Chapter 2: Molecules and Cells in Animal Physiology

Molecules and Cells in Animal Physiology reviews the chemical makeup and structural functions of lipids, proteins, carbohydrates, and nucleic acids, stressing how molecular shape determines function. Proteins are discussed in terms of their levels of structure, active sites, enzyme kinetics, and the influence of temperature and pH. The chapter then turns to cellular organization, introducing membrane structure with the fluid mosaic model and membrane function including selective permeability, passive and active transport, and the role of transport proteins. Special attention is given to osmosis, tonicity, and ion gradients that sustain membrane potential and cellular communication. Cell signaling mechanisms are described through receptor types (ionotropic, metabotropic), second messengers, and G protein-coupled responses. Cellular homeostasis is further examined via intracellular compartmentalization and organelles such as mitochondria, rough and smooth ER, and the Golgi complex. The chapter concludes by linking cell function to tissue specialization, such as epithelial polarity and the role of gap junctions in direct intercellular communication, building the foundation for tissue-level and system-level integration in upcoming chapters.