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B1B - Coggle Diagram
B1B
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Diffusion
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It is the spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration.
Cells need oxygen for respiration - carried out by mitochondria. Cells are surrounded by a high concentration of oxygen. Oxygen is transported in the bloodstream from the lungs. Because there is a high concentration outside the cell because of the oxygen provided by the bloodstream, and a low concentration inside the cell, oxygen moves in.
Respiration also produces carbon dioxide inside the cell. This means that there is a higher concentration of carbon dioxide inside the cells than outside and so it moves out through diffusion.
Urea is a waste product produced inside the cells. It diffuses out of the cells into the blood plasma and is excreted by the kidneys.
The rate of diffusion is affected by 3 main factors. The first is the difference in concentrations. This is also known as the concentration gradient. The smaller the concentration gradient, the slower diffusion is. The second factor is the temperature. The higher the temperature the greater the rate of diffusion. This is because the heat gives the molecules more kinetic energy and makes them move faster. The final factor is the surface area of the membrane. This is because there is more space for more cells to diffuse in at once.
Osmosis
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
Dilute solutions contain a high concentration of water. Concentrated solutions contain a low concentration of water.
Partially permeable membranes allow some molecules to pass through but not all molecules. In Osmosis water diffuses from dilute to concentrated solutions because ot goes from a high concentration of water to a low concentration of water, just like in diffusion.
The cytoplasm of cells is a relatively concentrated solution is contains a relatively low concentration of water. If we place this cell in water then osmosis will take place. Water will move by Osmosis from outside to inside the cell.
If we place a plant cell in water, then water will move into the cell by osmosis and the cell will expand. The cell wall prevents the plant cell from bursting. Instead, the cell becomes turgid (swollen).
If we place a plant cell into a concentrated solution, then water moves out of the plant cell by osmosis. This causes the cell to shrink. Scientists call this flaccid.
Active Transport
Active Transport moves substances from a more dilute solution to a more concentrated solution. (against the concentration gradient) This requires energy from respiration.
One example is the sugars found in the lumen of the small intestine. There is a lower concentration of sugars in the lumen than in the walls of the intestine, so it has to use active transport. Once inside the cell they can be transported to the blood and carried around the body.
If a cell needs to bring a molecule into it that is already at a higher concentration inside the cell than outside the cell then it can use active transport.
The cells that carry out active transport have to have a lot of mitochondria to provide the energy for it.
In the soil there is a lower concentration of ions than inside the root hair cell. This means it has to use active transport to bring the ions into it and transport them to xylem tubes.
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