Algae.pdf

1 Biodiversity: Biodiversity is the existence of a wide variety of plants, animals and micro-organisms living in their natural environment. Taxonomy: Taxonomy is the branch of biology which deals with the ,...

1 Biodiversity: Biodiversity is the existence of a wide variety of plants, animals and micro-organisms living in their natural environment. Taxonomy: Taxonomy is the branch of biology which deals with the , , and of organisms. The term taxonomy was coined by De Candolle in 1813. is considered as father of taxonomy. Classification: Classification is the process of in a hierarchial system on the basis of similarities and dissimilarities in their characters. Plantae  2 It includes multicellular, eukaryotic and chlorophyllous organisms. They are found in aquatic and terrestrial habitat. They have autotrophic mode of nutrition. They are known as producers of environment. They include vascular and non-vascular plants. Reserved food material is starch. Cell wall is made up of cellulose*. Cell division takes place by mitosis and meiosis. Reproduction takes place by vegetative, asexual and sexual methods. Embryo is formed after fertilization. *Cellulose is a linear polysaccharide polymer with many glucose monosaccharide units. Plantae  3 Generally, algae are found in habitat but some may be found in terrestrial and parasitic habitat also. Algae have mode of nutrition. The plant body of algae is and and may be and. Usually covered with (prevents dessication and decaying). Photosynthetic pigments like chlorophyll, carotene, xanthophylls, phycobillins are present. Reserve food material is in the form of. Cell wall is made up of and. Reproduction takes place by vegetative, asexual and sexual methods. Embryo is not formed after fertilization. Example: Spirogyra, Chlamydomonas, etc. *Pectin is a polysaccharide starch found in the cell walls of fruits and vegetables. In terms of food composition, pectin is a gelling agent. Plantae  4 Photosynthetic Pigments Photosynthetic pigments are the most important coloured components of the chloroplast lamellae. These pigments are molecules that strongly absorb visible light. They interact with sunlight to alter the wavelengths that are either reflected or transmitted by the plant tissue. These pigments are also found in cyanobacteria and algae. Pigment Common Types Occurrence Chlorophyll Chlorophyll All photosynthetic plants Aurones Anthocyanins Common in plants including gymnosperms, Flavonoids Flavonols angiosperms, bryophytes and ferns. Chalcones Proanthocyanidins orange, yellow and red pigments found Carotenes largely in fruit, vegetables and dark green leafy vegetables. Carotenoids responsible for the color of many of the Xanthophylls yellow, orange, and red hues (varieties) of flowers, fruits, vegetables (corn, pepper, etc.) Phycoerythrobilin Red algae, cryptomonads, glaucophytes and Phycobilins Phycocyanobilin cyanobacteria. Phycourobilin Plantae  Fritsch classified algae into eleven classes. 5 Comparative study of the three major classes of algae S.N Chlorophyceae Phaeophyceae Rhodophyceae. 1 They are known as They are known as brown They are known as red green algae. algae. algae. 2 They comprise 425 They comprise 240 genera They comprise 400 genera genera and 7000 and 2000 species. and 5000 species. species. 3 They are mostly grown They are mostly grown in They are mostly grown in in fresh water. marine water. marine water but few in fresh water. 4 They contain They contain chlorophyll- They contain chlorophyll- chlorophyll-a, a, chlorophyll-c, a, chlorophyll-d, chlorophyll-b, carotenoides and carotenoides and carotenes and siphonein xanthophylls phycobillins as major photosynthetic (fucoxanthin) as major (phycoerythrin) as major pigments. photosynthetic pigments. photosynthetic pigments. Plantae  6 Comparative study of the major classes of algae S.N. Chlorophyceae Phaeophyceae Rhodophyceae 5 Starch is the major food Main food reserves are Floridean starch is the major reserve. laminarin and mannitol. food reserve. 6 Cell wall is made up of Cell wall is made up of Cell wall is made up of outer outer pectose layer and outer phycolloids layer pectic layer and inner cellulosic inner cellulosic layer. and inner cellulosic layer. layer. 7 They range from They are multicellular. They are usually multicellular unicellular to and a few are unicellular also. multicellular. 8 Reproduce by vegetative, Reproduce by vegetative, Reproduce by vegetative, asexual asexual and sexual means. asexual and sexual means. and sexual means. Mannitol and laminarin are considered as reserve food material in many brown algae species. These are complex carbohydrates. Mannitol is a sugar alcohol form of mannose, while laminarin is a linear polysaccharide of mannitol-containing β- 1,3-linked glucose. Acronematic: When there is no hair-like structure that is no mastigonemes are present, they appear to have a smooth flagella and the terminal part have a fiber-like structure it is called acronematic flagella. Plantae  Comparative study of the major classes of algae 7 S.N Chlorophyceae Phaeophyceae Rhodophyceae. 9 Asexual reproduction Asexual reproduction Asexual reproduction by: by: zoospore and by: zoospore. non-motile spores aplanospore. (monospores, carpospores, neutral spores or meiospores). 10 Sexual reproduction by: Sexual reproduction by: Sexual reproduction only by: isogamous, isogamous, oogamous. anisogamous and anisogamous and oogamous. oogamous. 11 Examples: Spirogyra, Examples: Fucus, Examples: Bangia, Porphyra, Chara, Vaucheria, Laminaria, Ectocarpus Dumontia, Palmaria etc. Chlamydomonas etc. etc. Plantae  8 1. Isogamous: This is a first stage of sexual reproduction in which fusion of both identical gametes occurs. It is found in Algae, fungi, and lower plants. 2. Anisogamous / heterogamous: This is a second stage of sexual reproduction in which fusion of large female gamete and small male gamete occurs [i.e. union/fusion of dissimilar (in size and form) gametes occurs]. It occurs in some fungi, higher invertebrates, and all vertebrates 3. Oogamous / heterogamy: This is a third stage of sexual reproduction in which fusion of smaller and flagellate male gamete occurs with large and non-flagellate female gamete rich in food materials. It is found in higher groups of algae-like Volvox and Oedogonium, plants like bryophytes ferns and gymnosperm. Note: The first, second and third stages are on the basis of evolution. Isogamous is least developed and oogamous is well developed. Plantae  9 Spirogyra: Systematic position: Kingdom: Plantae Division: Chlorophyta Class: Chlorophyceae Order: Conjugales Family: Zygnemataceae Genus: Spirogyra Species: S. zonata Common name: Pond scum / Pond silk Plantae  10 Occurrence: Spirogyra is at large genus consisting of about 300 species and is cosmopolitan in distribution. They are found in fresh water such as pools, ponds, lakes, ditches etc and also in slow running water of rivers and streams. Plantae  11 Structure of spirogyra: The plant body of spirogyra is a gametophytic, elongated, cylindrical, unbranched, silky, thread like thallus which is known as filament. Each filament consists of numerous elongated rectangular cells joined end to end in a row. The cells are separated by a partition wall known as Septum. Each cell can be differentiated in to two regions: cell wall and protoplast. Cell wall is covered by mucilage sheath. Cell wall is the outermost protective double layer structure, outer composed of pectin and inner of cellulose. Plantae The protoplast contains plasma membrane, cytoplasm, single large centrally 12 located vacuole and spirally coiled ribbon shaped chloroplast containing series of pyrenoids. The plasma membrane lies inner to the cell wall and semi permeable in nature (allows the passage of selective substance). The granular cytoplasm is distributed in the peripheral region of the cell. Single large vacuole is bounded by tonoplast and contains watery fluids. The number of chloroplast ranges from 1-16 depending upon the species. Single prominent uninucleated nucleus lies at the center of the cell which is held in position by the thin delicate, radiating cytoplasmic strands. Number of chromosomes range from 2n = 8 to 76, with the vast majority of reported numbers being between 16 and 24 (Sarma, 1982) Plantae  13 Reproduction: The reproduction in Spirogyra takes place by three methods: A. Vegetative reproduction, B. Asexual reproduction and C. Sexual reproduction A. Vegetative reproduction: The vegetative reproduction in Spirogyra commonly takes place by means of fragmentation. Fragmentation: During unfavourable conditions like sudden change in temperature, change in pH, severe water currents, movement of aquatic animals or their biting, death of some intercalary cells, by softening and dissolution of the cross walls etc, the filaments of Spirogyra breaks into one or more segments or fragments. The process is called fragmentation. Each of the fragments can develop into new filament by the process of repeated cell division and growth. Plantae  14 Plantae  15 B. Asexual reproduction: The asexual reproduction in Spirogyra is rare which takes place during unfavourable conditions by the formation of akinetes and aplanospores. a. Akinetes: In this method, the protoplast of few cells of the filaments of some species like Spirogyra farlowii lose water, get contracted, round off and develop thick walls around themselves due to the extra deposition of cellulose and pectin and form the akinetes. Akinete is a thick walled resting spore containing abundant reserved food materials that can develop into new filament when it comes to favourable conditions. Plantae  16 Plantae  17 b. Aplanospores: In some species of Spirogyra like Spirogyra aplospora and Spirogyra kanalae, the protoplast of the cell lose water, contracts and rounds off developing thin cellulosic walls around themselves and form the aplanospore. Aplanospores are the thin walled, non motile spores which arise singly inside cell and developed by loss of water from protoplast. They can dissolve wall and germinate into new filament when they returns to the favorable condition. Plantae  18 C. Sexual reproduction: Sexual reproduction in spirogyra occurs by conjugation. Conjugation is the process of fusion of two gametes out of which one acts as the male gamete (+ve) and other as female gamete (- ve). Conjugation in Spirogyra occurs by two methods: A.Scalariform conjugation and B.Lateral conjugation. Plantae  19 A. Scalariform conjugation: Scalariform conjugation is the most common method of sexual reproduction in Spirogyra that occurs between the two filaments and seen in heterothallic / dioecious species. The two filaments of opposite strands come closer and lie parallel to eachother throughout their length and are hold by common mucilaginous sheath. The opposite cells of two filaments produce small papillae outgrowth from their opposite walls. The outgrowths increase in their size and connect two filaments. By this time, filaments secrete enzyme cytase by the action of which the partition walls dissolve forming a free passage between two cells. This passage is known as conjugation tube. At the same time, the protoplast gets contracted forms gametes known as gametangia (bag to hold gamete). Thus the isogametes are formed in gametangia. The motile male gametes enter through conjugation tube to fuse with the stationary female gametes and forms spherical zygote. The zygote when secretes thick wall, it is known as Zygospores. At this stage, the cells of one filament become empty while the cells of other filament carry a row of zygospores. Hence, ladder like appearance is formed known as scalariform conjugation. Plantae  20 Plantae  21 B. Lateral conjugation: Lateral conjugation occurs between the adjacent cells of single filament. The lateral conjugation is also known as chain conjugation. This type of sexual reproduction is rare and seen in homothallic / monoecious speceis. It is of two types: indirect lateral conjugation and direct lateral conjugation. i. Indirect lateral conjugation: In species like Spirogyra affinis, on the lateral side of filament above the septum the two adjacent cells gives papillate out growth. The septum gets stretched and dissolves between two papillae forming conjugation passage. The protoplast of the cells develops into the isogametes. The cells are referred to as gametangia. After sometime one of the two gamete shows motility known as male gamete. The male gamete passes through conjugation tube and enters the female gametangia and fuses with female gamete to form zygote. The zygote then forms thick walled Zygospore. Plantae  22 Plantae  23 ii. Direct lateral conjugation: In species like Spirogyra jogensis, the upper cell acts as male gametangium and lower cell as female gametangium. The lower female cell get enlarged and forms barrel shaped structure while upper male cell remains smaller, elongated, cylindrical and pointed lower end. The protoplasm of both cells contract to become gametes. The upper cell forms male gamete and lower cell forms female gamete. The conjugation tubes are not formed in this process. The male gamete with pointed end directly pierces the septum and forms a hole in septum and passes through the hole into female gametangia where it fuses with female gamete to form zygote. The zygote after developing thick wall develops into zygospore. Plantae  24 [Parthenogenesis: Most of the times, in some species like Spirogyra sahnii and Spirogyra daedalea the protoplast of the conjugating cells form gametes. But due to some environmental, mechanical and physiological reasons these gametes fail to fuse and develop thick walls around them which are known as Azygospores or Parthenospores. Returning to favourable condition in next season, the parthenospores germinate directly into new filaments of Spirogyra without undergoing meiosis.] Plantae  25 Zygospore: Zygospore represents the only diploid stage in the lifecycle of spirogyra and it is yellowish brown ellipsoidal structure having diploid nucleus, oil drops, minute chloroplast and other cell organelles. It is covered by three layered wall: the outer exospore/exine, the middle mesospore/mesine and the innermost endospore/ intine. The zygospore remains dormant due to the presence of thick wall that can withstand long period of dry condition and dessication. Germination of zygospores: Zygospores are liberated after the decay of mother cell or mother filament and they remain at the bottom of water body. Before germination, the diploid nucleus divides meiotically and forms four haploid nuclei. Three of them degenerate and only one remains as functional nucleus. In favourable condition like rainy season, the zygospores start to germinate. At the time of germination, it absorbs water and swells up rupturing the outer two walls: exine and mesine. The intine along with functional nucleus comes out as single cell germinating tube which immediately divides into two celled structure called as germling. The basal cell forms the rhizoidal cell (holdfast) and the upper cell by repeated division and growth develops into new Spirogyra filament. As soon as the filaments detach from the holdfast (hapteron), it floats in water. Plantae  26 Plantae  27 Plantae  28 Why is the name Spirogyra given? It is due to the presence of ribbon shaped spirally coiled chloroplast. Write the functions of akinetes in Spirogyra. Akinetes are the thick walled resting spores that contain abundant reserve food material. On returning favourable conditions, it germinates into new filament of Spirogyra. Hence, it helps in asexual reproduction in Spirogyra. Why is the Spirogyra included in algae? Because it is primitive plant with thalloid body and presence of chloroplast. Define algae. Algae are the chlorophyll bearing thalloid plants which show autotrophic mode of nutrition. Thallus: Thallus is a plant body that is not differentiated into stem and leaves and lacks true roots and a vascular system. Algae, fungi, lichens, and some liverworts have typical thallus. Plantae  29 Gamete: A gamete is the male or female reproductive haploid cell produced by diploid germ cells in sexually reproducing organisms that contain half genetic material of the organism. Thallophytes / thallophyta: A plant that consists of a plant body that is not differentiated into stem and leaves and lacks true roots and a vascular system. Why are green algae called producer? Because they bear chlorophyll and synthesize their own food by photosynthesis. Parthenogenesis: Parthenogenesis is a form of asexual reproduction in which an unfertilized gamete develops into a new individual. Plantae  30 Vegetative reproduction: The reproduction occurring in plants in which multicellular structures become detached from the parent plant and develop into new individuals that are genetically identical to the parent plant is called vegetative reproduction. Asexual reproduction: The process of reproduction which occurs without the fertilization of gametes in which new individuals are genetically similar to parent plant is called asexual reproduction. Sexual reproduction: Reproduction in which offsprings are produced by the fusion of gametes, resulting in offspring genetically different from the parent or parents is called sexual reproduction. Plantae  31 Economic importance of algae: Beneficial aspects of algae Role as Primary Producers: algae are one of the most important producers of an ecosytem. Example: Spirogyra, marine algae, cyanobacteria, etc. Algae as Food: Algae contains several healthy elements including carbohydrates, fats, proteins, and vitamins A, B, C, and E. Commonly used species, are mostly marine, and they belong to Chlorophyceae [Ulva lactuca (Sea lettuce), Enteromorpha compressa, Caulerpa racimosa], Phaeophyceae (Laminaria saccharina, Alaria esculenta, A. fistulosa, Sargassum sp., Durvillea sp.), Rhodophyceae [Porphyra tenera, P. umbilicalis, P. laciniata, Rhodymenia palmata, (Dulse), Chondrus crispus (Irish moss), Gigartina stellata, Gracilaria sp.] and Cyanophyceae (Nostoc sp.). Algae as Fodder: Algae, especially seaweed, is used as a feed for a variety of farm animals. For example, Rhodymenia palmate, or so-called "Sheep’s weed," is used in order to feed livestock such as cattle and chickens. Laminaria, Sargassum, Macrocystis, etc are some other fooder algae. Plantae  32 Algae in Pisciculture: The industry involved in the breeding and farming of fish, also known as fish farming or pisciculture. Blue-green algae, green algae and microalgae are most common sources of food for fishes. Algae as fertilizer: Rice producers in India typically employ blue-green algae in order to fertilize their agricultural fields. Cyanophyceae (Nostoc, Anabaena, etc.) are used for their capacity to fix atmospheric nitrogen and thus enriching the soil. Algae in reclamation of Alkaline, ‘Usar’ Land: The ‘usar’ lands would be cultivable, if their pH could be lowered, and organic contents and the water holding capacity of the soil increased and blue-green algae is used for that. Algae in commercial Products: Many forms of marine algae, Phaeophyceae and Rhodophyceae, are highly valuable for certain commercial products, chiefly agar- agar, algin or alginic acid and carrageenin. Plantae  33 Algae in medicinal use: Alaria was once used for strengthening the stomach and restoring the appetite after sickness. Laminaria japonica and L. religiosa contain iodine and used in treatment of goiter. Algae as antibiotics: The antibacterial product chlorellin, obtained from Chlorella is well known.  Some algae are also used in sewage treatment and helps in preventing pollution. Harmful aspects of algae Harmful to living stock: Volvocales, Chlorococcales, Myxophyceae and several others occur in such a great abundance in water, that they colour the whole water either green or blue green and cause the death of fishes and livestock. Blocking of photosynthesis:The epiphytic algae which are found upon other plants and trees block photosynthesis and indirectly harm the trees and plants. Plantae  34 Parasitic algae: The well known disease ‘red rust of tea’ is not caused by any parasitic fungus but an algal form Cephaleuros virescens. This parasitic form attacks several other plants, like Mangifera, Rhododendron, coffea, etc. The heavy losses are caused to tea and coffee by this parasitic algal form. Contamination of water supply: Many blue-green, green and other algae contaminate the water of city reservoirs. This contamination develops a foul odour in the water and makes the water unhygienic. Fouling of ships: Some algae are attached to the ships, and this is called fouling of ship. The fouling retards the speed of the ship. To avoid this nuisance the ships are periodically dried up and painted with copper paint. Water blooms: An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. As algal blooms grow on water bodies, they deplete the oxygen in the water and block sunlight from reaching fish and plants. besides these, they also produce extremely dangerous toxins that can sicken or kill people and animals, create dead zones in the water, raise treatment costs for drinking water and harm industries that depend on clean water. Plantae  35 Very short answer questions: 1. Define algae. 2. Define gamete. 3. Define biodiversity. 4. Define pyrenoids. 5. What is oogamous? 6. Define taxonomy. 7. Define thallophytes. 8. What is azygospores? 9. Why green algae are called producer? 10. Why is Spirogyra included in algae? 11. Function of akinetes in algae. Plantae  36 Short answer questions: 1. Scalariform conjugation. 2. Lateral conjugation. 3. Asexual reproduction in Spirogyra. 4. Structure of Spirogyra. 5. Characteristics of red and brown algae. Also mention differences. Long answer question: Describe in detail about structure and reproduction of Spirogyra with necessary diagrams. Plantae  37 Plantae