1. The CHEMICAL Basis of LIFE
Chapter 4!
The CHEMICAL Basis of LIFE

2. Life Requires About 25 Elements (4.1)
Living things share the same building blocks
Oxygen (O)
Carbon (C)
Hydrogen (H)
Nitrogen (N)

3. Elements Matter Element Anything that takes up space and has mass
Pure substance
Can not be broken down any further by chemical means

5. Elements cont’ Trace Elements Eg: Elements < than .01% of your body
Iodine (I) – lack causes thyroid problems
Iron (Fe) – carries O2
Fig 4-1

6. Compounds Compounds Eg: Properties change
Contains 2 or more elements in a fixed ratio
Eg:
Water, H2O
Properties change
H vs. O

7. Chemical Properties Are Based on the Structure of Atoms (4.2)
Greek word atomos : “indivisible”
Smallest piece of an element

8. Atoms cont’ – Subatomic particles (fig 4-4)
Nucleus
Protons and neutrons
Most of atom’s mass
Proton
Positive charge
An atom model
Neutron
Neutral charge
Electron
Negative charge
No significant mass

9. Atoms cont’
“Electron Cloud”
Video

10. Atoms cont’ Atomic Number Atomic Mass What can change? # of protons
Does not change
(eg: N has 7 protons, O has – 8 protons)
What can change?
Neutrons and e- can change
Determines interactions / rxns
Atomic Mass
#P + #N

11. Isotopes Isotope Eg: What is changing??
Same # of protons, but different # of neutrons
Eg: What is changing??
Carbon-12, Carbon-13 and Carbon-14
Fig 4-5

12. Isotopes cont’ Radioactive Isotope Nucleus “breaks down”
Gives off radiation
Can be used in organisms

13. Chemical bonds join atoms to one another (4.3)
Rxns between atoms result in filled outer energy levels
Atoms and e- get rearranged
Chemical bond(s) form
Two types… 2

14. Ionic Bonds Covalent Bonds Atoms transfer e- Atoms share e- Molecule
Video
Ionic Bonds
Atoms transfer e-
Eg: NaCl (table salt)
more info…
Covalent Bonds
Video
Atoms share e-
Ex: H2
Molecule
Any atoms held together w/ covalent bonds

15. Formulas Chemical formula Structural formula Space-filling model Eg:
Fig 4-10
C6H12O6
Structural formula
Space-filling model

16. Chemical Rxns Formation of new substance(s) Exothermic Endothermic
rxn releases energy
Endothermic
rxn absorbs energy

17. Chemical Rxns cont’ 2 H2 + O2  2 H2O + energy Reactants Products
Starting material (on left)
Products
Ending material (on right)
Matter is rearranged
Video
Fig 4-11

18. Life depends on the unique properties of H2O (4.4)
All living things depend on water
Human cells are 70 to 90 % H2O

19. Structure of Water Hydrogen bonds Polar molecule Bond strengths:
Ends have opposite charges
Hydrogen bonds
Hydrogen (weakly) attracted to ANY slight neg.
Fig 4-12
Bond strengths:
hydrogen < ionic < covalent

20. Water’s Life Supporting Properties
Cohesion vs. Adhesion
Cohesion
molec. of same kind “stick”
Adhesion
unlike molec. “stick”

21. Life Supporting Properties cont’
Eg’s of Water’s
Polar Properties
Water being pulled through a plant
Surface tension
Fig 4-13

22. Life Supporting Properties cont’
Low Density of ice
Water vs Ice density
Usually solid is MORE dense than liquid
Ice is LESS dense than water
D = M/V
WHY?
Polarity and hydrogen bonding!
Floating ice is important…
Fig 4-15

23. Life Supporting Properties cont’
H2O’s ability to dissolve other substances
Solution
A uniform mixture of 2 or more substances
Solvent
Dissolves other substance, greater amnt.
Solute
Being dissolved, lesser amnt.
Aqueous Solution
water is the solvent, (aq)
Video
Fig 4-16
H2O dissolves ionic
Ex: NaCl (salt, sodium chloride)
Video
H2O dissolves molecular
Sugar (sucrose, C12H22O11)

24. Acids, Bases and pH pH Scale
Describes how acidic or basic based on H+ ions
Range 0 (acidic) to 14 (basic)
7 is neutral
Fig 4-17

25. Acids, Bases and pH cont’
Cells are sensitive to pH changes
Eg: Human Blood
pH of 7.4 (slightly basic)
Buffers
Substance that helps soln. resist pH change

26. Permission Statement:
Restricted to the use of New Berlin Eisenhower High School Students, Faculty and Staff.
Contact the Science Department for usage permissions.
®2005, 2007
Video Citations:
Holman, John (1996). Atlantis Soars Toward Mir. CNN Interactive. Retrieved on Oct 20th, 2005 from
Mackenzie (2002). Sugar Dissolving. Charlotte County Day School. Retrieved on Oct 18th, 2005 from
No Author (2005). NaCl Dissolving. Western Oregon University. Retrieved on Oct 18th, 2005 from
No Author (2004). Jesus Lizard Running. I Blogger.com. Retrieved on Oct 24th, 2005 from
White, Brian (n.d.) Hydrogen Covalent Bonding. University of Massachusetts. Retrieved on Oct 20th, 2005 from

27. More on Ionic bonds
“cation”
“anion”
Fig 4-8
Back to slide # 15…