Active transport is reliant on carrier proteins and thus follows the same rules as facilitated diffusion in that they are specific have a maximum rate and are subject to competition. Crucially they transport substances against their concentration gradient and so require energy to work.

Biology 2e is designed to cover the scope and sequence requirements of a typical two-semester biology course for science majors. The text provides comprehensive coverage of foundational research and core biology concepts through an evolutionary lens. Biology includes rich features that engage students in scientific inquiry, highlight careers in the biological sciences, and offer everyday applications. The book also includes various types of practice and homework questions that help students understand—and apply—key concepts. The 2nd edition has been revised to incorporate clearer, more current, and more dynamic explanations, while maintaining the same organization as the first edition. Art and illustrations have been substantially improved, and the textbook features additional assessments and related resources.

By the end of this section, you will be able to do the following:

Define osmosis and explain its role within molecules
Explain why osmoregulation and osmotic balance are important body functions
Describe active transport mechanisms
Explain osmolarity and the way in which it is measured
Describe osmoregulators or osmoconformers and how these tools allow animals to adapt to different environments

Principles of mass transport and electrical signal generation for biological membranes, cells, and tissues. Mass transport through membranes: diffusion, osmosis, chemically mediated, and active transport. Electric properties of cells: ion transport; equilibrium, resting, and action potentials. Kinetic and molecular properties of single voltage-gated ion channels. Laboratory and computer exercises illustrate the concepts. For juniors and seniors. Students engage in extensive written and oral communication exercises.