Biology: The Study of Life

Definition and Etymology

Biology is the scientific study of life. The term is derived from the Greek words "bio-" meaning "life" and "-ology" meaning "the study of." Biology encompasses the investigation of living organisms, their structure, function, growth, origin, evolution, and distribution.

• Cell: The smallest, most basic/fundamental unit of life.

• Organism: Any individual form of life (can be applied to all forms of life).

Example: Humans, plants, animals, fungi, and bacteria are all considered organisms.

Unicellular vs. Multicellular Organisms

Types of Living Organisms

Living organisms can be classified as unicellular (single-celled) or multicellular (composed of multiple cells).

• Unicellular organisms: Forms of life that consist of a single cell (usually only seen with microscopes). Example: Bacteria, some protists.

• Multicellular organisms: Forms of life that consist of multiple cells. Example: Animals, plants, fungi.

Characteristics of Life

Defining Features of Living Things

All living organisms share eight characteristics that distinguish them from nonliving things:

• 1. Composed of cells: Smallest unit of life.

• 2. Organization: Living things have a complex, ordered structure.

• 3. Respond to environmental stimuli: Ability to sense and react to changes.

• 4. Maintain homeostasis: Maintain stable internal conditions.

• 5. Reproduce: Capacity to produce new organisms.

• 6. Grow and develop: Increase in size and complexity over time.

• 7. Genetic information: DNA contains hereditary information.

• 8. Evolution: Populations change over generations through adaptation.

Note: Viruses are not considered alive because they do not meet all these criteria.

Organization of Life: Hierarchical Structure

Levels of Biological Organization

Life consists of multiple parts organized into a hierarchical pattern, from the smallest to the largest scale:

Example: A forest ecosystem includes populations of trees, animals, and microorganisms, all interacting with each other and their environment.

Emergent Properties

Definition and Examples

Emergent properties are characteristics that arise when combining smaller parts, even though the individual parts do not display these properties. At each new level of the hierarchy, the whole is greater than the sum of its parts.

• Example: Cells are made of simple molecules, but when organized together, these molecules can perform living functions.

Emergence of Life: Life emerges at the cellular level in the organizational hierarchy.

Summary Table: Hierarchy of Life

Key Terms and Definitions

• Homeostasis: The maintenance of stable internal conditions in an organism.

• Stimulus: Any change in the environment that elicits a response from an organism.

• Evolution: The process by which populations of organisms change over generations.

• Genetic Information: Hereditary material (DNA) that is passed from one generation to the next.

Practice and Application

• Biology is the study of life and its processes.

• All living things share eight key characteristics, including organization, homeostasis, and the ability to evolve.

• Life is organized in a hierarchy from atoms to the biosphere, with emergent properties arising at each level.

• Cells are the basic unit of life, and life emerges at the cellular level.