Ch. 4 Evolutionary Origin of Cells and Their General Features

Anoxic: Refers to an environment or condition that lacks oxygen. Anoxic conditions are often found in deep water, soil, or other environments where oxygen does not readily diffuse.

Protobionts: Simple, prebiotic structures that are considered to be precursors to living cells. Protobionts are thought to have been the first steps toward life, capable of undergoing basic processes like simple metabolism or replication.

Liposomes: Small, spherical vesicles made of lipid bilayers that are similar to the membranes of cells. Liposomes are often used in scientific research for drug delivery and as models for studying cell membranes.

Prokaryote: A single-celled organism that lacks a nucleus and membrane-bound organelles. Prokaryotes include bacteria and archaea. Their genetic material is typically organized into a single, circular DNA molecule in the nucleoid region.

Eukaryote: An organism whose cells have a defined nucleus and membrane-bound organelles. Eukaryotes include plants, animals, fungi, and protists. The nucleus houses the cell’s DNA, and organelles perform specialized functions.

Cytosol: The gel-like substance that fills the interior of the cell, in which the organelles are suspended. It is part of the cytoplasm but excludes the organelles. It plays a role in the transport of materials within the cell.

Nucleus: The membrane-bound organelle in eukaryotic cells that contains the cell's genetic material (DNA). The nucleus controls most cell functions by regulating gene expression and mediating cell division.

Endomembrane System: A network of membranes within a eukaryotic cell that includes the nuclear envelope, the endoplasmic reticulum (ER), the Golgi apparatus, lysosomes, and vesicles. This system is involved in the synthesis, modification, and transport of proteins and lipids.

Semiautonomous Organelles: Organelles that have their own DNA and can reproduce independently to some extent, but still rely on the cell for some functions. Examples include mitochondria and chloroplasts. These organelles are believed to have evolved from free-living bacteria.

Endosymbiosis: A theory that suggests mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by a host cell, forming a mutualistic relationship. Over time, these engulfed prokaryotes became permanent parts of the host cell, evolving into the organelles we see today.