Protists Flashcards
What are protists?
- A very diverse group
- Basically everything that is a eukaryote but not a land plant, fungi or animal
- Most are very small
Who discovered protists?
Leeuwenhoek looking down early microscope:
» “No more pleasant sight has met my eye than this, of so many thousands of living creatures in one small drop of water”
Are protists uni or multicellular?
Most unicellular, some form colonies, and simple multicellular forms
How do Protists get their nutrition and reproduce?
- Most nutritionally diverse of all eukaryotes, include:
1. Photoautotrophs, which contain chloroplasts
2. Heterotrophs, which absorb organic molecules or ingest larger food particles
3. Mixotrophs, which combine photosynthesis and heterotrophic nutrition - Can reproduce asexually or sexually
What are the four super groups of protist phylogeny?
» Excavata
» SAR
» Archaeplastida
» Unikonta
What is clade excavata?
- Monophyletic group
- Some have an “excavated” feeding groove
- Can be predatory heterotrophs, photosynthetic autotrophs, mixotrophs, and parasites
- Example: Giardia intestinalis
» Flagellated unicellular eukaryote
» Parasitic in human intestine
What is Giardia?
- A parasitic protist from the excavata clade:
- shed in faeces
- Commonly transmitted in contaminated water
- Giardia has protective outer shell → can survive outside the body for long periods + is resistant to chlorine disinfection
» ≈2% adults, 6-8% children in developed countries
» Nearly 33% people in developing countries have had giardiasis
What are the symptoms of Giardia?
- Symptoms appear around 1-3 weeks after infection, last 1-2 weeks or longer
- Acute symptoms include
» Diarrhea
» Gas
» Greasy stools that tend to float
» Stomach or abdominal cramps
» Upset stomach or nausea/vomiting
» Dehydration (loss of fluids)
What is the SAR Clade?
- Diverse monophyletic group of protists defined by DNA similarities
- divided into three main groups:
1) Stramenopiles
2) Alveolates
3) Rhizarians
What are Stramenophiles?
- A main group of the SAR Clade
- Key organism in many environments
» Diatoms, brown algae and several pathogens - Diatoms are a key group of unicellular photosynthetic algae
» Highly diverse (≈100,000 species)
» Glass-like wall made of silicon dioxide (protection from predation)
» Yellow/brown due to brown plastids
» Usually reproduce asexually
» Store food in a form of oil, which make cells buoyant
What are Diatoms?
- A branch of the Stramenophiles group in the SAR Clade
- Important component of plankton (free floating microorganism in marine and freshwater)
- Important source of fixed carbon
(20% of global carbon fixation) and 40% of marine primary productivity - Boom and bust population cycles
» Boom when conditions favourable (lots of nutrients, low predation)
» Then fall to the ocean floor, then when new nutrient upwelling, boom again
What is brown algae
- A branch of the Stramenophiles group in the SAR Clade
- » All multicellular and mostly in marine
» Largest and most complex algae
» Have chlorophyll-a, chlorophyll-c & carotenoid pigments
» Store carbohydrate food reserves in the form of laminarin
» Cell walls consist of cellulose and lignin
What are Alveolates?
- A main group of the SAR Clade
- Membrane-enclosed sac (“alveoli”) under the plasma membrane
What are dinoflagellates?
- A branch of the Alveolates group in the SAR Clade
- Have flagella, and often encased in “armour plates”
- Important in phytoplankton (small marine photosynthetic organisms)
- Can have carotenoids as pigments giving rise to “red tides” when population blooms
» Some produce toxins, and can contaminate (and kill) invertebrates and fish (and humans who consume them)
What are Apicomplexans?
- A branch of the Alveolates group in the SAR Clade
- Nearly all are parasites of animals
- Non-photosynthetic
» Although they have retained plastid - Example:
» Plasmodium and malaria
What are the symptoms of plasmodium and malaria
- Symptoms appear 1-2 weeks after being bitten by mosquito carrying Plasmodium
- Symptoms include fever, headache, chills, muscle and joint pain, diarrhea, vomiting, confusion … if not treated can progress to severe illness, often leading to death
What can be done to control malaria
Controlling malaria incl. vector control: insecticide-treated mosquito nets, indoor residual spraying and outdoor spraying
What is Archaeplastida?
- Third protist subgroup: Archaeplastida
- Red and green algae (protists), but also include land plants
What is Rhodophyta (red algae)
- A branch of Archaeplastida
- Multicellular organisms with moderately large body and distinctive structure
- Nearly all marine
- Possess chlorophyll-a and red accessory pigment (phycoerythrin)
» Shallow = greenish; intermediate = red; deepest = black - Occurs deeper than any other photosynthetic organisms (>250m)
What is Chlorophyta (green algae)
- A branch of Archaeplastida
- Most plant-like of all algae
- Chlorophyll-a and chlorophyll-b (no others)
- Most live in freshwater
- Various shapes:
» Some unicellular and form green scum in water
» Others filamentous
» Many others form two dimensional sheet (thallus) such as sea lettuce (Ulva)
» Others have complex three-dimensional structures like “true” plants - Some eaten for food (eg Ulva in Japan)
- Studied intensively for bio-technology
What is Unikonta?
Includes protists that are closely related to fungi and animals, as well as fungi and animals
What are Amoebozoans
- A branch of the Unikonta Clade
- Slime moulds (once thoughts to be fungi)
» 2 main branches: plasmodial slime moulds and cellular slime moulds
What are Plasmodial Slime moulds?
» All heterotrophs and many brightly pigmented
» Feeding stage of lifecycle consisting of amoeboid mass engulfs food by phagocytosis
» Live in moist soils, leaf mulch, rotting logs
» When stressed (lack of food, drying) ceases growth, forms sexually reproductive structures called fruiting bodies or sporangia
What are symbiotic protists?
Protists play key roles in ecological communities
- Some form symbiotic relationships (one or both species benefit from interaction)
- Can be mutualism where both benefit
» Eg, coral rely on photosynthetic protists called zooxanthellae, a type of dinoflagellate; protist benefit from protected living space
