The cellular level of organization

Cell

The smallest unit of life, with varying shapes, sizes, and functions.

Homeostasis

The process by which each cell maintains a stable internal environment.

Plasma membrane

A thin, flexible barrier that surrounds and contains the cytoplasm of a cell.

Phospholipid bilayer

The basic framework of the plasma membrane, consisting of two layers of phospholipid molecules.

Diffusion

The natural tendency for dissolved substances to spread from an area of higher concentration to an area of lower concentration.

Facilitated diffusion

Diffusion of substances through channels in membrane proteins that cannot pass through the phospholipid bilayer.

Osmosis

The diffusion of water through a selectively permeable membrane.

Active transport

The process of pumping atoms or molecules into or out of a cell through channels in special membrane proteins against a concentration gradient.

Endocytosis

The process of bringing molecules or particles into a cell by engulfing them within a vesicle.

Exocytosis

The reverse of endocytosis, where substances are transported out of a cell in vesicles.

Cytoplasm

The liquid and organelles within a cell, excluding the nucleus.

Cytoskeleton

A network of protein fibers that maintain cell shape and facilitate movement.

Ribosomes

The sites of protein synthesis in the cell.

Endoplasmic reticulum (ER)

A network of flattened membrane tubes involved in protein and lipid synthesis.

Golgi apparatus

An organelle that modifies, sorts, and packages proteins and lipids for transport.

Mitochondria

Organelles known as the powerhouses of the cell, generating ATP through cellular respiration.

Lysosomes

Organelles that contain digestive enzymes to break down waste materials within the cell.

Nucleus

The control center of a cell, containing genetic material and regulating cell activity.

Chromosomes

Structures made of DNA that contain genes.

Gene expression

The process by which information from a gene is used to synthesize a functional gene product, usually a protein.

Transcription

The process of copying a segment of DNA into RNA.

Translation

The process in which ribosomes interpret mRNA sequences to assemble proteins.

Stem cell

An unspecialized cell that can divide to produce more cells or differentiate into specialized cell types.