Protists

Question 1

What are protists?

Answer 1

• A very diverse group
• Basically everything that is a eukaryote but not a land plant, fungi or animal
• Most are very small

Question 2

Who discovered protists?

Answer 2

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”

Question 3

Are protists uni or multicellular?

Answer 3

Most unicellular, some form colonies, and simple multicellular forms

Question 4

How do Protists get their nutrition and reproduce?

Answer 4

• 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

Question 5

What are the four super groups of protist phylogeny?

Answer 5

» Excavata
» SAR
» Archaeplastida
» Unikonta

Question 6

What is clade excavata?

Answer 6

• 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

Question 7

What is Giardia?

Answer 7

• 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

Question 8

What are the symptoms of Giardia?

Answer 8

• 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)

Question 9

What is the SAR Clade?

Answer 9

• Diverse monophyletic group of protists defined by DNA similarities
• divided into three main groups:
  1) Stramenopiles
  2) Alveolates
  3) Rhizarians

Question 10

What are Stramenophiles?

Answer 10

• 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

Question 11

What are Diatoms?

Answer 11

• 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

Question 12

What is brown algae

Answer 12

• 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

Question 13

What are Alveolates?

Answer 13

• A main group of the SAR Clade

- Membrane-enclosed sac (“alveoli”) under the plasma membrane

Question 14

What are dinoflagellates?

Answer 14

• 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)

Question 15

What are Apicomplexans?

Answer 15

• 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

Question 16

What are the symptoms of plasmodium and malaria

Answer 16

• 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

Question 17

What can be done to control malaria

Answer 17

Controlling malaria incl. vector control: insecticide-treated mosquito nets, indoor residual spraying and outdoor spraying

Question 18

What is Archaeplastida?

Answer 18

• Third protist subgroup: Archaeplastida

- Red and green algae (protists), but also include land plants

Question 19

What is Rhodophyta (red algae)

Answer 19

• 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)

Question 20

What is Chlorophyta (green algae)

Answer 20

• 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

Question 21

What is Unikonta?

Answer 21

Includes protists that are closely related to fungi and animals, as well as fungi and animals

Question 22

What are Amoebozoans

Answer 22

• A branch of the Unikonta Clade
• Slime moulds (once thoughts to be fungi)
  » 2 main branches: plasmodial slime moulds and cellular slime moulds

Question 23

What are Plasmodial Slime moulds?

Answer 23

» 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

Question 24

What are symbiotic protists?

Answer 24

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

Question 25

What is an example of a photosynthetic protist

Answer 25

Phytoplankton ≈30% all photosynthesis – includes diatoms, dinoflagellates, multicellular algae and other aquatic protists

Question 26

What are some examples of parasitic Protists?

Answer 26

- Malaria-causing Plasmodium - Dinoflagellate parasites (Pfiesteria sp.) can cause massive fish kills - Stramenophile Phytophthora cinnamoni is a major threat to forest of Western and South Australia - Phytophtora infestans caused potato late blight (→ Irish famine of the 19th century – 1 million dead and many forced to leave)