Current Affairs 11th Class

Protista (Protistos = Primary) includes unicellular eukaryotes and show the following characters : (1) Protists include solitary unicellular or colonial unicellular eukaryotic organisms which not form tissues. (2) The unicells may be naked or covered by cell wall, pellicle, cuticle or shell. (3) Simple multinucleate organisms or stages of life cycles occur in a number of groups. (4) The organisms possess double and porous nuclear membranes, mitochondria, golgibody, plastids (in many), vacuoles, lysosomes and ribosomes is also present. Centrosome is occur in many cases. (5) In many forms, plastids, (9+2 strand) flagella and other organelles are present. (6) Some protists possess contractile vacuole for regulation of their water content. (7) Their reproductive cycles typically include both asexual divisions of haploid forms and true sexual processes with karyogamy and meiosis. (8) The organisms move by flagella or by other means or are non-motile. (9) It may be photosynthetic, holotrophic, saprotrophic, parasitic and symbionts. Some have mixotrophic nutrition (holotrophic + saprobic). The photosynthetic, floating protists are collectively called phytoplankton. The free-floating, holozoic protozoans are collectively termed zooplankton. (10) Asexual reproduction is the most common method in protists. It involve binary fission (Paramecium, Euglena, Amoeba), multiple fission (Amoeba), plastotomy (Opalina), budding (Paracineta, Arcella) and spore formation (Slime moulds). (11) Sexual reproduction is believed to have originated in primitive protists. It involve isogamy (Monocystis), anisogamy (e.g., Ceratium) and oogamy (e.g., Plasmodium). (12) Unicellular protists have been broadly divided in to three major groups : Photosynthetic protists : e.g., Dinoflagellates, Diatoms, Euglenoids. Consumer protists : e.g., Slime moulds or Myxomycetes. Protozoan protists : e.g., Zooflagellata, Sarcodina, Sporozoa, Ciliata.

(1) Capsule : In a large number of bacteria, a slimy capsule is present outside the cell wall. It is composed of polysaccharides and the nitrogenous substances (amino acids) are also present in addition. This slime layer becomes thick, called capsule. The bacteria, which form a capsule, are called capsulated or virulent bacteria. The capsule is usually found in parasitic forms e.g., Bacillus anthracis, Diplococcus pneumoniae, Mycobacterium tuberculosis. It provides protection against phagocytosis and antibiotics. Capsule also protects the cell against dessication and viral attack. The capsulated bacteria are usually non-flagellated (i.e., Atrichous). Capsulated bacteria form smooth colonies and are known as S-type bacteria, which are highly virulent. Non-capsulated bacteria form rough colonies and are known as R–type bacteria. (2) Cell wall : All bacterial cells are covered by a strong, rigid cell wall. Therefore, they are classified under plants. Inner to the capsule cell wall is present. It is made up of polysaccharides, proteins and lipids. In the cell wall of bacteria there are two important sugar derivatives are found i.e., NAG and NAM (N-acetyl glucosamine and N-acetyl muramic acid) and besides L or D - alanine, D-glutamic acid and diaminopimelic acid are also found. One of the unique components of cell wall of bacteria is peptidoglycan or mucopeptide or murien (made of mucopolysaccharide + polypeptide). In peptidoglycan, NAG and NAM are joined by short peptide chains or cross bridges of amino acids. Outer layer of cell wall of Gram –ve bacteria is made up of lipopolysaccharides and cell wall of Gram +ve bacteria of teichoic acid. The cell wall of Gram positive bacteria is much thicker and contains less lipids as compared to that of Gram –ve bacteria. The enzyme lysozyme can dissolve the bacterial cell wall.     (3) Plasma membrane : Each bacterial cell has plasma membrane situated just internal to the cell wall. It is a thin, elastic and differentially or selectively permeable membrane. It is composed of large amounts of phospholipids, proteins and some amounts of polysaccharides but lacks sterols. It is characterised by possessing respiratory enzymes. Mesosome : On the plasma membrane generally at mid point, there are present some circular coiled bodies called mesosomes. So mesosomes are simply infoldings of plasma membrane. Mesosomes contain respiratory enzymes like oxidases and dehydrogenases and hence they help in respiration. Hence mesosomes are also known as "mitochondria of bacterial cell" or chondrioides. Mesosomes are more prominent in Gram +ve bacteria.
  • It receive DNA during conjugation and DNA replication enzyme.
  • Mesosome participate in the formation of septa during cell division.
(4) Cytoplasm and Cytoplasmic inclusions : The cytoplasm is a complex aqueous fluid or semifluid ground substance (matrix) consisting of carbohydrates, soluble proteins, enzymes, co-enzymes, vitamins, lipids, mineral salts and nucleic acids. The organic matter is in the colloidal state. The cytoplasm is granular due to presence of a large number of ribosomes. Ribosomes in bacteria are found in more...

(1) Simple staining : The coloration of bacteria by applying a single solution of stain to a fixed smear is termed simple staining. The cells usually stain uniformly. (2) Gram staining : This technique was introduced by Hans Christian Gram in 1884. It is a specific technique which is used to classify bacteria into two groups Gram +ve and Gram –ve. The bacteria are stained with weakly alkaline solution of crystal violet. The stained slide of bacteria is then treated with 0.5 percent iodine solution. This is followed by washing with water or acetone or 95% ethyl alcohol. The bacteria which retain the purple stain are called as Gram +ve. Those which become decolourised are called as Gram –ve. In general the wall of Gram +ve bacteria have simpler nature as compared to Gram –ve bacteria. E.coli is a Gram –ve bacterium. Gram negative bacterium can be seen with other stain safranin.     Gram positive bacteria : e.g., Pneumococcus, Streptococcus, Staphylococcus, Bacillus, Clostridium, Mycobacterium, Streptomyces. Gram negative bacteria : e.g., Salmonella, Pseudomonas, Escherichia, Haemophilus, Helicobacter, Vibrio, Rhizobium.   
Gram -Positive Gram - Negative
Cell wall thick (250 - 300 Å). Cell wall thin (100 - 150 Å)
Cell wall homogenous. Cell wall heterogenous.
Cell wall single layered. Cell wall 3-layered.
Cell wall more rigid. more...
These are free inhabitants of mud and water, and are chemoheterotrophic unicellular bacteria. These are spiral or helicoid in shape, covered by flexible cell wall. In spirochaetes flagella are absent but the cells are able to swim over solid surface by the fibrillae. Many diseases are caused by them as Treponema pallidum causes syphilis, Leptospira causes infectious jaundice and Borrelia causes relapsing fever. Besides some spirochaetes are found in teeth.

They are gram negative obligate pleomorphic but walled obligate intracellular parasites which are transmissible from arthropods. They are intermediate between true bacteria and viruses. Rickettsias require exogenous factors for growth. Cell wall is like typical bacterial wall. ATP synthesis is absent but ADP is exchanged with host cell ATP. They have genome and size (0.3-0.5\[\mu m\]) smaller than true bacteria but have a longer generation time. Internally the cells of rickettsias contain DNA as well as RNA in a ratio of 1 : 3 .5. The cell walls contain muramic acid and are sensitive to lysozyme. Flagella, pili and capsule are absent. Reproduction occurs by binary fission. The natural habitat of rickettsiae is in the cells of arthropod gut. They cause typhus group of fevers. Spread by droplet method, lice, ticks, fleas, etc. Human diseases
Disease Casual organism
Typhus fever Rickettsia prowazekii.
Rocky mountain spotted fever Rickettsia rickettsii
Q fever Coxiella burnetti

With respect to oxygen requirement and mode of cellular respiration, bacteria distinctly belong to two broad categories : (1) Aerobic respiration Obligate aerobes : These bacteria grow exclusively in presence of molecular oxygen and fail to survive in its absence, e.g., Bacillus subtilis, Azotobactor, Arthrobactor, Mycobacterium etc. Facultative anaerobes : The aerobic bacteria which can also survive in absence of oxygen, e.g., Aerobacter, Klebsiella, Pseudomonas, etc. (2) Anaerobic respiration Obligate anaerobes : These bacteria grow and multiply in the absence of free oxygen. They fail to survive under aerobic conditions, e.g., Clostridium botulinum. Facultative aerobes : The anaerobic bacteria which can also survive in presence of oxygen, e.g., Chlorobium limicola.

Vegetative reproduction (1) By budding : According to Bisset and Hale, reproduction by budding takes place in Bigidi bacterium bifidus. (2) By binary fission : This type of reproduction is most common in all kinds of bacteria. Under favourable conditions bacterial cell expands. Cytoplasm divides into two parts due to constriction and formation of a transverse septum in the centre of the cell. Later on, these two parts separate from each other and give rise to two cells. The speed of binary fission is decreased due to low temperature. Therefore, food is preserved in the cold storage. The cause of food spoilage and bacterial infection is the rapid multiplication of bacteria. Asexual reproduction (1) By endospores : Endospores are formed in all species of the genera Bacillus and Clostridium. In each cell only one endospore is formed. Endospore is highly resistant to very high and very low temperature. Endospore is found either in the centre or near the cell wall. Under unfavourable conditions cytoplasm shrinks and gets rounded and around it a hard protective three layer is formed. Each endospore may be either circular, ellipsoidal or semicircular. When favourable conditions come, outer layers rupture and active bacterial cell comes out. So this is a method of perennation (i.e., to tide over unfavourable condition) and some people say it “reproduction wihtout multiplication”. (2) By conidia : Some filamentous bacteria e.g., Streptomyces  reproduce by means of conidia. The conidia are spore like in structure and are formed in chains. Each conidium gives rise to a new bacterium. (3) By zoospores : In rare cases bacterial cell forms some motile spores which give rise to new cells. This process has been rarely seen. e.g., Rhizobium. Sexual reproduction (Genetic recombination) Sometimes it was believed that sexual reproduction does not take place in bacteria. Lederberg and Tatum (1946) proved that sexual reproduction takes place in bacteria. On the basis of this discovery they were awarded Nobel Prize. According to the present view, three types of sexual reproduction are found in bacteria : (1) Transformation : In this process one kind of bacterium is transformed into another kind. It takes place by transferring DNA from capsulated to non-capsulated bacterium. For the first time Griffith (1928) reported transformation in mice. Later on, Avery, Mcleod and McCarty (1944) studied transformation in Diplococcus pneumoniae. (2) Transduction : In this process DNA of a bacterial cell is transferred into another bacterial cell through bacteriophage – a kind of virus which is parasitic upon bacteria. Bacteriophage consists of DNA. It has been now accepted that DNA of a bacterial cell is transferred through bacteriophage to another bacterium. Transduction was first of all reported by N.D. Zinder and Lederberg (1952) in bacteria Salmonella typhimurium. (3) Conjugation : In this process genetic material from one strain of bacterium which is known as male is transferred into another strain of bacterium which is known as female. On the experimental basis it is believed that genetic material of male enters into female bacterium in the more...

On the basis of mode of nutrition, bacteria are grouped into two broad categories. First is autotrophic and second is heterotrophic bacteria.    Autotrophic bacteria : These bacteria are able to synthesize their own food from inorganic substances, as green plants do. Their carbon is derived from carbon dioxide. The hydrogen needed to reduce carbon to organic form comes from sources such as atmospheric \[{{H}_{2}},{{H}_{2}}S\] or \[N{{H}_{3}}.\]These are divided into two categories.   (1) Photoautotrophic bacteria : These bacteria are mostly anaerobic bacteria. They use sunlight as source of energy to synthesize food.  They possess a pigment called bacteriochlorophyll which is different from the chlorophyll pigment found in higher plants. This is known as anoxygenic photosynthesis. e.g., Green sulphur (Thiothrix) and purple sulphur (Chromatiun) bacteria. They can perform photosynthesis in far-red light. Rhodospirillum bacteria fixes \[C{{O}_{2}}\] into carbohydrate (Photoautotrophic).   Green sulphur bacteria : They are autotrophic. The hydrogen donor is \[{{H}_{2}}S\] and the pigment involved in the process is chlorobium chlorophyll (Bacterioviridin) e.g., Chlorobium.   \[6C{{O}_{2}}+12{{H}_{2}}S\underset{\text{Chlorobium}\,\,\text{chlorophyll}}{\mathop{\xrightarrow{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}}}\,{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+12S\].   Purple sulphur bacteria : They are also autotrophic. The hydrogen donor is thiosulphate and the pigment involved in photosynthesis is bacteriochlorophyll e.g., Chromatium.   \[6C{{O}_{2}}+15{{H}_{2}}O+3N{{a}_{2}}{{S}_{2}}{{O}_{3}}\underset{\text{Bacteriochlorophyll}}{\mathop{\xrightarrow{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}}}\,{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+6NaHS{{O}_{4}}.\]   Purple non-sulphur bacteria : They are heterotrophic utilizing succinate or malate or alcohol. e.g., Rhodospirillum, Rhodopseudomonas.   \[6C{{O}_{2}}+12C{{H}_{3}}CHOHC{{H}_{3}}\xrightarrow{{}}{{C}_{6}}{{H}_{12}}{{O}_{6}}+12C{{H}_{3}}COC{{H}_{3}}+6{{H}_{2}}O.\]   (2) Chemoautotrophic bacteria : Some bacteria manufacture organic matter form inorganic raw materials (such as carbon dioxide) and utilize energy liberated by oxidation of inorganic substances present in the external medium such as ammonia, ferrous ion, nitrates, nitrites, molecular hydrogen, etc. The energy liberated from exergonic chemical reactions is trapped in the ATP molecules which is used in carbon assimilation to synthesize organic matter.   Sulphur bacteria : These bacteria derive energy by oxidizing hydrogen sulphide or molecular sulphur. Beggiatoa, a colourless sulphur bacterium oxidises hydrogen sulphide \[({{H}_{2}}S)\] to water and sulphur. The energy released is used up and the sulphur granules are deposited inside or outside the body of bacterial cell.   \[2{{H}_{2}}S+{{O}_{2}}\xrightarrow{{}}2{{H}_{2}}O+2S+\text{Energy}\].   Iron bacteria : Some chemoautotrophic bacteria such as Gallionella, Sphaerotilus, Ferrobacillus, etc, inhabit the environments where irons to ferric form. The Ferric ions are deposited in the form of soluble ferric hydroxide and the energy released during the conversion is used in the production of carbohydrates.   \[4FeC{{O}_{3}}+{{O}_{2}}+6{{H}_{2}}O\xrightarrow{{}}4Fe{{(OH)}_{3}}+4C{{O}_{2}}+\text{Energy}\,\text{(81}\,\text{k}\text{.cal)}\]   Hydrogen bacteria : These bacteria utilize free molecular hydrogen and oxidize to hydrogen into water with the help of either oxygen or oxidize salts e.g., Hydrogenomonas. \[2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O+\text{Energy}\] (56 kcal). Amonifying bacteria : They oxidise protein and amino acid into NH3 (ammonia). e.g., Proteus vulgaris, Bacillus mycoids. Nitrifying bacteria : They oxidise ammonia to nitrites and then into nitrates.   \[N{{H}_{3}}+{{O}_{2}}\xrightarrow{\text{Nitrosomonas}}N{{O}_{2}}+{{H}_{2}}O+\text{Energy}\] and    \[2N{{O}_{2}}+{{O}_{2}}\xrightarrow{\text{Nitrobacter}}2N{{O}_{3}}+\text{Energy}\].   Denitrifying bacteria : They change nitrogen compound into molecular nitrogen. So that they reduce fertility of soil e.g., Micrococcus denitrificans, Pseudomonas denitrificans.   Methane bacteria : The bacterium Methanomonas utilizes methane as source of carbon and energy.   \[C{{H}_{4}}+2{{O}_{2}}\xrightarrow{{}}C{{O}_{2}}+2{{H}_{2}}O+\text{Energy}\].   Methane producing bacteria : These are spherical or rod shaped bacteria which produce methane \[(C{{H}_{4}})\] from hydrogen gas more...

(1) Diseases in human beings : Mycoplamsa hominis causes pleuropneumonia, inflammation of genitals and endocarditis, etc. Mycoplasma pneumoniae causes primary a typical pneumonia (PAP), haemorrhagic laryngitis, etc. Mycoplasma fermentatus and M. hominis cause infertility in man, otitis media (inflamation of middle ear). (2) Diseases in animals : Mycoplasma mycoides causes pneumonia in cattle. Mycoplasma bovigenitalum, causes inflamination of genitals in animals. Mycoplamsa agalactia causes agalactia of sheep and goat. (3) Diseases in plants : Common mycoplasmal diseases of plants are: Bunchy top of papaya, witches' broom of legumes, yellow dwarf of tobacco, stripe disease of sugarcane, little leaf of brinjal, clover phylloidy, big bud of tomato etc. The new name of cyanobacteria has been given to myxophyceae or cyanophyceae. Cyanobacteria form a group of ancient Gram negative, photosynthetic prokaryotes. Many botanists prefer to call them blue-green algae. They have survived successfully for about 3 billion years. They may cause water blooms. Cyanobacteria are predominantly fresh water forms, a few are marine. They impart unpleasant taste and smell to the water. One species of cyanobacteria containing red pigment (Trichodesmium erythraeum) flourishes in red sea and is responsible for the red colour of its water. A few species grow in hot water springs having a temperature range of 70°–75°C (e.g., Phormidium, Hastigocladus) and other grow at very low temperature in the polar regions (e.g., Nostoc, Schizothrix, Microcoleus etc.).Some grow in the soil and help in fixation of nitrogen and utilize it in metabolism. Nostoc colony is found into the thallus of Anthoceros. Colonies of Nostoc and Anabaena grow in paddy fields. Anabaena cycadeae is found in coralloid roots of cycads.  Characteristics of Cyanobacteria (1) They have prokaryotic type of cells. (2) Cells do not have any organised nucleus. The nucleolus is absent and the nucleoid is not to be bounded by a nuclear membrane. The type of nucleus called incipient nucleus. (3) The photosynthetic pigments present in the cell are – chlorophyll a, b carotene, myxoxanthophyll, myxoxanthin, C-phycocyanin and C-phycoerythrin. The C-phycocyanin is blue and C-phycoerythrin is red in colour. If C-phycocyanin is more as compared to C-phycoerythrin, it gives characteristic blue- green colour to the algae. (4) The photosynthetic pigment are present in lamellae, called thylakoids. (5) The presence of chlorophyll–a, cyanobacteria synthesis their own food from carbon dioxide and water in the presence of sunlight. Certain cyanobacteria fix atmospheric nitrogen in the presence of oxygen. (6) In cyanobacteria food is stored as cyanophycean starch or a–granules.  (7) Some members possesses simple unbranched filament with heterocyst like Nostoc, Anabaena, Aulosira, Cylindrospermum etc. (8) Some members possesses simple unbranched filamentous forms without heterocysts and akinetes, e.g., Arthospira, Oscillatoria, Spirulina, Phormidium, Lyngbya, Symploca, Microcoleus, Schizothrix etc. (9) Cyanobacteria reproduce asexually by fission and fragmentation. Unicellular forms multiply by binary fission. Sexual reproduction is totally absent. (10) Flagella are completely absent but the movement occurs in some genera by special gliding motion. Such movements are connected with the secretion of mucilage. The genus Oscillatoria exhibits pendulum more...

Bacteria are our ‘friends and foes’ as they have both useful and harmful activities. Useful activities (1) In agriculture or In soil fertility : Some bacteria increase soil fertility. Nitrogen is essential for all plants. Nitrogen occupies 80% of the atmosphere. The plants take nitrogen in the form of nitrates. In soil, nitrates are formed by three processes : By nitrogen fixing bacteria : Bacteria are found in soil either free e.g., Azotobacter and Clostridium or in root nodules of leguminous plants e.g., Rhizobium leguminosarum. These bacteria are capable of converting atmospheric free nitrogen into nitrogenous compounds. Nitrifying bacteria : These bacteria convert nitrogen of ammonia into nitrite (NO2) e.g., nitrosomonas and convert nitrite compounds into nitrates e.g., nitrobacter. Decay of dead plants and animals : Some bacteria attack on dead bodies of plants and animals and convert their complex compounds into simpler substances e.g., carbon dioxide (CO2), water (H2O), nitrate (NO3), sulphate (SO4) etc. (2) In dairy : Bacterium lactici acidi and B. acidi lactici are found in milk. These bacteria ferment lactose sugar found in milk to form lactic acid by which milk becomes sour. Lactic acid bacteria bring together droplets of casein a protein found in milk and help in the formation of curd. On freezing of casein of milk protein it is fermented by bacteria with the result that foamy and soft substance, different in taste is formed. (3) In industries : From industrial point of view bacteria are most important. Some of the uses of bacteria in industries are as follows : Vinegar industry : Vinegar is manufactured from sugar solution in the presence of Acetobacter aceti. Alcohol and acetone : Clostridium acetobutylicum takes part in the manufacture of butyl alcohol and acetone. Fibre retting : By this process fibres of jute, hemp and flax are prepared. In the preparation of flax, hemp and jute the retting of stems of Linum usitatissimum (Flax = Hindi Sunn), Cannabis sativa (Hemp = Hindi Patson) and Corchorus capsularis (Jute) respectively is done. Tobacco industry : Bacillus megatherium is used for its fermentative capacity for developing flavour and taste in tobacco leaves. Tea industry : By fermentative action of Mycococcus condisans curing of tea leaves is done. By this process special taste is developed in the tea leaves. Tanning of leather : Some bacteria decompose fats which are found in skin of animal with the result that skin and hairs are separated from each other and this leather becomes ready for use. Disposal of sewage : Some bacteria convert organic faecal substances e.g., cow dung, decaying leaves of plants, etc. into manure and humus. Human symbionts : Escherichia coli inhabitats the large intestine of man and other animals and it synthesizes vitamins. (4) In medicines : Some of the antibiotics are manufactured by bacterial actions e.g., Bacillus brevis – antibiotic thyrothricin and B. subtilis – antibiotic subtelin. Vitamin B2 is manufactured by fermentative action of Clostridium acetobutylicum. Antibiotics : These are the chemical substances produces by living microorganisms capable more...



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