| A | B |
|---|
| 152. ppm | parts per million |
| 153. precipitation | water released from the clouds in the form of rain, sleet snow or hail. |
| 154. predator | An animal that hunts another as a food source. |
| 155. pressure | The amount of force applied per unit area. |
| 157. probability | The likelihood that an event will occur. |
| 158. producer | An organism that makes its own food. |
| 159. prokaryotic cell | A cell that does not have a nucleus. |
| 160. prophase | The stage in mitosis where the nucleus disappears. |
| 161. proton | A positively charged particle in an atom. |
| 162. punnett square | A diagram used to determine the outcome of offspring from a genetic cross. |
| 163. recessive | A trait that is expressed with two lower case letters. |
| 164. recharge | The act of rain water replacing water used ifrom an aquifer. |
| 165. revolution | The movement of one object in orbit around another object in space. |
| 166. ribonucleic acid | RNA assembles proteins. |
| 167. ribosomes | These structures are made in the nucleolus and make proteins. |
| 168. rough endoplasmic reticulum | The transportation system of a cell that contains riboosmes. |
| 170. rRNA | Ribosomal RNA attaches to mRNa to send a message. |
| 171. saturated zone | The area below the water table where open spaces are filled with water. |
| 172. science | The study of the world around us. |
| 173. scientific law | A statement that summarizes observed experimental facts. |
| 174. scientific method | The approach scientists take to solve a problem. |
| 175. scientific theory | A logical explanation of events that occur in the natural world. |
| 151. ppb | Parts per billion |
| 156. prey | An animal that is hunted by another as a food source. |
| 169. rotation | The time it takes a planet to spin once on its axis. |
