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Organelle

A membrane-bounded structure that has a specific function within a cell.

Cell

The fundamental unit of life; multicellular organisms consist of many cells; unicellular organisms consist of one cell.

Tissue

A collection of specialized cells that function in a coordinated fashion.

Molecule

A group of joined atoms.

Atom

The smallest chemical unit of a type of pure substance (element).

Organism

A single living individual.

Population

A group of the same species of organism living in the same place and time.

Organ

A structure consisting of tissues organized to interact and carry out specific functions.

Organ System

Organs connected physically or chemically that function together.

Community

All populations that occupy the same region.

Ecosystem

The living and nonliving components of an area.

Biosphere

The global ecosystem; the parts of the planet and its atmosphere where life is possible.

Cell Theory

Three principles stating that all living organisms are made up of cells, all known lifeforms are composed of cells, and all cells come from pre-existing cells.

Surface Area to Volume Ratio

A factor limiting cell size; as cell size increases, volume increases faster than surface area.

Phospholipid Bilayer

A double layer of phospholipids that makes up the cell membrane.

Selectively Permeable Membrane

A membrane that allows certain molecules to pass through while blocking others.

Ribosomes

RNA/protein organelles that synthesize proteins from RNA nucleotide codes.

Lysosome

An organelle that recycles old or damaged cell components and removes cellular wastes.

Cytoskeleton

An internal scaffolding of the cell made up of a complex network of interlinking protein filaments.

Plasmodesmata

Channels in plant cell walls that connect neighboring cells and allow for transport and communication.

Cell Junctions

Structures that connect animal cells together, including tight junctions, anchoring junctions, and gap junctions.