BSC 314 Lecture Notes - Lecture 50: Ciliate, Amoeba, Paramecium
27 Jun 2018
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Algae
Some marine algae—the kelps—look like plants with stem like stalks supporting ‐
“leaf” blades and a holdfast that anchors the kelp to rocks on the sea bottom. Growing
offshore in colder northern waters they sometimes attain a height of 50–60 meters—the
largest protists. Most of the algae are constructed more simply and are smaller—many
are unicellular and microscopic in size. The algae, like the rest of the protists, have
evolved a wondrous array of body forms and lifestyles—unicellular, motile free living; ‐
complex aggregations of cells in colonies; filaments, nets, coenocytic tubes;
microscopic, slimy green threads—all are common algal forms.
The variable body structure is not useful taxonomically to separate the major groups, nor
are the reproductive structures particularly helpful. Instead, the following five features are
more definitive and used in algal classification:
The photosynthetic pigments they contain.
Kind of stored foods.
Materials composing the wall.
Number, kind, and position of the flagella.
Details of cell structure, such as the shape of the chloroplasts or the presence of pyrenoids or eye
spots.
Today, a sixth characteristic is added:
The molecular sequences of their DNA and RNA.
Data obtained by using this newest approach are shaking the algal phylogenetic tree and
revising many long-held ideas of relationships within the algae. Newly acquired data,
however, have not changed the belief that members of the green algae orders
Coleochaetales and Charales of the Class Charophyceae are the closest living relatives of the
plants.
The green algae are green because they contain chlorophylls a and b and carotenoids in the
same proportions as the green plants. Like the green plants, they store starch inside the
plastids and most have cellulose cell walls. Some have reproductive cells that are structured
with two whiplash flagella—like green plant sperm cells. These common features led
biologists in the past to the green algae as the protistan ancestors of green plants—if one
defines “plants” as “land plants” (embryophytes). With today's available data, some
biologists say that algae are green plants of the aquatic kind and suggest a general category
of Chlorobiota to include all green plants, aquatic and terrestrial. There are strong advocates
for both approaches, but no clear majority for one over the other.
A Mixture of Life Forms
The Kingdom Protista (Protoctista) is a hodgepodge of organisms with little relationship
to one another. Most members of this kingdom have features of one or more of the
other kingdoms, but not enough to place them legitimately into any one of these as
currently defined. Cladists (those who classify organisms based on cladistics) suggest
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Some marine algae the kelps look like plants with stem like stalks supporting. Leaf blades and a holdfast that anchors the kelp to rocks on the sea bottom. Growing offshore in colder northern waters they sometimes attain a height of 50 60 meters the largest protists. Most of the algae are constructed more simply and are smaller many are unicellular and microscopic in size. The algae, like the rest of the protists, have evolved a wondrous array of body forms and lifestyles unicellular, motile free living; complex aggregations of cells in colonies; filaments, nets, coenocytic tubes; microscopic, slimy green threads all are common algal forms. The variable body structure is not useful taxonomically to separate the major groups, nor are the reproductive structures particularly helpful. Instead, the following five features are more definitive and used in algal classification: Number, kind, and position of the flagella.
