AP Biology Unit 2

Ribosomes

Non-membrane organelles made of rRNA and protein; synthesize proteins based on mRNA. Found in all life, reflecting common ancestry.

Endomembrane system

Group of membrane-bound organelles (ER, Golgi, lysosomes, vacuoles, vesicles, nuclear envelope, plasma membrane) that modify, package, and transport molecules.

Rough ER

Endoplasmic reticulum with bound ribosomes; carries out protein synthesis and compartmentalizes the cell.

Smooth ER

Endoplasmic reticulum lacking ribosomes; functions in lipid synthesis and detoxification.

Golgi complex

Series of flattened membrane sacs that fold, modify, and package proteins for trafficking.

Mitochondria

Double-membrane organelles that perform aerobic cellular respiration; inner membrane folds (cristae) increase surface area for ATP synthesis.

Lysosomes

Membrane-enclosed sacs containing hydrolytic enzymes; digest material and play a role in apoptosis.

Vacuoles (plant)

Large central vacuole maintains turgor pressure through nutrient and water storage.

Vacuoles (animal)

Smaller and more plentiful than in plants; store cellular materials.

Chloroplasts

Double-membrane organelles found in plants and photosynthetic algae; site of photosynthesis.

Surface area-to-volume ratio

Ratio that affects exchange of nutrients, waste, and heat; smaller cells have higher SA/V and exchange more efficiently and bigger cells have smaller SA/V and are better suited for storage

Effect of size on metabolic rate

Smaller organisms typically have a higher metabolic rate per unit body mass than larger organisms.

Phospholipid bilayer orientation

Polar hydrophilic phosphate heads face the aqueous environment; nonpolar hydrophobic fatty acid tails face inward.

Embedded membrane proteins

Hydrophilic regions face cytosol or protein interior; hydrophobic regions interact with the fatty acid interior of the membrane.

Fluid mosaic model

Model describing the membrane as a fluid framework of phospholipids embedded with proteins, steroids, glycoproteins, and glycolipids that move laterally.

Selective permeability

Property of plasma membranes that results from a hydrophobic interior; allows some molecules to pass and not others.

Molecules that freely cross membrane

Small nonpolar molecules: N2, O2, CO2 freely cross; small polar uncharged molecules (H2O, NH3) cross in small amounts.

Cell wall function

Found in Bacteria, Archaea, Fungi, and plants; provides a structural boundary, permeability barrier, and protection from osmotic lysis.

Concentration gradient

Difference in solute concentration across a membrane; the basis for diffusion and transport.

Passive transport

Net movement of molecules from high to low concentration without metabolic energy input.

Active transport

Movement of molecules requiring direct energy input; can move solutes from low to high concentration.

Endocytosis

Cell engulfs large molecules by folding the plasma membrane inward, forming vesicles.

Exocytosis

Internal vesicles fuse with the plasma membrane to release large molecules from the cell.

Facilitated diffusion

Passive transport of charged ions or large polar molecules through transport or channel proteins down a concentration gradient.

Aquaporins

Membrane channel proteins that transport large quantities of water across membranes.

Hypotonic solution

Solution with a lower solute concentration than the cell; water moves into the cell.

Hypertonic solution

Solution with a higher solute concentration than the cell; water moves out of the cell.

Isotonic solution

Solution with equal solute concentration to the cell; no net water movement.

Osmosis

Movement of water from regions of high water potential to low water potential, or hypotonic to hypertonic.

Water potential (Ψ)

Sum of pressure potential (Ψp) and solute potential (Ψs); water flows from high to low Ψ.

Solute potential equation

Ψs = −iCRT (i = ionization constant; C = molar concentration; R = pressure constant; T = temperature in K).

Osmoregulation

Maintains water balance and allows organisms to control internal solute composition and water potential.

Sodium-potassium pump

Active transport protein using ATP to pump 3 Na+ out and 2 K+ in; helps maintain membrane potential.

Membrane compartmentalization

Internal membranes minimize competing interactions and increase surface area for reactions, enabling specialized functions.

Endosymbiotic theory

Mitochondria and chloroplasts evolved from once free-living prokaryotic cells via endosymbiosis.

Prokaryote vs eukaryote compartmentalization

Prokaryotes lack membrane-bound organelles but have specialized internal regions; eukaryotes have internal membranes that partition the cell.