Unit 2: Cell Structure and Function

Comprehensive vocabulary flashcards covering AP Biology Unit 2: Cell Structure and Function, including cell organelles, membrane transport, endosymbiosis, compartmentalization, surface area to volume ratios, and water potential calculations.

Homeostasis

The maintenance of a stable internal environment that supports life, carried out in cells through selectively permeable membranes, organelles, and regulation of solutes and water.

Prokaryotic Cell

A simpler cell lacking a membrane-bound nucleus and membrane-bound organelles; possesses a circular chromosome in a nucleoid region, ribosomes, cytosol, a plasma membrane, and usually a peptidoglycan cell wall.

Eukaryotic Cell

A structurally complex cell containing membrane-bound organelles and linear chromosomes enclosed within a membrane-bound nucleus; found in animals, plants, fungi, and protists.

Nucleoid

The non-membrane-enclosed central region of a prokaryotic cell where the circular chromosome is located.

Plasmid

A small circular piece of extra chromosomal DNA found in bacteria that exists separately from the main bacterial chromosome.

Cytosol

The fluid portion of the cytoplasm found in all cells where free ribosomes and cellular components are suspended.

Ribosome

A non-membrane-bound subcellular structure composed of proteins and ribosomal RNA ($\text{rRNA}$) that synthesizes proteins by assembling amino acids into polypeptides according to mRNA sequence.

Free Ribosome vs. Bound Ribosome

Free ribosomes float freely in the cytosol in both prokaryotes and eukaryotes, whereas bound ribosomes are attached to the membrane of the rough endoplasmic reticulum in eukaryotes.

Rough Endoplasmic Reticulum (RER)

A series of membrane channels in eukaryotic cells studded with bound ribosomes that functions in protein synthesis.

Smooth Endoplasmic Reticulum (SER)

A series of membrane channels in eukaryotic cells devoid of ribosomes that functions in lipid synthesis and the detoxification of harmful substances.

Golgi Complex

A stack of flattened membrane sacs called cisternae that modifies, finishes, and packages proteins into vesicles for transport throughout or out of the cell.

Cisternae

The flattened membranous sacs that comprise the Golgi complex.

Lumen (Golgi)

The interior space within each cisterna of the Golgi complex containing the enzymes necessary for protein modification.

Lysosome

A membrane-bound sac containing hydrolytic enzymes that digests macromolecules, recycles worn-out organelles, destroys pathogens, and participates in apoptosis.

Apoptosis

Programmed cell death, often triggered by mutations that could otherwise cause tumor formation; lysosomal hydrolytic enzymes are the primary cellular tools executing this process.

Vacuole

A membrane-bound organelle that functions in nutrient or water storage, waste sequestration, and maintenance of turgor pressure and structural support in plant cells.

Contractile Vacuole

A specialized organelle found in freshwater protists like paramecia that collects excess internal water and pumps it out of the cell to prevent lysis.

Mitochondrion

A double-membrane organelle that synthesizes $\text{ATP}$ via cellular respiration; features a smooth outer membrane, a folded inner membrane (cristae), an enzyme-containing matrix, its own circular DNA ($\text{mtDNA}$), and ribosomes.

Mitochondrial Matrix

The enzyme-rich fluid occupying the innermost compartment of a mitochondrion where the reactions of the Krebs cycle (citric acid cycle) take place.

Cristae

The inward folds of the inner mitochondrial membrane that increase the surface area available for electron transport chains and $\text{ATP}$ synthesis.

Chloroplast

A double-membrane photosynthetic organelle found in plants and algae containing thylakoids arranged into grana, stroma fluid, circular DNA ($\text{cpDNA}$), and ribosomes.

Thylakoid

A pancake-shaped membranous sac inside a chloroplast whose membrane contains the machinery for the light-dependent reactions of photosynthesis.

Granum

A stacked column of thylakoid membranes within a chloroplast (plural: grana).

Stroma

The fluid-filled interior space of a chloroplast surrounding the grana where the light-independent reactions of photosynthesis take place.

Centrosome

An animal-cell structure that organizes microtubule assembly into spindle fibers during cell division; defects in its function are linked to cell cycle dysregulation in cancers.

Amyloplast

A specialized plant organelle found in roots and tubers (such as potatoes) that synthesizes and stores starch from excess glucose produced during photosynthesis.

Peroxisome

A membrane-bound eukaryotic organelle that oxidizes molecules and breaks down metabolic toxins inside the cell.

Nucleolus

A non-membrane-bound dense subregion within the eukaryotic nucleus where ribosomes are assembled.

Cytoskeleton

An intracellular network of protein fibers that provides structural support, establishes cell shape, and facilitates directed organelle and vesicle transport.

Cell Wall

A rigid external layer surrounding the plasma membrane in plant cells (cellulose), fungal cells (glucans), and prokaryotic cells (peptidoglycan) that provides physical support and protection.

Plant Cell vs. Animal Cell

Plant cells uniquely contain chloroplasts, amyloplasts, a rigid cellulose cell wall, and a large central vacuole; animal cells uniquely feature centrosomes and prominent lysosomes.

Endomembrane System

The eukaryotic system consisting of the nuclear envelope, endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, transport vesicles, and plasma membrane that modifies, packages, and transports macromolecules.

Endosymbiosis Hypothesis

The theory that eukaryotic membrane-bound organelles (mitochondria and chloroplasts) originated when ancestral host prokaryotes engulfed free-living prokaryotes that evolved into mutualistic intracellular components.

Kleptoplasty

A symbiotic process where a eukaryote (such as $Paramecium\ bursaria$) engulfs photosynthetic green algae and maintains their chloroplasts intact and active for months to receive photosynthetic nourishment without digesting them.

Compartmentalization

The division of the eukaryotic cell interior into distinct, membrane-bound organelles, isolating conflicting enzymatic reactions to maximize metabolic efficiency and regulation.

Surface Area to Volume Ratio

The quantitative ratio of outer surface area to internal volume ($\frac{\text{SA}}{V} = \frac{3}{r}$ for spheres); decreases as cell radius increases, restricting cell expansion and favoring multicellularity.

Phospholipid Bilayer

A two-layered membrane framework composed of amphipathic phospholipids arranged with polar, hydrophilic phosphate heads facing outward and nonpolar, hydrophobic fatty acid tails facing inward.

Fluid Mosaic Model

A model of biological membranes describing a dynamic, fluid phospholipid bilayer embedded with laterally drifting proteins, glycoproteins, glycolipids, and steroids.

Glycoproteins and Glycolipids

Carbohydrate-modified proteins and lipids situated on the extracellular face of the plasma membrane that function in cell recognition and identification.

Membrane Steroids (Cholesterol)

Lipid molecules inserted into the phospholipid bilayer that adjust membrane fluidity and stability across changing temperatures.

Aquaporin

A specialized membrane channel protein that enables the rapid, high-volume facilitated diffusion of water across the plasma membrane.

Selective Permeability

The barrier property of plasma membranes that allows small nonpolar molecules ($\text{O}_2$, $\text{CO}_2$, $\text{N}_2$) to diffuse freely across while barring large polar molecules and charged ions without transport proteins.

Passive Transport

The spontaneous movement of molecules across a membrane down their concentration gradient (from higher to lower concentration) without requiring cellular energy.

Diffusion

The net passive movement of solute particles down their concentration gradient directly through the phospholipid bilayer without the aid of membrane proteins or energy.

Osmosis

The passive diffusion of free water molecules across a selectively permeable membrane from an area of higher water potential to an area of lower water potential.

Facilitated Diffusion

The passive transport of ions or polar substances across a membrane through specific channel or transport proteins down their concentration gradient, which is saturable at high solute concentrations.

Active Transport

The movement of ions or molecules across a cellular membrane against their concentration gradient (from low to high concentration), requiring cellular energy expenditure in the form of $\text{ATP}$.

Na/K pump

A primary active transport membrane protein that consumes $\text{ATP}$ to pump $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell, generating a net positive extracellular charge and maintaining the membrane potential.

Endocytosis and Exocytosis

Bulk active transport processes where endocytosis enfolds extracellular matter into membrane-derived vesicles to bring it into the cell, and exocytosis fuses intracellular vesicles with the plasma membrane to secrete substances out.

Hypotonic Solution

A solution that contains a lower relative solute concentration (and thus a higher concentration of free water / higher water potential) compared to another solution.

Hypertonic Solution

A solution that contains a higher relative solute concentration (and thus a lower concentration of free water / lower water potential) compared to another solution.

Isotonic Solution

A solution possessing the same solute concentration and water potential as another solution, resulting in zero net movement of water.

Water Potential ($\Psi$)

The measure of potential energy of water in a solution or its ability to do work; water always flows spontaneously from areas of higher water potential to areas of lower water potential.

Solute Potential ($\Psi_s$)

The component of water potential determined by the concentration of dissolved solutes, calculated via $\Psi_s = -iCRT$; pure distilled water has a solute potential of $0\,\text{bars}$, and adding solute makes it increasingly negative.

Pressure Potential ($\Psi_p$)

The physical component of water potential exerted by mechanical pressure; equals $0\,\text{bars}$ in open atmospheric containers, becomes positive in turgid plant cells, and is negative under tension or suction.

Ionization Constant ($i$)

The number of discrete particles or ions a compound dissociates into in aqueous solution; equals $1$ for non-ionizing covalent solutes (glucose, sucrose), $2$ for $\text{NaCl}$, and $3$ for $\text{CaCl}_2$.

Pressure Constant ($R$)

The universal gas constant used in the solute potential formula, which equals $0.0831\,\frac{\text{liters-bars}}{\text{mole-K}}$.

Osmolarity

The total concentration of all dissolved solute particles in an aqueous solution that organisms must tightly balance to maintain osmotic equilibrium.