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Animations
(Animation Requirements)

• Sarcodines
• Chlamydomonas
• Life Cycle of Plasmodium vivax
• Deoxygenation of Lakes

Diversity of Protists. The protists are an extremely diverse group of eukaryotes, and as such, they present a classification challenge. One possible phylogeny for the five groups of protists discussed in this text is a tree in which all branches are equally related to each other. Among the groups of protists, life cycles, structure, and a variety of other characteristics vary greatly.

1. Five groups of protists
2. Heterotrophs with no permanent locomotor apparatus
3. Heterotrophs with flagella
4. Nonmotile spore-formers
5. Photosynthetic protists
6. Heterotrophs with restricted mobility

Investigating the Origin of Life
Few questions have fascinated mankind so intensely as the origin of life. There are both religious and scientific views about how life arose on earth. We will limit ourselves to scientific ones here, proposals that are at least in principle subject to test and rejection. There are a great many intriguing ideas advanced by scientists to explain how life may have originated on our planet, but there is very little that we know for sure. It seems clear the earth itself was formed about 4.6 billion years ago. The oldest clear evidence of life--microfossils in ancient rock--are 3.5 billion years old. Thus life arose quickly on earth, within the first billion years, at a time when chemically rich oceans covered much of the earth. One scenario for the origin of life is that it originated spontaneously in this dilute hot chemical soup; another is that it arose in hydrothermal deep-sea vents. Yet another is that life arrived on earth from an extraterrestrial source. Experiments have shown that many of the organic molecules needed to assemble an organism can be produced spontaneously from simple chemicals thought to be present in earth's early oceans, but little is known about how the first cells originated.

Tracking Iron Stress in Diatoms
Algae serve a very important role in many aquatic environments, forming the base of the food chain. Indeed, many of the aquatic animals in such habitats survive solely by eating phytoplankton (small photosynthetic algal organisms). A delicate balance of phytoplankton is needed to maintain a healthy aquatic environment: too much phytoplankton (so-called algal blooms) will deplete the oxygen dissolved in the water; too little phytoplankton creates a food shortage. Diatoms, a type of algae, are important in the aquatic ecosystem of the subarctic Pacific off the western coast of Canada. Scientists monitoring unexpectedly low levels of diatoms and other algae in the North Pacific have discovered that limited iron stores are responsible for the low phytoplankton stocks there. Michael McKay at Bowling Green State University is working on developing biochemical probes that can be used to identify areas of iron deficiencies. Diatoms contain an iron-sulfur protein called ferredoxin. Under low-iron conditions, ferredoxin is replaced by another protein, flavodoxin. McKay uses flavodoxin as a biochemical probe to detect iron deficiency in diatoms.