Algae (DIVERSITY OF MICROBES)

Introduction, characteristics, classification,Thallus organisation,reproduction and its types, algal blooms, causes of algal blooms, biological and economic importance of algae.
B.SC 1st Year (BOTANY)

1. ALGAE B.SC 1 st Year

2. “Alga is a term that describes a large and incredibly diverse group of eukaryotic, photosynthetic lifeforms”. These organisms do not share a common ancestor and hence, are not related to each other (polyphyletic). It is an important group of Thallophyta (Gr. Thallos — a sprout; phyton — a plant), the primitive and simplest division of the plant kingdom. The orderly system­atic study of algae is called Phycology ( Gr.phycos — seaweeds; logos — study or discourse).

3. Characteristics of Algae Algae are photosynthetic organisms Algae can be either unicellular or multicellular organisms Algae lack a well-defined body, so, structures like roots, stems or leaves are absent Algae are found where there is adequate moisture. Reproduction in algae occurs in both asexual and sexual forms. Asexual reproduction occurs by spore formation. Algae are free-living, although some can form a symbiotic relationship with other organisms.

4. Thallus Organisation in Algae: The algal thalli are grouped into the following, based on their organization: A. Unicellular Algae: Unicellular forms of algae are also called acellular algae as they function as complete living organisms. Unicellular forms are common in all the groups of algae except Rhodophyceae, Phaeophyceae and Charophyceae. The unicells may be motile or non-motile. The motile unicells are either rhizopo­dial or flagellated.

5. The non-motile cells may be spiral filament as found in Spirulina ( Cyanophyceae ) The coccoid unicellular algae are the simplest forms of algae found in Cyanophyceae , Chlorophyceae etc., e.g., Gloeocapsa , Chlorella

6. B. Multicellular Algae: 1. Colonial: The colonial habit is achieved by loose aggregation of cells within a common mucilaginous investment. The cells of these usually remain connected with each other by cytoplasmic threads. a. Coenobium: When a colony has a defi­nite number of cells with a definite shape and arrangement, it is called coenobium.

7. Coenobium may be: i . Motile, or ii. Non- motile. i . In motile form, cells are flagellated and whole coenobium can move by the organised beating action of flagella, e.g., Volvox , Pandorina, Eudorina etc. In Volvox the coenobium is a hollow sphere. ii. In non-motile form, the cells are without flagella, thereby the coenobium is non- motile, e.g., Scenedesmus (Fig. 3.3C), Hydro- dictyon

8. Aggregated Form: Unlike coenobium the cells are aggregated irregularly showing a colonial mass of various size and shape. It is of three types: i . Palmelloid , ii. Dendroid, and iii. Rhizopodial.

9. i . Palmelloid : In this type the non- motile cells remain embedded in an amorphous gelatinous or mucilaginous matrix. Each and every cell of the organisation is independent and can perform all the functions as an individual. Chlamydomonas and Chromulina represent palmelloid as a temporary feature in their life cycle.

10. ii. Dendroid: In this type the number, shape and size of the cell is variable. They look like microscopic trees (e.g., Prasinocladus , Ecballocystis , Chrysodendron , . A mucilaginous thread is present at the base of each cell, thus showing a sort of polarity. iii. Rhizopodial: In this type the cells are united through rhizopodia. e.g., Chrysidias­trum

11. Filamentous: The filamentous plant body is formed through repeated cell divisions in a single plane and in a single direction, where the cells remain firmly attached to each other — end to end forming a chain or a thread. The fila­ments may be unbranched or branched. a. Unbranched Filament: It may be free-floating (e.g., Spirogyra,) or attached to the substratum (e.g., Ulothrix, Oedogonium , etc.). The free-floating unbranched filaments are not differentiated into basal and apical ends. All the cells in the filament are alike. But the Unbranched filaments that remain attached to the substratum are differentiated into base and apex.

12. b)Branched Filament: It is formed when a filament occasionally starts division in a second plane. It is of two types: i . Falsely branched, and ii. Truly branched. i . Falsely Branched: The trichomes of blue greens may break either due to death or decay of the intercalary cells. The broken ends emerge out of the mucilaginous sheath in the form of a branch. They do not arise as lateral out­growths, e.g., Scytonema

13. ii. Truly Branched: When a cell in the filament occasionally starts division in a second plane, true branch is formed. Thus true branches arise as lateral outgrowths of the main filament. True branches are of the following three types: Simple filament, Heterotrichous habit, and Pseudoparenchymatous habit.

14. Reproduction in Algae (A) Vegetative Reproduction: Vegetative reproduction in algae takes place by the following methods: ( i ) Fragmentation: The filamentous thallus breaks into fragments, and each fragment is capable of forming new thallus. Fragmentation can take place due to mechanical pressure, insect bite etc. The common examples are Ulothrix, Spirogyra, Oedogoniwn , Zygnema , Oscillatoria etc.

15. (ii) Fission: Fission is common in desmids, diatoms and other unicellular algae. The cell divides mitotically into two the cells are separated by septum formation (iii) Adventitious branches: Adventitious branches like protonema develop on rhizoids of Chara. On detachment they form new thalli. Similar adventitious structures are formed on thalli of Dictyota and Fucus. (iv) Hormogonia: In blue green algae like Nostoc , Cylindrospermum , the main filament breaks into small fragments of varying length called hormogonia. The hormogonia may be formed at the place of heterocyst in the filaments.

16. (B) Asexual Reproduction: Asexual reproduction takes place with the help of some spores and structures. Fertilization and fusion of nuclei does not take place. The reproduction takes place only by protoplasm of the cell. Different methods of asexual reproduction are: Aplanospores - are formed under unfavorable conditions. Aplanospores are non-motile structures, in which protoplasm gets surrounded by thin cell wall. The aplanospores on release form new plants, e.g., Ulothrix.

17. Hypnospores - are thick walled structures. These are formed during unfavorable conditions. Under prolonged unfavorable conditions, the protoplasm of hypnospores divides to make cysts. The cysts are capable of forming new thallus. e.g., Chlamydomonas nivalis. Tetra spores - are non-motile spores formed in some members of Rhodophyceae and Phaeophyceae . In Polysiphonia , tetra spores are formed in tetra sporangia by reduction division on special tetrasporophytic plants.

18. Sexual reproduction takes place by fusion of gametes of different sexuality. The gametes are formed in gametangia by simple mitotic division or by reduction division. The haploid gametes fertilize to make diploid zygote Sexual reproduction Hologamy : In hologamy the unicellular thallus of opposite strains (-) and (+) behaves as gametes directly. The thalli fuse to make diploid zygote e.g., Chlamydomonas. Autogamy: In autogamy two gametes of same mother cell fuse to form diploid zygote. Since both gametes are formed by same cell there is no genetic recombination e.g., diatoms.

19. ALGAL BLOOMS

20. An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems, and is often recognized by the discoloration in the water from their pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic, multicellular organisms like seaweed and microscopic, unicellular organisms like cyanobacteria. Algal bloom commonly refers to rapid growth of microscopic, unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.

21. Algal blooms are known to be mainly composed of bio-toxins and are characterized by a distinct discoloration of water due to a large number of pigmented algae cells. The colors range from green, red, brown, and yellow. The major types of algal blooms are cyanobacteria (blue-green algae) and red tides (red algal blooms).

22. Causes of Algal Bloom in Aquatic Ecosystems 1. Runoff of Nutrients An algal bloom is mostly caused by the presence of large amounts of nitrogen and phosphorus present in water. These nutrients are washed away from lands and farms that are heavily riddled with nitrogenous and phosphatic fertilizers. Rain acts as an agent by washing these leachable nutrients from the soil into water bodies such as rivers and streams, which eventually end up in large reservoirs such as lakes and oceans.

23. 2. High Temperatures The global world is facing the destruction of the  ozone layer   caused by global warming . This is one of the main reasons algal bloom is thriving at a fast rate. Conducive temperature is needed for certain bacteria to survive both in and out of water. 3. Presence of Dead Organic Matter Generally, there are many kinds of bacteria present in the atmosphere, as well as in water. They are all in search of suitable media for growth and nutrition. 4. Slow-moving Water Algal blooms need large masses of water, which are almost still to thrive. Most of the blue-green algae prefer stable water conditions with low flows, long retention times, light winds and minimal turbulence; other prefer mixing conditions and turbid environments. 

24. 5. Light When blue-green algae populations are exposed to long periods of high light intensity (photo-inhibition), these are diminished but have optimal growth when intermittently exposed to high light intensities. These conditions prevail under the water surface, where the light environment is fluctuating. 6. Turbidity The presence of suspended particles and organic matter (flocs) in the water column cause turbidity. High turbidity occurs when a lot of water is running through the system (high discharge after a rain event). Low turbidity occurs when there is only a small amount of suspended matter present in the water column.

25. Algae Constitute the Link of Food Chain  Algae is Useful in Fish Culture Algae is Used for Recreational Purposes Algae is Useful in Sewage Treatment Plants Algae and Water Supplies  Algae as the Origin of Petroleum and Gas Algae and Limestone Formation

26. Algae is Used in Space Research and Other Fundamental Studies Algae is Used as Food Algae is Used as Fodder Algae is Used as Fertilizers Algae is Used as Medicine Industrial Utilization of Algae