Biology Notes FA FSc Chapter No 6 Prokaryotic

Chapter No 6 Prokaryotic biology class 11 notes short question, long question, and pdf file download now for free KPK, fbise, Sindh, Karachi, and Punjab boards.

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Short Questions Biology Notes Class 11

Q.2 i) What are archaea?

Answer:
Archaea:
      Archaea are single-celled organisms that have distinct molecular characteristics separating them from bacteria (the other, more prominent group of prokaryotes) as well as from eukaryotes (organisms, including plants and animals whose cells contain a defined nucleus).
    Archaea live in both extreme and moderate environments.
Extremophiles:
  Those inhabiting extreme conditions are called extremophiles (lovers of an extreme environment).
Methanogens:
  The archea living in moderate conditions are known as methanogens. Methanogens live in a strict anaerobic environment. They obtain energy in a unique way by using CO2 to oxidize hydrogen releasing methane as a waste product. They may be found living in marshes, lake bottoms, and intestines of some animals and water thick ice layers in Greenland.
Types of extremophiles:
    The extremophiles are further divided into extreme halophiles and extreme thermophiles.
Extreme halophiles:
    Extreme halophiles live in high-salt environments such as Utah’s Great Salt Lake and the Dead Sea. The proteins and cell walls of these archaea help to survive in saline conditions. These organisms cannot survive if the salinity (tops below a certain level.
Extreme thermophiles:
    Extreme thermophiles thrive in very hot environments. Some of these organisms live in sulfur-rich volcanic springs as hot as 90C where most other organisms do not survive because their DNA cannot maintain its double helical structure and many proteins denature at this temperature. Some extreme thermophiles are found forming dense communities in boiling water 1210C above an active volcano 150 feet below the surface of Pacific Ocean at Macdonald Seamount.

Q.2 ii) Why has monera become obsolete?

Answer:
   In five kingdom system of classification of Whittaker, all prokaryotes are placed in kingdom Monera, whereas eukaryotes are distributed in four other kingdoms viz, Protista, Plantae, Fungi, and Animalia. Some prokaryotes differed so much from each other as they did form eukaryotes, so their placement in one group i.e. monera could not be justified. Monera has thus become obsolete and its members are divided into two different domains namely archaea and bacteria.  

What is the domain? Why is this term coined?

Domain:
 “Domain is the highest taxonomic rank of organisms in which there are three groupings archaea, bacteria, and eukaryotes.”
  In a recently proposed system of classification, the domain is a term coined to represent a classified level higher than a kingdom.   The domain is also called “super-kingdom” and is regarded as a top-level grouping of organisms in scientific classification.

In biological taxonomy, a domain is the highest taxonomic rank of organisms in the three-domain system of taxonomy designed by Carl Woese, an American microbiologist, and biophysicist. According to the Woese system, introduced in 1990, the tree of life consists of three domains: Archaea, Bacteria, and Eukaryote. The first two are all prokaryotic microorganisms or single-celled organisms whose cells have no nucleus. All life that has a nucleus and membrane-bound organelles, and most multicellular life, is included in the Eukaryota.

Q.2 iv) What is the role of prokaryotes is supporting life on earth?

Answer:
Role of prokaryotes in supporting life on earth:
    The first life on Earth came in the form of a prokaryotic cell. Prokaryotic cells are the most abundant and diverse organisms on Earth. Prokaryotic cells make up the organisms found in the two Kingdoms of life known as Bacteria and Archaea. Bacteria and archaea are literally found almost everywhere on Earth and in far greater abundance than any eukaryotic organism such as plants and animals. Prokaryotes are important to all life on Earth for a number of reasons.

  • They play a critical role in the recycling of nutrients by decomposing dead organisms and allowing their nutrients to be re-used.
  • Carbon and nitrogen are both macronutrients that are necessary for life on earth; prokaryotes play vital roles in their cycles.
  • The carbon cycle is maintained by prokaryotes that remove carbon dioxide and return it to the atmosphere.
  • Prokaryotes play a major role in the nitrogen cycle by fixing atmospheric nitrogen into ammonia that plants can use and by converting ammonia into other forms of nitrogen sources.

Q.2 v) What are main difference between archaea and bacteria?

Answer:
    Some of the major differences which exist between archaea and bacteria are:

  • The plasma membrane of both is made up of lipid bilayers but archaea contain different kinds of lipids. The cell wall in bacteria is made up of carbohydrates-protein complex called peptidoglycan but the cell wall of archaea lacks this complex.
  • Archaea have a unique type of ribosomal RNA different from that of bacteria.
  • Archaea live in both extreme and moderate environments. Those inhabiting extreme conditions are called extremophile (lovers of an extreme environment) and the other group living in moderate conditions are known as methanogens.

Q.2 vi) Name major groups of bacteria.

Answer:
Major groups of bacteria:

  • Proteobacteria
  • Chlamydias
  • Spirochetes
  • Gram positive bacteria
  • Cyanobacteria

Q.2 vii) What is the role of cyanobacteria in the evolution of life?

Answer:
Role of cyanobacteria in the evolution of life:
 Cyanobacteria play important role in the evolution of life as their photosynthetic activity gradually oxygenated the atmosphere and the oceans about two billion years ago. It was the beginning of a great transition that changed the conditions on earth permanently. The level of oxygen was raised from 1% to the current level of 21%. With the increase of oxygen, the amount of ozone also increased in the upper layers of the atmosphere. The thick layer of ozone acted as a screen protecting the proteins and nucleic acids from destruction by ultraviolet radiation from the sun. It encouraged the other autotrophs to appear and survive on earth. Some members of this group like Nostoc are involved in the fixation of atmospheric nitrogen.

Q.2 viii) What are plasmids and what is their importance?

Answer:
Plasmids:
  
“Plasmids are extra-chromosomal DNA molecules that can replicate in a cell separately from the chromosome.”
Importance of plasmids:
  
Plasmids are the vectors used to transfer genetic information either within species or between different species. Plasmids carry genes for antibiotic resistance and fertility. They may contain genes that enhance the survival of an organism, either by killing other organisms or by defending the host cell by producing toxins. Some plasmids facilitate the process of replication in bacteria. Since plasmids are so small, they usually only contain a few genes with a specific function.

Q.2 ix) What is the function of endospores?

Answer:
Function of endospores:
   Some Gram-positive bacteria produce highly resistant structures called endospores. The spores remain alive for many years under extremely harsh conditions with regarded to temperature, radiations and water shortage prevailing on earth in its early days. Endospore may develop near the end or in the centre of the cell. It contains little water.  The cell membrane grows in to seal off the developing spore. It is further protected by thick layers of peptidoglycan. When the external environment is favourable the protective layers break down and the spore is released which acts as a vegetative cell. Endospore formation is not a reproductive process as a vegetative cell forms a single endospore which later on produces one vegetative cell.

Q.2 x) How do the chemoautotrophic bacteria work?

Answer:
    Chemoautotrophic bacteria do not use sunlight as a source of energy. They derive the energy by the oxidation of inorganic substances such as hydrogen sulphide, ammonia, nitrates, nitrites and iron compounds. Such a process of food formation is called chemosynthesis.

Q.2 xi) What is genetic recombination?

Answer:
Genetic recombination:
  Genetic recombination refers to the process of recombining genes to produce new gene combinations that differ from those of either parent. Genetic recombination produces genetic variation in organisms that reproduce sexually. Genetic recombination happens as a result of the separation of genes that occurs during gamete formation in meiosis, the random uniting of these genes at fertilization.
Genetic recombination in bacteria:
  In bacteria, sexual reproduction occurs by genetic recombination which is a primitive type of sexual reproduction. In genetic recombination, DNA from two different sources combine. The cells do not fuse, only a piece of DNA of donor cell is inserted in the recipient cell. In recipient cell, the DNA portion of the donor cell orients itself in such a way that the homologous genes come close to one another. A fragment of the DNA of the recipient is knocked off and DNA of donor is integrated into it. The recipient cell is now called a recombinant cell. There are three methods of bacterial recombination i.e transformation, transduction and conjugation.

Q.2 xii) What are saprobes?

Answer:
Saprobes/Saprophytic bacteria (Scavengers of the earth):  
 
Saprophytic bacteria, commonly known as saprobes, feed exclusively on dead organic matter which is derived from plants and animals remain. These bacteria possess a powerful enzyme system which helps in the breakdown of complex organic compounds to simpler substance. They utilize the energy released in the process. The chemicals thus released become available to other organisms. The saprobes are called recyclers of nutrients. As they clean the earth by their action, they are also called the scavengers of the earth.

Q.2 xiii) Define symbiosis.

Answer:
Symbiosis:
  “Symbiosis is a relationship between two types of organisms in which each provides for the other the conditions necessary for its continued existence.”
                                         “Or”
   “A symbiosis is an evolved interaction or close living relationship between organisms from different species, usually with benefits to one or both of the individuals involved.”

Q.2 xiv) Are bacteria immortal?

Answer:
   Biological immortality is a state in which the rate of mortality from death is stable or decreasing. All the living entities existing on this planet are subjected to death. Many unicellular organisms age as time passes, they divide more slowly and ultimately die. Asymmetrically dividing bacteria also age. However, symmetrically dividing bacteria can be biologically immortal under ideal growing conditions. In these conditions, when a cell splits symmetrically to produce two daughter cells, the process of cell division can restore the cell to a youthful state. However, if the parent asymmetrically buds off a daughter only the daughter is reset to the youthful state; the parent isn’t restored and will go on to age and die.

Q.2 xv) Define transformation in bacteria.

Answer:
Transformation: 
   “Transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of external genetic material from its surroundings through the cell membrane.”
Transformation in bacteria:
   Transformation is one of three processes by which exogenous genetic material may be introduced into a bacterial cell; the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact), and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium).

Q.2 xvi) Why are the bacteria called nutrient recyclers?

Answer:
Bacteria as nutrient recyclers:
Saprophytic bacteria are decomposers and they are termed as natural recyclers because they break down organic compounds like proteins and carbohydrates into a simpler compound like CO2 which is released in the atmosphere for recycling. It is fixed by green plants in photosynthesis. Other nutrients released in the process enter the soil and become available to plants. Bacteria can decompose the dead remains of plants and animals. Because of their cleaning action, they are called the scavengers of planet earth. In sewage treatment, the bacteria bring about the break down of organic compounds and convert them into harmless ions such as nitrates and sulphates.

Q.2 xvii) Discuss the role of radiation in controlling bacterial growth.

Answer:
Radiations are used to inhibit bacterial growth. There are three types of radiations which are:
1. Ionizing Radiation:
      Gamma rays, X rays, electron beams, or higher energy rays are the form of ionizing radiation which causes mutations in DNA. It is used to sterilize pharmaceuticals and disposable medical supplies. Food industry is interested in using ionizing radiation.
2. Microwave Radiation: 
    Bacterial endospores, which do not contain water, are not damaged by microwave radiation. Solid foods are unevenly penetrated by microwaves.
3. Ultraviolet light (Nonionizing Radiation):
Ultraviolet light which damages DNA and causes mutations. It is used to disinfect operating rooms, nurseries, cafeterias from bacteria.


Long Questions

Q.3 i) Give an account of the structure of a bacterium.

Answer:
Bacteria:
  “Bacteria are microscopic living organisms, usually one-celled, that can be found everywhere on earth.”
    They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.
Structure of bacteria:
a. Capsule:
        Many species of bacteria possess a tight protective covering around the cell called capsule. It is a very sticky, gelatinous structure made up of polysaccharides and proteins. These bacteria arc called capsulated bacteria.
Functions of the capsule:  The capsule prevents dehydration of bacterial cell. A capsule which is less tightly bound to the cell is commonly called glycocalyx.
b.  Cell wall:
        The cell wall protects the cell and also gives it a definite shape. It is made up of peptidoglycan which is a carbohydrate-protein complex. The wall is laid in many layers and it makes the cell wall rigid. Based on the variations in the chemical constituents of cell wall, Hans Christian Gram, a Danish physician, developed a staining technique in 1884. He divided bacteria in two groups i.e. Gram-positive and Gram-negative bacteria. 

Gram-positive bacteria cell wall:
  Gram-positive bacteria which are stained blue-purple with crystal violet dye, possess-thick walls of peptidoglycan; they retain the dye when the cells are washed with an organic solvent like alcohol.
Gram-negative bacterial cell wall:
    Gram-negative bacteria have a thinner layer of peptidoglycan and lose the dye easily when rinsed with alcohol. Cell walls in Gram-negative bacteria are more complex; the thin peptidoglycan layer is covered externally by a layer of lipopolysaccharides. Gram-negative bacteria are more resistant than Gram-positive bacteria because the outer layer of lipopolysaccharides impedes the entry of antibiotics.
c. Flagella:
    Many species of bacteria possess thin hair-like appendages which help them in motility. Flagella are anchored in the cell wall and spin like a propeller, pulling the cell through the water.
Composition of flagella:
   A flagellum is composed of three parts i.e.
a. A basal apparatus associated with the cytoplasmic membrane and cell wall
b. A short curved hook and a helical filament. The hook and the filament are made up of a protein called flagellin.
Types of flagellum:
   The flagella may vary in number and placement.
i. A monotrichous bacterium possesses a single flagellum.
ii. A lophotrichous organism has a group of two or more flagella inserted at one pole of the cell.
iii. An amphitrichous bacterium is characterized by groups of flagella inserted both ends of the cell.
iv. In the peritrichous bacterium, flagella are dispersed on the entire surface of the cell.
Some bacteria lack flagella and are called as atrichious.
d. Pilli:
        Pilli is small filamentous appendages scattered all over the surface of the bacterial cell. They play no part in motility. Pilli is smaller than flagella in size. They are made up of a protein called pillin.
Functions of pilli:
  Pilli helps the bacteria to attach to various surfaces but in some cases, they are involved in the transfer of genetic material from one to another bacterium.
e.  Cell membrane:
       Cell membrane lies inner to the cell wall. It is thin, delicate, flexible and selectively permeable. In its chemical composition, it resembles the membrane of eukaryotic cells with the exception that the lipids are of different kinds in these membranes.
Function of cell membrane:
  Cell membrane regulates the transport of material into and out of the cell. The enzymes involved in the production of energy are all located in the cell membrane and in this way it resembles the membrane of the mitochondrion in a eukaryotic cell. It helps in the replication of DNA.
f. Mesosomes:
      Cell membrane invaginates into the cytoplasm to form a pocket-like structure called mesosome. The mesosomes are prominent in Gram-negative bacteria. They help in cell division and replication of DNA.
g. Cytoplasm:
Cytoplasm lies inside the cell membrane. It is a gelatinous mass of proteins, carbohydrates, lipids, nucleic acids, salts, and inorganic ions dissolved in water. It is thick, semi-transparent, and elastic and lacks membrane-bounded organelles. The semi-fluid jelly-like portion of the cytoplasm enclosed by the cell membrane is called cytosol.
h. Ribosomes:
      Ribosomes are RNA-protein bodies found freely dispersed within the cytoplasm.
The function of ribosomes:
   They are associated with the synthesis of proteins. They are smaller in size than the ribosomes of eukaryotic cells.

Biology Notes FA FSc Chapter No 6 Prokaryotic
Give an account of the structure of a bacterium

Q.3 ii) Discuss various methods of sexual reproduction of a bacteria.

Answer:
Reproduction in bacteria:
Sexual reproduction:
    In bacteria, sexual reproduction occurs by genetic recombination which is a primitive type of sexual reproduction. In genetic recombination, DNA from two different sources combine. The cells do not fuse, only a piece of DNA of a donor cell is inserted in the recipient cell. In recipient cell, the DNA portion of the donor cell orients itself in such a way that the homologous genes come close to one another. A fragment of the DNA of the recipient is knocked off and DNA of a donor is integrated into it. The recipient cell is now called a recombinant cell.
Methods of genetic recombination:
   There are three methods of bacterial recombination.
1. Transformation
2. Transduction
3. Conjugation
1- Transformation:
      Streptococcus pneumonia has two strains, one causes pneumonia but the other is unable to do so.
a. The cells of the virulent strain are capsulated from smooth colonies and are called S-types.
b. The non-virulent strain is non-capsulated forms rough colonies and is called R-type.
Experiment:
    In 1928 Fredrich Griffith, a German microbiologist injected live R- type cell into the body of a healthy mouse, the mouse remained alive and showed no symptoms of pneumonia. Then S-type live cells were injected into the body of another mouse, the mouse suffered from pneumonia and died. Heat-killed S-type cells were injected into the body of a healthy mouse, the mouse remained alive. These results were all according to the expectations of the researchers. But what happened next puzzled Griffith and his associates.


  A mixture of heat-killed S-type and live R-type was injected into the body of a healthy mouse, the mouse died from pneumonia. The autopsy revealed the presence of many living S-type cells in the dead body of the mouse. He concluded that the head-killed S-type cells released some substances which changed some of the R-type non-virulent cells into S-type virulent cells. The live R-type non-virulent bacteria were transformed into live S-type virulent bacteria.
    Later Avery and his co-worker in 1944 isolated and identified the transforming substance as DNA. It is now known that during transforming a small fragment of DNA is released by donor bacteria and it is taken by the recipient where it replaces a similar piece of DNA.

ii. Transduction:
     Transduction was first reported by Lederberg and Zinder in 1952.
Process of transduction:
   A piece of DNA is transmitted from a donor cell to a recipient cell through a third party called bacteriophage. The phage attaches itself to the surface of the bacterial cell called the donor bacterium and injects its DNA into the cell. The viral DNA directs the formation of protein coats.
Prophage:
  Sometimes, a piece of DNA of donor bacterium may become attached to the DNA of the phage, the recombinant DNA is known as a prophage.
Virulent phage:
    Many phages are assembled in a bacterial cell which bursts and a crop of phages is released completing a lytic cycle. Phages which causes lysis is called virulent phage.
Temperate phage:
  Newly formed phage now attacks a new bacterium, inserts its DNA into the bacterium which is now called recipient bacterium. The lysogenic life cycle starts. The phage is called temperate phage. The recipient bacterium at this stage contains three types of DNA i.e DNA of its own, DNA of donor bacterium and DNA of phage. Now recipient cell’s chromosome becomes a combination of DNA derived from both the bacterial cells i.e the recipient and the donor cells. With the division of recipient bacterium. All three types of DNA also replicate. In some daughter bacteria, some genes of donor DNA also express themselves donor and recipient bacteria. In this way, the genetic material of donor bacterium is carried to the recipient through a bacteriophage completing the process of transduction.

iii. Conjugation:
        “Conjugation is a recombination process in which living bacteria come into direct contact and the donor cell transfers DNA to the recipient cell.”
 The DNA transfer is one way. The process was studied in 1946 by Lederberg and Tatum in Escherichia coli.
   Normally Escherichia coli can synthesize all amino acids it requires. It was exposed to shortwave radiation and two mutants were isolated. One mutant was unable to synthesize biotin (a vitamin) and amino acid methionine. The other mutant could not synthesize amino acids threonine and leucine. The four chemicals are essential for the growth of bacteria. The two mutants were mixed and cultured in a common medium lacking in all the four compounds. None of the cells would have grown in the absence of essential chemicals, but to the great astonishment of researchers, hundreds of colonies of bacteria developed. This suggests that the exchange of genes has occurred between two parental bacteria and new recombinants were formed which did not require the four essential compounds for growth. Later studies made by electron microscope confirmed the close contact and the formation of a conjugation tube between the parental cells.

Q.3 iii) Describe the mode of nutrition in bacteria.

Answer:
Mode of nutrition in bacteria:
   Bacteria like other organisms, require food or growth and other vital activities. They need carbon and energy for their nutrition.
Type of bacteria on the basis of their mode of nutrition:
 Bacteria are divided into two groups on the basis of their nutritional approach.
I- Autotrophs / autotrophic bacteria
II- Heterotrophs/ Heterotrophic bacteria 

I- Autotrophs / autotrophic bacteria:
       Autotrophic bacteria synthesize their food from simple carbon sources. They use inorganic carbon compounds such as carbon dioxide and ions like carbonates, nitrates and sulphates. The energy needed for the synthesis of food comes from the sun and chemical reactions occur in the cytoplasm.
Types of autotrophic bacteria:
   The autotrophic bacteria are further divided into two groups namely photoautotrophs and chemoautotrophs.
1- Photoautotrophic bacteria:
        Photoautotrophic bacteria possess chlorophyll and can manufacture their food. The source of energy is sunlight which they capture through chlorophyll. The chlorophyll is not contained in chloroplasts but it dispersed in the infolded region of the cell membrane in the cytoplasm. The source of hydrogen is hydrogen sulphide instead of water. Sulphur is released in the process instead of oxygen.
Example:
  Some other photoautotrophic bacteria are purple sulphur bacteria, sulphur bacteria and non-sulphur bacteria.
2- Chemoautotrophic bacteria:
         These bacteria do not use sunlight as a source of energy. They derive the energy by the oxidation of inorganic substances such as hydrogen sulphide, ammonia, nitrates, nitrites and iron compounds. Such a process of food formation is called chemosynthesis.
II- Heterotrophs/ Heterotrophic bacteria: 
        Heterotrophic bacteria are unable to prepare their own food and obtain energy from organic compounds prepared by other organisms.
Types of heterotrophic bacteria:
    There are three types of heterotrophic bacteria
1- Saprophytic bacteria (Scavengers of the earth):  
     Saprophytic bacteria, commonly known as saprobes, feed exclusively on dead organic matter which is derived from plants and animals remain. These bacteria possess a powerful enzyme system which helps in the breakdown of complex organic compounds to simpler substance. They utilize the energy released in the process. The chemicals thus released become available to other organisms. The saprobes are called recyclers of nutrients. As they clean the earth by their action, they are also called the scavengers of the earth.
2- Parasitic bacteria:
        The parasitic bacteria do not possess the enzyme system for the breakdown of organic matter of their living hosts which include humans, plants and animals. Many parasitic bacteria cause diseases and are called pathogens.
3- Symbiotic bacteria:
      Symbiosis means living together. Symbiotic bacteria develop a nutritional relationship with other organisms.
Mutualism:
   The relationship may be beneficial to both partners and is called mutualism.
Commensalism:
    Another type of relationship is commensalism in which one partner is benefitted while the other is neither benefitted nor harmed.
Example:
    Rhizobium radiciola develops a symbiotic association with roots of leguminous plants. It forms nodules on the roots, fix atmospheric nitrogen and supply nitrogenous compounds to the plant and gets food and shelter in return from the plant.

Q.3 iv) Give an account of bacterial diseases of plants.

Answer:
Bacterial diseases of plants:
   Some important bacterial diseases of plants are:
1. Bacterial leaf spots:
Pathogenic agent of disease:
      Cucurbits beans, com and many other plants are infected by Pseudomonad spp. causing leaf diseases. The infected plant parts are leaves, stems, fruits, and seeds.
Symptoms of disease:
  Symptoms of the disease are different in different plants. Some have small spots of different colours on their leaves. In peppers and cucurbits, as the disease progresses, large irregular holes appear in leaves.
Conditions of disease spread:
   The conditions favourable for the development of leaf spot disease are warm temperature, frequent rains, high relative humidity, use of diseased seeds, over-crowding of plants and poor soil drainage.
Preventive measures:
   Preventive measures include crop rotation, hot water seed treatment, uses of disease-free seeds and removal of infected plants.

2. Bacterial wilt:
A pathogenic agent of disease:
   The causal organism of bacterial wilt disease is Ralstonia solanacearum and the host plants are potato, tobacco, brinjal, banana, cotton, sweet potato and others.
Symptoms of disease:
  The disease symptoms differ from plant to plant. In tomato and brinjal, initial symptoms of the disease are the wilting of terminal leaves and after 2-3 days entire plants wilt. In potato, the plant wilt quickly without yellowing.
Conditions of disease spread:
   The conditions which are ideal for the development of disease are: leaving the infected crop residues in the field, warm temperature, high moisture contents of soil, high soil pH and poor and infertile soil.
Preventive measures of disease:
   Preventive measures of disease are destroying the infected plants immediately, crop rotations, control of nematodes and use of disinfected farm tools.

3. Bacterial soft rot:
A pathogenic agent of disease:
   Soft rot disease of potato, sweet potato, onion, carrot, tomato, beans, com, cotton and crucifers is caused by Erwinia carotovora.
Symptoms:
    The infected parts and the symptoms of disease differ in different plants. In crucifers, generally, the petiole is infected which becomes soft, spongy and dark in colour. In carrot, the taproot is infected; it becomes soft and watery and sometimes it is lost completely. The infected plant of com becomes dark brown. Water-soaked soft stalk suddenly collapses and become twisted.
   The initial signs of disease are premature withering and drying up of the tips of uppermost leaves, then the lower leaves, soon followed by the appearance of a slimy soft rot at the bases of leaves. The infection in potato converts the tuber into a cream to tan coloured soft tissues.
Preventive measures:
   Preventive measures are the preparation of properly drained soil, control of nematodes, removal of infected plants immediately, crop rotation etc.

4. Bacterial galls:
A pathogenic agent of disease:
   Galls caused by bacteria are a very small but important group of bacterial plant pathogens. Most common is crown gall caused by Agrobacterium tumefaciens, which is a soil-inhabiting bacterium.
Symptoms:
   The bacterium causes abnormal growths or galls on the roots, twigs and branches of plants of family Rosaceae. The bacterium stimulates the rapid growth of plant cells that results in the galls. Galls are most commonly found near ground level on roots and lower branches of the plants. As the galls enlarge, they become woody and hard. The plants become weak and stunted. Symptoms of the disease may not develop immediately after infection. Gall grow most rapidly during warm months of the years. The disease can spread through contaminated soils and tools.

5. Bacterial blights:
A pathogenic agent of disease:
Bacterial blights on different plants are known by different names and are caused by different species of bacteria. The plants infected by blight disease include wheat, barley, oat and beans. Common bacterial blight on beans is caused by Xanthomonas campestris pv. Phaseoli. 
Symptoms:    Symptoms of the disease first appear on leaves as small water-soaked light green spots. The spots enlarge and the tissue in the centre dies and turns brown. These irregularly shaped spots are bordered by a lemon yellow ring. These spots grow, leaf dies and are shed and the plant is defoliated. Common bacterium blight is favoured by conditions of high moisture and humidity.
Preventive measures:
  Control measures include the use of tested seeds, a practice of crop rotation, avoidance of overhead irrigation and the elimination of crop residue.

Q.3 v) Describe the normal flora of some important organs of humans and also discuss its benefits.

Answer:
Bacterial flora of humans:
    The assemblage of microorganisms that constantly and consistently inhabit the human body is called human flora. They include bacteria, fungi and other organisms. Some of these organisms are known to perform tasks that are useful for the human body, while most of them produce no known beneficial or harmful effects. The microorganisms which are expected to be present and under normal circumstances do not cause disease are considered member of the normal flora.
Bacterial flora of humans:

 Body PartHuman flora
Oral cavityStreptococci and lactobacilli.
 2  Respiratory tractStreptococci, corynebacteria, streptococci,
Neisseria sp.,
 Gram-negative rodand cocci.
 Urinogenital tractStreptococci, corynebacteria and lactobacilli
Large intestine Helicobacter sp., Bifidobacteria, Bacteroides
sp., Lactic acid bacteria, Clostridia
 and
Methanogens.

 
Benefits of normal bacterial flora:

  • Normal flora synthesizes and excretes vitamins in excess of their own needs. These vitamins are absorbed as nutrients by the human body.
  • It prevents colonization of pathogens by competing for attachment sites or for essential nutrients. In this way, the normal flora of the human organs inhibits the growth of pathogenic bacteria through competitive exclusion. This is thought to be the most important beneficial effect of normal bacterial flora.
  • Normal flora of bacteria may antagonize other bacteria through the production of substances which inhibit or kill non-indigenous bacteria. The intestinal bacteria produce many substances which inhibit or kill other bacteria.
  • Normal flora stimulates the production of natural antibodies inducing an immunological response. Such antibodies are lacking in germ-free individuals.

Q.3 vi) Describe the symptoms, causative bacteria, treatment and preventive measures of tuberculosis.

Answer:
Tuberculosis (TB): 
  “Tuberculosis is a contagious infection that usually attacks the lungs.”
  Tuberculosis has remained a great killer disease for thousands of years. Generally, the people living in slums and suffering from malnutrition contract tuberculosis. Poor quality of life and overcrowding increase the chances of occurrence of disease in a locality.
Causative agent:
  Tuberculosis is caused by Mycobacterium tuberculosis which is an acid-resistant bacillus bacterium.
Symptoms:
   The patient experience chronic cough, chest pain and high fever and expel sputum which is rust coloured mucous indicating the entrance of blood into lungs. A hard nodule called tubercle is formed in the lung. The tubercle expands and the lungs slowly deteriorate.
Treatment:
    The basic principle of TB treatment and control is to make sure that the patient completes a full course of medication so that all the bacteria causing infection are killed and drug-resistant strains are not allowed to develop. TB patient is largely treated with isoniazid (isonicotinylhydrazine (INH)) and rifampin and to a lesser extent by ethambutol and streptomycin. The drug administration is supplemented with a good meal and living condition.
Vaccination:
  Immunization to tuberculosis is rendered by injecting the vaccine called Bacille Calmette Guerin (BCG).
Preventive Measures: 

  • TB should be treated early in order to prevent deterioration of the disease and the spread of the infection.
  • The close contacts of TB patients, usually the household contacts, should be examined.
  • This includes tuberculin skin testing and/or chest x-ray examination for young children and chest x-ray examination for older children and adults.
  • A healthy lifestyle in order to minimize the chance of contracting the illness. This includes adequate exercise, enough rest and sleep, balanced diet, avoidance of smoking and alcohol, breathing fresh air and maintaining good indoor ventilation, good personal hygiene (e.g., avoid coughing and sneezing directly at other persons).

Q.3 vii) Write an essay on the importance of bacteria.

Answer:
Importance of bacteria:
1. Use of bacteria in Gene cloning:
     Escherichia coli are used in gene cloning. Agrobacterium tumefaciens is used in producing transgenic plants such as Golden Rice which prevents blindness that occurs in those whose diet is deficient in vitamin A. Golden Rice contains beta-carotene precursor of vitamin A.  
2. Use of bacteria in bioremediation:
       Bacteria are used as an agent in bioremediation. They are used to remove pollutants from soil, air and water. Anaerobic bacteria decompose the organic matter in sewage and convert it to such material that can be used as fertilizer. Bioremediation applications include cleaning up of oil spills and precipitation of radioactive material in groundwater.
3. Role of bacteria in biodegradation:
      Bacteria play important role in the plastic industry. Billions of pounds of plastics are produced from petroleum and used in making toys, containers, bottles and other items. These products degrade slowly creating environmental problems. Bacteria are now used to make natural plastics which are biodegradable.
4. Role of bacteria in genetic engineering:
      Bacteria are modified by genetic engineering to produce vitamins, antibiotics, hormones and other products. Humulin, human insulin is produced by using recombinant DNA technology. It also helps in producing disease-resistant crop plants. Ethanol is used as a substitute for fossil fuel. Bacteria help to produce ethanol from various forms of biomass such as agricultural wastes, willows and corn.
5. Bacteria as nutrient recyclers:
Saprophytic bacteria are decomposers and they are termed as natural recyclers because they break down organic compounds like proteins and carbohydrates into a simpler compound like CO2 which is released in the atmosphere for recycling. It is fixed by green plants in photosynthesis. Other nutrients released in the process enter the soil and become available to plants. Bacteria can decompose the dead remains of plants and animals. Because of their cleaning action, they are called the scavengers of planet earth. In sewage treatment, the bacteria bring about the break down of organic compounds and convert them into harmless icons such as nitrates and sulphates.
6. Role in bacteria in ecology:
         Bacteria play important role in ecological interactions. They are involved in symbiotic nitrogen fixation in the roots of leguminous plants. Herbivorous mammals cannot break down cellulose. Bacteria live in their guts and help in the digestion of cellulose by breaking it down. The relationship is called commensalisms.
  Soil bacteria decompose the organic matter and make the soil fertile. Bacteria also play important role in nitrogen, phosphorus, sulphur and carbon cycles.
7. Use of bacteria in the food industry:
       Bacteria are used in the preparation of dairy products such as butter, cheese and yoghurt. They are involved in the preparation of antibiotics, vinegar, ammo acids and proteins. Bacteria are employed in retting of fibres and making of silage.
8. Spoilage of food by bacteria:
        Bacteria spoil food items. Foods with high protein contents are decomposed by bacteria. Eggs, fish and cooked food and milk are all spoiled by bacterial action.


11 class biology notes Chapter No 6 Prokaryotic

Definition:“That organism, whose genetic materials are not enclosed by a double nuclear membrane and most of their cytoplasmic organelles are absent are known as prokaryotes.”

Example:– Archaea, Bacteria, and cyanobacteria.

Question: explain the taxonomy of prokaryotes.

Taxonomy of prokaryotesdefinition: “The identification, description and naming of prokaryotes are known as Taxonomy of prokaryotes.”

Five kingdom system of classification: 1959

11 class biology notes kpk pdf

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