Chapter 5

Membranes and Cellular Transport

The Fluid Mosaic Model
The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of…
What is an Electrochemical Gradient?
5.2: What is an Electrochemical Gradient?
Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient…
Diffusion
5.3: Diffusion
Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances,…
Osmosis
5.4: Osmosis
Approximately 60% to 95% of the weight of living organisms is attributed to water. Therefore, maintaining appropriate water balance within cells is…
Tonicity in Animals
5.5: Tonicity in Animals
The tonicity of a solution determines if a cell gains or loses water in that solution. The tonicity depends on the permeability of the cell membrane…
Tonicity in Plants
5.6: Tonicity in Plants
Tonicity describes the capacity of a cell to lose or gain water. It depends on the quantity of solute that does not penetrate the membrane. Tonicity…
Protein Associations
5.7: Protein Associations
The cell membrane—or plasma membrane—is an ever-changing landscape. It is described as a fluid mosaic as various macromolecules are embedded in…
Facilitated Transport
5.8: Facilitated Transport
The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and…
Primary Active Transport
5.9: Primary Active Transport
In contrast to passive transport, active transport involves a substance being moved through membranes in a direction against its concentration or…
Secondary Active Transport
5.10: Secondary Active Transport
One example of how cells use the energy contained in electrochemical gradients is demonstrated by glucose transport into cells. The ion vital to this…
Receptor-mediated Endocytosis
5.11: Receptor-mediated Endocytosis
Overview Receptor-mediated endocytosis is a process through which bulk amounts of specific molecules can be imported into a cell after binding to…
Pinocytosis
5.12: Pinocytosis
Cells use energy-requiring bulk transport mechanisms to transfer large particles, or large amounts of small particles, into or out of the cell. The…
Phagocytosis
5.13: Phagocytosis
Cells pull particles inward and engulf them in spherical vesicles in an energy-requiring process called endocytosis. Phagocytosis (“cellular…
Exocytosis
5.14: Exocytosis
Exocytosis is used to release material from cells. Like other bulk transport mechanisms, exocytosis requires energy. While endocytosis takes…
Immunology and Infection: Molecular Diffusion in Plasma Membranes
5.16: Immunology and Infection: Molecular Diffusion in Plasma Membranes
Biological membranes are complex and many factors influence functions such as protein diffusion. In this article, biologists use fluorescence…
Biology: Endocytosis and Recycling of Plasma Membrane Proteins
5.17: Biology: Endocytosis and Recycling of Plasma Membrane Proteins
Endocytic and recycling pathways are dynamic and involve the transport of molecules from the cell surface to its interior. In this article, an…
Neuroscience: Examination of Synaptic Vesicle Recycling
5.18: Neuroscience: Examination of Synaptic Vesicle Recycling
Synaptic vesicle recycling in stimulated cells can be analyzed using fluorescence. In this protocol, researchers use hippocampal neurons and FM dyes…