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Crossing the cell membrane without any energy input from the cell. There are many ways for molecules to diffuse across the plasma membrane such as: diffusion, osmosis, facilitated diffusion, carrier proteins, ion channels, and channel proteins.
The movement of molecules from an area of higher concentration to an area of lower concentration. This is the simplest form of passive transport.
A solution is in this state when the concentration of molecules is the same throughout the area the molecules are in.
Diffusion directly across the cell membrane from a high concentration to a low concentration. Without any other influences.
When the concentration of solute outside the cell is lower than the concentration of solute inside the cell. Water moves into the cell. The cell swells.
When the concentration of solute outside the cell is higher than the concentration of solute inside the cell. Water moves out of the cell. The cell shrivels up.
When the concentration of solute outside the cell is equal to the concentration of solute inside the cell. The net movement of water is none. The cell remains the same shape.
Organelles that remove water. They collect excess water and contract, pumping water out of the cell, this requires energy.
The cell wall is strong enough to resist the pressure that water molecules exerted by the water inside the expanding cell. The pressure that water molecules exert against the cell wall is call this.
When molecules can't diffuse across the membrane, the cell does a variety of things. In this process specific carrier proteins engulf a molecule, change shape, and release the molecule inside the cell. This process can be used to move glucose inside a cell.
Pores in the cell membrane for molecules who can't diffuse across the cell membrane directly. This allows them to diffuse into the cell.
Ion Channel Proteins
They transport ions such as Na+ and Ca2+ and Cl- ions across the cell membrane because they cannot readily diffuse. These proteins give the ions an opening or passageway for them to diffuse across into the cell.
Cell Membrane "Pumps"
They are called this because they move molecules from a lower concentration to a higher concentration.
This protein transports Na+ (sodium ions) and K+ (potassium ions) into and out of the cell.
1. Three Na+ ions bind to the carrier protein on the cytosol side of the plasma membrane.
2. The same time this happens, the carrier protein removes a phosphate group from a molecule of ATP, and the phosphate group binds to the protein.
3. The phosphate group from the ATP supplies the energy needed to change the shape of the carrier protein. The protein changes shape and carries the Na+ ion across the membrane and forces them outside the cell where the concentration of Na+ ions must remain higher.
4.Two K+ ions bind to the carrier protein.
5. The phosphate group is released.
6. The carrier protein changes shape and releases the K+ ions inside the cell and the process starts over again. At top speed it can transport 450 Na+ ions and 300 K+ ions per second.
The process by which cell ingest external fluid, macromolecules, and large particles, including other cells. The cell membrane folds itself around the molecules and the membrane pinches off into a vesicle inside the cell. There are two types of this process: pinocytosis and phagocytosis.
Cells that use phagocytosis to ingest bacteria and viruses that invade the body. They then use lysosomes to digest the contents of the vesicle.
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