Introduction to Cyanobacteria, Biology tutorial

Introduction to Cyanobacteria:

Cyanobacteria are true bacteria (singular, bacterium). They are prokaryotes and don't have the true nucleue or memberrane-bound organelles like mitochondria or plastids. Similar to other prokaryotes they possess 70S ribosomes. Though there are other bacteria that can photosynthesise, cyanobacteria are exclusive in having pigment chlorophyll a. This pigment is present in algae and plants and is liable for evolution of oxygen in photosynthesis. Photosynthetic bacteria have the different type of pigment, bacteriochlorophyll that doesn't allow oxygen evolution in bacterial photosynthesis. Term "cyan" in cyanobacteria signifies to color, blue. Cyanobacteria have definite accessory pigment like phycocyanin and phycoerythrin. The existence of the pigments and chlorophyll together inform characteristic color to the organisms. It is for this reason that cyanobacteria are generally called as blue-green algae. Similar to true algae they also evolve oxygen in photosynthesis and frequently dwell in habitats where algae happen, in fresh, marine and brackish water bodies and on moist soil surface. Though, true algae are eukaryotic and two are not immediately associated.

As affinities of cyanobacteria are with other bacteria we should briefly study the organisms for more complete picture of position of cyanobacteria in world of living things. Approx 4,000 species of bacteria have been explained so far. These comprise about 1,700 species of cyanobacteria. Though small in number of species, bacteria are most plentiful of all organisms. They are also ancient. Bacteria are known in fossil record as far back as 3.5 billion years ago. Bacteria are morphyologically and anatomically simplest of organisms. So far, metabolically they are extremely varied. Several bacteria are recognized not by morphology of individuals but by their characteristics in culture.

Bacteria are extremely small, ranging in size between 1 to few ym. Many strange discovery was prepared in 1993 of bacterium living in intestinal tracts of surgeonfish which is 600 um in length. Bacteria differ in shape. Few are rod shaped, others spherical and yet others spiral or even comma-shaped. Minute as they are, bacteria are liable for activities which strongly affect the lives. Several are agents of severe diseases of human beings, animals and plants. Other ferment food and are therefore helpful in making differed products like curd or idli and several industrial chemicals. Few are ources of life-saving antibiotics. Bergey's Manual of Determinative Bacteriaiology is standard reference for categorization of bacteria. As adequate information is not accessible to place all bacteria into hierarchical system of categorization, Bergey's Manual identifies 19 major groups like spirochaetes, Gram-positive cocci, gliding bacteria, mycoplasma and actinomycetes. Cyanobacteria is comprised in one such group. Categorization of bacteria is the active area of research. In current years molecular biologists have examined structure of ribosoma RNA (Rrna) and sequence of rRNA nucleotides in bacteria and other organisms. This analysis has discovered fundamental differences among 2 main bacteria groups, archaebacteria and eubacteria.

Differences have been noted in chemical composition of cell membranes of two bacterial groups and eukaryotes. American scientist Carl Woese thinks that differences between archaebacteria and eubacteria are as essential as between the groups and eukaryotes. Therefore, life on the planet is thought to include 3 ancient and main lineages. Syanobacteria are members of true bacterial lineage. Archaebacteria comprise members which live in most strange environments like very hot and acidic pools or in waters with very high salt contents. Few members of the group live in deep sea vents many kilometers below ocean surface. Bacteria that create methane gas are known as methanogens.

Fungi:

Fungi are a huge grouping of 95,000 organisms. All of them entirely lack photosynthesis. They are heterotrophs which depend on other living or dead matter for nutrition. As parasites several are severe pathogens on other plants. As saprotrophs they together with bacteria, degrade dead organisms and discharge organic chemicals and nutrient elements so they can be recycled.

Approx 13,500 fungi species have the exclusive relation with few algal partners resulting in symbiotic structures called lichens. Majority of higher plants have mycorhizal association where few species of fungi live as symbionts inside or around roots. Fungi are eukaryotes. They are the ancient group. Fossil proof illustrates that all main fungal groups known today had developed by the end of Paleozoic era, roughly 280 million years ago. At the time when all living things were clustered under either animal or plant kingdom fungi were considered to be plants. Fungi are now place in kingdom, fungi (MYceate). Members of the kingdom do not have plactids. They are generally filamentous in construction. Except in one group the walls comprise chitin rather than cellulose. Fungi don't store starch as plants stores. The filamentous structures which make up fungi body are called as mycelia (singular, mycelium). Though filaments are microscopic, wide growth of fungal mycelium can be seen as fuzzy mass. Reproductive bodies of some fungi like mushrooms are composed of well stated aggregates of mycelia. The characteristics of complex organs and tissues of plants are never found among fungi reproduce by spores. In spite of several characteristics which appear to unite members of fungi kingdom fungi are a teterogenous group. Fungi are categorized into seven divisions.

The slime molds (myxomycota) aren't true fungi. They seem to have developed independently from few protpzoan ancestors. In the vegetative stage slime molds lack cell wall. Wall-less cells aggregate to form amocha-like mass which moves around and engulfs bacteria and other organio matter. 2 groups of slime molds are known: plasmodial slime molds with the multinucleate true plasmodium and cellar slime mold. Vegetative body of cellular slime molds is pseudoplasmodium where aggregating cells keep their cell membranes and uniqueness. Slime molds make motile spores. Omycetes or water molds vary from other fungi by possession of cellulose in cell walls. Fungal body is diploid rather than haploid as in true fungi. These are other characteristics of reproduction and metabolism recommends that oomycetes are not connected to other fungal groups. They might have developed from few green or yellow green algal ancestors after losing plastids.

Chytrids are simple water molds which live as parasites or saprotrophs. As they have mostile spores they are frequently categorized with oomycetes. Though, chytrids possess chitin and the filaments are haploid. They are perhaps distantly associated to bread molds and other true fungi. Zygomycetes (bread molds), ascomycetes (sea fungi) and basidiomycete (club fungi) are evolutionarily associated. None of them produce motile cells at any phase of the life cycle. Fungal filaments don't possess septa (cross walls) in zygomycetes. Mycelium is septate in other two groups. Fungi reproduce asexually and sexually. In sexual reproduction ascomycetes make characteristic structures called as asci (singular, ascus). Basidia are corresponding structures among basidiomycetes. The fungi species can be allotted to either one of the groups only when they make ascus basidium. The huge number of fungi, approx 22,000 species, reproduces only asexually, or sexual cycle hasn't been observed yet. As their life cycle is imperfectly known and they can't be allotted with confidence to either one of groups they are called as fungi Imperfecti. Divisional name Deuteromycota is frequently for the group of imperect fungi. When sexual life cycle is called as species is automatically allotted to either ascomycetes or basidiomycetes.

Lichens are exclusive organisms comprising of fungal and algal partner. Less than 40 algal or cyanobacteria species enter into association. Yet there are roughly 13.500 species of lichens. Characteristic form of every lichen seems to be found out by fungal component. Approx 2% of species have either basidiomycete or imperfect fungus as fungal partner. Remaining 98% of lichens are made up of ascomycete species. Lichens are not thought to be separate taxonomic category. Rather, they are treated as members of respective fungal divisions, and name of lichen refers to name of the fungal partner.

Algae:

Algae are eukaryotes. Many algae live in marine and fresh water habitats. In five-kingdom system algae are comprised in kingdom Protista. This is plainly artificial grouping, for some of green algae are more associated to and cryptomonads are possibly protozoans which obtained plastids through endosymbiosis heterotrophs. There are approx 24,000 species of algae described so far. Algae as a group are autotrophic, synthesizing food by photosynthesis. In photosynthesis they develop oxygen as plants do. Plants and algae vary in several respects. One main difference between groups concerns way in which reproductive structures are organized. Reproductive structures of algae aren't covered by protective sterile tissue. Instead all cells are converted in spores or gemetes. In plants sterile Jacket is present as the necessary part of reproductive structures. Phycologists (also called as algalogists), use as diversity of characters to assist delimits different algal groups. These are given below.

Pigments in plastids: Presence of various chlorophyll pigments and photosynthetic accessory pigments.

Food reserves: Various algal groups accumulate food as oils, starch, etc.

Cell wall: Cell wall may comprise cellulose or other polysaccharides. Few algae contain naked cells; cell walls possibly incrusted with silica, calcium carbonate and scaly structures.

Flagella: Number and types of flagella and location of flagella are useful Whiplash flagella have even surface while tinsel flagella have fine hairs flagella are entirely lacking in red algae.

Cell Division: Four various types of cytokinesis are known in algal groups:  furrowing cell division by phycoplast and 2 types of phragmoplasts.

  • Choloroplast organization: Ultra structure of chloroplast exposes differences in organization of photosynthetic and surrounding membranes.
  • Morphological organization: Algal thallus possibly unicellular, motile, sessile, colonial flamentous, branched, coenocytic or multi-cellular with parenchymatous organization

Life cycle: Morphology of haphoid and diploid generations also assists in acknowledgment of different algal groups.

Many algae groups treated as division are at times collectively called as chromophyes. This group includes cryptomonads (cyptophyta), dinoflallates (dinophyta), yellow-green algae (Xanthophyta),brown algae (phaeophyta) and diatoms and golden-brown algae (chrysophyceae). Unlike red algae all chromophytes have motile cells at some stage of the life cycles. Dinoflagellates don't have histones which are feature of other eukaryotes. Chromosomes remains permanently condensed. These and other characteristic recommends that dinoflagellates might represent the independent line of evolution. Green algae (chlorophyceae) and euglenoids (Euglenophyceae) have both chlorophyll a and b. In this respect they look like higher plants. Though, euglenoids are perhaps more associated to protozoans. Green algae comprise the significant subgroup, charophytes that is considered to be ancestors of true plants. Plastids of green algae might have originated from cells like Prochloron by endosymbiosis. These prokaryotes are unusual in having both chlorophylls a and b. Several green algae comprising charophytes and red algae are known from fossils dated to be million years old.

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