1.6 ATP, water and inorganic ions

• What is the biological importance of water?

  Water is the medium in which all metabolic reactions take place in cells.
• What percentage of a cell's mass is water?

  Between 70% to 95% of the mass of a cell is water.
• Why is water considered a major habitat for organisms?

  Because 71% of the Earth’s surface is covered in water.
• What are the components of water?

  Water is composed of atoms of hydrogen and oxygen.
• How do hydrogen and oxygen atoms combine in water?

  One atom of oxygen combines with two atoms of hydrogen by sharing electrons (covalent bonding).
• What is the significance of the uneven sharing of electrons in water?

  It results in a weak negatively charged region on the oxygen atom and a weak positively charged region on the hydrogen atoms.
• What is a dipole in the context of water molecules?

  A dipole is when a molecule has one end that is negatively charged and one end that is positively charged.
• Is water a polar molecule?

  Yes, water is a polar molecule.
• What type of bonds form between water molecules?

  Hydrogen bonds form between water molecules.
• What causes hydrogen bonds to form between water molecules?

  The polarity of water causes hydrogen bonds to form between the positive and negatively charged regions of adjacent water molecules.
• What happens to hydrogen bonds when there are few present?

  They are constantly breaking and reforming.
• What is the effect of having a large number of hydrogen bonds in water?

  They form a strong structure.
• What are the properties of water that make it important for living organisms?

  • Excellent solvent
  • Relatively high specific heat capacity
  • Relatively high latent heat of vaporisation
  • Less dense when solid
  • High surface tension and cohesion
  • Acts as a reagent
• Why is water considered an excellent solvent?

  Because many substances can dissolve in water due to its polar nature.
• What is the specific heat capacity of water?

  Water’s specific heat capacity is $4200 \text{ J/kg°C}$.
• What does specific heat capacity measure?

  It measures the amount of thermal energy required to raise the temperature of 1 kg of a substance by 1°C.
• Why does water have a high specific heat capacity?

  Because of the many hydrogen bonds present in water, which require a lot of thermal energy to break and build.
• What advantage does the high specific heat capacity of water provide for living organisms?

  It helps maintain a constant temperature, which is vital for enzyme activity.
• How does water in blood plasma help maintain temperature?

  Water in blood plasma helps transfer heat around the body, maintaining a fairly constant temperature.
• What is the latent heat of vaporisation in water?

  It is the large amount of thermal energy that must be absorbed to change water from liquid to gas.
• Why is the latent heat of vaporisation advantageous for living organisms?

  Because only a little water needs to evaporate to lose a great amount of heat, providing a cooling effect.
• What roles do cohesion and adhesion play in water's behavior in living organisms?

  • Cohesion allows strong attraction between water molecules.
  • Enables columns of water to move through the xylem of plants and blood vessels in animals.
  • Surface tension allows insects to float on water.
  • Adhesion allows water to bond with other molecules, aiding in transpiration.
• Where do hydrogen bonds form between water molecules?

  Between the oxygen of one water molecule and the hydrogen atom of another.