1. Difference Between Passive Transport and Active Transport
Passive Transport:
- Passive transport is the movement of molecules across a cell membrane without the need for energy input. This process relies on the concentration gradient, meaning substances move from areas of high concentration to areas of low concentration.
- Examples include diffusion, facilitated diffusion (via channel or carrier proteins), and osmosis (the movement of water).
Active Transport:
- Active transport, on the other hand, requires energy to move substances against their concentration gradient, i.e., from low concentration to high concentration.
- The energy typically comes from ATP or other forms of chemical energy. Active transport often involves specific transport proteins or pumps.
2. Functions of Carrier Proteins in Active Transport
Carrier proteins in active transport serve several functions:
- Specificity: They selectively bind to specific molecules or ions that need to be transported.
- Energy Utilization: They utilize energy (usually from ATP) to change shape, allowing the transport of substances against their concentration gradient.
- Molecular Conformation Change: After binding the substrate, the carrier protein undergoes a conformational change that helps to shuttle the molecule across the membrane.
- Regulation: Carrier proteins can be regulated, allowing the cell to control the uptake of nutrients or ions based on the cell’s needs.
3. Energy Source for the Sodium-Potassium Pump
The sodium-potassium pump (Na+/K+ ATPase) is an example of active transport that requires energy to function. The energy that drives this pump comes from the hydrolysis of ATP (adenosine triphosphate). Specifically:
- The pump moves three sodium ions (Na+) out of the cell and two potassium ions (K+) into the cell against their concentration gradients.
- During this process, ATP is converted into ADP and inorganic phosphate, releasing energy that is used to change the conformation of the pump and facilitate the movement of ions.
4. Difference Between Pinocytosis and Phagocytosis
Pinocytosis:
- Often referred to as "cell drinking," pinocytosis is a form of endocytosis where the cell engulfs extracellular fluid along with its dissolved solutes.
- This process allows cells to sample the chemical composition of their environment and typically results in the uptake of smaller molecules or fluid.
Phagocytosis:
- Known as "cell eating," phagocytosis is a form of endocytosis used by some cells (e.g., macrophages) to engulf larger particles, such as bacteria, cellular debris, or foreign materials.
- In this process, the cell membrane extends around the particle and engulfs it, forming a phagocytic vesicle.
Overall, the main difference lies in the size of the materials being transported: pinocytosis handles small solutes and fluids, while phagocytosis is aimed at larger particles.
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