Mic 101: L 19 ALGAE

Characteristics of Algae Eukaryotic Photoautotrophs and lack the tissues of plants like roots, stem and leaves Have chlorophyll and other pigments for carrying out photosynthesis can be multicellular or unicellular. Mostly aquatic, although some are found in soil or on trees when sufficient moisture is present

Vegetative structures of Algae The body of multicellular alga is called a thallus Thalli of the larger multicellular algae consists of branched holdfasts (which anchors the alga to a rock), stemlike and often hollow stipes and leaflike blades The cell covering the thallus can carry out photosynthesis. Thallus lacks the conductive tissue (Xylem and phloem), characteristic of vascular plants Algae absorb nutrients from the water over their entire surface.

Selected Phyla of Algae Brown Algae (Phaeophyta) Red Algae (Rhodophyta) Green Algae (Chlorophyta) Diatoms (Bacillariophyta) Dinoflagellates (Dinoflagellata) Water molds (Oomycota)

Phaeophyta Brown algae Cell wall: Cellulose and alginic acid Multicellular Cholorophyll a and c and Xanthophylls Store carbohydrate

Rhodophyta Red algae Cellulosic cell wall Mostly multicellular Chlorophyll a, d and phycobiliproteins Store glucose polymer

Chlorophyta Green algae Cellulose cell walls Unicellular or multicellular Chlorophyll a and b Store glucose polymer(starch)

Bacillariophyta Diatoms Complex cell wall contains pectin and a layer of silica Unicellular Chlorophyll a and c, carotene, xanthophylls Store oil Fossilized diatoms formed oil Produce domoic acid

Dinoflagellata Dinoflagellates Cellulose in plasma membrane Unicellular Chlorophyll a and c, carotene xanthophylls Store starch Some are symbionts in marine animals

Oomycota Water molds Colorless, white Cell wall contains cellulose Multicellular No photosynthetic pigments Asexually, the oomycotes resemble the zygomycete fungi in which produce spores in sporangium Oomycote spores is called zoospore, have two flagella

Characteristics of Selected phyla of Algae

Reproduction of algae Algae can reproduce asexually and sexually. Asexual Reproduction: All algae can reproduce asexually Multicellular algae with thalli and filamentous form can fragment Each piece is capable of forming a new thallus or filament When a unicellular alga divides, its nucleus divides (mitosis) and the two nuclei move to opposite part of the cell The cell then divides into two complete cells

Asexual Reproduction

Sexual Reproduction of algae Although most algae reproduce asexually, the proper environmental stimulus may initiate sexual reproduction. The process of gamete formation is called gametogenesis. The relative form of the two fusing gametes defines two categories of sexual reproduction -- isogamy and heterogamy. Isogamy Isogamy is the form of sexual reproduction in which the gametes produced are identical in shape, size and motility. There is no structural distinction between "male" and "female" gametes. Pairs of isogametes align themselves with their flagellar poles touching and after several seconds, the motile gametes fuse to form a single, non-motile, diploid zygote.

Conjugation,in filamentous green alga,Spirogyra a. Resting filaments of alga cells. b. Formation of conjugation tubes between two adjacent filaments. c. Cytoplasmic contents of each cell form a compact mass, representing an isogamete. The isogametes from one filament migrate through the conjugation tubes into the adjacent filament. The two isogametes unite to form a zygote. Each zygote eventually undergoes meiosis to form four haploid cells. One haploid cell will form a new filament by mitosis, the other three degenerate.  

Sexual Reproduction of Algae Heterogamy In heterogamy, two different types of gametes are produced. The male gamete, the sperm cell, is typically very small, highly motile and is produced in very large numbers. The female gamete, the egg cell, is much larger and non-motile. Oedogonium sp. is a green alga that produces heterogametes

Life Cycle of algae

Importance of Algae Brown Algae: Algin, a thickener used in many foods (ice ceram and cake decorations), is extracted from their cell walls. Algin is also used in the production of a wide range of nonfood goods, including rubber tires and hand lotion. Red Algae: The agar used in microbiological media is extracted from many red algae. Another gelatinous material, carrageenan comes from a species of red algae called Irish moss Diatoms: Domoic acid produced by the diatoms, is concentrated in the mussels. After eating the mussels, the people were affected by diarrhea and memory losss (1987) Dinoflagellates: The genus Alexandrium produce neurotoxin (saxitoxin) that cause paralytic shellfish poisoning. Gymnodinium breve, trapped in the gills of the fish release a neurotoxin that stops the fish from breathing. Water molds or Oomycota: mainly decmposers. Phytophthora infestans, is associated with potato blight disaease. It also infects soybeans and cocoa.

Role of Algae in Nature Primary producer: Algae are an important part of any aquatic food chain because they fix CO2 into organic molecules that can be consumed by chemoheterotrophs. Increases O2 concentration: Molecular O2 is a by product of their photosynthesis. As 75% of the earth is covered with water, it is estimated that 80% of the earth’s O2 os produced by planktonic algae. Much of the world’s petroleum is formed from diatoms and other planktonic organism.