Algae PDF

ALGAE Introduction ► Algae are ubiquitous ► Live in aquatic environment ► It contains chlorophyll and are photosynthetic. ► Some are motile by flagella – single or pair of flagella may be present ► There are three types of flagella ► Whiplash – cylindrical and smooth ► Tin...

ALGAE Introduction ► Algae are ubiquitous ► Live in aquatic environment ► It contains chlorophyll and are photosynthetic. ► Some are motile by flagella – single or pair of flagella may be present ► There are three types of flagella ► Whiplash – cylindrical and smooth ► Tinsel - cylindrical and hair like appendage ► Ribbon - strap like ► A small red or orange spot on the anterior of motile algae is called eyespot. Classification ► The classification of algae is based on the ► The nature and properties of pigments ► Reserve food products ► Flagella ► Nature of flagella ► Morphological characteristics of cellwall ► Mode of reproduction Ultrastructure of algae Algae is eucaryotic and has thin, rigid cell wall. Some algae have an outer matrix lying outside the cell wall - flexible and gelatinous. The flagella are the locomotor organelles. The nucleus has a typical nuclear envelope with pore. The nucleus contains nucleolus, chromatin, and karyolymph. The chloroplasts have membrane-bound sacs called thylakoids that carry out the light reactions of photosynthesis. A dense proteinaceous area, the pyrenoid that is associated with synthesis and storage of starch may be present in the chloroplasts. Mitochondrial structure varies greatly in the algae. Some algae (euglenoids) have discoid cristae; some, lamellar cristae (green and red algae); and the remaining, (golden-brown and yellow-green, brown, and diatoms) have tubular cristae. Vegetative structures ► The body of a multicellular alga is called a thallus. ► Thalli of the larger multicellular algae, those commonly called seaweeds, consist of branched holdfasts (which anchor the alga to a rock), stem like and often hollow stipes, and leaflike blades. ► The cells covering the thallus can carry out photosyn thesis. ► The thallus lacks the conductive tissue (xylem and phloem) characteristic of vascular plants. ► Algae absorb nutrients from the water over their entire surface. ► The stipe is not lignified o r woody, so it does not offer the support of a plant's stem; instead, the surrounding water supports the algal thallus. ► Some algae are also buoyed by a floating, gas-filled bladder called a pneumatocyst. Nutrition ► Algae can be either autotrophic or heterotrophic. ► Most are photoautotrophic; ► They require only light and CO2 as their principal source of energy and carbon. ► Chemoheterotrophic algae require external organic compounds as carbon and energy sources. Reproduction Algae carry out both sexual and asexual reproduction Asexual reproduction (vegetative) Sexual reproduction ► Complex ► Fusion of gametes produce zygote ► Produce unicellular spores ► If the gametes are identical, the fusion process is isogamy ► Zoospores – motile flagellated ► If the gametes are differing in size, spores the fusion is heterogamous ► Aplanospores – non motile spores ► Oogonium-Ovum – large female non-motile egg cell ► May develop into zoospores ► Anteridium-Sperm – Male small actively motile gamete ► Fusion of oogonium and antheridium produce diploid zygote Chlorophyta (Green Algae) ► The Chlorophyta or green algae [Greek chloros, green] are an extremely varied division. ► They grow in fresh and salt water, in soil. ► The Chlorophyta have chlorophylls a and b along with specific carotenoids. ► They store carbohydrates as starch. ► Many have cell walls of cellulose. ► Exist as unicellular to colonial, filamentous, membranous or sheetlike, and tubular types. ► Reproduce asexual and sexually. Chlyamydomonas ► Chlamydomonas is a representative unicellular green alga. ► Individual cells have two flagella of equal length at the anterior end by which they move rapidly in water. ► Each cell has a single haploid nucleus, a large chloroplast, and a pyrenoid ► Stigma (eyespot) that aids the cell in phototactic responses. ► Two small contractile vacuoles at the base of the flagella function as osmoregulatory organelles that continuously remove water. ► Chlamydomonas reproduces asexually by producing zoospores through cell division. Lifecycle of Chylamydomonas The alga also reproduces sexually. When some products of cell division act as gametes and fuse to form a four flagellated diploid zygote. Zygote enters a resting phase losing its flagella. Meiosis occurs at the end of this resting phase and produces four haploid cells that give rise to adults. From organisms like Chlamydomonas, several distinct lines of evolutionary specialization have evolved in the green algae. Lifecycle of Chylamydomonas Chlorella ► Chlorella - nonmotile unicellular green algae. ► Chlorella is widespread both in fresh and salt water and also in soil. ► It only reproduces asexually and lacks flagella, eyespots, and contractile vacuoles ► The nucleus is very small. ► Chlorella is a spherical single-cell nonmotile organism, ► its diameter ranges from 2 to 10 μm. ► It has a high growth rate and relatively cheap growth medium for large-scale production in open raceway ponds and photobioreactors Volvox ► Volvox - Motile, colonial organisms ► A Volvox colony is a hollow sphere made up of a single layer of 500 to 60,000 individual cells. ► Each containing two flagella and resembling a Chlamydomonas cell. ► The flagella of all the cells beat in a coordinated way to rotate the colony in a clockwise direction as it moves through the water. ► Only a few cells are reproductive, and these are located at the posterior end of the colony. ► Some divide asexually and produce new colonies. ► Others produce gametes. ► After fertilization, the zygote divides to form a daughter colony. ► In both cases the daughter colonies stay within the parental colony until it ruptures. Prototheca moriformis ► A green alga, Prototheca moriformis, causes the disease protothecosis in humans and animals. ► Prototheca cells are fairly common in the soil, and it is from this site that most infections occur. ► Severe systemic infections, such as massive invasion of the bloodstream, have been reported in animals. ► More common in humans is the subcutaneous type of infection. ► It starts as a small lesion and spreads slowly through the lymph glands, covering large areas of the body. Euglenophyta (Euglenoids) ► The euglenoids share with the Chlorophyta and Charophyta ► Euglenoids contain chlorophylls a and b in their chloroplasts. ► The primary storage product is paramylon ► Paramylon is a polysaccharide composed of -1,3 linked glucose molecules, which is unique to euglenoids. ► They occur in fresh, brackish, and marine waters and on moist soils. ► They often form water blooms in ponds and cattle water tanks. ► The representative genus is Euglena. ► A typical Euglena cell is elongated and bounded by a plasma membrane. ► Inside the plasma membrane is a structure called the pellicle, which is articulated proteinaceous strips lying side by side. ► The pellicle is elastic enable turning and flexing of the cell, yet rigid enough to prevent excessive alterations in shape. ► The several chloroplasts contain chlorophylls a and b together with carotenoids. ► The large nucleus contains a prominent nucleolus. ► The stigma is located near an anterior reservoir. ► A large contractile vacuole near the reservoir continuously collects water from the cell and empties it into the reservoir to regulate the osmotic pressure within the organism. ► Two flagella arise from the base of the reservoir-one is active. ► Reproduction in euglenoids is by longitudinal mitotic cell division. Chrysophyta (Golden-Brown and Yellow-Green Algae; Diatoms) ► The division Chrysophyta is quite diversified with respect to pigment composition, cell wall, and type of flagellated cells. ► These algae are associated with the stramenopiles and have mitochondria with tubular cristae ► The division is divided into three major classes: ► golden-brown algae [Greek chrysos, gold], ► yellow-green ► algae, and diatoms. ► The photosynthetic pigments are chlorophylls a and c1/c2, and the carotenoid fucoxanthin. ► When fucoxanthin is the dominant pigment, the cells have a golden-brown color. ► The major carbohydrate reserve is chrysolaminarin (a polysaccharide -1,3 linked glucose residues). ► Some Chrysophyta lack cell walls; others have intricately patterned coverings external to the plasma membrane, such as scales walls, and plates. ► Diatoms have a distinctive two-piece wall of silica, called a frustule. ► Two anteriorly attached flagella of unequal length are common ► Some species have no flagella; others have either one flagellum or two that are of equal length. ► Most Chrysophyta are unicellular or colonial. ► Reproduction usually is asexual but occasionally sexual. ► Yellow-green and golden-brown algae live in fresh water. ► Blooms of some species produce unpleasant odors and tastes in drinking water. Diatoms (Greek diatomsos-cut in two) ► The diatoms are photosynthetic ► Circular or oblong cells with frustules composed of two halves or thecae that overlap like a petri dish ► The larger half is the epitheca ► The smaller half is the hypotheca. ► Diatoms grow in freshwater, salt water, and moist soil. ► Chlorophylls a and c as well as carotenoids are the pigments present. ► Facultative heterotrophs ► The vegetative cells of diatoms are diploid; exist as unicellular, colonial, or filamentous shapes; lack flagella; and have a single large nucleus and smaller plastids. ► In asexual reproduction - the organism divides, with each half then constructing a new theca within the old one. ► Because of asexual reproduction, diatoms get smaller with each reproductive cycle. ► When size reduce to 30% of their original size, sexual reproduction usually occurs. ► The diploid vegetative cells undergo meiosis to form gametes. ► Gametes then fuse to produce a zygote. ► The zygote develops into an auxospore, which increases in size again and forms a new wall. ► The mature auxospore divides mitotically to produce vegetative cells with normal frustules are composed of crystallized silica [Si(OH)4] ► They have distinctive, and often exceptionally beautiful, patterns that are different for each species. ► Frustule morphology is very useful in diatom identification. Asexual reproduction of diatoms Rhodophyta (Red Algae) ► The division Rhodophyta, the red algae [Greek rhodon, rose], includes most of the seaweeds. ► They are unicellular, filamentous and multicellular. ► Some red algae are up to 1 m long. ► The stored food is the carbohydrate called floridean starch (composed of -1,4 and -1,6 linked glucose residues). ► The red algae contain the red pigment phycoerythrin, one of the two types of phycobilins that they possess. ► The other accessory pigment is the blue pigment phycocyanin. ► The presence of these pigments, red algae can live at depths of 100 m or more. ► The wavelengths of light (green, violet, and blue) that penetrate these depths are not absorbed by chlorophyll a but instead by these phycobilins. ► The phycobilins, after absorbing the light energy, pass it on to chlorophyll a. ► The algae appear decidedly red when phycoerythrin predominates over the other pigments. ► When phycoerythrin undergoes photodestruction in bright light, other pigments predominate and the algae take on shades of blue, brown, and dark green. ► The cell walls of most red algae include a rigid inner part composed of microfibrils and a mucilaginous matrix. ► The matrix is composed of sulfated polymers of galactose called agar, funori, porphysan, and carrageenan. ► These four polymers give the red algae their flexible, slippery texture. ► Agar is used extensively in the laboratory as a culture medium component. ► Many red algae also deposit calcium carbonate in their cell walls and play an important role in building coral reefs. Cyanophyta (Cyanobacteria/ Blue Green Algae) ► The phylum consist of free living bacteria. ► Cyanobacteria are Gram-negative bacteria appear as unicellular or filamentous forms ► Cyanobacteria are prokaryotes ► They live in freshwater, marine water or a terrestrial environment. ► Cyanobacteria contains photosynthetic membrane called thylakoids ► It contains photosynthetic pigments and components of the electron transport chain. ► The photosynthetic pigments are chlorophylls and accessory pigments such as carotenoids and phycobilins. ► They exist as endosymbionts ► They carryout oxygenic photosynthesis. ► They fix atmospheric nitrogen Filamentous cyanobacteria ► Differentiate into several different cell types: ► vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions; ► akinetes – climate-resistant spores that may form when environmental conditions become harsh; and ► heterocysts – thick-walled cells contain the enzyme nitrogenase, vital for nitrogen fixation in an anaerobic environment due to its sensitivity to oxygen. ► Trichome- The simplest filamentous forms are made up of a long series of cells placed one upon the other. ► The trichome may be straight or spirally coiled ► Gas vacuoles are present in cyanobacteria, which gives buoyancy to the cell. ► Representative genera: Oscillatoria, Anabaena Reproduction ► Sexual reproduction is completely absent. ► Propagation takes place by ► simple division, ► by spores (akinetes, endospores, and exospores) or ► by fragmentation (fission). ► The multiplication of unicelluar and colonial forms is brought about mainly by simple cell division. Xanthophyta (Yellow green algae) ► Xanthophyta includes morethan 600 species. ► Lives in fresh water, marine and soil habitats. ► They form single celled flagellates to simple colonial and filamentous forms. ► They are photosynthetic-chlorophyll a and c, ß-carotene and carotenoid diadinoxanthin. ► The storage carbohydrate is chrysolaminarian. ► The cellwall is made up of cellulose and hemicellulose. ► Due to the presence of excess of carotinoids, the colour of chromatophores is yellow-green. ► Chlorophyll a and chlorophyll e are present. ► The chromatophores lack pyrenoids. ► Possesses two flagella of unequal length. Reproduction ► Asexual reproduction-Vegetative reproduction is by accidental breaking of the vegetative body. ► Produce zoospores and aplanospores. ► Sexual reproduction is isogamous and oogamous. Food nutrients Carbohydrates Proteins Fats Vitamins minerals