Today we will discuss about the Bacteria
Definition of Bacteria: They are prokaryotic, achlorophyllous and single cellular simple organisms and can survive in extreme conditions eg. Rhizobium, Pseudomonas, Clostridium
- They are prokaryotic (true nucleus is absent)
- They are achlorophyllous
- Mesosome is present
- Cell wall is present
- It can withstand very high temperature
- Reproduction mainly asexual or vegetative
- Rhizobium, Pseudomonas, Clostridium, etc.
- Define bacteria (1)
Ans. Bacteria are defined as one type of aerobic or anaerobic, smallest and simplest unicellular microscopic autoreplicating prokaryotic organism found to occur in air, in water, in living organisms etc. familiarly called as microbes.
- Discuss the general structure of bacteria. (6)
Structure of the Bacteria:
Bacteria are single cell organisms. Their cells are Prokaryotic, meaning that they lack a membrane-bound nucleus and many of the cell parts of Eukaryotes (Cells that have a nucleus and many membrane-bound organelles). Some of their parts are:
a) Capsule – Outermost protective layer usually found on disease causing bacteria. Most bacteria contain some sort of a polysaccharide layer outside the cell wall or outer membrane. In a general sense, this layer is called capsule. A true capsule is a discrete detectable layer of polysaccharides deposited outside the cell wall. A less discrete structure or matrix which embeds the cells is called slime layer.
b) Cell Wall – It gives bacteria their shape and additional durability.
The cell wall of a bacterium is an essential structure that protects the delicate cell protoplast from osmotic lysis. The cell wall of Bacteria consists of a polymer of disaccharides cross-linked by short chains of amino acids (peptides). This molecule is a type of peptidoglycan called murein. In the Gram-positive bacteria the cell wall is thick (15-80 nanometers), consisting of several layers of peptidoglycan complexed with molecules called teichoic acids . In the Gram-negative bacteria the cell wall is relatively thin (10 nanometers) and is composed of a single layer of
peptidoglycan surrounded by a membranous structure called the outer membrane. Murein is a substance unique in nature to bacterial cell walls. Also, the outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS or endotoxin), which is toxic to animals.
c) Cell Membrane (plasma membrane) – Permeable membrane that has a variety of functions, including bringing chemicals and nutrients in and out of the cell.
The membranes of Bacteria are structurally similar to the cell membranes of eukaryotes, except that bacterial membranes consist of saturated or monounsaturated fatty acids (never polyunsaturated fatty acids) and do not normally contain sterols. The plasma membrane is an exceptionally dynamic structure in bacteria which mediates permeability, transport, secretion and energy generation. In terms of pathogenesis of a bacterium, it is absolutely dependent upon the integrity and function of its plasma membrane. The membrane might be responsible for secretion of toxins, resistance to antimicrobial agents, tactic responses or sensing other environmental signals to turn on or off genes for virulence.
d) Cytoplasm – Gel-like material inside cell that protects cell parts and helps to move materials around the cell.e. Ribosomes – Make various proteins.
e) DNA – Genetic material that controls the functions of the cell.
f) Flagella – A tail used for moving around. Flagella are filamentous protein structures attached to the cell surface that provide swimming movement for most motile bacterial cells. The diameter of a bacterial flagellum is about 20 nanometers, well below the resolving power of the light microscope. The flagellar filament is rotated by a motor apparatus in the plasma membrane allowing the cell to swim in fluid environments. Bacterial flagella are powered by proton motive force (chemiosmotic potential) established on the bacterial membrane.
g) Pilus – Small hairs used for sticking to surfaces or each other. Also used in reproduction.
- Justify: Bacterial cell resembles plant cell. (2)
a) Like plants the cell wall of bacteria is composed of lipid, protein and polysaccharides.
b) Like plants bacteria can also synthesize vitamins.
c) Like plants bacteria also reproduce by means of vegetative reproduction.
d) There is presence of bacteriochlorophyll in the body of some bacteria.4. Write a short note on Mesosome. (4)
Definition: The vesicular, convoluted or multilaminated structures formed as invaginations of the plasma membrane in a prokaryotic cell are called mesosomes or chondroids.
a) They are more prominent in Gram positive bacteria.
b) They are the principal sites of respiratory enzymes in bacteria and are analogous to the mitochondria of eukaryotes, and hence often considered as incipient mitochondria.
a) Mesosomes are often seen in relation to the nuclear body and the site of synthesis of cross wall septa, suggesting that they coordinate nuclear and cytoplasmic division during binary fission.
b) It forms the replica of DNA.
- What do you mean by: (5×2)
b) Volutin granules
e) Generation time
a) Bacteriocins: These are a group of highly specific antibiotic like substances produced by certain strains of bacteria, which are active against other strains of the same or different species.
I) Bacteriocins are proteins but some may have associated lipopolysaccharides.
II) They resemble phages in many aspects.
Examples: I) Colicins from E.coli and II) Pyocins from Pseudomonas pyocyanea.
b) Volutin granules: These are highly refractive, strongly basophilic bodies consisting of polymetaphosphate.
Characteristic features are:
I) They appear reddish when stained with polychrome methylene blue (metachromasia)
II) Volutin granules are characteristically present in diptheria bacilli.
III) They have been considered to represent a reserve of energy and phosphate for cell metabolism.
Other names: Metachromatic or Babes-Ernst granules.
c) Ammonification: It is the process of release of ammonia and its formation of ammonium ions.
Examples: Bacillus mycoides and Bacillus ramosus.
d) Pleomorphism: It is the property by which the same species or strain of micro-organism exists in different morphological forms. Pleomorphism is often due to defective cell wall synthesis.
Examples: Mycobacteria and Azotobacters, they change their forms from rod to oval or irregularly branched bodies.
- e) Generation time or population doubling time: It is the interval of time between cell divisions, or time required for the bacterium to double under optimum condition. Example: Generation time for most medically important bacteria (eg. E. coli) is about 20 minutes, whereas in Mycobacterium leprae it is as long as 24 days.
- Name the bacteria causing: (10x 1)
b. Gas gangrene
h. Enteric fever (typhoid)
a) Corynebacterium diptheriae
b) Clostridium perfringens
c) Mycobacterium tuberculosis
d) Bacillus anthracis
e) Clostridium tetani
f) Treponema pallidum
g) Vibrio cholerae
h) Salmonella typhi
i) Mycobacterium leprae
j) Yersinia pestis (Previously called Pasteurella pestis)
7. a)Mention three main methods of Bacterial reproduction. (3)
b) What is the most common mode of reproduction? ( 1)
a) Modes of reproduction:
I) Vegetative Reproduction: A) Budding and B) Binary fission
II) Asexual reproduction: By spore formation
III) Sexual reproduction: A) Conjugation, B) Transformation, C) Transduction
- a) Who devised the Gram staining technique? (1)
b) What is the principle of Gram staining? (2)
c) What type of stain is it? (1)
d) Name a few Gram positive and Gram negative bacteria (2)
e) Name the staining technique implied for Mycobacterium tuberculosis (1)
a) Christian Gram devised the Gram staining technique.
b) Principle: I) The Gram positive cells have a more acidic protoplasm, which may account for retaining the basic primary dye more strongly than the Gram negative bacteria.
The Gram reaction may be related to be permeability of the bacterial cell wall and cytoplasmic membrane to the dye-iodine complex, the Gram negative, but not the Gram positive cells permitting the outflow of the complex during decolourisation. Gram positive bacteria appears violet whereas Gram negative bacteria appears red after Gram Staining.
c) It is a differential stain as it imparts different colours to different bacteria or bacterial structures.
d) Gram positive bacteria are:
I) Staphylococcus aureus
II) Streptococcus pyogenes
III) Clostridium tetani
IV) Bacillus anthracis
Gram negative bacteria are:
I) Salmonella typhi
II) Escherichia coli
III) Vibrio cholerae
IV) Neisseria gonorrhoeae
e) Ziehl-Neelsen technique or Acid fast staining.
a) What are Capnophilic Bacteria? Give one example. (2)
b) What is the thermal death point? (1)
Ans. a) Bacteria which require high amount of carbondioxide (5-10%) for growth, especially on fresh isolation, are called Capnophilic bacteria.
Example: Brucella abortus
b) The lowest temperature that kills a bacterium under standard conditions in a given time is known as thermal death point.
10. Write a short note on flagella. Name a Bacteria, which is motile though it lacks
Ans. Definition – These are unbranched, long, sinuous filaments present in most of the motile bacteria.
Parts: I) Filaments, II) Hook, III) Basal body
Function: It is responsible for the motility of the bacteria.
Composition: It is made up of a protein called flagellin.
Spirochete lacks flagella though it is motile due to the presence of endoflagella.
Give examples: (3×1)
a) Bacteria devoid of cell wall.
b) First pathogenic bacteria to be observed under microscope.
c) First Bacillus to be isolated in pure cultures.
a) Mycoplasma (Mycoplasma pneumoniae)
b) Bacillus anthracis
c) Bacillus anthracis
- What is pili?
Ans. Pili are minute projections helping in conjugation.
- What are fimbriae?
Ans. Fimbriae are small projections helping in attachment of cells.
- What is the function of mesosomes?
- What is episome?
Ans. Accessory DNA in a bacterial cell, which remains attached to the nucleoid.
- What is plasmid?
Ans. A circular, autonomous, self-replicating extranuclear DNA of a bacterial cell helping in the transfer of genetic information is known as plasmid.
- What is periplasm?
Ans. A jelly like homogeneous layer formed between the cell wall and plasma membrane of bacteria.
- What are the bacterial photosynthetic pigments?
Ans. Chlorobium chlorophyll and bacteriochlorophyll
- What are the two components of bacterial cell wall?
Ans. Glucosamine and muramic acid.
- What are the different parts of bacterial flagella?
Ans. Bacterial flagella have a basal body composed of two pairs of rings, a short stalk and long shaft composed of flagellin.
- What are spinae?
Ans. Small tubular bodies attached externally to the cell wall of gram positive bacteria helping it to adjust to the external environment is called spinae.
- Name a toxin-producing bacteria.
Ans. Clostridium botulinum producing botulin toxin.
- Name a disease caused by Spirochaeta
Ans. Syphillis induced by Treponema pallidum
- What are the storage food of bacteria?
Ans. It includes the polyphosphate bodies, glycogen residues, lipid and oil droplets etc.
- Name two phototrophic bacteria.
Ans. Chlorobium, Chromatium, Rhodospirillum rubrum and Rhodopseudomonas palustris
- Name two chemoautotrophs bacteria
Ans. Thiobacillus and Nitrosomonas
- Name two photoheterotrophic bacteria
Ans. Rhodospirillum rubrum and Rhodopseudomonas palustris
- Name one total or obligate parasitic bacteria.
Ans. Neisseria gonorrhoeae
- Name one partial or facultative parasitic bacteria
Ans. Staphylococci sp.
- Name one total or obligate saprophytic bacteria.
Ans. Clostridium sp.
- Name one partial or facultative saprophytic bacteria
Ans. Vibrio cholerae
- Name two photoorganotroph bacteria.
Ans. Rhodospirillum rubrum and Rhodopseudomonas palustris
- Name the three kinds of respiration in bacteria
Ans. a) Aerobic respiration: Cornybacterium diptheri and Mycobacterium tuberculosis
- b) Anaerobic respiration: Clostriudium tetani and Clostridium septicum
- Facultative respiration: Lactobacillus, Pseudomonas and Escherichia
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