Membranes and Cellular Transport

A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved semi-permeable …

Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are …

The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of …

Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient of an …

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as …

Approximately 60% to 95% of the weight of living organisms is attributed to water. Therefore, maintaining appropriate water balance within cells is of …

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 for …

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 …

The cell membrane, or plasma membrane, is an ever-changing landscape. It is described as a fluid mosaic where various macromolecules are embedded in the …

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and …

In contrast to passive transport, active transport involves a substance being moved through membranes in a direction against its concentration or …

One example of how cells use the energy contained in electrochemical gradients is demonstrated by glucose transport into cells. The ion vital to this …

Overview Receptor-mediated endocytosis is a process through which bulk amounts of specific molecules can be imported into a cell after binding to cell …

Cells use energy-requiring bulk transport mechanisms to transfer large particles, or large amounts of small particles, into or out of the cell. The cells …

Cells pull particles inward and engulf them in spherical vesicles in an energy-requiring process called endocytosis. Phagocytosis (“cellular eating”) …

Exocytosis is used to release material from cells. Like other bulk transport mechanisms, exocytosis requires energy. While endocytosis takes particles …