Domain Bacteria and Archaea

What diversity do prokaryotes display in size and shape?

Prokaryotes vary widely in shape and size. Common forms include spheres (cocci), rods (bacilli), and spirals (spirilla). Their sizes range from 0.1 to 5 μm, allowing them to thrive in almost every environment, from deep oceans to hot springs.

Compared to eukaryotic cells, how is the prokaryotic cell wall unique in its structure and function?

Prokaryotic cell walls provide shape, support, and protection. Bacterial walls contain peptidoglycan, a unique polymer of sugars and amino acids not found in eukaryotic cells. Archaea lack peptidoglycan and instead use other structural molecules such as polysaccharides or proteins.

In what ways is the internal organization of a prokaryotic cell different than that of a eukaryotic cell?

Prokaryotic cells lack a true nucleus and membrane-bound organelles. Their DNA is found in a nucleoid region, and their cytoplasm is simpler. Some prokaryotes have folded membranes that perform specialized metabolic functions like photosynthesis or respiration.

How are prokaryotes able to exist in populations of immense size?

Prokaryotes reproduce rapidly through binary fission, sometimes doubling in minutes. Combined with their small size and diverse metabolic pathways, this allows them to reach massive population sizes and adapt quickly through mutations and gene exchange.

What are the four major modes of nutrition? Be able to outline the energy sources, carbon sources and types of organisms that utilize these methods.

1) Photoautotrophs: energy from light, carbon from CO₂ (e.g., cyanobacteria). 2) Chemoautotrophs: energy from inorganic compounds, carbon from CO₂ (e.g., some Archaea). 3) Photoheterotrophs: energy from light, carbon from organic compounds (e.g., certain aquatic prokaryotes). 4) Chemoheterotrophs: energy and carbon from organic compounds (most bacteria and animals).

How do prokaryotes vary with respect to their requirements for oxygen?

Obligate aerobes require oxygen for respiration, obligate anaerobes are poisoned by oxygen, and facultative anaerobes can survive with or without it, switching metabolic pathways depending on conditions.

Which organisms are capable of nitrogen fixation and why is this process vital to the survival of other organisms?

Certain bacteria and archaea (e.g., cyanobacteria, Rhizobium) can fix nitrogen by converting atmospheric N₂ into ammonia (NH₃), a form plants can use. This process is essential because it makes nitrogen biologically available for amino acids, nucleic acids, and other vital molecules.

Describe three examples of metabolic cooperation between prokaryotes.

1) Biofilms: surface-attached communities that share nutrients and protection. 2) Cyanobacteria: some cells perform photosynthesis while others fix nitrogen. 3) Gut microbiomes: multiple species cooperate to digest food and recycle nutrients.

What are some unique features of organisms placed in the Domain Archaea?

Archaea have cell membranes made of unique lipids with ether bonds and lack peptidoglycan in their cell walls. Many live in extreme environments such as hot springs or salt lakes. Their genetic and metabolic pathways share similarities with both bacteria and eukaryotes.

What are the various roles that bacteria play in the biosphere?

Bacteria are crucial decomposers, breaking down dead matter and recycling nutrients. They also perform nitrogen fixation, photosynthesis (e.g., cyanobacteria), and form symbiotic relationships with plants and animals that help maintain ecosystem balance.

In what ways do bacteria impact humans?

Bacteria can be both beneficial and harmful. Beneficial bacteria aid digestion, produce vitamins, and are used in biotechnology and medicine. Harmful bacteria cause diseases such as tuberculosis and strep throat. Many also play key roles in agriculture and environmental cleanup.