Introduction to Biology: Characteristics, Principles, and Organization of Life

Biology: The Study of Scientific Life

Big Picture

Biology is the scientific study of living things, known as organisms. It distinguishes living things from nonliving things based on several key characteristics, including response to the environment, growth, reproduction, homeostasis, complex chemistry, and cellular structure. Biologists use these characteristics to understand how organisms interact with each other and their environment, and to explore major concepts such as the cell theory, gene theory, homeostasis, and evolution.

Key Terms

• Biology: The study of living things.

• Evolution: Change in characteristics of living things over time.

• Natural Selection: The process by which organisms with favorable traits produce more offspring and pass on those traits.

• Adaptation: A characteristic that helps organisms survive and reproduce in a specific environment.

• Population: A group of organisms of the same species living in a given area.

• Community: All organisms living in a given area.

• Ecosystem: All living and nonliving factors in a given area.

• Biome: A group of similar ecosystems.

• Biosphere: The part of Earth where all life exists.

• Symbiosis: A relationship between different organisms where at least one benefits.

• Competition: The relationship between organisms needing the same resources in the same place at the same time.

Characteristics of Life

What Makes an Organism Alive?

• Response to the Environment: Organisms detect and respond to changes in their environment.

• Growth and Development: Organisms grow and develop over time.

• Reproduction: Organisms produce offspring to continue their species.

• Homeostasis: Organisms maintain stable internal conditions (e.g., body temperature).

• Complex Chemistry: Organisms are made of complex molecules that undergo chemical changes to stay alive.

• Cellular Organization: Organisms are made up of cells, the basic unit of structure and function.

Unifying Principles of Biology

• Cell Theory: All living things are made up of cells, and all cells come from other cells.

• Gene Theory: Genes, located on chromosomes, determine the characteristics of living things and are passed from parents to offspring.

• Homeostasis: Living things maintain constant internal conditions despite external changes.

• Evolution: Through natural selection, organisms become better suited to their environments over time by developing adaptations.

Organization and Interdependence of Living Things

Levels of Biological Organization

• Population: A group of the same species living in an area.

• Community: All populations of different species in an area.

• Ecosystem: All living (biotic) and nonliving (abiotic) factors in an area.

• Biome: A group of similar ecosystems.

• Biosphere: The global sum of all ecosystems; where all life exists on Earth.

Example: A herd of giraffes, all the plants, animals, bacteria, water, and soil in the savanna make up different levels of biological organization, from population to biosphere.

Interactions Among Organisms

• Organisms depend on their environment and other organisms for survival.

• Key relationships include symbiosis (mutually beneficial relationships) and competition (organisms competing for the same resources).

Table: Characteristics of Life vs. Unifying Principles of Biology

Characteristics of Life	Unifying Principles of Biology
Response to environment	Cell theory
Growth and development	Gene theory
Reproduction	Homeostasis
Homeostasis	Evolution
Complex chemistry	—
Cellular organization	—

Additional info: The above table summarizes how the basic characteristics of life relate to the foundational principles that unify the field of biology.