The Algae
Chapter
Overview
This
chapter discusses the characteristics of the diverse polyphyletic group of
organisms known as the algae. They range from single cells to multicellular
organisms over 75 meters in length. They are found in oceans and freshwater
environments and are the major producers of oxygen and organic material. A few
algae live in moist soil and other terrestrial environments. They do not
constitute a unique kingdom. An overview of their characteristics is presented,
followed by discussion of each of the major groups of algae.
Chapter
Objectives
After
reading this chapter you should be able to:
1.
discuss the various habitats in which algae are found
2.
discuss the various morphological characteristics of algae
3.
discuss the taxonomic relationships of this diverse polyphyletic group of
organisms
4.
discuss asexual and sexual reproduction of algae
5.
discuss the various classical divisions of algae and the characteristics used
to establish the divisions
These are the most important concepts you are learning in this
chapter:
- Most algae are found in freshwater and marine environments; a few grow in terrestrial habitats.
- The algae are not a single, closely related taxonomic group but, instead, are a diverse, polyphyletic assemblage of unicellular, colonial, and multicellular eucaryotic organisms.
- Although algae can be autotrophic or heterotrophic, most are photoautotrophs. They store carbon in a variety of forms, including starch, oils, and various sugars.
- The body of an alga is called the thallus. Algal thalli range from small solitary cells to large, complex multicellular structures.
- Algae reproduce asexually and sexually.
- The following classical divisions of the algae are discussed: Chlorophyta (green algae), Charophyta (stoneworts/brittleworts), Euglenophyta (euglenoids), Chrysophyta (golden-brown and yellow-green algae; diatoms), Phaeophyta (brown algae), Rhodophyta (red algae), and Pyrrhophyta (dinoflagellates).
Study
Outline
I.
Introduction
A.
Algae-not
a monophyletic group; instead the term is used to describe a group of organisms
that lack roots, stems, and leaves, but that have chlorophyll and other
pigments for carrying out oxygenic photosynthesis
B.
Phycologists
(algologists)-scientists who study algae
C.
Phycology
(algology)-the study of algae
II.
Distribution
of Algae
A.
Primarily
aquatic
1.
Planktonic-suspended
in the aqueous environment
a.
Phytoplankton-algae
and other small aquatic plants
b.
Zooplankton-animals
and other nonphotosynthetic protists
2.
Benthic-attached
and living on the bottom of a body of water
3.
Neustonic-living
at the air-water interface
B.
Moist
rocks, wood, trees, and soil
C.
Some
are endosymbionts in protozoa, mollusks, worms, corals, and plants
D.
Some
associate with fungi to form lichens
E.
Some
are parasitic
III.
Classification
of Algae
A.
In
the Whittaker system
1.
Divided
into seven divisions within two different kingdoms
2.
Primary
classification is based on cellular properties
a.
Cell
wall (if present) chemistry and morphology
b.
Storage
food and photosynthetic products
c.
Types
of chlorophyll and accessory pigments
d.
Number
of flagella and their insertion location
e.
Morphology
of cells and/or thallus (body)
f.
Habitat
g.
Reproductive
structures
h.
Life
history patterns
B.
Molecular
systems have reclassified the algae as polyphyletic; they fall into five
different lineages
1.
Plants
2.
Red
algae
3.
Stramenopiles
(this lineage also includes some protozoa)
4.
Alveolates
(this lineage also includes some protozoa)
5.
Amoeboflagellates
(this lineage also includes some protozoa)
IV.
Ultrastructure
of the Algal Cell
A.
Surrounded
by a thin, rigid cell wall (some also have an outer matrix)
B.
Some
are motile by flagella
C.
The
nucleus has a typical nuclear envelope with pores
D.
Chloroplasts
have thylakoids (sacs) that are the site of photosynthetic light reactions; may
also have a dense proteinaceous pyrenoid that is associated with the synthesis
and storage of starch
E.
Mitochondria
can have discoid cristae, lamellar cristae, or tubular cristae
V.
Algal
Nutrition
A.
Most
are autotrophic-require only light and inorganic compounds for energy; use CO2
as carbon source
B.
Some
are heterotrophic-use external organic materials as source of energy and carbon
VI.
Structure
of the Algal Thallus (Vegetative Form)
A.
Thallus-vegetative
body of algae; can be unicellular or multicellular
B.
Algae
can be unicellular, colonial, filamentous, membranous, or tubular
VII.
Algal
Reproduction
A.
Asexual-occurs
only with unicellular algae
1.
Fragmentation-thallus
breaks up and each fragment forms a new thallus
2.
Spores
formed in ordinary vegetative cell or in sporangium
a.
Zoospores
are flagellated motile spores
b.
Aplanospores
are nonmotile spores
3.
Binary
fission-nuclear division followed by cytoplasmic division
B.
Sexual-occurs
in multicellular and unicellular algae
1.
Oogonia-relatively
unmodified vegetative cells in which eggs are formed
2.
Antheridia-specialized
structures in which sperm are formed
3.
Zygote-product
of fusion of sperm and egg
VIII.
Characteristics
of the Algal Divisions
A.
Chlorophyta
(green algae)-molecular classification places these with plants
1.
Are
extremely varied
a.
Contain
chlorophylls a and b and carotenoids; store carbohydrate as starch; cell walls
are made of cellulose
b.
Live
in fresh and salt water, soil, and associated with other organisms
c.
Can
be unicellular, colonial, filamentous, membranous, or tubular
d.
Exhibit
both asexual and sexual reproduction
2.
Genus
Chlamydomonas-Members of this genus are microscopic, rounded, with two flagella
at anterior end; have single haploid nucleus, a large chloroplast with
conspicuous pyrenoid for starch production and storage, a stigma (phototactic
eyespot), and contractile vacuole (acts as osmoregulator); exhibit asexual
reproduction (zoospores) and sexual reproduction
3.
Genus
Chlorella-members of this genus are nonmotile, unicellular algae; are
widespread in aquatic habitats and in soil; only reproduce asexually; lack
flagella; have eyespots, contractile vacuoles, and a very small nucleus
4.
Genus
Volvox-members of the genus exist as hollow spheres made up of a single layer
of 500-60,000 flagellated cells; flagella beat in a coordinated fashion; some
cells are specialized for reproduction
5.
Prototheca
moriformis, which is common in soil, causes the disease protothecosis in humans
and other animals
B.
Charophyta
(stoneworts/brittleworts)
1.
Abundant
in fresh and brackish waters; worldwide distribution
2.
Some
species precipitate calcium and magnesium carbonate from water to form a
limestone covering (helps preserve them as fossils)
C.
Euglenophyta
(euglenoids)-molecular classification places these with amoeboflagellates
1.
Same
chlorophylls (a and b) as Chlorophyta and Charophyta; found in fresh and
brackish waters and in moist soils
2.
Genus
Euglena-members of this genus:
a.
Have
elongated cells bounded by a plasma membrane; inside the plasma membrane is a
pellicle (articulated proteinaceous strips lying side-by-side), which is
elastic enough to enable turning and flexing of the cell, yet rigid enough to
prevent excessive alterations in cell shape
b.
Have
a stigma located near an anterior reservoir
c.
Have
a large contractile vacuole, which collects water and empties it into the
reservoir for osmotic regulation
d.
Have
paired flagella at anterior end that arise from reservoir base; only one beats
to move the cell
e.
Reproduce
by longitudinal mitotic cell division
D.
Chrysophyta
(golden-brown and yellow-green algae and diatoms)-molecular classification
places these with the stramenopiles
1.
Divided
into three classes: golden-brown algae, yellow-green algae, and diatoms
2.
Contain
chlorophylls a and c1/c2, and the carotenoid fucoxanthin
3.
Major
carbohydrate reserve is chrysolaminarin
4.
Some
lack cell walls; some have intricately patterned scales on the plasma membrane;
diatoms have a distinctive two-piece wall of silica called a frustule; have
zero, one, or two flagella (of equal or unequal length)
5.
Most
are unicellular or colonial; reproduction is usually asexual, but occasionally
sexual
6.
Diatoms
are photosynthetic, circular or oblong cells with overlapping silica shells
(epitheca-larger half and hypotheca-smaller half)
a.
Grow
in aquatic habitats and moist soil
b.
Some
are faculatative heterotrophs
c.
Vegetative
cells are diploid and reproduce asexually with each daughter getting one old
theca and constructing one new theca; this type of reproduction results in
diatoms getting progressively smaller with each reproductive cycle; when
diminished to 30% of original size, sexual reproduction occurs
E.
Phaeophyta
(brown algae)-molecular classification places these with stramenopiles
1.
Multicellular
seaweeds; some species have the largest linear dimensions known in the
eucaryotic world
2.
Simplest
species have branched filaments; more complex species (kelps) are
differentiated into flattened blades, stalks, and holdfast organs that anchor
them to rocks
3.
Contain
chlorophylls a and c; carotenoids include fucoxanthin, violaxanthin, and
b-carotene
F.
Rhodophyta
(red algae)-molecular classification gives these a separate lineage
1.
Some
are unicellular, but most are multicellular, filamentous seaweeds; comprise
most of the seaweeds
2.
Carbohydrate
reserve is floridean starch
3.
Contain
phycoerythrin (red pigment) and phycocyanin (blue pigment), and can therefore
live in deeper waters
4.
Their
cell walls include a rigid inner part composed of microfibrils and a
mucilaginous matrix consisting of sulfated polymers of galactose (agar); many
also deposit calcium carbonate in their cell walls and contribute to coral reef
formation
G.
Pyrrhophyta
(dinoflagellates)-molecular classification places these with the alveolates
1.
Unicellular,
photosynthetic protists
2.
Most
are marine organisms but a few are freshwater dwellers; some are responsible
for phosphorescence in ocean waters and for toxic red tides
3.
Their
flagella and protective coats are distinctive
a.
Are
clad in stiff, patterned, cellulose plates (thecae)
b.
Most
have two perpendicular flagella that function in a manner that causes organism
to spin
4.
Contain
chlorophylls a and c, carotenoids, and xanthophylls
5.
Some
can ingest other cells; some are heterotrophic; some are endosymbiotic, living
within host cells where they lose their cellulose plates and flagella
(zooxanthellae)
