Q. 30. Write short notes on following.
(i) Alternation of generation. (1994,96, 2006)
(ii) Algal pigment. (2000, 09)
(iii) Cell structure of blue green, algae.
(iv) Cystocarp or Carporsporaphyte (1994,99, 2007)
(v) Branching of Syctonema. (1995, 97)
(vi) Carpospore (1994, 99)
(vii) Pyrenoid (1993, 94)
(viii) Coenobium. (1995)
(ix) Nannandrium. (1991, 94)
(x) Reproduction in blue green algae. (1994, 95, 97)
Ans. (i) Alternation of Generation: - There is distinct alternation of generations in the sexual life cycle of algae. In alternation of generation there is haploid and diploid phases are present. Haploid phase is known as gametophyte while diploid phase called sporophyte, this type of life pattern are found in various algae. The dominant phase may be haploid in some species or diploid in some species of algae. The alternation of phases take place by meiosis division.
The sporophyte generation in the brown algae may be Perennial or annual but gametophyte in alway annual. The life cycle of fucus does not shows morphological alternation of generation. The sex organs are born on the sporophyte plant. The haploid condition restricted to the gamates only.
(ii) Algal Pigments: - Algal cells have characteristic colour due to the presence of a combinatinon of pigments specific to each class, in all classes, except cyanophyceae. These pigments are present within membrane bound organelles, known as plastids. Plastids are of two types.
1. Leucoplast - colourless plastids
2. Chromoplast - these are coloured plastid those containing both chlorophyll-a and chlorophyll-b are called chloroplast.
The various types of pigments found in the algae cell are-
1. Chlorophyll: - There are five types of chlorophyll, like, ohla, n, c, d and c. chiorophyll-a is present in all groups of algae. chl b in chioro and Euglenophyceae chlc in phaeophyceae, Bacillariophyceae and chrysophyceae ched in some red algae, che e in xanthophyceae.
2. Xanthophyll: - More than 20 types of xanthophylls are known. Many xanthophylls, common to higher plants (lutein, violaxauthin) are found in the members of chlorophyceae and phaeophyceae. Fucoxanthin is the main xanthophyll pigment of phaeophyceae and diatoms.
3. Carotenes: - These are oxygen free alicyclic compounds, composed of isoprene units five types of carotenes occur in algae are g - carotene to chlorophyceae and Rhodophyceae, b - carotene in all algae groups,- carotene in chlorophyceae, E-carotene in Bacillariophyceae, phaeophyceae and cyanophyceae.
4. Phycobilins: - These are water soluble complexes of protein and bi pigments, present in the photosynthetic tissue of plants. Phycobilins are red (Phycoerythin) and blue (Phycocyanin) pigments which are confined to Rhodophyceae and cyanophyceae respectively thus like cárotenoides, phycobilins, are also acessory pigments.
(iii) Cell Structure of Blue-green Algae: - A myxophycean or cyanophyceam, cell appears surrounded by distinct cell wall which enveloped by a mucilaginous sheath.
1. Mucilaginous Sheath: - A gelatinous, diffirent sheath made up of hanogenous surface is present in all the blue green algae. It is thin and delicate but think in Anabaena which made up of many cellulose fibrils.
2. Cell wall: - The cell wall is present between mucilaginous sheath and plasmalemma, the cell wall is rigid and complex structure usually made up of four layers which indicated from LI, LII, LIII and LIV. The layer LI is electron transport zone.
3. Cytoplasmic Membrane: - It is made up of two electron opaque layers of proteins Both these layers are separated by less opaque lipid layer.
4. Photosynthetic Structure: - The chromatoplasm region cosist of a complex lamellar system called photosynthetic lamellae or thylakoid these lamellae are not enclosed with chloroplast each membrane of lamella is 70-80A° thick. Thylakoids as photosynthetic respiratory membranes. On the surface of the thylakoids are attached the particles of phycobilisome and biliprotien.
5. Other Cytoplasmic inclusions: - In cyanophycean cell many gas vacuole, ribosonw, cyanophycean granules polyhedral bodies and lipid droplets are found in the cytoplasm. Gas vacuoles are common in planktonic species. Ribosomes are the sites of photosynthesis.
6. Nucleoplasm: - Nucleoplasm region is transparent having lower electron capacity many time strands of DNA are present in the nucleoplasm. Nucleolus is absent. His tones, and protamines are also not present in the DNA fibrels Nuclear body is not bounded in nuclear membrane.
(v) Branching of Scytonema: - Scytonema shows false branching. The branches may be single or germinate. This type of branching start with the breaking of trichome at a certain paint. One or both the ends perforate the shealth and grow out as branches. It is peculiar. It is formed by lateral pratrusion of a call and its subs equent division to form a full branch. The trichome are generally of uniform thickness enveloped with sheath. The shealth generally lameleate, colourless and colourd. The colouring pigment is known as scytonemin. In some specious the sheath is smooth and not lameleate. The trichome is composed of a single raw of cells to form a long or short thread-like structure. The trichomes have haterocysts distributed regular or irregular intervals throughout its length. The cells may be discoid, squarish, cylindrial or rectangular in shape.
(vi) Carpospores: - These found in life-cycles of red algae. These are either haploid or diploid in nature. These are format after post fertilization changes in carposporangia of their life-cycles. It is also known as asexual spore. In lower form of red algae, the carpospore and haploid naked and non-flagellate. They are realese by the breakdown of the surrounding cells walls or through outside. The liberated carpospore becomes amoeboid and shows amoeboid movements for 2 or 3 days then it germinated into newplant. While in higher forms of Red-Algae the carpospores may be diploid naked and nonflagellate. It liberated through ostiole and conses to less than at germinates into new gymatophytic plant with meaisis division with many other sparaphytes.
(vii) Pyrenoid: - In the member of chlorophyceae algae the chloroplast contain one or more highly differentiated organs which are the site of starch formation. These are called pyrenoids. A pyrenoid made up of many densly packed proteinuceous fibrils. They are generally situated with in the chromatophore but some time they may be on it surface also. The proteinaceous core of pyrenoid in generally encircled by starch plates. Its function in starch formation.
According to griffiths (1970) it is the region of temporary storage for the products of photosynthesis.
(viii) Coenobium: - A coenobium (plural coenobia) is a colony containing a fixed number of cells, with little or no specialization. They occur in several groups of algae. The cells are often embedded in a mucilaginous matrix and may be motile or non-motile.
Examples include Volvox and its relatives, Scenedesmus, Pediastrum, and Hydrodictyon.
The number of cells in each colony ranges from 500 to 50,000. It may be 1500 to 20,000 cells in each coenobium. All cells of coenobium is chiamydomonos type. They posses cup shaped chloroplasts.The mature coenobium swim over the water surface.
(ix) Nannandrium: - On the basis of sex organs the species of Oedogonium divided into two groups one is Macrandrous species and other is Nannandrous species.
In nannandrous species filament bearing antheridia and oogonia shows morphological distinction. The male filaments, which are much smaller than the female filaments are called dwarf male or “nannandrium”. The nanandrium species are always dioccious i.e. antheridia and oogonia are born on different filaments. Thus nannrandrous forms show heteromonohic dioecism.
(x) Reproduction in Blue-green Algae (Myxophyceae): - In blue green algae there is two types of reproduction present. These are vegetative and asexual reproduction or by spore formation.
1. Vegetative Reproduction: - It takes place by following methods -
(i) Cell division or fission (ii) Fragmentation and (iii) Hormogonis.
(i) Cell division or Fission: - This is a common method in blue green algae. The cell of alga divides by the formation of septum from periphery to the central region thus division of the cytoplasm takes place and resultant two doughter protoplasm so two cells are formed from one cell. Each cell developed into a new individual.
(ii) Fragmentation: - On the favourable condition of growth non-filamentous such as microcystis colony splits into small parts. Each parts, which is called a fragment grow into a new colony.
(iii) Harmogonia: - Harmogones are small pieces of trichome which makes by the death of intercallary cells. Each harmogonia develops into a new plant.
2. Asexual Reproduction: - It takes place by following method-
(i) Endospores: - In endospore formation the vegetative cell known as sporangium increases in size and its protoplast undergoes division to form several spores called endospores which are germinate to produce new plants.
(ii) Exospores: - These are formed exogenously. The cell increases and cut off from the open ends by transverse division called exospores which germinates into new youngones.
(iii) Nannospores: - In some non-filamentous algae such as microcystis the cell contents divide repeatedly. Numerous daughter cells are produced in each parent cell. These are nannocytes with naked protoplasm. The nannocytes germinate in sit to give rise to new typical colony.
(iv) Akinets: - These are thick walled enlarged vegetative cells. Food reserves in this cell. These cells formed in filamentous blue green algae which undergoes a resting period and germinate on the return of favourable coudition. Ex- Gloeotrichii Nostoc etc.