Movement of biological molecules

• Diffusion involves the net movement of any type of molecules.
• Osmosis involves the net movement of water molecules.
• The energy required by the cells comes from the food we eat.
• Active transport is important because it moves substances against their concentration gradient.
• Active transport involves the movement of all particles except water molecules.
• Diffusion does not require energy.
• Osmosis does not require energy.
• Active transport requires energy.
• Examples of the importance of diffusion include the absorption of dissolved mineral salts by the root hairs, the absorption of glucose and amino acids by cells in the small intestines, and gaseous exchange in lungs.
• Examples of the importance of osmosis include the absorption of water by root hairs, the movement of water molecules out of a dilute solution, and the movement of water molecules into a concentrated solution.
• Active transport is important in the absorption of water by root hairs as the root hair cells want to collect as much water and mineral salts from the soil.
• Water potential is defined as the measure of the tendency of water to move from one place to another.
• A dilute solution contains more water molecules per unit volume than a concentrated solution, so it has a higher water potential than a concentrated solution.
• A hypertonic solution has lower water potential than a hypotonic solution.
• Two solutions are isotonic if they have the same water potential.
• Sugars such as starch and sucrose molecules cannot pass through the partially permeable membrane because they are too big.
• In a plant cell, the vacuole decreases in size and the cell becomes soft and flaccid.
• Examples of active transport include the uptake of mineral salts from the soil solution by the roots of plants and the absorption of glucose and amino acids by the cells lining the small intestine of a mammal.
• Water molecules leave the visking tubing (partially permeable membrane) by osmosis, from a region of higher water potential to a region of lower water potential, causing the Visking tubing to shrink and becomes soft.
• Both solutions are of equal water potential when placed in a glass tube.
• Water molecules enter the cell by osmosis when placed in a solution of higher water potential.
• Water molecules enter the visking tubing (partially permeable membrane) by osmosis, from a region of higher water potential to a region of lower water potential, causing the Visking tubing to swell and becomes firm.
• Water level in a glass tube decreases when water is added, indicating that water has a higher water potential compared to sugar solution.
• Active transport is a process by which energy is used to move substances from a region of lower concentration to a region of higher concentration against a concentration gradient.
• In a plant cell, the vacuole increases in size and the cell becomes firm and turgid as the cell wall is rigid.
• The cell sap in the large central vacuole of a plant cell is highly concentrated.
• Osmosis is the process where water molecules enter the visking tubing (partially permeable membrane) by osmosis, from a region of higher water potential to a region of lower water potential, causing the Visking tubing to swell and becomes firm.
• Water level in a glass tube increases when sugar solution is added, indicating that sugar solution has a lower water potential compared to water in the beaker.
• In a plant cell, the vacuole membrane (tonoplast) is also partially permeable.
• No net movement of water molecules into and out of the Visking tubing occurs when placed in a glass tube.
• Sugar such as glucose can pass through the partially permeable membrane (small enough).
• Eventually, the cytoplasm shrinks away from the cellulose cell wall, through a process known as plasmolysis.
• Water molecules leave the cell by osmosis when placed in a solution of lower water potential.