Protists Flashcards
Protists
Unicellular eukaryotes (the majority) but also multicellular eukaryotes.
Have varied sizes and morphologies.
Have great phylogenetic diversity.
Therefore, defined by exclusion: not animal, plant or fungus
Abundant in aquatic ecosystems.
Examples are Amoebas, paramecia, parasites, some unicellular algae, oomycetes.
Classification of protists
Motile – they are free-living and need motility to access food and avoid predation
Nonmotile – Parasites of animals.
Multicellular protists
Brown algae (Phaeophyta) including kelps are multicellular protists (grow up to 60 cm/day)
Kelps contain different photosynthetic pigments than plants such as chlorophyll C and fucoxanthin.
The giant kelp Macrocystis pyrifera can grow up to 60 cm per day.
Red algae (Rhodophyta) are multicellular protists. Red algae:
- have chlorophyll a and reddish pigment phycobilins.
- not all are red
- some algae used for sushi
- coralline algae can be yellow, white or grey-green
Unicellular protists - some photosynthetic
- Coccolithophores
- Diatoms
- Dinoflagellates
Coccolithophores
Use CO2 for photosynthesis and to make chalky (CaCO3) shells (coccoliths). These organisms can sequester atmospheric CO2
As they grow bigger and/or divide they shed the coccoliths which sink in the ocean.
White cliffs of dover = graveyard of coccolithophores
Coccolithophores make massive blooms that can cover vast surfaces of the ocean.
These blooms are highly reflective causing light and heat to be reflected into space. Coccolithophores make the Earth brighter.
CaCO3 shells are highly reflective when large quantities are present, they create colorful patterns on the ocean surface (bright blue-green)
Coccolithophores produce DMSP which contributes cloud formation: site of nucleation of a raindrop
Dimethylsulfoniopropionate (DMSP) converted Dimethylsulfide (DMS) which is converted to Sulphate in the atmosphere
Sulphate acts a nucleating agent for water vapor to become water droplets
Clouds are formed
Diatoms
Photosynthetic
Abundant in marine and freshwater environments.
Are important food source for marine organisms.
Cell wall made of silicon dioxide (SiO2) - glass jars are made of SiO2
Cell wall very tough and resistant to mechanical breakage.
Features on their cell wall (pores and indentations) facilitate exposure of the cell to water and CO2 (photosynthesis).
The shells of certain diatoms are made of two unequal parts that fit into one another.
During replication, each part serves as a template for a new shell.
1. During asexual reproduction, top shell of the cell serves as a template for “the bottom.”
2. New bottom becomes a top and acts as template for another bottom.
3. The ‘new new’ bottom becomes a top, and another bottom is made; with each division the shell becomes smaller and smaller.
4. When the shell is too small, the cell exits the shell undergoes meiosis and forms gametes
5. Gametes can fuse to form a zygote, which can grow a new shell.
Diatom shells are indestructible and have accumulated over geological time forming deposits of fossil diatom shells called diatomite or diatomaceous earth.
Dinoflagellates
Are protists with a shell made of cellulose or other organic polymers.
Some of them are photosynthetic and others are heterotrophs (they prey on other organisms including other dinoflagellates).
Most of them are marine, but some are also found in freshwater.
Some dinoflagellates produce photosynthetic red pigments.
Their blooms make “red tides”
A small proportion of dinoflagellates produce neurotoxins that can contaminate seafood.
Some dinoflagellates are bioluminescent….(e.g., Noctiluca scintillans)
Predatory behaviour of protists
Some protists are predatory and the feed on other microbes (e.g., bacteria and other protists).
Protists preying on bacteria is the major cause of death among prokaryotes (it keeps the number of bacteria in check)
Protists feeding on cyanobacteria prevent cyanobacterial blooms.
Cyanobacterial blooms can release toxins in water and deplete aquatic environments of oxygen.
Protists help purify wastewater
Team up with aerobic bacteria in aeration tanks to degrade the organic matter.
When nutrients are gone, protists eat the bacteria.
Pathogenic behaviour of protists
Includes Oomycetes are fungus-like protists – “water mold”
Parasites/pathogens plants and fish.
As fungal-like heterotrophs they have branching tip-growing mycelia,
Unlike fungi they have cellulose and only a little chitin in their cell wall.
The potato has been introduced to Ireland 100 years before and became a staple food source.
1845–49/52 caused the death of 1 million people.
Unique cell structure of protists
Most protists have eukaryotic cell organization i.e., nuclei, mitochondria, and plastids (photosynthetic mostly; some are not).
Some of these structures can have unusual forms/variations:
Some protists carry more than one nucleus.
Some protists (anaerobes) do not have true mitochondria.
Protists w more than one nucleus
Paramecia have two nuclei both contain a full complement of genes.
macronucleus is ellipsoid in shape and contains multiple copies of a subset of genes required for growth (as well as all copies of genes) (polyploid)
micronucleus is essential for reproduction as the storage site for the germline material
Micronucleus contains 2 copies of all the genes (diploid)
Two nuclei means paramecia divide faster
Multiple copies of the same gene within the macronucleus mean genes transcribed faster and proteins made faster.
Plasmodium can have thousands of nuclei.
Malarial parasite Plasmodium malariaecan reproduce asexually by schizogony.
Schizogony process where cell size increases and the nucleus and other organelles divide repeatedly.
Forming a cell called a schizont
Eventually ruptures releasing tiny cells
Some anaerobic protists don’t have mitochondria
They do have mitochondrion-related organelles. These include:
1. Mitosomes which do not produce ATP
2. Hydrogenosomes produce ATP via reactions that generates hydrogen as a by-product.
Mitosomes or hydrogenosomes membrane-bound organelles do not contain DNA unlike mitochondria.
Lack of DNA in mitosomes and hydrogenosomes suggests that these organelles surrendered all their genes to the nucleus.
Non photosynthetic protists
- Paramecia (Ciliates)
- Plasmodium (Apicomplexa)
- Labyrinthulomycetes
Paramecia
Use short appendages (cilia) to move around.
Inhabit pond water, rivers, lakes, oceans and soils.
Paramecia are predators but also prey.
Paramecia are an excellent food source for larval fish
eat organic particles, bacteria, yeasts and other protists.
move via cilia - aligned in rows, move like little whips to propel the cell
use cillia to drag nutrients towards it, including other microbes.
use cilia sweep the food directly into the gullet (mouth)
food is digested in the food vacuole
nutrients are released into the cytoplasm
undigested food material is excreted through the anal pore.
Paramecia and bacteria symbiosis.
- Paramecia swallow any particles they find in their path, including bacteria.
- Some bacteria produce toxins that kill paramecia.
- Some paramecia have developed resistance to bacterial toxins and ingest and carry the killer bacteria (Caedibacter).
- Bacteria find shelter inside the paramecium and the paramecium becomes toxic to predators.
Paramecia and algae symbiosis.
- Paramecium and algae come together when nutrients are scarce.
- Algae give the paramecia nutrients from photosynthesis
- Paramecia protect the algae and use their cilia to reach the surface where light and CO2 are more abundant (algae often migrate up towards the light and down to get nutrients during the dark period of the day
