Levels of Biological Organization

The Chemical Context of Life

Chemical Elements and Compounds

• Matter- anything that takes up space : has a mass and a volume.– Example: DNA, ________

– Is air matter? Yes OR No• How can we prove this?

• Element- a substance that cannot be broken down into other substances– Example: sodium (Na) and chlorine (Cl)• Compound- a substance consisting of two

or more elements. Example: Salt NaCl, HCO3 (important buffer involved in respiration)

• Life requires approximately 25 chemical elementsThese six elements make 98% of all living

organisms:- Carbon- Hydrogen - Nitrogen - Oxygen- Phosphorous -Sulfur (sulphur)

(The remaining % = K, Ca, Na etc)

• Trace Elements- small amount required by an organism, but very important.

- example Iron or Iodine

Iodine Deficiency

Iron Deficiency

• Atom-smallest unit of matter made up of protons, electrons, and neutrons.

Neutron: no chargeProton :+ chargeElectron: -charge

• Ion-Charged particle-cation: positive ion (Na1+)

-Has one less electron, therefore it is positive

-anion: negative ion (Cl1-)-Has one more electron, therefore it

is negative

• Atomic Number- Indicates the number of protons (can also predict size of the atom)

He = 2 protonsC = 6 protons

(if the atom is neutral then the atomic # = the # of electrons)

• Mass Number- sum of the protons plus the number of neutrons.

• Standard Notation:

4 atomic mass # He

element symbol 2 atomic #

12C

6

• Isotope- Different atomic forms of an element due to a different number of neutrons.Example: 12 13 14

C C C 6 6 6

• Radioactive Isotopes are useful in-carbon dating-metabolism tracers-medicine

• Why do some ions have less electrons?• Why do some ions have more electrons?– Think back to chemistry 11/Science 10/Science 9– Outer Electron Shells/orbitals (valence electron

shells)Bohr Models:First Shell: 2 electronsSecond Shell: 8 electronsThird Shell: 8 electronsFourth Shell: 18 electrons

Bohr Models

• Lithium atom Chlorine atom

Bohr Models

• Lithium Ion Chlorine Ion

To make you chuckle