Final answer:
Sample B - Root tip is most likely to contain meristematic tissue, as apical meristems responsible for plant growth are found there.
Step-by-step explanation:
Plant scientists are interested in isolating meristematic tissue for an experiment. When sampling various regions of a plant, the sample most likely to contain meristematic tissue would be Sample B - Root tip. This is because apical meristems are located at the tips of stems and roots, and are responsible for the elongation in length of these plant parts. As the apical meristem comprises undifferentiated cells that continuously divide, it's a key site of growth in plants. Therefore, the root tip is the area where you would find the actively dividing cells that make up meristematic tissue. This differs from other parts such as mature leaves, stems with bark, or leaf midribs which do not have the same concentration of meristematic cells.