Unit 4 (Cell Membrane/Transport)

Phospholipid Head

The polar, water-attracting region of a membrane lipid molecule containing a phosphate group.

Hydrophilic

Having an affinity for water; capable of interacting with or dissolving in polar substances.

Phospholipid Tail

The nonpolar, water-repelling portion of a membrane lipid composed of fatty acid hydrocarbon chains.

Hydrophobic

Lacking affinity for water; tending to repel or not dissolve in polar substances.

Cell Transport

The movement of substances across the cellular boundary, either passively down a concentration gradient or actively using metabolic energy.

Fluid Mosaic Model

A framework describing biological membranes as flexible structural layers composed of freely moving proteins embedded within a dynamic lipid sheet.

Phospholipid Bilayer

A two-layered arrangement of amphipathic lipid molecules that forms the foundational structural barrier of cellular membranes.

Polar

Describing a molecule or chemical bond with an unequal sharing of electrons, creating localized partial positive and negative charges.

Nonpolar

Describing a molecule or chemical bond with an equal distribution of electrical charge, resulting in an absence of dipoles.

Semi-Permeable

Allowing certain molecules or ions to pass through via diffusion while blocking others based on physical properties.

Protein Channel

A transmembrane passage that allows specific ions or small polar molecules to cross the lipid core down their concentration gradient.

Cholesterol

A steroid lipid embedded within animal plasma membranes that regulates bilayer fluidity across varying temperatures.

Extracellular Fluid

The bodily aqueous solution that surrounds and bathes cells outside of their plasma boundary.

Cell Membrane

The selectively permeable plasma boundary surrounding the cytoplasm that regulates molecular entry and exit.

Cell Wall

A rigid outer structural layer surrounding the plasma membrane in plants, fungi, and bacteria that provides shape and protection.

Nucleus

The double-membrane-bound organelle in eukaryotic cells containing the genome and serving as the administrative control center.

Nucleolus

A dense region within the eukaryotic nuclear matrix where ribosomal RNA is transcribed and subunit components are assembled.

Cytoplasm

The entire cellular contents enclosed by the plasma membrane outside of the nuclear envelope, including the cytosol and suspended structures.

Cytoskeleton

A network of protein filaments and tubules extending throughout the interior that provides structural support, facilitates movement, and organizes components.

Microtubules

Hollow cylindrical polymers of tubulin that maintain cellular architecture, form spindle fibers during division, and act as transport tracks.

Ribosomes

Complex molecular structures composed of RNA and catalytic proteins that translate messenger RNA into polypeptide chains.

Endoplasmic Reticulum (ER)

An extensive network of folded membranes and branching tubules involved in lipid synthesis, carbohydrate metabolism, and protein processing.

Golgi Apparatus

A series of flattened membrane-bound cisternae that modifies, sorts, and packages proteins and lipids for delivery or secretion.

Lysosomes

Membrane-bound digestive vesicles containing acid hydrolase enzymes that degrade cellular waste, foreign debris, and macromolecules.

Vacuole

A large membrane-bound storage compartment that sequesters water, nutrients, and waste products, while maintaining internal hydrostatic pressure.

Mitochondria

Double-membrane-bound organelles that generate the majority of cellular ATP through the biochemical steps of aerobic respiration.

Centrioles

Paired barrel-shaped cylindrical organelles composed of tubulin triplets that organize the mitotic spindle during animal cell division.

Chloroplasts

Double-membraned photosynthetic organelles containing light-capturing pigments that synthesize glucose via light-driven reactions.

Eukaryote

An organism whose cells possess a membrane-enclosed nucleus and specialized internal compartments.

Organelle

A specialized, membrane-bound or discrete subcellular structure that performs a specific metabolic or physiological function.

Selective Permeability

A property of biological barriers that regulates molecular passage, permitting certain solutes while excluding others.

Passive Transport

The spontaneous net movement of substances across a biological membrane down their concentration gradient without consuming cellular energy.

Diffusion

The spontaneous net movement of particles from a region of higher concentration to one of lower concentration until uniform distribution is achieved.

Osmosis

The net movement of water across a selectively permeable membrane toward a region of higher solute concentration.

Isotonic Solution

An external environment having an equivalent solute concentration to the interior, resulting in zero net water movement across the membrane.

Hypertonic Solution

An external environment with a greater solute concentration than the cellular interior, drawing water outward and causing cellular shrinkage.

Hypotonic Solution

An external environment with a lower solute concentration than the cellular interior, causing net water entry and potential swelling or lysis.

Facilitated Diffusion

The passive movement of polar or charged molecules across a membrane through specialized transmembrane proteins without ATP usage.

Active Transport

The movement of ions or molecules across a cellular boundary against their concentration gradient via metabolic energy consumption.

Protein Pumps

Transmembrane carrier proteins that consume chemical energy (such as ATP) to drive ions or solutes across a membrane against an electrochemical gradient.

Endocytosis

The bulk uptake of external materials into the cell via the invagination and pinching off of the plasma membrane into vesicles.

Exocytosis

The bulk transport process in which intracellular vesicles fuse with the plasma membrane to release their contents into the external surroundings.

Phagocytosis

A cellular process in which large solid particles, such as pathogens or debris, are engulfed by extending pseudopodia to form internal vacuoles.