Cell Structure, Membranes, and Transport: Key Organelles and Processes

Organelle

A specialized structure within a cell that performs a specific function. Many are membrane-bound in eukaryotes.

Plasma Membrane

Barrier between inside/outside; phospholipid bilayer; selectively permeable.

Nucleus

Stores and protects DNA; controls cell functions.

Nucleolus

Inside nucleus; makes ribosomes.

Smooth ER

Makes lipids, detoxifies, stores Ca²I.

Rough ER

Studded with ribosomes; makes and packages proteins.

Golgi Apparatus

Modifies, folds, and ships proteins.

Vesicle

Small sacs for transporting molecules.

Lysosome

Vesicle with hydrolytic enzymes; breaks down macromolecules/waste, also involved in apoptosis.

Vacuole

Storage; central vacuole in plants maintains turgor pressure, animal vacuoles are smaller and more numerous.

Peroxisome

Breaks down toxins (e.g., hydrogen peroxide).

Ribosome

Made of rRNA + proteins; protein synthesis in both prokaryotes and eukaryotes — reflects common ancestry.

Mitochondria

Double membrane; inner folds (cristae) increase surface area for ATP synthesis.

Chloroplast

Double membrane; photosynthesis occurs in thylakoid membranes, producing carbohydrates.

Extracellular Matrix (ECM)

Network of proteins + carbs; support, communication, adhesion.

Cytoskeleton structures

Microtubules, Intermediate Filaments, Microfilaments.

SA:V ratio

High = efficient exchange.

Active Transport

ATP needed; low → high.

Passive Transport

No energy; high → low.

Selective permeability

Hydrophobic interior restricts passage.

Hypotonic

Water enters, cell swells.

Isotonic

Equilibrium.

Hypertonic

Water leaves, cell shrinks.

Osmoregulation

Regulation of water/solute balance (contractile vacuole, central vacuole, kidneys).

Endosymbiotic Theory

Mitochondria + chloroplasts evolved from prokaryotes.