2.2: Comparing Bacteria and Archaea
pg. 59
Prokaryotic cells (no true nucleus or membrane bound organelles)
are found in two domains, Archaea and Bacteria. These two cells
are more different then the same.
Comparing Morphology
There are two common forms for Archaea and Bacteria; Spheres
(cocci) and rods (bacilli), a third form that is less common is the
spiral shape (spirallia).
Bacteria have other forms, not seen in Archaea, such as; cubes,
pyramids, and rods with star shaped cross sections.
Archaea also have other forms, such as; plates and rectangular rods.
Figure 2.5 There are three common shapes of prokaryotes: (A) cocci (spherical), (B)
Bacilli (rod-shaped), (C) spiral shaped
Aggregations: Cells Grouped Together
Prokaryotes are singled celled organisms, but they may live in
colonies or groups, such as: Streptobacillus or Anabaena.
Comparing Nutrition
There are many ways Archaea and bacteria may obtain their
energy. Some can perform photosynthesis, others must consume
nutrients, and finally some can obtain energy from various
inorganic compounds.
Methane-producing Archaea live in the digestive system of
animals, such as; cows. Methanogenesis, is unique to Archaea, is a
biological (or chemical) a process that produces methane as a byproduct.
Methanogenesis is an anaerobic process. It occurs in environments
lacking oxygen, final stage of decomposition and the product is
methane gas.
Some bacteria are able to perform photosynthesis. Bacteria which
can use sunlight energy to create their own food are called
Cyanobacteria. These types of bacteria can be found in both fresh
and salt water environments. Since the product of photosynthesis is
oxygen, cyanbacteria account for much of the atmospheric oxygen
on Earth.
Comparing Habitats
Extremophile: an organism that lives in habitats characterized by
extreme conditions.
Mesophile: an organism that lives in habitats characterized by
moderate conditions.
Comparing Reproduction
Binary Fission: the asexual form of reproduction used by most
prokaryotes (and some eukaryotic organelles), in which a cell
divides into two genetically identical cells (or organelles).
Figure 2.9 Cell division in prokaryotes occurs by binary fission. In favourable conditions,
a prokaryotic cell can grow and divide in as little as 20 minutes. Each new cell can then
grow and produce two more cells 20 minutes later. A sequence of repeated doubling like
this allows bacteria to produce huge populations in a fairly short time.
Conjugation: New Genetic Content
Conjugation: a process in which there is a transfer of genetic
material involving two cells.
Figure 2.10 Genetic material being transferred through a long tube-like pilus.
Plasmids: Small Loops of DNA
- small loops of DNA that are separate form the main
chromosome.
- Plasmids contain genes which are different from the genes on
the chromosome.
- Plasmids can attach to the chromosome and separate from it
again.
- Plasmids are transferable from one cell to another during
conjugation. (Recombination)
Endospores: Protecting Genetic Material
- Bacteria can produce hard walled structures to protect and
store the genetic material when there are extreme
environmental changes.
- Environmental changes, such as; high temperatures, drying
out, freezing, radiation, and toxic chemicals.
- The endospore will disappear once the environmental
conditions return to normal.
Classifying and Identifying Bacteria and Archaea
Gram stain: is a technique that divides bacteria into two groups.
Gram Positive: is a bacteria cell that has a thick protein layer on
their cell wall and stains purple.
Gram Negative: is a bacteria cell that has a thin protein layer on
their cell wall and stains pink.
Prokaryotes can also be identified and classified by size and shape,
nutrition, movement, and genetic components.
DNA comparisons are favored by modern Biologists.
Bacteria and Human Health
Diseases caused by bacteria, occurs as the result of normal bacteria
activity. E.g. botulism, food poisoning, is caused by Clostridium
botulism.
The metabolism of Clostridium botulism cell can produce toxic
products that cause nausea and possibly death.
When bacteria are trapped in an anaerobic environment they
produce toxins, such as; cans, bottles or jars.
The heating of food under high pressure will kill the bacteria
before sealing food in contains.
Other diseases caused by bacteria are: strep throat, ear infections,
and tooth cavity.
Bacteria and the Environment
Bacteria are also decomposers, that breakdown organic matter,
releasing carbon, hydrogen, and other elements back into the
environment, to be used by other organisms, plants.
Cyanobacteria are major producers of oxygen, through the process
of photosynthesis. These bacteria are what probably produce the
atmosphere, 21% oxygen.
Archaea and Biotechnology
Archaea are organisms that live under extreme conditions of heat,
cold, acidity, and salinity.
These organisms can be used Biotechnology and other industries.
The enzymes produces by Archaea can function in these extreme
conditions.
Learning Check: questions 7 – 12, pg. 62
Activity 2.2 Classifying Bacteria, pg. 64
Section 2.2 Review: questions 1 – 12, pg. 66