Cell Theory and Organisms

Cell Theory

• All living things are composed of one or more cells.
• Cells are the fundamental units of structure and function in living organisms.
• All cells arise from pre-existing cells through cell division.

Classifying Cells

• All cells (prokaryotic and eukaryotic) share basic components: DNA, cytoplasm, ribosomes, and a cell membrane.
• Eukaryotic cells contain membrane-bound organelles, specialized structures performing specific tasks within the cell.
• Cytoplasm is largely water, containing organelles and cytosol (the jelly-like substance).

Prokaryotes

• Small, simple, single-celled organisms.
• Lack a membrane-bound nucleus.
• Possess DNA, cytoplasm, ribosomes, and a cell membrane.
• Some employ pili, cilia, or flagella for movement in aquatic environments.
• The number of prokaryotes in a simple sample of soil far exceeds the number of humans who have ever lived.

Eukaryotes

• Large, complex, single-celled or multicellular organisms.
• Possess a membrane-bound nucleus.
• The nucleus houses genetic material (DNA) and functions as the cell's control center.

Species

• A group of organisms capable of interbreeding naturally and producing fertile offspring.

Species Concepts

• Various definitions of species exist.
• Morphological species concept: Focuses on physical characteristics (morphology).
• Biological species concept: Focuses on interbreeding potential.
• Phylogenetic species concept: Emphasis on evolutionary history (phylogeny).

Taxonomy

• The branch of biology concerned with identifying, naming, and classifying species.
• Binomial nomenclature: Standardized two-part naming system (e.g., Homo sapiens).
  • First part: Genus; capitalized.
  • Second part: Species; lowercase.
  • Entire name italicized when typed or underlined when handwritten.
  • Carl Linnaeus (or Carl von Linné) is the "father" of taxonomy and binomial nomenclature.

Taxonomic Categories

• Organisms are grouped into hierarchical categories—ranks or taxa.
• Eight ranks are used to classify organisms.
  • Examples: Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Example hierarchical organization: King Philip Came Over For Good Soup (Kingdom, Phylum, Class, Order, Family, Genus, Species).

Classification

• Modern classification reflects perceived evolutionary relationships, combining morphological and phylogenetic similarities.
• Evidence types used to establish relationships include anatomical, physiological, and DNA data.

Ancestor

• An organism from which other groups evolved.

Anatomical Evidence

• Structural features (bone structures, internal systems) are compared.
• Evidence of shared structures suggests common ancestors.
  • Example: Similar bone structures in the limbs of various mammals (whales, bats, horses, humans).

Physiological Evidence

• Internal processes (e.g., protein functions) are analyzed.
• Comparing proteins' structures provides evidence of relatedness.
  • Example: Comparing insulin protein in different species.

DNA Evidence

• DNA sequences are compared among organisms.
• DNA similarities provide evidence of evolutionary relationships.
  • Example: DNA evidence revealing that fungi are more closely related to animals than to plants.

Six Kingdoms (and Three Domains)

• Scientists recognized the need for a broader classification system (domains) than kingdoms.
• Bacteria and Archaea are now classified as separate domains.
• Eukarya now encompasses the other four kingdoms.

Autotroph

• Organisms that produce their own food through processes like photosynthesis.

Heterotroph

• Organisms that obtain energy by consuming other organisms.

Virus (Phage)

• Non-cellular infectious agent; requires a host cell for replication.
• Contains DNA or RNA (not both).
• Classified based on various criteria (size, shape, genetic material, host, diseases).

Viral Reproduction

• Lytic cycle: Virus replicates and lyses the host cell.
• Lysogenic cycle: Virus integrates its DNA into the host’s DNA, remaining dormant until activation.
• Retrovirus: Uses reverse transcriptase to convert RNA to DNA.

Prions

• Infectious proteins that cause misfolding of normal proteins (e.g., in the brain).
• Not a virus; lack genetic material.

Bacteria Characteristics

• Prokaryotic, single-celled organisms.
• Often have cell walls.
• Possess circular DNA (plasmids).
• Can be autotrophic or heterotrophic.
• Reproduce asexually via binary fission or sexually by conjugation.

Bacteria Shapes

• Cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

Extremophiles

• Organisms adapted to extreme conditions (e.g., high salt).

Mesophiles

• Organisms adapted to moderate environments.

Archaebacteria

• Methanogens: Methane-producing anaerobes.
• Halophiles: Salt-loving aerobes.
• Thermophiles: Heat-loving organisms.

Eubacteria

• Cyanobacteria: Photosynthetic bacteria, responsible for the Earth’s early oxygen production.

Binary Fission

• Asexual reproduction in bacteria, results in two identical daughter cells.