It is important to redo experiments for numerous reasons. You check your results from the first time the experiment happened, and if they are not the same you know there's something wrong. You ensure predictability and correctness.
Mendel studied several different traits of a pea plant. For example, some pea plants have purple flowers and others have white flowers. Pea plants can either self-fertilize or cross-fertilize. Crossing two plants is called hybridization. To start, however, Mendel needed plants that were true-breeding. This means that after generations of self-breeding, the pea plant expressed only one version of the trait. After many generations a purple flowered plant only produced plant never produced a white flowered plant.
a group of single-celled eukaryotes.