2. cannot be broken down into simpler substances Smallest unit is an atom. Examples: carbon, hydrogen, oxygen, and nitrogen

3. when two or more elements combine chemically Most elements occur in the form of compounds Smallest unit is a molecule Ex.: carbon dioxide

4. Carbohydrates Lipids Proteins Nucleic acids Water

5. Energy-rich Made up of carbon, hydrogen, and oxygen Sugars and starches May be the components of cell parts Ex. Found in cell membranes or as cellulose in cell walls

6. Made up of mostly carbon and hydrogen; contains some oxygen. Make up most of a cell membrane Ex. fats, oils, and waxes Cells store energy from fats and oils for later use

7. Large; made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Food examples: meat, dairy, fish, nuts, beans Within a cell: part of cell membranes and organelles Enzymes are proteins that speed up chemical reactions Ex.: Enzymes in your saliva that start to break down sugars

8. Long; consist of carbon, oxygen, hydrogen, nitrogen, and phosphorus. Deoxyribonucleic acid (DNA) – carries information about an organism passed from parent to offspring directs cell functions Shape = double helix

9. Required for most chemical reactions Helps cells retain their shape Changes temperature slowly keeps cells from heating up too quickly Helps carry substances into and out of cells