Biology: Bacteria, Archaea, and Eukaryotic Diversity

Comprehensive practice flashcards reviewing bacterial and archaeal biology, prokaryotic and eukaryotic distinctions, metabolic diversity, the human microbiome, and eukaryotic life cycles.

What are the three domains of life in the tree of life?

The three domains are Bacteria, Archaea, and Eukarya.

When does fossil evidence suggest life first appeared on Earth, and what cellular organization did it have?

Fossil evidence indicates life arose approximately $3.5\text{ billion}$ years ago as prokaryotic cells.

When did oxygen begin to accumulate in Earth's atmosphere, and what organisms were responsible?

Oxygen began to accumulate approximately $2.4\text{ billion}$ years ago due to photosynthetic cyanobacteria.

What was life's ancestral condition according to the tree of life?

Prokaryotic cell organization.

Are Archaea more closely related to Bacteria or to Eukarya?

Archaea are more closely related to Eukarya because they share a similar central dogma mechanism (transcription, translation, and replication machinery).

What two main mechanisms drive rapid evolution and high genetic diversity in prokaryotes?

Rapid reproduction (short generation times causing mutations to accumulate quickly) and genetic recombination (via horizontal gene transfer).

What are the four primary nutritional modes based on energy source and carbon source?

1. Photoautotrophs: Energy from sunlight, carbon from $CO_2$ (e.g., Cyanobacteria, Vascular plants). 2. Photoheterotrophs: Energy from sunlight, carbon from organic compounds (e.g., Heliobacteria, most green non-sulfur bacteria). 3. Chemoautotrophs: Energy from chemical compounds, carbon from $CO_2$ (e.g., Sulfur-oxidizing bacteria, Hydrogen bacteria). 4. Chemoheterotrophs: Energy from chemical compounds, carbon from organic compounds (e.g., most bacteria, all non-phototrophic eukaryotes).

How does the prokaryotic cell wall protect the cell in a hypotonic environment?

In a hypotonic environment, water enters the cell by osmosis and internal pressure rises; the cell wall maintains cell shape, provides physical protection, and prevents the cell from bursting.

What structural component distinguishes bacterial cell walls from archaeal cell walls?

Bacterial cell walls contain peptidoglycan (a network of sugar molecules joined by polypeptides), whereas archaeal cell walls contain polysaccharides and proteins but lack peptidoglycan.

Why is the antibiotic penicillin effective against bacteria but not archaea or human cells?

Penicillin specifically inhibits the crosslinking of peptidoglycan molecules, which are present only in bacterial cell walls.

Why are prokaryotic cells typically constrained to very small sizes?

Prokaryotes obtain nutrients by diffusion. A smaller cell size provides a higher surface-area-to-volume ratio, keeping internal components close to the surrounding environment so materials can cross the plasma membrane efficiently.

If the mutation rate in an E. coli gene is $1 \times 10^{-7}$ per cell division and $2 \times 10^{10}$ cells arise daily in a human intestine, how many mutant bacteria for that gene are generated each day?

$1 \times 10^{-7} \times (2 \times 10^{10}) = 2{,}000$ mutant bacteria per day.

What is the difference between vertical gene transfer and horizontal gene transfer?

Vertical gene transfer passes alleles down generations from parent to offspring. Horizontal gene transfer passes alleles within the same generation from one cell to another.

How does horizontal gene transfer spread antibiotic resistance in wastewater?

Step 1: Antibiotics in wastewater select for antibiotic-resistant bacteria. Step 2: When resistant cells die, they release their DNA, and living sensitive cells take up this free DNA through transformation to acquire resistance genes.

What are halophiles and thermophiles, and how does Halobacterium utilize light?

Halophiles thrive in highly saline environments, and thermophiles thrive in extremely hot environments. Halobacterium uses a red pigment to capture light and drive proton pumps to generate ATP.

What are the balanced general chemical equations for photosynthesis and cellular respiration?

Photosynthesis: $6H_2O + 6CO_2 + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$. Cellular respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$.

How are the two stages of photosynthesis coupled together?

Light-dependent reactions convert solar energy into ATP and NADPH. The Calvin cycle (light-independent reactions) uses that ATP and NADPH to fix $CO_2$ into carbohydrates.

How are microbial mats stratified from surface to deep layers?

They are stratified by steep gradients of light and oxygen: surface layers have high light and oxygen (dominated by diatoms and cyanobacteria), while deeper, darker, anoxic layers are dominated by purple sulfur bacteria and sulfate-reducing bacteria.

According to the human microbiome data, what is the distribution percentage of bacterial species across major body sites?

GI tract: $29\%$, Mouth: $26\%$, Skin: $21\%$, Airways: $14\%$, Urogenital tract: $9\%$, and Blood: $1\%$.

How does the intestinal microbiota of African children differ from that of European children?

The gut biota of African children is enriched in the phylum Bacteroidetes (such as Prevotella and Xylanibacter) to break down cellulose in fiber-rich diets, whereas European children are enriched in the phylum Firmicutes.

What therapy has shown a $90\%$ cure rate for severe human microbiome disturbances like C. diff infection?

Fecal transplants.

How does the eukaryotic nuclear membrane affect the central dogma processes compared to prokaryotes?

The eukaryotic nuclear membrane physically separates transcription (which takes place inside the nucleus) from translation (which takes place in the cytoplasm on ribosomes), whereas both occur simultaneously in prokaryotes.

How do single-celled eukaryotic heterotrophs engulf food particles unlike bacteria?

Unlike bacteria (which absorb individual molecules), eukaryotes use a dynamic cytoskeleton and flexible membrane system to engulf large food particles via endocytosis/phagocytosis.

How does chromosome structure differ between typical prokaryotes and eukaryotes?

Prokaryotes typically have a single circular chromosome, while eukaryotes have multiple linear chromosomes packaged with histones into nucleosomes.

What is a protist, and why is it considered a paraphyletic group?

A protist is any eukaryote that is not a plant, animal, or fungus. It is paraphyletic because it includes a common ancestor and some, but not all, of its descendants.

How do meiosis and fertilization contribute to ploidy transitions in the human life cycle?

Meiosis reduces diploid germ cells ($2n = 46$) into haploid gametes ($n = 23$), and fertilization combines sperm and egg nuclei ($23 + 23$) to restore a diploid zygote ($2n = 46$).

What are the specific internal locations of chlorophyll and the Calvin cycle in chloroplasts?

Chlorophyll is located in the thylakoid membranes (the site of light-dependent reactions), while the Calvin cycle occurs in the stroma.

What distinct biological sources formed coal versus petroleum and natural gas?

Coal formed from ancient terrestrial land plants buried in swamps under heat and pressure, while petroleum and natural gas formed from tiny marine algae and animals buried on the ocean floor under heat and pressure.