Chlamydomonas. Organelle?

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Beverly Ward
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Chlamydomonas Organelle? Structure? Organelle? Unicellular thalli typically spherical to subspherical. Eyespot prominent in many species, at cell anterior embedded in chloroplast.

1 Chlamydomonas Organelle? Structure? Organelle? Unicellular thalli typically spherical to subspherical. Eyespot prominent in many species, at cell anterior embedded in chloroplast. Nucleus single and typically central. (1) Asexual reproduction (A) Zoospore formation: Occurs in favorable conditions. Active cells come to rest, the flagella become withdrawn, and thec ell contents divide into four, eight or sixteen parts, which become zoospore. These daughter individuals develop their individual cell wall and are released from parent cell. (B) Palmella stage: Under unfavorable (i.e.dry conditions) zoospores remain within the parent cell wall, grows in size and divides and large number of zoospores without flagella may be found in clusters inside an envelope of mucilage. Cell aggregation = palmella stage. When condition change, cells become motile. (2) Sexual Reproduction: Some species are monecious and others are diecious. Vegetative cell contents of cell divide to form 2 to 64 biflagellate gametes (like zoospores but with flagellae). Gametes may be naked or may have a cell wall. These are identical in shape and size and are called isogametes. They unite in pairs from their anterior end and form quadric-flagellate zygospore, which lose their cilia and becomes rounded.

2 Sexual Reproduction

3 Dunaliella Dunaliella sp. are motile, unicellular, rod to ovoid shaped (9 11 µm) green algae (Chlorophyceae), which are common in marine waters. The organisms are relatively simple to cultivate and do not clump or form chains.

Scenedesmus Organelle? Organelle? Organelle? Organelle? Single celled or colonial, forming 2-32-celled (usually 4- or 8-celled coenobia).

Cells arranged linearly are spherical to ellipsoidal, elongate or fusiform in shape.

Cells uninucleate; chloroplast single with single pyrenoid.

into singe cells; spore release by rupture of parental cell wall.

4 Scenedesmus Organelle? Organelle? Organelle? Organelle? Single celled or colonial, forming 2-32-celled (usually 4- or 8-celled coenobia). Mucilaginous matrix present or absent. Cells arranged linearly are spherical to ellipsoidal, elongate or fusiform in shape. Cell wall with hemicellulosic and pectinate layer, usually smooth. Cells uninucleate; chloroplast single with single pyrenoid. Asexual reproduction by autospores; 2-32 per sporangium, usually organized in one coenobium or disintegrated into singe cells; spore release by rupture of parental cell wall. Sexual reproduction apparently extremely rare. Species tolerate or prefer eutrophic water with slight acidity but only low salinity. Temperature optima at 28-30%C, but with some strains or taxa at 36%C or above. Some species of Scenedesmus highly polymorphic in culture with variation induced by various culture conditions.

Pediastrum Pediastrum is a genus of disk-shaped colonial green algae, characterized by peripheral hornlike projections, comprising part of the freshwater plankton.

5 Pediastrum Pediastrum is a genus of disk-shaped colonial green algae, characterized by peripheral hornlike projections, comprising part of the freshwater plankton. The number of cells per colony varies (2 128) depending on the species. Young cells are uninucleate, whereas mature cells may have up to eight nuclei. During asexual reproduction the cell contents divide and form motile spores that arrange themselves into colonies before being liberated. Sexual reproduction is by motile gametes.

Pandorina Structure?( Structure?( Colonies ellipsoidal to spherical, mostly of 8 or 16 cells of similar size (may be up to 32 cells), arranged in a common gelatinous matrix.

Cells are generally closely packed, flattened by mutual compression and contiguous in the center.

6 Pandorina Structure?( Structure?( Colonies ellipsoidal to spherical, mostly of 8 or 16 cells of similar size (may be up to 32 cells), arranged in a common gelatinous matrix. The colonial boundary is smooth, part of it penetrating between cells into central region of colony forming individual sheaths around cells. Cells are generally closely packed, flattened by mutual compression and contiguous in the center. Cells are obovate or wedge-shaped or more rounded, bearing 2 equal flagella, eyespot present and nucleus central. Asexual reproduction occurs by formation of 8- or 16-celled plakea which inverts to form a spheroidal daughter colony; sexual reproduction isogamous with the constitutive cells of the colony escaping from the gelatinous matrix and functioning as gametes; gametes fuse to form a 4-flagellated planozygote (see Chlamydomonas), motile for some time. The resting zygote is spherical, often with reddish contents. Upon germination, one or two biflagellate cells from zygote wall and dividing into a colony.

7 Pandorina Lifecycle

Tetraspora Structure?( Organelle? Structure?( Spherical to amorphous or highly elongate cylindrical to irregular colonies with tens to thousands of cells embedded in mucilaginous matrix 10-40 μm thick.

Cells spherical to oval 6-12 μm diameter with pair of anterior pseudoflagella at least several times cell length, projecting towards exterior of colony; in some species pseudoflagella

8 Tetraspora Structure?( Organelle? Structure?( Spherical to amorphous or highly elongate cylindrical to irregular colonies with tens to thousands of cells embedded in mucilaginous matrix μm thick. Cells scattered or arranged in groups of 2 or 4 often with sheath boundaries remaining distinct within wall matrix. Cells spherical to oval 6-12 μm diameter with pair of anterior pseudoflagella at least several times cell length, projecting towards exterior of colony; in some species pseudoflagella project beyond colony envelope. Cells uni-nucleate with single chloroplast and pyrenoid with conspicuous starch sheath. Colony growth by mitotic division of cells. Asexual reproduction by zoospores, akinetes and colony fragmentation.

9 Hydrodictyon Thalli coenobial, macroscopic, mostly 20 (-40) cm in length when mature. Comprised of cylindrical or broadly ovoid cells, up to 1 cm long when mature, joined at ends to form cylindrical net closed at poles. Within network, individual net units comprised of 3-9 (mostly 6) cells, with cell number species specific. Cells highly multinucleate, chloroplast present and pyrenoids numerous. Nuclei generally dispersed but aggregations associated with localized growth.

10 Chlorella Chlorella is a unicellular, coccoid green alga of about 2-10μm, lacking flagellae. It contains the chlorophyte typical photosynthetic pigments and requires only minimal carbon dioxide, water, sunlight and minerals to reproduce asexually only. Chlorella is a model organism that was used by Melvin Calvin to determine pathways of carbon dioxide assimilation (for which he won the Nobel Prize in Chemistry). Chlorella is high in protein and may thus be used as a food supplement. It has also recently been used in experiments regarding the production of biofuels.

11 Micrasterias The species of the desmid genus Micrasterias are well known for their beauty. Their graceful- ly built cells in symmetry inspire the microscopist again and again anew, and their cell size facilitates the observation even with simpler microscopical equipment. Micrasterias means little star. The genus occurs worldwide and covers approx. 40 species. They populate oligotrophe, stand- ing water bodies up to acidic and very nutrient-poor biotopes like bogs. These representatives of the unicellular, unflagellated green algae from the group of desmids (Zygnematales / Strep- tophyta) are built up of large, flattened cells, whose lateral view is fusiform. A central con- striction called sinus separates them in two halves. The nucleus is situated at the so-called isthmus, the narrow junction point of the two half-cells. Every half-cell owns its chloroplast with pyrenoids. Symmetrical cuts within the half-cells shape lobes, so the cells appear as small stars. Some species wear prickles on the cell surface.

12 Cosmarium Cosmarium is a non-motile, freshwater member of division Chlorophyta (green algae). Cosmarium is a relatively large unicell characterized by a constriction in the middle of the cell (termed the isthmus) which divides it into two symmetrical halves or semicells. A single haploid nucleus occupies the isthmus. Each semicell is partly filled by a large green chloroplast containing one-two pyrenoids. The cell wall is composed of cellulose, a polysaccharide found in the cell walls of most members of the division Chlorophyta and all members of the more highly evolved plant groups.

14 Plastid Types

Planktonic Chlorophytes I. Chlorophyceae

Planktonic Chlorophytes I. Chlorophyceae Planktonic Chlorophytes Chlorophyta are commonly known as green algae. This is the most diverse group of algae, with over 10,000 species. The majority of organisms in this group are unicelluar, but there