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They key points covered in this video include:
1. Water as a Solvent
2. Water as a Transport Medium
3. Water as a Reaction Medium
Water as a Solvent
The liquid inside cells and in fluids such as blood and sap is not just pure water - it is an aqueous solution. Aqueous solutions are formed when solutes are dissolved in the solvent water. Water is a powerful solvent because it is a polar molecule which allows it to easily dissolve ionic and polar molecules. When ionic substances are added to water, the water molecules are attracted to the ions that are in contact with the water. The water molecules cluster around each ion, separating them from the ionic lattice. The slightly positive hydrogens in each water molecule are attracted to the negative ions. The slightly negative oxygen in each water molecule is attracted to the positive ions. When all the ions have been surrounded by water molecules, the solute is fully dissolved.
Water as a Transport Medium
Because water is a solvent, it can be used as a transport medium for solutes. This can be seen in animals, where water in the blood carries a range of important solutes, including:Gases e.g. carbon dioxide and oxygen, Polar biological molecules e.g. amino acids, glucose, nucleotides, Inorganic ions e.g. sodium, chloride, potassium. Plants also use water in the sap in the phloem to carry important solutes, including amino acids, sugars and ions.
Water as a Reaction Medium
The cytoplasm in cells is an aqueous solution where many chemical reactions happen. When solutes dissolve in water, they are able to freely move around. This allows molecules like enzymes to collide and interact with substrates to catalyse reactions. The ability of water to act as a solvent therefore makes it an excellent reaction medium in cells.
Summary
Water is a polar molecule so it is attracted to charged and polar molecules
Water dissolves these molecules by surrounding them
The solvent property of water allows water to act as a transport medium in the blood and plant phloem sap
Water can also act as a reaction medium as solutes are able to move around and react with each other