Molecules are always in constant motion which enables them to move from one region to another. The motion of molecules in the solution are constantly affected by the collision with molecules, which results in random motion. Diffusion is needed for the cells so they could survive. It occurs in response ti the molecular motion and to a concentration gradient (moving from areas of higher concentration to lower concentration until it reaches equilibrium). Osmosis is the movement of water molecules from a higher concentration of water molecules to a lower concentration of water molecules through a partially permeable membrane. When it is under normal condition, the concentration of water molecules and salt is same in both cells and plasma. However, if you are sweating for example, the water and salt is lost from the plasma and then there is a lower concentration of water in the plasma than inside the cell. Water molecules diffuse out from the cells through cell membrane. A membrane like this is called partially permeable. Since the water molecules are small, it could pass through the membrane more easily than salt. There are some factors that affect osmosis; temperature, surface area, time spent in solution, volume of water.
There is osmosis in plants. The root hairs when together increase surface area of root. It enables water and mineral ions to be absorbed quickly. In soil solution, water contain low concentrations of mineral ions, called dilute solution. The cytoplasm and vacuole of the root hair contains high concentration of mineral ions than soil solution. The water molecules move from soil solution to cytoplasm and vacuole of the cell by osmosis. In plant cells, there is a strong cell wall that surrounds the cell. When it is taken up by osmosis, it starts to swell. The cell wall prevents it from bursting, this causes it to become turgid (swollen and hard) when put in dilute solution. The pressure in cell rises, the internal pressure in cell eventually gets really high to the point that no more water is allowed to enter. Turgidity is important because it makes the green parts of a plant stand up into the sunlight. Plants placed in concentrated sugar, however, loses water by osmosis. This becomes flaccid (opposite of turgid). The cells have shrunken and have been pulled away from the cell wall, it have become plasmolysed. Incipient Plasmolysis is when plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity.
Osmosis also occurs in animal cells. Animal cells do not have cell walls. In very dilute solutions, animal cells swell up and burst. Since it does not have a cell wall, it does not become turgid. In concentrated solution, water is being sucked out of the cell by osmosis causing the cell to shrink. Animal cells must be bathed in a solution having the same osmotic strength as their cytoplasm, one of the reasons why we have kidneys. The exact amount of water and salt removed from out blood by our kidney is under the control of a part of the brain called hypothalamus. The process of regulating the amounts of water and mineral salts in the blood is called osmoregulation.
There is osmosis in plants. The root hairs when together increase surface area of root. It enables water and mineral ions to be absorbed quickly. In soil solution, water contain low concentrations of mineral ions, called dilute solution. The cytoplasm and vacuole of the root hair contains high concentration of mineral ions than soil solution. The water molecules move from soil solution to cytoplasm and vacuole of the cell by osmosis. In plant cells, there is a strong cell wall that surrounds the cell. When it is taken up by osmosis, it starts to swell. The cell wall prevents it from bursting, this causes it to become turgid (swollen and hard) when put in dilute solution. The pressure in cell rises, the internal pressure in cell eventually gets really high to the point that no more water is allowed to enter. Turgidity is important because it makes the green parts of a plant stand up into the sunlight. Plants placed in concentrated sugar, however, loses water by osmosis. This becomes flaccid (opposite of turgid). The cells have shrunken and have been pulled away from the cell wall, it have become plasmolysed. Incipient Plasmolysis is when plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity.
Osmosis also occurs in animal cells. Animal cells do not have cell walls. In very dilute solutions, animal cells swell up and burst. Since it does not have a cell wall, it does not become turgid. In concentrated solution, water is being sucked out of the cell by osmosis causing the cell to shrink. Animal cells must be bathed in a solution having the same osmotic strength as their cytoplasm, one of the reasons why we have kidneys. The exact amount of water and salt removed from out blood by our kidney is under the control of a part of the brain called hypothalamus. The process of regulating the amounts of water and mineral salts in the blood is called osmoregulation.
About picture
Dialysis tubing is used to demonstrate properties of semi-permeable membrane in relation to osmosis. If you fill the tube with 95% water and 5% salt and place the tube in a 100% water bath the water molecules will move from the water bath, into the water tubing which has lower concentration of water molecules. Since the tubing is semi-permeable, it allows only smaller water molecules to move through the pores. The membrane is impermeable to salt not allowing it to move through pores. The net result is a swelling in the bag size due to the influence of water molecules. The 100% water bath is a 5% salt solution then there will be a flux if water out of tubing, causing a shrinkage of tubing. If there is a concentration of water is equal on both sides of the analysis membrane, that is, liquid in bath is the same concentration as that in the dialysis tubing, there is no change in tubing.
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