One day, a glucose molecule from Bloodstream arrived at the city gate, wanting to enter Cellville. However, the gatekeeper, a protein called a cotransporter, said, "I can let you in, but you need to hitch a ride with a sodium ion." The glucose molecule was happy to oblige and jumped onto the cotransporter's back, along with a sodium ion.
| Feature | Active Transport | Passive Transport | | :--- | :--- | :--- | | | Low → High (Against gradient) | High → Low (With gradient) | | Energy Required | Yes (ATP) | No | | Key Example | Sodium-Potassium Pump, Stomach Acid | Oxygen diffusion, Water osmosis | | Speed | Slower (needs energy input) | Faster (spontaneous) | examples of active transport
is the biological equivalent of swimming upstream. It requires energy (usually in the form of ATP) and specialized protein pumps to move molecules against their concentration gradient—from low to high concentration. One day, a glucose molecule from Bloodstream arrived
This process is called .
This is a special type of active transport known as . When a white blood cell (phagocyte) spots a harmful bacterium, it doesn't just open a door to let it in. Instead, the cell membrane wraps around the invader, engulfing it completely. It requires energy (usually in the form of