CHAPTER 28 PROTISTS
Using lenses he developed, Anton von Leeuwenhoek (17th century) was the first to
describe the diversity of microscopic protists.
I. Introduction to the Protists
Protists are the earliest eukaryotic descendants of prokaryotes. Protists arose a billion
years before the emergence of other eukaryotes such as plants, fungi, and animals.
Precambrian rock dated to about 2.1 billion years of age contain acritarchs, the oldest
commonly accepted fossils of protists.
- Adaptive radiation produced a diversitty of protists over the next billion years.
- The variations present in these organiisms were representative of the structure and
function possible in eukaryotic cells.
A. Protists are the most diverse of all the eukaryotes
Because protists vary so much in structure and function, more so than any other group,
few other general characteristics besides their being eukaryotes can be cited without
exception.
There are about 60,000 species of protists that occur today.
- Most are unicellular, but colonial forrms and even some simple multicellular forms exist.
- Their eukaryotic structure makes even the simplest protist more complex than
prokaryotes.
- Primal eukaryotes not only gave rise tto current protists, but also to plants, fungi, and
animals.
Protists are considered the simplest eukaryotic organisms because most are unicellular.
- At the cellular level, protists are exxtremely complex.
- The unicellular protist is not analogoous to a single plant or animal cell, but is a
complete organism.
- The single cell of a protist must perfform all the basic functions carried out by the
specialized cells of plants and animals.
Protists are metabolically diverse, and as a groups, they are the most nutritionally
diverse of all eukaryotes.
- Almost all protists are...