To BIO 155 students, Another attempt to give you these PowerPoints. Best regards, Professor Jenkins

1. Topic 2: Molecular Biology
2.2 Water
Romy Friedman
DP Biology

2. Syllabus

3. Essential idea:
Water is the medium of life

4. Water (H2O)
• There is a ratio of 2:1 for Hydrogen: Oxygen
• Water is a compound formed from two elements:
oxygen and hydrogen

5. Forming a water molecule
covalent bonding
• Hydrogen has 1 valence electron
• An oxygen shares an electron with two hydrogen
atoms, forming two covalent bonds
• Oxygen has 6 valence electrons

6. Polarity of water
• Water is a unique substance earth, and
therefore essential to life, because of
its polar nature

8. Partial Charge
• Oxygen exerts a great pull over the shared
electrons. They move a little closer to the oxygen
• That means that the oxygen part of the molecule is
slightly negative
• The hydrogen end of the molecule is slightly
positive

9. Hydrogen bonding in water

10. Polarity relates to
solubility in water
Hydrophillic
• A substance that is attracted to water and forms
intermolecular bonds with water molecules
• Ionic compounds and substances with polar molecules
Hydrophobic
• Means that waters molecules are more strongly attracted to
each other than to the substances
• Hydrophobic substances are insoluble in water

11. Water as the Universal Solvent

12. The Nature of Science
• Theories are used to explain natural
phenomena
• Hydrogen bonding explains the unique
behaviour of water that allows life on
earth

13. 4 Property types of Water
• Cohesive
• Adhesive
• Thermal
• Solvent

14. Water is Cohesive
Explanation
• Water molecules cohere because hydrogen
bonds form between them
Example of benefits to organisms
• Transpiration stream

15. Water is Adhesive
Explanation
• The polarity of water molecules makes them
adhere to surfaces that are polar (and therefore
hydrophillic)
Example of benefits to organisms
• Transpiration stream & gas exchange in plants

17. Water has Thermal
Properties
Explanation
• High melting point & boiling point
• High latent heat of vaporization
• High specific heat capacity
Example of benefits to organisms
• Liquid (aquatic) habitats that are stable
• Effective coolant in leaves or sweat

18. Water as a habitat

19. Water as a Coolant

20. Water is a Solvent
Explanation
• Many molecules dissolve in water due to its
polarity including ions or polar molecules
Example of benefits to organisms
• Medium for metabolic reactions

23. Water as the medium of life