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2. Immagini e concetti della biologia Sylvia S. Mader
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

3. A2 - The Chemistry of Life
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

4. The Chemical Elements That Make Up Living Organisms
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

5. The Chemical Elements That Make Up Living Organisms
Both living and nonliving things are composed of matter.
Matter is composed of elements and exists in three states: solid, liquid or gas.
An element is a substance consisting of one type of atoms and is characterized by a chemical symbol.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

6. The Chemical Elements That Make Up Living Organisms
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
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

7. The Chemical Elements That Make Up Living Organisms
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

8. The Chemical Elements That Make Up Living Organisms
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 + 1
Nucleus
Neutron
Electron -
Electronic shell
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

9. The Chemical Elements That Make Up Living Organisms
Atomic number: number of protons in the nucleus.
Atomic mass: number of protons and neutrons in the nucleus.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

10. The Chemical Elements That Make Up Living Organisms
Atoms of the same element showing the same atomic number but different atomic mass are called isotopes. C 12 6 13 14 *
*radioactive
Carbon-14 is chemically unstable and emits radiations. For this reason carbon-14 is called “radioactive isotope”.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

11. Atoms React with one another and form Chemical Bonds
Elements are arranged in the Periodic Table.
Here elements with similar chemical properties are regrouped together into groups and periods.
Small section of the Periodic Table of Elements
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

12. Atoms React with one another and form Chemical Bonds
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

13. Atoms React with one another and form Chemical Bonds
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

14. Atoms React with one another and form Chemical Bonds
A molecule is the smallest part of a compound that has the same properties of that compound.
A chemical bond is an attraction between atoms that allows the formation of molecules.
There are two main types of bonds:
IONIC BOND
COVALENT BOND
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

15. Atoms React with one another and form Chemical Bonds
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

16. Atoms React with one another and form Chemical Bonds
Thus, two electrically charged atoms, called ions, form and attract to one another.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

17. Atoms React with one another and form Chemical Bonds
Many ions are important in all living organisms
Significant Ions in the human body
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

18. Atoms React with one another and form Chemical Bonds
A covalent bond occurs when electrons are shared between the two atoms.
In a molecule of hydrogen (H2), each atom shares one electron.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

19. Atoms React with one another and form Chemical Bonds
A covalent bond is very strong (a lot of energy is required to break it) and can be:
Nonpolar
Polar
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

20. Atoms React with one another and form Chemical Bonds
Nonpolar: it occurs when the two atoms attract the electrons with similar strength.
methane (CH4)
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

21. Atoms React with one another and form Chemical Bondsδ+ δ-
Polar: the sharing of electrons is not equal. The atoms acquire a slight charge (positive and negative) and the forming molecule is polar.
water (H2O)
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

22. Atoms React with one another and form Chemical Bonds
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

23. Atoms React with one another and form Chemical Bonds
A hydrogen bond is a weak attraction between a slightly positive hydrogen atom and a slightly negative atom of another molecule.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

24. What Properties of Water make it so Important for Life?
COHESION AND ADHESION
Water molecules stick together and to other biologically important polar molecules.
Hence, water is used as transport medium for nutrients and waste.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

25. What Properties of Water make it so Important for Life?
THERMAL CAPACITY
High heat capacity: protects from rapid changes in temperature.
High heat of vaporization: helps organisms resist overheating through sweating.
Animal’s body cools down when the heat is used to evaporate water from the skin
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

26. What Properties of Water make it so Important for Life?
Water as a solvent
Owing to its polarity, water is a good solvent.
Hydrophilic molecules as salt attract water.
Hydrophobic molecules do not attract water.
Table salt (NaCl) is an ionic salt and easily dissolves in water
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

27. What Properties of Water make it so Important for Life?
Density of water and ice
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

28. Living Organisms Requires a Narrow pH range
Water is a polar liquid that slightly dissociates into (H+) ions and (OH−) ions in equal concentrations (10-7 moles/liter).
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

29. Living Organisms Requires a Narrow pH range
pH<7 ➡ H+ ions are more than OH- ions ➡ the solution is acid
An acid is a substance which increases the concentration of hydrogen ions (H+) in a solution.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

30. Living Organisms Requires a Narrow pH range
pH>7 ➡ H+ ions are less than OH- ions ➡ the solution is basic
A base is a substance which increases the concentration of hydroxide ion (OH−) in a solution.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

31. Living Organisms Requires a Narrow pH range
The pH scale measures the acidity of a solution
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

32. Acid deposition has many harmful effects on living and nonliving things
Acid depositions have a pH lower than 5 and form when pollutants, as sulfur dioxide (SO2), combine with water to produce acids, as sulfuric acid.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018