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2. 2 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Sylvia S. Mader Immagini e concetti della biologia

3. 3 A2 - The Chemistry of Life Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

4. 4 The Chemical Elements That Make Up Living Organisms

5. 5 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Both living and nonliving things are composed of matter. Matter is composed of elements and exists in three sates: solid, liquid or gas. An element is a substance consisting of one type of atoms and is characterized by a chemical symbol. The Chemical Elements That Make Up Living Organisms

6. 6 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Six elements are biologically important and compose 95% of the organisms total weight: Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorous (P) and Sulfur (S). The most abundant elements in the Earth’s Crust and in living organisms The Chemical Elements That Make Up Living Organisms

7. 7 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Matter is composed of atoms, the smallest unit of an element. Protons (positively charged) and neutrons (uncharged): located in the nucleus. Electrons (negatively charged): orbiting around the nucleus in electronic shells. The Chemical Elements That Make Up Living Organisms

8. 8 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Most of the mass of an atom is localized in the nucleus, being the mass of the electrons negligible. Subatomic particle Electric Charge Atomic Mass Location in the Atom Proton+1Nucleus Neutron01Nucleus Electron-0Electronic shell The Chemical Elements That Make Up Living Organisms

9. 9 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Atomic number: number of protons in the nucleus. Atomic mass: number of protons and neutrons in the nucleus. The Chemical Elements That Make Up Living Organisms

10. 10 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Atoms of the same element showing the same atomic number but different atomic mass are called isotopes. Carbon-14 is chemically unstable and emits radiations. For this reason carbon-14 is called “radioactive isotope”. C 12 6 C 13 6 C 14 6 *radioactive * The Chemical Elements That Make Up Living Organisms

11. 11 Small section of the Periodic Table of Elements Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Elements are arranged in the Periodic Table. Here elements with similar chemical properties are regrouped together into groups and periods. Atoms React with one another and form Chemical Bonds

12. 12 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Elements of the same period have the same number of electronic shells. Elements in the same group show the same number of electrons in the external electronic shell. Atoms React with one another and form Chemical Bonds

13. 13 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The Octet Rule: “the outer electronic shell is most stable when it has eight electrons”. In the case of the first element of the Periodic Table, Hydrogen (H), the maximum number of electrons in the outer shell is two. Atoms React with one another and form Chemical Bonds

14. 14 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 A chemical bond is an attraction between atoms that allows the formation of molecules. There are two main types of bonds: IONIC BONDCOVALENT BOND A molecule is the smallest part of a compound that has the same properties of that compound. Atoms React with one another and form Chemical Bonds

15. 15 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 An ionic bond occurs when electrons are transferred from one atom to the other. This transfer of electrons brings to a disequilibrium in the electric charge of both atoms. Atoms React with one another and form Chemical Bonds

16. 16 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Thus, two electrically charged atoms, called ions, form and attract to one another. Atoms React with one another and form Chemical Bonds

17. 17 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Many ions are important in all living organisms Significant Ions in the human body Atoms React with one another and form Chemical Bonds

18. 18 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 In a molecule of hydrogen (H 2 ), each atom shares one electron. Atoms React with one another and form Chemical Bonds A covalent bond occurs when electrons are shared between the two atoms.

19. 19 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 A covalent bond is very strong (a lot of energy is required to break it) and can be: Atoms React with one another and form Chemical Bonds NonpolarPolar

20. 20 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Nonpolar: it occurs when the two atoms attract the electrons with similar strength. Atoms React with one another and form Chemical Bonds methane (CH 4 )

21. 21 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Polar: the sharing of electrons is not equal. The atoms acquire a slightly charge (positive and negative) and the forming molecule is polar. δ+δ+ δ+δ+ δ-δ- Atoms React with one another and form Chemical Bonds water (H 2 O)

22. 22 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The type of bond between two atoms depends on the electronegativity: the attractive force that an atomic nucleus exerts on electrons. Electronegativity depends on the nuclear positive charge and the distance between the nucleus and electrons. Atoms React with one another and form Chemical Bonds

23. 23 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 A hydrogen bond is a weak attraction between a slightly positive hydrogen atom and a slightly negative atom of another molecule. Atoms React with one another and form Chemical Bonds

24. 24 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Water molecules stick together and to other biologically important polar molecules. Hence, water is used as transport medium for nutrients and waste. COHESION AND ADHESION What Properties of Water make it so Important for Life?

25. 25 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 High heat capacity: protects from rapid changes in temperature. High heat of vaporization: helps organisms resist overheating through sweating. THERMAL CAPACITY Animal’s body cools down when the heat is used to evaporate water from the skin What Properties of Water make it so Important for Life?

26. 26 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Owing to its polarity, water is a good solvent. Hydrophilic molecules as salt attract water. Hydrophobic molecules do not attract water. Water as a solvent Table salt (NaCl) is an ionic salt and easily dissolves in water What Properties of Water make it so Important for Life?

27. 27 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Owing to its particular crystalline structure, ice is less dense than liquid water. This is due to the empty spaces that form between molecules. Thus ice forms on the top of lakes, protecting the organisms below. Density of water and ice What Properties of Water make it so Important for Life?

28. 28 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Water is a polar liquid that slightly dissociates into (H + ) ions and (OH − ) ions in equal concentrations (10 -7 moles/liter). Living Organisms Requires a Narrow pH range

29. 29 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 An acid is a substance which increases the concentration of hydrogen ions (H + ) in a solution. pH<7 ➡ H + ions are more than OH - ions ➡ the solution is acid Living Organisms Requires a Narrow pH range

30. 30 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 A base is a substance which increases the concentration of hydroxide ion (OH − ) in a solution. pH>7 ➡ H + ions are less than OH - ions ➡ the solution is basic Living Organisms Requires a Narrow pH range

31. 31 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The pH scale measures the acidity of a solution Living Organisms Requires a Narrow pH range

32. 32 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Living organisms need to maintain the pH of the body fluids constantly within a range. For example, the human blood pH has to remain between 7.35 and 7.45. Illnesses arise if the pH increases (acidosis) or decreases (alkalosis). Living Organisms Requires a Narrow pH range

33. 33 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 A buffer is a combination of chemicals that confer resistance to a change in the pH of a solution when OH − or H + ions are added or removed. In human blood is the carbonic-acid-bicarbonate buffer H 2 CO 3 HCO 3 + H + - carbonic-acidbicarbonate Living Organisms Requires a Narrow pH range Carbonic-acid-bicarbonate buffer

34. 34 When a base releases OH − ions in the blood, H + ions react and form H 2 O When an acid releases H + ions in the blood, carbonic- acid forms from the reaction with bicarbonate Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 OH - + H + H2OH2O H 2 CO 3 HCO 3 + H + - Living Organisms Requires a Narrow pH range Carbonic-acid-bicarbonate buffer

35. 35 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Acid depositions have a pH lower than 5 and form when pollutants, as sulfur dioxide (SO 2 ), combine with water to produce acids, as sulfuric acid. Acid Deposition has many harmful effects on living and nonliving things