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Chpt. 21 Monera

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Chpt. 21 Monera. Monera Bacteria belong to the kingdom monera. Bacteria are present in a wide range of habitats including both land and water environments e.g. salt water, soil, plants, animals etc. Bacteria also survive in extreme environments e.g. hot

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Chpt. 21




  • Bacteria belong to the kingdom monera.
  • Bacteria are present in a wide range of habitats
  • including both land and water environments e.g. salt
  • water, soil, plants, animals etc.
  • Bacteria also survive in extreme environments e.g. hot
  • springs, swamps, human intestines, human stomach
  • (pH 2) etc.
  • Bacteria are prokaryotes i.e. no nucleus or membrane
  • enclosed organelles – mitochondria.
  • Bacteria are unicellular – single celled.
  • Bacteria contain DNA plasmids.

Bacterial Structure

Food Reserve

Cell wall

Cell membrane



DNA (Chromosome)





General Structure of Bacterium

Cell Wall: - made of sugars and protein

- prevents bacteria from swelling with water and bursting

Cell Membrane: often has infoldings called mesosomes which:

a) carry out respiration

b) help during cell division

Capsule: - sometimes present

- takes form of a semi-solid capsule or a more liquid slime layer.


General Structure of a Bacterium

Chromosome: - one chromosome

- consists of a strand of DNA

- no surrounding membrane

- does not contain protein

Plasmids: - sometimes present

- small DNA loops

- contain genes that are responsible for bacterial resistance to antibiotics

Cytoplasm: - contain ribosome's and numerous storage granules (food or waste)

Flagellum: - sometimes present

- flagella allows bacteria to move by themselves i.e. they are motile.


Bacterial Types

  • Bacteria are classified according to three shapes:
          • Spherical (Cocci)
          • Rod (Bacillus)
          • Spiral (Spirrillum)

Bacterial Types

  • Spherical (Cocci):
  • Round bacteria which can be found in pairs, chains or
  • clusters.
  • -E.g. Staphoolococcus aureus
  • causes pneumonia

Bacterial Types

Rods (Bacillus):

- E.g. Bacillus anthracis

Cause of anthrax

- Escherichia coli (E.coli)

Live in human gut


Bacterial Types

Spiral (Spirillum):

- E.g. Treponema pallidum

Causes syphilis

- E.g. Cholera


Reproduction in Bacteria

  • Bacteria reproduce asexually
  • The method used by a bacteria to reproduce is called
  • Binary Fission.

Binary Fission

  • The chromosome attaches to the plasma membrane
  • and the DNA is replicated.

Cell wall


Plasma membrane



Binary Fission

  • The cell elongates and the two chromosomes separate

Binary Fission

  • The cell wall grows to divide the cell in two

Binary Fission

  • Two identical daughter cells are formed

Mutations in Bacteria

  • Bacteria reproduce asexually - their offspring are genetically identical.
  • As there is little recombination of genetic material in this method of reproduction one would expect that bacteria would be slow to evolve.
  • New mutations can spread very quickly within rapidly growing bacteria allowing them to evolve very fast.
  • This is how bacteria evolve resistance to new antibiotics.


  • Some bacteria can withstand unfavourable conditions
  • by producing endospores.

Endospore Formation

  • These are formed when the bacterial chromosome
  • replicates.

Endospore Formation

  • One of the new strands becomes enclosed in a tough-
  • walled capsule called an endospore.


  • The parent cell then breaks down and the
  • endospore remains dormant.

Endospore Formation

  • When conditions are favourable the spores absorb
  • water, break their walls and reproduce by binary
  • fission.
  • Note: endospores are very difficult to kill – can
  • withstand lack of food and water, high temperatures
  • and most poisons.

Bacterial Nutrition

  • Bacteria obtain food in four different ways which can
  • be grouped under two headings:
  • Autotrophic Heterotrophic






Autotrophic Organisms: are organisms which can make their own food.

Photosynthetic bacteria:

  • Source of energy = light
  • Chlorophyll on membranes within the cell.
  • Some bacteria have different pigments than plants –
  • use mostly red light.
  • Some bacteria live on hydrogen sulphide gas instead of
  • water – purple sulphur bacteria.

Autotrophic Bacteria

  • Chemosynthetic Bacteria:
  • make their own food using energy from reactions
  • involving ammonia, sulphur and iron compounds.
  • E.g. Nitrifying bacteria that convert ammonia
  • to nitrates in the nitrogen cycle

Heterotrophic Organisms: organisms which take in food made by other organisms.

  • Saprophytes:
  • take in food from dead organic matter e.g. bacteria of
  • decay in the soil.
  • some use petrol and oil products as a food source –
  • clean up oil spills.

Heterotrophic Bacteria

  • Parasites:
  • take in food from a live host resulting in damage to
  • host.
  • Examples of disease causing bacteria include:
  • cholera
  • pneumonia

Factors Affecting Growth

Growth of bacteria is affected by five factors.

  • Too much or too little of any of these five factors will slow down the growth of bacteria:
  • Temperature
  • Oxygen concentration
  • pH
  • External solute concentration
  • Pressure


  • Most bacteria grow well between 20°C and 30°C.
  • Some can tolerate much higher temperatures
  • without their enzymes becoming denatured.
  • Low temperatures slow down the rate of bacterial
  • growth.
  • High temperature bacteria used in biotechnology
  • resulting in a) faster bacterial metabolism
  • b) higher rate of product formation

Oxygen Concentration

  • Aerobic bacteria: require oxygen for respiration e.g.
  • Streptococcus.
  • Anaerobic bacteria: do not require oxygen to respire
  • e.g. Clostridium.
  • Facultative anaerobes: can respire with or
  • without oxygen e.g. E.Coli (found in intestines)
  • Obligate anaerobes: can only respire in the
  • absence of oxygen e.g. Clostridium tetani
  • (causes tetanus)


  • Bacterial enzymes work at specific pH values, outside
  • this pH value they become denatured.
  • For most bacteria the most suitable pH is pH7.
  • Some bacteria can survive at very low or high pH
  • values.

External Solute

Bacteria can gain or loose water by a process called osmosis.

Case 1: If environment outside a bacterial cell has a higher solute concentration than the bacterial cytoplasm, water will move out of the bacteria (osmosis). As a result bacterium becomes dehydrated preventing further growth or reproduction.

Case 2: If environment outside a bacterial cell has a lower solute concentration than the bacterial cytoplasm, water will enter the bacteria (osmosis).

- cell wall prevents bacterium from bursting

- most bacteria live in these conditions.



  • High pressure damages bacterial cell walls.
  • Some bacteria can withstand very high pressures –
  • bacteria in deep-sea vents.
  • Genetically modified bacteria are used to allow
  • bacteria to survive in bioreactors that require high
  • pressure.

Economic Importance of Bacteria

( Must know 2 beneficial and 2 disadvantages of bacteria)

Beneficial Bacteria:

Bacteria such as Lactobacillus are used to convert milk to products such as cheese and yoghurt

Genetically modified bacteria e.g. E. Coli are used to make products such as insulin, enzymes, drugs, food flavourings and vitamins


Economic Importance of Bacteria

Harmful Bacteria:

  • Micro-organisms that cause disease are called pathogens.
  • E.g. Bacillus anthracis causes anthrax in humans
  • - If they enter the body through a wound they can
  • multiply and effect the nerves and activity of
  • muscles.
  • - Other bacterial diseases include tuberculosis,
  • typhoid, cholera, diphtheria and brucellosis.
  • Bacteria cause food decay:
  • E.g. Lactobacilli cause milk to turn sour

Beneficial and harmful bacteria


  • Pathogenic Bacteria can
  • cause diseases in humans
  • and animals.
  • Pathogenic Bacteria can
  • cause diseases in plants.
  • Bacteria can cause food
  • spoilage
  • Bacteria can cause tooth
  • decay.


  • Lactobacillus converts milk
  • to yoghurt and cheese
  • Antibiotics can be formed by
  • some microorganisms
  • Bacteria in the colon help
  • produce vitamins
  • G.M.O.’s are used to make
  • insulin and other useful
  • compounds
  • Bacteria are active in the
  • Carbon and Nitrogen Cycles


Antibiotics are substances produced by micro-organisms that stop the growth of, or kill, other micro-organisms without damaging human tissue



Antibiotics can be used to control bacterial and fungal infections but do not effect viruses

E.g. Penicillin, streptomycin



  • The first antibiotic, Penicillin, was isolated from a
  • fungus by Sir Alexander Fleming.
  • Now antibiotics are mostly produced by genetically
  • engineered bacteria.

Antibiotic Resistance

  • When an antibiotic is used to treat an infection most of
  • the bacteria are killed.
  • However mutations in bacterial genes can allow
  • bacteria to develop antibiotic resistance.
  • Antibiotics will then kill ‘sensitive’ bacteria and favour
  • resistant bacteria.
  • Bacterial strains have emerged which are resistant to
  • almost all known antibiotics (multi-resistant). As a
  • result present day antibiotics become ineffective. MRSA
  • is one example.

Potential Abuse of Antibiotics

Overuse of antibiotics:

  • This results in the increased growth of antibiotic
  • resistant bacteria.
  • Failure of some patients to complete a course of
  • antibiotics prescribed to them by a doctor allows the
  • bacteria to survive and re-grow.

Growth Curves of Monera

Higher Level

Binary Fission in monera can occur every 20 minutes resulting in a very fast increase in bacterial numbers.

Because of this we use a special scale called the logarithmic scale to represent these large numbers.

In a logarithmic scale each division represents a unit increase in the value of x in the term 10x.

100 = 0

101 = 10

102 = 100

103 = 1000

104 = 10,000

105 = 100,000 etc


Growth Curve for Bacteria

This scale allows huge numbers of bacteria to be represented on a graph as shown below:

Lag phase

Log Phase



Decline Phase

Number of Bacteria

Logarithmic Scale



The Lag Phase:

  • During this phase the bacteria are adapting themselves to their new environment.
  • Bacteria are producing the enzymes necessary to digest the nutrients on which they are to grow.
  • The rate of growth begins to increase towards the end of this phase.

The Log (Exponential) Phase:

  • There is a rapid period of growth during this phase due to the fact that:
    • The rate of cell division is currently at its maximum with the number of bacteria doubling as often as every 20 minutes.
    • Bacteria have developed the necessary enzymes and there are plenty of nutrients.
    • Ideal conditions are present i.e. plenty of food, moisture, oxygen etc.

The Stationary Phase:

  • The rate of growth levels off during this period. This is because:
    • During this period there is a lack of space, moisture, oxygen etc.
    • The nutrients are becoming used up.
    • The amount of waste produced by the bacteria themselves is increasing.
    • The rate at which new cells are produced is equal to the rate at which other cells are dying.

Decline Phase(Death):

  • During this phase more bacteria are dying than are being produced. This is because:
    • Very few nutrients are left.
    • Many bacteria are poisoned by the waste produced by such large numbers.
  • Thus the rate of growth is falling.

The Survival Phase:

Normally not all bacteria die a small number may survive as spores.

These spores survive by remaining dormant until conditions are again suitable.


Food Processing

  • Modern bio-processing methods involve the use of bacteria (and other organisms) to produce a wide range of products.
  • These include dairy products e.g. yoghurts and cheeses, artificial sweeteners, flavourings, vitamins and alcohol products such as wines and beers.
  • It is becoming more and more common to use micro-organisms as a food source, in particular as a source of protein.
  • The use of bacteria to produce edible forms of protein is called single-cell protein (SCP) production.

Food Processing

  • There are two main methods of food processing (fermentation):
    • Batch food processing
    • Continuous flow food processing

Batch Food Processing

  • In batch food processing a fixed amount of sterile nutrient is added to the micro-organisms in the bioreactor.
  • The micro-organisms go through the stages of a typical growth curve i.e. the Lag, Log, Stationary and Death stages.
  • As this happens the nutrients are used up and the product formed.
  • Product normally forms at the log or stationary stage.
  • Process is stopped before the death phase because there is very little product formed at this stage.

In Batch Processing most of the product is formed during the stages highlighted below

Lag phase



Log Phase

Death Phase

Number of Bacteria

Time (days)


Batch Food Processing

  • At the end of production the bioreactor is cleared out.
  • The product is separated from the rest of the solution and is purified.
  • The bioreactor is cleaned, re-sterilised and the process can then be repeated.

Batch processing


Continuous Flow Food Processing

  • In continuous flow food processing nutrients are continuously fed into the bioreactor.
  • At the same time the culture medium (containing some micro-organisms) is continually withdrawn.
  • In this method of food processing micro-organisms are maintained in the Log phase of growth. This means they are growing rapidly and producing the product at a fast rate.
  • In continuous flow bioreactors factors such as temperature, pH, rate of stirring, concentration of nutrients, oxygen and waste products are constantly monitored in order to maintain growth in the Log phase and therefore produce the maximum yield.

In Continuous Flow Processing most of the product is formed during the stage highlighted below

Lag phase

Log Phase

Number of Bacteria

Time (months)


Continuous Flow Food Processing

  • Maintaining constant conditions is very difficult, as a result this method of food processing is limited to a small number of applications e.g.:
  • - production of single-cell protein
  • - some methods of waste water treatments.

Continuous flow processing


Advantages of Batch Food Processing

  • Easier process to control compared to continuous flow food processing.
  • Product may be needed only in small amounts.
  • Product may be needed only at particular times.
  • Large amount of product formed allows for some losses during separation and purification.
  • Micro – organisms grow well over short periods of time. In continuous flow food processing long periods of time are required which may not suit all micro-organisms.