
Ingestion; use pseudopodia to capture food.
- Unicellular
- Silica skeletons
- Needle-lie pseudopodia extrude from skeleton
