Cell Structure, Transport, and Tonicity

Comprehensive vocabulary flashcards covering cell structure, organelles, membrane transport, tonicity, water potential, and immune cell functions.

Cells

The basic structural and functional units of every organism.

Prokaryotes

Organisms such as Bacteria and Archaea that lack membrane-bound organelles, have DNA localized in a nucleoid region, and are smaller than eukaryotes.

Eukaryotes

Organisms including protists, fungi, animals, and plants that contain membrane-bound organelles and house their DNA inside a nucleus.

Compartmentalization

The division of cellular space by membranes into distinct environments, which allows specific metabolic reactions to occur in different locations, increases surface area, and prevents interfering reactions from occurring in the same place.

Nucleus

An organelle enclosed by a double membrane (nuclear envelope) with pores that regulate the entry and exit of materials, functioning to contain chromosomes and genetic information.

Nucleolus

A dense region within the nucleus where ribosomal RNA (rRNA) is synthesized and assembled with proteins to form the large and small subunits of ribosomes.

Ribosomes

Cellular structures composed of ribosomal RNA and proteins that synthesize proteins; found floating freely in the cytosol or bound to the endoplasmic reticulum and nuclear envelope.

Rough Endoplasmic Reticulum

A network of membranous sacs and tubes bound with ribosomes that functions to synthesize proteins and compartmentalize them away from free ribosomes.

Smooth Endoplasmic Reticulum

A region of the endoplasmic reticulum lacking ribosomes that synthesizes lipids, metabolizes carbohydrates, and detoxifies the cell.

Golgi Complex

An organelle made of flattened membranous sacs (cisternae) with distinct cis and trans faces that receives, modifies, sorts, adds molecular tags to, and packages materials into transport vesicles for secretion.

Cisternae

Flattened membranous sacs of the Golgi complex that are not physically connected to each other and separate the internal lumen from the cytosol.

Lysosomes

Membranous sacs found in animal cells containing hydrolytic enzymes that catalyze hydrolysis reactions to break down macromolecules.

Autophagy

A recycling process in which lysosomes break down and recycle the cell's own organic material using hydrolytic enzymes.

Peroxisomes

Membrane-bound metabolic compartments that catalyze reactions producing $H_2O_2$, which enzymes inside then break down into water.

Endosymbiont Theory

The theory stating that an early eukaryotic cell engulfed a prokaryotic cell that established an endosymbiotic relationship, eventually evolving into mitochondria and chloroplasts.

Cristae

The internal folds of the inner mitochondrial membrane that divide the organelle into compartments and increase surface area for cellular respiration.

Mitochondrial Matrix

The internal fluid compartment enclosed by the inner mitochondrial membrane containing enzymes that catalyze the Krebs cycle, mitochondrial DNA, and ribosomes to produce ATP.

Thylakoids

Membranous sacs within chloroplasts that organize into stacks called grana and serve as the site where light-dependent reactions occur.

Stroma

The fluid surrounding the thylakoids inside a chloroplast's double membrane; contains chloroplast DNA, ribosomes, and enzymes, and hosts the Calvin cycle.

Cytoskeleton

A network of fibers spanning the cytoplasm that provides mechanical and structural support, anchors organelles, and facilitates movement of vesicles and cells via motor proteins.

Microtubules

Rod-like cytoskeletal fibers made of the protein tubulin that grow from centrosomes to provide structural support, assist in chromosome separation during cell division, and enable cell mobility in cilia and flagella.

Microfilaments

Thin, solid cytoskeletal rods made of the protein actin that maintain cell shape, assist in cell mobility, interact with myosin to cause muscle contraction, and form the cleavage furrow during animal cell division.

Intermediate Filaments

Permanent structural fibrous proteins made of varying subunits that maintain cell shape, anchor the nucleus and organelles, and form the nuclear lamina lining the nuclear envelope.

Plasmodesmata

Hole-like channels through plant cell walls filled with cytosol that connect and facilitate communication between adjacent plant cells.

Fluid Mosaic Model

A model describing the structure of cell membranes as a dynamic, fluid phospholipid bilayer held together by weak hydrophobic interactions, interspersed with a mosaic of proteins, steroids, and carbohydrates.

Selective Permeability

The regulatory capacity of biological membranes to allow certain substances to pass through more easily than others.

Integral Proteins

Amphipathic proteins embedded into the hydrophobic interior of the lipid bilayer, often functioning as transmembrane proteins.

Peripheral Proteins

Membrane proteins that are not embedded in the lipid bilayer but are loosely bound to the external or internal surface of the membrane.

Glycolipids

Carbohydrates covalently bonded to membrane lipids that act as recognition markers in cell-to-cell identification.

Glycoproteins

Carbohydrates covalently bonded to membrane proteins that serve as the most abundant markers for cell-to-cell recognition.

Passive Transport

The movement of molecules across a cellular membrane down their concentration or electrochemical gradient without the expenditure of cellular energy.

Diffusion

The passive net movement of substances from an area of high concentration to an area of low concentration down their concentration gradient.

Osmosis

The diffusion of water across a selectively permeable membrane down its concentration gradient, moving from an area of low solute concentration to high solute concentration.

Facilitated Diffusion

The passive movement of polar or charged solutes down their concentration gradient through the membrane with the assistance of channel or carrier transport proteins.

Aquaporins

Specific channel proteins embedded in the membrane that facilitate the rapid passage of water molecules.

Carrier Proteins

Membrane transport proteins that undergo conformational shape changes to move specific solute molecules across the membrane.

Active Transport

The movement of a substance across a cellular membrane against its concentration gradient, requiring metabolic energy such as ATP.

Membrane Potential

An electrical charge difference across a membrane caused by unequal ion concentrations, where the cytoplasm remains relatively negative compared to the extracellular fluid.

Electrogenic Pumps

Membrane proteins that generate voltage across a membrane by pumping ions, storing energy as an electrochemical gradient for cellular processes.

Sodium-Potassium Pump

An electrogenic pump in animal cells that exports $3\,Na^+$ ions out of the cell and imports $2\,K^+$ ions into the cell, yielding a net $+1$ charge to the extracellular fluid.

Proton Pump

An integral membrane protein utilized by plants, fungi, and bacteria that actively pumps $H^+$ out of the cell to build up an electrochemical proton gradient.

Cotransport

A mechanism coupling the favorable downhill diffusion of one substance to the unfavorable uphill transport of a second substance against its concentration gradient.

Exocytosis

The active cellular export of materials where intracellular vesicles fuse their lipid bilayer with the plasma membrane to release contents into the extracellular fluid.

Endocytosis

The cellular uptake of extracellular molecules and matter through the invagination and pinching off of the plasma membrane into vesicles.

Phagocytosis

A form of endocytosis ('cell eating') in which a cell wraps pseudopodia around a large particle, encapsulating it into a food vacuole that fuses with a lysosome for digestion.

Pinocytosis

A form of endocytosis ('cell drinking') characterized by the nonspecific uptake of extracellular fluid and dissolved solutes inside protein-coated vesicles.

Receptor-Mediated Endocytosis

A targeted form of endocytosis where specific solute molecules bind to surface receptors, clustering together to be internalized in coated vesicles.

Tonicity

The ability of an extracellular solution to cause a cell to gain or lose water, which depends directly on the concentration of nonpenetrating solutes.

Osmoregulation

The cellular process of regulating internal solute concentrations and water balance to maintain homeostasis.

Plasmolysis

The shrinkage of a plant cell's central vacuole and detachment of the plasma membrane from the cell wall when placed into a hypertonic solution.

Water Potential

A physical property denoted by $\Psi$ that predicts the direction of water flow based on solute concentration and physical pressure, defined by $\Psi = \Psi_s + \Psi_p$.

Solute Potential

The component of water potential denoted by $\Psi_s$ that is calculated using $\Psi_s = -iCRT$; it is always zero or negative and decreases as solute concentration increases.

Pressure Potential

The physical pressure exerted on a solution denoted by $\Psi_p$, which typically equals $0\,\text{bars}$ ($0\,\text{MPa}$) in an open container.

Dialyzer

An artificial kidney apparatus that uses a thin semi-permeable membrane and counter-current fluid flow to remove toxins and excess water from blood via diffusion and osmosis.

Macrophage

An immune cell that captures and destroys viruses and foreign pathogens while seeking out specific antigens.

Dendritic Cell

An antigen-presenting immune cell that alerts and activates other immune cells against infectious pathogens.

B-cell

An immune cell that produces antibodies to recognize and fight specific antigens.