. Compare and contrast active and passive transport widely and discuss with all their examples
Active transport and passive transport are two mechanisms by which cells move molecules across their cell membranes. The key difference between active and passive transport lies in the use of energy during the process.
Active Transport:
1. Definition: Active transport is the movement of molecules across the cell membrane against the concentration gradient, i.e., from an area of lower concentration to an area of higher concentration. This process requires the expenditure of energy in the form of ATP (adenosine triphosphate).
2. Energy Usage: ATP is utilized to pump molecules across the membrane, thereby increasing their concentration on one side.
3. Examples:
a. Sodium-Potassium Pump: This pump uses ATP to actively transport sodium ions out of the cell and potassium ions into the cell.
b. Calcium Pump: It moves calcium ions against its concentration gradient, which is crucial for muscle contraction and nerve impulse transmission.
c. Hydrogen Ion Pump: It moves hydrogen ions across the cell membrane, creating a hydrogen ion gradient that drives various cellular processes.
4. Characteristics:
a. Requires energy.
b. Moves molecules against the concentration gradient.
c. Specific carrier proteins are involved.
d. It can transport molecules in either direction.
Passive Transport:
1. Definition: Passive transport is the movement of molecules across the cell membrane along the concentration gradient, i.e., from an area of higher concentration to an area of lower concentration. This process does not require the use of energy.
2. Energy Usage: No energy is consumed, as molecules move down their concentration gradient through channels or pores in the membrane.
3. Examples:
a. Diffusion: Small, non-polar molecules such as oxygen and carbon dioxide passively diffuse across the cell membrane.
b. Facilitated Diffusion: Larger molecules, polar molecules, and ions move across the membrane through specific protein channels or carriers.
4. Characteristics:
a. Does not require energy.
b. Moves molecules along the concentration gradient.
c. Can occur through simple diffusion or facilitated diffusion.
d. Channels or carrier proteins are involved.
In summary, the main difference between active and passive transport is the energy usage and movement against or along the concentration gradient. Active transport requires energy to move molecules against the concentration gradient, while passive transport does not. Both types of transport involve specific carrier proteins or channels, but the use of energy is the key distinguishing factor.