Ch 24: Early Life & Prokaryotes

Question 1

Evaluate the evolutionary relationships among Bacteria, Archaea, and Eukarya

Answer 1

• Domain Bacteria and Domain Archaea are characterized by prokaryotic cell structure
  
  • Bacteria are the most abundant prokaryotes
    
    • Cyanobacteria transformed the atmosphere on early Earth by releasing oxygen produced by the photosynthesis; Surviving prokaryote lineages either avoided or adapted to the newly aerobic environment

Question 2

Describe and contrast different mechanisms of horizontal gene transfer (conjugation, transformation, transduction) in Bacteria and explain how this increases genetic diversity in Bacteria

Answer 2

• Conjugation: DNA from a donor cell is transferred to an adjacent recipient cell. First, a pilus tethers the donor to the recipient and brings the cells together. Once the cells are closely aligned, the DNA passes through a small opening formed between the cells.
• Transformation: DNA released into the environment by dead cells is taken up by a recipient cell.
• Transduction: DNA is transferred from a donor to a recipient by a virus.

Prokaryotic cells have developed these methods for recombining their genetic material, which, in turn, contributes to their genetic diversity.

Question 3

Recognize that Bacteria and Archaea employ a diversity of metabolic pathways and play key roles in nutrient cycling

Answer 3

• Prokaryotes play major roles:
  
  • Recycling chemical elements between the living and nonliving components of ecosystems
    
    • Decomposers: organisms that break down dead organic materials and release mineral nutrients
    • Convert molecules, into forms that can be taken up by other organisms. Ex:
      
      • make sugars via photosynthesis from CO2 & H2O
      • transform atmospheric nitrogen (N2) into nutrients that plants require for growth

Question 4

Recognize that bacteria and archaea have ecological interactions with eukarya

Answer 4

• Ecological Interactions
  
  • Symbiosis: relationship between two species that live in close contact: a larger host and smaller symbiont. These symbiotic relationships increase the fitness of one or both organisms
    
    • In mutualism, both organisms benefit
    • In commensalism, one organism benefits while neither harming nor helping the other in any significant way
    • In parasitism, an organism called a parasite harms but does not kill its host. Parasites that cause disease are called pathogens

Question 5

NOTES

Answer 5

• Chemoautotrophsoxidize inorganic substances for energy and use CO2as a carbon source.
• Organisms that obtain energy from light are called phototrophs, and those that obtain energy from chemicals are called chemotrophs. Organisms that need only CO2or related compounds as a carbon source are called autotrophs. In contrast, heterotrophs require at least one organic nutrient, such as glucose, to make other organic compounds.
• The role of decomposer does not involve symbiosis.