Biology » The Study of Life » Themes and Concepts of Biology

Summary and Main Ideas

Summary of Lessons So Far

Biology is the science of life. All living organisms share several key properties such as order, sensitivity or response to stimuli, reproduction, growth and development, regulation, homeostasis, and energy processing.

Living things are highly organized parts of 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.

The great diversity of life today evolved from less-diverse ancestral organisms over billions of years. A diagram called a phylogenetic tree can be used to show evolutionary relationships among organisms.

Biology is very broad and includes many branches and subdisciplines. Examples include molecular biology, microbiology, neurobiology, zoology, and botany, among others.

Glossary of Words

Atom

smallest and most fundamental unit of matter

Biochemistry

study of the chemistry of biological organisms

Biosphere

collection of all the ecosystems on Earth

Botany

study of plants

Cell

smallest fundamental unit of structure and function in living things

Community

set of populations inhabiting a particular area

Ecosystem

all the living things in a particular area together with the abiotic, nonliving parts of that environment

Eukaryote

organism with cells that have nuclei and membrane-bound organelles

Evolution

process of gradual change during which new species arise from older species and some species become extinct

Homeostasis

ability of an organism to maintain constant internal conditions

Macromolecule

large molecule, typically formed by the joining of smaller molecules

Microbiology

study of the structure and function of microorganisms

Molecule

chemical structure consisting of at least two atoms held together by one or more chemical bonds

Molecular Biology

study of biological processes and their regulation at the molecular level, including interactions among molecules such as DNA, RNA, and proteins

Neurobiology

study of the biology of the nervous system

Organ

collection of related tissues grouped together performing a common function

Organ system

level of organization that consists of functionally related interacting organs

Organelle

small structures that exist within cells and carry out cellular functions

Organism

individual living entity

Paleontology

study of life’s history by means of fossils

Phylogenetic tree

diagram showing the evolutionary relationships among various biological species based on similarities and differences in genetic or physical traits or both; in essence, a hypothesis concerning evolutionary connections

Population

all of the individuals of a species living within a specific area

Prokaryote

single-celled organism that lacks organelles and does not have nuclei surrounded by a nuclear membrane

Tissue

group of similar cells carrying out related functions

Zoology

study of animals

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