Biology 05B – Spring Quarter 2006
The term protist refers to an organism belonging to an alliance of organisms that are diverse in
form, life style, and ancestry.
The primary feature that distinguishes protists from other eukaryotic
organisms is that most of its members are unicellular.
As mentioned in the introduction, the focus of
study in Biology 5B is introduce students to the diversity of organisms and the different ways that
organisms confront some of the basic physiological challenges of life.
While the protists may not be
the best organisms to use for introducing some of the basic concepts of organismal diversity (the
relationships among these organisms are very complicated and occurred over a very long time span),
they do provide many excellent examples how organisms fulfill some of the basic requirements of life.
Their suitability for this lies in their unicellular
As unicells they are very accessible for
use in the teaching lab, and easy to observe and study in their entirety than are multicellular organisms.
All organisms share many common needs.
Among these are the need to acquire nutrients from the
environment, distribute these nutrients to all parts of the body, exchange gasses (0
) with the
environment, eliminate metabolic wastes, and reproduce.
Many organisms must also be able to move
Most maintain the form or shape characteristic of their species.
perform all, or most of these
requirements in the context of a single cell.
Before going on with
discussions of how each of these requirements are met by protists, it must be mentioned that most of
the principles to be described also apply to the cells of multicellular organisms.
Given this fact, you
should see that your efforts in this lab are also relevant to more complex organisms including yourself.
Protists are either autotrophic or heterotrophic.
Autotrophic protists, collectively
referred to as algae, make their own food by photosynthesis.
Their primary photosynthetic pigment is
chlorophyll A, but also utilize a wide array of other pigments in light capture.
They are often green,
but may vary in color because of the presence of these other pigments.
In fact, the classification of
algae is based in part upon the combination of photosynthetic pigments present and upon the chemical
composition of their stored photosynthate (e.g. the green algae use chlorophyll A and B, yellow
pigments called carotenoids, and store starch).
It should be mentioned that some heterotrophic protists
acquire an autotrophic capacity
by incorporating algal endosymbionts into their cells.
Heterotrophic protists may be either saprozoic, that is they absorb complex dissolved nutrients
from their environment, or holozoic.
Holozoic forms ingest solid food from their environment which
must be broken down by a process of enzymatic digestion before it can be utilized.
The presence of
specialized structures , e.g., tentacles and cytostome, for the capture and ingestion of food is often