#1) " Protist" means approximately "lower eucaryotes", most of which are unicellular, but brown algae include kelp - which can be very big. And many green algae and almost all red algae are multicellular. Protists are "everything else", besides fungi, multicellular animals, and higher plants. Protists are thus not a natural group that would belong together on the evolutionary tree; and they differ VERY widely! They are not a monophyletic group, but polyphyletic. Protists include protozoa (e.g. amoebae & ciliates like Paramecia, slime molds, dinoflagellates, Euglena, etc. etc. etc. #2) Gene sequencing, and other cell-level differences between these different groups indicates that they differ from each other much more fundamentally than, say, humans vs. trees! Multicellular animals seem to be closer to fungi, while higher plants are closer to green algae. (in terms of evolutionary branch points) #3) Each of the following are fundamentally very different Green Algae - more closely related to higher plants Chlamydomonas is a single-cell green alga that is very closely related to the multicellular alga Volvox. These are off on a side branch of the green algae, however, and are not ancestral to land plants. Contrary to what your textbook says on page 339, the cell wall of Chlamydomonas and Volvox is NOT made of cellulose. Actually it's made of glycoprotein (protein with attached sugars). Also, contrary to what is implied on page 341, although Chlamydomonas and Volvox are a very simple example of the progression from unicellular to multicellular forms in evolution, so far as we know Volvox isn't the ancestor of anything else. The green algae that are the direct ancestors of plants are a different group altogether. See page 347 in the textbook. Red Algae - some of which secrete coral-like deposits Brown Algae - kelp, etc. #4) Euglena were thought to be green algae; but turn out to be trypanosomes (protozoa, like those that cause Sleeping Sickness!) whose "chloroplasts" were symbiotic green algae. Many other groups that were thought to be green algae, but their "chloroplasts" turned out to be green algae, and sometimes to be animals with symbiotic algae. (like "Russian dolls") #5) Giardia have no mitochondria, two nuclei per cell, cause very bad diarrhea, are hard to kill, and contaminate most springs in National Parks, and city tap water in St. Petersburg ("Leningrad") #6) Malaria is caused by a kind of "protozoa", that invade human blood cells, are spread by mosquito bites, now only in tropical countries, but previously as far north as Philadelphia. Until almost 1900, it was believed to be caused by "bad air" Malaria still kills a little more than one million people per year. #7) Paramecia (and other "ciliates") are unicellular, but often bigger than small multicellular animals (1/5 millimeter long) The have "micronuclei" with one set of chromosomes and also "macronuclei" with 100s of copies of their DNA. If you imagine a multinucleate animal, without boundaries between cells, but with 100s nuclei worth of DNA concentrated in one place, that would be sort of like what ciliates are. #8) Diatoms are one-celled algae, that live in box-like shells made of silica. Many species of diatom crawl by exerting forces along grooves in these shells. (But the round ones have no locomotion) #9) "Amoeboid locomotion" occurs differently in many species, including individual cells of humans & other multicellular animals. Such cell locomotion is very important in embryonic development. Muscle and pigment cells crawl to their eventual locations, for example #10) Slime molds were at one time grouped with the fungi but now are considered to be amoeboid protists unrelated to fungi. The cellular slime mold Dictyostelium is another important model organism, which spends part of its life as single amoebae. When the amoebae run out of food, they aggregate into a multicellular "slug" form that crawls around for a while, then settles down and creates a spore forming body. See page 337. ------- Questions that might be on an exam: a) Are the protists a natural group, in the sense of being monophyletic, and having a common evolutionary origin? (hint: no; but can you explain?) b) What are some of the kinds of organisms that are classified as protists? c) What are three major groups of eucaryotes that are not included among the protists? Is this because their evolutionary origin is different from the protists? *d) It used to be supposed that the one-celled "plant" called Euglena was similar to the common evolutionary ancestors or both plants and animals. What is now believed about their evolution? e) In what sense are Euglena partly plants and partly animals, after all?! f) Why was it somewhat misguided to think about protozoa as just one-celled equivalents of animals? g) Is it closer to the truth to regard green algae as simpler relatives to higher plants? (hint: yes) h) What about Red Algae and Brown Algae: are they closely related to Green Algae, or what? (hint: no) i) Because of what weird nasty protist with 2 nuclei will you get sick if you drink water from an appalachian spring? j) What else is weird about the cell structure of these organisms? k) What sort of organism causes malaria? How are they spread? *l) The name "malaria" comes from what mistaken belief about the causes of diseases spread by mosquitoes? Until about when did medical science still believe this false theory? (1900) m) How big can Paramecia and other ciliates become, more or less? n) How can ciliates be so much bigger than the individual cells of humans and other multicellular animals (and plants)? o) The shape of diatoms is caused by the shape of what part of them? p) Is there more than one form of "amoeboid locomotion"? (hint: doggone right, there are!) *q) Thinking back to what you learned in an earlier lecture about Thomas Kuhn's writings on philosophy of science, was it paradigm science to show that mosquitoes cause malaria? **r) Which was the weirdest kind of organism you have heard of? **s) In Star Trek, why do all the different intelligent life forms differ mostly in the shapes of their foreheads? Compare this to the magnitudes of the differences among "Protists"!

 

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