Cell Structure and Function

Matthew Cabrera - AP Bio

Light Microscope (LM)

Uses visible light to magnify; lower resolution than EM; can view living cells

Electron Microscope (EM)

Uses electron beams; very high resolution; requires vacuum so specimens are dead

Scanning Electron Microscope (SEM)

Electron beam scans surface; produces detailed 3D-like surface images

Transmission Electron Microscope (TEM)

Electrons pass through thin sections; reveals internal ultrastructure

Organelles

Membrane-bound structures in eukaryotes that perform specialized functions

Cytosol

Aqueous cytoplasmic fluid where many metabolic reactions occur

Prokaryotic Cell

No nucleus; DNA in nucleoid; lacks membrane-bound organelles; generally smaller

Eukaryotic Cell

Has nucleus and membrane-bound organelles; generally larger and compartmentalized

Plasma Membrane

Phospholipid bilayer with proteins that controls substance movement and cell signaling

Nucleus

Double-membrane organelle with pores; houses most DNA and controls gene expression

Nucleoid

DNA-containing region in prokaryotes that is not membrane-bound

Chromosomes

DNA-protein structures carrying genes; condense during cell division

Ribosome

rRNA-protein complex that synthesizes polypeptides; free in cytosol or bound to rough ER

Smooth Endoplasmic Reticulum (SER)

Lacks ribosomes; synthesizes lipids; detoxifies; stores Ca²⁺

Rough Endoplasmic Reticulum (RER)

Studded with ribosomes; makes membrane and secretory proteins

Golgi Apparatus

Stacks of cisternae that modify

Lysosome

Acidic vesicle with hydrolytic enzymes for digestion and recycling of cellular materials

Phagocytosis

Cell engulfs large particles into a food vacuole that fuses with a lysosome

Vacuole

Large vesicle for storage

Food Vacuole

Vesicle formed by phagocytosis for intracellular digestion

Contractile Vacuole

Organelle in many freshwater protists that expels excess water for osmoregulation

Central Vacuole

Large plant organelle for storage and turgor; supports growth by water uptake

Mitochondria

Double-membrane organelles that generate ATP by cellular respiration; have own DNA and ribosomes

Chloroplasts

Photosynthetic organelles in plants and algae; contain thylakoids and stroma; have own DNA

Thylakoids

Chloroplast membrane sacs housing light reactions; often stacked as grana

Stroma

Chloroplast fluid outside thylakoids; site of Calvin cycle; contains enzymes

Plasmodesmata

Channels through plant cell walls that connect cytoplasm of adjacent cells for transport and signaling

Selective Permeability

Membrane property allowing some substances to cross more easily than others

Fluid Mosaic Model

Membrane is a fluid phospholipid bilayer with mobile proteins embedded

Concentration Gradient

Difference in solute concentration across space or a membrane

Passive Transport

Movement down a gradient without energy input; includes diffusion

Active Transport

Movement against a gradient using energy often ATP via pumps or transporters

Sodium-Potassium Pump

Animal cell membrane pump that moves 3 Na⁺ out and 2 K⁺ in per ATP

Membrane Potential

Voltage across a membrane due to unequal ion distribution

Electrochemical Gradient

Combined effect of concentration gradient and membrane potential on ion movement

Osmosis

Diffusion of water across a selectively permeable membrane toward higher solute concentration

Isotonic

Equal solute concentrations; no net water movement across the membrane

Hypertonic

Higher external solute; cell loses water; animal cells shrivel and plant cells plasmolyze

Hypotonic

Lower external solute; cell gains water; animal cells may lyse and plant cells become turgid

Osmoregulation

Control of water balance to maintain homeostasis

Turgid

Firm state of a plant cell in a hypotonic environment due to high turgor pressure

Flaccid

Limp state of a plant cell in an isotonic environment with low turgor pressure

Facilitated Diffusion

Passive transport via channel or carrier proteins down a gradient

Endocytosis

Uptake of materials by forming vesicles from the plasma membrane

Pinocytosis

Nonspecific uptake of extracellular fluid into small vesicles

Receptor-Mediated Endocytosis

Specific uptake via ligand binding to membrane receptors in coated pits

Exocytosis

Secretion by fusion of intracellular vesicles with the plasma membrane