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Organism

A living thing that maintains an internal order that is separated from the environment.

Cell

The simplest unit of a living organism.

Cell Theory

A theory that states that all organisms are made of cells, cells are the smallest units of living organisms, and new cells come from pre-existing cells by cell division.

Respiration

Metabolic reactions that a cell uses to get energy from food molecules and release waste products.

Metabolism

The sum total of all chemical reactions that occur within an organism. Also, a specific set of chemical reactions occurring at the cellular level.

Photosynthesis

The process whereby light energy is captured by plant, algal, or bacterial cells and used to synthesize organic molecules from carbon dioxide and water.

Homeostasis

The process whereby living organisms regulate their cells and bodies to maintain relatively stable internal conditions.

Growth

An increase in weight or size.

Development

A series of changes in the state of a cell, tissue, organ, or organism; the underlying process that gives rise to the structure and function of living organisms.

Reproduce

To generate offspring by sexual or asexual means.

DNA

The genetic material that provides a blueprint for the organization, development, and function of living things.

Gene

A unit of heredity that contributes to the characteristics or traits of an organism. At the molecular level, a gene is composed of organized sequences of DNA.

RNA

One of two classes of nucleic acids; consists of a single strand of nucleotides.

Polypeptide

A linear sequence of amino acids; the term denotes structure.

Protein

A functional unit composed of one or more polypeptides. Each polypeptide is composed of a linear sequence of amino acids

Biological Evolution

The phenomenon that populations of organisms change from generation to generation.

Atom

The smallest functional unit of matter that forms all chemical substances and cannot be further broken down into other substances by ordinary chemical or physical means.

Molecules

Two or more atoms that are connected by chemical bonds.

Macromolecule

Many molecules bonded together to form a polymer. Carbohydrates, proteins, and nucleic acids are important macromolecules found in living organisms.

Tissue

The association of many cells of the same type.

Organ

Two or more types of tissue combined to perform a common function.

Species

A group of related organisms that share a distinctive form in nature and are capable of interbreeding.

Population

A group of individuals of the same species that occupy the same environment and can interbreed with one another.

Community

An assemblage of populations of different species that live in the same place at the same time.

Ecosystem

The biotic community of organisms in an area as well as the abiotic environment affecting that community.

Biosphere

The regions on the surface of the Earth and in the atmosphere where living organisms exist.

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