Bacteria
Bacteria are single celled, prokaryotic microorganisms. They lack a membrane-
bound nucleus and other internal structures and are therefore ranked among the unicellular
life-forms called prokaryotes. Prokaryotes are the dominant living creatures on Earth, and have
adapted to almost all available ecological habitats. As a group, they display exceedingly diverse
metabolic capabilities and can use almost any organic compound, and some inorganic
compounds, as a food source. Some bacteria can cause diseases in humans, animals, or plants,
but most are harmless and are beneficial ecological agents whose metabolic activities sustain
higher life-forms. Other bacteria are symbionts of plants and invertebrates, where they carry
out important functions for the host, such as nitrogen fixation and cellulose degradation.
STRUCTUREOFBACTERIALCELL
I. Prokaryotic cells (i.e., Bacteria and Archaea) are fundamentally different from the
eukaryotic cells in the lack of intracellular organelles, which are features characteristic
of eukaryotic cells. Organelles are discrete membrane-enclosed structures that are
contained in the cytoplasm and include the nucleus, where genetic information is
retained, copied, and expressed; the mitochondria and chloroplasts, where chemical or
light energy is converted into metabolic energy. All of the activities performed by
organelles also take place in bacteria, but they are not carried out by specialized
structures.
II. Cell Morphology
Individual bacteria can assume one of three basic shapes:
o spherical (coccus)
o rod-like (bacillus)
o curved (vibrio, spirillum, or spirochete).
Considerable variation is seen in the actual shapes of bacteria, and cells can be
stretched or compressed in one dimension. Bacteria that do not separate from one
another after cell division form characteristic clusters that are helpful in their
identification.
1 Department of Botany
PM
, III. INTERNALSTRUCTURE
2 Department of Botany
PM
Bacteria are single celled, prokaryotic microorganisms. They lack a membrane-
bound nucleus and other internal structures and are therefore ranked among the unicellular
life-forms called prokaryotes. Prokaryotes are the dominant living creatures on Earth, and have
adapted to almost all available ecological habitats. As a group, they display exceedingly diverse
metabolic capabilities and can use almost any organic compound, and some inorganic
compounds, as a food source. Some bacteria can cause diseases in humans, animals, or plants,
but most are harmless and are beneficial ecological agents whose metabolic activities sustain
higher life-forms. Other bacteria are symbionts of plants and invertebrates, where they carry
out important functions for the host, such as nitrogen fixation and cellulose degradation.
STRUCTUREOFBACTERIALCELL
I. Prokaryotic cells (i.e., Bacteria and Archaea) are fundamentally different from the
eukaryotic cells in the lack of intracellular organelles, which are features characteristic
of eukaryotic cells. Organelles are discrete membrane-enclosed structures that are
contained in the cytoplasm and include the nucleus, where genetic information is
retained, copied, and expressed; the mitochondria and chloroplasts, where chemical or
light energy is converted into metabolic energy. All of the activities performed by
organelles also take place in bacteria, but they are not carried out by specialized
structures.
II. Cell Morphology
Individual bacteria can assume one of three basic shapes:
o spherical (coccus)
o rod-like (bacillus)
o curved (vibrio, spirillum, or spirochete).
Considerable variation is seen in the actual shapes of bacteria, and cells can be
stretched or compressed in one dimension. Bacteria that do not separate from one
another after cell division form characteristic clusters that are helpful in their
identification.
1 Department of Botany
PM
, III. INTERNALSTRUCTURE
2 Department of Botany
PM
