1. Passive Transport:
- Diffusion: Substances move from an area of higher concentration to lower concentration without energy input. Substances diffuse through the cell membrane based on concentration gradients.
- Osmosis: Water molecules move across the membrane from an area of lower solute concentration to higher solute concentration, balancing the concentration.
2. Active Transport:
- Requires energy (ATP) to move substances against their concentration gradient, from lower concentration to higher concentration.
- Performed by carrier proteins or pumps, which have specific binding sites for the transported molecules.
3. Facilitated Transport:
- Involves membrane proteins that aid in the movement of molecules across the cell membrane without directly requiring energy.
- Facilitated diffusion: Molecules move down their concentration gradient using membrane channels or transport proteins.
- Active transport: Molecules move against their concentration gradient using membrane proteins that bind and release molecules.
4. Endocytosis:
- Process of taking substances into a cell by engulfing them with the cell membrane.
- Forms a vesicle around the ingested material, bringing it into the cell's interior.
- Types of endocytosis include phagocytosis (ingestion of solid particles), pinocytosis (cellular drinking), and receptor-mediated endocytosis (specific molecules are recognized and taken in).
5. Exocytosis:
- Process of releasing substances from a cell by transporting them within vesicles to the cell membrane.
- The vesicle fuses with the cell membrane, and its contents are released into the extracellular environment.
- Used to secrete various substances, such as hormones, enzymes, or waste products.
These mechanisms ensure the controlled movement of molecules, maintaining the cell's internal environment, enabling nutrient uptake, waste removal, and various physiological functions.
