Domain Eukarya

Overview of Domain Eukarya

Domain Eukarya comprises all organisms composed of eukaryotic cells. Eukaryotes are characterized by their complex cellular organization, including a distinct, membrane-bound nucleus that houses the organism's genetic material.

Key Characteristics

Membrane-Bound Nucleus: Genetic material (DNA) is organized into linear chromosomes associated with histone proteins and enclosed within a nuclear envelope.
Organelles: Contains specialized, membrane-bound structures such as mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes (and chloroplasts in photosynthetic organisms).
Cellular Size: Typically much larger than prokaryotic cells, ranging from approximately $10\,\mu m$ to $100\,\mu m$ in diameter.
Cell Division: Reproduces cellularly through mitosis (for asexual division/growth) and meiosis (for sexual reproduction).
Ribosomes: Contains $80S$ ribosomes in the cytoplasm (composed of $60S$ and $40S$ subunits), distinct from the $70S$ ribosomes found in prokaryotes.

Major Taxonomic Kingdoms

Protista
- Unicellular or simple multicellular organisms.
- Highly diverse group including protozoa, algae, and slime molds.
Fungi
- Heterotrophic organisms that absorb nutrients from their environment.
- Possess cell walls composed of chitin.
- Examples include yeasts, molds, and mushrooms.
Plantae
- Multicellular, autotrophic organisms capable of photosynthesis.
- Possess cell walls composed of cellulose and chloroplasts containing chlorophyll.
- Examples include mosses, ferns, gymnosperms, and angiosperms.
Animalia
- Multicellular, heterotrophic organisms that ingest other organisms for nutrition.
- Lack cell walls and typically exhibit motility at some life stage.
- Examples include invertebrates and vertebrates.

Evolutionary Origins

Endosymbiotic Theory: Explains the evolution of eukaryotic cells from ancestral prokaryotic hosts that engulfed aerobic bacteria (which evolved into mitochondria) and photosynthetic cyanobacteria (which evolved into chloroplasts).