Glossary
ATP
Adenosine triphosphate, the primary energy currency of the cell, used to power most cellular processes, including active transport.
Example:
Muscle contraction requires a constant supply of ATP to fuel the movement of protein filaments.
Active Transport
The movement of substances across a cell membrane against their concentration gradient, from an area of low concentration to an area of high concentration, requiring energy (ATP).
Example:
Nerve cells use the sodium-potassium pump for active transport to maintain ion gradients crucial for transmitting signals.
Bulk Transport
A type of active transport that moves large molecules or large quantities of smaller molecules into or out of the cell using vesicles.
Example:
Immune cells engulfing bacteria is an example of bulk transport, specifically phagocytosis.
Concentration Gradient
The difference in the concentration of a substance between two areas, driving passive transport from high to low concentration.
Example:
The movement of carbon dioxide out of your cells is driven by a concentration gradient where CO2 is higher inside the cell than outside.
Endocytosis
A form of bulk transport where the cell membrane engulfs substances from the extracellular fluid, forming a vesicle to bring them into the cell.
Example:
When a white blood cell 'eats' a pathogen, it's performing endocytosis to internalize the foreign material.
Exocytosis
A form of bulk transport where vesicles fuse with the cell membrane, releasing their contents from inside the cell to the extracellular environment.
Example:
Pancreatic cells release insulin into the bloodstream through exocytosis.
Facilitated Diffusion
The movement of polar molecules or ions across a cell membrane from high to low concentration with the assistance of specific transport proteins, but without energy expenditure.
Example:
Glucose enters red blood cells via facilitated diffusion, using a specific protein channel to cross the membrane quickly.
Membrane Transport
The process by which substances move across the cell membrane, essential for maintaining cell function and homeostasis.
Example:
Understanding membrane transport helps explain how cells absorb nutrients and expel waste products to survive.
Osmosis
The facilitated diffusion of water across a selectively permeable membrane from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).
Example:
If you place a plant cell in pure water, osmosis will cause water to move into the cell, making it turgid.
Passive Transport
Movement of substances across a cell membrane that does not require cellular energy (ATP). It occurs down the concentration gradient.
Example:
When you smell perfume across a room, the scent molecules are spreading via passive transport from an area of high concentration to low.
Phagocytosis
A specific type of endocytosis, often called 'cellular eating,' where the cell engulfs large particles, whole cells, or debris by extending pseudopods.
Example:
A macrophage performing phagocytosis consumes bacterial cells as part of the immune response.
Pinocytosis
A type of endocytosis, known as 'cellular drinking,' where the cell takes in extracellular fluid containing dissolved solutes by forming small vesicles.
Example:
Cells lining capillaries use pinocytosis to absorb small molecules and fluid from the blood.
Receptor-Mediated Endocytosis
A highly specific type of endocytosis where specific molecules bind to receptors on the cell surface, triggering the formation of a coated vesicle to internalize the bound substances.
Example:
Cells take up cholesterol from the blood via receptor-mediated endocytosis, using specific LDL receptors.
Simple Diffusion
The direct movement of small, nonpolar molecules from an area of high concentration to an area of low concentration across the cell membrane, without the help of transport proteins.
Example:
Oxygen easily moves from the high concentration in your lungs into the lower concentration in your bloodstream through simple diffusion.
Transport Protein
A protein embedded in the cell membrane that facilitates the movement of specific substances across the membrane, either through facilitated diffusion or active transport.
Example:
Ion channels are a type of transport protein that allows specific ions to pass through the cell membrane.