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Worksheet 12.1
Chapter 12: Microbes and biotechnology – fifteen
summary facts
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After studying the newly mapped molecule of rRNA, Carl Woese realized that the five-kingdom
system of classification was inaccurate. By examining the sequence of nucleotides in ribosomal
RNA (rRNA), he reclassified all living things into three domains. The three domains are:
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Eubacteria – true bacteria with no organized nucleus and no membrane-bound organelles
Archaea bacteria or ‘ancient bacteria’ – bacteria living in extreme environments
Eukarya – single-celled and multicellular organisms with an organized nucleus and
membrane-bound organelles.
Distinguishing characteristics of the three domains can be found in the chart on page 383.
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The Archaea live in a wide range of habitats. They can be methanogens, thermophiles, and
halophiles.
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The Eubacteria have wide diversity of shape. They can be rods, spheres or helices. They can also
be divided into two groups – Gram-positive or Gram-negative – based on their cell wall structure
(Figure 12.3, page 386).
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The wide diversity of microscopic eukaryotes is illustrated by Saccharomyces, Amoeba,
Plasmodium, Paramecium, Euglena and Chlorella (table, page 389).
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Viruses are not cellular and cannot reproduce without using the cell machinery of another
organism. They are not considered living things. Viruses do show great diversity in their structure.
Their protein coat (capsid) can be naked or enveloped.
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Diversity allows microbes to exploit many niches in the ecosystem. They may be producers (e.g.
bacteria) which use chlorophyll to trap sunlight, nitrogen fixers which take nitrogen gas from the
atmosphere and fix it into nitrogen usable for plants, or decomposers which release inorganic
nutrients back into the ecosystem. Bacteria play a huge role in the nitrogen cycle (Figure 12.6,
page 392).
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Release of raw sewage into the water supply can transmit pathogens to those who drink or bathe in
the water. Release of nitrates into the water supply can cause increased growth of algae (algal
blooms). As the algae die, they are decomposed by aerobic bacteria which use up the oxygen in
the water (high biochemical oxygen demand, BOD). Water becomes low in oxygen and many
other organisms die. To prevent disease and algal blooms, raw sewage is treated with saprotrophic
bacteria using a trickling filter system or reed bed system (pages 395–6).
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Biomass can be used as raw material for the production of fuels such as methane and ethanol.
Manure from farm animals and cellulose from plants are put into an anaerobic digester with no
© Pearson Education Ltd 2010. For more information about the Pearson Baccalaureate series please visit
www.pearsonbacc.com
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free oxygen, temperature of 35 °C, and regulated pH. Acidogenic bacteria produce organic acids
and alcohol. Next, acetogenic bacteria make acetate with carbon dioxide and hydrogen as byproducts. Finally, methanogenic bacteria produce methane from the carbon dioxide and hydrogen
or from the break down of acetate (Figure 12.7, page 397).
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Reverse transcriptase is an enzyme used by retroviruses (e.g. HIV) to catalyse the production of
DNA from RNA. Using reverse transcriptase, molecular biologists have made therapeutic proteins
such as insulin. First, a human DNA molecule with its introns is taken from a pancreas cell. Next,
mRNA copies the DNA without its introns. Reverse transcriptase, working backward, produces a
new single-stranded cDNA. From single-stranded cDNA, double-stranded DNA is made using
DNA polymerase. The double-stranded DNA is inserted into a plasmid and put into a bacterial
cell. The bacteria cell multiplies and makes insulin. Insulin is harvested and used by diabetics
(Figure 12.11, page 401).
10 Gene therapy involves replacing a defective gene with an effective gene which will make a correct
protein. Genes are delivered to cells by vectors (e.g. a virus). If the vector delivers the gene to a
gamete cell, it is germ-line therapy; if the gene is delivered to a body cell, it is somatic therapy.
Children affected with SCID do not produce a protein called ADA. This weakens their immune
system. Stem cells from 11 children with SCID were mixed with a virus containing the gene for
making ADA. The virus transferred the normal gene into the stem cells of each child. The stem
cells were infused back into the bone marrow of the children and their immune systems were
restored. However, two years later, two of the children contracted leukaemia as a result of this
procedure and one of them died. Risks of gene therapy can include: the virus vector inserting the
new gene in the wrong cell, a new gene making too much protein, the virus stimulating an immune
reaction in the patient or the risk of children being too underdeveloped to have this procedure
safely.
11 Saccharomycetes cerevisae (yeast) is a common fungus used in the production of bread, wine and
beer.
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In beer-making, a grain is germinated to release sugars. This is called malt. Hops are added
and the mixture is boiled. After cooling, the yeast is added to break down the malt into
ethanol and carbon dioxide. The beer is then pasteurized to kill any remaining yeast cells.
In wine-making, yeast is added to the crushed grapes. The grape sugar is fermented by the
yeast to produce carbon dioxide and ethanol. The carbon dioxide escapes and 11% ethanol is
left in the wine.
In bread-making, yeast acts on sugars in the dough and produces carbon dioxide and ethanol.
The carbon dioxide makes the bread rise. The yeast is killed and the ethanol is evaporated as
the bread is baked in the oven.
12 Soy sauce is produced from fermented soy beans. The organism responsible is a fungus called
Aspergillus oryzae. The process is 5000 years old.
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13 Preserved foods like jams and pickled vegetables make seasonal fruits and vegetables available for
longer periods of time. When preserving fruit with sugar by making jam, a hypertonic environment
is created to prevent the growth of mould and bacteria which would spoil the fruit.
14 An acid environment can also prevent the growth of mould and bacteria. Pickles are vegetables
preserved in vinegar. Spices like dill can be added to enhance the flavour. The hot vinegar and
spices poured over vegetables such as small onions or cucumbers create a very acidic
environment. The very low pH restricts the growth of microbes.
15 Food poisoning occurs when food is not treated properly and becomes contaminated with diseasecausing organisms. One of the commonest is Salmonella. Symptoms of food poisoning can last
several days and severe cases can be fatal. Poor food-handling hygiene is the major transmission
route of Salmonella food poisoning.
© Pearson Education Ltd 2010. For more information about the Pearson Baccalaureate series please visit
www.pearsonbacc.com
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