AP Biology Unit 2: Cell Structure and Function

Ribosomes

Non-membrane structures made of rRNA and protein that synthesize proteins; found in all life forms as evidence of common ancestry.

Endomembrane System

Network of membrane-bound organelles (ER, Golgi, lysosomes, etc.) that modify, package, and transport molecules intercellularly.

Rough vs. Smooth Endoplasmic Reticulum

Rough ER has ribosomes for protein synthesis; smooth ER detoxifies cells and synthesizes lipids.

Golgi Complex

Flattened membrane sacs that correctly fold, chemically modify, and package proteins for trafficking.

Lysosomes

Membrane-enclosed sacs containing hydrolytic enzymes to digest waste material and mediate apoptosis.

Vacuoles

Membrane-bound sacs; plant vacuoles store water/nutrients and maintain turgor pressure, while animal vacuoles are smaller and more numerous.

Mitochondria

Double-membraned organelles where aerobic cellular respiration and ATP synthesis occur.

Chloroplasts

Specialized double-membraned organelles found in plants and photosynthetic algae that serve as the site for photosynthesis.

Endosymbiotic Theory

Theory that mitochondria and chloroplasts evolved from once free-living prokaryotic cells engulfed by an ancestral eukaryote.

Prokaryotic vs. Eukaryotic Cells

Eukaryotes have membrane-bound organelles for compartmentalization, while prokaryotes lack them but possess specialized internal regions.

Effect of Cell Size on SA:Vol Ratio

As cell size increases, the surface area-to-volume ratio decreases and internal resource demands increase.

Efficiency of Smaller Cells

Smaller cells have a higher surface area-to-volume ratio, allowing faster and more efficient exchange of materials with the environment.

Cellular Adaptations for SA:Vol

Complex structures like membrane folds, microvilli, or root hairs that maximize surface area for environmental exchange.

Organism Size and Metabolic Rate

Smaller organisms have a higher metabolic rate per unit body mass because they lose heat to the environment more rapidly.

Phospholipids

Lipids with polar hydrophilic phosphate heads and nonpolar hydrophobic fatty acid tails forming a protective bilayer.

Membrane Proteins

Embedded proteins with hydrophobic regions interacting with lipid tails and hydrophilic regions exposed to the cytosol or extracellular space.

Fluid Mosaic Model

Model describing the plasma membrane as a flexible phospholipid bilayer embedded with movable proteins, steroids, and carbohydrates.

Cholesterol in Animal Membranes

A steroid that acts as a fluidity buffer, helping animal cell membranes maintain constant consistency across varying temperatures.

Glycolipids and Glycoproteins

Sugar-linked membrane molecules found on the extracellular surface that are involved in cell-to-cell recognition and interactions.

Selective Permeability

Property of biological membranes allowing some substances to cross more easily than others due to a hydrophobic interior.

Freely Permeable Molecules

Small nonpolar molecules such as N2, O2, and CO2 that pass freely across the biological membrane without transport proteins.

Cell Wall

Rigid structural boundary found in plants, fungi, bacteria, and archaea that provides protection from osmotic lysis.

Passive Transport

Net movement of molecules from high to low concentration across a membrane without the direct input of metabolic energy.

Simple vs. Facilitated Diffusion

Simple diffusion passes directly through the lipid bilayer; facilitated diffusion uses protein channels for large polar molecules or ions.

Active Transport

Movement of molecules across a membrane requiring metabolic energy (ATP), often moving substances against their concentration gradient.

Sodium-Potassium Pump

Active transport protein that pumps 3 Na+ out of cells and 2 K+ into cells to help establish membrane potential.

Endocytosis and Exocytosis

Energy-requiring bulk transport processes; endocytosis brings large materials in via vesicles, while exocytosis pushes them out.

Direction of Osmosis

Water moves by osmosis from hypotonic (low solute) regions toward hypertonic (high solute) regions to establish balance.

Osmoregulation

The process by which organisms maintain water balance and control their internal solute composition and water potential.

Water Potential

A measure of free water molecule movement; water moves spontaneously from regions of high water potential to low water potential.