Study Guide

Prokaryotes vs. Eukaryotes

Key differences between prokaryotic and eukaryotic cells include organization, size, and complexity. Prokaryotes lack a nucleus and membrane-bound organelles, while eukaryotes do have a nucleus.

Shapes of Prokaryotes

Main shapes of prokaryotes include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).

Cell Wall Differences

Prokaryotic cell walls differ from those of fungi and plants in composition: prokaryotes generally have peptidoglycan, while fungi have chitin and plants have cellulose.

Gram Staining

Three differences between Gram-positive and Gram-negative bacteria are:

  1. Cell wall structure: Gram-positive has a thick peptidoglycan layer, whereas Gram-negative has a thin layer plus an outer membrane.

  2. Staining reaction: Gram-positive retains crystal violet stain, resulting in a purple appearance.

  3. Sensitivity to antibiotics: Gram-positive is generally more susceptible to certain antibiotics than Gram-negative.

Bacterial Structures and Functions

  1. Capsule: Protects against desiccation and phagocytosis.

  2. Fimbriae: Aids in attachment to surfaces.

  3. Pili: Facilitates genetic transfer (conjugation).

  4. Flagellum: Provides motility.

  5. Nucleoid: Contains genetic material (DNA).

  6. Plasmid: Carries extra-chromosomal genes.

  7. Endospores: Enable survival in harsh conditions.

Plasma Membrane Infoldings

Specialized infoldings include thylakoids (photosynthesis) and mesosomes (aids in cell division).

Metabolic Types

Distinctions among metabolic types: photoautotrophs (light for energy), chemoautotrophs (chemicals for energy), photoheterotrophs (light for energy and organic compounds), and chemoheterotrophs (organic compounds for both).

Oxygen Requirements

  1. Obligate aerobes require oxygen.

  2. Obligate anaerobes cannot tolerate oxygen.

  3. Facultative anaerobes can use oxygen but can also live without it.

Nitrogen Fixation

Heterocysts are specialized cells in cyanobacteria that perform nitrogen fixation, converting atmospheric nitrogen into a usable form for the organism.

Binary Fission

Binary fission is the asexual reproduction process in prokaryotes where a cell divides into two identical cells.

Horizontal Gene Transfer

Horizontal gene transfer includes transformation (uptake of DNA), transduction (transfer via viruses), and conjugation (direct transfer between bacteria), which contribute to genetic diversity.

Conjugation Mechanisms

The F factor is a plasmid that allows gene transfer during conjugation. R plasmids carry genes that confer antibiotic resistance.

Endosymbiosis Definitions

Definitions include:

  • Endosymbiosis: a symbiotic relationship where one organism lives inside another.

  • Serial endosymbiosis: a theory suggesting a sequential process of symbiotic events.

  • Primary endosymbiosis: initial incorporation of prokaryotic cells into eukaryotic ancestors.

  • Secondary endosymbiosis: incorporation of eukaryotic cells into other eukaryotes.

Evidence for Endosymbiont Theory

Evidence supporting this theory includes genetic, structural, and functional similarities between mitochondria, plastids, and prokaryotes.

Multicellularity Evolution Hypotheses

Various hypotheses address the evolution of multicellularity, focusing on diversification and specialization of cells within organisms.

Choanoflagellates

Choanoflagellates are identified as the closest living relatives of animals based on genetic and morphological evidence.

Organisms from Excavata Supergroup

  1. Giardia - intestinal parasite.

  2. Trichomonas vaginalis - sexually transmitted parasite.

  3. Trypanosoma cruzi - causes Chagas disease.

  4. Euglena - photosynthetic flagellate.

Organisms from SAR Supergroup

  • Stramenopiles: Diatoms (silica cell walls) and Brown Algae (complex multicellular structures).

  • Alveolates: Peridinium (dinoflagellate), Plasmodium (malaria agent), Paramecium (ciliate), and Stentor (trumpet-shaped ciliate).

  • Rhizarians: Foraminifera (calcium carbonate shells) and Radiolarians (silica-based skeletons).

Organisms from Archaeplastida

  1. Red Algae - important in marine ecosystems.

  2. Spirogyra - filamentous green algae.

  3. Volvox - colonial green algae.

Unikonta Organisms

  • Amoeba proteus (Amoebozoan) - versatile protozoan.

  • Rhizopus (Opisthokont) - bread mold isotopes and functions.