Glossary
atom: a basic unit of matter that cannot be broken down by ordinary chemical reactions
biology: the study of living organisms and their interactions with one another and their environments
biosphere: a collection of all ecosystems on Earth
cell: the smallest fundamental unit of structure and function in living things
community: a set of populations inhabiting a particular area
ecosystem: all living things in a particular area together with the abiotic, nonliving parts of that environment
eukaryote: an organism with cells that have a membrane-bound nucleus and many organelles
evolution: the process of gradual change in a population that can also lead to new species arising from older species
homeostasis: the ability of an organism to maintain constant internal conditions despite the external environment
macromolecule: a large molecule typically formed by the joining of smaller molecules
molecule: a chemical structure consisting of at least two atoms held together by a chemical bond
organ: a group of tissues operating together to perform a common function
organ system: two or more organs that perform a common function
organelle: a membrane-bound compartment or sac within a cell
organism: an individual living entity
phylogenetic tree: a diagram showing the evolutionary relationships among biological species based on similarities and differences in genetic or physical traits or both
population: all individuals within a species living within a specific area
prokaryote: a unicellular organism that lacks a membrane-bound nucleus and few organelles
tissue: a group of similar cells carrying out the same function
Section Summary
Themes and Concepts of Biology
Biology is the science of life. All living organisms share several key characteristics such as order, response to stimuli, reproduction, adaptation, growth and development, maintaining homeostasis, and obtaining materials and energy. Living things are highly organized following a hierarchy that includes atoms, molecules, organelles, cells, tissues, organs, and organ systems. Organisms, in turn, are grouped as populations, communities, ecosystems, and the biosphere. Evolution is the source of the tremendous biological diversity on Earth today. A diagram called a phylogenetic tree can be used to show evolutionary relationships among organisms.