Prokaryotes- Grade 11 Biology

PROKARYOTES

Bacteria (old kingdom Monera) & Archaea Introduction

• microscopic unicellular prokaryotic organisms
• lack of a membrane-bound nucleus and membrane-bound organelles (p. 25)

Classification

Based on

Shape (morphology):

 rod-shaped (bacillus),

 spherical/round (coccus), and

 spiral (spirillum)..

in chains: strepto-

in clusters: staphylo-

 

eg. Streptococcus (round cells that grow in chains), staphylobacillus (rod-shaped cells that grow in clusters)

 

Respiration:

Aerobic bacteria; can function metabolically only in the presence of free or atmospheric oxygen

Anaerobic bacteria: cannot grow in the presence of free oxygen but obtain oxygen from compounds.

Facultative anaerobes can grow with or without free oxygen;

Obligate anaerobes are poisoned by oxygen.

Nutrition:

 Heterotrophic: living off other organisms. Most of these are

saprophytes, bacteria that live off dead organic matter.

Autotrophic: manufacture their own food by the processes of

 Photosynthesis: include the green and purple bacteria and the cyanobacteria

Chemosynthesis: obtain energy directly from inorganic molecules like hydrogen sulfide (eg. deep sea thermal vents)

Gram Stain:

Gram positive: crystal violet (purple) appear

Gram negative: cells appear pink

  Reproduction

Binary fission: asexual reproduction yields identical daughter cells. About every 20 minutes. (p. 62)

Some bacteria reproduce by budding or fragmentation

 

Spore formation: Under unfavorable conditions some bacteria form highly resistant spores with thickened coverings

Sources of Genetic Variation:

Some bacteria are capable of specialized types of genetic recombination

1.  Conjugation: the transfer of DNA (chromosomal or plasmid) through a cytoplasmic bridge between bacterial cells created by their pili

2.  Transformation: a bacterial cell can absorb DNA from dead bacteria in its environment

3.  Transduction: bacterial genes can be carried from one bacterial cell to another via bacteriophage viruses (recall  lysogenic cycle of viral replication: bacterial DNA flanking the proviral DNA can be packaged into a virion during the assembly phase)

                        
    Beneficial Bacteria

• Cycling nutrients in ecosystems
  • nitrogen cycle (soil enrichment with leguminous crop)
  • Carbon cycle(decomposition)
  • Sulfur cycle
• for preservation by pickling, for fermentation (as in the manufacture of alcoholic beverages, vinegar)
• production of dairy foods(yoghurt, cheese)
• decomposition of organic wastes (in septic tanks, in some sewage disposal plants, and toxic wastes
• symbiotic bacteria in animal intestines
• for genetic engineering

    Pathogenic Bacteria

Bacterial parasites that cause disease are called pathogens. Among bacterial plant diseases are

leaf spot,

fire blight (the rapid and extensive discoloration, wilting, and death of plant tissues), and

wilts;

animal diseases caused by bacteria include

tuberculosis, pneumonia, legionnaires (air borne)

leprosy, botulism, meningitis

cholera, diphtheria, anthrax, gangrene

syphilis, gonorrhea(sexually transmitted diseases)

typhoid fever, tetanus, and black death(Bubonic plague)