Answer to Question 1
Figure 6-17 gives some examples of endangered and threatened animal species. Answers will vary based on the species that each student chooses.
Answer to Question 2
The atmosphere is a collection of gases that gravity holds in a thin envelope around the Earth. The gases within the lowest layer, the troposphere, are responsible for moderating the flow of energy to Earth. The troposphere ranges in thickness from 10 miles in the tropics and 5 miles in high latitudes. . . . This layer contains practically all the water vapor and clouds in the atmosphere; it is the site and source of our weather. Above the tropopause is the stratosphere, a layer within which temperature increases with altitude, up to about 40 miles above the surface of Earth. The temperature increases primarily because the stratosphere contains ozone (O3), a form of oxygen that absorbs high-energy radiation emitted by the Sun. Because there is little vertical mixing of air masses in the stratosphere and no precipitation from it, substances that enter it can remain there for a long time.
The fossil Runcaria heinzelinii, a plant with a probable seed precursor.
Schematic of typical plant cell
Plant
Plant
Plant
Controlled Scientific Experiments Scientists use experimental research to test hypotheses