A Level Biology - Water notes PDF

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Summary

Summary of notes discussing the structure, function and importance of water in A Level Biology. The importance of each property of water is discussed in detail, to help you answer application questions in the exam. ...

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Water Structure: -

Polar  Polarity between slightly +ve H, slightly -ve O. Interaction between opposite charges = hydrogen bonds. Hydrogen bonds are weak, but strong together (link to cohesion).

Properties: 1. High Specific Heat Capacity  Energy needed to raise the temperature of 1kg of water by 1 degree.  Water heated  most energy used to break bonds, less to change temperature = water takes a lot of energy to heat up. Importance to organisms: -

H20 doesn’t experience rapid temp changes  it buffers / resists change. Our cells can absorb heat energy without temp increasing too much. Aquatic animals  ocean temp more stable than on land. Maintain constant internal body temperature.

2. High latent heat  Water evaporates when the hydrogen bonds break.  Water molecules on surface have highest kinetic energy so escape, lowering the average kinetic energy of the water = cools.  Energy lost is the latent heat. Importance to organisms: -

Animals can sweat and stay cool (evaporation of water loses heat energy). Plants have a transpiration stream  water pulled up through stem and evaporates from leaves.

3. Cohesion  Cohesion  attraction between molecules of the same type.  Opposite polarities are attracted, and hydrogen bonds form.  These hydrogen bonds help hold water together, so they can flow as a continuous stream. Strong cohesion = mass flow. Importance to organisms: -

Mass flow  water surface tension. Behaves as a skin between water and air. Small animals (pond skaters) can live on the surface of lakes.

4. Good solvent  A liquid that other substances can dissolve in.  Important biological substances are ionic  opposite charges of H20 means the ions separate and dissolve.  Free to move. Importance to organisms: -

Organisms can take up dissolved mineral ions and transport them around. Metabolic reactions  some can only happen when reactants are dissolved in H20.

5. Metabolite  A substance involved in a metabolic reaction.  H20 assists in hydrolysis reactions....