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
Phycologists (algologists)-scientists who study algae
Phycology (algology)-the study of algae
Distribution of Algae
Primarily aquatic
Planktonic-suspended in the aqueous environment
Phytoplankton-algae and other small aquatic plants
Zooplankton-animals and other nonphotosynthetic protists
Benthic-attached and living on the bottom of a body of water
Neustonic-living at the air-water interface
Moist rocks, wood, trees, and soil
Some are endosymbionts in protozoa, mollusks, worms, corals, and plants
Some associate with fungi to form lichens
Some are parasitic
Classification of Algae
In the Whittaker system
Divided into seven divisions within two different kingdoms
Primary classification is based on cellular properties
Cell wall (if present) chemistry and morphology
Storage food and photosynthetic products
Types of chlorophyll and accessory pigments
Number of flagella and their insertion location
Morphology of cells and/or thallus (body)
Habitat
Reproductive structures
Life history patterns
Molecular systems have reclassified the algae as polyphyletic; they fall into five different lineages
Plants
Red algae
Stramenopiles (this lineage also includes some protozoa)
Alveolates (this lineage also includes some protozoa)
Amoeboflagellates (this lineage also includes some protozoa)
Ultrastructure of the Algal Cell
Surrounded by a thin, rigid cell wall (some also have an outer matrix)
Some are motile by flagella
The nucleus has a typical nuclear envelope with pores
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
Mitochondria can have discoid cristae, lamellar cristae, or tubular cristae
Algal Nutrition
Most are autotrophic-require only light and inorganic compounds for energy; use CO2 as carbon source
Some are heterotrophic-use external organic materials as source of energy and carbon
Structure of the Algal Thallus (Vegetative Form)
Thallus-vegetative body of algae; can be unicellular or multicellular
Algae can be unicellular, colonial, filamentous, membranous, or tubular
Algal Reproduction
Asexual-occurs only with unicellular algae
Fragmentation-thallus breaks up and each fragment forms a new thallus
Spores formed in ordinary vegetative cell or in sporangium
Zoospores are flagellated motile spores
Aplanospores are nonmotile spores
Binary fission-nuclear division followed by cytoplasmic division
Sexual-occurs in multicellular and unicellular algae
Oogonia-relatively unmodified vegetative cells in which eggs are formed
Antheridia-specialized structures in which sperm are formed
Zygote-product of fusion of sperm and egg
Characteristics of the Algal Divisions
Chlorophyta (green algae)-molecular classification places these with plants
Are extremely varied
Contain chlorophylls a and b and carotenoids; store carbohydrate as starch; cell walls are made of cellulose
Live in fresh and salt water, soil, and associated with other organisms
Can be unicellular, colonial, filamentous, membranous, or tubular
Exhibit both asexual and sexual reproduction
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
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
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
Prototheca moriformis, which is common in soil, causes the disease protothecosis in humans and other animals
Charophyta (stoneworts/brittleworts)
Abundant in fresh and brackish waters; worldwide distribution
Some species precipitate calcium and magnesium carbonate from water to form a limestone covering (helps preserve them as fossils)
Euglenophyta (euglenoids)-molecular classification places these with amoeboflagellates
Same chlorophylls (a and b) as Chlorophyta and Charophyta; found in fresh and brackish waters and in moist soils
Genus Euglena-members of this genus:
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
Have a stigma located near an anterior reservoir
Have a large contractile vacuole, which collects water and empties it into the reservoir for osmotic regulation
Have paired flagella at anterior end that arise from reservoir base; only one beats to move the cell
Reproduce by longitudinal mitotic cell division
Chrysophyta (golden-brown and yellow-green algae and diatoms)-molecular classification places these with the stramenopiles
Divided into three classes: golden-brown algae, yellow-green algae, and diatoms
Contain chlorophylls a and c1/c2, and the carotenoid fucoxanthin
Major carbohydrate reserve is chrysolaminarin
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)
Most are unicellular or colonial; reproduction is usually asexual, but occasionally sexual
Diatoms are photosynthetic, circular or oblong cells with overlapping silica shells (epitheca-larger half and hypotheca-smaller half)
Grow in aquatic habitats and moist soil
Some are faculatative heterotrophs
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
Phaeophyta (brown algae)-molecular classification places these with stramenopiles
Multicellular seaweeds; some species have the largest linear dimensions known in the eucaryotic world
Simplest species have branched filaments; more complex species (kelps) are differentiated into flattened blades, stalks, and holdfast organs that anchor them to rocks
Contain chlorophylls a and c; carotenoids include fucoxanthin, violaxanthin, and b-carotene
Rhodophyta (red algae)-molecular classification gives these a separate lineage
Some are unicellular, but most are multicellular, filamentous seaweeds; comprise most of the seaweeds
Carbohydrate reserve is floridean starch
Contain phycoerythrin (red pigment) and phycocyanin (blue pigment), and can therefore live in deeper waters
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
Pyrrhophyta (dinoflagellates)-molecular classification places these with the alveolates
Unicellular, photosynthetic protists
Most are marine organisms but a few are freshwater dwellers; some are responsible for phosphorescence in ocean waters and for toxic red tides
Their flagella and protective coats are distinctive
Are clad in stiff, patterned, cellulose plates (thecae)
Most have two perpendicular flagella that function in a manner that causes organism to spin
Contain chlorophylls a and c, carotenoids, and xanthophylls
Some can ingest other cells; some are heterotrophic; some are endosymbiotic, living within host cells where they lose their cellulose plates and flagella (zooxanthellae)
