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Brown Algae · Heterokontophyta (Class: Phaeophyceae)

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Brown Algae · Heterokontophyta (Class: Phaeophyceae) BROWN ALGAE · HETEROKONTOPHYTA (CLASS: PHAEOPHYCEAE) Objectives In this lab we will examine members of the Heterokontophyta (Class Phaeophyceae), observing differences in their morphology and reproductive structures. You will be using live specimens, herbarium pressings, and prepared slides. Introduction As beachcombers observe large mounds of beach wrack following storms, brown algae typically make up a prominent portion of their biomass, especially off the west coast of North America. The brown algae include the large kelps that form beds that dominate the subtidal habitat in the temperate to polar regions of the world, where the marine environment is fertilized by upwelling. Brown algae are of large economic importance and are consumed as a “sea vegetable” in many regions of the world, and are harvested here in California as a source of alginic acid. Brown algae are the predominant algae in the intertidal and subtidal zones of cold temperate to polar regions, becoming progressively less conspicuous at lower latitudes. Brown algae are usually not found at depths greater than 90 feet, although some, such as the giant kelp Macrocystis pyrifera, are the largest of the non-vascular plants and may reach lengths in excess of 150 feet. Plants as large as this are found along the west coast from Alaska to California. The greatest degree of tissue differentiation occurs in this group. No unicellular forms are known and only certain reproductive structures (zoospores and some gametes) are planktonic. The evolutionary origins of these organisms remain obscure. Algae in the class Phaeophyceae are almost entirely marine and are characterized by the presence of two dissimilar flagella (heterokontic), which are laterally inserted in kidney-bean shaped (reniform) reproductive bodies. Brown algae contain chlorophyll a and c, b-carotene, and an accessory xanthophyll pigment (fucoxanthin). This latter pigment gives most brown algae their characteristic brownish-green coloration. The cell walls of many brown algae are composed of two components: cellulose microfibrils provide the main structural support while alginic acid (a mucopolysaccharide) functions to protect the thallophytes from desiccation and freezing, as well as provide flexibility and elasticity to the thallus. Alginates (the salt form of alginic acid) are extracted from some of the “giant” kelps (Laminariales) and have many human uses: such as preventing ice crystal formation in ice cream, preventing frosting from drying out, and acting as an emulsifying agent in paints to keep pigments suspended in solution and prevent brush streaking. Morphology The Heterokontophyta (Class Phaeophyceae) includes forms which range from simple branched filaments to extremely complex parenchymatous tissues with differentiated conductive (sieve-like) cells. Unlike green algae, browns have no unicellular forms. However, the browns do include filamentous, parenchymatous, complex parenchymatous, and pseudoparenchymatous forms. Systematics Each order in the brown algae is characterized by genera having similar life histories and patterns of development from a single celled zygote to a mature vegetative thallus. The following table and list describe orders we will consider within the class Phaeophyceae. Distinguishing Between Orders within Division: Heterokontophyta Class: Phaeophyceae Orders Life History Sexual Reproduction Growth Thallus Construction Alternation of - Apical Dictyotales Generations: Oogamy Parenchymatous - Marginal - Isomorphic Isomorphic Species Alternation of - Morphological - Diffuse Generations: isogamy with - Filamentous Ectocarpales Heteromorphic species - Isomorphic functional anisogamy - Pseudoparenchymatous - Sporophyte: Trichothallic - Heteromorphic - Oogamy - Gametophyte: Apical Morphological isogamy - Sporophyte: Trichothallic - Filamentous Ralfsiales with functional - Gametophyte: Apical - Pseudoparenchymatous anisogamy Gametophyte (small) filamentous Desmarestiales Alternation of Oogamy Trichothallic Sporophyte (large) Generations: pseudoparenchymatous - Heteromorphic Gametophyte (small) - Sporophyte: Intercalary Oogamy; eggs filamentous Laminariales - Gametophyte: Apical sometimes flagellate Sporophyte (large) (Sze) - Meristodermal Parenchymatous Fucales Diplontic Mostly oogamy Apical Parenchymatous 2 Taxonomy/Classification for Brown Algae Domain: Eukarya Group: Stramenopiles Division: Heterokontaphyta Class: Phaeophyceae (~1,800 species – 99% marine) Notebook Requirements (15 drawings) 1) Fucus gardneri- 2 drawings (thallus and conceptacle cross section) 2) Silvetia compressa- 2 drawings (thallus and conceptacle cross section) 3) Pelivetiopsis arborescens- 1 drawings (thallus) 4) Cystoseira osmundacea- 1 drawing (thallus) 5) Sargassum muticum- 1 drawing (thallus) 6) Desmarestia spp- 2 drawings (entire thallus and prepared slide) 7) Ectocarpus- 2 drawings (plurilocular and unilocular material) 8) Leathesia difformis - 2 drawings (thallus and cross section) 9) Dictyota binghamiae – 1 drawings (prepared slide) 10) Unkowns - 1 drawing (thallus) and steps in key A. Order Fucales Family Fucaceae Species: Fucus gardneri (hint: name change) 1. Examine and draw the entire plant, noting the branching pattern. Look for and label receptacles and conceptacles. Q: What type of growth does the alga exhibit? 2. Cross section through a conceptacle. Find and label: oogonia, eggs, antheridia, and sperm (sperm may not be visible but are found in the antheridia). You can view these reproductive structures on permanent slides if you want to see a clear view of structures, but you should also look at live specimens (you should be familiar with both live specimens and prepared slides for practical). Q: Is this species monoecious or dioecious? (hint: the answer varies between live and fixed material) Q: What type of life history does this alga exhibit? Species: Silvetia compressa (formerly Pelvetia fastigiata) and Pelvetiopsis arborescens/limitata • For this exercise you will be given the two genera listed above but you will not be told which is which, your job will be to figure that out using your MAC, Marine Algae of California book. • Cross section through a conceptacle of each species draw what you see (you may work in pairs for this, i.e. one partner cross sections Silvetia and the other Pelvetiopsis). Q: How many eggs are in each oogonium for each species? Read the Genera descriptions for the above species in your MAC. This information along with your cross section should allow you to determine which Genera you are observing. • Finally, quickly sketch the entire thallus of Silvetia and Pelvetiopsis. Q: Explain how you figured out which alga is which • Write some notes about how the two forms are similar and how they are different. (i.e. if you were in the field and could not do a cross section how would you tell the two genera apart). Family: Cystoseiraceae Family: Sargasseaceae Species: Stephanocystis osmundacea Species: Sargassum muticum 1. Look at these two species and compare and contrast their macroscopic features. Sketch both thalli. B. Order Desmarestiales Species: Desmarestia spp. • Draw the entire thallus of Desmarestia. (Use the herbarium pressing or live specimen) • Look at a prepared slide and draw what you see. Q: What kind of growth does Desmarestia exhibit? C. Order Ectocarpales Species: Ectocarpus spp. 1. Examine the prepared slides of Ectocarpus plurilocular and unilocular material. Contrast and draw the different types of reproductive material. Q: What type of thallus construction does it have? Q: What does each type tell you about the ploidy of the parent thallus? 2. Species: Leathesia difformis (hint: name change) - 2 drawings (thallus and cross section) Q: What type of growth pattern does this species display? 4 D. Order Dictyotales Species: Dictyota binghamiae 1. Examine pressing or picture of Dictyota binghamiae. Examine prepared slides of oogonia, tetraspores, antheridia, and apical region from Dictyota binghamiae. Draw what you see. How many cells thick is the thallus? F. Unknowns Key to species the unknown you are given, as you have done in previous labs. Be sure to write out each step of your path in the dichotomous key. 5 6 7 8 9 10 .
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