In facilitated diffusion , the molecules can pass both in direction and opposite of the concentration gradient. Simple diffusion is the process by which solutes are moved along a concentration gradient in a solution or across a semipermeable membrane. Unlike simple diffusion , cell membranes often incorporate specialized membrane proteins which help transport substances across the membrane.
This is known as facilitated diffusion. Simple Diffusion across the Cell Plasma Membrane. The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane , down their concentration gradient, by simple diffusion. Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient.
Will diffusion ever stop completely? When does diffusion stop? As the difference in concentration decreases, diffusion slows down. Particles are moving in all directions, but these movements do not change the concentrations thus a net movement of particles has occurred. Diffusion stops when the concentration of particles in both areas are equal. What affects net diffusion? Several factors affect the rate of diffusion of a solute including the mass of the solute, the temperature of the environment, the solvent density, and the distance traveled.
What is the difference between diffusion and net diffusion? The flow of solute particles moving in any direction equals the flow of particles moving in the opposite direction. Net diffusion is when the flow of solute particle moving in one direction is bigger than the flow of solute particles moving in the opposite direction. What is the difference between diffusion and diffusion? The main difference between the two is that diffusion can occur in any mixture, even when two solutions are separated by a semipermeable membrane, whereas osmosis exclusively occurs across a semipermeable membrane.
There are actually three types of passive transport processes. Is diffusion active or passive? Crossing a membrane by simple diffusion can be distinguished from facilitated diffusion because: A. Simple diffusion does not require energy: facilitated diffusion requires a source of ATP. Simple diffusion can only move material in the direction of a concentration gradient; facilitated diffusion moves materials with and against a concentration gradient.
Simple diffusion is found only in prokaryotes while facilitated diffusion is found only in eukaryotes. Tutorial Diffusion Diffusion means that the net movement of particles molecules is from an area of high concentration to low concentration. Because the molecules are moving down a concentration gradient, the process is driven by simple diffusion and does not require the input of additional energy from the cell. Cells continually encounter changes in their external environment.
Most cells have a similar blend of solutes within them, but interstitial or extracellular fluid can vary. As you know, molecules will tend to move down their concentration gradients until equilibrium is reached.
You might think that solutes will flow into our out of the cell until the solute concentrations are equal across the membrane. However, not all molecules can pass through the cell membrane. The plasma membrane lipid bilayer is significantly less permeable to most solutes than it is to water.
Therefore the WATER tends to flow in a way that establishes an equal concentration of solutes on either side of the membrane. The water flows down its own concentration gradient, with a net movement toward the region that has a higher concentration of solutes. This movement of water across a semipermeable membrane in response to an imbalance of solute is called osmosis.
The relationship between the solute concentration and amount of water is an inverse relationship. The more concentrated a solution is, the less water it contains.
The fewer solutes, the more water — i. Water follows gradients and moves from an area of more water to less water but in reality water is moved to the area with the greater number of solutes. This creates a pressure termed osmotic pressure. Cells cannot actively move water, it must follow osmotic gradients. Solutions that have a greater solute concentration will pull water via osmotic pressure. This depends on the total number of solutes, not the type. Note that some water can pass through the cell membrane but most water passes through protein membrane channels termed aquaporins.
Cells may find themselves in three different sorts of solutions. The terms isotonic, hypertonic, and hypotonic refer to the concentration of solutes outside the cell relative to the solute concentration inside the cell.
In an isotonic solution, solutes and water are equally concentrated within and outside the cell. The cell is bathed in a solution with a solute concentration that is similar to its own cytoplasm. Many medical preparations saline solutions for nasal sprays, eye drops, and intravenous drugs are designed to be isotonic to our cells. Distilled pure water is the ultimate hypotonic solution. If a cell is placed in a hypotonic solution, it will tend to gain water. A hypertonic solution has a high solute concentration lower water concentration compared to the cell cytoplasm.
Very salty or sugary solutions brines or syrups are hypertonic to living cells. If a cell is placed in such a solution, water tends to flow spontaneously out of the cell. Filtration is another passive process of moving material through a cell membrane. While diffusion and osmosis rely on concentration gradients, filtration uses a pressure gradient.
Molecules will move from an area of higher pressure to an area of lower pressure. Filtration is non-specific. If molecules are small enough to pass through the membrane, they will.
The force that pushes the molecules is termed hydrostatic pressure. One example of filtration is making coffee. Think of the coffee filter as the cell membrane and the coffee grounds, flavor and caffeine as the molecules.
The pressure is exerted by the water from the machine. It forces materials through the coffee filter into the coffee pot. Small molecules like caffeine, water, and flavor pass through the filter but the coffee grounds do not. They are too big. If you poked holes in the filter, the coffee grounds would end up in your coffee! The coffee filter represents the filtration membrane which is typically a layer of cells.
Filtration is one of the main methods used for capillary exchange. Blood pressure provides the driving force or hydrostatic pressure to force materials out of capillaries to cells or to form the filtrate fluid in the nephron of the kidney. Hydrostatic pressure is countered by osmotic pressure. Remember osmotic pressure is created due to increased solute concentration and will pull water toward the area of higher solutes.
These two pressures must be in balance for homeostasis of fluid volumes. In our body large molecules such as plasma proteins and red blood cells should not pass out of the blood through the cell membranes lining the capillaries. If they pass through and end up in in the tissues or in the kidney and later the urine it is abnormal and a sign of disease.
In active methods the cell must expend energy ATP to do the work of moving molecules. Active transport often occurs when the molecule is being moved against its concentration gradient or when moving very large molecules into our out of the cell. There are 3 main types of active processes.
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