Bellwork: What is a protist Bellwork: What is a protist? What problems have they caused with classification?

Protist classification: The saga continues Section 21.1

When did the first Eukaryotes appear on Earth? What were they like? More than a billion years ago Still exist today Group together by name protists – meaning first Classified as members of the kingdom protista Protists are Eukaryotes that are not part of the plant, animal or fungi kingdoms There are a wide variety of characteristics Most are unicellular, but some aren’t Kelp for example (Brown algae) is considered a protist as it resembles more unicellular organisms than it does any of the other kingdoms

The dilemma Protists are more diverse than any other Eukaryotic kingdom Many ‘protists’ are also more closely related to other Eurkaryotic kingdoms than they are to other protists So Protists should not form their own kingdom…… BUT, no one can agree on a solution Attempts to classify on the basis of plant like, animal like and fungus like failed…

So, what to do….. Protists can be divided into six major clades You can actually fit plant, animal and fungi kingdoms into these clades Animals and fungi kingdoms appear to actually have a shared common protist ancestor Is this surprising?

So, how should you use the term protist? Although biologists generally prefer the classification cladogram with six major groups of protists, the term protists is still widely used Just remember – technically it’s not a kingdom!

How are protists related to other Eukaryotes? Modern day protists will have evolved greatly since the evolution of the first protists To understand the connection between protists and other Eukaryotes you must look at the fossil record Microscopic eukaryotic cells have been found in rocks up to 1.5 billion years old! Evidence that Eukaryotes evolved from prokaryotes, and are more closely related to Archaea than Bacteria Actual split between Archaea and Eukarya may be 2.5 billion years ago Protists have diversified, most have remained unicellular, but two groups produced plants, animals and fungi.

Key questions What is a protist? What is the dilemma associated with protists? How is a protist related to other Eukaryotes?

Protist structure and function Section 21.2

How do Protists move? Early protists evolved virtually every possible form of cellular movement before they gave rise to multicellular Eukaryotes They can move by: Changing cell shape Through specialized organelles Others are moved by the wind, water or other organisms

Ameoboid movement Many unicellular protists move by changing their shapes – using cytoplasmic projections known as pseudopods Common in amoebas Powered by cytoskeletal protein called actin (which is also found in a animal muscle cells)

Cilia and Flagella Both structures supported by microtubules Cilia are numerous and move like oars on a boat Flagella are relatively long and short, some have propellor like motion, but most produce a wavelike motion from base to tip

Passive movement Many protists are non motile Rely on air or water currents or other organisms to transport them Protists form reproductive cells called spores Can enter cells of other organisms and live as parasites Plasmodium – protist carried by mosquitoes and can cause malaria Cryptosporidium – carried by water and can cause sever intestinal diseases

How do protists reproduce? There are many different ways! Not surprising considering how diverse protists are Asexual and sexual reproduction is common..

Cell division Ameobas reproduce by mitosis Most protists have phases in their life cycle during which they produce new cells by mitosis Allows rapid expansion under ideal conditions

Conjugation Paramecia and most ciliates reproduce asexually using mitosis When under stress, paramecia can remake themselves via conjugation Paramecia have two nuclei Macro nucleus (lending library) Micro nucleus (back up reserve library) Not reproduction ( No new individuals formed), but is a sexual process

Sexual reproduction Many protists have complex life cycles during which they alternate between a diploid and haploid phase Known as alternation of generations Example - water mold Reproduce asexually by producing spores in a sporangium Also reproduce sexually by producing male and female structures Haploid and fuse during fertilization Zygote begins new life

Key points How do protists move in their environments? How do protists reproduce?