Cell Transport Mechanisms

Cell Transport Mechanisms

Active Transport

• Active Transport is a process that moves ions, molecules, and other substances across cellular membranes.
• It uses ATP (adenosine triphosphate) as a power source to move materials against a concentration gradient.
• Active transport can be broken down into two mechanisms: Primary Active Transport and Secondary Active Transport.

Primary Active Transport

• Primary active transport directly uses chemical energy (ATP) to transport all species of ions across a membrane.
• An example is the Sodium-Potassium pump. This moves three sodium ions out of the cell, and two potassium ions into the cell, helping to maintain the cell’s resting potential.
• ATP is hydrolysed during these processes, releasing energy.

Secondary Active Transport

• Secondary active transport uses an electrochemical gradient established by primary active transport to move another substance.
• An example is the glucose-sodium co-transport system in the small intestine. Sodium ions are moved down their concentration gradient, which provides energy for the transport of glucose against its concentration gradient into the cell.

Passive Transport

• Passive transport is the movement of substances across membrane without the use of energy (ATP).
• Examples are osmosis, diffusion, and facilitated diffusion.

Diffusion

• Substances move from an area of higher concentration to an area of lower concentration.
• It’s a form of passive transport, meaning it doesn’t require energy.
• An example would be the spread of oxygen from the alveoli into the blood cells in the lungs.

Osmosis

• Osmosis is the diffusion of water through a partially permeable membrane from a dilute solution (high water concentration) to a concentrated solution (low water concentration).
• It’s important in controlling water levels in cells.

Facilitated Diffusion

• This involves substances moving across cell membranes with the help of carrier proteins or channel proteins.
• It’s also a type of passive transport, meaning it doesn’t require energy.
• An example is the transport of glucose and amino acids into cells.

Endocytosis and Exocytosis

• Endocytosis is an active process that uses energy to bring substances into a cell by engulfing them in a portion of the plasma membrane, forming a vesicle inside the cell.
• Exocytosis is also an active process that moves particles, such as waste materials out of the cell by enveloping them in an outward bulge, which then pinches off becoming a vesicle and fusing with the plasma membrane.