1. Essential Chemistry for Biology
CHAPTER 2
Essential Chemistry for Biology

6. Biology and Society: Aids: A Matter of Chemistry
In 1981, the Centers for Disease Control (CDC)
Began tracking high numbers of otherwise healthy young men who were coming down with extremely rare diseases.
Examinations of these patients showed that they all had a failing immune system.
This condition was caused by the human immunodeficiency virus (HIV).
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

7. HIV binds to certain molecules found on cells of the immune system called “helper” T cells.
The virus kills these cells and wipes out one part of the body’s defenses.
HIV Reproductive Cycle

8. Figure 2.1

9. Some Basic Chemistry
Take any biological system apart, and you eventually end up at the chemical level.

10. Matter: Elements and Compounds
Matter is anything that occupies space and has mass.
Matter is found on the Earth in three physical states:
Solid
Liquid
Gas

11. Matter is composed of chemical elements.
Elements are substances that cannot be broken down into other substances.
There are 92 naturally occurring elements on Earth.
All the elements are listed in the periodic table.

12. Figure 2.2

13. Twenty-five elements are essential to life.
Four of these make up about 96% of the weight of the human body.
Trace elements occur in smaller amounts.

14. Figure 2.3

15. Trace elements are essential for life.
An iodine deficiency causes goiter.

16. Figure 2.4

17. Elements can combine to form compounds.
These are substances that contain two or more elements in a fixed ratio.
Example: NaCl (salt)

18. Each element consists of one kind of atom.
Atoms
Each element consists of one kind of atom.
An atom is the smallest unit of matter that still retains the properties of an element.

19. Figure 2.5

20. Atoms are composed of subatomic particles.
The Structure of Atoms
Atoms are composed of subatomic particles.
A proton is positively charged.
An electron is negatively charged.
A neutron is electrically neutral.

21. Most atoms have protons and neutrons packed tightly into the nucleus.
The nucleus is the atom’s central core.
The electrons orbit the nucleus.

22. Elements differ in the number of subatomic particles in their atoms.
The number of protons, the atomic number, determines which element it is.
An atom’s mass number is the sum of the number of protons and neutrons.
Mass is a measure of the amount of matter in an object.

23. Isotopes are alternate mass forms of an element.
They have the same number of protons and electrons.
But they have a different number of neutrons.

24. Table 2.1

25. In radioactive isotopes,
The nucleus decays, giving off particles and energy.
Radioactive isotopes have many uses in research and medicine.
Example: PET scans

26. Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA.
Example: the 1999 Chernobyl nuclear accident

27. The Process of Science: Can Alzheimer’s Disease Be Detected Early?
Alzheimer’s disease is a devastating illness.
It gradually destroys a person’s memory and ability to think.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

28. Doctors are now using PET scans
In an attempt to diagnose Alzheimer’s disease before the onset of symptoms.

29. Figure 2.6

30. Electron Arrangement and the Chemical Properties of Atoms
Electrons determine how an atom behaves when it encounters other atoms.
Electrons orbit the nucleus of an atom in specific electron shells.
The number of electrons in the outermost shell determines the chemical properties of an atom.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

31. Figure 2.7

32. Chemical Bonding and Molecules
Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells.
These interactions usually result in atoms staying close together.
The atoms are held together by chemical bonds.

33. Ionic Bonds
When an atom loses or gains electrons, it becomes electrically charged.
Charged atoms are called ions.
Ionic bonds are formed between oppositely charged ions.
Ionic Bonds

34. Figure 2.8

35. Covalent Bonds
A covalent bond forms when two atoms share one or more pairs of outer-shell electrons.
Covalent Bonds

36. Figure 2.9

37. Hydrogen Bonds
Water is a compound in which the electrons in its covalent bonds are shared unequally.
This causes it to be a polar molecule, one with opposite charges on opposite ends.

38. Unnumbered Figure, p. 26

39. The polarity of water results in weak electrical attractions between neighboring water molecules.
These interactions are called hydrogen bonds.
Water Structure

40. Figure 2.10

41. Chemical Reactions
Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones.
Such changes in the chemical composition of matter are called chemical reactions.

42. Unnumbered Figure, p. 27

43. Chemical reactions include:
Reactants, the starting materials
Products, the end materials

44. Chemical reactions cannot create or destroy matter,
They only rearrange it.

45. Life on Earth began in water and evolved there for 3 billion years.
Water and Life
Life on Earth began in water and evolved there for 3 billion years.
Modern life still remains tied to water.
Your cells are composed of 70%–95% water.
The abundance of water is a major reason Earth is habitable.

46. Figure 2.11

47. Water’s Life-Supporting Properties
The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties:
Water’s cohesive nature
Water’s ability to moderate temperature
Floating ice
Versatility of water as a solvent

48. Water molecules stick together as a result of hydrogen bonding.
The Cohesion of Water
Water molecules stick together as a result of hydrogen bonding.
This is called cohesion.
Cohesion is vital for water transport in plants.
Water Transport

49. Figure 2.12

50. Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.
Hydrogen bonds give water an unusually high surface tension.

51. Figure 2.13

52. How Water Moderates Temperature
Because of hydrogen bonding, water has a strong resistance to temperature change.

53. Heat and temperature are related, but different.
Heat is the amount of energy associated with the movement of the atoms and molecules in a body of matter.
Temperature measures the intensity of heat.
Water can absorb and store large amounts of heat while only changing a few degrees in temperature.

54. Water can moderate temperatures.
Earth’s giant water supply causes temperatures to stay within limits that permit life.
Evaporative cooling removes heat from the Earth and from organisms.

55. Figure 2.14

56. The Biological Significance of Ice Floating
When water molecules get cold, they move apart, forming ice.
A chunk of ice has fewer molecules than an equal volume of liquid water.

57. The density of ice is lower than liquid water.
This is why ice floats.

58. Figure 2.15

59. Since ice floats, ponds, lakes, and even the oceans do not freeze solid.
Marine life could not survive if bodies of water froze solid.

60. Water as the Solvent of Life
A solution is a liquid consisting of two or more substances evenly mixed.
The dissolving agent is called the solvent.
The dissolved substance is called the solute.

61. Figure 2.16

62. When water is the solvent, the result is an aqueous solution.

63. To describe the acidity of a solution, we use the pH scale.
Acids, Bases, and pH
Acid
A chemical compound that donates H+ ions to solutions.
Base
A compound that accepts H+ ions and removes them from solution.
To describe the acidity of a solution, we use the pH scale.

64. Figure 2.17

65. Buffers are substances that resist pH change.
They accept H+ ions when they are in excess.
They donate H+ ions when they are depleted.
Buffering is not foolproof.
Example: acid precipitation

66. Figure 2.18

67. Evolution Connection: Earth Before Life
Chemical reactions and physical processes on the early Earth created an environment that made life possible.

68. Earth began as a cold world about 4.5 billion years ago.
The planet eventually melted from heat produced by:
Compaction
Radioactive decay
Impact of meteorites

69. The first atmosphere was probably composed of hot hydrogen gas.
This gas escaped because the gravity of Earth was not strong enough.
A new atmosphere was formed from the gases belched from volcanoes.

70. Figure 2.19