Biology XI Notes - Kingdom Prokaryota (Monera) - Theory & Question Answers
Chapter # 06
Theory & Question Answers
Section III - Biodiversity
KINGDOM PROKARYOTA (MONERA)
Prokaryotae is a group of living organisms which are unicellular, having prokaryotic or a primitive nucleus, i.e., lack nuclear membrane, nucleolus, and nucleoplasm. Prokaryotic cells lack all membrane-bound organelles, e.g., mitochondria, plastids, endoplasmic reticulum, etc. Bacteria and cyanobacteria (blue-green algae) are included in this group.
BACTERIA:
Discovery:
- Antony Van Leeuwenhoek (1673) was the first to observe bacteria. In 16 he wrote an article on bacteria, the very first description of bacteria.
Habitat:
- Bacteria are found everywhere in the world. They are found in all possible environmental conditions of earth.
Structure:
- Bacteria are considered the smallest and simplest living organisms. Bacteria are the pioneers of cellular organization and strictly unicellular size.
Size:
- Bacterial cell measures from 0.2 microns (μ) to 2 μ in breadth and 2 to 10 μ in length.
Parts Of Bacteria: A bacterial cell may consist of the following parts.
Flagella:
- They are long thread-like structures. They originate from the basal body in the cytoplasm. They are made up of flagellin protein. Flagella help in motility.
Pilli:
- They are hollow, filamentous appendages smaller than flagella. They help in conjugation and not in locomotion.
Capsule:
- It is a protective shield composed of polysaccharides and proteins. Some bacteria have a slime capsule that provides greater pathogenicity (disease-causing ability) and protects them against phagocytosis.
Cell Wall:
- The cell wall is found surrounding the cell membrane. It is rigid, determines the shape, and protects from osmotic lysis. It is composed of amino acids, sugar, and chitin, but cellulose is totally absent. Most bacteria have a unique macromolecule peptidoglycan. Teichoic acid, lipoprotein, and lipopolysaccharides are also present in the cell wall. Archaebacteria do not contain peptidoglycan.
Cell Membrane:
- It lies inside the cell wall. It is attached to the cell wall at a few places. It has many pores. Chemically, it is made up of lipids and proteins. The cell membrane performs the function of respiration as mitochondria are absent in them. It also acts as a selective membrane.
Cytoplasm:
- It is granular, present between the cell membrane and nuclear region. It has many but small vacuoles, free ribosomes, and glycogen particles. It has no membranous organelles like Golgi compounds, endoplasmic reticulum, etc.
Mesosomes:
- These are invaginations of the cell membrane into the cytoplasm. Their function is to help in DNA replication, cell division, respiration, and in the export of enzymes.
Nucleoid:
- There is a distinct nuclear region in the bacterial cell containing genetic material DNA in the form of a single circular molecule called the chromatin body or bacterial chromosome.
Plasmids:
- It is a small fragment of extra genetic material. Plasmids serve as vectors in genetic engineering.
- Cocci: (Singular Coccus)
- They are spherical, non-flagellated, and according to cell arrangement, they are:
- Monococcus: Bacterium found in solitary form.
- Diplococcus: Found in pairs.
Streptococcus:
It is a long chain of cocci.Tetrad:
Having four cocci.Sarcina:
Cube of eight cocci.Staphylococcus:
Has grape-like arrangement.Bacilli: (Singular Bacillus)
They are rod-shaped. They may be flagellated. Bacilli are of the following types:- Bacillus:
A single rod-shaped bacterium. - Diplobacillus:
A pair of bacilli. - Streptobacillus:
A chain of bacilli.
- Bacillus:
Spirilla: (Singular Spirillum)
They are spiral or corkscrew-shaped. E.g., spirochaeta.Vibrio Or Commas:
They are slightly curved, e.g., vibrio cholera. They may be flagellated.
Form (Shapes) Of Bacteria: There are four shapes of bacteria.
Diversity: Bacteria are difficult to classify. Taxonomists classify bacteria using a variety of criteria.
On The Basis Of Flagella: On the basis of presence, pattern of attachment, and the number of flagella present, bacteria are classified into the following taxonomic groups.
Atrichous:
Bacteria are without any flagella.Monotrichous:
When a single polar flagellum is present.Lophotrichous:
If a tuft of flagella is present only at one pole of bacteria.Peritrichous:
Flagella surround the whole cell.
On The Basis Of Staining: Christian Gram developed the technique of gram staining, dividing bacteria into two groups.
- Gram positive: Bacteria stained purple
- Gram negative: Bacteria stained pink.
On The Basis Of Origin: Some microbiologists place bacteria into two major categories.
- Eubacteria: True bacteria
- Archaebacteria: Ancient bacteria
Occurrence: Bacteria are omnipresent, which can be found distributed on the earth from air to soil and water and from dead to living organisms.
Nutrition: There are two types of bacteria on the basis of nutrition.
- Autotrophic bacteria.
- Heterotrophic bacteria.
Autotrophic Bacteria: The bacteria which utilize CO₂ and get energy from sunlight or from some chemical reactions are called autotrophic bacteria. They can synthesize organic compounds. They may be further divided into two groups.
Photosynthetic Autotrophs:
These bacteria have chlorophyll called bacteria chlorophyll or chlorobium chlorophyll dispersed in the cytoplasm. They utilize atmospheric CO₂ and get energy from sunlight and perform the process of photosynthesis, but they use hydrogen sulfide (H₂S) instead of water as a source of hydrogen and liberate sulfur instead of oxygen.Chemosynthetic Bacteria Or Chemoautotrophs:
These bacteria use inorganic compounds as a source of carbon and get energy by oxidation and reduction processes. They oxidize compounds like nitrate, sulfur, ammonia, and ferrous iron.
Heterotrophic Bacteria: Most bacteria are heterotrophic, which cannot synthesize their organic compounds from simple inorganic substances. According to their mode of feeding, heterotrophic bacteria may be saprotroph, symbiotic, or parasite. These bacteria cannot synthesize their organic compounds; they get energy by decomposition of organic compounds and live either as parasites or saprophytes.
- Parasite:
These bacteria obtain their food from the body of living organisms. They live in or on the body surface of other organisms and are fully dependent on the host. These bacteria cause diseases in hosts and sometimes cause death.
Saprophytes:
- They obtain their food from dead organic substances. The soil humus is formed from the decay of plants and animals, and it is rich in organic compounds. The bacteria produce enzymes that break down the complex substances of humus into simpler compounds. These compounds are easily absorbed by bacteria, and they use them as a source of energy.
Symbiotic Bacteria:
- Some bacteria form an association with other organisms, and both get benefits from each other; such bacteria are called symbiotic bacteria. For example, Rhizobium radicicola bacteria live in the roots of leguminous plants (e.g., pea plants). These bacteria convert nitrogen into its compounds, nitrites, and nitrates. This process is called nitrogen fixation. As a result of this process, bacteria get food material from plants. Such bacteria are called symbiotic bacteria.
Nitrogen Fixation By Bacteria: It is a process in which nitrogen is changed into ammonium and ammonia compounds. Because nitrogen cannot be used in a free state by plants, it is only used when it is converted into simple nitrogenous compounds. This process is mainly performed by bacteria.
In the first step, dead plants, animals, and excretory nitrogenous products are converted into simpler compounds like water, CO₂, and amino acids by the activity of fungi and bacteria. This process is called ammonification. Then the nitrifying bacteria act upon ammonia and ammonium ions and change them into nitrites. The conversion of ammonia and ammonium ions into nitrites takes place by Nitrosomonas bacteria, and nitrites are changed into nitrates by Nitrobacter bacteria. Some bacteria live in the roots of leguminous plants. In the roots of these plants, small rounded bodies are produced, called nodules, in which bacteria are present. These bacteria convert nitrogen into nitrites and nitrates, which are used by plants. As a result of this process, the bacteria get their food from the plant. This process is called symbiosis. In this nitrogen fixation, Rhizobium bacteria take part.
Another way is non-symbiotic nitrogen fixation. Two types of bacteria, Azotobacter and Clostridium, help in this process. They convert nitrogen into chemical compounds like nitrites and nitrates. They do not form any association with plants. Some bacteria are called denitrifying bacteria (Bacillus denitrificans). They change the ammonia and nitrates into free nitrogen. In this way, the nitrogen remains in constant amount in the atmosphere by a cycle called the nitrogen cycle.
Respiration: Bacteria are also classified according to their need for oxygen in respiration.
- Aerobes:
Require oxygen for respiration. ingdom Prokaryota (Monera) - Theory & Question Answers
Anaerobes:
Respire without oxygen.Facultative Bacteria:
Respire with or without oxygen.Microaerophilic:
Bacteria require a low concentration of oxygen for growth.Obligate Anaerobes:
Some bacteria are killed in the presence of oxygen; they are called obligate anaerobes.Facultative Anaerobes:
Others use oxygen but can respire without it; they are called facultative anaerobes.Obligate Aerobes:
Bacteria which can only survive in the presence of oxygen are obligate aerobes.
Locomotion In Bacteria:
Some bacteria use flagella for locomotion. Flagella are attached with a unique wheel-like structure. Bacterial flagella can rotate rapidly.
Taxis Behavior:
Flagellated bacteria show orientation toward various stimuli, a behavior called taxis.Chemotactic Bacteria:
Bacteria are moving toward chemicals or away from toxic chemicals.Phototactic Bacteria:
These are moving toward or away from light.Magnetotactic Bacteria:
These detect earth’s magnetic field using magnets formed from iron crystals within their cytoplasm.
Growth:
During favorable conditions, bacteria can grow very rapidly. Important environmental factors affecting growth are temperature, nutrient availability, pH, ionic concentration, and oxygen (absence or presence).
Four distinct phases are recognized in the bacterial growth curve.
Lag Phase:
Inactive phase or phase during which bacteria prepare themselves for division.Log Phase:
Bacteria grow and multiply very rapidly.Stationary Phase:
Bacterial multiplication is equal to the death rate.Death/Decline Phase:
Death rate is more rapid than multiplication.
Reproduction:
Bacteria reproduce by two methods.
- Asexual reproduction
- Genetic recombination
Asexual Reproduction:
Fission:
Bacteria generally reproduce asexually by a process called binary fission. Fission is the fastest mode of asexual reproduction found in living organisms, particularly unicellular organisms.Fission takes place when there is an ample supply of food and moisture with favorable conditions. During fission, first, the hereditary material (DNA) in the form of chromatin-body is replicated. Chromatin bodies formed then move apart. A construction appears around the middle of the cell and it splits into two parts. These parts grow in size and form mature bacterial cells. The single fission takes about 20-30 minutes to complete.
Endospore Formation:
During endospore formation, when conditions are not favorable, the whole protoplasmic content shrinks into a small mass. A cyst is formed inside the parental wall around this mass to form an endospore. When the parental wall ruptures due to decay, the endospore is set free. On the return of favorable conditions, this endospore enlarges to form a mature bacterial cell.
Genetic Recombination: The re-union of genetic material from two different sources is called genetic recombination. Three methods by which genetic recombination takes place in bacteria are conjugation, transduction, and transformation.
Conjugation:
Conjugation is a simple process of genetic recombination in which genetic material is transferred from one bacterium to another through a tube called the conjugating tube or cytoplasmic bridge. This process was carried out experimentally by Laderberg and Tatum in 1946.Transduction:
It is a mode of genetic recombination in which genetic material is transferred from one bacterium to another by a third party, which is a bacteriophage. This process was carried out experimentally by Laderberg and Zinder in 1952.Transformation (Transforming Principle):
It is a process of transmitting genetic information from one bacterium to another bacterium through the environment, causing it to transform (undergo change). This principle was first notified by Fred Griffith in 1928.
Importance And Control:
Importance of Bacteria:
Useful Bacteria:
Decomposers:
Bacteria are an important biotic component of each and every ecosystem. They act on dead plant and animal bodies, decomposing various organic compounds into simple forms such as nitrates, sulfates, phosphates, etc., for utilization by green plants again. Nitrifying bacteria convert the proteins of these dead bodies into nitrates. Soil bacteria increase the fertility of the soil by bringing about physical and chemical changes in the soil.Alimentary Canal Bacteria:
They help herbivores in the digestion of cellulose by an enzyme called cellulase. They are present in the appendix or in the cecum of cows, goats, etc.Industrial Bacteria:
They are symbionts that help in curing and ripening tobacco leaves, fermentation of sugar into alcohol, ripening of cheese, retting of fibers, curdling of milk, conversion of hides into leather, etc.Medicinal Bacteria:
Valuable antibiotic drugs have been obtained from bacteria, e.g., thyrothricin, subtilin. Riboflavin is a vitamin produced by clostridium.Genetically Engineered Bacteria (Biotechnology):
E. coli has already been programmed to make human growth hormones for the treatment of growth deficiencies and insulin for diabetics.
Harmful Bacteria:
Pathogenic Bacteria:
They are responsible for many diseases in humans, animals, and plants. They may be called the invisible enemies of man. Some diseases found in humans due to bacteria are typhoid, tetanus, food poisoning, diphtheria, tuberculosis, etc. Plant diseases caused by bacteria are black rot of cabbage, citrus canker, fire blight of pear and apple, and ring rot of potato, etc.Food Spoilage:
Bacteria spoil food by fermentation, putrefaction, or decomposition.
Control Of Bacteria:
The term control of pathogenic organisms refers to bringing infections in a population to a tolerable limit. Control of bacteria is essential to prevent diseases and avoid spoilage of food and other industrial products. Several measures are taken to control infectious microorganisms. Such measures involve the following:
- Treatment of the infected individuals.
- Prophylactic treatment of the population at risk through immunization or vaccination.
- Disruption of the life cycle of the pathogen at all possible stages.
- In case of epidemics, prevention of the spread of infection to non-infected individuals through quarantine.
- Identification and control or treatment of the reservoir hosts if any.
- Health awareness in masses primarily to reduce the risk factors related to some diseases.
- Establishing a surveillance system.
- Killing of bacteria is brought about by several sterilization methods, like exposing bacteria to ultraviolet rays or high temperatures. Certain antiseptics, antibodies, and chemotherapy agents are used to kill the bacteria present in a living tissue.
Use And Misuse Of Antibiotics:
Antibiotics:
Antibiotics are chemical substances produced by certain microorganisms that inhibit or kill other microorganisms.Uses:
Antibiotic drugs are of two types:- Narrow spectrum: Effective against only certain types of bacteria.
- Broad spectrum: Effective against a wide range of bacteria.
Misuse:
Antibiotics also have many side effects, and their unnecessary and prolonged use disturbs the metabolic activities of the user.
Cyanobacteria: (Blue Green Algae)
Salient features:
- They are Prokaryotic.
- They are unicellular or may occur in colony form.
- Cell wall is double layered.
- Protoplasm is differentiated into an outer colored region (chromoplasm) and an inner colorless region (centroplasm).
- Chromoplasm contains various pigments in which chlorophyll-x and phycocyanin are in abundance, imparting bluish-green color.
- They are aquatic (freshwater, with a few marine forms).
- Total absence of sexual reproduction.
- Asexual reproduction takes place by means of hormogonia, zoospores, akinetes, and fragmentation.
- Nostoc may be taken as a typical example of Blue-green algae.
NOSTOC:
Nostoc: It is a blue-green algae.
Habit And Habitat: Nostoc is found in freshwater as well as in a terrestrial habitat. It always occurs in colonies. The colony of Nostoc floats on water like a ball. The terrestrial forms are found in wet soil.
Structure: Nostoc is a unicellular alga found in a colony as filamentous algae. Many filaments of Nostoc are intermixed in a gelatinous mass, forming a ball-like structure called coenobium. Each filament is enveloped in a mucilaginous sheath. It is unbranched, with a narrow curved structure. The filaments are made up of round or oval cells, which are arranged in the form of beaded strings.
Heterocysts: Here and there in the filaments, transparent, enlarged, thick-walled, round or barrel-shaped cells are found, which are known as heterocysts. They are terminal or intercalary in position. Heterocysts are specialized cells that differ from vegetative cells in lacking protoplasm.
Akinetes: Some of the cells in filaments accumulate reserve food materials and swell. These are known as akinetes.
Cell Wall Structure: The cell wall is made up of two layers. The outer thick layer is made up of cellulose mixed with pectic compounds, and the inner thin layer is made up of only cellulose.
Protoplasm: The protoplasm is differentiated into:
Chromoplasm:
Outer peripheral zone. It is colored and has pigments like chlorophyll, xanthophyll, carotene, phycocyanin, and phycoerythrin.Centroplasm:
Inner central zone. It is an irregular structure that consists of an incipient nucleus. It looks like a mass of chromatin granules.
Reproduction In Nostoc: Nostoc reproduces asexually, and there is no sexual reproduction. The following are the methods of reproduction:
Fragmentation:
Sometimes the filament divides into pieces by some means. These pieces develop into new filaments.Hormogonia:
The cells of the filament break at the point of heterocyst. The fragment between two heterocysts is known as hormogonium. Each hormogonium develops into a new filament.Akinetes:
These are the resting spores formed under unfavorable conditions. During the formation of an akinete, a vegetative cell enlarges, accumulates reserve food within it, and becomes thick-walled. The akinetes are resistant to unfavorable conditions. On the approach of favorable conditions, they germinate into new filaments.
Importance Of Cyanobacteria:
- Capable of making organic compounds.
- Able to fix atmospheric nitrogen.
- Nostoc anabaena is used as nitrogen fertilizer in agriculture.
