Biology Ch. 28 - Protists

Most are unicellular, although there are some colonial and multicellular species

Single Cell protists are the simplest eukaryotes

Becuase us, multicellular species have different organs with different cells with different roles, the protist has to carry out all the roles in one cell (usually), our organs are like their organelles

Contractile vacuoles - pump out excess water from the cell

Some are photoautotrophs, and hae chloroplasts
Some are heterotrophs and absorb molecules or ingest them
Some are mixotrophs that combine photosynthesis and heterotrophic nutrition

Some are asexual, others can reproduce sexually, or employ meiosis

Scientists say its endosymbiosis - certain unicellular organisms engulf other cells which become endosymbionts and ultimately organelles in the host cell

An aerobic prokaryote; cyanobacteria

When the things that went through endosymbiosis, become eaten again, ingested into the food vacuole of heterorophic or autotrophic eukaryotes
Ex: green algae eatn by heterotropic thing and it becomes a plastid and the whole thing is a euglenid

Most, some exceptions (red/green algae)

Well the plastids genes in red and green algae closely resemble the DNA of cyanobacteria.

So they believe that a heterotrophic eukaryote phagocytized a cyanbacterium and it became phoyosynthetic and evolved into red/green alga

Red algae - Rhodophyta - phycoerythrin (absorbs blue light, reflects red light), can live in great depths, mostly unicellular, no flagellum

Green algae - Chlorophyta - green pigment, plant-like chloroplast, complex life-cycles (sexual/assexual rep stages), aquatic

They belong to a diverse clade that includes predatory heterotrophs, photosynthestic autotrophs, parasites

There are two types:
* Kinetoplastids - single, large mitochondrion that has mass of DNA called kinetoplast, feed on prokaryotes in freshwater, marine, moist ecosystems, some are important parasites
* Euglenid - has one or two flagella, many are mixotrophs, have an eyespot and light detector

Eyespot - pigmented organelle, functions as a light shield, allowing light from only a certain direction to strike the light detector

Light detector - swelling near base of flagellum, detects light that is not blocked by the eyespot, helps euglena moves towards light

Euk - has a ring of microtubules (tubulin), whip-like motion

Prok - propeller, made of flagellin

Antigenic variation is the process by which an infectious organism alters its surface proteins in order to evade a host immune response. Antigenic variation not only enables immune evasion but also allows pathogens to cause reinfection as they are not recognised by the host's immune system. When an organism is exposed to a particular antigen (i.e. a protein on the surface of a bacterium) an immune response is stimulated and antibodies are generated to target that specific antigen. The immune system will then "remember" that particular antigen (immunological memory) and if the host is exposed to that same antigen again, those antibodies will act rapidly to destroy the pathogen. However, if the antigen is changed, the host's immune system will not recognise it and the pathogen can cause infection again whilst the immune system generates new antibodies to target the new antigen. Antigenic variation enables viruses to cross the species barrier (e.g. H5N1 virus "jumping" from birds to then infect humans). Finally, it also allows pathogens to establish persistent infections in their host.