Water

Water

Vital to living organisms
1. It is a reactant in loads of important chemical reaction, like photosynthesis and hydrolysis reactions.
2. It is a solvent (some substances dissolve in it. Most biological reactions take place in solution.
3. It transports substances. As it's a liquid and a solvent, it easily transports lots of materials, like glucose and oxygen around plants and animals.
4. Helps with temperature control. It carries away heat energy when it evaporates from a surface. This cools the surface and lowers the temperature.
Water molecules have a simple structure
1. A molecule of water (H2O) is one atoms of oxygen (O) joined to two atoms of hydrogen (H2) by shared electrons.
2. As the shared negative hydrogen electrons are pulled towards the oxygen atoms, the other side of each hydrogen atom is left with a slight +charge.
3. The unshared negative electrons on the oxygen atom give it a slight negative charge.
4. Water is a polar molecule - negative charge on one side and a positive charge on the other.
5. The negatively charged oxygen atoms of water attract the positively charged hydrogen atoms of other water molecules.
6. This attraction is called hydrogen bonding and gives water some of its useful properties.
Water's structure is related to its properties and functions.
1. Its structure of gives it some if its useful properties, and these may help to explain some of its functions.
Hydrogen bonds give water a high specific heat capacity
1. Specific heat capacity is the energy needed to raise the temperature of 1 gram of a substance by a small amount (1C)
2. Hydrogen bonds between water molecules can absorb a lot of energy.
3. Water has a high specific heat capacity - a lot of energy is needed to heat it up.
4. Useful for living organisms because it stops rapid temperature changes, allowing them to keep their temperature fairly stable.
Hydrogen bonds also give water a high latent heat of evaporation.
1. It takes a lot of heat energy to break the hydrogen bonds between water molecules.
2. Water has a high latent heat of evaporation - a lot of energy is used up when water evaporates.
3. Useful for living organisms as it means water's great for cooling things.
Water's polarity makes it very cohesive.
1. Cohesion is the attraction between molecules of the same type (e.g. 2 water molecules).
2. Water molecules are very cohesive (they tend to stick together) because they're polar.
3. This helps water to flow, making it great for transporting substances.
Water's polarity also makes a good solvent
1. A lot of important substances in biological reactions are ionic (like salt).
  1. This means they're made from one + charged atom or molecule and one - charged atom or molecule (e.g. salt = + sodium ion and a - chloride ion).
2. As water is polar, the + end of a water molecule will be attracted to the negative ion.
  1. The negative end will be attracted to the positive ion.
3. Ions will get totally surrounded by water molecules - they'll dissolve.

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	Created by Shauna Lake about 11 years ago