Key concepts
Organelles are specialized parts of one connected system. Materials, information, and energy move between them. A change in one organelle can affect the whole cell.
The membrane is selectively permeable. Passive transport follows a concentration or electrochemical gradient without direct ATP use. Active transport uses energy to move substances against a gradient.
DNA remains protected in the nucleus. Messenger RNA carries a copied instruction to ribosomes. Proteins enter the rough ER, travel in vesicles to the Golgi, and are sorted to their destinations.
Applications and misconceptions
Secretory cells such as pancreatic cells have abundant rough ER and Golgi. Muscle cells contain many mitochondria. Immune cells use lysosomes for digestion.
Misconception: organelles do not work independently. Their pathways exchange instructions, cargo, energy, and recycled materials.