AP Biology Unit 2: Cell Structure, Function, Transport, and Water Potential

Comprehensive vocabulary flashcards covering cell structure and function, membrane transport mechanisms, endosymbiosis, and water potential calculations for AP Biology Unit 2.

Prokaryotic cell

A simpler cell lacking a membrane-bound nucleus and membrane-bound organelles, with its DNA situated in a nucleoid region.

Eukaryotic cell

A larger, compartmentalized cell characterized by a membrane-bound nucleus and internal membrane-bound organelles such as the ER, Golgi complex, and mitochondria.

Nucleus

The organelle that stores genetic instructions (DNA), directs cellular activities, and serves as the site of transcription.

Nuclear envelope and pores

A double membrane enclosing the nucleus containing channels that regulate the traffic of RNA and proteins between the nucleus and cytosol.

Ribosomes

Non-membrane-bound complexes composed partly of rRNA and protein that assemble polypeptides during translation.

Rough endoplasmic reticulum (Rough ER)

A ribosome-studded membrane network involved in manufacturing, folding, and modifying proteins destined for membranes, organelles, or cellular secretion.

Smooth endoplasmic reticulum (Smooth ER)

A membrane network devoid of ribosomes that synthesizes lipids and steroid hormones, metabolizes and detoxifies chemicals, and stores calcium ions.

Golgi complex

A series of flattened membrane sacs that modify, sort, tag, and package proteins and lipids into transport vesicles.

Mitochondria

Double-membrane organelles that generate ATP via cellular respiration; their inner membrane is folded into cristae to maximize surface area for reaction sites.

Chloroplast

A photosynthetic organelle found in plants and algae that contains internal thylakoid membranes arranged to provide high surface area for light-dependent reactions.

Lysosome

A specialized membrane-enclosed sac containing digestive enzymes that breaks down macromolecules, damaged organelles, and engulfed foreign materials.

Vacuole

A membrane-bound storage organelle; in plants, a large central vacuole stores water and solutes and generates internal turgor pressure.

Vesicle

A small membrane-bound sac that stores or transports materials by budding off from and fusing with other cellular membranes.

Cytoskeleton

A network of internal protein fibers providing mechanical support, maintaining cell shape, anchoring organelles, and facilitating intracellular transport and motility.

Centrioles

Microtubule-based paired cylinder structures located within the centrosome of animal cells that assist in organizing the microtubule network during cell division.

Cell wall

A rigid, protective extracellular structure located outside the plasma membrane in plants, fungi, prokaryotes, and certain protists.

Plasmodesmata

Microscopic open channels perforating plant cell walls that connect the cytoplasm of adjacent cells to allow intercellular transport and communication.

Cytosol

The gel-like intracellular fluid component of cytoplasm in which cellular structures and organelles are suspended.

Cytoplasm

The total region and content enclosed by the plasma membrane outside of the nucleus, consisting of cytosol along with suspended organelles.

Compartmentalization

The division of a eukaryotic cell's interior into membrane-bound spaces, establishing unique chemical environments, separating incompatible reactions, and concentrating reactants.

Cristae

Infoldings of the inner mitochondrial membrane that enhance ATP production efficiency by increasing the membrane surface area available for respiration enzymes.

Surface-area-to-volume (SA:V) ratio

The mathematical quotient of surface area divided by volume ($\frac{\text{Surface Area}}{\text{Volume}}$), which decreases as cell size increases, making smaller cells more efficient at material exchange.

Phospholipid bilayer

A structural membrane arrangement consisting of two opposing leaflets of amphipathic phospholipids, with hydrophilic phosphate heads facing aqueous environments and hydrophobic fatty-acid tails facing inward.

Fluid mosaic model

A model of biological membrane structure that visualizes the membrane as a flexible phospholipid bilayer embedded and associated with freely drifting proteins, steroids, and carbohydrates.

Channel proteins

Transmembrane proteins containing a hydrophilic interior passageway that allows specific ions or polar molecules to pass across the membrane down their concentration gradient.

Aquaporins

Specialized transmembrane channel proteins designed to facilitate the rapid passive transport of water molecules across biological membranes.

Integral / transmembrane protein

A membrane protein embedded directly within the lipid bilayer, often spanning both leaflets of the membrane.

Peripheral proteins

Membrane-associated proteins loosely bound to the exterior or interior hydrophilic surface of the lipid bilayer rather than embedded in its core.

Cholesterol

A membrane steroid that functions as a fluidity buffer, stabilizing membrane fluidity across fluctuating temperatures by restraining phospholipid movement at high temperatures and preventing packing at low temperatures.

Glycoproteins

Membrane proteins covalently linked to short carbohydrate chains on their extracellular surface, serving crucial roles in cell recognition, signaling, and tissue adhesion.

Glycolipids

Lipids modified with carbohydrate chains facing the extracellular space that assist in cell-to-cell identification and tissue attachment.

Selectively permeable

A property of biological membranes that permits certain molecules to pass across freely while restricting or preventing the crossing of others.

Simple diffusion

The passive net movement of small, nonpolar solute molecules directly through the phospholipid bilayer from an area of higher concentration to lower concentration without energy input.

Facilitated diffusion

The spontaneous passive movement of polar molecules or ions down their concentration gradient through transmembrane channel or carrier proteins without ATP consumption.

Osmosis

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

Active transport

The energy-dependent translocation of a solute across a biological membrane against its concentration gradient ($\text{low} \rightarrow \text{high}$) using membrane carrier proteins or pumps.

Endocytosis

An active transport process wherein the plasma membrane invaginates, engulfs extracellular substances, and pinches off to create an internal vesicle.

Exocytosis

An active vesicular transport process wherein intracellular vesicles migrate to and fuse with the plasma membrane, releasing their contents outside the cell.

Phagocytosis

A specialized form of endocytosis commonly referred to as 'cell eating,' in which a cell engulfs solid bulk particles, whole debris, or microorganisms.

Pinocytosis

A non-specific form of endocytosis known as 'cell drinking,' where a cell invaginates its membrane to sample droplets of extracellular fluid and dissolved solutes.

Receptor-mediated endocytosis

A targeted type of endocytosis triggered when specific external ligands bind to corresponding cell-surface receptor proteins, initiating vesicle formation.

Sodium-potassium pump

An electrogenic active transport protein that hydrolyzes ATP to export $3\,\text{Na}^+$ ions and import $2\,\text{K}^+$ ions per cycle against their concentration gradients.

Hypotonic

A relative classification for an extracellular solution possessing a lower nonpenetrating solute concentration than the cell's interior, promoting net water entry into the cell.

Hypertonic

A relative classification for an extracellular environment having a higher nonpenetrating solute concentration than the cell's cytoplasm, resulting in net water outflow and cell shrinking.

Isotonic

A state wherein the extracellular solution features an effective solute concentration equal to that of the cell interior, resulting in dynamic equilibrium with zero net water movement.

Osmolarity

The total concentration of dissolved solute particles present within a unit volume of a given liquid solution.

Tonicity

The capacity of an extracellular solution to alter cellular volume by dictating net water gain or loss via nonpenetrating solutes.

Osmoregulation

The active processes and physiological mechanisms by which organisms control internal solute concentrations and regulate water balance.

Turgor pressure

The hydrostatic outward pressure applied by the swollen vacuole and cytosol against the rigid plant cell wall after water uptake in a hypotonic medium.

Plasmolysis

The phenomenon occurring in hypertonic solutions where plant cells lose substantial water, causing the protoplast to shrink and peel inward away from the rigid cell wall.

Water potential ($\Psi$)

A physical metric representing the potential energy of water relative to pure water under defined conditions, determining the direction of water movement ($\Psi = \Psi_s + \Psi_p$).

Solute potential ($\Psi_s$)

The component of water potential determined by the concentration of dissolved solute molecules, described by $\Psi_s = -iCRT$; it is zero for pure water and becomes increasingly negative as solute is added.

Pressure potential ($\Psi_p$)

The component of water potential accounting for physical mechanical pressure exerted upon a liquid, which can be positive, negative, or zero.

Isotonic point

The specific solute concentration in an osmosis tissue experiment where the line of best fit crosses $0\%$ mass change, denoting the point of zero net water movement.

Endosymbiotic theory

The evolutionary framework stating that mitochondria and plastids (chloroplasts) originated from free-living aerobic prokaryotes engulfed by an ancestral host cell.

Apoptosis

An orderly, genetically regulated mechanism of programmed cell destruction and disassembly.

Necrosis

Uncontrolled cell death and tissue breakdown initiated by acute external trauma, infection, or severe physiological injury.