p36 Active versus Passive Transport
Active Transport
Active transport requires the cell to use its own energy, while passive transport does not.
If you have ever ridden a bicycle down a long hill, you know that it doesn’t take any of your energy to go fast. But you do have to use some of your energy to pedal back up the hill. For a cell, moving materials through the cell membrane by diffusion and osmosis is like cycling downhill. These processes do not require the cell to use its own energy. The movement of dissolved materials through a cell membrane without using cellular energy is called passive transport.
What if a cell needs to take in a substance that is present in a higher concentration inside the cell than outside? The cell would have to move the molecules in the opposite direction than they naturally move by diffusion. Cells can do this, but they have to use energy—just as you would use energy to pedal back up the hill. Active transport is the movement of materials through a cell membrane using cellular energy. Active transport requires the cell to use its own energy, while passive transport does not.
Transport Proteins
Cells have several ways of moving materials by active transport. In one method, transport proteins in the cell membrane “pick up” molecules outside the cell and carry them in, using energy. Figure 25 illustrates this process. Transport proteins also carry molecules out of cells in a similar way. Some substances that are carried into and out of cells in this way include calcium, potassium, and sodium.
Transport by Engulfing
Figure 26 shows another method of active transport. First, the cell membrane surrounds and engulfs, or encloses, a particle. Once the particle is engulfed, the cell membrane wraps around the particle and forms a vacuole within the cell. The cell must use energy in this process.
Active transport requires the cell to use its own energy, while passive transport does not.
If you have ever ridden a bicycle down a long hill, you know that it doesn’t take any of your energy to go fast. But you do have to use some of your energy to pedal back up the hill. For a cell, moving materials through the cell membrane by diffusion and osmosis is like cycling downhill. These processes do not require the cell to use its own energy. The movement of dissolved materials through a cell membrane without using cellular energy is called passive transport.
What if a cell needs to take in a substance that is present in a higher concentration inside the cell than outside? The cell would have to move the molecules in the opposite direction than they naturally move by diffusion. Cells can do this, but they have to use energy—just as you would use energy to pedal back up the hill. Active transport is the movement of materials through a cell membrane using cellular energy. Active transport requires the cell to use its own energy, while passive transport does not.
Transport Proteins
Cells have several ways of moving materials by active transport. In one method, transport proteins in the cell membrane “pick up” molecules outside the cell and carry them in, using energy. Figure 25 illustrates this process. Transport proteins also carry molecules out of cells in a similar way. Some substances that are carried into and out of cells in this way include calcium, potassium, and sodium.
Transport by Engulfing
Figure 26 shows another method of active transport. First, the cell membrane surrounds and engulfs, or encloses, a particle. Once the particle is engulfed, the cell membrane wraps around the particle and forms a vacuole within the cell. The cell must use energy in this process.