Unit 2 AP Bio RHS

Cell Theory

Cell = basic unit of life; All living things are composed of cells; All cells come from pre-existing cells.

Surface Area:Volume Ratio

Must maintain high surface area:volume ratio for efficient exchange across the membrane.

Prokaryotic Cells

Domains: Bacteria & Archaea; Smaller & simpler; DNA: circular, in nucleoid (no nucleus); No membrane-bound organelles.

Eukaryotic Cells

Larger & more complex; Organelles: specialized compartments; DNA in nucleus (nuclear envelope).

Plasma Membrane

Phospholipid bilayer; regulates what enters/exits; fluid mosaic model; contains proteins & cholesterol for fluidity.

Nucleus

Stores DNA, organizes chromosomes, contains nucleolus (makes rRNA & assembles ribosomes).

Ribosomes

Protein synthesis; free-floating or on Rough ER; made of RNA + proteins.

Endoplasmic Reticulum

Rough ER: protein synthesis/trafficking; Smooth ER: lipid, hormone, steroid production, detox.

Golgi Apparatus

Processes, sorts, packages proteins; produces vesicles & lysosomes.

Mitochondria

"Powerhouse"; produces ATP via cellular respiration; double membrane w/ cristae.

Lysosomes

Digestive enzymes; break down organelles & debris; acidic environment.

Centrioles

Form microtubules for cell division; only in animal cells.

Vacuoles

Store water, nutrients, waste; larger in plants.

Peroxisomes

Break down fatty acids via beta-oxidation.

Cytoskeleton

Maintains shape, movement, division (microtubules & microfilaments).

Cilia & Flagella

Movement; cilia sweep debris, flagella (e.g., sperm) swim.

Extracellular Matrix (ECM)

Structure & biochemical support; glycoproteins (collagen).

Plant Cells

Have cell wall, chloroplasts, and plasmodesmata.

Animal Cells

Have centrioles, but no cell wall or chloroplasts.

Semipermeable Membrane

Small hydrophobic molecules pass easily; hydrophilic/large need transport proteins.

Fluid-Mosaic Model

Proteins float in phospholipid bilayer; cholesterol & unsaturated fats affect fluidity.

Diffusion

movement down concentration gradient

Simple diffusion

hydrophobic molecules cross directly

Facilitated diffusion

channel/carrier proteins help hydrophilic molecules

Osmosis

diffusion of water

Water movement

Water moves from high → low water concentration

Isotonic

equal solute; no net water movement

Hypertonic

more solute outside; cell loses water

Hypotonic

less solute outside; cell gains water

Water potential (Ψ)

predicts water movement

Water potential formula

Ψ = Ψp + Ψs (pressure + solute potential)

Active Transport

Moves molecules against concentration gradient using energy

Ion pumps

e.g., sodium-potassium pump (3 Na⁺ out, 2 K⁺ in)

Primary active transport

ATP directly used

Secondary active transport

uses energy from another molecule moving down gradient

Cotransport

movement of one molecule drives movement of another

Endocytosis

cell engulfs substances → vesicles

Pinocytosis

liquids

Phagocytosis

solids

Receptor-mediated endocytosis

specific molecules via receptors

Exocytosis

vesicles fuse with membrane to release contents

Bulk flow

one-way fluid movement via pressure

Dialysis

solute diffusion across selective membrane

Desmosomes

hold cells together

Gap junctions

cytoplasm connections for small molecule transfer

Tight junctions

seal off spaces between cells

Signal Transduction

Cells respond to signals via receptors & pathways

Steps of Signal Transduction

Reception: signal binds receptor (intracellular or membrane), Transduction: signal converted, often via phosphorylation cascade; amplification occurs, Response: changes in gene expression or enzyme activity

Types of Receptors

Ligand-gated ion channels, Catalytic (enzyme-linked) receptors, G-protein coupled receptors (GPCRs), Receptor tyrosine kinases (RTKs), Intracellular receptors: for small/hydrophobic messengers (steroids, thyroid)

Apoptosis

programmed cell death, carried out by caspases; essential for development & homeostasis

SA:V ratio

importance for cell size

ATP

powers active transport & organelle functions (mitochondria)