Membrane Function

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All cells have cell membranes that control and regulate the passage of materials across their boundaries. The chemical nature of these membranes differentially restricts and promotes the movement of particles through them. Similarly, most organelles have membranes distinguishing their contents from the cytoplasm. The only membrane that prokaryotic cells have is a cell membrane. They lack all internal membranes, and therefore all membrane-bound organelles.

It is important for cells and membrane-bound organelles to be able to regulate the inward and outward passage of materials. This helps them control their contents. While they are at the mercy of the Law of Diffusion, and will gain or lose ions and water because of environmental concentrations, they are dynamic in their ability to participate in this movement. Membranes have specialized proteins embedded in them that serve as transportation routes for certain substances into or out of cells. Sometimes this passage requires energy, but other times it does not.

Many cells also require the ability to move large substances through their membranes—substances too large to pass through the biochemical structure itself. In cases like these, the membranes have to be chemically broken and reformed. Knowledge of membrane structure and the nature of the biochemicals present is essential to understanding how cells interact with their surroundings, and is the focus of the Membrane Function unit.

Membrane Function is excerpted from our Biology 12 Study Guide, which is the sixth edition of a student study guide written to match the curriculum of British Columbia. The concepts presented are applicable to the biology curricula of other educational jurisdictions as well.

As with each of the biology study guide units in this series, this unit contains:

  • Biological terms linked to a Glossary where they are carefully and contextually defined
  • Biological names in the Glossary linked to a useful Taxonomic Guide
  • Diagrams that display fullscreen views when double-tapped
  • Quiz-view formats of many diagrams in the enhanced version
  • Sets of Concept Check-up questions dispersed in the unit that are linked to their answers
  • Sets of Discussion Questions dispersed in the unit designed to challenge you as you work through it
  • A concluding set of Check Your Understanding of Concepts multiple choice questions linked to their answers
  • A set of Build Your Understanding questions designed to push you beyond the limitations of this unit.

Note: Discussion Questions and Build Your Understanding questions are not linked to their answers.