Chapter 3: The Cellular Level of Organization

Vocabulary practice flashcards covering cell structure, organelles, membrane transport mechanisms, gene expression, and cell division.

Prokaryotic Cell

A simple cell lacking a nucleus, named from Pro ("before") and karyon ("nucleus"); mostly unicellular bacteria.

Eukaryotic Cell

A complex cell containing a nucleus and subcellular structures called organelles; includes all fungi, plants, and animals.

Plasma Membrane

The flexible yet sturdy, selectively permeable outer boundary of a cell that separates its internal environment from the external environment and regulates transport and communication.

Cytoplasm

All cellular contents located between the plasma membrane and the nucleus, consisting of the fluid cytosol along with structural fibers and organelles.

Cytosol

The intracellular fluid portion of the cytoplasm (mostly water) surrounding the organelles, serving as the site of many metabolic chemical reactions.

Nucleus

A large organelle surrounded by a nuclear envelope that stores the cell's genetic material in DNA molecules organized into chromosomes.

Gene

A hereditary unit located on a chromosome containing instructions that control specific cellular structures and functions.

Fluid Mosaic Model

A model describing the structural arrangement of the plasma membrane as a sea of phospholipids in which protein "icebergs" float.

Integral Protein

A membrane protein that extends into or through the lipid bilayer; most are transmembrane proteins spanning the entire layer.

Peripheral Protein

A membrane protein attached to the inner or outer surface of the lipid bilayer that does not extend through the membrane.

Glycocalyx

The carbohydrate coating on the outer surface of the plasma membrane, formed by the carbohydrate portions of glycolipids and glycoproteins.

Ligand

A specific molecule that binds to a membrane receptor to alter cellular activity.

Selective Permeability

The property of the plasma membrane that permits certain substances to pass through freely while restricting others.

Passive Process

A transport mechanism in which substances move across a cell membrane down their concentration gradient without cellular energy input.

Active Process

A transport mechanism requiring cellular energy (primarily ATP) to move a substance across a cell membrane against its concentration gradient.

Osmosis

The net movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

Tonicity

A measure of the concentration of salt solutions relative to intracellular fluids, determining the osmotic movement of water into or out of cells.

Sodium-Potassium Pump

An active transport carrier protein ($\text{Na}^+/\text{K}^+$ ATPase) found in all cells that maintains ion gradients by pumping $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell using ATP.

Antiporter

A secondary active transport carrier protein that moves two substances across the membrane in opposite directions.

Symporter

A secondary active transport carrier protein that moves two substances across the membrane in the same direction.

Endocytosis

A vesicular transport process in which extracellular materials are brought into a cell within vesicles formed from the plasma membrane.

Phagocytosis

A form of endocytosis in which a cell extends pseudopods to engulf large solid particles or microbes into a phagosome.

Exocytosis

A transport process where membrane-bound vesicles fuse with the plasma membrane to release their contents into the extracellular fluid.

Transcytosis

A transport process combining endocytosis and exocytosis to transport a substance across and out of a cell.

Cytoskeleton

A network of protein filaments—comprising microfilaments, intermediate filaments, and microtubules—extending throughout the cytosol to provide structural support.

Centrosome

An organelle near the nucleus consisting of two centrioles surrounded by pericentriolar material, serving as the organizing center for microtubule growth and mitotic spindle formation.

Cilia

Short, hair-like projections extending from the cell surface that move fluids along the cell surface.

Flagella

Long cell surface projections that move an entire cell; the sperm cell tail is the only human example.

Ribosome

An organelle composed of large and small subunits that serves as the site of cellular protein synthesis.

Rough Endoplasmic Reticulum

A network of flattened membrane sacs continuous with the nuclear envelope and studded with ribosomes, involved in protein production.

Smooth Endoplasmic Reticulum

A network of membrane tubules lacking ribosomes that synthesizes fatty acids and steroids and detoxifies drugs.

Golgi Complex

An organelle consisting of 3 to 20 flattened membranous sacs called cisternae that modifies, sorts, and packages proteins for transport.

Lysosome

A membrane-bound vesicle formed from the Golgi complex that contains digestive enzymes for degrading waste and foreign material.

Peroxisome

A small organelle abundant in liver cells that detoxifies toxic substances such as alcohol.

Proteasome

A protein-degrading structure found in the cytosol and nucleus that continuously destroys unneeded, damaged, or faulty proteins.

Mitochondrion

The "powerhouse" of the cell responsible for generating ATP, featuring outer and inner membranes, folded cristae, and a central matrix.

Nuclear Envelope

A double membrane perforated by nuclear pores that separates the nuclear interior from the cytoplasm.

Nucleolus

A spherical structure inside the nucleus that produces ribosomal subunits.

Transcription

The first step of gene expression occurring in the nucleus, in which a specific DNA sequence is transcribed into RNA.

Translation

The second step of gene expression occurring in the cytoplasm, where ribosomes read mRNA codons to assemble a protein.

Interphase

The non-dividing phase of the cell cycle consisting of $G_1$ (organelle duplication), S (DNA replication), and $G_2$ (cell growth and enzyme synthesis) phases.

Mitosis

The nuclear division phase of somatic cell division, comprised of prophase, metaphase, anaphase, and telophase.

Cytokinesis

The division of a cell's cytoplasm into two identical daughter cells, marked by the formation of a cleavage furrow during late anaphase.

Homologous Chromosomes

Two matching chromosomes that form a pair in diploid somatic cells, containing genes controlling the same traits.

Diploid Cell

A cell containing two sets of chromosomes ($2n$ = 46 in human somatic cells).

Haploid Cell

A cell containing a single set of chromosomes ($n$ = 23 in human gametes).

Meiosis

Reproductive cell division in the gonads comprising two successive divisions (meiosis I and meiosis II) that yields four genetically distinct haploid gametes.