AP Biology Unit 2: Cell Structure, Function, and Membrane Transport

Vocabulary flashcards covering cell structure, organelles, endomembrane system, compartmentalization, membrane transport mechanisms, and water potential formulas for AP Biology.

Ribosomes

Non-membrane, subcellular structures composed of ribosomal RNA (rRNA) and protein that synthesize proteins according to messenger RNA (mRNA) sequences; found in all forms of life, reflecting common ancestry.

Endomembrane System

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

Rough ER

A compartmentalized region of the endoplasmic reticulum studded with membrane-bound ribosomes that functions directly in protein synthesis.

Smooth ER

A region of the endoplasmic reticulum responsible for lipid synthesis and the detoxification of cells.

Golgi Complex

A membrane-bound structure consisting of a series of flattened membrane sacs that functions to correctly fold and chemically modify newly synthesized cellular products and package proteins for trafficking.

Mitochondria

Organelles that provide compartments for metabolic reactions involved in aerobic cellular respiration; feature a highly folded inner membrane (cristae) to help ATP be synthesized more efficiently.

Lysosomes

Membrane-enclosed sacs containing hydrolytic enzymes that function in intracellular digestion and apoptosis.

Vacuoles

Membrane-bound sacs with specialized roles: central vacuoles maintain turgor pressure and store nutrients/water in plant cells; contractile vacuoles maintain osmoregulation in some single-celled organisms; food vacuoles form during phagocytosis and fuse with lysosomes.

Chloroplast

Specialized double-membrane organelles found in plants and photosynthetic algae that contain thylakoids, stroma, grana, and lamellae, serving as the location for photosynthesis.

Cell Compartmentalization

The organization of intracellular metabolic processes and specific enzymatic reactions into membrane-bound organelles and internal membranes, minimizing competing interactions and increasing surface area.

Surface Area-to-Volume Ratio

A physical ratio that affects a cell's ability to obtain nutrients, eliminate waste products, acquire/dissipate heat, and exchange chemicals/energy with the environment; smaller cells typically have a higher ratio and more efficient exchange.

Phospholipid

The basic constituent of the plasma membrane, composed of a polar, hydrophilic phosphate head oriented toward aqueous extracellular/intracellular environments and nonpolar, hydrophobic fatty acid tails oriented toward the membrane interior.

Cell Wall

A structural barrier for substances found in bacteria, archaea, fungi, and plants that prevents osmotic lysis.

Simple Diffusion

Passive transport requiring no energy or transport proteins, where small, nonpolar molecules (such as $CO_2$, $O_2$, $N_2$, and steroids) move down their concentration gradient directly across the plasma membrane.

Facilitated Diffusion

Passive transport requiring no energy that moves small molecules down their concentration gradient through membrane transport proteins (channel or carrier proteins).

Active Transport

Transport requiring an input of energy (such as ATP) and carrier proteins to move solutes against their concentration gradient, maintaining membrane potential (e.g., $Na^+/K^+$ pump and ATPase).

Aquaporins

Membrane transport proteins that facilitate the movement of large quantities of water across membranes via facilitated diffusion.

Exocytosis

Process where internal vesicles release materials from cells by fusing with the plasma membrane; follows the path: Rough ER (synthesize) $\rightarrow$ Golgi complex (package/modification) $\rightarrow$ Transport Vesicle $\rightarrow$ Plasma Membrane.

Endocytosis

Process where the cell takes in large molecules and particulate matter by folding the plasma membrane inward to form new vesicles, encompassing pinocytosis, phagocytosis, and receptor-mediated endocytosis.

Pinocytosis

A form of endocytosis characterized as cellular drinking, taking in fluid and dissolved solutes into tiny vesicles.

Phagocytosis

A form of endocytosis characterized as cellular eating, taking in large particulate matter or cellular debris.

Hypotonic Solution

A solution with a low solute concentration and high free water concentration compared to another solution, causing cells placed in it to gain water.

Hypertonic Solution

A solution with a high solute concentration and low free water concentration compared to another solution, causing cells placed in it to lose water.

Isotonic Solution

A solution with equal solute concentration and equal free water concentration relative to another solution, resulting in equal water movement into and out of the cell.

Water Potential ($\Psi$)

The total water potential of a system defined by $\Psi = \Psi_p + \Psi_s$, where $\Psi_p$ is pressure potential and $\Psi_s$ is solute potential; water moves by osmosis from high water potential to low water potential.

Solute Potential ($\Psi_s$)

The component of water potential calculated as $\Psi_s = -iCRT$, where $i$ is the ionization constant, $C$ is molar concentration, $R$ is the pressure constant ($0.0831\,\text{L}\cdot\text{bars}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}$), and $T$ is temperature in Kelvin ($^\circ\text{C} + 273$).