3.2 Water Flashcards
Functions of water
1) It is a reactant in many chemical reactions e.g hydrolysis reactions
2) It is a solvent, which means some substances dissolve in it.
3) Water transports substances
4) Water helps with temperature control because it has a high specific heat capacity and a high latent heat of vaporisation.
5) Water is a habitat.
What gives water a high specific heat capacity?
Hydrogen bonds.
1) Specific heat capacity is the energy needed to raise the temperature of 1g by 1 degree.
2) The hydrogen bonds between water molecules can absorb a lot of energy. So water has a high specific heat capacity- it takes a lot of energy to heat up.
3) This means water doesn’t experience rapid temperature changes, which is one of the properties that makes it a good habitat.
4) It also helps maintain constant temperatures in cellular environments.
What gives water a high latent heat of vaporisation?
Hydrogen bonds.
1) It takes a lot of energy to break the hydrogen bonds between water molecules.
2) So water has a high latent heat of evaporation - a lot of energy is used up when water evaporates.
3) This is useful for living organisms because it means water’s great for cooling things. E.g mammals sweat when they’re too hot, when sweat evaporates, it cools the surface of the skin.
What makes water very cohesive?
Its polarity.
1) Cohesion is the attraction between molecules of the same type.
2) Water molecules are very cohesive because they’re polar.
3) This helps water to flow, making it great for transporting substances. It also helps water to be transported up plant stems in the transpiration stream. Cohesion also gives the water a high surface tension, allowing small organisms, such as Pond Skaters, to walk along it.
What causes water to exhibit capillary action?
The effects of cohesion and adhesion cause water to exhibit capillary action.
1) Adhesion is when water molecules are attracted to other materials and cohesion is when water molecules are attracted to each other.
2) This causes capillary action- The process by which water can rise up a narrow tube against the force of gravity.
3) This causes water to make a very efficient transport medium within living things e.g in the xylem
What makes water a good solvent?
Its polarity.
1) Because it is a polar molecule, water acts as a solvent in which many of the solutes in an organism can be dissolved. E.g amino acids, proteins
2) Water acts as a medium for chemical reactions and also helps transport dissolved compounds into and out of cells.
When is water less dense?
When it is solid.
1) Water molecules are held further apart in ice than they are in liquid water because each water molecule forms four hydrogen bonds to other water molecules, making a lattice shape. This makes ice less dense than liquid water, which is why ice floats.
2) This is useful for living organisms because in cold temperatures ice forms an insulating layer on top of water- the water below doesn’t freeze. So organisms that live in water, like fish, don’t freeze and can still move around.
