ap bio unit 2 vocab

Plasma Membrane

The cell boundary that separates internal conditions from the external environment.

Nucleus and Nuclear Envelope

The DNA-containing control center enclosed by a double membrane with pores continuous with the ER.

Ribosomes

Nonmembranous rRNA-protein complexes that translate mRNA sequences into polypeptides.

Free vs. Bound Ribosomes

Free make cytosolic proteins; bound on rough ER make secreted or membrane proteins.

Endomembrane System

A network of membranes that modifies, packages, and transports proteins, lipids, and polysaccharides.

Transport Vesicles

Small membrane sacs that move materials between organelles in the endomembrane system.

Golgi Apparatus

A stack of flattened sacs that modifies, sorts, folds, and packages cellular products.

Mitochondria

Double-membraned organelles that carry out aerobic respiration and produce most cellular ATP.

Lysosomes

Membrane-bound sacs of hydrolytic enzymes that digest materials and recycle cell components.

Chloroplasts

Double-membraned organelles in plants and algae where photosynthesis converts light energy to chemical energy.

Prokaryotic vs. Eukaryotic Cells

Prokaryotes lack membrane-bound organelles and a nucleus; eukaryotes contain both.

Plant vs. Animal Cells

Plant cells have cell walls and chloroplasts; animal cells lack them and typically have centrioles.

Endoplasmic Reticulum (Rough and Smooth)

A membrane network that supports cell shape, transports materials, and synthesizes proteins or lipids.

Vacuoles

Membrane-bound sacs that store materials; plant central vacuoles maintain turgor pressure.

Surface Area-to-Volume Ratio

The amount of membrane surface available for exchange relative to internal cell volume.

Surface Area and Volume Formulas

Sphere: $SA = 4\pi r^2$, $V = \frac{4}{3}\pi r^3$; cube: $SA = 6s^2$, $V = s^3$; rectangular solid: $SA = 2lh + 2lw + 2wh$, $V = lwh$; cylinder: $SA = 2\pi r^2 + 2\pi rl$, $V = \pi r^2 l$.

Calculating SA:V Ratio

Find surface area and volume with the correct formula, then divide surface area by volume.

Exchange of Materials and SA:V

Higher ratios allow faster nutrient uptake, waste removal, and chemical exchange across membranes.

Membrane Folding and SA:V

Folds increase surface area greatly without much increase in volume.

Root Hairs

Thin extensions of root epidermal cells that increase surface area for water and mineral absorption.

Guard Cells and Stomata

Paired cells regulate stomatal openings, controlling gas exchange and water loss in leaves.

Gut Epithelial Cells and Microvilli

Intestinal lining cells have membrane projections that increase surface area for nutrient absorption.

Cilia

Short hairlike cell projections that increase exposed surface and help move materials past cells.

Heat Exchange and Body Size

Smaller bodies lose heat faster because they have more surface area relative to volume.

Metabolic Rate per Unit Body Mass

Smaller multicellular organisms usually use energy faster per gram than larger organisms.

Cell Size Limits and Plasma Membrane Exchange

As cells grow, volume increases faster than membrane area, limiting efficient material exchange.

Phospholipid Bilayer

A double phospholipid layer with a hydrophobic interior that causes selective permeability.

Integral and Peripheral Proteins

Integral proteins penetrate the bilayer; peripheral proteins attach loosely to the membrane surface.

Cholesterol

A steroid in animal membranes that stabilizes the bilayer and buffers fluidity changes.

Fluid Mosaic Model

A dynamic membrane model with moving phospholipids and embedded proteins forming a flexible mosaic.

Factors Affecting Membrane Fluidity

Higher temperature and unsaturated tails increase fluidity; cholesterol buffers fluidity across temperatures.

Selective Permeability

A membrane property where small nonpolar molecules cross easily but polar molecules and ions do not.

Transport Proteins and Channel Proteins

Embedded membrane proteins that move hydrophilic substances across the bilayer; channels are passive, transport proteins may actively pump.

Amphipathic Phospholipids

Phospholipids have hydrophilic phosphate heads and hydrophobic fatty acid tails.

Membrane Proteins

Embedded or attached proteins have hydrophobic regions in the bilayer and hydrophilic regions exposed to water.

Glycoproteins, Glycolipids, and Glycocalyx

Carbohydrate-tagged membrane molecules form an outer coat used for recognition, adhesion, and protection.

Unsaturated Fatty Acids

Fatty acid tails with double bonds create kinks that increase membrane fluidity.

Saturated Fatty Acids

Straight fatty acid tails pack tightly together and decrease membrane fluidity.

Cell Wall

A rigid outer layer that supports cells, limits some substances, and prevents osmotic lysis.

Selective Permeability

A membrane property that allows some substances to cross more easily than others.

Concentration Gradient

A difference in the concentration of a substance across space or across a biological membrane.

Osmosis

The diffusion of water across a selectively permeable membrane toward the region with a higher solute concentration.

Passive Transport

The net movement of substances down their concentration gradient without direct energy input.

Active Transport

The movement of substances across a membrane using cellular energy, often against their concentration gradient.

Transport Proteins

Membrane proteins that move specific substances across the bilayer through channels, carriers, or pumps.

Aquaporins

Channel proteins that allow rapid movement of water across cell membranes.

Sodium-Potassium Pump

An ATP-powered membrane pump that exports $Na^+$ and imports $K^+$ against their concentration gradients.

Membrane Permeability by Molecule Type

Small nonpolar molecules cross freely; water crosses slowly or via aquaporins; large polar molecules and ions require transport proteins.

Cell Wall and Membrane Transport

A rigid outer layer that provides structural support and filtering, while the plasma membrane serves as the primary selective barrier.

Diffusion

The passive movement of particles from an area of high concentration to an area of low concentration.

Endocytosis and Exocytosis

Energy-requiring vesicle transport processes that move materials into cells or out of cells.

Tonicity

The relative solute concentration of a solution that determines the direction and extent of water movement across a membrane.

Facilitated Diffusion

Passive movement of polar molecules or ions through membrane proteins down their concentration gradient.

Large Polar Molecules and Membrane Passage

Substances that cannot pass easily through the hydrophobic bilayer directly and must move through transport proteins.

Concentration Gradient

A difference in substance concentration across space that drives net movement from high to low concentration.

Membrane Polarization

An unequal distribution of electrical charge across a membrane caused by ion movement.

Aquaporins

Channel proteins that allow rapid movement of large quantities of water across membranes.

Simple Diffusion vs. Facilitated Diffusion

One process crosses the bilayer directly while the other uses transport proteins, though both move substances down gradients without energy input.

Channel Proteins and Ion Passage

Membrane proteins forming hydrophilic pathways that let charged particles cross the hydrophobic bilayer.

Passive Transport

Movement of substances across membranes down their concentration gradient without direct energy input.

Hypotonic, Hypertonic, and Isotonic Solutions

Hypotonic solutions have lower solute concentration, hypertonic solutions have higher solute concentration, and isotonic solutions have equal solute concentration relative to another solution.

Osmosis

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

Solute Potential

The component of water potential that reflects the effect of dissolved solutes, which is always zero or negative.

Solute Potential Equation

The equation $\Psi_s = -iCRT$, where $i$ is the ionization constant, $C$ is molar concentration, $R$ is the pressure constant, and $T$ is temperature in Kelvin.

Osmolarity

The total concentration of dissolved solute particles in a solution.

Concentration Gradient

A difference in substance concentration across space that drives net movement from high to low concentration.

Osmoregulation

The control of internal water balance and solute concentration by an organism to maintain homeostasis.

Contractile Vacuole

An organelle in many freshwater protists that pumps out excess water entering the cell by osmosis.

Central Vacuole

A large organelle in plant cells that stores water and helps maintain turgor pressure.

Plasmolysis

The shrinking of a plant cell membrane away from the cell wall due to water loss in a hypertonic environment.

Lysis and Crenation

Lysis is cell bursting from excessive water gain, whereas crenation is cell shriveling from water loss in animal cells.

Water Potential

The potential energy of water per unit volume, represented by the equation $\Psi = \Psi<em>p + \Psi</em>s$.

Pressure Potential and Turgor Pressure

Pressure potential is physical pressure that raises water potential, while turgor pressure is the outward hydrostatic pressure against a plant cell wall.

Water Potential Gradient

The path along which water passively moves, from areas of higher water potential to lower water potential.