Final answer:
Mendel studied pea plants because they are fast growing, easy to raise, and have several visible characteristics that vary. Pea plants also allowed for controlled and observed results of crosses between different plants.
Step-by-step explanation:
Mendel studied pea plants because they are fast growing, easy to raise, and have several visible characteristics that vary. These characteristics include seed form and color, flower color, pod form and color, placement of pods and flowers on stems, and stem length. Furthermore, pea plants can either self-pollinate or be cross-pollinated, allowing for controlled and observed results of crosses between different plants.