Answer to Question 1
During a star's lifetime, it fuses hydrogen into helium and helium into carbon. If it is more massive, it also creates heavier elements, up to iron, by fusion, and even heavier elements, up to uranium, during a supernova event. When the star ends its life as a planetary nebula or in a supernova explosion, it disperses these elements into the interstellar medium. The interstellar medium thus gains these heavier elements and has a smaller proportion of hydrogen but a larger proportion of heavier elements than it did before. The interstellar medium cools, forms molecular clouds, and then forms new stars, which are made out of the material of the interstellar medium.
Answer to Question 2
B
Menstrual cycle
Lycophyte Life Cycle
Fern life cycle
Calvin Cycle
Plant life cycle
The three-step cycle of PCR