AP Biology Unit 2: Cell Structure and Function

Comprehensive vocabulary flashcards reviewing cell structure and function, membrane transport mechanisms, cell compartmentalization, and the endosymbiotic theory.

Prokaryote

A single-celled organism (such as a bacterium or archaeon) that lacks a nucleus and membrane-bound organelles, contains circular plasmid DNA, and generates only $2\,\text{ATP}$ molecules per glucose molecule through glycolysis.

Ribosome

A non-membrane-bound subcellular structure composed of ribosomal RNA (rRNA) and protein that synthesizes proteins according to messenger RNA (mRNA) sequences and reflects common ancestry across all known life.

Endomembrane System

A coordinated group of membrane-bound organelles and subcellular components—including the endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, transport vesicles, nuclear envelope, and plasma membrane—that work together to intercellularly modify, package, and transport polysaccharides, lipids, and proteins.

Rough Endoplasmic Reticulum (Rough ER)

A region of the endoplasmic reticulum associated with membrane-bound ribosomes that aids in compartmentalization of the cell and carries out protein synthesis.

Smooth Endoplasmic Reticulum (Smooth ER)

A region of the endoplasmic reticulum that functions in lipid synthesis and cellular detoxification while providing mechanical support to maintain cell shape.

Golgi Complex

A membrane-bound organelle consisting of a series of flattened membrane sacs that correctly folds and chemically modifies newly synthesized cellular products and packages proteins for trafficking.

Mitochondria

Double-membrane organelles featuring a smooth outer membrane and a highly convoluted, folded inner membrane that provides distinct compartments for aerobic cellular respiration to synthesize $ATP$ efficiently.

Lysosome

A membrane-enclosed sac containing hydrolytic enzymes used to digest intracellular materials and execute programmed cell death (apoptosis).

Large Central Vacuole

A large, specialized plant cell organelle that maintains turgor pressure through water and nutrient storage and serves as the primary site for waste processing.

Chloroplast

A specialized double-membrane organelle found in photosynthetic algae and plants that serves as the cellular site for photosynthesis.

Plant Cell vs. Animal Cell Dimensions

Plant cells are typically rectangular or cubic in shape and range from $10\,\mu\text{m}$ to $100\,\mu\text{m}$ in length, whereas animal cells are typically round or irregular in shape and range from $10\,\mu\text{m}$ to $30\,\mu\text{m}$ in length.

Surface Area-to-Volume Ratio

A critical geometric ratio that restricts cell size and shape; smaller cells possess a higher ratio, allowing significantly more efficient exchange of materials, waste removal, and thermal dissipation than larger cells.

Villi

Finger-like multicellular projections located in the small intestine, lined with microvilli-bearing cells and containing a capillary network and lacteal, that function to maximize surface area for absorption.

Fluid Mosaic Model

A model describing biological membranes as a fluid framework composed of a phospholipid bilayer embedded with mobile proteins, steroids (such as cholesterol in vertebrates), glycoproteins, and glycolipids.

Selective Permeability

A property of the plasma membrane resulting from its hydrophobic core, allowing small nonpolar molecules ($N_2$, $O_2$, $CO_2$) to pass freely while preventing large polar molecules and charged ions from crossing without transport proteins.

Cell Wall

A structural outer boundary found in bacteria, archaea, fungi, and plants that provides a permeability barrier, structural shape, and protection against osmotic lysis.

Passive Transport

The net movement of solute molecules down a concentration gradient from high to low concentration without requiring the direct input of metabolic energy.

Active Transport

The movement of solute molecules against a concentration gradient from low to high concentration, requiring the direct expenditure of metabolic energy ($ATP$).

Endocytosis

An active transport process where the plasma membrane folds inward to form vesicles that engulf extracellular macromolecules, particulate matter, liquids, or solids into the cell.

Pinocytosis

A specialized cellular form of endocytosis involving the active engulfment and internalization of external liquids and fluids.

Phagocytosis

A specialized cellular form of endocytosis involving the active engulfment and internalization of external solid materials.

Exocytosis

An active transport process wherein internal transport vesicles fuse with the plasma membrane to secrete macromolecules and cellular contents outside the cell.

Facilitated Diffusion

The passive movement of large polar molecules or charged ions (such as $Na^+$ and $K^+$) down their concentration gradient through transmembrane channel or carrier proteins without direct energy input.

Aquaporins

Specialized transmembrane channel proteins that permit the rapid, high-volume diffusion of water molecules across biological membranes.

Osmosis

The net movement of water across a selectively permeable membrane from an area of higher water potential (low solute concentration or osmolarity) to an area of lower water potential (high solute concentration or osmolarity).

Water Potential Equation

The biophysical formula defining total water potential as $\Psi = \Psi_s + \Psi_p$, where $\Psi$ is total water potential, $\Psi_s$ is solute potential, and $\Psi_p$ is pressure potential.

Solute Potential Equation

The mathematical formula $\Psi_s = -iCRT$, used to calculate solute potential based on the ionization constant ($i$), molar concentration ($C$), pressure constant ($R$), and temperature in Kelvin ($T$).

Osmoregulation

The homeostatic process by which organisms control and maintain internal solute concentration and water balance (water potential) relative to external environmental tonicities.

Cell Compartmentalization

The structural division of eukaryotic cells by internal membranes and organelles that prevents competing chemical interactions, isolates metabolic reactions, and increases functional surface area.

Endosymbiotic Theory

The evolutionary theory stating that eukaryotic membrane-bound organelles—specifically mitochondria and chloroplasts—originated from previously free-living prokaryotic cells that were engulfed by ancestral host cells.

Evidence for Endosymbiosis

Key evolutionary data supporting the endosymbiotic origin of mitochondria and chloroplasts: both contain their own circular plasmid DNA, contain their own ribosomes, and reproduce independently via binary fission.