AP Biology Unit 2: Cell Structure and Function Flashcards

Vocabulary flashcards covering cell structure, organelles, membrane structure, transport mechanisms, endosymbiont theory, and intercellular junctions based on AP Biology Unit 2.

Surface Area-to-Volume Ratio (SA/V)

A ratio that decreases as a cell grows because volume increases much faster than surface area; smaller cells have a higher ratio, allowing efficient exchange of nutrients and wastes across the membrane to support life.

Multicellularity Solution

An adaptation where organisms grow larger without losing transport efficiency by dividing into many smaller cells.

Prokaryotes

Organisms (Bacteria and Archaea) that lack a nucleus, having DNA located in an unbound nucleoid region, and lack membrane-bound organelles.

Eukaryotes

Larger, complex organisms (Plants, Animals, Fungi, and Protists) that contain a membrane-enclosed nucleus and membrane-bound organelles that compartmentalize chemical reactions.

Nucleus & Nucleolus

Subcellular structures where the nucleus stores DNA/chromosomes and the nucleolus synthesizes rRNA and builds ribosome subunits.

Ribosomes

Structures made of rRNA and proteins that carry out protein synthesis (translation); exist as free ribosomes suspended in cytosol or bound ribosomes attached to the Rough ER.

Free Ribosomes

Ribosomes suspended in the cytosol that build proteins used within the cytosol.

Bound Ribosomes

Ribosomes attached to the Rough ER that build proteins destined for membranes or export.

Rough ER

A membrane network studded with ribosomes that folds and packages newly made proteins into transport vesicles.

Smooth ER

A membrane network that synthesizes lipids (phospholipids, steroids), metabolizes carbohydrates, and detoxifies drugs/poisons.

Golgi Apparatus

An organelle consisting of flattened sacs (cis face receives, trans face ships) that modifies, sorts, tags, and packages proteins into vesicles for delivery.

Lysosomes

Membrane sacs containing hydrolytic digestive enzymes that break down waste, old organelles, and food particles, and trigger apoptosis (programmed cell death).

Central Vacuole

A large single vacuole in plant cells used for water storage, ion storage, and maintaining turgor pressure.

Mitochondria

The site of aerobic cellular respiration that converts glucose/fuels into ATP; features folded inner membranes (cristae) to maximize surface area for chemical reactions.

Chloroplasts

The site of photosynthesis in plants/algae that converts solar energy into chemical energy (sugars); contains stacks of thylakoids (grana).

Cytoskeleton

A network of protein fibers (microtubules, actin filaments) providing structural support and facilitating organelle/vesicle movement.

Extracellular Matrix (ECM)

A network of glycoproteins used by animal cells for cell adhesion and signaling.

Endosymbiont Theory

The theory stating that mitochondria and chloroplasts originated as free-living prokaryotic cells that were engulfed by an ancestral eukaryote, forming a mutually beneficial symbiotic relationship.

Fluid Mosaic Model

A structural model describing the plasma membrane as a mosaic of phospholipids, proteins, cholesterol, and carbohydrates.

Phospholipid Bilayer

An amphipathic structure with hydrophilic (polar) heads facing outward toward water and hydrophobic (nonpolar) fatty acid tails facing inward.

Cholesterol

A membrane component that buffers membrane fluidity, preventing it from becoming too fluid at high temperatures or too rigid/solid at low temperatures.

Glycoproteins & Glycolipids

Carbohydrate chains attached to surface proteins or lipids that are used for cell-to-cell recognition and identification.

Passive Transport

Membrane transport that requires NO ATP and moves substances down their concentration gradient (High $\rightarrow$ Low).

Simple Diffusion

The movement of small, nonpolar molecules directly through the lipid bilayer down their concentration gradient without energy input.

Facilitated Diffusion

The passive movement of polar or charged molecules down their concentration gradient via specific transport proteins (channel or carrier proteins).

Aquaporins

Channel proteins that facilitate rapid water transport across the plasma membrane.

Active Transport

Membrane transport that requires ATP energy to pump solutes against their concentration gradient (Low $\rightarrow$ High).

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ Pump)

A primary active transport protein that pumps $3\text{ Na}^+$ out of the cell and $2\text{ K}^+$ into the cell to maintain membrane potential.

Cotransport

A transport process that uses the downhill diffusion of one solute to drive the uphill transport of another solute against its concentration gradient.

Exocytosis

A bulk transport process where vesicles fuse with the plasma membrane to secrete materials out of the cell using ATP.

Endocytosis

A bulk transport process where the cell takes in macromolecules by forming new vesicles from the plasma membrane using ATP.

Phagocytosis

A type of endocytosis referred to as "cellular eating," involving the engulfing of solids or particles.

Pinocytosis

A type of endocytosis referred to as "cellular drinking," involving non-specific uptake of extracellular fluid.

Receptor-Mediated Endocytosis

A specific form of endocytosis where receptor proteins bind target ligands before triggering vesicle formation.

Osmosis

The passive diffusion of free water across a selectively permeable membrane from high water concentration (low solute) to low water concentration (high solute).

Hypertonic Solution

A solution with a higher solute concentration outside the cell, causing water to move out of the cell (animal cells shrivel; plant cells undergo plasmolysis).

Hypotonic Solution

A solution with a lower solute concentration outside the cell, causing water to move into the cell (animal cells swell/burst via cytolysis; plant cells become turgid).

Isotonic Solution

A solution with equal solute concentration inside and outside the cell, resulting in zero net movement of water (animal cells prefer isotonic; plant cells become flaccid).

Plasmodesmata

Channels penetrating plant cell walls that allow passage of water, ions, and small molecules between adjacent cells.

Tight Junctions

Intercellular junctions in animal cells that press membranes together to form watertight seals, preventing fluid leakage between cells.

Desmosomes

Intercellular junctions in animal cells that fasten cells together into strong structural sheets (anchoring).

Gap Junctions

Cytoplasmic channels in animal cells that allow chemical or electrical signal passage between neighboring cells.